Novel bifunctional linking compounds, conjugates and methods for their production

Bifunctional N-substituted hydrazine compounds, processes for their preparation and process for the preparation of conjugates using them

This invention relates to novel bifunctional compounds and methods for their preparation and use. More particularly, the invention relates to N-substituted hydrazine compounds that can be incorporated into molecules to target cell populations.

Bifunctional compounds that allow the attachment of two or more molecules have been described. For example, bifunctional compounds are known for incorporating cytotoxic reagents into molecules for targeting cell populations. Bifunctional compounds must be able to transport and release these types of cytotoxic agents in vivo, for example, to provide adequate, i.e., therapeutic, levels of the agents in vivo without compromising the activity of the targeting molecules. For certain applications, it is desirable to form a conjugate containing a pH-sensitive bond between the reagent and the targeting molecules, wherein the bond provides release of the cytotoxic reagent over certain pH ranges.

Particularly useful reagents for the treatment of cancers are anthracyclines. Anthracyclines are antibiotic compounds with cytotoxic activity. Studies have revealed that anthracyclines can act by killing cells through a number of different mechanisms, including: 1) the adaptation of drug molecules to the cell

Between DNA, thereby inhibiting DNA-dependent nucleic acid synthesis; 2) the production of free radicals by a drug, wherein the radicals then react with cellular macromolecules, causing cell damage, or 3) the interaction of drug molecules with the cell membrane [Peter35 son et al., Transport and Storage Of Anthracyclines In

Experimental Systems and Human Leukemia, in Anth- 100718 racycline Antibiotics In Cancer Therapy, Muggia et al. (editors), pp. 132 (Martinus Nijhoff Publishers (1982); and Bachur, Free Radical Damage, same publication, pp. 97 102)]. Due to its cytotoxic potential, anthracyclines have been used to treat numerous cancers, including leukemia, breast cancer, lung cancer, ovarian glandular cancer, and sarcoma species [Wiernik, Current Status Of Adriamycin and Daunomycin In Cancer Treatment, in Anthracyclines: Current Status. (editors), pp. 273-94 (Academic Press 1980)]. Commonly used anthracyclines include e.g. adriamycin (ADM, also known as doxorubicin) and daunomycin (DAU, also known as daunorubicin).

Although these compounds may be useful in the treatment of tumors and other disease states in which an attempt is made to reduce or eliminate a target cell population, their therapeutic efficacy is often limited by the dose-dependent toxicity associated with their administration. For example, in the treatment of tumors, typical adverse side effects of these compounds include e.g. bone marrow inhibition and cardiotoxicity (Crooke, Goals For Anthracycline Analog Development At Bristol Laboratories, Anthracyclines: Current Status and New Developments, supra, p. 11). Therefore, in the treatment of tumors, efforts have been made to enhance the therapeutic effects of these compounds by coupling anthracycline to antibodies directed against tumor-associated antigens to form immunoconjugates for the selective release of drugs into cells. [Hermentin and Seiler, Investigations with Monoclonal antibody drug (anthracycline) conjugates, Behring Insti. YL What. 82 (1988) 197-215]. In this way, the drug can be released or targeted to the tumor site, and its toxic side effects on normal cells in the body can be reduced. Immunoconjugates consisting of anthracyclines ADM or DAU linked to polyclonal 100718 or monoclonal antibodies to tumor-associated antigens are known in the art [e.g., Gallego et al. ai., Preparation Of Four Daunomucin-Monoclonal Antibody 791T / 36 Conjugates With Anti-Tumor Activity, Int. J. Cancer 33 (1984) 737-44; and Arnon et al., In Vitro and In Vitro Efficacy Of Conjugates Of Daunomycin With Anti-Tumor Antibodies, Immunological Rev. 62 (1982) 5 27].

The most commonly used approaches for attaching anthracycline to an antibody have used a bond in the amino sugar group of the anthracycline. For example, the amino sugar is oxidized by sodium periodate treatment and attached directly to the lysine residues of the antibody by Schiff's base formation [Hurwitz et al., The Covalent Binding Of Daunomycin and Adriamycin To Antibodies, With Retention of Both Drug and Antibody Activities, Cancer Res. 35 (1975) 1175-1181]. Alternatively, anthracyclines have been coupled to antibodies by carbodiimide-mediated coupling of the amino group of the anthracycline to the carboxyl groups of the antibody [Hurwitz et al., Supra) or to an aminoalkyl group (Hurwitz et al., The Effect in vivo of Chemotherapeutic drug-antibody conjugates in two murine experiments). systems, Int. J. Cancer 21 (1978) 747-755] These bonds are not easily hydrolyzed and make it difficult to control anthracycline release. Anthracyclines have also been coupled to antibodies by cross-linking the amino sugar of the drug and the amino groups of the antibody with glutaraldehyde [Belles-Isles et al., In Vitro Activity of Daunomycin-Anti-AlphaFetoprotein Conjugate On Mouse Hepatoma Cells, Br. J. Cancer 41 (1980) 841-42]. However, studies with immunoconjugates in which the amino sugar portion of the anthracycline molecule was modified by binding to an antibody show a loss of cytotoxic activity of the conjugated drug (Arnon et al., Supra, pp. 7-8). In addition, studies with anthracycline analogs have shown that modifications to the amino sugars of anthracyclines result in a decrease in the cytotoxic activity of the drug analog.

1C0718 dilution relative to parent drug activity [Yamamoto et al., Antitumor Activity of Some Derivatives of Daunomycin At The Amino and Methyl Ketone Functions, J. Med. Chem. 15 (1972) 872-75].

Further, other immunoconjugates have been prepared in which the anthracycline DAU is coupled directly to the antibody at the carbon-14 (C-14) position of the drug. However, the selective cytotoxic activity of these immunoconjugates against tumor cells was not readily reproducible and consistently occurred only at a concentration of 20 pg / ml (Gallego et al., Supra).

JP Patent Application 274,658 discloses the incorporation of an anthracycline into an antibody by a C-13 acylhydrazone bond. This coupling was performed using methods involving antibody derivatization and subsequent reaction of this derivative with an anthracycline. These methods are not favorable because of the undesired non-specific reactions associated with antibody derivatization and the methods produce very low anthracycline: antibody ratios. According to the first method, the antibody was treated with carbodiimide in the presence of hydrazine to give a hydrazide antibody derivative, which was then reacted with an anthracycline so that the anthracycline was directly attached to the antibody structure. However, the resulting immunoconjugates are prone to aggregation into antibody molecules. In addition, because this method requires a limited number of carboxyl groups, these immunoconjugates have low anthracycline: antibody ratios (approximately 1.1 to 1.3). Another method involves reacting the antibody with succinic anhydride to give a hemisuccinate derivative of the antibody. Next, this derivative is reacted with hydrazine to give an antibody hydrazide derivative, which is then reacted with an anthracycline, daunomycin. The disadvantage of this second nearly 100718 approach is that the reaction of the antibody derivative with hydrazine is nonspecific, resulting in the formation of a mixture of different antibody derivatives in addition to the formation of the desired hydrazide derivative. Thus, the anthracycline: antibody molar ratio was reported to be very low in JP 274,658 (approximately 1, see JP 26, p. 264, column 1). See also EP Patent Application 294,294, which describes the incorporation of a C-13 hydrazone derivative of anthracycline into the carbohydrate moiety of an antibody.

Other anthracycline hydrazones are described by Tong et al., J. Med. Chem. 21 (1978) 732-37, Smith et al., J. Med. Chem. 21 (1978) 280-83, and Brownlee et al., J. Chem. Soc. (1986) pp. 659-61. See also U.S. Patent 4,112,217, which describes the bishydrazones of DAU and ADM.

