Fluorescent imaging agents

Description of equivalent WO 2009092062 A2

FLUORESCENT IMAGING AGENTS CROSS-REFERENCE TO RELATED APPLICATION

0002[0001] This application claims the benefit of and priority to co-pending U.S. Provisional Patent Application No. 61/022,014, filed January 18, 2008, the entire contents of which are herein incorporated by reference. BACKGROUND

0003[0002] Current approaches for assessing of molecular endpoints in disease usually require tissue and blood sampling, surgery, and in the case of experimental animals, sacrifice at different time points. Despite improvements in noninvasive imaging, more sensitive and specific imaging agents and methods are urgently needed. Imaging techniques capable of visualizing specific molecular targets and/or entire pathways would significantly enhance the ability to diagnose and assess treatment efficacy of therapeutic interventions for many different disease states. Most current imaging techniques report primarily on anatomical or physiological information (e.g., magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound). Newer modalities, such as, optical imaging and new molecular imaging probes have the potential to revolutionize the way disease is detected, treated, and monitored.

0004[0003] Molecular imaging is a developing field in the imaging sciences that transcends the traditional boundaries of imaging structure or physiology, and has the potential to revolutionize current research and clinical practices towards real molecular medicine. The one paradigm for molecular imaging involves the use of a "molecular" probe or agent that selectively targets a particular gene, protein, receptor or a cellular function, with the absence, presence, amount or concentration of the specific target being indicative of a particular disease state.

0005[0004] In particular, optical imaging offers several strong performance attributes that make it a truly powerful molecular imaging approach, both in the research and clinical settings. Specifically, optical imaging is fast, safe, cost effective and highly sensitive. Scan times typically are on the order of seconds to minutes, there is no ionizing radiation, and the imaging systems are relatively simple to use. In addition, optical probes can be designed as dynamic molecular imaging agents that can alter their reporting profiles in vivo to provide molecular and functional information in real time. In order to achieve maximum penetration and sensitivity in vivo, the choice for most optical imaging in biological systems is within the red and near-infrared (NIR) spectral region, although other wavelengths in the visible region can also be used. In the NIR wavelength range, absorption by physiologically abundant absorbers such as hemoglobin or water is minimized.

0006[0005] Although different types of optical imaging probes have been developed including (1) probes that become activated after target contact (e.g., binding or interaction), (2) wavelength shifting beacons, (3) multicolor fluorescence probes, (4) probes that have high binding affinity to targets, i.e., that remain within a target region while non-specific probes are cleared from the body (Achilefu et al, Invest. Radiol., 35:479-485, 2000; Becker et al, Nature Biotech. 19:327-331, 2001; Bujai et al, J. Biomed. Opt. 6:122-133, 2001; Ballou ef al Biotechnol Prog. 13:649-658, 1997; and Neri et al, Nature Biotech. 15:1271-1275, 1997), and (5) fluorescent semiconductor based probes, there is still an ongoing need for imaging probes that, for example, are capable of providing high quality images and molecular information.

SUMMARY OF THE INVENTION

0008[0006] The present invention provides fluorescent imaging agents that have significantly enhanced fluorescent properties upon activation and can be used for in vivo and in vitro imaging applications. The imaging agents have a fluorescent reporter system, which in certain embodiments, contains two fluorophores or a fluorophore and a quencher, where one fluorophore quenches the other fluorophore or the quencher quenches the fluorophore. Although the imaging agents may have no more than two fluorophores they still have an extinction coefficient sufficient for in vivo imaging applications.

0009Furthermore, their size permits the agents to become quickly distributed through the tissues or body fluid of a subject, which allows the agent to travel to tissues or cells for activation by proteases, binding to cell surface receptors or internalization within cells.

0010[0007] The imaging agents have enhanced fluorescent properties upon activation and under certain circumstances can have magnetic properties, for example, paramagnetic or superparamagnetic properties, so that the imaging agents can be used as MRI or multi- modality imaging agents (for example, optical imaging and magnetic resonance imaging). In addition, the imaging agents optionally can include diagnostic and or therapeutic moieties, for example, radioactive metals, so that the resulting imaging agents can be used like radiopharmaceuticals, nuclear imaging agents or multi-modality imaging agents (for example, in an optical imaging and nuclear imaging environment).

0011[0008] In one aspect, the invention provides an intramolecularly-quenched imaging agent. The agent comprises (a) an enzymatically cleavable oligopeptide comprising from about 2 to about 30 amino acid residues; (b) an optional biological modifier chemically linked to the enzymatically cleavable oligopeptide; and (c) either two fluorophores or one fluorophore and one quencher, each covalently linked, directly or indirectly, to the oligopeptide or to the optional biological modifier, wherein one fluorophore quenches the other fluorophore or the quencher quenches the fluorophore and upon enzymatic cleavage of the oligopeptide, at least one fluorophore becomes unquenched and is capable of producing a greater fluorescent signal when excited by electromagnetic radiation than before enzymatic cleavage of the oligopeptide.

0012[0009] The oligopeptide can comprise from about 2 to about 25 amino acid residues, from about 2 to about 14 amino acid residues, from about 4 to about 10 amino acid residues, or from about 5 to about 8 amino acid residues.

0013[0010] In certain embodiments, the imaging agent can be represented by Formula I: G_f

0014/ K_n-B-G_f (I) wherein: B is [M_m-EC0-M_m];

0015ECO is an enzymatically cleavable oligopeptide;

0016G is L-F;

0017F is a fluorophore or quencher;

0018M is a biological modifier; K is N-L;

0019N is a non-fluorescent reporter;

0020L, independently, for each occurrence, is a linker moiety or a bond; - A - n is an integer from 0 to 3 ; m, independently, for each occurrence, is 0 or 1, and optionally at least one m is 1; and f, independently, for each occurrence, is an integer from 0 to 2, wherein the total number of fluorophores F in the agent is no greater than 2.

0021[0011] Each F can be chemically linked, directly or through the linker moiety L, to a separate amino acid of the oligopeptide. Alternatively, at least one F is chemically linked, directly or through the linker moiety L, to M. In certain embodiments, ECO is a cyclic oligopeptide. [0012] In addition, in certain embodiments, the imaging agent is represented by Formula II:

0022M_m-[[X]_r-Xr-[X]p-X₂*-[X]_q ] (II) wherein:

0023X, independently, for each occurrence, is an amino acid residue; Xi^* and X₂* are each independently X-L-F;

0024L, independently, for each occurrence, is a linker moiety or a bond;

0025F is a fluorophore;

0026M is a biological modifier; m is 0, 1 or 2; r is an integer from 0 to 28; p is an integer from 1 to 28; q is an integer from 0 to 28; wherein the sum of r, p and q is no greater than 28.

0027[0013] Depending upon the circumstances, amino acid residue X₁* is a lysine and/or amino acid residue X₂* is a lysine.

0028[0014] In another aspect, the invention provides an intramolecularly-quenched imaging agent represented by Formula III:

0029[[EC0-G_g]_p-M]- K_n (III) wherein:

0030ECO is an enzymatically cleavable oligopeptide; G is L-F;

0031F, independently, is selected from a fluorophore or quencher, wherein at least one F is a fluorophore;

0032L, independently for each occurrence, is selected from a linker moiety or a bond;

0033M is a biological modifier; K is L-N; N is a non-fluorescent reporter; p is an integer from 1 to 4; n is an integer from 0 to 3; and g, independently, for each occurrence, is an integer from 1 to 2, wherein the sum of each occurrence of g is no greater than 2. [0015] The oligopeptide can comprise from about 2 to about 25 amino acid residues, from about 2 to about 14 amino acid residues, from about 4 to about 10 amino acid residues, or from about 5 to about 8 amino acid residues. In certain embodiments, at least one F is chemically linked, directly or indirectly, to a lysine residue.

0034[0016] In another aspect the invention provides cyclic intramolecularly quenched imaging agent comprising (a) a first fluorophore chemically linked, directly or indirectly, to the C-terminus of a first cleavable oligopeptide and chemically linked, directly or indirectly, to the N-terminus of a second, optionally cleavable, oligopeptide; (b) a second fluorophore chemically linked, directly or indirectly, to the N-terminus of the first cleavable oligopeptide and chemically linked directly or indirectly, to the C-terminus of the second, optionally cleavable oligopeptide; and (c) optionally, at least one biological modifier chemically linked to the first or second oligopeptide or fluorophore.

0035[0017] In one embodiment, the imaging agent can be represented by Formula IV: <img file="WO2009092062A2_D0001.tif" />

0036G ECO (IV) wherein,

0037ECO, independently, for each occurrence, is an enzymatically cleavable oligopeptide;

0038G is L-F-L; F, independently, for each occurrence, is a fluorophore;

0039L, independently, for each occurrence, is a linker moiety or a bond;

0040M is a biological modifier;

0041K is L-N;

0042N is a non-fluorescent reporter; n is an integer from 0 to 3 ; and m is an integer from 0 to 3.

0043[0018] In another aspect, the invention provides an intramolecularly-quenched imaging agent comprising (a) an enzymatically cleavable oligopeptide comprising from 2 to 14 amino acid residues; (b) at least one biological modifier with a molecular weight of from about 5 kDa to about 35 kDa covalently linked to the enzymatically cleavable oligopeptide; and (c) two fluorophores, each covalently linked, directly or indirectly, to the oligopeptide at locations so that the fluorophores quench one another, and wherein, upon enzymatic cleavage of the oligopeptide, at least one fluorophore becomes unquenched and is capable of emitting a fluorescent signal when excited by electromagnetic radiation.

0044[0019] In another aspect, the invention provides an intramolecularly-quenched imaging agent represented by Formula V:

0045<img file="WO2009092062A2_D0002.tif" /> (V) wherein

0046X₁^* independently, at each occurrence, is X-L-; X is an amino acid residue; L is a linker moiety or a bond; and F, independently, at each occurrence, is a fluorophore.

0047[0020] In another aspect, the invention provides an intramolecularly-quenched imaging agent represented by Formula VI:

0048<img file="WO2009092062A2_D0003.tif" />

0049(VI) wherein

0050Xi , independently, at each occurrence, is X-L-;

0051X is an amino acid residue;

0052L is a linker moiety or a bond;

0053F, independently, at each occurrence, is a fluorophore. [0021] In any of the foregoing imaging agents, the fluorophore preferably is a far-red or a near-infrared fluorophore. Exemplary fluorophores include carbocyanine fluorophore and indocyanine fluorophore. It is understood that when the agent comprises two fluorophores, they can be the same or different. Other useful fluorophores and quenchers, as well as useful linkers, biological modifiers, and non- fluorescent reporters are described in more detail below.

0054[0022] In certain embodiments, the enzymatically cleavable oligopeptide is cleavable by at least one enzyme selected from the group consisting of a cathepsin, a matrix metalloprotease, a peptidase, a carboxypeptidase, a glycosidase, a lipase, a phospholipase, a phosphatase, a phosphodiesterase, a sulfatase, a reducatese, and a bacterial enzyme. [0023] In addition, the invention provides methods of imaging in-vivo or in-vitro. In one aspect, the invention provides a method for performing in vivo optical imaging in a subject, for example, a mammal, for example, an animal or a human. The method comprises the steps of (a) administering to a subject one of more of the foregoing imaging agents, (b) allowing the agent or agents to distribute within the subject; (c) exposing the subject to light of a wavelength absorbable by at least one fluorophore in the agent; and (d) detecting a signal emitted by the fluorophore. The emitted signal can be used to construct an image, for example, a tomographic image. Furthermore, steps (c) - (d) can be repeated at predetermined intervals thereby to permit evaluation of the emitted signals of the agent in the subject over time. Similarly, steps (a) - (d) can be repeated at predetermined time intervals thereby to permit evaluation of the emitted signals of the agent in the subject over time. The presence, absence, or level of emitted signal can be indicative of a disease state and or can be used to detect and/or monitor a disease.

0055[0024] In another aspect, the invention provides an in vitro imaging method. The method comprises (a) contacting a sample, for example, a biological sample, with any one ore more of the foregoing imaging agents, (b) allowing the agent to bind to or associate with a biological target; optionally, removing unbound agents; and (d) detecting a signal emitted from the fluorophore thereby to determine whether the agent has been activated by or bound to the biological target.

0056[0025] The imaging agents can also be incorporated into a kit, for example, a kit with optional instructions for using the agents during in vivo or in vitro imaging. The kit optionally comprises components that aid in the use of the imaging agents for the disclosed methods, such as buffers, and other formulating agents. Alternatively, the kit can comprise medical devices that aid in the administration and/or detection of the agents to subjects. [0026] The imaging agents and methods disclosed herein provide various advantages and have broad applications in both research and clinical settings. For example, the imaging agents and methods permit the acquisition of molecular images and optionally, high resolution anatomical images. The imaging agents and methods may provide insights into specific molecular abnormalities that form the basis of many diseases, and can be used to assess efficacy of established therapies at the molecular level. This, in turn, is expected to have an impact in drug development, drug testing, disease diagnosis, and choosing appropriate therapies and therapy changes in a given subject.

0057[0027] Other features and advantages of the invention will be apparent from the following figures, detailed description, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

0058[0028] Figure 1 depicts a planar image of bilateral tumors at 6 hours after administration of an exemplary imaging agent referred to as Q65.

0059[0029] Figure 2 depicts fluorescence tomography bilateral images of tumors at 6 hours after administration of the exemplary imaging agent Q65. [0030] Figure 3 depicts planar fluorescence reflectance images of 4Tl Xenograft tumors using an exemplary agent referred to as Q66.

0060[0031] Figure 4 depicts a planar fluorescence reflectance image of HT-29 Xenograft tumors using an exemplary agent referred to as Q91.

0061[0032] Figure 5 depicts the enzymatic activation profile of the imaging agent Q65. [0033] Figure 6 depicts the enzymatic activation profiles of the exemplary imaging agents, referred to as Q92 (Figure 6A) and Q93 (Figure 6B).

0062[0034] Figure 7A depicts fluorescent images of control (Figures 7A and 7C) and ovariectomy induced osteoporosis (Figures 7B and 7D) in mice taken 4 hours (Figures 7A and 7B) and 24 hours (Figures 7C and 7D) after administering an exemplary imaging agent referred to as Q94. Figure 7E is a bar chart showing quantitation of tibial fluorescence of induced osteoporosis 4 hours and 24 hours after administration of imaging agent Q94.

0063[0035] Figure 8 depicts an image produced by fluorescence reflectance imaging of cardiovascular disease using the exemplary imaging agent Q65. [0036] Figure 9 depicts an image of a mouse following carrageenan induced paw edema using the exemplary imaging agent Q91.

0064[0037] Figure 10 is a schematic representation of an exemplary cyclic imaging agent that comprises two fluorophores separated by two peptides. Each peptide contains a proteolytic cleavage site where, when intact, the imaging agent is quenched and when the peptides are cleaved by exposure to one or more proteases, at least one fluorophore is no longer quenched by the other.

0065[0038] Figure 11 is a bar chart showing the enzyme activation profile for exemplary imaging agents referred to as R20, R21, R23, R24, R26, and R27.

0066[0039] Figure 12 shows images of mice on a control or low sodium diet using two exemplary imaging agents, wherein Figure 12A represents a mouse on a control diet having received the imaging agent R20, Figure 12B represents a mouse on a low sodium diet having received the imaging agent R20, Figure 12C represents a mouse on a control diet having received the imaging agent R21, and Figure 12D represents a mouse on a low sodium diet having received the imaging agent R21.

0067[0040] Figure 13 is a bar chart showing an enzyme activation panel for an exemplary imaging agent referred to as R22.

0068[0041] Figure 14 show images created by fluorescent reflectance imaging after 6 hours (Figure 14A) and after 24 hours (Figure 14B) and by tomographic imaging after 6 hours (Figure 14C) and after 24 hours (Figure 14D) using the exemplary imaging agent R22.

0069[0042] Figure 15 is a bar chart showing enzyme activation profiles of exemplary imaging agents referred to as R51, R52, R53, R55, R56, R57, R58, and R59.

0070[0043] Figure 16 depicts images and quantification of the images in ApoE -/- and control mice using the exemplary imaging agent R51. Figure 16A shows images taken by fluorescent tomography, and Figure 16B is a bar chart showing quantification of the resulting images. Figure 16C is a reflectance image, and Figure 16D is a bar chart showing quantification of the resulting images.

0071[0044] Figure 17 depicts images and quantification of the images in ApoE -/- and control mice using the exemplary imaging agent R55. Figure 17 A shows images taken by fluorescence tomography, and Figure 17B is a bar chart showing quantification of the resulting images.

DETAILED DESCRIPTION

0073[0045] This invention provides imaging agents that include one or more fluorescently labeled peptides. The fluorescence of the imaging agents is enhanced upon activation, e.g, an increase of fluorescence occurs, due to a cleavage of a peptide sequence by a protease after, before or during binding of the agent or following internalization of the imaging agent. [0046] For example, the imaging agents of the present invention includes at least one oligopeptide comprising a proteolytic cleavage site, and two fluorophores or a single fluorophore and a quencher) covalently linked (directly or indirectly) to the oligopeptide or an optional biological modifier such that the fluorescence of at least one fluorophore is significantly quenched. Cleavage of the peptide by, for example, enzymatic cleavage, the agent emits a fluorescent signal when excited by electromagnetic radiation of appropriate wavelength and frequency. In certain embodiments, the imaging agents contain no more than two fluorophores. For example, the imaging agents may contain a fluorescent reporter system consisting of, or consisting essentially of, (i) two fluorophores, (ii) two fluorophores and two quenchers, (iii) two fluorophores and one quencher, or (iv)one fluorophore and one quencher.

0074[0047] As used herein, the term "quench" is understood to mean the process of partial or complete reduction of the fluorescent signal from a fluorophore. For example, a fluorescent signal can be reduced inter-molecularly or intra-molecularly through the placement of another fluorophore (either the same or a different fluorophore) in fluorescent quenching proximity to the first fluorophore or the placement of a non- fluorogenic quenching chromophore molecule (quencher) in fluorescent quenching proximity to the first fluorophore. The agent is de-quenched (or activated), for example, through the enzymatic cleavage of a peptide sequence.