In other studies, anthracyclines have been coupled to high molecular weight carriers such as dextran or polyglutamic acid to enhance cytotoxic activity and reduce drug toxicity [Arnon et al., Supra, p. 5; and Hurwitz et al., Soluble Macromolecules As Carriers For Daunorubicin, J. Appl. Biochem. 2 (1980) 25-35]. These carrier-bound anthracyclines have also been covalently bound to antibodies to tumor-associated antigens to form immunoconjugates to specifically target a cytotoxic drug to tumor cells. For example, ADM is coupled to such an anti-tumor antibody by a carboxymethyldextran hydrazide bridge, wherein the ADM molecule is coupled to a hydrazine derivative of carboxymethyldextran with C-13 carbonyl of ADM to form a hydrazone. The antibody is then coupled to a dextran hydrazide derivative with glutaraldehyde to form an adriamycin-dex antibody conjugate [Arnon et al., Monoclonal Antibodies As Carriers For Immunotargeting Of Drugs, in Monoclonal Antibodies For Cancer Detec100718 thion and Therapy. (editors), pp. 365 83 (1985); and Hurwitz et al., A Conjugate Of Adriamycin And Monoclonal Antibodies To Thy-1 Antigen Inhibits A Human Neuroblastoma Cells In Vitro, Ann. NY Acad. Sci. 417 (1983) 125-36].

However, there are certain disadvantages associated with the applicants' use. For example, carrier-containing immunoconjugates are quite large in size and are rapidly eliminated by the reticuloendothelial system in vivo [Dillman et al., Preclinical Trials With Combinations and Conjugates Of T101 Monoclonal Antibody and Doxorubicin, Cancer Res. 46 (1986) 4886-91]. This rapid elimination of carrier-containing immunoconjugates may not be of therapeutic benefit, as the conjugated drug may never reach its intended site of action, i.e., the target group of cells to be killed. In addition, the presence of a high molecular weight carrier may adversely affect the stability of the immunoconjugate and has been shown to reduce the antibody binding activity of the conjugate [Embleton et al., Antibody Targeting Of Anti-Cancer Agents, in Monoclonal Antibodies For Cancer Detection and Therapy, Baldwin et al. (eds.), pp. 323-24 (1985)]. In addition, studies in tumor cells have found no evidence that immunoconjugates containing high molecular weight carriers could localize to tumor cells in vivo, [cf. Ford et al., Localization and Toxicity Study Of A Vindesine-Anti-CEA Conjugate In Patients With Advanced Cancer, Br. J. Cancer 47 (1983) 35-42, which demonstrates the localization of directly conjugated drug / antibody conjugates to tumor cells in vivo].

Thus, conjugation of anthracyclines to antibodies using specific linkages and carriers has been described. As discussed above, the use of these immunoconjugates has clear disadvantages depending on the particular dressing or carrier used.

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Certain ligand / toxin conjugates have also been described. U.S. Patent 4,545,985 to Pasta discloses an exotoxin conjugate in which Pseudomonas exotoxin (PE) is coupled to EGF in a 1: 2 ratio for use against cells with a large number of EGF receptors. EGF / ricin A and EGF / diphtheria toxin conjugates have also been prepared [Cawley et al., Epidermal Growth Factor-Toxin A Chain Conjugates: EGF-Ricin A Is A Potent Toxin While EGF-Diphtheria Fragment A Is Nontoxic, Cell 22 (1980) 563 - 70; and Shimizu et al., A Cytotoxic Epidermal Growth Factor Cross-Linked To Diphtheria Toxin A-Fragment, FEBS Letters 118 (No. 2) (1980) 274-278]. In addition, Pseudomonas exotoxin fusion proteins have been prepared using proteins, polypeptides, and growth factors such as TGF-β, IL-2, IL-6, and CD4 [Pastan et al., Novel Cytotoxic Agents Created By The Fusion Of Growth Factor and Toxin Genes, Fourth Internatl. Conference On Monoclonal Antibody Immunoconjugates For Cancer, p. 36 (March 30-April 1, 1989); Lorberboum et al.,

Proc. Natl. Acad. Sci. USA 85 (1988) 1922-1926; Chaudhary et al., Proc. Natl. Acad. Sci. USA 84 (1987) 4538 4542; Siegall et al., Proc. Natl. Acad. Sci. USA 85 (1988) 9738-9742; and Chaudhary et al., Nature 335 (1988) 369 372]. A diphtheria toxin / tt melanocyte stimulating hormone fusion protein has been prepared [Murphy et al., Genetic Construction, Expression and Melanoma-Selective Cytotoxicity Of A Diphtheria Toxin-Related «Melanocyte-Stimulating Hormone Fusion Protein, Proc. Natl. Acad. Sci. USA 83 (1986) 8258-8262; and U.S. Patent 4,675,382 to Murphy]. However, ligand conjugates containing protein toxins may prove immunogenic in xenogeneic hosts.

In addition, anthracyclines such as ADM or DAU have been coupled to chemically defined protein or polypeptide ligands such as transferrin (GB Patent Application 2,116,979 A) and melanotropin [Varga et al., Melanotro.100718 pin-Daunomycin Conjugate Shows Receptor-Mediated Cot Murine Melanoma Cells, Nature 267 (1977) 56 - 58]. PCT Patent Application WO 88/00837 describes EGF coupled via a polymeric carrier to a cytotoxic agent such as DAU, and U.S. Patent Nos. 4,522,750 and 4,590,001 describe transferrin coupled to vinca alkaloid and platinum, respectively.

The cytotoxic drug to be used in the immunoconjugate should be released by a conditional release mechanism, i.e., the cytotoxic drug should be released at a specific site rather than by gradual hydrolysis at a non-specific site. It has been suggested that specific immunoconjugates migrate into place in lysosomes [deDuve, Lysosomes Revisited, Eur. J. Biochem. 137 (1983) 391-397], which are slightly acidic (pH 5.0-5.5) [Poznansky and Juliano; Biological Approaches to the Controlled Delivery of Drugs: A Critical Review, Pharmacol. Rev. 36 (1984) 277-336]. The use of acidic conditions to release a conjugated drug has been described in the development of ADM cis-aconityl linkers [Shen and Reiser, Cis-Aconityl Spacer Between Daunomycin and Macromolecular Carriers: A Model of pH-sensitive Linkage Releasing Drug From a Lysosomotrophic Conjugate, Biophys. Res. Commun. 102 (1981) 1048-1054; and Doxorubicin Conjugates With a Directed to a Human MelanomaProteoglycan Suppresses the Growth of Established Tumor Xenografts in Nude Mice, Proc. Natl. Acad. Sci. 85 (1988) 1189-1193), and ketal linkers to diphtheria toxin [Srinivasachar and Neville; New Protein Cross-Linking Reagents That Are Cleaved by Mild Acid, Biochemistry 28 (1989) 2501-2509].

Greenfield et al. has recently described the formation of acid-sensitive immunoconjugates containing an acylhydrazine compound, 3- (2-pyridyldithio) proYang, and Reisfeld, a monoclonal Antibody Associated anionic al., EP Patent Application 328,147, published August 16, 1989).

It would be useful to provide additional bifunctional compounds formed to provide an acid-sensitive bond between molecules, including targeting and reagent molecules for use in therapy in vivo.

This invention relates to novel bifunctional compounds that are readily conjugated to useful molecules and to methods for preparing the bifunctional compounds. Bifunctional compounds contain a reactive pyridinyldithio group. The invention also relates to a method for preparing novel conjugates, wherein a cytotoxic molecule is coupled to the bifunctional compounds of the invention to form a derivative of the cytotoxic molecule, and further to a molecule that can react with a target cell population to be killed. This targeting molecule is a sulfhydryl group-containing monoclonal antibody.

More specifically, the invention is characterized by what is stated in the claims.

In one embodiment, a novel bifunctional compound, N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinecarboxamide (Compound 10), is synthesized and used to form a semicarbazone derivative of ADM that contains a semicarbazone bond at the C-13 position of ADM. acts as an ADM attachment site for compound 10.

According to another preferred embodiment, a novel bifunctional compound, 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] carbonide dihydrazide (Compound 11a) is synthesized and used to form a carbazone derivative of ADM containing C At the 13-position, carbazone 100718 would act as an ADM attachment site for compound 11a.

In another preferred embodiment, a novel bifunctional compound, N- [4 - [(2-pyridinyl) dithio] -2-butenyl] hydrazinecarbothioamide (Compound

12) and is used to form a thiosemicarbazone derivative of ADM containing a thiosemicarbazone bond at the C-13 position of ADM that acts as an attachment site for ADM to compound 12.

According to another preferred embodiment, a novel bifunctional compound, 2 [(2-pyridinyl) dithio] ethylhydrazine carboxylate (Compound 13), is synthesized and used to form a hydrazone derivative of ADM containing a carboxylate hydrazone bond at the C-13 position of ADM that acts on the ADM compound. 13.

In a further preferred embodiment, a novel bifunctional compound, N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinobenzamide (Compound 15), is synthesized and used to form a phenylhydrazone derivative of ADM containing an arylhydrazone bond at the C-13 position of ADM which acts as an attachment site for ADM to compound 15.

A number of molecules of the above novel anthracycline derivatives are then coupled to a molecule that is reactive with the selected target cell population, i.e., a monoclonal antibody containing a sulfhydryl group. Each anthracycline derivative molecule is attached to the antibody via a bifunctional compound linked to the anthracycline via a semicarbazone, carbazone, thiosemicarbazone, carboxylate hydrazone, or phenylhydrazone linkage at the C-13 position of the anthracycline molecule. For example, a preferred embodiment of the invention involves the synthesis of a novel adriamycin derivative molecule which is condensed with a thiolated antibody, followed by attachment of the anthracycline to the agent 100718 via a bifunctional compound. The hydrazone bond formed at the C-13 position of the ADM acts as an attachment site to the ADM. In this embodiment, a disulfide bond attached to the antibody is present in the bifunctional compound. According to another preferred embodiment, the adriamycin derivative molecule (ADM attached to the bifunctional compound) is reduced to form a sulfhydryl group, and the resulting derivative is condensed with a maleimide-derivatized antibody. This results in the formation of an immunoconjugate with an N-substituted hydrazone bond as the attachment site of the bifunctional compound to the C-13 position of ADM, and in the bifunctional compound with a thioether bond through which it is attached to the antibody.

The immunoconjugates of the invention have an anthracycline: antibody molar ratio of at least 1: 1 and even 10: 1, and preferably about 4: 1 to 10: 1, and retain the activity of both antibody and cytotoxic drug in killing selected target cells. The acid-sensitive bond present at the anthracycline attachment site to the bifunctional compound of these conjugates is ideally suited for the release of the active drug under acidic conditions, such as those typically prevalent within the cell, e.g., lysosomal vesicles.

The release of adriamycin by hydrolysis from each of the above-mentioned derivatives as a function of pH showed that the new derivatives had broad release rates under acidic conditions mimicking the lysosomal environment. These derivatives also demonstrated cytotoxicity as immunoconjugates with anti-transferrin receptor monoclonal antibody 5E9.

The N-substituted bifunctional hydrazine compounds include a hydrazine moiety and a reactive pyridinyldithio moiety. These novel bifunctional compounds can be used to attach a wide variety of molecules to form useful conjugates. The molecule to be attached to the hydrazine moiety of the bifunctional compound 100718 contains a free carbonyl group or a group derivatized to contain a carbonyl group, such as a cytotoxic reagent molecule. When a molecule containing a carbonyl group is attached to the hydrazine portion of a bifunctional compound, a hydrazone bond is formed, which is a semicarbazone, carbazone, thiosemicarbazone, carboxylate hydrazone, or phenylhydrazone bond, depending on which bifunctional compound of the invention is used to form the conjugate. The molecule to be attached to the end of a bifunctional compound containing a pyridinyldithio group contains a free sulfhydryl group or a group that can be derivatized to contain a sulfhydryl group, such as an antibody molecule. The pyridinyldithio moiety is released during the reaction between the antibody and the bifunctional compound. The molecule containing the free carbonyl group is preferably a cytotoxic reagent molecule, such as an anthracycline, which can kill selected cells. In a preferred embodiment, the hydrazone bond that attaches the cytotoxic reagent molecule to the bifunctional compound allows for the pH-sensitive release of the cytotoxic reagent.

Conjugates formed by coupling molecules with the bifunctional compounds of the invention may be used in pharmaceutical compositions, such as those containing a pharmaceutically effective amount of at least one immunoconjugate and a pharmaceutically acceptable medium.

The compounds, conjugates, pharmaceutical compositions and methods described herein advantageously provide a useful approach for targeting cytotoxic reagents to selected populations of cells for the primary killing of these target cells in the treatment of diseases such as cancers and other tumors, non-cell killing viral or other pathogenic infections.

Figure 1 depicts the structures of adriamycin derivatives prepared by reacting the bifunctional compounds of the invention with adriamycin as described in Examples 1-5 below.

Figure 2 is a schematic representation of the synthesis of a bifunctional N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinecarboxamide compound used in the preparation of a semicarbazone derivative of adriamycin as described in Example 1 below.

Figure 3 is a schematic representation of the synthesis of a bifunctional 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] carboxylic acid dihydrazide compound used in the preparation of the carbazone derivative of adriamycin as described in Example 2 below.

Figure 4 is a schematic representation of the synthesis of a bifunctional N- [4 - [(2-pyridinyl) dithio] -2-butenyl] hydrazinecarbothioamide compound used in the preparation of a thiosemicarbazone derivative of adriamycin as described in Example 3 below.

Figure 5 is a schematic representation of the synthesis of a bifunctional 2 - [(2-pyridinyl) dithio] ethylhydrazinecarboxylate compound used in the preparation of the carboxylate hydrazone derivative of adriamycin as described in Example 4 below.

Figure 6 is a schematic representation of the synthesis of a bifunctional N- [2 - [(2-pyridinyl) dithio] ethyl] -4-hydrazinobenzamide compound used in the preparation of an arylhydrazone derivative of adriamycin as described in Example 5 below.

Figure 7 is a schematic representation of the preparation of immunoconjugates of the invention using an antibody thiolated with SPDP, which is reacted with the bifunctional compounds of the invention as described in Example 7 below.

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Figure 8 is a schematic representation of the preparation of immunoconjugates of the invention using an antibody thiolated with 2-IT that is reacted with bifunctional compounds of the invention.

Figure 9 is a schematic representation of the preparation of immunoconjugates of the invention having a thioether bond between an antibody and a reduced bifunctional compound using an antibody reacted with SMPB to add maleimide groups.

Figure 10 is a graph of adriamycin release as a function of time after incubation of adriamycin derivatives in buffer at pH 4.5, as described in Example 6 below.

Figure 11 is a graph of adriamycin release as a function of time after incubation of adriamycin derivatives in buffer at pH 5.0, as described in Example 6 below.

Figure 12 is a graph of adriamycin release as a function of time after incubation of adriamycin derivatives in buffer at pH 7.4, as described in Example 6 below.