0075[0048] The peptide of the imaging agents optionally can be chemically linked to a biological modifier. Furthermore the imaging agents optionally can be chemically linked to another non-fluorescent reporter. As used herein, the term "chemically linked" is understood to mean connected by an attractive force between atoms strong enough to allow the combined aggregate to function as a unit. This includes, but is not limited to, chemical bonds such as covalent bonds, non-covalent bonds such as ionic bonds, metallic bonds, and bridge bonds, hydrophobic interactions, hydrogen bonds, and van der Waals interactions. [0049] In one aspect of the invention, the agents of the present invention are intramolecularly-quenched agents that include (a) an enzymatically cleavable oligopeptide comprising from about 2 to about 30 amino acid residues; (b) an optional biological modifier chemically linked to the enzymatically cleavable oligopeptide; and (c) either two fluorophores or one fluorophore and one quencher, each covalently linked, directly or indirectly, to the oligopeptide or to the biological modifier, wherein one fluorophore quenches the other fluorophore or the quencher quenches the fluorophore and upon enzymatic cleavage of the oligopeptide, at least one fluorophore becomes unquenched and is capable of producing a greater fluorescent signal when excited by electromagnetic radiation than before enzymatic cleavage of the oligopeptide.

0076[0050] For example, the imaging agent can comprise one or more oligopeptides from about 2 to about 25 amino acid residues in length, from about 2 to about 14 amino acid residues in length, from about 5 to about 8 amino acid residues in length, or from about 4 to about 10 amino acid residues in length. In certain embodiments, the oligopeptide comprises 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 amino acids.

0077[0051] The biological modifier, before being chemically linked to the enzymatically cleavable oligopeptide, can have a molecular weight less than about 35 kDa, for example, from about 10 kDa to about 35 kDa, from about 5 kDa to about 30 kDa, or from about 15 kDa to about 25 kDa. The biological modifier preferably is linked to the oligopeptide at a position that does not interfere with fluorescent quenching. For example, the biological modifier may be chemically linked to a moiety of the oligopeptide that is not positioned between two fluorophores that quench one another or between a fluorophore and a quencher. [0052] In some embodiments, the imaging agents disclosed herein comprise two fluorophores, which may be the same or different. Imaging agents of the invention can further comprise a non-fluorescent reporter chemically linked to the enzymatically cleavable oligopeptide or the biological modifier.

0078[0053] In one embodiment, the imaging agent is represented by Formula I: G_f /

0079K_n-B-G_f (I) wherein: <img file="WO2009092062A2_D0004.tif" />

0080ECO is the enzymatically cleavable oligopeptide;

0081G is L-F;

0082F is a fluorophore or quencher;

0083M is a biological modifier; K is N-L;

0084N is a non-fluorescent reporter;

0085L, independently, for each occurrence, is a linker moiety or a bond; n is an integer from 0 to 3 (for example, 0, 1, 2, or 3); m, independently, for each occurrence, is 0 or 1, and optionally at least one m is 1; and f, independently, for each occurrence, is an integer from 0 to 2, wherein the total number of fluorophores F in the agent is no greater than 2.

0086[0054] In one embodiment, f is 2 and at least one F is a fluorophore.

0087[0055] Each F may be covalently linked, directly or indirectly (for example, through a linker moiety L), to a different amino acid residue (for example, a lysine) of the oligopeptide. In another embodiment, at least one F is covalently linked, directly or indirectly (for example, through a linker moiety L), to the biological modifier M. It is understood that ECO can be a linear oligopeptide, or can be a cyclic oligopeptide.

0088[0056] In another aspect, the imaging agent is represented by formula II:

0089M_m-[[X]_r-Xr-[X]_p-X₂*-[X]_q ] (II) wherein:

0090X, independently, for each occurrence, is an amino acid residue; X₁ and X₂* are each independently X-L-F;

0091L, independently, for each occurrence, is a linker moiety or a bond; F is a fluorophore;

0092M is a biological modifier; m is 0, 1 or 2; r is an integer from 0 to 28; p is an integer from 1 to 28; q is an integer from 0 to 28; wherein the sum of r, p and q is no greater than 28.

0093[0057] In certain embodiments, the sum of r, p and q is 3, 4, 5, 6, 7, 8, 9 or 10. The amino acid residue X₂* and/or X₁* can be, for example, a lysine.

0094[0058] In another aspect, the imaging agent is represented by Formula III:

0095[[ECO-G_g]_p-M]- K_n (III)

0096wherein:

0097ECO is an enzymatically cleavable oligopeptide; G is L-F;

0098F, independently, is selected from a fluorophore or quencher, wherein at least one F is a fluorophore;

0099L, independently, for each occurrence, is selected from a linker moiety or a bond;

0100M is a biological modifier; K is L-N; N is a non-fluorescent reporter; p is an integer from 1 to 4; n is an integer from 0 to 3 ; and g, independently, for each occurrence, is an integer from 1 to 2, wherein the sum of each occurrence of g is no greater than 2. [0059] For example, ECO can be about 5 to about 8 amino acid residues in length. The integer n can be 0, 1, 2 or 3; g of formula III can be, independently for each occurrence, 1, 2, 3, 4 5 or 6. In certain embodiments, at least one F is chemically linked, directly or indirectly, to a lysine residue of the oligopeptide ECO. For example, F, for each occurrence, is covalently bound to the oligopeptide ECO. [0060] In another aspect, the imaging agent is a cyclic intramolecularly quenched imaging agent comprising: a) a first fluorophore chemically linked, directly or indirectly, to the C-terminus of a first cleavable oligopeptide and chemically linked, directly or indirectly, to the N-terminus of a second, optionally cleavable oligopeptide; b) a second fluorophore chemically linked, directly or indirectly, to the N-terminus of the first cleavable oligopeptide and chemically linked directly or indirectly, to the C-terminus of the second, optionally cleavable, oligopeptide; and c) optionally, at least one biological modifier chemically linked to the first or second oligopeptide or fluorophore.

0101[0061] In one embodiment, the cyclic agents can be represented by Formula IV: E₉CM xn ^" M_n

0102-ECO (IV) wherein ECO, independently for each occurrence, is an enzymatically cleavable oligopeptide;

0103G is L-F-L;

0104F, independently, for each occurrence, is a fluorophore;

0105L, independently, for each occurrence, is a linker moiety or a bond; M is a biological modifier;

0106K is L-N;

0107N is a non-fluorescent reporter; n is an integer from 0 to 3 (for example 0, 1, 2 or 3); and m is an integer from 0 to 3 (for example 0, 1, 2 or 3). [0062] Also contemplated herein are stereoisomeric forms, mixtures of stereoisomeric forms, and pharmaceutically acceptable salt forms of the disclosed imaging agents.

0108I. Fluorophores

0109[0063] As used herein, the term "fluorophore" is understood to mean a fluorochrome, a dye molecule, a organic or inorganic fluorophore, or metal chelate. A fluorophore can include a far-red or a near-infrared fluorophore. In certain embodiments, imaging agents disclosed herein include a fluorophore selected from the group consisting of a carbocyanine fluorophore or an indocyanine fluorophore. Exemplary fluorophores include sulfonated fluorophores. It is understood that fluorophores can also be nanoparticles having fluorescent or luminescent properties. [0064] In certain embodiments, the fluorophores are near infrared fluorophores (NIRFs) with absorption and emission maximum between about 600 nm and about 900 nm. It is appreciated that the use of fluorophores with excitation and emission wavelengths in other spectrums can also be employed in the compositions and methods of the present invention. [0065] For example, certain exemplary NIRFs have an extinction coefficient of at least 30,000 M ¹Cm^"1 per fluorophore molecule in aqueous medium, or at least 50,000 M ¹Cm^"1 per fluorophore molecule in aqueous medium. NIRFs preferably also have (1) high quantum yield (i.e., quantum yield greater than 5% in aqueous medium), (2) narrow excitation/emission spectrum, spectrally separated absorption and excitation spectra (i.e., excitation and emission maxima separated by at least 15 nm), (3) high chemical and photostability, (4) little or no nontoxicity, (5) good biocompatibility, biodegradability and excretability, and (6) commercial viability and scalable production for large quantities (i.e., gram and kilogram quantities) required for in vivo and human use.

0110[0066] An extinction coefficient of the agents that include a fluorophore can be calculated as the ratio of the absorbance of fluorophore at its absorption maxima (for example at -750 nm for VivoTag-S-750, VisEn Medical) in a 1 cm path length cell to the concentration of particles, (ε = A/cl, where A is absorbance, c is molar concentration and 1 is path length in cm).

0111[0067] In particular, certain carbocyanine or polymethine fluorescent fluorophores can be used to produce the imaging agents of the invention, for example, those described in

0112U.S. Patent No. 6,747,159; U.S. Patent No. 6,448,008; U.S. Patent No.6,136,612; U.S.

0113Patent No. 4,981,977; 5,268,486; U.S. Patent No. 5,569,587; U.S. Patent No. 5,569,766;

0114U.S. Patent No. 5,486,616; U.S. Patent No. 5,627,027; U.S. Patent No. 5,808,044; U.S.

0115Patent No. 5,877,310; U.S. Patent No. 6,002,003; U.S. Patent No. 6,004,536; U.S. Patent No. 6,008,373; U.S. Patent No. 6,043,025; U.S. Patent No. 6,127,134; U.S. Patent No.

01166,130,094; U.S. Patent No. 6,133,445; also WO 97/40104, WO 99/51702, WO 01/21624, and EP 1 065 250 Al; and Tetrahedron Letters 41, 9185-88 (2000).

0117[0068] Various useful, exemplary fluorophores are commercially available and include, for example: Cy5.5, Cy5 and Cy7 (GE Healthcare); AlexaFlour660, AlexaFlour680, AlexaFluor750, and AlexaFluor790 (Invitrogen); VivoTag680, VivoTag-S680, and VivoTag-S750 (VisEn Medical); Dy677, Dy682, Dy752 and Dy780 (Dyomics); DyLight547, DyLight647 (Pierce); HiLyte Fluor 647, HiLyte Fluor 680, and HiLyte Fluor 750 (AnaSpec); IRDye800CW, IRDye 800RS, and IRDye 700DX (Li-Cor) ; and ADS780WS, ADS830WS, and ADS832WS (American Dye Source).

0118[0069] Table 1 lists a number of exemplary fluorophores useful in the practice of the invention together with their spectral properties.

TABLE 1

0120<img file="WO2009092062A2_D0005.tif" />

0121[0070] For example, certain useful fluorophores are represented by the following general Formula VII:

0122<img file="WO2009092062A2_D0006.tif" />

0123or a salt thereof, wherein:

0124X is independently selected from the group consisting of C(CH₂Yi)(CH₂Y₂), O, S, and Se;

0125Y₁ and Y₂ are independently selected from the group consisting of H, Ci- C₂o aliphatic group and a Ci-C₂O aliphatic group substituted with -OR*, N(R^*)₂ or -SR*; W represents a benzo-condensed, a naphtho-condensed or a pyrido- condensed ring;

0126R₁ is selected from the group consisting of (CH₂)_XCH₃, (CH₂)_nSO₃^~ and (CH₂)_nSθ₃H, wherein x is an integer selected from 0 to 6 and n is an integer selected from 2 to 6;

0127R₂ and R₃ independently are selected, for each occurrence, from the group consisting of H, carboxylate, carboxylic acid, carboxylic ester, amine, amide, sulfonamide, hydroxyl, alkoxyl, a sulphonic acid moiety and a sulphonate moiety;

0128R₄ is selected from the group consisting of (CH₂)_XCH₃, (Ct^_nSCV and (CH₂)_nSθ₃H, wherein x is an integer selected from 0 to 6 and n is an integer selected from 2 to 6; and

0129Q is selected from a group consisting of a heteroaryl ring substituted with a carboxyl group or 6-membered heteroaryl ring substituted with a carbonyl group. [0071] In certain embodiments, Q can be selected from the group consisting of (i) a carboxyl functionalized heterocyclic ring, (ii) a carboxyl functionalized nitrogen containing heterocyclic ring, (iii) a carboxyl functionalized nitrogen containing 6- membered heterocyclic ring, such as pyridine, pyrimidone, pyrazine, and pyridazine, (iv) a carboxyl functionalized nitrogen containing 6-membered heterocyclic ring, such as pyridine, (v) a carbonyl functionalized nitrogen containing 6-membered heterocyclic ring, such as pyridine, (vi) an isonicotinic acid, nicotinic acid and picolinic acid, and a group selected from:

0130<img file="WO2009092062A2_D0007.tif" /> wherein the carboxyl group may also be in the form of an ester, an activated ester or carbonyl halide that is capable of reacting with nucleophiles, and can be, for example, a CO-O-benzotriazolyl, CO-ON-hydroxysuccinimidyl, CO-O-tetrafluorophenyl, CO-O- pentafluorophenyl, CO-0-imidazole, and CO-O-p-nitrophenyl.

0131[0072] Other useful, exemplary fluorophores are represented by the general Formula VII: -[(CH₂)_m-W-(CH₂)_p-(O)_k]_h(CH₂)_dZ

0132<img file="WO2009092062A2_D0008.tif" />

0133(VIII) or a salt thereof, wherein:

0134Xi and X₂ are independently selected from the group consisting of C(CH₂K₁)(CH₂K₂), O, S and Se;

0135Ki and K₂ are independently selected from the group consisting of H, a Ci-C_2O aliphatic group and a Ci-C_2O aliphatic group substituted with -OR*, N(R )₂ or- SR*; or Ki and K₂ together are part of a substituted or unsubstituted carbocyclic, or heterocyclic ring; Yi and Y₂ are each independently a benzo-condensed ring, a naphtha-condensed ring or a pyrido-condensed ring; ni is 1, 2, or 3;

0136R₂, Rn and R_J2 are independently H, F, Br, Cl, Ci-C₆ alkyl, Ci-C₆ alkoxy, aryloxy, a nitrogen-containing heterocyclic ring, a nitrogen-containing heteroaromatic ring, a sulfonate, an iminium ion, or any two adjacent Ri₂ and Rn substituents or R₂ and Rn substituents, when taken in combination, form a A-, 5-, or 6-membered substituted or unsubstituted carbocyclic ring, substituted or unsubstituted non-aromatic carbocyclic ring or a substituted or unsubstituted carbocyclic aryl ring, wherein the carbocyclic rings are each independently optionally substituted one or more times by Ci-C₆ alkyl, halogen, or OR* or SR*;

0137Ri and Ri₃ are (CH₂)_XCH₃, when x is an integer selected from 0 to 6; or Ri and Ri₃ are independently (CH₂)_nSθ₃^~ or (CH₂)_nSθ₃H when n is an integer selected from 2 to 6;

0138R₃, R₄ and R₅ are independently selected from the group consisting of H, carboxylate, carboxylic acid, carboxylic ester, amine, amide, sulfonamide, hydroxyl, alkoxyl, a sulphonic acid moiety and a sulphonate moiety;

0139Q is absent, or is selected from a carbonyl moiety or a substituted or unsubstituted Ci-C₆ alkyl group, wherein 0-2 of the methylene groups of the alkyl group can optionally be replaced by NH, O or S, or a substituted or unsubstituted Ci-C₆ carbocyclic, non-aromatic carbocyclic, heterocyclic or non-aromatic heterocyclic ring wherein the heterocyclic rings contains 1-2 heteroatoms;

0140R₆ is selected from the group consisting of H, a substituted or unsubstituted C₁-C₂₀ aliphatic group, a substituted or unsubstituted aryl, a substituted or unsubstituted alkylaryl, wherein R₆ is optionally substituted with halogen, OR*,

0141N(R )₂ or SR*, when Q is absent, a carbonyl group, a substituted or unsubstituted C₁-C₆ alkyl group, wherein 0-2 of the methylene groups of the alkyl group are replaced by NH, O or S, or a substituted or unsubstituted Ci-C₆ carbocyclic, non- aromatic carbocyclic, heterocyclic or non-aromatic heterocyclic ring wherein the heterocyclic rings contains 1-2 heteroatoms; or

0142R₆ is H, when Q is a carbonyl; and

0143R₇ is selected from the group consisting of H, a substituted or unsubstituted C₁-C₂₀ aliphatic group, a substituted or unsubstituted aryl, a substituted or unsubstituted alkylaryl, wherein R₇ is optionally substituted with halogen, OR*, N(R^*)₂ or SR*; or

0144R₆ and R₇, taken together form a 4-, 5-, 6- or 7-membered heterocyclic or non-aromatic heterocyclic ring optionally substituted with halogen, OR*, N(R )₂ or SR*; or

0145NR₆, Q and CHR₇ together form a substituted or unsubstituted or heterocyclic or non-aromatic heterocyclic ring system wherein the rings contain 1 or 2 heteroatoms, wherein rings are optionally substituted with -OR*, N(R )₂ or- SR*; and

0146W is absent or is a group selected from the group consisting Of -SO₂NR₆- Q-CHR₇-, -O-, -COO-, and -CONH-; h = 0-70; k = 0 or 1; d = 0-12; m = 0-12; p = 0-12; and

0147Z is, or contains a N, O or S nucleophile functionality or is, or contains a functionality capable of reacting with N, O or S nucleophiles; and each R* is independently H or Ci_-20 alkyl.

0148[0073] The imaging agents disclosed herein can include various fluorophore derivatives and other forms of fluorophores, such as N-hydroxysuccinimide forms of fluorophores. The fluorophores may be chemically linked to enzymatically cleavable oligopeptides using chemistries known in the art. [0074] Exemplary fluorophores that can be used in the synthesis of the imaging agents of the invention include, for example, those listed in Table 2.

TABLE 2

0150<img file="WO2009092062A2_D0009.tif" /><img file="WO2009092062A2_D0010.tif" />

0151[0075] In another embodiment, the fluorophore is a nanoparticle having fluorescent or luminescent properties. For example, an enzymatically cleavable oligopeptide can be grafted onto nanoparticles comprising silicon in a form that has fluorescent or luminescent properties or fluorescent nanoparticles. Aggregates of crystalline silicon (as multiple or single crystals of silicon), porous silicon, or amorphous silicon, or a combination of these forms, can form the nanoparticle. Preferred fluorescent silicon nanoparticles have a diameter from about 0.5 nm to about 25 nm, more preferably from about 2 nm and about 10 nm. The size of nanoparticles can be determined by laser light scattering or by atomic force microscopy or other suitable techniques.