Figure 13 is a diagram of the release of adriamycin from the carbazone derivative of adriamycin and the 5E9 immunoconjugate of this derivative as a function of time after incubation in buffer at pH 4.5, as described in Example 7 below.

The following detailed description is provided in order that the invention described herein may be more fully understood.

This invention relates in particular to novel bifunctional N-substituted hydrazine compounds: N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinecarboxamide (Compound

10); 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl) carbonide dihydrazide (Compound 11a); N- [4 - [(2-pyridinyl) dithio] -2-butenyl] hydrazinecarbothioamide (Compound

12); 2 - [(2-pyridinyl) dithio] ethylhydrazinecarboxy100718 (Compound 13); and N- [2 - [(2-pyridinyl) dithio] ethyl] -4-hydrazinobenzamide (Compound 15). These compounds are used to form new N-substituted hydrazone derivatives of cytotoxic reagents, such as anthracyclines, and when coupled to an antibody to form immunoconjugates. The invention also relates to processes for the preparation of bifunctional compounds and to a process for the preparation of immunoconjugates. Immunoconjugates are useful in pharmaceutical compositions for releasing cytotoxic reagents into target cells to treat diseases such as cancers and other tumors, non-cell killing viral or other pathogenic infections, and autoimmune disorders.

The conjugates contain at least one cytotoxic derivative molecule fused by one of the bifunctional compounds to at least one molecule reactive with the target cell population, i.e., a monoclonal antibody containing a sulfhydryl group.

Thus, in one preferred embodiment, a novel compound, N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinecarboxamide, Compound 10 was synthesized and used to form a semicarbazone derivative of ADM containing a semicarbazone bond at the C-13 position of ADM. In another preferred embodiment, a novel compound 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] carbonide hydrazide, Compound 11a, was synthesized and used to form a carbazone derivative of ADM having a carbazone bond at the C-13 position of ADM. . According to a further preferred embodiment of the invention, a new compound N [4 - [(2-pyridinyl) dithio] -2-butenyl] hydrazinecarbothioamide, compound 12, was synthesized and used to form a thiosemicarbazone derivative of ADM having an ADM in the C-13 position. tiosemikarbatsonisidos. In a further preferred embodiment, a novel compound 2 [(2-pyridinyl) dithio] ethyl hydrazinecarboxylate, compound 13, was synthesized.

1CG718 and was used to form a hydrazone derivative of ADM having a carboxylate hydrazone bond at the C-13 position of ADM. In a further preferred embodiment, a novel compound, N- [2 - [(2-pyridinyl) dithio] ethyl] -4-hydrazinobenzamide, Compound 15, was used to form an arylhydrazone derivative of ADM having a phenylhydrazone bond at the C-13 position of ADM.

In other embodiments, the invention relates to a method of preparing conjugates comprising at least one molecule reactive with a target cell population, i.e., a sulfhydryl group-containing monoclonal antibody, and at least one cell-killing cytotoxic molecule coupled to the novel bifunctional compounds of the invention. Thus, the invention relates to a method for preparing immunoconjugates comprising a monoclonal antibody containing a sulfhydryl group directed against a target cell population, for example a tumor cell population having a number of anthracycline derivative molecules incorporated into the antibody structure. The anthracycline derivative molecules are covalently attached to the thiolated antibody so that a disulfide bond is formed between each drug molecule and the antibody, with the bifunctional compound attached to the anthracycline derivative by a hydrazone bond at the C-13 position of the anthracycline. More than one drug molecule can be attached to each antibody molecule using a single bifunctional compound / drug molecule of the invention. A molar ratio of 4: 1 indicates that four drug, (i.e., anthracycline derivative) molecules bind to a single antibody.

In an alternative embodiment, the anthracycline derivative is reduced to form a sulfhydryl group, and this ADM derivative is condensed with a maleimide-modified antibody to form a thioether bond between the antibody and the anthracycline.

These conjugates allow for the pH-sensitive release of an unmodified anthracycline drug, preventing structural changes in the drug that could cause a decrease in cytotoxicity.

Conjugates are prepared stepwise by first forming a new N-substituted hydrazine compound which is used to form a hydrazone derivative of a cytotoxic reagent, which is then reacted with a protein of suitable specificity [see Hardy, Purification and Coupling of Fluorescent Proteins For Use In Flow Cytometry, manual. Immunology, vol. 1: Immunochemistry, DM Weir et al. (editors), pp. 31.4 - 31.12 (4. 1986 edition) regarding a representation of conventional antibody coupling techniques; and Varga et al., supra, for the preparation of ligand conjugates].

The length of a bifunctional compound that combines a cytotoxic reagent with the cell-reactive component of the conjugates may vary as long as the bifunctional compound is attached to the carbonyl group of the cytotoxic reagent molecule or molecules by one of the aforementioned hydrazone bonds.

Cytotoxic reagents include anthracyclines: adriamycin, daunomycin, detorubicin, carminomycin, idarubicin, epirubicin, esorubicin, 4'-THP-adriamycin, AD-32 and 3'-deamino-3'-3-cyano-4-morpholinyl) Experimental Studies On New Anthracyclines, in Adriamycin: Its Expanding Role In Cancer Treatment, M. Ogawa et al. (editors), pp. 439-52 (Excerpta Medica, 1984)].

The cell-reactive molecules to which the cytotoxic reagent is attached in the conjugate via the bifunctional compound can be any sulfhydryl group-containing antibodies that are reactive with a particular target cell population that is desired to be eliminated or killed. Examples of such antibodies include e.g. antibodies that bind to tumor-associated antigens, such as antigens present in carcinoma, melanoma, lymphoid tumors, bone or soft tissue sarcoma, as well as other tumors; antibodies that bind to antigens associated with viral or other pathogens; and antibodies that bind to abnormal cell surface antigens. These antibodies can be prepared using techniques well known in the art [Yeh et al., Cell Surface Antigens Of Human Melanoma Identified By Monoclonal Antibody, Proc. Natl. Acad. Sci. 76 (1979) 2927-31, and Brown et al., Structural Characterization Of Human Melanoma-Associated Antigen p97 With Monoclonal Antibodies, J. Immunol. 127 (No. 2) (1981) 539-46 (tumor-specific monoclonal antibodies produced)]. For example, monoclonal antibody L6, which is specific for human lung cancer cells, or monoclonal antibody 791T / 36, which is specific for bone-derived cancer cells, can be used.

The cell-reactive targeting molecule of the conjugates of the invention, the antibody, acts to release the cytotoxic reagent molecules to a particular population of target cells with which the antibody is reactive. For example, an antibody directed against an antigen present on the surface of tumor cells binds and releases cytotoxic reagents to these tumor cells, or an antibody directed against the AIDS-causing HIV (Human Immunodeficiency Virus) protein releases its cytotoxic reagent to HIV-infected patients. cells.

The release of a cytotoxic reagent within a particular cell population or to the location of a particular cell population to which the antibody reacts results in the primary killing of those particular cells. Thus, it will be appreciated that the conjugates of the present invention are useful in the treatment of any disease in which an attempt is made to eliminate a particular cell population having a cell surface antigen or receptor that allows the conjugate to bind. Diseases for which the conjugates are useful include, but are not limited to, cancers and other tumors, non-cell killing viral or other pathogenic infections such as AIDS, herpes, CMV (cytomegalovirus), EBV (Epstein-Barr virus), SSPE (subacute schlerosis panencephalitis; slow-progressing, degenerative brain disease) and rheumatoid arthritis.

Without wishing to be bound by theory, it is believed that antibody-associated cytotoxic reagent molecules, i.e., conjugates, are released into killable target cells through antibody specificity and thus may enter the cell via the same endocytic pathway leading to internalization of membrane-bound, unconjugated antibodies. Pathway Of Endocytosis, in Endocytosis, I. Pastan et al. (editors), pp. 1-44 (Plenum Press, 1985)]. Once the conjugate-containing endocytic vesicles are inside the cell, they fuse with the primary lysosomes to form secondary lysosomes [Embleton et al., Supra, p. 334). Because cytotoxic molecules are attached to the antibody component of the conjugate by acid-sensitive hydrazone bonds, exposure of the conjugate to the acidic environment of endocytic vesicles and lysosomes results in the release of the cytotoxic reagent from the conjugate. Further, the released reagent is believed to be in the form of a relatively unmodified reagent with full cytotoxic activity. Thus, the acid-sensitive bond of the conjugate is highly preferred for the release of the cytotoxic reagent within the target cells, increasing the cytotoxicity of the conjugate to these cells. Alternatively, the hydrazone bond may cleave under acidic and reducing conditions in the immediate environment outside or surrounding the target cells, e.g., tumor

<img file="FI100718B_D0001.tif" />

location, and tumor cells can take up the released drug.

The invention is described in preferred embodiments using the anthracycline adriamycin. In general, the carbonyl derivatives of adriamycin were prepared by treating adriamycin hydrochloride with one of the five bifunctional compounds of the invention in methanol at room temperature. It was found that the addition of a catalytic amount of trifluoroacetic acid (TFA) accelerated the condensation reactions so that the reaction proceeded to completion after stirring overnight. Few by-products were formed in these reactions, and the purification procedure required only precipitation with acetonitrile. These simplified methods represent an improvement over those previously described by Greenfield et al., Supra, in that they are easier to perform, more economical, and faster, and provide additional novel bifunctional compounds for conjugation with a variety of molecules.

In a first embodiment, a novel bifunctional compound was prepared by first reacting methoxycarbonylsulfenyl chloride with 2-aminoethanethiol hydrochloride, then with 2-mercaptopyridine to form 2 - [(2-pyridinyl) dithio] ethanamine hydrochloride (see Figure 2). This compound was then reacted with phosgene in the presence of triethylamine (TEA), then with t-butyl carbazate to form N- [2 - [(2-pyridinyl) dithio] ethyl] -2- (tert-butoxycarbonyl) hydrazinecarboxamide. Next, hydrazinecarboxamide was dissolved in TFA to form N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinecarboxamide, compound 10, a semicarbazide, which was then reacted with adriamycin hydrochloride to form a semicarbazone derivative of ADM containing a reactive pyridone 1 containing a reactive pyridone.

In another preferred embodiment, a novel bifunctional carbazide compound was prepared (Figure 3). The compound t-butyl carbazate was reacted with triphosgene in the presence of TEA. 2- (2-Pyridinyldithio) ethanamine hydrochloride was then added to form 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] -2,2'-bis (tertbutoxycarbonyl) carbonide hydrazide. This intermediate was added to TFA to form 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] carbonide dihydrazide, compound 11a, which was then added to adriamycin hydrochloride to form the carbazone derivative of ADM (Compound 2, Figure 1), which contained a reactive pyridinyldithio group.

In a further preferred embodiment, a novel bifunctional thiosemicarbazide compound was prepared (Figure 4). In this embodiment, potassium phthalimide was reacted with 1,4-dibromo-2-butene to form 1-bromo-4- (N-phthalimido) -2-butene. This compound was reacted with potassium thioacetate to form 1- (acetylthio) -4- (N-phthalimido) -2-butene, which was then reacted with hydrazine and treated with methoxycarbonylsulfenyl chloride, followed by 2-mercaptopyridine-1-amino-4 - [(2- pyridinyl) dithio] -2-butene hydrochloride. This compound was combined with TEA, and with it di-2-pyridylthionocarbonate, then t-butyl carbazate was added to form N- [4 - [(2-pyridinyl) dithio] -2-butenyl] hydrazinecarbothioamide t-boc derivative, compound 12. This compound was dissolved in TFA to form a gummy compound which was then reacted with adriamycin hydrochloride and TFA to form a thiosemicarbazone derivative of ADM having a thiosemicarbazone bond at the C-13 position of ADM (Compound 3, Figure 1) and having a reactive pyridyl group. .

Another preferred embodiment further involves the formation of a novel bifunctional compound (Figure 5). Chlorocarbonylsulfenyl chloride was reacted with 2-mercaptoethanol and 2-mercaptopyridine. Ammonium carbonate solution was added to form 2- (2-pyridinyl) dithio) ethanol as a colorless oil. Carbonyldiimidazole was added, and the mixture was reacted with hydrazine to form 2 - [(2-pyridinyl) dithio] ethylhydrazine carboxylate, compound 13. This compound was reacted with adriamycin hydrochloride and TFA, and then with acetonitrile to form a carboxylate hydrazone derivative of ADM (Compound 4, Figure 1) having a carboxylate hydrazone bond at the C-13 position of ADM and having a reactive pyridinyl dithio group.

In a further preferred embodiment, a novel bifunctional compound was synthesized (Figure 6). This compound was prepared by reacting p-hydrazinobenzoic acid with di-t-butyl pyrocarbonate to form 4- (N-bochydrazino) benzoic acid. This compound was reacted with N-hydroxysuccinimide and DCC to give N-hydroxysuccinimide ester of 4-N-boc- (hydrazino) benzoic acid. This material was reacted with 2- (2-pyridinyl) dithio) ethanamine hydrochloride and TEA to give N- [2- (2-pyridinyl) dithio] ethyl 4-N-boc- (hydrazino) benzamide. This compound was then treated with TFA to form N- [2 - [(2-pyridinyl) dithio] ethyl] -4-hydrazinobenzamide, compound 15, which was then reacted with adriamycin hydrochloride to form the phenylhydrazone derivative of ADM (Compound 5, Figure 1). having an arylhydrazone bond at the C-13 position of ADM and having a reactive pyridinyldithio group.

The novel N-substituted hydrazone derivatives of ADM described above were used in the preparation of conjugates according to the invention. Each derivative was reacted with a monoclonal antibody previously thiolated with SPDP or 2-IT (2iminothiolane), respectively, as shown in Figures 7 and 8, Brochure 100718. The resulting immunoconjugates consisted of ADM molecules conjugated to a monoclonal antibody by a bifunctional compound attached to the C-13 position of each ADM molecule by a hydrazone bond. The bifunctional compounds also contained a disulfide bond through which each was attached to the antibody.

A bifunctional compound that combines ADM and an antibody may consist of a number of components and bonds as long as these bonds include an acid-sensitive hydrazone bond at the C-13 position of the anthracycline. The antibody of the preferred embodiments was monoclonal antibody 5E9.

In another preferred embodiment of the invention, the novel bifunctional compounds are combined with adriamycin to form a derivative which is then further treated with a reducing agent dithiothreitol (DTT) or tributylphosphine to produce an adriamycin derivative containing a sulfhydryl (-SH) group bifunctional compound. This derivative is then reacted with a monoclonal antibody to which the maleimide groups are attached, for example, by reaction of the antibody with succinimidyl 4- (p-maleimidophenyl) butyrate (SMPB). An immunoconjugate is formed with a bifunctional compound attached by a hydrazone bond at the C-13 position of each ADM and with a thioether bond as part of the antibody attachment (see Figure 9).

Thus, it will be appreciated that a bifunctional compound linking ADM and an antibody may be composed of a number of components and bonds provided that these bonds include a hydrazone bond at the 13-keto position of ADM and a reactive pyridinyldithio group for attachment to the antibody.