0152[0076] Fluorescent silicon nanoparticles can have excitation and emission spectra 200 nm to 2000 nm, however, preferred fluorescent silicon nanoparticles have excitation and emission maximum from about 400 nm to about 1200 nm (and preferably 500 nm-900 nm, for example, 500 nm-600 nm, 600 nm-700 nm, 700 nm-800 nm, or 800 nm-900 nm). Preferred fluorescent silicon nanoparticles also have extinction coefficients of at least 50,000 M ¹Cm^"1 in aqueous medium. Although fluorescent silicon nanoparticles with excitation and emission maximum between 400 nm and 1200 nm are preferred, it will be appreciated that the use of fluorescent silicon nanoparticles with excitation and emission wavelengths in other spectrums can also be employed in the compositions and methods of the present invention. For example, in certain embodiments, the particles can have excitation approximately about 300-350 nm, and emission approximately about 400-450 nm. [0077] Fluorescent silicon nanoparticles also have the following properties: (1) high quantum yield (i.e., quantum yield greater than 5% in aqueous medium), (2) narrow emission spectrum (i.e., less than 75 nm; more preferably less than 50 nm), (3) spectrally separated absorption and emission spectra (i.e., separated by more than 20 nm; more preferably by more than 50 nm), (3) have high chemical stability and photostability (i.e., retain luminescent properties after exposure to light), (4) are biocompatible (as discussed below) or can be made more biocompatible; (5) are non toxic or minimally toxic to cells or subjects at doses used for imaging protocols, (as measured for example, by LD₅₀ or irritation studies, or other similar methods known in the art) and/or (6) have commercial viability and scalable production for large quantities (i.e., gram and kilogram quantities) required for in vivo use, for example use in humans.

0153[0078] Fluorescent quantum dots are also contemplated, for example, enzymatically cleavable oligopeptide can be grafted onto a fluorescent quantum dot such as amine T2 MP EviTags (Evident Technologies) or Qdot Nanocrystals (Invitrogen). In general, fluorescent quantum dots are nanocrystals containing several atoms of a semiconductor material (including but not limited to those containing cadmium and selenium, sulfide, or tellurium; zinc sulfide, indium-antimony, lead selenide, gallium arsenide, and silica or ormosil, which have been coated with zinc sulfide to improve the properties of these fluorescent agents.

0154[0079] Fluorophores can include metal oxide nanoparticles that are fluorescent and can be used in a variety of in vitro and vivo applications. In an embodiment, an enzymatically cleavable oligopeptide is conjugated to at least one fluorescent metal oxide nanoparticle with one or more of the following features: (1) a polymer coating suitable for attaching a plurality of fluorophores thereby achieving large extinction coefficients (in excess of 1,000,000 M^"1 cm^"1), (2) a non-crosslinked polymer coating suitable for attaching from about 10 to about 300 fluorophores per particle, (3) a polymer coating suitable for attaching a plurality of fluorophores in a manner that does not significantly compromise the quantum yield of the fluorophores (e.g., the nanoparticles retain at least 50% of the fluorescent signal that is created by substantially the same number of free fluorophores when tested under the same conditions), and (4) a polymer coating that is amenable to efficient chemical linking of biomolecules with retention of their biological properties to yield molecular imaging agents. The fluorescent metal oxide nanoparticles can be highly stable molecular imaging agents in vitro, both before and after chemical linking of fluorophores and agents, but yet are labile and/or degradable in vivo.

0155[0080] In certain embodiments, one or more different fluorophore molecules can be covalently linked to the oligopeptide, or alternatively, two substantially similar fluorophores can be covalently linked to the oligopeptide, at fluorescene-quenching permissive locations to produce the imaging agents of the present invention.

0156[0081] In certain embodiments, a quencher is used to quench the fluorescent signal from the fluorophore covalently linked to the oligopeptide. For example, an agent can be designed such that the quencher quenches the fluorescence of the fluorophore of the imaging agent when the agent is in an unactivated state, so that the imaging agent exhibits little or no signal until it is activated. It is understood that the quencher can be a non- fluorescent agent, which when suitably located relative to a fluorophore (i.e., at a fluorescence-quenching permissive location) is capable of quenching the emission signal from the fluorophore. As discussed above, it is understood that certain of the foregoing fluorphores can act to quench the fluorescent signal of another spaced apart fluorophore, when the two fluorophores are positioned at fluorescence-quenching interaction permissive locations.

0157[0082] A number of quenchers are available and known to those skilled in the art including, but not limited to 4-{[4-(dimethylamino)-phenyl]-azo}-benzoic acid (DABCYL), QSY^®-7 (9-[2-[(4-carboxy-l-piperidinyl)sulfonyl]phenyl]-3,6- bis(methylphenylamino)- xanthylium chloride) (Molecular Probes, Inc., OR), QSY^®-33 (Molecular Probes, Inc., OR), ATTO612Q, ATTO580Q (ATTO-TEC, Germany); Black Hole Quenchers® (Bioresearch Technologies, Novato, CA), QXL™680 Acid (AnaSpec, San Jose CA), and fluorescence fluorophores such as Cy5 and Cy5.5 (e.g., 2-[5-[3-[6- [(2,5-dioxo-l-pyrrolidinyl)oxy]-6-oxohexyl]-l,3-dihydro-l,l-dimethyl-6,8-disulfo-2H- benz[e]indol-2-ylidene]-l,3-pentadienyl]-3-ethyl-l,l-dimethyl-6,8- disulfo-lH- benz[e]indolium, inner salt) (Schobel, Bioconjugate 10:1107, 1999). Other quenching strategies can be used, for example, using various solvents to quench fluorescence of the agents.

0158[0083] Exemplary fluorophores that can quench the emission of other fluorophores are represented in Table 3.

TABLE 3

0160<img file="WO2009092062A2_D0011.tif" /> [0084] As with all the imaging agents discussed herein, the two fluorophores or the fluorophore and the quencher are located within the intact imaging agent at fluorescent- quenching interaction permissive positions. In other words, a first fluorophore is located close enough in the intact imaging agent to a second fluophore (or quencher) to permit them to interact photochemically with one another so that the second fluorophore (or quencher) quenches the signal from the first fluorophore. In the case of the imaging agents with two fluorophores, one fluorophore preferably quenches the other fluorophore. For principles of quenching, see U.S. Patent No. 6,592,847.

0161II. Non-Fluorescent Reporters [0085] The term "non-fluorescent reporter" as used herein, refers to a chemical moiety that is not fluorescent but which can be used to provide the contrast or signal in imaging and is detectable by a non-fluorescent imaging technique. In certain embodiments, other non-fluorescent reporters can be chemically linked with the imaging agents, or can be administered to a subject simultaneously or sequentially with the imaging agents of the invention. Such reporters can include photoluminescent nanoparticles, radioisotopes, superparamagnetic agents, X-ray contrast agents, and ultrasound agents. A reporter may also comprise therapeutic reporters such as porphyrins, Photofrin®, Lutrin®, Antrin®, aminolevulinic acid, hypericin, benzoporphryrin derivatives used in photodynamic therapy, and radionuclides used for radiotherapy. (A) Radioactive Reporters

0162[0086] The imaging agents can include one or more radioactive labels. Radioisotopic forms of metals such as copper, gallium, indium, technetium, yttrium, and lutetium can be chemically linked to the metallic imaging agents and can be used for nuclear imaging or therapeutic applications. Exemplary radioactive labels include, without limitation, ^99mTc, ¹¹¹In, ⁶⁴Cu, ⁶⁷Ga, ¹⁸⁶Re, ¹⁸⁸Re, ¹⁵³Sm, ¹⁷⁷Lu, and ⁶⁷Cu.

0163[0087] Other exemplary labels include, for example, ¹²³1, ¹²⁴I, ¹²⁵1, ¹¹C, ^:3N, ¹⁵O, and

1 R

0165F. Other exemplary labels can be therapeutic radiopharmaceuticals including for example,¹⁸⁶Re, ¹⁸⁸Re, ¹⁵³Sm, ¹⁶⁶Ho, ¹⁷⁷Lu, ¹⁴⁹Pm, ⁹⁰Y, ²¹²Bi, ¹⁰³Pd, ¹⁰⁹Pd, ¹⁵⁹Gd, ¹⁴⁰La, ¹⁹⁸Au, ¹⁹⁹Au, ¹⁶⁹Yb, ¹⁷⁵Yb, ¹⁶⁵Dy, ¹⁶⁶Dy, ⁶⁷Cu, ¹⁰⁵Rh, ¹¹¹Ag, and ¹⁹²Ir. [0088] Chelators or bonding moieties for diagnostic and therapeutic radiopharmaceuticals are also contemplated and can be chemically associated with the imaging agents. Exemplary chelators can be selected to form stable complexes with radioisotopes that have imageable gamma ray or positron emissions, such as ^99mTc, ¹¹¹In, 4Cu, and ⁷Ga. Exemplary chelators include diaminedi thiols, monoamine- monoamidedithiols, triamide-mono thiols, monoamine-diamide-monothiols, diaminedioximes, and hydrazines. Chelators generally are tetradentate with donor atoms selected from nitrogen, oxygen and sulfur, and may include for example, cyclic and acyclic polyaminocarboxylates such as diethylenetriaminepentaacetic acid (DTPA), 1,4,7, 10-tetraazacyclododecane-l,4,7,10-tetraacetic acid (DOTA), (D03A), 2-benzyl- DOTA, alpha-(2-phenethyl)l,4,7,10-tetraazazcyclododecane-l-acetic-4,7,10- tris(methylacetic)acid, 2-benzyl-cyclohexyldiethylenetriaminepentaacetic acid, 2-benzyl- 6-methyl-DTPA, and 6,6"-bis[N,N,N",N"-tetra(carboxymethyl)aminomethyl)-4'-(3- amino-4-methoxyphenyl)-2,2':6',2"-terpyridine.

0166[0089] Chelators or bonding moieties for therapeutic radiopharmaceuticals can be selected to form stable complexes with the radioisotopes that have alpha particle, beta particle, Auger or Coster-Kronig electron emissions, such as ¹⁸ Re, ¹⁸⁸Re, ^{1 3}Sm, ¹⁷⁷Lu, and ⁶⁷Cu. Chelators can be selected from diaminedithiols, monoamine - monoamidedithiols, triamide-mono thiols, monoamine-diamide-monothiols, diaminedioximes, and hydrazines, cyclic and acyclic polyaminocarboxylates such as DTPA, DOTA, D03A, 2-benzyl-DOTA, alpha-(2-phenethyl) 1,4,7, 10- tetraazacyclododecane- l-acetic-4,7, 10-tris(methylacetic)acid, 2-benzyl- cyclohexyldiethylenetriaminepentaacetic acid, 2-benzyl-6-methyl-DTPA, and 6,6"- bis[N,N,N",N"-tetra(carboxymethyl)aminomethyl)-4'-(3-amino-4-methoxyphenyl)- 2,2':6',2"-terpyridine. (B) Magnetic Reporters

0167[0090] Other exemplary reporters can include a chelating agent for magnetic resonance agents. Such chelators can include for example, polyamine-polycarboxylate chelators or iminoacetic acid chelators that can be chemically linked to the agents.

0168[0091] Chelators for magnetic resonance imaging agents can be selected to form stable complexes with paramagnetic metal ions, such as Gd(III), Dy(III), Fe(III), and Mn(II), are selected from cyclic and acyclic polyaminocarboxylates such as DTPA, DOTA, D03A, 2- benzyl-DOTA, alpha- (2-phenethyl)l ,4,7, 10-tetraazacyclododecane- l-acetic-4,7, 10- tris(met hylacetic)acid, 2-benzyl-cyclohexyldiethylenetriaminepentaacetic acid, 2-benzyl- 6-methyl-DTPA, and 6,6"-bis[N,N,N",N"-tetra(carboxymethyl)aminomethyl)-4'-(3- amino-4-methoxyp henyl)-2,2' : 6' ,2 " -terpyridine. [0092] In one embodiment, the imaging agents are chemically linked to superparamagnetic metal oxide nanoparticles that are either (a) non-fluorescent or (b) are fluorescent and can be used in a variety of in vitro and in vivo applications. Fluorescent metal oxide nanoparticles that also have magnetic properties can be used for MRI, thus providing a multi-modality imaging agent. [0093] In certain embodiments, the imaging agents can include a fluorescent and/or non- fluorescent superparamagenetic metal oxide nanoparticle with one or more of the following features: (1) a polymer coating suitable for attaching a plurality of agents (2) a non-crosslinked polymer coating suitable for attaching from about 10 to about 300 agents per particle, and (3) a polymer coating that is amenable to efficient chemical linking of the agents with retention of their biological properties to yield molecular imaging agents. The agent modified metal oxide nanoparticle can be a highly stable molecular imaging agent in vitro, both before and after chemical linking of the agents, but yet are labile and/or degradable in vivo.

0169(C) Ultrasound Reporters [0094] A non-fluorescent reporter can include gas-filled bubbles such as Levovist, Albunex, or Echovist, or particles or metal chelates where the metal ions have atomic numbers 21-29, 42, 44 or 57-83, for example to facilitate ultrasound imaging. Examples of such compounds are described in Tyler et al., Ultrasonic Imaging, 3, pp. 323-29 (1981) and D.P. Swanson, "Enhancement Agents for Ultrasound: Fundamentals," Pharmaceuticals in Medical Imaging, pp. 682-87 (1990).

0170(D) X-Ray Reporters

0171[0095] Exemplary reporters can comprise of iodinated organic molecules or chelates of heavy metal ions of atomic numbers 57 to 83, for example, for X-ray imaging. Examples of such compounds are described in M. Sovak, ed., "Radiocontrast Agents," Springer- Verlag, pp. 23-125 (1984) and U.S. Patent No. 4,647,447. III. Linkers

0172[0096] Linker or spacer moieties can be used to covalently link one or more fluorophores, quenchers, biological modifiers and non-fluorescent reporters to an enzymatically cleavable oligopeptide or to an optional biological modifier to produce agents of the present invention. It is understood that there is no particular structural, size or content limitation of a linker, if present. Linkers can include, for example, a variety of functional groups such as maleimide, dithiopyridyl, thiol, azide, alkene, or alkyne that permit the assembly of molecules of diverse architecture.

0173[0097] Linkers can be homofunctional linkers or heterofunctional linkers. For example, amine (Nty-functionalized moieties can be reacted with bifunctional cross-linkers designed to react with amino groups. Particularly useful conjugation reagents that can facilitate formation of a linker or facilitate covalent linkage between, for example, a fluorophore, and an enzymatically cleavable oligopeptide can include a N- hydroxysuccinimide (NHS) ester and/or a maleimide. The NHS ester can react with the amine group of, for example, a peptide or fluorophore. The maleimide can react with the sulfhydryl group of another molecule. Other particularly useful linker moieties are bifunctional crosslinkers such as N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP), long chain-SPDP, maleimidobenzoic acid-N-hydroxysuccinimide ester (MBS), succinimidyl trans-4-(maleimidylmethyl)cyclohexane- 1-carboxylate (SMCC), succinimidyl iodoacetate (SIA).

0174[0098] In certain embodiments a linker, if present, may be a derivative of a diamine. A diamine moiety or derivative can provide a linker arm of varying lengths and chemistries for chemically linking molecules by derivatizing, optionally, with carboxylic acids. Non- limiting examples of diamines include ethylenediamine (EDA), propylenediamine, spermidine, spermine, hexanediamine, and diamine-amino acids, such as homolysine, lysine, ornithine, diaminobutyric acid and diaminopropionic acid. In other embodiments, moieties of an imaging agent can be chemically linked to a dicarboxylic acid, for example, succinic acid, glutaric acid, suberic acid, or adipic acid. In one embodiment, the linker is aminoethylmaleimide . [0099] In certain embodiments, a linker can be formed from an azide moiety that can react with substituted alkynes in an azide- acetylene Huisgen [3+2] cycloaddition. In certain embodiments the azide or alkyne linker can link a polyethyleneglycol (PEG) moiety to, for example, an enzymatically cleavable oligopeptide. Other contemplated linkers include propargylglycine, pentanoyl, pentynoic acid, propargylic acid, and/or propargylamine moieties. [00100] In certain embodiments, fluorophores, quenchers, or other reporters are directly linked to the imaging agent using reactive NHS ester groups on the fluorophores, quenchers, or reporters which react with an amine group on the enzymatically cleavable oligopeptide. In certain other embodiments, carboxylic acid groups on the fluorophores, quenchers, or other reporters can be activated in situ by activating agents known in the art, such as 2-(lH-benzotriazole-l-yl)-l,l,3,3,-tetramethyluronium hexafluorophosphate

0175(HBTU), l-ethyl-3-(3'-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), N,N'- dicyclohexylcarbodiimide (DCC), N,N'-disuccinimidyl carbonate (DSC). In other embodiments, reporters including a sulfhydryl or thiol group, can be chemically linked to the agent via a bifunctional cross-linker that has a second moiety that can react with a sulfhydryl (thiol) group. Such crosslinking agents include, for example and as described above, SPDP, long chain-SPDP, SIA, MBS, SMCC, and others that are well known in the art.

0176[00101] Useful linker moieties include both natural and non-natural amino acids, oligopeptides, for example, linear or cyclic oligopeptides, and nucleic acids. [00102] The linker can be a peptide or peptide moiety which optionally includes a proteolytic or non-proteolytic cleavage site, such as anester linkage, that can be cleaved due to pH changes at the site of interest.

0177IV Biological Modifiers

0178[00103] As used herein, the term "biological modifier" is understood to mean any moiety that can be used to alter the biological properties of the imaging agent, such as, without limitations, making the imaging agent more water soluble or more dispersible in media for administration, increasing binding specificity, decreasing immunogenicity or toxicity, or modifying pharmacokinetic profile compared to the non-biological modifier modified agents. [00104] In an embodiment, one or more biological modifiers can be chemically linked to the enzymatically cleavable oligopeptide or fluorophore. In one embodiment, the biological modifier is covalently linked to the enzymatically cleavable peptide at a position that is not between two amino acids covalently linked to a fluorophore or a quencher. [00105] Exemplary biological modifiers include polyethylene glycol (PEG) and derivatives thereof (for example, alkoxy polyethylene glycol (for example, methoxypolyethylene glycol, ethoxypolyethylene glycol and the like), branched polypropylene glycol, polypropylene glycol, a graft copolymer of poly-lysine and methoxypolyethyleneglycol, amino acids, peptides, lipids, fatty acids, palmitate, phospholipids, phospholipid-PEG conjugates, carbohydrates (such as dextran, amino- dextran, carboxymethyl-dextran), iron oxide nanoparticles, sulfonates, poly sulfonates, cysteic acid, naphthylalanine, phenylalanine, and 3,3-diphenylpropylamine.