It is clear that the present invention provides novel hydrazone derivatives of the anthracyclines of the following general formula I:

<img file="FI100718B_D0002.tif" />

where:

R_x is NHCONH (CH₂)_ofSSR₈; NHCONHNHCONH (CH₂ )_ofSSR₈; NHCSNH (CH₂ )_bCH = CH (CH₂ )_ofSSR_e; NHCOO (CH₂ )_ofSSR_a; or NHArCONH (CH₂) _ofSSR ';

<img file="FI100718B_D0003.tif" />

m is an integer from 1 to 10, and n is an integer from 1 to 4;

R₂ is CH₃, CH₂OH, CH₂OCO (CH₂)₃CH₃ or CH₂OCOCH (OC₂B₅)₂;

R₃ is OCH₃, OH or hydrogen;

R₄ is NH₂, NHCOCF₃, 4-morpholinyl, 3-cyano-4-morpholinyl, 1-piperidinyl, 4-methoxy-1-piperidinyl, benzylamine, dibenzylamine, cyanomethylamine or 1-cyano-2-methoxyethylamine;

R₅ is OH, O-THP or hydrogen; and

R₆ is OH or hydrogen, provided that R₆ is not OH when R₅is OH or O-THP, and new hydrazone derivatives of anthracyclines of formula II:

<img file="FI100718B_D0004.tif" />

where:

R_x is NHCONH (CH₂) _ofSSR₈; NHCONHNHCONH (CH₂) _ofSSR_e ; NHCSNH (CH₂ )_bCH-CH (CH₂ )_ofSSR_e; NHCOO (CH₂ ) "SSR_e; or NH-Ar-CONH (CH₂) _ofSSR₈;

<img file="FI100718B_D0005.tif" />

m is an integer from 1 to 10, and n is an integer from 1 to 4;

R₂ is CH₃, CH₂OH, CH₂OCO (CH₂)₃CH₃ or CH₂OCOCH (OC₂B₅ )₂;

R₃ is OCH₃, OH or hydrogen;

R₄ and R 1 are independently hydrogen, alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl, aryl, substituted aryl, aralkyl, or substituted aralkyl; or R₄, R₇ and N together form a 4- to 7-membered ring, said ring being optionally substituted;

R₅ is OH, O-THP or hydrogen; and

R₆ is OH or hydrogen, provided that R₆ is not OH when R₅is OH or O-THP.

The bifunctional compounds described above and the N-substituted hydrazone derivatives of anthracycline are novel compounds. Hydrazone derivatives of anthracycline can be used as novel cytotoxic reagents, and also represent intermediates in the preparation of novel conjugates according to the invention. Examples of anthracycline hydrazone derivatives are adriamycin semicarbazone; adriamysiinikarbatsoni; adriamysiinitiosemikarbatsoni; adriamysiinikarboksylaattihydratsoni; and adriamycinarylhydrazone, respectively, as described in the preferred embodiments disclosed herein.

As can be seen from the above formulas, N-substituted hydrazone ADM derivatives include N-substituted hydrazones from any of the known anthracyclines, such as adriamycin, daunomycin and carminomycin. In addition, derivatives include e.g. N-substituted hydrazones derivatized at specific sites in the anthracycline structure (e.g., 4'-THP-adriamycin hydrazone and 3'-deamino-3 '- (3-cyano-4-morpholinyl) adriamycin hydrazone). The latter derivatives can be synthesized by first derivatizing the anthracycline to form the desired analog and using this analog to prepare N-substituted hydrazone derivatives. Known anthracycline analogs include e.g. those described in U.S. Patent Nos. 4,464,529 and 4,301,277 (3'-deamino-3 '- (4-morpholinyl) or 3'-deamino-3' (3-cyano-4-morpholinyl) anthracycline analogs),

202 967 and 4,314,054 (3'-deamino-3 '- (1-piperidinyl) or 3'-deamino-3' - (4-methoxy-1-piperidinyl) anthracycline analogues), 4,250,303 (N-benzyl or N , N-dibenzyl anthracycline analogs), 4,591,637 (N-methoxymethyl or N-cyanomethylanthracycline analogs) and 4,303,785 (acetal analogs of anthracyclines). Thus, these known anthracycline analogs can be reacted as described hereinabove to produce novel hydrazone derivatives of ADM, which can then be conjugated to a cellular reactive molecule, such as an antibody having the desired specificity, as described above.

Alternatively, a non-derivatized N-substituted hydrazone derivative can be prepared from a non-derivatized anthracycline such as adriamycin, daunomycin or carminomycin as described herein, and then this new derivative can be derivatized to produce a novel N-substituted hydrazone substituted as desired. For example, a semicarbazone ADM derivative can be derivatized from its amino sugar group by reductive amination with 2,2'-oxoacetaldehyde using the method described in U.S. Patent 4,464,529 to prepare 3'-deamino-3 '- (4-morpholino) anthracycline semicarbazene. In addition, N-substituted hydrazone derivatives can be derivatized with formulas I and II R₅to the process described in U.S. Patent 4,303,785 for the preparation of acetal derivatives of hydrazone, such as the N-substituted hydrazone of 4'-THP-ADM.

It should be understood that in these methods for derivatizing hydrazones, N-substituted hydrazones from other reagents can be used as starting materials, including N-substituted hydrazones of various chemotherapeutic agents. And anthracyclines other than ADM, such as daunomycin or carminomycin, can be used to produce novel compounds such as N-substituted hydrazone of N-benzyldaunomycin or N-substituted hydrazone of 3'-deamino-3 '- (4-morpholinyl) carminomycin and others. other derivatives, which other compounds are also within the scope of the invention.

The release rates of anthracycline derivatives for the drug adriamycin were evaluated at pH 4.5, 5.0, and 7.4 and had a wide range of release rates. In addition, immunoconjugates containing derivatives conjugated to a monoclonal antibody were evaluated for adriamycin release at pH 4.5. The cytotoxicity of the immunoconflux 100718 jugates was tested using Daudi cells in a colony formation inhibition assay, and a correlation was observed between the stability of the hydrazone derivatives. Immunoconjugates also showed a wide range of release rates and showed antibody-directed cell killing (cytotoxicity) in tumor cell assays.

The N-substituted hydrazine compounds of the invention provide useful bifunctional compounds for the attachment of molecules such as targeting and cytotoxic reagents. When used to attach cytotoxic molecules containing a carbonyl group, the bifunctional compounds provide an acid-sensitive bond that cleaves within the pH range to release the cytotoxic reagent. The anthracycline immunoconjugates prepared in accordance with the invention appear to improve compared to previously described immunoconjugates in which the anthracyclines were directly attached to antibodies via the anthracycline amino sugar moiety because these amino sugar conjugates often contain lower anthracycline: antibody-mole ratios; impaired antibody binding properties [Arnon et al., Immunological Rev. 62, supra; Hurwitz et al., Cancer Res. 35, supra; and Yamamoto et al., supra]. In addition, stability studies with the immunoconjugates of the invention showed that the anthracycline was released from the immunoconjugates under acidic conditions similar to those found in the cellular environment. Thus, these immunoconjugates can release a relatively unmodified drug for release into target cells. The conjugates described herein provide drug release over a wide range of pH values, which may be advantageous for drug release.

The bifunctional compounds of the invention and immunoconjugates prepared therefrom and methods for their preparation are exemplified by preferred embodiments in which anthracycline adriamycin derivatives are conjugated to an anti-transferrin receptor monoclonal antibody 5E9.