0179[00106] In general, the biological modifier may have a molecular weight of from about 2 kDa to less than 50 kDa, such as from about 5 kDa to about 40 kDa, such as from about 10 kDa to about 35 kDa, further such as from about 15 kDa to 30 kDa. In another embodiment, the biological modifier may have a molecular weight of from about 5 kDa to about 45 kDa, such as from about 5 kDa to about 40 kDa, such as from about 5 kDa to about 35 kDa, such as from about 5 kDa to about 30 kDa, such as from about 5 kDa to about 25 kDa, such as from about 5 kDa to about 20 kDa, such as from about 5 kDa to about 15 kDa, further such as from about 5 kDa to 10 kDa. In another embodiment, the biological modifier may have a molecular weight of from about 2 kDa to less than 50 kDa, such as from about 2 kDa to about 45 kDa, such as from about 2 kDa to about 40 kDa, such as from about 2 kDa to about 35 kDa, such as from about 2 kDa to about 30 kDa, such as from about 2 kDa to about 25 kDa, such as from about 2 kDa to about 10 kDa, further such as from about 2 kDa to 5 kDa.

0180[00107] In certain embodiments, as discussed above, the biological modifier may be a PEG moiety that has a molecular weight, for example, from about 0.5 kDa to about 50 kDa, about 5 kDa to about 35 kDa, or about 10 kDa to about 30 kDa. Alternatively, the PEG may be dPEG, functionalized at a discrete molecular weight, for example, of about HOO daltons.

0181[00108] In certain embodiments, the PEG is methoxyPEG₍₅ooo₎-succinimidylpropionate (mPEG-SPA), methoxyPEG₍₅ooo₎-succinimidylsuccinate (mPEG-SS). Such PEGS are commercially available from Nektar Therapeutics or SunBiowest or LaysanBio or NOF.

0182[00109] In one embodiment, a PEG moiety may be conjugated to reactive amines on the enzymatically cleavable oligopeptide or fluorophore via a carboxyl functionality. Alternatively, the PEG modifier can be conjugated to the enzymatically cleavable oligopeptide or fluorophore by using a thiol reactive cross linker and then reacting with a thiol group on the PEG.

0183[00110] In one embodiment, the PEG may be branched, or Y-shaped, as available from JenKem USA or NOF, or comb-shaped, or synthesized by coupling two or more PEGs to a small molecule such as glutamic acid.

0184[00111] The omega position of PEG may include a hydroxyl group or a methoxy group and the PEG may also contain an amino group in the omega position. Such an amino group can in turn be coupled to a variety of agents. In another embodiment of the present invention, the biological modifier can be a pegylated poly-L-lysine or a pegylated poly-D- lysine.

0185[00112] In other embodiments, the biological modifier can be polyvinylpyrrolidone (PVP)-type polymers. The biological modifier can be a functionalized polyvinylpyrrolidone, for example, carboxy or amine functionalized on one (or both) ends of the polymer (as available from Polymersource) or within the polymer chain. [00113] Alternatively, the biological modifier can include Poly N-(2- hydroxypropyl)methacrylamide (HPMA), or functionalized HPMA (amine, carboxy, etc.), Poly(N-isopropyl acrylamide)or functionalized poly(N-isopropylacrylamide).

0186[00114] Biological modifiers can include straight or branched chain acyl groups, such as pentynoyl; acidic groups, such as succinyl; lower alkyl groups, such as methyl, ethyl, propyl, etc.; carboxyalkyl groups, such as carboxyethyl; haloalkyl groups, such as trifluoromethyl; and the like.

0187[00115] In other embodiments, the biological modifier can include, but is not limited to, proteins, peptides, antibodies and antigen binding fragments thereof (for example, Fab, Fab', (Fab')₂ fragments), single chain antibodies or sFvs, oligonucleotides, aptamers, glycoproteins, ligands for cell receptors, polysaccharides, cell receptors, enzyme substrates, enzyme cofactors, biotin, hormones, neurohormones, neurotransmitters, growth factors, cytokines, lymphokines, lectins, selectins, toxins, nucleic acids, oligonucleotides and derivatives thereof. Other biomolecules can also be used, such as folate-mediated targeting molecules(Leamon &amp; Low, Drug Discovery Today, 6:44-51, 2001), transferrin, vitamins, carbohydrates and ligands that target internalizing receptors, including, but not limited to, asialoglycoprotein receptor, somatostatin, nerve growth factor, oxytocin, bombesin, calcitonin, arginine vasopressin, angiotensin II, atrial natriuretic peptide, insulin, glucagons, prolactin, gonadotropin, various opioids and urokinase-type plasminogen activator. Biomolecules such as integrin targeting agents are contemplated, such as α_vβ3 and GPccπbβ3, bombesin, CD4 and VCAM-I. Also contemplated are peptides for Hepsin, SPARC, PARl, colon cancer, Factor 13.

0188[00116] Exemplary peptides for use as biological modifiers include: (Hepsin) Ile-Pro- Leu-Val-Leu-Pro-Leu (SEQ ID NO: 1); (SPARC) Ser-Pro-Pro-Thr-Gly-Ile-Asn (SEQ ID NO:2); (VCAMl) Val-His-Pro-Lys-Gln-His-Arg (SEQ ID NO:3); (Cathepsin K) Val-His- Pro-Lys-Gln-His-Arg (SEQ ID NO:4); (E-selection binding peptide) Cys-Asp-Ser-Asp- Ser-Asp-Ile-Thr-Trp-Asp-Gln-Leu-Trp-Asp-Asp-Leu-Met-Lys (SEQ ID NO:5); and (Tat) Arg-Arg-Arg-Arg-Gly-Arg-Arg-Arg-Arg (SEQ ID NO:6).

0189[00117] Other contemplated biological modifiers include membrane, transmembrane, and nuclear translocation signal compounds and sequences, which can be derived from a number of sources including, without limitation, viruses and bacteria. Non- limiting examples include HIV-tat derived peptides, protamine, and polyArg and Arg-rich peptides.

0190[00118] Biological modifiers can also include synthetic compounds including, but not limited to, small molecule drugs, phototherapeutic molecules and derivatives thereof. Other contemplated biological modifiers include antibiotics such as vancomycin, clindamycin, chemotherapeutics such as doxorubicin, molecules such as glycine, derivatives of AMG706, Zactima™, MP-412, erlotinib, sorafenib, dasatinib, lestaurtinib, lapatinib, XL647, XL999, MLN518, PKC412, STI571, AMN107, AEE788, OSI-930, OSI-817, sunitinib, AG-013736; molecules that target/inhibit VEGF receptors, PDGF receptor, HER2, SSKI, EphB4, EGFR, FGFR, VEGFR-2, VEGFR-3, serine/threonine and receptor kinases, FLT-3, type III RTKs, c-KIT, Bcr-Abl, CSF-IR, CCR-2, RET, VDGF-2 and photodynamic reagents including but not limited to Chlorin e6, Photofrin®, Lutrin®, Antrin®, aminolevulinic acid, hypericin, porphyrins, and porphyrin derivatives, for example, benzoporphyrin derivative.

0191[00119] The biological modifiers may, under certain circumstances, render the imaging agents more useful for biological imaging. For example, the biological modifer may render agents more water soluble, and/or more dispersible in media for administration and/or may have an increased binding specificity, and/or may be less immunogenic and/or less toxic, and/or have a reduced non-specific binding and/or altered biodistribution and/or pharmacokinetic profile as compared to a non-biologically modified agents. For example, incorporation of methoxypolyethylene glycol (mPEG) or polypeptides may function to modify the pharmacodynamics and blood clearance rates of the agents in vivo. Other biological modifiers may be chosen to accelerate the clearance of the agents from background tissue, such as muscle or liver, and/or from the blood, thereby reducing the background interference and improving image quality. Additionally, the biological modifiers may also be used to favor a particular route of excretion, e.g., via the kidneys rather than via the liver. The biological modifiers may also aid in formulating agents in pharmaceutical compositions or may be used to alter or preserve the signal reporting properties of the agents. In one embodiment of the present invention, the biological modifier can be a polyamino acid or a peptide, including cyclic peptides. In particular, chemical linking of polyethylene glycol (PEG) or a derivative thereof to agents can result in longer blood residence time (longer circulation) and decreasing immunogenicity.

0192V. Enzymatically Cleavable Oligopeptides

0193[00120] As used herein, the term "enzymatically cleavable oligopeptide" is understood to mean a peptide comprising two or more amino acids (as defined herein) that are linked by means of a enzymatically cleavable peptide bond. Also included are moieties that include a pseudopeptide or peptidomimetic. Examples of cleavable peptide substrates can be found in U.S. Patent No. 7,439,319.

0194[00121] The term "amino acid" as used herein is understood to mean an organic compound containing both a basic amino group and an acidic carboxyl group. Included within this term are natural amino acids (e.g., L-amino acids), modified and unusual amino acids (e.g., D-amino acids), as well as amino acids which are known to occur biologically in free or combined form but usually do not occur in proteins. Natural amino acids include, but are not limited to, alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, serine, threonine, tyrosine, tyrosine, tryptophan, proline, and valine. Other amino acids include, but not limited to, arginosuccinic acid, citrulline, cysteine sulfinic acid, 3,4-dihydroxyphenylalanine, homocysteine, homoserine, ornithine, carnitine, selenocysteine, selenomethionine, 3-monoiodotyrosine, 3,5-diiodotryosine, 3,5,5'- triiodothyronine, and 3,3',5,5'-tetraiodothyronine.

0195[00122] Modified or unusual amino acids which can be used to practice the invention include, but are not limited to, D-amino acids, hydroxylysine, dehydroalanine, pyrrolysine, 2-aminoisobutyric acid, gamma aminobutyric acid, 5 -hydroxy tryptophan, S- adenosyl methionine, S-adenosyl homocysteine, 4-hydroxyproline, an N-Cbz-protected amino acid, 2,4-diaminobutyric acid, homoarginine, norleucine, N-methylaminobutyric acid, naphthylalanine, phenylglycine, .beta.-phenylproline, tert-leucine, A- aminocyclohexylalanine, N-methyl-norleucine, 3,4-dehydroproline, N,N- dimethylaminoglycine, N-methylaminoglycine, 4-aminopiperidine-4-carboxylic acid, 6- aminocaproic acid, trans-4-(aminomethyl)-cyclohexanecarboxylic acid, 2-, 3-, and A- (aminomethyl)-benzoic acid, 1-aminocyclopentanecarboxylic acid, 1- aminocyclopropanecarboxylic acid, and 2-benzyl-5-aminopentanoic acid. [00123] As used herein, a "pseudopeptide" or "peptidomimetic" is a compound which mimics the structure of an amino acid residue or a peptide, for example, by using linking groups other than via amide linkages (pseudopeptide bonds) and/or by using non-amino acid substituents and/or a modified amino acid residue. A "pseudopeptide residue" means that portion of a pseudopeptide or peptidomimetic that is present in a peptide. The term "pseudopeptide bonds" includes peptide bond isosteres which may be used in place of or as substitutes for the normal amide linkage. These substitute or amide "equivalent" linkages are formed from combinations of atoms not normally found in peptides or proteins which mimic the spatial requirements of the amide bond and which should stabilize the molecule to enzymatic degradation. The following conventional three-letter amino acid abbreviations are used herein: Ala = alanine; Aca = aminocaproic acid, Ahx = 6-aminohexanoic acid, Arg = arginine; Asn = asparagines; Asp = aspartic acid; Cha = cyclohexylalanine; Cit = citrulline; Cys = cysteine; Dap = diaminopropionic acid; GIn = glutamine; GIu = glutamic acid; GIy = glycine; His = histidine; lie = isoleucine; Leu = leucine; Lys = lysine; Met = methionine; NaI = naphthylalanine; NIe = norleucine; Om = ornithine; Phe = phenylalanine; Phg = phenylglycine; Pro = praline; Sar = sarcosine; Ser = serine; Thi = Thienylalanine; Thr = threonine; Trp = tryptophan; Tyr = tyrosine; and VaI = valine. Use of the prefix D- indicates the D-isomer of that amino acid; for example D- lysine is represented as D-Lys.

0196[00124] The peptides can be synthesized using either solution phase chemistry or solid phase chemistry or a combination of both (Albericio, Curr. Opinion. Cell Biol., 8, 211-221 (2004), M. Bodansky, Peptide Chemistry: A Practical Textbook, Springer- Verlag; N.L. Benoiton, Chemistry of Peptide Synthesis, 2005, CRC Press).

0197[00125] Selective or orthogonal amine protecting groups may be required to prepare the agents of the invention. As used herein, the term "amine protecting group" means any group known in the art of organic synthesis for the protection of amine groups. Such amine protecting groups include those listed in Greene, "Protective Groups in Organic

0198Synthesis" John Wiley &amp; Sons, New York (1981) and "The Peptides: Analysis, Synthesis, Biology, Vol. 3, Academic Press, New York (1981). Any amine protecting group known in the art can be used. Examples of amine protecting groups include, but are not limited to, the following: 1) acyl types such as formyl, trifluoroacetyl, phthalyl, and p- toluenesulfonyl; 2) aromatic carbamate types such as benzyloxycarbonyl (Cbz or Z) and substituted benzyloxycarbonyls, l-(p-biphenyl)-l-methylethoxycarbonyl, and 9- fluorenylmethyloxycarbonyl (Fmoc); 3) aliphatic carbamate types such as tert- butyloxycarbonyl (Boc), ethoxycarbonyl, diisopropylmethoxycarbonyl, and allyloxycarbonyl; 4) cyclic alkyl carbamate types such as cyclopentyloxycarbonyl and adamantyloxycarbonyl; 5) alkyl types such as triphenylmethyl and benzyl; 6) trialkylsilane such as trimethylsilane; and 7) thiol containing types such as phenylthiocarbonyl and dithiasuccinoyl. Also included in the term "amine protecting group" are acyl groups such as azidobenzoyl, p-benzoylbenzoyl, o-benzylbenzoyl, p- acetylbenzoyl, dansyl, glycyl-p-benzoylbenzoyl, phenylbenzoyl, m-benzoylbenzoyl, benzoylbenzoyl.

0199[00126] In certain embodiments the enzymatically cleavable oligopeptide can include oligo-L-arginine, oligo-L-lysine, oligo-L-aspartic acid or oligo-L-glutamic acid.

0200[00127] In certain embodiments the enzymatically cleavable oligopeptide includes lysine and arginine. In certain embodiments of the present invention, the enzymatically cleavable oligopeptide can include lysine, arginine and phenylalanine, or may include lysine, phenylalanine and glycine. In another embodiment, the enzymatically cleavable oligopeptide can include lysine, phenylalanine, leucine, and glycine, or can include ornithine, phenylalanine, leucine, and glycine. In one embodiment, the enzymatically cleavable oligopeptide may include diaminopropionic acid, ornithine, phenylalanine, leucine, and glycine.

0201[00128] Exemplary enzymatically cleavable oligopeptides are set forth in Table 4.

TABLE 4

0203<img file="WO2009092062A2_D0012.tif" /><img file="WO2009092062A2_D0013.tif" /><img file="WO2009092062A2_D0014.tif" /><img file="WO2009092062A2_D0015.tif" /><img file="WO2009092062A2_D0016.tif" />

0204<img file="WO2009092062A2_D0017.tif" />

0205[00129] Other exemplary enzymatically cleavable oligopeptides include a Cys-S-S-Cys moiety.

0206[00130] In one embodiment of the present invention, the enzymatically cleavable oligopeptide can be a enzymatically cleavable cyclic peptide, which may for example, include about 4 to about 30 amino acids. In one embodiment of the present invention, the agent can include 2-5 cyclic peptides. In another embodiment of the present invention, the cyclic peptide may include an acyclic component.

0207[00131] Cyclic peptides can be prepared by methods known in the art, for example, by the linking the N-terminus of a linear peptide with the C-terminus of the linear peptide: head-to-tail cyclization. Such linkages can be via a bond, for example, an amide bond or through a linker. In one embodiment, cyclic peptides can be prepared by the linking the N-terminus of a linear peptide with the side chain carboxylic acid of a linear peptide, by the linking the side chain amine of a linear peptide with the C-terminus carboxylic acid of a linear peptide, or by the linking the side chain amine of a linear peptide with the side chain carboxylic acid of a linear peptide. For example, cyclic peptides can be prepared by the linking the side chain thiol group of a linear peptide with the side chain thiol group of a linear peptide; for example by forming a Cys-Cys disulfide bond. Cyclic peptides can be made in solution phase or on solid phase and that cyclization of linear peptides can be achieved in solution phase or on solid phase.

0208[00132] Cyclic peptides are described using conventional nomenclature. For example a head to tail cyclic peptide containing Arg, GIy, Asp, Phe, Lys can be written as cyclo(Arg- Gly-Asp-Phe-Lys)(SEQ ID NO:224); a cyclic peptide containing Cys, Arg, GIy, Asp, Cys can be shown as follows: head to tail: cyclo(Cys-Arg-Gly-Asp-Cys)(SEQ ID NO:225); disulphide: Cvs-Arg-Glv-Asp-Cvs (SEQ ID NO:225).

0209[00133] In certain embodiments, the enzymatically cleavable cyclic oligopeptide can include oligo-L-arginine, oligo-L-lysine, oligo-L-aspartic acid or oligo-L-glutamic acid. In certain embodiments the enzymatically cleavable cyclic oligopeptide includes lysine and arginine. In another embodiment of the present invention, the enzymatically cleavable cyclic oligopeptide includes lysine, arginine and phenylalanine. In one embodiment, an enzymatically cleavable cyclic oligopeptide includes lysine, phenylalanine and glycine, or includes lysine, phenylalanine, leucine, and glycine, or includes ornithine, phenylalanine, leucine, and glycine. In another embodiment, the enzymatically cleavable cyclic oligopeptide comprises diaminopropionic acid, ornithine, phenylalanine, leucine, and glycine.

0210[00134] In one embodiment of the present invention, the enzymatically cleavable cyclic oligopeptide may include one or more enzymatically cleavable oligopeptide units.

0211[00135] Exemplary enzymatically cleavable cyclic oligopeptides include those shown in Table 5. TABLE 5

0212<img file="WO2009092062A2_D0018.tif" />

0213[00136] Such cyclopeptides may include peptide structures wherein one or two proteolytic events may be required for activation of the agent.

0214[00137] The enzymatically cleavable oligopeptide is cleavable by at least one enzyme chosen from hydrolases, elastases, cathepsins, matrix metalloproteases, peptidases, exopeptidases, endopeptidases, carboxypeptidases, glycosidases, lipases, nucleases, lyases, amylases, phospholipases, phosphatases, phosphodiesterases, sulfatases, serine proteases, subtilisin, chymotrypsin, trypsin, threonine proteases, cysteine proteases, calpains, papains, caspases, aspartic acid proteases, pepsins, chymosins, glutamic acid proteases, renin, reductases, and parasitic, viral and bacterial enzymes.

0215VI. Exemplary Imaging Agents

0216[00138] Useful imaging agents can be created using one or more of the enzymatically cleavable oligopeptides, fluorophores, quenchers (if appropriate), biological modifiers and non- fluorescent reporters described herinabove and coupled together using standard chemistries known in the art. The imaging agents can be water soluble or water dispersible (i.e., sufficiently soluble or suspendable in aqueous or physiological media solutions). The in vivo half-life of the agent can be designed to be at least about 10 minutes, but more preferably 30 minutes to several hours. The in vivo half-life of the agent preferably is a time (for example, at least about 30 minutes) sufficient to achieve good tissue exposure, target binding, and imaging signal. In a preferred embodiment, the agent imaging probe is water soluble or dispersible in aqueous media, and is biocompatible i.e., non-toxic having, for example, an LD₅₀ of greater than about 50 mg/kg body weight. The imaging agents also preferably do not have any undesired phototoxic properties and/or display low serum protein binding affinity.

0217[00139] In certain embodiments, the disclosed agents include peptide or linker moieties capable of releasing one, two or more fluorophores from the oligopeptide and/or biological modifier upon contact with an enzyme. Such imaging agents can include a biological modifier that can be released from a cleavable oligopeptide by an enzyme that is different from the one that cleaves the peptide.

0218[00140] Certain preferred imaging agents are disclosed in the sections that follow. [00141] One exemplary imaging agent represented by Formula Q77 includes [Ac]-

0219Lys(F5)-Gly-Phe-Leu-Gly-Gly-Lys(F5)-[OH] (SEQ ID NO:235), wherein Ac is an acetyl group and F5 is represented by:

0220<img file="WO2009092062A2_D0019.tif" /> [00142] One exemplary imaging agent represented by Formula Q77 includes

0221<img file="WO2009092062A2_D0020.tif" />

0222[00143] One exemplary imaging agent represented by Formula Q88 includes [Ac]- Lys(F6)-Gly-Phe-Leu-Gly-Gly-Lys(F6)-[OH] (SEQ ID NO:236), wherein Ac is an acetyl group and F6 is

0223<img file="WO2009092062A2_D0021.tif" />

0224[00144] One exemplary imaging agent represented by Formula Q88 includes

0225<img file="WO2009092062A2_D0022.tif" />

0226[00145] An exemplary imaging agent represented by Q90 includes [F5]-Gly-Phe-Leu-Gly-Gly-Lys(F5)-[OH] (SEQ ID NO:237), wherein F5 is

0227<img file="WO2009092062A2_D0023.tif" />

0228[00146] An exemplary imaging agent represented by the Formula Q90 can be depicted as:

0229<img file="WO2009092062A2_D0024.tif" />

0230[00147] Other exemplary imaging agents can include moieties set forth in Table 6.

TABLE 6

0232<img file="WO2009092062A2_D0025.tif" /><img file="WO2009092062A2_D0026.tif" /><img file="WO2009092062A2_D0027.tif" /><img file="WO2009092062A2_D0028.tif" />

0233<img file="WO2009092062A2_D0029.tif" />

0234[00148] As used in Table 6, F5 is the fluorochrome as depicted above in agent Q77, F6 is the fluorochrome as depicted above in agent Q88, MPEG is methoxypolyethylene glycol of a specified molecular weight (for example, mPEG20K is a 20 kDa methoxypolyethylene glycol). Ahx is aminohexanoic acid, Orn is ornithine, and DAP is 2,3-diaminopropionic acid.

0235[00149] Figure 10 is a schematic represention of an exemplary cyclic imaging agent. The cyclic imaging agent comprises two peptides connected at each end to a fluorophore. A first peptide has a first fluorophore attached in the vicinity of its N-terminus and a second fluorophore attached in the vicinity of its C-terminus, and a second oligopeptide has the first fluorophore attached in the vicinity of its C-terminus and the second fluorophore attached in the vicnity of its N-terminus. When intact, the fluorophore quenches the other fluorophore, and more preferably each fluorophore quenches the other fluorophore. It is understood, howver, that one of the fluorophores could be replaced with a suitable non fluorescent quencher. Although both peptides, as shown, contain a proteolytic cleavage site, it is understood that, under certain circumstances, only one of the two peptides may have a proteolytic cleavage site. Upon cleavage of the proteolytic cleavage site(s), the fluorophores are no longer constrained in fluorescent quenching proximity to one another and the fluorophores can now fluorescence upon excitation following exposure to light of an appropriate wavelength.

0236[00150] Exemplary cyclic imaging agents can include an enzymatically cleavable cyclic oligopeptide, for example, an agent represented by Formula IX, wherein, for each occurrence, X is an amino acid residue, M is a biological modifier, F is a fluorophore or quencher, X₁* is X-L, X₂* is X-L, and L is a linker moiety or a bond:

0237<img file="WO2009092062A2_D0030.tif" />

0238[00151] Another exemplary enzymatically cleavable cyclic oligopeptide is represented by Formula X, wherein each X, M, F, X₁* and X₂* is as defined for Formula IX:

0239<img file="WO2009092062A2_D0031.tif" /> [00152] In another embodiment, an enzymatically cleavable cyclic oligopeptide is represented by Formula XI, wherein each X, M, F, X₁* and X₂* is as defined in Formula II, above:

0240<img file="WO2009092062A2_D0032.tif" />

0241[00153] Other exemplary enzymatically cleavable cyclic oligopeptides are represented by Formulas V, VI, and XII-XVII wherein, each F, M, X₁*, and X₂* is as defined in Formula IX:

0242<img file="WO2009092062A2_D0033.tif" /><img file="WO2009092062A2_D0034.tif" /> ID NO:446) (XIII) <img file="WO2009092062A2_D0035.tif" /><img file="WO2009092062A2_D0036.tif" /><img file="WO2009092062A2_D0037.tif" /><img file="WO2009092062A2_D0038.tif" />

0243[00154] An enzymatically cleavable cyclic oligopeptide is represented by Formula XIII, wherein the fluorophore and modifiers are as discussed hereinabove: MODIFIER <img file="WO2009092062A2_D0039.tif" />

0244[00155] In an exemplary embodiment, an enzymatically cleavable cyclic oligopeptide imaging agent can also be represented as Formula XIX wherein the biological modifiers are as described hereinabove:

0245<img file="WO2009092062A2_D0040.tif" />

0246[00156] The resulting imaging agents preferably have a molecular weight from about 2 kDa to about 60 kDa, such as from about 5 kDa to about 50 kDa, such as from about 10 kDa to about 40 kDa, or from about 20 kDa to about 30 kDa. In certain embodiments, the imaging agent may have a molecular weight of from about 2 kDa to about 50 kDa, such as from about 2 kDa to about 45 kDa, such as from about 2 kDa to about 40 kDa, such as from about 2 kDa to about 35 kDa, such as from about 2 kDa to about 30 kDa, such as from about 2 kDa to about 25 kDa, such as from about 2 kDa to about 10 kDa, or such as from about 2 kDa to 5 kDa. In certain other embodiments, the intact imaging agent may have a molecular weight of from about 5 kDa to about 50 kDa, such as from about 5 kDa to about 45 kDa, such as from about 5 kDa to about 40 kDa, such as from about 5 kDa to about 35 kDa, such as from about 5 kDa to about 30 kDa, such as from about 5 kDa to about 25 kDa, such as from about 5 kDa to about 20 kDa, such as from about 5 kDa to about 15 kDa, or such as from about 5 kDa to about 10 kDa. VII. Formulations

0247[00157] The imaging agents disclosed herein can be formulated into a pharmaceutical composition suitable for administration to a subject, for example, an animal and/or a human. The pharmaceutical composition can include one or more imaging agents and one or more excipients, for example, a stabilizer in a physiologically relevant carrier. [00158] For in vivo use, the compositions of the present invention can be provided in a formulation suitable for administration to a subject, for example, an animal or a human. Accordingly, the formulations include the agents together with a physiologically relevant carrier suitable for the desired form and/or dose of administration. The term, "physiologically relevant carrier" is understood to mean a carrier in which the agents are dispersed, dissolved, suspended, admixed and physiologically tolerable, i.e., can be administered to, in, or on the subject's body without undue discomfort, or irritation, or toxicity. The preferred carrier is a fluid, preferably a liquid, more preferably an aqueous solution; however, carriers for solid formulations, topical formulations, inhaled formulations, ophthalmic formulations, and transdermal formulations are also contemplated as within the scope of the invention.

0248[00159] It is contemplated that the agents can be administered orally or parenterally. For parenteral administration, the agents can be administered intravenously, intramuscularly, cutaneously, percutaneously, subcutaneously, rectally, nasally, vaginally, and ocularly. Thus, the composition may be in the form of, e.g., solid tablets, capsules, pills, powders including lyophilized powders, colloidal suspensions, microspheres, liposomes granulates, suspensions, emulsions, solutions, gels, including hydrogels, pastes, ointments, creams, plasters, irrigation solutions, drenches, osmotic delivery devices, suppositories, enemas, injectables, implants, sprays, or aerosols. The pharmaceutical compositions can be formulated according to conventional pharmaceutical practice (see, e.g., Remington: The Science and Practice of Pharmacy, 20th edition, 2000, ed. A.R. Germaro, Lippincott Williams &amp; Wilkins, Philadelphia, and Encyclopedia of Pharmaceutical Technology, eds. J. Swarbrick and J. C. Boylan, 1988-1999, Marcel Dekker, New York).

0249[00160] It is understood that the formulation of the agents, the choice of mode of administration, the dosages of agents administered to the subject, and the timing between administration of the agents and imaging is within the level of skill in the art.

0250VIII. Imaging Methods

0251[00161] The present invention provides methods for in vitro and in vivo imaging using the imaging agents disclosed herein. For a review of optical imaging techniques, see, e.g., Alfano et al., Ann. NY Acad. ScL 820:248-270 (1997); Weissleder, Nature Biotechnology 19, 316 - 317 (2001); Ntziachristos et al., Eur. Radiol. 13:195-208 (2003); Graves et al., Curr. MoI. Med. 4:419-430 (2004); Citrin et al., Expert Rev. Anticancer Ther. 4:857-864 (2004); Ntziachristos, Ann. Rev. Biomed. Eng. 8:1-33 (2006); Koo et al., Cell Oncol. 28:127-139 (2006); and Rao et al., Curr. Opin. Biotechnol. 18:17-25 (2007).

0252[00162] Optical imaging includes all methods from direct visualization without use of any device and use of devices such as various scopes, catheters and optical imaging equipment, for example computer based hardware for tomographic presentations. The imaging agents are useful with optical imaging modalities and measurement techniques including, but not limited to: endoscopy; fluorescence endoscopy; luminescence imaging; time resolved transmittance imaging; transmittance imaging; nonlinear microscopy; confocal imaging; acousto-optical imaging; photoacoustic imaging; reflectance spectroscopy; spectroscopy; coherence interferometry; interferometry; optical coherence tomography; diffuse optical tomography and fluorescence mediated molecular tomography (continuous wave, time domain frequency domain systems and early photon), and measurement of light scattering, absorption, polarization, luminescence, fluorescence lifetime, quantum yield, and quenching.

0253[00163] An imaging system useful in the practice of the invention typically includes three basic components: (1) an appropriate light source for inducing excitation of the imaging agent, (2) a system for separating or distinguishing emissions from light used for fluorophore excitation, and (3) a detection system. The detection system can be hand-held or incorporated into other useful imaging devices, such as intraoperative microscopes. Exemplary detection systems include an endoscope, catheter, tomographic system, hand- held imaging system, or a intraoperative microscope.

0254[00164] Preferably, the light source provides monochromatic (or substantially monochromatic) light. The light source can be a suitably filtered white light, i.e., bandpass light from a broadband source. For example, light from a 150-watt halogen lamp can be passed through a suitable bandpass filter commercially available from Omega Optical (Brattleboro, VT). Depending upon the system, the light source can be a laser. See, e.g., Boas et al, Proc. Natl. Acad. ScL USA 91:4887-4891, 1994; Ntziachristos et al, Proc. Natl. Acad. ScL USA 97:2767-2772, 2000; and Alexander, /. Clin. Laser Med. Surg. 9:416-418, 1991. Information on lasers for imaging can be found, for example, at Imaging Diagnostic Systems, Inc., Plantation, FL and various other sources. A high pass or bandpass filter can be used to separate optical emissions from excitation light. A suitable high pass or bandpass filter is commercially available from Omega Optical, Burlington, VT.

0255[00165] In general, the light detection system can be viewed as including a light gathering/image forming component and a light/signal detection/image recording component. Although the light detection system can be a single integrated device that incorporates both components, the light gathering/image forming component and light detection/image recording component are discussed separately.

0256[00166] A particularly useful light gathering/image forming component is an endoscope. Endoscopic devices and techniques which have been used for in vivo optical imaging of numerous tissues and organs, including peritoneum (Gahlen et al, J. Photochem. Photobiol. B 52:131-135, 1999), ovarian cancer (Major et al., Gynecol. Oncol. 66:122- 132, 1997), colon and rectum (Mycek et al., Gastrointest. Endosc. 48:390-394, 1998; and Stepp et al, Endoscopy 30:379-386, 1998), bile ducts (Izuishi et al, Hepato gastroenterology 46:804-807, 1999), stomach (Abe et al, Endoscopy 32:281-286, 2000), bladder (Kriegmair et al, Urol. Int. 63:27-31, 1999; and Riedl et al, J. Endourol 13:755-759, 1999), lung (Hirsch et al, Clin Cancer Res 7:5-220, 2001), brain (Ward, /. Laser Appl 10:224-228, 1998), esophagus, and head and neck regions can be employed in the practice of the present invention. [00167] Other types of light gathering components are catheter-based devices, including fiber optics devices. Such devices are particularly suitable for intravascular imaging. See, e.g., Tearney et al, Science 276:2037-2039, 1997; and Circulation 94:3013, 1996.

0257[00168] Still other imaging technologies, including phased array technology (Boas et al, Proc. Natl. Acad. Sci. USA 91:4887-4891, 1994; Chance, Ann. NY Acad. Sci. 838:29-45, 1998), optical tomography (Cheng et al., Optics Express 3:118-123, 1998; and Siegel et al., Optics Express 4:287-298, 1999), intravital microscopy (Dellian et al., Br. J. Cancer 82:1513-1518, 2000; Monsky et al, Cancer Res. 59:4129-4135, 1999; and Fukumura et al., Cell 94:715-725, 1998), confocal imaging (Korlach et al, Proc. Natl. Acad. Sci. USA 96:8461-8466, 1999; Rajadhyaksha et al, J. Invest. Dermatol. 104:946-952, 1995; and Gonzalez et al., J. Med. 30:337-356, 1999) and fluorescence molecular tomography (FMT) (Nziachristos et al., Nature Medicine 8:757-760, 2002; U.S. Patent No. 6,615,063, PCT WO 03/102558, and PCT WO 03/079015) can be used with the imaging agents of the invention. Similarly, the imaging agents can be used in a variety of imaging systems, for example, (1) the IVIS® Imaging Systems: 100 Series, 200 Series (Xenogen, Alameda, CA), (2) SPECTRUM and LUMINA (Xenogen, Alameda, CA), (3) the SoftScan® or the eXplore Optix™ (GE Healthcare, United Kingdom), (4) Maestro™ and Nuance™-2 Systems (CRi, Woburn, MA), (5) Image Station In- Vivo FX from Carestream Molecular Imaging, Rochester, NY (formerly Kodak Molecular Imaging Systems), (6) OVlOO, IVlOO (Olympus Corporation, Japan), (7) Cellvizio Mauna Kea Technologies, France), (8)] NanoSPECT/CT or HiSPECT (Bioscan, Washington, DC), (9) CTLM®or LILA™ (Imaging Diagnostic Systems, Plantation, FL), (10) DYNOT™ (NIRx Medical Technologies, Glen Head, NY), and (11) NightOWL Imaging Systems by Berthold Technologies, Germany. [00169] A variety of light detection/image recording components, e.g., charge coupled device (CCD) systems or photographic film, can be used in such systems. The choice of light detection/image recording depends on factors including the type of light gathering/image forming component being used. It is understood, however, that the selection of suitable components, assembling them into an optical imaging system, and operating the system is within ordinary skill in the art.

0258[00170] For agents that have magnetic properties, MRI imaging well known in the art can also be applied in the practice of the invention. For a review of MRI techniques see Westbrook, Handbook of MRI Technique, 2^nd Edition, 1999, Blackwell Science. It is possible that images obtained, for example, by optical imaging and by magnetic resonance imaging can be co-registered or fused with one another to provide additional information about the item being imaged. Furthermore, multi-modality imaging systems (i.e., combined optical and MR imaging systems) can be used to create combined optical MR images.

0259[00171] In addition, the compositions and methods of the present invention can be used for other imaging compositions and methods. For example, the agents of the present invention can be imaged by other imaging modalities, such as, X-ray, computed tomography (CT), MR imaging, ultrasound, positron emission tomography (PET), and single photon computerized tomography (SPECT).

0260[00172] In addition, the compositions and methods of the present invention can be used in combination with other imaging compositions and methods. For example, the agents of the present invention can be imaged by optical imaging protocols either alone or in combination with other traditional imaging modalities, such as, X-ray, computed tomography (CT), MR imaging, ultrasound, positron emission tomography (PET), and single photon computerized tomography (SPECT). For instance, the compositions and methods of the present invention can be used in combination with CT or MRI to obtain both anatomical and molecular information simultaneously, for example, by co- registration of with an image generated by another imaging modality. The compositions and methods of the present invention can also be used in combination with X-ray, CT, PET, ultrasound, SPECT and other optical and MR contrast agents or alternatively, the agents of the present invention may also include imaging agents, such as iodine, gadolinium atoms and radioactive isotopes, which can be detected using CT, PET,

0261SPECT, and MR imaging modalities in combination with optical imaging. The imaging agents can be linked to or incorporated in the agents.

0262(A) In Vivo Imaging

0263[00173] With respect to optical in vivo imaging, such a method comprises (a) administering to a subject one or more imaging agents; (b) allowing the agent(s) to distribute within the subject; (c) exposing the subject to light of a wavelength absorbable by at least one fluorophore in the imaging agent; and (d) detecting an optical signal emitted by the fluorophore. The emitted optical signal can be used to construct an image. The image can be a tomographic image. Furthermore, it is understood that steps (a)-(d) or steps (c)-(d) can be repeated at predetermined intervals thereby to permit evaluation of the subject over time.