In alternative embodiments of the methods of this invention, e.g. either simultaneously or sequentially, a variety of conjugates, i.e., those with different cytotoxic reagents and different antibodies for use in combination chemotherapy methods. For example, anthracycline immunoconjugates can be prepared in which the specificity of the antibody component of the conjugate varies, i.e., a plurality of immunoconjugates are used, each having an antibody that specifically binds to a different antigen or to different sites or epitopes of the same antigen in the cell population of interest. The anthracycline component of these immunoconjugates may be the same or may vary. Such an embodiment may be particularly useful, for example, in the treatment of certain tumors in which the amounts of different antigens on the tumor surface are unknown or the antigen expression of the tumor cell population is heterogeneous and it is desired to ensure that a sufficient amount of drug is applied to all tumor cells. Using a variety of conjugates with different antigenic or epitope specificities for a tumor increases the likelihood that sufficient drug will be delivered to the tumor site. In addition, such an embodiment is important in achieving a high degree of specificity for the tumor because the probability that normal tissue possesses all of the tumor-associated antigens is low [see Hellström et al., Monoclonal Antibodies to Two Determinants of Melanoma-Antigen p97 Act Synergistically In Complement-Dependent Cytotoxicity, J. Immunol. 127 (No. 1) (1981) 157-160].

Alternatively, a variety of immunoconjugates can be used in which only the anthracycline component of the conjugate varies. For example, a particular antibody may be coupled to adriamycin to form one immunoconjugate, and may be coupled to daunomycin to form another immunoconjugate. Both conjugates can then be administered to the host to be treated, and the conjugates are localized at the location of the selected cell population to be eliminated due to antibody specificity. Both drugs are then released at this point. This embodiment may be important when there is uncertainty about the drug resistance of a particular cell population, such as a tumor, because in this way a number of different drugs are released at or within the target cells. Thus, more than one type of anthracycline can be conjugated to a particular antibody to form an immunoconjugate having along its surface a number of different anthracycline molecules, all attached to the antibody via a 13-ketohydrazone bond. Administration of such an immunoconjugate results in the release of a variety of drugs at or within the location of the target cells.

The conjugates of the invention may be administered in the form of pharmaceutical compositions using conventional routes of administration, including, but not limited to, intravenous, intraperitoneal, oral, lymphatic, or direct administration to a selected cell population, such as a tumor site. Intravenous administration is preferred.

Pharmaceutical compositions containing conjugates may be in a variety of dosage forms, including, but not limited to, solid, semi-solid, and liquid dosage forms such as tablets, pills, powders, liquid solutions or suspensions, suppositories, polymeric microcapsules, or microcapsules. solutions for infusion. The form of Edul100718 depends on the route of administration and the therapeutic application.

The pharmaceutical compositions may also contain conventional pharmaceutically acceptable media known in the art, such as serum proteins, such as human serum albumin, buffers, such as phosphates, water or salts, or electrolytes.

The most effective mode of administration and order of administration of the conjugate compositions will depend on the severity and development of the disease, the condition of the patient and the response to treatment, and the judgment of the attending physician. Thus, doses of conjugates and all of the following compounds should be titrated to the individual patient. In any case, the effective dose of the anthracycline immunoconjugate may be in the range of about 1 to 100 mg / m 2² anthracycline or about 500 to 5000 mg / m 2² antibody.

The following examples are provided to provide a more complete understanding of the invention. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting the scope of the invention in any way.

eXAMPLES

Preparation of bifunctional compounds and adriamycin (ADM) derivatives

Melting points were determined on a Fisher-Johns (Medford, MA) melting point apparatus and are uncorrected. NMR spectra were obtained on a Brucker AM 300 instrument. Infrared (IR) spectra were run as KBr pellets or CHCl 3₃as solutions on a PE FTIR (Fourier Transform Infrared) (Norwalk, CT), model 1800. MS (mass spectrum) and HRMS (high resolution mass Spectrum) were obtained on Kratos MS25RFA and MS50TC (Manchester, England), respectively. Flash chromatography was performed using Woelm (Atlanta, GA) silica gel (silica 32-63). Thin layer chromatography (TLC) was performed on Analtec (Newark, DE) GHLF silica gel plates or RPS-F reverse phase 100718 plates, both 250. For routine HPLC (High Pressure Liquid Chromatography), a PE pump, a series of 4 LC, an HP 1046A fluorescence detector, and a Phenomenex (Torrance, CA) IB Sil-5C18 column (150 x 4.6 mm) were used. The mobile phase was 70:30 methanol / phosphate buffer (50 mmol ammonium phosphate, pH 4.4) at a flow rate of 1.5 ml / min. The HPLC system comprised 2 Waters pumps Model 510, an Autosampler Model 712, and a Gradient Controller Model 680 for release rate measurements. Chromatography was performed on a Waters C-18 column, and the mobile phase was a 68:32 mixture of triethylammonium formate buffer (0.05 M, pH 2.8) and acetonitrile, respectively. The fluorescence of the eluted adriamycin was detected using an ABI fluorescence detector Model 980 (excitation, 254 nm; emission, 550 nm) obtained from Applied Biosystems, Ramsey, NJ. At pH 4.5 and 5.0, acetate buffer was used; At pH 7.4, phosphate / saline buffer was used. Adriamycin HCl was obtained from Sanraku Inc. (Japan). All other chemicals were obtained from commercial sources. Elemental analyzes were performed in the analytical department at Bristol-Myers Squibb Company, Wallingford, CT, and Oneida Research Services.

Example 1

Preparation of bifunctional compound 10 and semicarbazone derivative of ADM

The following example illustrates the preparation of a bifunctional compound and a semicarbazone derivative of ADM having a semicarbazone bond at the C-13 position of ADM. In this example, N- [2 - [(2-pyridinyl) dithio) ethyl] hydrazinecarboxamide, Compound 10, is prepared by the reaction sequence shown in Figure 1. Cysteine ​​amine hydrochloride was reacted with methoxycarbonylsulfenyl chloride and then 2-mercaptopyridine to give 2- (2-pyridinyl) dithioethanamine hydrochloride (Compound 9 in Figure 1). This in turn was reacted with phosgene and t-butyl carbazate and then trifluoroacetic acid (TFA) to give the desired product (Compound 10).

Preparation of 2 - [(2-pyridinyl) dithiolethanamine hydrochloride

A solution of methoxycarbonylsulfenyl chloride (Zumach et al., Angew. Chem. International Edit. 9 (1970) 54-63, 6.33 g, 50 mmol) in HPLC grade methanol (100 mL) was stirred under N₂and cooled in ice. To this was added dropwise a solution of 2-aminoethanethiol hydrochloride (5.7 g, 50 mmol) in methanol (50 mL). When the addition was complete, the solution was stirred for 2 hours at room temperature. The solvent was then evaporated and the residual oil was crystallized from acetone (100 ml) to give a solid (6.9 g). This solid was dissolved in methanol (100 mL). The solution was cooled in ice, stirred with N₂and treated dropwise with a solution of 2-mercaptopyridine (3.82 g, 34 mmol) in methanol (50 mL). The solution was stirred for 1 hour at room temperature, concentrated to a small volume and slowly diluted with acetone until crystallization occurred. After 1 hour in the refrigerator, the solid was collected by filtration and dried to give 2 - [(2-pyridinyl) dithio] ethanamine hydrochloride (Compound 9). This compound has been described by: Field et al., J. Org. Chem. 29 (1964) 1632-1635; and Connor and Schroit, Biochem. 27 (1988) 848-851). The compound was characterized as follows: m.p. 123-125 ° C (5.8 g, 52%). IR (KBr) 2952, 2913, 1610, 1575, 1559, 1451, 1115, 767 cm -1¹. NMR (D₂0) δ 8.46, 7.83, 7.34 (d, m, m 4H, Py), 3.37 (t, 2H, CH₂CH₂NH₂), 3.12 (t, 2H, ££ H₂CH₂). MS (m / e):

187 (corresponds to [M + H] ⁺ : aa), 170, 152, 142, 112, 104, 76. Elemental Analysis C₇B_UCLN₂S₂ · 1 / 4Η₂Ο: 11θ:

Calculated: C, 37.00; H, 5.06; N, 12.33.