0264[00174] The illuminating and/or detecting steps (steps (c) and (d), respectively) can be performed using an endoscope, catheter, tomographic system, planar system, hand-held imaging system, goggles, or an intraoperative imaging system or microscope.

0265[00175] Before or during these steps, a detection system can be positioned around or in the vicinity of a subject (for example, an animal or a human) to detect signals emitted from the subject. The emitted signals can be processed to construct an image, for example, a tomographic image. In addition, the processed signals can be displayed as images either alone or as fused (combined) images.

0266[00176] In addition, it is possible to practice an in vivo imaging method that selectively detects and images one or more molecular imaging probes, including the imaging agents simultaneously. In such an approach, for example, in step (a) noted above, two or more imaging probes whose signal properties are distinguishable from one another are administered to the subject, either at the same time or sequentially, wherein at least one of the molecular imaging probes is a agent. The use of multiple probes permits the recording of multiple biological processes, functions or targets.

0267[00177] The subject may be a vertebrate, for example, a mammal, for example, a human. The subject may also be a non-vertebrate (for example, C. elegans, drosophila, or another model research organism, etc.) used in laboratory research.

0268[00178] Information provided by such in vivo imaging approaches, for example, the presence, absence, or level of emitted signal can be used to detect and/or monitor a disease in the subject. Exemplary diseases include, without limitation, autoimmune disease, bone disease, cancer, cardiovascular disease, environmental disease, dermatological disease, immunologic disease, inherited disease, infectious disease, metabolic disease, neurodegenerative disease, ophthalmic disease, and respiratory disease. In addition, in vivo imaging can be used to assess the effect of a compound or therapy by using the imaging agents, wherein the subject is imaged prior to and after treatment with the compound or therapy, and the corresponding signal/images are compared.

0269[00179] The invention also features an in vivo imaging method where labeled cells are administered to the recipient. The cells can be labeled with the imaging agents ex vivo. The cells can be derived directly from a subject or from another source (e.g., from another subject, cell culture, etc.). The imaging agents can be mixed with the cells to effectively label the cells and the resulting labeled cells administered to the subject into a subject in step (a). Steps (b)-(d) then are followed as described above. This method can be used for monitoring trafficking and localization of certain cell types, including T-cells, tumor cells, immune cells and stem cells, and other cell types. In particular, this method may be used to monitor cell-based therapies.

0270[00180] The methods of the invention can be used to determine a number of indicia, including tracking the localization of the agent in the subject over time or assessing changes or alterations in the metabolism and/or excretion of the agent in the subject over time. The methods can also be used to follow therapy for such diseases by imaging molecular events and biological pathways modulated by such therapy, including but not limited to determining efficacy, optimal timing, optimal dosing levels (including for individual patients or test subjects), and synergistic effects of combinations of therapy.

0271[00181] The methods and compositions described herein can be used to help a physician or surgeon to identify and characterize areas of disease, such as arthritis, cancers and specifically colon polyps, or vulnerable or unstable plaque, atherosclerosis, to distinguish diseased and normal tissue, such as detecting tumor margins that are difficult to detect using an ordinary operating microscope, e.g., in brain surgery, to help dictate a therapeutic or surgical intervention, e.g., by determining whether a lesion is cancerous and should be removed or non-cancerous and left alone, or in surgically staging a disease, e.g., intraoperative lymph node staging, sentinel lymph node mapping, or assessing intraoperative bleeding.

0272[00182] The methods and compositions described herein can also be used in the detection, characterization and/or determination of the localization of a disease, especially early disease, the severity of a disease or a disease- associated condition, the staging of a disease, and/or monitoring a disease. The presence, absence, or level of an emitted signal can be indicative of a disease state. [00183] The methods and compositions disclosed herein can also be used to monitor and/or guide various therapeutic interventions, such as surgical procedures, and monitoring drug therapy, including cell based therapies. The methods can also be used in prognosis of a disease or disease condition. [00184] With respect to each of the foregoing, examples of such disease or disease conditions that can be detected or monitored (before, during or after therapy) include inflammation (for example, inflammation caused by arthritis, for example, rheumatoid arthritis), cancer (for example, colorectal, ovarian, lung, breast, prostate, cervical, testicular, skin, brain, gastrointestinal, pancreatic, liver, kidney, bladder, stomach, leukemia, mouth, esophageal, bone), cardiovascular disease (for example, atherosclerosis and inflammatory conditions of blood vessels, ischemia, hypertension, stroke, thrombosis, disseminated intravascular coagulation), dermatologic disease (for example, Kaposi's Sarcoma, psoriasis, allergic dermatitis), ophthalmic disease (for example, macular degeneration, diabetic retinopathy), infectious disease (for example, bacterial, viral, fungal and parasitic infections, including Acquired Immunodeficiency Syndrome, Malaria, Chagas Disease, Schistosomiasis), immunologic disease (for example, an autoimmune disorder, lymphoma, multiple sclerosis, rheumatoid arthritis, diabetes mellitus, lupus erythematosis, myasthenia gravis, Graves disease), central nervous system disease (for example, a neurodegenerative disease, such as Parkinson's disease or Alzheimer's disease, Huntington's Disease, amyotrophic lateral sclerosis, prion disease), inherited diseases, metabolic diseases, environmental diseases (for example, lead, mercury and radioactive poisoning, skin cancer), bone-related disease (for example, osteoporosis, primary and metastatic bone tumors, osteoarthritis), neurodegenerative disease, and surgery-related complications (such as graft rejection, organ rejection, alterations in wound healing, fibrosis or other complications related to surgical implants).

0273[00185] The methods and compositions described herein, therefore, can be used, for example, to determine the presence and/or localization of tumor cells, the presence and/or localization of inflammation, including the presence of activated macrophages, for instance in atherosclerosis or arthritis, the presence and in localization of vascular disease including areas at risk for acute occlusion (i.e., vulnerable plaques) in coronary and peripheral arteries, regions of expanding aneurysms, unstable plaque in carotid arteries, and ischemic areas. The methods and compositions of the invention can also be used in identification and evaluation of cell death, injury, apoptosis, necrosis, hypoxia and angiogenesis. The methods and compositions can also be used for drug delivery and to monitor drug delivery, especially when drugs or drug-like molecules are chemically attached to the imaging agents.

0274(B) In Vitro Methods

0275[00186] With respect to in vitro imaging, the imaging agents can be used in a variety of in vitro assays. For example, an exemplary in vitro imaging method comprises: (a) contacting a sample, for example, a biological sample, with one or more imaging agents of the invention; (b) allowing the agent(s) to interact with a biological target in the sample; (c) optionally, removing unbound agents; (d) in the case of fluorescent agents, illuminating the sample with light of a wavelength absorbable by a fluorophore of the agents; and (e) detecting a signal emitted from fluorophore thereby to determine whether the agent has been activated by or bound to the biological target. [00187] After an agent has been designed, synthesized, and optionally formulated, it can be tested in vitro by one skilled in the art to assess its biological and performance characteristics. For instance, different types of cells grown in culture can be used to assess the biological and performance characteristics of the agent. Cellular uptake, binding or cellular localization of the agent can be assessed using techniques known in the art, including, for example, fluorescent microscopy, FACS analysis, immunohistochemistry, immunoprecipitation, in situ hybridization and Forster resonance energy transfer (FRET) or fluorescence resonance energy transfer. By way of example, the agents can be contacted with a sample for a period of time and then washed to remove any free agents. The sample can then be viewed using an appropriate detection device such as a fluorescent microscope equipped with appropriate filters matched to the optical properties of a fluorescent agent. Fluorescence microscopy of cells in culture or scintillation counting is also a convenient means for determining whether uptake and binding has occurred. Tissues, tissue sections and other types of samples such as cytospin samples can also be used in a similar manner to assess the biological and performance characteristics of the agents. Other detection methods including, but not limited to flow cytometry, immunoassays, hybridization assays, and microarray analysis can also be used. [00188] The invention will now be illustrated by the following examples, which are given for the purpose of illustration only and without any intention of limiting the scope of the present invention.

EXAMPLES

0277[00189] Representative materials and methods that may be used in preparing the materials of the invention are described below. All chemicals and solvents (reagent grade) were used as commercially obtained without further purification. HPLC Analysis: Analytical RP HPLC was performed on a Waters 2695 system using either a Phenomenex Phenyl-hexyl column (3μ, 100 x 4.6 mm) or C18 column (5μ, 50 x 4.6 mm) with a flow rate of 1 to 2 mL/min. Chromatograms were monitored at 254 nm and 675 nm. Preparative HPLC was performed on a Varian system using either a Phenomenex Phenyl- hexyl column or a Phenomenex Cl 8 column (250 x 10 mm) at 4.7 mL/min using similar gradient as the analytical run.

0278[00190] Example 1: Synthesis of the Succinimidyl Ester Form of Fluorophore Conjugated Peptides

0279[00191] The imaging agents set forth in Table 7 were made in accordance with the principles discussed in this Example.

TABLE 7

0281<img file="WO2009092062A2_D0041.tif" />

0282<img file="WO2009092062A2_D0042.tif" />

0283wherein F5 was the fluorohore described in the imaging agent of Formula Q77, and F6 was the fluorophore described in the imaging agent of Formula Q88.

0284Part A. Preparation of fluorophore conjugated peptide

0285[00192] Individual peptide (as set forth in Table 7; 0.45 μmol) and fluorophore No. 3 from Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N-methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC using a 10% to 35% gradient of acetonitrile in 25 mM triethylammonium acetate, pH 7, on a 10 mm X 250 mm 300 A Cl 8 column. The purified peptide was characterized by LC-MS. Part B. Preparation of the Succinimidyl Ester of the Labeled Peptide at the C-terminus [00193] The fluorophore labeled peptide (0.25 μmol) was dissolved in 50 μL DMF containing 0.5 mg of disuccinimidyl carbonate (DSC) and 0.5 μL NMM. The solution was placed on rotator shielded from light and rotated at room temperature for 4 h. The peptide succinimidyl ester was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant and dried briefly under vacuum.

0286Example 2: Synthesis of mPEG-5kPa Conjugated Peptide

0287[00194] Methoxypolyethylene glycol amine (mPEG-NH₂, Laysan Bio, molecular weight 5 kDa, 2.5 mg, 0.50 μmol) was dissolved in 100 μL DMF and 1 μL NMM. The solution was added to 0.25 μmol of the labeled peptide succinimidyl ester (from Example 1) and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC on a 10 mm X 250 mm 300 A C18 column. The pegylated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0288Example 3: Synthesis of mPEG-20kPa Conjugated Peptide

0289[00195] Methoxypolyethylene glycol amine (mPEG-NH₂, Laysan Bio, molecular weight 20 kDa, 10 mg, 0.50 μmol) was dissolved in 100 μL DMF and 1 μL NMM. The solution was added to 0.25 μmol of the labeled peptide succinimidyl ester (from Example 1) and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC on a 10 mm X 250 mm 300 A C18 column. The pegylated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0290Example 4: Synthesis of mPEG-30kPa Conjugated Peptide

0291[00196] Methoxypolyethylene glycol amine (InPEG-NH₂, Laysan Bio, molecular weight 30 kDa, 15 mg, 0.50 μmol) was dissolved in 100 μL DMF and 1 μL NMM. The solution was added to 0.25 μmol of the labeled peptide succinimidyl ester (from Example 1) and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC on a 10 mm X 250 mm 300 A C18 column. The pegylated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0292Example 5: Synthesis of Pegylated poly-L-lysine Conjugated Peptide

0293[00197] The peptide succinimidyl ester (0.25 μmol) from Example 1, was dissolved in 50 μL DMSO and added to a solution containing approximately 400,000-500,000 Da pegylated poly-L-lysine (0.17 μmol) in 1.5 mL HEPES buffer, pH 7. The solution was rotated at room temperature for 4 hours, then 20 μL of acetic anhydride and 1.0 mL of carbonate/bicarbonate buffer, pH 9 was added and rotation continued for 2 hours. The polymer conjugated peptide was purified from unreacted peptide by gel filtration using P- 100 gel (BioRad) and elution with IxPBS. Purity of the product was assessed by RP-18 HPLC and SEC HPLC.

0294Example 6: Synthesis of Pegylated Poly-D-lysine Conjugated Peptide

0295[00198] The peptide succinimidyl ester (0.25 μmol) from Example 1, is dissolved in 50 μL DMSO and added to a solution containing approximately 300,000-500,000 Da pegylated poly-L-lysine (0.17 μmol) in 1.5 mL HEPES buffer, pH 7. The solution is rotated at room temperature for 4 hours, then 20 μL of acetic anhydride and 1.0 mL of carbonate/bicarbonate buffer, pH 9 added and rotation continued for 2 hours. The polymer conjugated peptide is purified from unreacted peptide by gel filtration using P- 100 gel (BioRad) and eluted with IxPBS. Purity of the product is assessed by RP-18 HPLCand SEC HPLC. Example 7: Synthesis of a Branched PEG Peptide Conjugate

0296[00199] Methoxypolyethylene glycol amine (mPEG-NH₂, Laysan Bio, molecular weight 20 kDa, 100 mg, 5.0 μmol) was dissolved in 1000 μL DMF. The solution was added to 175 μL of DMF containing N-fmoc glutamic acid (0.9 mg, 2.5 μmol) and 2-(lH-7- Azabenzotriazol-l-yl)-l,l,3,3-tetramethyl uronium hexafluorophosphate (HATU, 1.9 mg, 5 μmol) followed by addition of 2.1 μL (12 μmol) of diisopropylethylamine. The solution was stirred at room temperature for 2 hours, and the resulting product was precipitated by addition of 10 mL of methyl tertiary-butyl ether. The solvent was decanted and the branched PEG was purified by by HPLC on a 21 mm X 250 mm 300 A C18 column.

0297[00200] The fmoc group of the purified product was deprotected with 20% v/v diethylamine in DMF for 30 minutes, followed by precipitation with methyl tertiary-butyl ether to yield amine-functionalized branched PEG. The amine-functionalized branched PEG (15 mg, 0.50 μmol) was dissolved in 100 μL DMF and 1 μL NMM. The solution was added to 0.25 μmol of the labeled peptide (from Example 1) along with l-ethyl-3-(3- dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) and the solution was placed on rotator shielded from light and rotated at room temperature for 16 h. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC using a 10% to 85% gradient of acetonitrile in 25 mM triethylammonium bicarbonate, pH 8.5, on a 21 mm X 250 mm 300 A C18 column. The branched PEG conjugated peptide was further purified by strong anion exchange chromatography. The branched PEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0298Example 8: Synthesis of a Polyvinylpyrrolidone Peptide Conjugate [00201] Carboxy functionalized polyvinylpyrrolidone (6 kDa, Polymersource, 20 mg, 3.3 μmol) was dissolved in 200 μL DMF with disuccinimidyl carbonate (5 mg, 20 μmol) and DMAP (0.5 mg, 5 μmol) and rotated at room temperature for 4 hours. The succinimidyl ester functionalized polyvinylpyrrolidone was precipitated with 1.5 mL of ethyl acetate.

0299[00202] The labeled peptide from Example IA above ( 0.75 μmol) along with l-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 2.5 mg, 13 μmol) and hydroxybenzotriazole (HOBT, 2.5 mg, 19 μmol) were dissolved in 750 μL of 0.1 M MES buffer, pH 6. To the solution was added 200 μL of 1 M ethylene diamine dihydrochloride in 1 M HEPES buffer, pH 7 and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The amine functionalized peptide was purified by HPLC.

0300[00203] The amine functionalized peptide (0.5 μmol) described in the paragraph above, was dissolved in 200 μL DMF containing 20 mg of the succinimidyl ester functionalized polyvinylpyrrolidone described above along with DMAP (0.5 mg, 5 μmol). The solution was rotated at RT for 24 hours. The polyvinylpyrrolidone conjugated peptide was precipitated by addition of 1.5 mL of MTBE and isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The polyvinylpyrrolidone conjugated peptide was further purified by strong anion exchange chromatography. The polyvinylpyrrolidone conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0301Example 9: Synthesis of an Aminodextran Peptide Conjugate [00204] Aminodextran (Invitrogen, molecular weight 10 kDa, 19 mg, 1.9 μmol) was dissolved in 150 μL 0.1 mM MES pH 6. The solution was added to 0.75 μmol of the labeled peptide (from Example 1) along with l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 2 mg, 10 μmol) and hydroxybenzotriazole (HOBT, 2 mg, 15 μmol) and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The aminodextran conjugated peptide was purified by HPLC. The aminodextran conjugated peptide was further purified by gel filtration chromatography using Biogel PlO (Biorad) and eluting with IXPBS. The aminodextran conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0302Example 10: Synthesis of an iron Oxide Nanoparticle Peptide Conjugate [00205] A solution of amine-functionalized iron oxide nanoparticles (16 mg total iron) in 8 mL 0.1 mM MES pH 6 was combined with 0.5 μmol of the labeled peptide (from Example IA above) along with l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 5 mg, 25 μmol) and hydroxybenzotriazole (HOBT, 5 mg, 38 μmol) and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The iron oxide nanoparticle conjugated peptide was purified by by gel filtration chromatography using Biogel PlOO (Biorad) and eluting with IXPBS. The aminodextran conjugated peptide was characterized by SEC HPLC.

0303Example 11: Synthesis of Exemplary Imaging Agent

0304[00206] This example describes the synthesis of an exemplary imaging agent denoted by Formula XXII. <img file="WO2009092062A2_D0043.tif" />

0305[00207] The fluorophore labeled, alkyne-modified peptide Lys-Pro-Leu-Gly-Val-Arg- Lys (SEQ ID NO:415) (400 μmol) was combined with the azide ll-azido-3,6,9- trioxaundecan-1 -amine (azido-PEG-amine, n=3) in 200 μL of 65 mM triethylammonium chloride, 25 mM sodium phosphate, pH 5 to which 0.2 mg of nano-sized copper powder was added. The mixture was rotated at room temperature for 1 hour, filtered, and purified by HPLC on a 10 mm X 250 mm 300 A Cl 8 column. The purified peptide was characterized by MALDI MS (calculated 3135.05, found 3135.13).

0306[00208] The resulting amine functionalized peptide (0.16 μmol) was dissolved in 200 μL DMSO with 0.35 μmol PoIyPEG NHS ester (Warwick Effect Polymers) and 0.2 μL diisopropylethylamine. The solution was rotated at RT for 24 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC on a 10 mm X 250 mm 300 A C18 column. The pegylated peptide was characterized by RP-18 HPLC and SEC HPLC.

0307Example 12: Cyclic Peptide Imaging Agent

0308[00209] This example describes the synthesis of the cyclic imaging agent represented by Formula XXIII.

0309<img file="WO2009092062A2_D0044.tif" /> (XXIII) [00210] The peptide Arg(Pbf)-Arg(Pbf)-Lys(boc)-Nal-Arg(Pbf)-Arg(Pbf)-Lys(boc)-Gly- OH (SEQ ID NO:416) is prepared using solid phase synthesis as known in the art of solid phase peptide synthesis using the Fmoc protection/deprotection strategy. The resin used is Fmoc-Gly-HMPB-MBHA resin that is commercially available. The peptide is cleaved off the resin using 1%TFA in methylene chloride to retain acid labile side chain protecting groups. Head-tail cyclization is effected by heating a solution of the peptide in DMF in the presence of Hunig's base and HBTU. After cyclization is achieved, the side chain protecting groups are removed under acidic conditions such as 95% TFA-5% water or other similar deprotection cocktails known in the art. Fluorophore 3 from Table 2 is coupled to the two lysine side chain amines and the product is isolated and purified by reversed phase HPLC.

0310Example 13: Synthesis of Exemplary Imaging Agent

0311[00211] This Example describes the synthesis of the exemplary imaging agent [F5]Lys(COCF₃)-His-Pro-Phe-His-Leu-Val-Ile-His-Lys(F5)-[OH] (SEQ ID NO:417). [00212] Starting material peptide Lys(COCF3)- His-Pro-Phe-His-Leu-Val-Ile-His-Lys- (OH) (SEQ ID NO:418) (6 μmol) and fluorophore No. 3 from Table 2 (20 μmol) were combined in 2 mL of N,N-dimethylformamide (DMF) with 6 μL of N-methylmorpholine (NMM). The solution was shielded from light and magnetically stirred at room temperature for 16 hOURS. The labeled peptide was precipitated by addition of 2 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 1.2 mL of 0.1 M sodium bicarbonate and stirred at room temperature for 4 hrs. The mixture then was purified by HPLC on a 10 mm X 250 mm phenyl hexyl column. The purified peptide was characterized by LC-MS (ESI+, (M+3)/3: 1,131.02). Example 14: Synthesis of Exemplary Imaging Agent

0312[00213] This Example describes the synthesis of the exemplary imaging agent [F5]Lys- His-Pro-Phe-His-Leu-Val-Ile-His-Lys(F5)-[OH] (SEQ ID NO:298) (agent R20).

0313[00214] Product agent from Example 13 (2 μmol) was dissolved in 0.9 mL of water and

03140.3 mL of concentrated ammonium hydroxide. The solution was shielded from light and magnetically stirred at room temperature for 16 hours. The mixture then was purified by HPLC on a 10 mm X 250 mm phenyl hexyl column. The purified peptide was characterized by LC-MS (ESI+, (M+3)/3: 1,099.03)

0315Example 15: Synthesis of Exemplary Imaging Agent

0316[00215] This Example describes the synthesis of the imaging agent [F5]Lys-His-Pro-Phe- His-Leu-Val-Ile-His-Lys(F5)-[NHmPEG20k (SEQ ID NO:419) (agent R21).

0317[00216] A mixture of product agent from Example 13 (9 μmol), methoxypolyethylene glycol amine (mPEG-NH₂, Laysan Bio, molecular weight 20 kDa, 220 mg, 11 μmol) was dissolved, EDC (52 μmol), HOBt (74 μmol), NMM (40 μL) in 6 mL of DMF and was shielded from light and magnetically stirred at room temperature for 3 days. The pegylated peptide was precipitated by addition of 20 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dissolved in 3 mL of 0.1 M aqueous sodium bicarbonate and stirred at room temperature for 4 hrs. Concentrated ammonium hydroxide (1.2 mL) was added and the resulting mixture was stirred at room temperature for 16 hours. The mixture was purified by HPLC. The pegylated peptide was further purified by anion exchange chromatography and characterized by RP-HPLC.

0318Example 16: Synthesis of Exemplary Imaging Agent

0319[00217] This Example describes the synthesis of the imaging agent [F5]Ile-His-Pro-Phe- His-Leu-Leu-Tyr-Tyr-Lys(F5)-[OH] (SEQ ID NO:420). [00218] Starting material peptide, He- His-Pro-Phe-His-Leu-Leu-Tyr-Tyr-Lys-(OH] (SEQ ID NO:421) (1.9 μmol) and fluorophore No. 3 from Table 2 (9 μmol) were combined in 900 μL of N,N-dimethylformamide (DMF) with 5 μL of N- methylmorpholine (NMM). The solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 0.9 mL of 0.1 M hydroxylamine and stirred at room temperature for 2 hrs. To this solution was added 0.3 mL of 0.1 M aqueous sodium bicarbonate and the mixture was stirred at room temperature for 3 days. The mixture was purified by HPLC. The purified peptide was characterized by LC-MS (ESI+, (M+3)/3: 1,124.03). Example 17: Synthesis of Exemplary Imaging Agent

0320[00219] This Example describes the synthesis of the imaging agent [F5]Lys-His-Pro-Phe- His-Leu-Val-Ile-His-Lys(F5)-[NHmPEG5k] (SEQ ID NO:304) (Agent R27)

0321[00220] A mixture of product from Example 13 (2.5 μmol), methoxypolyethylene glycol amine (mPEG-NH₂, Laysan Bio, molecular weight 5 kDa, 30 mg, 6 μmol), EDC (78 μmol), HOBt (111 μmol), NMM (15 μL) in 2 mL of DMF was shielded from light and magnetically stirred at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 10 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dissolved in 0.8 mL of 0.1 M aqueous sodium bicarbonate and stirred at room temperature for 5 hours. Concentrated ammonium hydroxide (0.6 mL) was added and the resulting mixture was stirred at room temperature for 16 hours. The mixture was purified by HPLC using a 10% to 85% gradient of acetonitrile in 25 mM triethylammonium bicarbonate, pH 8.5, on a 10 mm X 250 mm 300 A C18 column. The pegylated peptide was characterized by RP-HPLC. Example 18: Synthesis of Exemplary Imaging Agent

0322[00221] This Example describes the synthesis of the imaging agent [F5]Lys-His-Pro-Phe- His-Leu-Val-Ile-His-Lys(F5)- [NHdPEG₂₄] (SEQ ID NO: 305) (Agent R26)

0323[00222] A mixture of product agent from Example 13 (1.0 μmol), methyl-PEG₂₄- Amine (MA(PEG)24 Thermo Scientific, 5.5μmol), EDC (15 μmol), HOBt (17 μmol), NMM (20 μL) in 1 mL of DMF was shielded from light and magnetically stirred at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 10 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dissolved in 0.7 mL of 0.1 M aqueous sodium bicarbonate and stirred at room temperature for 2 hours. The main component of the mixture was isolated by preparative HPLC using a lO% to 85% gradient of acetonitrile in 25 mM triethylammonium bicarbonate, pH 8.5, on a C18 column. The combined fractions were treated with concentrated ammonium hydroxide (1.0 mL) and the resulting mixture was stirred at room temperature for 5 days. The mixture was purified by HPLC using a lO% to 35% gradient of acetonitrile in 25 mM triethylammonium bicarbonate, pH 8.5 on Cl 8 column. The pegylated peptide was characterized by RP-HPLC. Example 19: Synthesis of Exemplary Imaging Agent

0324[00223] This Example describes the synthesis of the imaging agent [F5]Lys(Ac)-His-Pro- Phe-His-Leu-Val-Ile-His-Lys(F5)-[OH] (SEQ ID NO:314) (Agent R23)

0325[00224] To a solution of product agent from Example 14 (1.0 μmol) in DMF (1 mL) was added N-methylmorpholine (30 μL) and a solution of succinimidyl acetate (2.8 μmol) in acetic acid (4 μL). The solution was placed on rotator shielded from light and rotated at room temperature for 17 hours. The peptide was precipitated by addition of ether followed by centrifugation and decanting of the supernatant. The crude product was dissolved in 1 mL of 0.1 M aqueous sodium bicarbonate and stirred at room temperature overnight. The mixture then was purified by HPLC using a 20% to 35% gradient of acetonitrile in 25 mM triethylammonium bicarbonate, pH 8.5 on phenyl hexyl column. The purified peptide was characterized by LC-MS (ESI+, (M+3)/3: 1,113.03).

0326Example 20: Synthesis of Exemplary Imaging Agent

0327[00225] This Example describes the synthesis of the exemplary imaging agent [F5]Lys(COCF₃)-His-Pro-Phe-ffis-Cha-Val-Ile-His-Lys(F5)-[OH] (SEQ ID NO:458).

0328[00226] Starting material peptide LyS(COCF₃)- His-Pro-Phe-His-Cha-Val-Ile-His-Lys- (OH) (7.8 μmol) and a fluorophore No. 3 of Table 2 (20 μmol) were combined in 2 mL of N,N-dimethylformamide (DMF) with 100 μL of N-methylmorpholine (NMM). The solution was shielded from light and magnetically stirred at room temperature for 16 hours. The labeled peptide was precipitated by addition of 20 mL of ether followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 1.2 mL of 0.1 M sodium bicarbonate and stirred at room temperature for 6 hours. The mixture then was purified by HPLC using a 10% to 40% gradient of acetonitrile in 25 mM triethylammonium bicarbonate, pH 8.5 on a phenyl hexyl column. The purified peptide was characterized by LC-MS (ESI+, (M+3)/3: 1,144.37).

0329Example 21: Synthesis of Exemplary Imaging Agent

0330[00227] This Example describes the synthesis of the exemplary imaging agent [F5]Lys- His-Pro-Phe-His-Cha-Val-Ile-His-Lys(F5)-[OH] (SEQ ID NO:430) (Agent R24).

0331[00228] Combined pure fractions of product from Example 20 (1 μmol, in 4 mL of HPLC solvent) were combined with 0.4 mL of concentrated ammonium hydroxide. The solution was shielded from light and stirred at room temperature for 16 hours. The mixture was concentrated in vacuo and then was purified by HPLC using a 10% to 40% gradient of acetonitrile in 25 mM triethylammonium bicarbonate, pH 8.5 on a phenyl hexyl column. The purified peptide was characterized by LC-MS (ESI+, (M+3)/3: 1,112.37). Example 22: Synthesis of Exemplary Imaging Agents

0332[00229] This Example describes the synthesis of the exemplary imaging agents denoted as Q65, Q66, Q91, Q92, Q93, Q94, R22, R51, R52, R53, R55, R56, R57, R58 and R59.

0333(Agent Q65) Pentynoyl-Lys(F5)-Gly-Phe-Leu-Gly-βAla-Lys(F5)-PEG20kDa (SEQ ID NO:422)

0334[00230] The peptide [pentynoylJ-Lys-Gly-Phe-Leu-Gly-βAla-Lys-tOH] (SEQ ID NO:459) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 3 from Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS. [00231] The labeled peptide (25 μmol) then was combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0335(Agent Q66) Pentynoyl-Lys(F6)-Gly-Phe-Leu-Gly-βAla-Lys(F6)-PEG20kDa (SEQ ID NO:423)

0336[00232] The peptide [pentynoylJ-Lys-Gly-Phe-Leu-Gly-βAla-Lys-tOH] (SEQ ID NO:460) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 (Table 2, 1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0337[00233] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0338(Agent 91) Pentynoyl-Lys(F5)-Pro-Leu-Gly-Val-Arg-Lys(F5)-PEG20kDa (SEQ ID

NO:424)

0340[00234] The peptide [pentynoyl]-Lys-Pro-Leu-Gly-Val-Arg-Lys (SEQ ID NO:461)

0341(Tufts University Core Facility, 0.45 μmol) and fluorophore No. 3 from Table 2) (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS. [00235] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0342(Agent Q92) [F5]-His-Gly-Pro-Arg-Lys(F5)-[PEG20kDa] (SEQ ID NO:425) [00236] The peptide [H]-His-Gly-Pro-Arg-Lys-[OH] (SEQ ID NO:85) (Tufts University Core Facility, 0.45 μmol) and fluorophore 3 (Table 2, 1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N-methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC on a 10 mm X 250 mm 300 A C18 column. The purified peptide was characterized by LC-MS.

0343[00237] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 h. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC on a 21 mm X 250 mm 300 A C18 column. The mPEG conjugated peptide was characterized by RP-18 HPLC and SEC HPLC.

0344(Agent Q93) [F5]-His-Gly-Pro-Asn-Lys(F5)-His-Gly-Pro-Asn-βA-[PEG20kDa] (SEQ ID NO:426)

0345[00238] The peptide [H]-HiS-GIy-PrO-ASn-LyS-HiS-GIy-PrO-ASn-[OH] (SEQ ID NO:462) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 3 from Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0346[00239] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 h. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0347(Agent Q94) [F5]-His-Gly-Pro-Asn-Lys(F5)-[PEG20kDa] (SEQ ID NO:427)

0348[00240] The peptide [H]-His-Gly-Pro-Asn-Lys-[OH] (SEQ ID NO:75) (Tufts University

0349Core Facility, 0.45 μmol) and fluorophore No. 3 from Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N-methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS. [00241] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0350(Agent R22) [F6]-Gly-Pro-Leu-Gly-Val-Arg-Lys(F6)-[YPEG 2x20kDa] (SEQ ID NO:434) [00242] The peptide [H]-Gly-Pro-Leu-Gly-Val-Arg-Lys-[OH] (SEQ ID NO:463) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0351[00243] The labeled peptide (25 μmol) was then combined Y-PEG-amine 2X20k (Y- shape PEG Amine, MW 40000, JenKem USA, 40 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The Y-PEG conjugated peptide was further purified by strong anion exchange chromatography. The Y-PEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC. (Agent R51) [mPEG-20kDa-Suc]-Lys(F6)-Gly-Phe-Leu-Gly-Lys(F6)-[NH₂] (SEQ ID NO:435)

0352[00244] The peptide [succinyl]-Lys-Gly-Phe-Leu-Gly-Lys-[NH₂] (SEQ ID NO:464) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0353[00245] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0354(Agent R52) [dPEG-lkDa-Suc]-Lys(F6)-Gly-Phe-Leu-Gly-Lys(F6)-[NH₂] (SEQ ID NO:436) [00246] The peptide [succinyl]-Lys-Gly-Phe-Leu-Gly-Lys-[NH₂] (SEQ ID NO:465)

0355(Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0356[00247] The labeled peptide (25 μmol) was then combined with Methyl-PEG₂₄- Amine (MA(PEG)24 Thermo Scientific, 0.54 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The discrete -pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The discrete -pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The dPEG conjugated peptide was characterized by RP- 18 HPLC and LC-MS

0357(Agent R53) [dppa-Suc]-Lys(F6)-Gly-Phe-Leu-Gly-Lys(F6)-[NH₂] (SEQ ID NO:437)

0358[00248] The peptide [succinyl]-Lys-Gly-Phe-Leu-Gly-Lys-[NH₂] (SEQ ID NO:466) (Tufts University Core Facility, 0.45 μmol) and fluorophore 2 (Table 2, 1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC on a 10 mm X 250 mm 300 A Cl 8 column. The purified peptide was characterized by LC-MS.

0359[00249] The labeled peptide (25 μmol) was then combined with 3,3-diphenylpropylamine (dppa, 0.11 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3- dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 h. The dppa conjugated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The dppa conjugated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The dppa conjugated peptide was characterized by RP-18 HPLC and LC-MS. (Agent R55) [mPEG-20kDa-Suc]-Lys(F6)-Arg-Arg-Lys(F6)-[NH₂] (SEQ ID NO:438) [00250] The peptide [succinyl]-Lys-Arg-Arg-Lys-[NH₂] (SEQ ID NO:467) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0360[00251] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH₂, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0361(Agent R56) [dPEG-lkDa-Suc]-Lys(F6)-Arg-Arg-Lys(F6)-[NH₂] (SEQ ID NO:439)

0362[00252] The peptide [succinyl]-Lys-Arg-Arg-Lys-[NH₂] (SEQ ID NO:468) (Tufts

0363University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS. [00253] The labeled peptide (25 μmol) was then combined with Methyl-PEG₂₄- Amine (MA(PEG)24 Thermo Scientific, 0.54 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The discrete -pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The discrete -pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The dPEG conjugated peptide was characterized by RP- 18 HPLC and LC-MS

0364(Agent R57) [dppa-Suc]-Lys(F6)-Arg-Arg-Lys(F6)-[NH₂] (SEQ ID NO:440)

0365[00254] The peptide [succinyl]-Lys-Arg-Arg-Lys-[NH₂] (SEQ ID NO:469) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0366[00255] The labeled peptide (25 μmol) was then combined with 3,3-diphenylpropylamine (dppa, 0.11 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3- dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The dppa conjugated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The dppa conjugated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The dppa conjugated peptide was characterized by RP-18 HPLC and LC-MS. (Agent R58) [mPEG-20kDa-Suc]-Lys(F6)-Ala-Arg-Arg-Lys(F6)-[NH₂] (SEQ ID NO:441)

0367[00256] The peptide [succinyl]-Lys-Ala-Arg-Arg-Lys-[NH₂] (SEQ ID NO:470) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS.

0368[00257] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC.

0369(Agent R59) [mPEG-20kDa-Suc]-Lys(F6)-Arg-Arg-Arg-Lys(F6)-[NH₂] (SEQ ID NO:442)

0370[00258] The peptide [succinyl]-Lys-Ala-Arg-Arg-Lys-[NH₂] (SEQ ID NO:471) (Tufts University Core Facility, 0.45 μmol) and fluorophore No. 2 of Table 2 (1.0 μmol) were combined in 100 μL of N,N-dimethylformamide (DMF) with 1 μL of N- methylmorpholine (NMM) and 0.25 mg of N,N-dimethylaminopyridine (DMAP). The solution was placed on a rotator shielded from light and rotated at room temperature for 16 hours. The labeled peptide was precipitated by addition of 1.5 mL of methyl-t-butyl ether (MTBE) followed by centrifugation and decanting of the supernatant. The solid peptide was dried briefly under vacuum, dissolved in 200 μL of 0.1 M sodium bicarbonate and purified by HPLC. The purified peptide was characterized by LC-MS. [00259] The labeled peptide (25 μmol) was then combined with methoxy polyethylene glycol amine (mPEG-NH2, Laysan Bio, 10 mg, 0.50 μmol) and dissolved in 100 μL DMF with 1 μL NMM. l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 0.25 mg, 1.3 μmol) and hydroxybenzotriazole (HOBT, 0.2 mg, 1.5 μmol) were added and the solution was placed on rotator shielded from light and rotated at room temperature for 16 hours. The pegylated peptide was precipitated by addition of 1.5 mL of MTBE, isolated by centrifugation and decanting of the supernatant. The pegylated peptide was dried briefly under vacuum, dissolved in 350 μL water and purified by HPLC. The mPEG conjugated peptide was characterized by RP- 18 HPLC and SEC HPLC. Example 23: Tumor Imaging

0371[00260] NU/NU mice 6-8 weeks old (Charles River Laboratory, Wilmington, MA) were injected SC with 2 x 106 4T-1 or HT-29 cells bilaterally in each mammary fat pad. When tumors reached an approximate size of 3 x 3 mm (around 7 days after cell injection), mice were injected intravenously with 2-4 nmoles of each imaging agent (5 mice/probe and 2 mice/ no probe as control) in 100 μL volume via tail vein. Imaging was conducted at 24 hours using a Fluorescence Molecular Tomography system (VisEn Medical, Woburn MA).

0372[00261] Pentynoyl-Lys(F5)-Gly-Phe-Leu-Gly-βAla-Lys(F5)-PEG20kDa (SEQ ID NO:422) (Agent Q65) was used to image tumors in vivo. Figure 1 shows the planar image of bilateral 4Tl tumors 6 hours after administration of the agent. Figure 2 shows a fluorescence molecular tomography bilateral image of 4Tl tumors 6 hours after administration of agent Q65.

0373[00262] Pentynoyl-Lys(F6)-Gly-Phe-Leu-Gly-βAla-Lys(F6)-PEG20kDa (SEQ ID NO:423) (Agent Q66) was also used to image tumors in vivo. Figure 3 shows the image of the 4Tl tumors at 5, 24 and 52 hours after administration of agent Q66.

0374[00263] Pentynoyl-Lys(F5)-Pro-Leu-Gly-Val-Arg-Lys(F5)-PEG20kDa (SEQ ID NO:424) (Agent Q91) was also used to image tumors in vivo. Figure 4 shows planar fluorescence reflectance images of HT-29 xenograft tumors at 2, 6 and 24 hour after administration of Agent Q91. Example 24: Enzyme Activation Profile of Imaging Agent 065

0375[00264] In this Example, the enzyme activation profile of imaging agent pentynoyl- Lys(F5)-Gly-Phe-Leu-Gly-βAla-Lys(F5)-PEG20kDa (SEQ ID NO:422) (Agent Q65) was characterized. [00265] The reactions were performed with appropriate buffer at room temperature in a 96-well plate with a final assay volume of 250 μL and probe and enzyme concentrations of 0.5 μM and 0.05μM, respectively. The buffer for Cathepsin B was 25 mM MES (pH 5.0), 1 mM DTT. Recombinant human Cathepsin B (R&amp;D Systems) was activated in buffer of 25 mM MES (pH 5.0) and 5 mM DTT for 15 minutes at room temperature. Recombinant human Cathepsin L (R&amp;D Systems) was activated in buffer of 50 mM MES (pH 6.0), 5 mM DTT, for 15 minutes on ice. Recombinant mouse Cathepsin Z (R&amp;D Systems) was activated in buffer of 25 mM NaOAc (pH 3.0), 5 mM DTT for 5 minutes at room temperature. The buffer for plasmin (CalBiochem) and trypsin (Sigma) was PBS at pH 7.4. [00266] The plate was incubated at room temperature and the activity monitored at 0, 1, 3, 5, and 24 hours with a Gemini (Molecular Devices) plate reader at excitation wavelength 663 nm, emission 690 nm, and cut off 665 nm. The activity was calculated as the fold of activation by comparing the fluorescence of the enzyme with probe to the fluorescence of probe alone. [00267] The results are shown in Figure 5, which show that the imaging agent Q65 is activated by Cathepsin B but not by plasmin, trypsin and Cathepsin Z.

0376Example 25: Enzyme Activation Profile of Imaging Agents Q92 and Q93

0377[00268] In this Example, the enzyme activation profile of imaging agents [F5]-His-Gly- Pro-Arg-Lys(F5)-[PEG20kDa] (SEQ ID NO:425) (Agent Q92) and [F5]-His-Gly-Pro- Asn-Lys(F5)-His-Gly-Pro-Asn-βA-[PEG20kDa] (SEQ ID NO:426) (Agent Q93) were characterized.

0378[00269] The reactions were performed with appropriate buffer at room temperature in a 96-well plate with a final assay volume of 250 μL and probe and enzyme concentrations of 0.5 μM and 0.05μM respectively. The buffer for activated humanized rabbit Cathepsin K (Merck) was 50 mM MES (pH 5.0), 2.5 mM EDTA, 2.5 mM DTT. The buffer for Cathepsin B was 25 mM MES (pH 5.0), 1 mM DTT. The recombinant human Cathepsin B (R&amp;D Systems) was activated in buffer of 25 mM MES (pH 5.0) and 5 mM DTT for 15 minutes at room temperature. The recombinant human Cathepsin L (R&amp;D Systems) was activated in buffer of 50 mM MES (pH 6.0), 5 mM DTT, for 15 minutes on ice. The buffer for MMP-2 (BIOMOL) and MMP-9 (BIOMOL) was 50 mM Tris (pH 7.5), 10 mM CaC12, 150 mM NaCl, and 0.05% Brij-35 detergent. The plate was incubated at room temperature and the activity was monitored at 0, 1, 3, 5, and 24 hours with a Gemini (Molecular Devices) plate reader at excitation wavelength 663 nm, emission 690 nm, and cut off 665 nm. The released fluorescent unit was determined by subtracting the fluorescence of the probe alone from the total fluorescence.

0379[00270] The results for Q92 are presented in Figure 6A, and the results for Q93 are shown in Figure 6B, which show that both Q92 and Q93 are activated primarily by Cathepsin K.

0380Example 26: Bone Imaging [00271] BALB/c female mice 7 weeks old (Charles River Laboratory, Wilmington, MA) were subjected to ovariectomy or sham surgery to induce osteoporosis. After one to two weeks after surgery, the mice were injected intravenously with imaging agent [F5]-His- Gly-Pro-Asn-Lys(F5)-[PEG20kDa] (SEQ ID NO:427) (Agent Q94). Imaging was conducted at various time points using a Fluorescence Molecular Tomography system (VisEn Medical, Bedford, MA). The results are shown in Figure 7.

0381[00272] Figure 7A shows images of an ovariectomized mouse (OVX) compared to a control (sham) mouse at 4 and 24 hours post-injection. The quantitation of absolute fluorescence of osteoporosis for the sham and ovariectomized mice is shown in Figure 7B. The increased probe signal detected in the tibia region appears to be due to increased Cathepsin K levels in bone loss induced by the ovariectomy procedure.

0382Example 27: Cardiovascular Disease Imaging

0383[00273] This Example show the imaging of cardiovascular disease using the imaging agent Pentynoyl-Lys(F5)-Gly-Phe-Leu-Gly-βAla-Lys(F5)-PEG20kDa) (SEQ ID NO:422) (Agent Q65). [00274] High cholesterol fed apoE-/- mice were injected with 2 nmol of imaging agent and in vivo imaging was performed with ex vivo fluorescence reflectance imaging. Figure 8 shows fluorescence reflectance imaging of cardiovascular disease in inflamed atherosclerotic plaques of mice 24 hours post-injection of agent Q65. Fluorescence was detected in plaque-laden vascular sections in the aortic root, the arch and carotid arteries. Example 28: Inflammation Imaging (Carrageenan Induced Paw Edema)

0384[00275] This Example shows the imaging of inflammation in a mouse model. Breifly, BALB/c female mice 6-8 weeks old (Charles River Laboratory, Wilmington, MA) were injected subcutaneously with a 1% solution of carrageenan in PBS. After 1 minute post- injection, mice were injected the imaging agent Q91. Imaging was conducted at various time points using a Fluorescence Molecular Tomography system (VisEn Medical, Woburn MA). An image is shown in Figure 9, which shows that significantly more fluorescence is observed in the mouse paw injected with carrageenan compared to the control paw (no injection).

0385Example 29: Enzyme Activation Profiles of Agents R20. R21. R23. R24. and R27 [00276] In this Example, the enzyme activity profiles of the agents ([F5]-Lys-His-Pro- Phe-His-Leu-Val-Ile-His-Lys(F5)-[OH]) (SEQ ID NO:401) (R20), ([F5]-Lys-His-Pro- Phe-His-Leu-Val-Ile-His-Lys(F5)-[NHmPEG20k]) (SEQ ID NO:428) (R21), ([F5]- Lys(Ac)-His-Pro-Phe-His-Leu-Val-Ile-His-Lys(F5)-[OH]) (SEQ ID NO:429) (R23), ([F5]-Lys-His-Pro-Phe-His-Cha-Val-Ile-His-Lys(F5)-[OH]) (SEQ ID NO:430) (R24), and ([FS]-LyS-HiS-PrO-PhC-HiS-LeU-VaI-IIe-HiS-LyS(FS)-[NHmPEGSk]) (SEQ ID NO:433) (R27) were characterized.

0386[00277] The reactions were performed with appropriate buffer in a 96- well plate with a final assay volume of 250 μL and probe and enzyme concentrations of 1 μM and 100 nM, respectively. The reactions were incubated at 37 C for Renin and room temperature for the other proteases. The buffer for human neutrophil Cathepsin G (BIOMOL) was 100 mM Tris (pH 7.5), 1.6 M NaCl. The buffer for Cathepsin D (BIOMOL) was 100 mM Formic Acid (pH 3.3). The buffer for recombinant human neutrophil elastase (Innovative Research) was 100 mM Tris (pH 7.5). The buffer for plasmin (CalBiochem) and trypsin (Sigma) was IX phosphate buffered saline (PBS) (pH 7.4). The buffer for recombinant human Renin (rhRenin) (Proteos) and recombinant rat Renin (rrRenin) (Proteos) was 50 mM MOPS (pH 7.4), 100 mM NaCl, with freshly prepared 0.002% tween-20. The plate was incubated at the appropriate temperature and the activity was monitored at 24 hours with a Gemini (Molecular Devices) plate reader at excitation wavelength 663 nm, emission 690 nm, and cut off 665 nm. The released fluorescent unit was determined by subtracting the fluorescence of the probe alone from the total fluorescence.

0387[00278] The results are shown in Figure 11, which show that agents R20, R23, and R24 were activated primarily by recombinant human rennin. Agents R21 and R27 were activated by recombinant human rennin, human neutrophil elastase, human neutrophil cathepsin, and trypsin. Example 30: Renal Imaging

0388[00279] This example shows the in vivo imaging of kidneys in mice on a control diet versus a low sodium diet.

0389[00280] C57BL6 mice (Jackson Laboratories) were fed a sodium deficient diet (0.02% Na) and water was replaced with a solution of amiloride (0.1 mg/5mL or 5 mg/kg/day) for 2 days. Control C57BL6 mice were fed regular chow diet and water. Imaging agents [F5]-Lys-His-Pro-Phe-His-Leu-Val-Ile-His-Lys(F5)-[OH] (SEQ ID NO:401) (R20) and ([F5]-Lys-His-Pro-Phe-His-Leu-Val-Ile-His-Lys(F5)-[NHmPEG20k] (SEQ ID NO:428) (R21) were injected intravenously at different concentrations (0.2, 0.7, 2 and 4 nmol/mouse) following 2 days on a low salt diet. Imaging was conducted at 24 hrs using a Fluorescence Molecular Tomography system (VisEn Medical, Woburn MA).

0390[00281] The results are shown in Figure 12, which demonstrate that for both imaging agents, the kidneys in the mice on the low sodium diet (Figures 12B and 12D) gave an increased signal relative to the kidneys in the mice on the control diet (Figures 12A and 12C). Example 31: Enzyme Activation of Imaging Agent R22

0391[00282] In this Example, the enzyme activation profile of the imaging agent [F6]-Gly- Pro-Leu-Gly-Val-Arg-Lys(F6)-[YPEG 2x20kDa] (SEQ ID NO:434) (R22) was characterized.

0392[00283] Activation by recombinant enzymes was carried out in 250 μL volumes set up in 96 well plates. MMPs were activated prior to the reaction according to manufacturers' protocols. Reactions contained 0.5 μM of R22 and 0.05 μM of activated enzyme in the appropriate activation buffer for each enzyme and incubated at room temperature for 24 hours. The plates were read at 24 hours with excitation/emission wavelength 740/770 nm. Fluorescence readings were performed using a Gemini (Molecular Devices) Fluorescence Plate Reader. Wells in which no enzyme was added were used as controls. Fold activation was obtained by dividing the enzyme-activated read-out (in relative fluorescence units) by its corresponding control well.

0393[00284] An example of the activation of the R22 by MMPs and other proteases is shown in Figure 13, which shows that R22 is activated primarily by recombinant human MMP- 13 and trypsin.

0394Example 32: Tumor Imaging With Agent R22

0395[00285] This Example describes the imaging of tumors in vivo using imaging agent R22.

0396[00286] Male and female NU/NU Mice (Charles River Laboratories, Wilmington, MA), 6-8 weeks of age, were injected with tumor cells bilaterally in the first or second mammary fat pads (human colorectal cancer cell line HT-29: 3 x 10⁶ cells/site). Once the tumors reached the desired volume, as measured with calipers (100 mm³) mice were injected intravenously with 2 nmoles of compound R22. Imaging was performed at 6 and 24 hours later using the Fluorescence Tomography System (FMT2500) (VisEn Medical, Bedford, MA). For in vivo imaging, mice were anesthetized by gas anesthesia (isoflurane/oxygen mixture), placed in the FMT2500 system imaging chamber one at a time and imaged using the reflectance and tomographic modes. Examples of imaging with the agent in the HT-29 tumor model are shown in Figure 14.

0397[00287] The images taken by reflectance imaging after 6 hours are shown in Figure 14A and after 24 hours in Figure 14B. Tomographic images taken after 6 hours are shown in Figure 14C and after 24 hours in Figure 14D.

0398Example 33: Enzyme Activation Profiles of Agents R51, R52, R55, R56, R57, R58, and R59

0399[00288] This Example shows the enzymatic activation profiles for compounds ([mPEG- 2OkDa-SUC]-LyS(Fo)-GIy-PhC-LeU-GIy-LyS(Fo)-[NH₂]) (SEQ ID NO:435) (R51), (CdPEG-IkDa-SuC]-LyS(FO)-GIy-PhC-LeU-GIy-LyS(Fo)-[NH₂]) (SEQ ID NO:436) (R52), ([dppa-Suc]-Lys(F6)-Gly-Phe-Leu-Gly-Lys(F6)-[NH₂]) (SEQ ID NO:437) (R53), ([mPEG-20kDa-Suc]-Lys(F6)-Arg-Arg-Lys(F6)-[NH₂]) (SEQ ID NO:438) (R55), ([dPEG-lkDa-Suc]-Lys(F6)-Arg-Arg-Lys(F6)-[NH₂]) (SEQ ID NO:439) (R56), ([dppa- Suc]-Lys(F6)-Arg-Arg-Lys(F6)-[NH₂]) (SEQ ID NO:440) (R57), ([mPEG-20kDa-Suc]- Lys(F6)-Ala-Arg-Arg-Lys(F6)-[NH₂]) (SEQ ID NO:441) (R58), and ([mPEG-20kDa- Suc]-Lys(F6)-Arg-Arg-Arg-Lys(F6)-[NH₂]) (SEQ ID NO:442) (R59).

0400[00289] Compounds at a concentration of 0.5 uM were incubated with Cathepsin B, Cathepsin K, Cathepsin L, or Cathepsin S at a concentration of 0.05 uM. The reaction buffers used were as follows: Cathepsin K - 50 mM MES, pH 5.0, 2.5 mM EDTA, 2.5 mM DTT; Cathepsin B - 25 mM MES, pH 5.0, 1 mM DTT; Cathepsin S - 50 mM

0401NaOAc, pH 4.5, 5 mM DTT, 0.25M NaCl; Cathepsin L - 50 mM MES, pH 6, 5 mM DTT. The activity was monitored for 24 hours with a Gemini (Molecular Devices) fluorescence plate reader at excitation 663 nm and emission 690 nm with a cut off of 690 nm. Figure 15 indicates that activation of imaging agent R51 by various Cathepsin proteases is greater than that of the other imaging agents.

0402Example 34: Imaging of Macrophage Activity in Atherosclerotic Plaque

0403[00290] Age-matched C57BL6 wild type female mice (Charles river Laboratories) were fed a normal diet and ApoE -/- knockout female mice (Jackson Laboratories) were fed a high cholesterol diet for 10-20 weeks. The mice were injected intravenously with compounds of formula R51 ([mPEG-20kDa-Suc]-Lys(F6)-Gly-Phe-Leu-Gly-Lys(F6> [NH2]) (SEQ ID NO:435) and R55 ([mPEG-20kDa-Suc]-Lys(F6)-Arg-Arg-Lys(F6> [NH2]) (SEQ ID NO:438). The mice were then imaged at 6 and 24 hours by fluorescence molecular tomography or fluorescence reflectance using an FMT2500 (VisEn Medical, Bedford, MA). [00291] Figure 16 shows an example of fluorescence imaging using compound R51.

0404Figure 16A shows fluorescence imaging of the aortic arch in ApoE -/- and wild type mice at 6 hours post-injection. Figure 16B compares the quantified fluorescence of wild type versus ApoE -/- knockout mice at 6 hours post-injection with compound R51. Fgiure 16C displays the reflectance imaging of the same mice with compound R51 at 6 hours. Figure 16D compares the quantified fluorescence of wild type versus ApoE -/- knockout mice at 6 hours post-injection with compound R51. Imaging agent R51 produced a greater fluorescent signal in the ApoE knockout mice over controls demonstrating the use of R51 in imaging cardiovascular disease models.

0405[00292] Figure 17A shows an example of fluorescence molecular tomographic imaging of mice at 6 hours post-injection with R55. Figure 17B compares the quantified fluorescence of wild type versus ApoE knockout mice at 6 hours post-injection with compound R55. Imaging agent R51 produced a greater fluorescent signal in the ApoE knockout mice over controls, demonstrating the use of R51 in imaging cardiovascular disease models.

0406INCORPORATION BY REFERENCE [00293] All publications, patents, and patent applications cited herein are hereby expressly incorporated by reference in their entirety and for all purposes to the same extent as if each was so individually denoted.

EQUIVALENTS

0408[00294] The invention may be embodied in other specific forms without departing form the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting on the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.