Found: C, 36.82; H, 4.99; N, 12.37.

Preparation of N- [2 - [(2-pyridinyl) dithiolethyl] -2- (tert-butoxycarbonyl) hydrazinecarboxamide 2 - [(2-pyridinyl) dithio] ethanamine hydrochloride (2.22 g, 10 mmol) was suspended in dry methylene chloride (100 mL). and treated with triethylamine (TEA) (5.8 mL). This solution was added dropwise to an ice-cold stirred solution of phosgene (10 mL of a 1.93 M toluene solution) in methylene chloride (200 mL). The reaction was monitored by TLC, and when the starting material was no longer present, the mixture was passed through N for some time.₂Added. T-butyl carbazate (1.32 g, 10 mmol) was then added and the mixture was stirred overnight. The solution was washed with water and the solvent was evaporated. The residue was chromatographed on silica gel using a methylene chloride: methanol solvent system (100: 2). The appropriate fractions were combined to give 1.74 g of N- [2 - [(2-pyridinyl) dithio] ethyl] -2- (tert-butoxycarbonyl) hydrazinecarboxamide (Compound 9a) as a foam, which was characterized as follows: IR (KBr) 3281, 2979, 2932, 1723, 1672, 1577, 1560, 1545, 1448, 1419,

1253, 1161, 762 cm¹. NMR (CDCl 3)₃) Δ 8.50, 7.56, 7.51, 7.12 (4H, Py), 3.51 (2H, £ H₂), 2.89 (2H, CH₂S), 6.84, 6.37, 6.17 (3H, NH), 1.44 (9H), (CH₃) 3C). MS (m / e) 345 (corresponding to [M + H] &amp; lt; + &amp; gt;), 317, 289, 245, 213, 178, 134, 112.

Preparation of N- [2 - [(2-pyridinyl) dithio) ethyl] hydrazinecarboxamide

N- [2 - [(2-pyridinyl) dithio] ethyl] -2- (tert-butoxycarbonyl) hydrazinecarboxamide (570 mg, 1.66 mmol) was dissolved in ice-cold TFA (10 mL). The solution was stirred on ice for 10 min and for an additional 10 min without cooling. Excess TFA was evaporated under reduced pressure as much as possible, and the residue was chromatographed on silica gel using a methylene chloride: methanol: concentrated ammonium hydroxide solvent system (100: 5: 0.5). The appropriate fractions were combined by TLC and the solvent evaporated to leave a crystalline residue (0.42 g, quantitative). An analytical sample was prepared by crystallization from IPA, m.p. 105-107 ° C. N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinecarboxamide (Compound 10) was characterized as follows: IR (KBr) 3336, 3220, 3064, 2949, 2934, 1670, 1623, 1575, 1562, 11-33, 1452, 1369 , 1172, 1046, 770 cm¹. NMR (CD₃OD) δ 8.41, 7.78, 7.21 (4H, Py), 3.43 (2H, NCH₂, 2.91 (2H ££ H₂). MS (m / e) 245 (corresponding to [M + H] +), 221, 213, 162, 134, 112.

Elemental analysis₈B₁₂OF₄OS₂: lie:

Calculated: C, 39.32; H, 4.95; N, 22.93; S, 26.24. Found: C, 39.19; H, 4.86; N, 22.48; S, 25.02.

Preparation of semicarbazone derivative of adriamycin hydrochloride and N- [2 - [(2-pyridinyl) dithio] ethyl] hydrazinecarboxamide

Compound 10 (0.37 g, 1.5 mmol) in methanol (25 mL) was added to a stirred suspension of adriamycin hydrochloride (0.66 g, 1.14 mmol) in methanol (50 mL). TFA (5 drops) was added and the mixture was stirred overnight. The clear solution was concentrated and chromatographed on a C-18 column using methanol: water (60:40) containing 0.3% ammonium acetate as the solvent system. The appropriate fractions were combined and as much methanol as possible was evaporated. The aqueous phase was lyophilized and the residue was dissolved in methanol and added to acetonitrile. The red solid (0.65 g, 68%) was collected by centrifugation and dried. The semicarbazone derivative of ADM was characterized as follows: IR (KBr) 3399, 2976, 2936, 1671, 1618, 1578, 1538, 1417, 1286, 1210, 1117, 1015, 989, 764 cm -1¹. NMR (CD 3 OD) δ 8.25, 7.76, 7.62, 7.48, 7.07 (py, ph, H), 4.95 (anomeric H), 4.63 (CH 2 OH), 4.24 (CH 3 CH), 3.97 (OCH 3), 3.5 - 2.9 (group absorption of SSCH 2, -CH 2 -, CH 2 NH), 1.29 (HC-CH 3). MS (m / e) 770 (corresponding to [M + H])⁺ : aa), 641, 437, 346. HRMS: calcd for C35H₄₀OF₅O_ofS₂: lie: 770.2166; Found: 770.2157.

Example 2

Preparation of bifunctional compound 11a and carbazone derivative of ADM

The following example illustrates the preparation of a bifunctional carbazide compound and a carbazone derivative of ADM having a carbazone bond at the C-13 position of ADM. In this example, the reaction between 2 - [(2- (pyridinyl) dithio] ethanamine hydrochloride and t-butyl carbazate shown in Figure 2 and described in Example 1 was initiated as shown in Figure 3 with t-butyl carbazate and triphosgene to give the bifunctional compound, (Compound 11a), carbazide. In this case, the excess t-butyl carbazate was reacted with phosgene to give a carbonide hydrazide.

Preparation of 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] -2,2'-bis (tert-butoxycarbonyl) carbonide dihydrazide t-butyl carbazate (0.396 g, 3 mmol) was dissolved in dry chloroform (10 mL). The solution was stirred at room temperature N₂and TEA (0.6 g, 6 mmol) was added. Triphosgene (0.296 g, 1 mmol) was then added in one portion. A vigorous reaction followed, and when this subsided, 2- (2-pyridinyldithio) ethanamine hydrochloride (0.667 g, 3 mmol) in chloroform containing TEA (0.3 g, 3 mmol) was added. The mixture was stirred for 1 1/2 hours at room temperature, then washed with water (3 x 20 ml), dried and the solvent evaporated under reduced pressure to leave a foam (0.91 g). This material was chromatographed on silica gel using a methylene chloride: methanol solvent system (100: 2). The distribution was monitored by TLC and combined accordingly to give 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] -2,2'-bis (tert-butoxycarbonyl) carbonide dihydrazide (Compound 11 ) as a foam (0.54 g, 52%). Compound 11 was characterized as follows: IR (KBr) 3302, 2980, 2933, 1726, 1683, 1498, 1252, 1160, 1047, 1018,

<td>763cm '¹.</td><td colspan="4">NMR (CDCl 3)₃) δ 8.50, 7.57, 7.49, 7.10,</td><td colspan="2">(d, q, d, t, 4H,</td>

<td>Py), 3,</td><td>52 (t, 2H,</td><td>SSCH₂ ),</td><td>2.90 (t,</td><td>2H</td><td>conch₂ ),</td><td> 1,46</td>

<td>[C (CH₃)₃;</td><td> 1, 8,30, 6,</td><td> 50, 6,29</td><td>(B, s, s,</td><td>NH).</td><td>MS (m / e)</td><td> 503</td>

<td>(equivalent to</td><td>[M + H] ⁺ : Aa)</td><td> 447, 431,</td><td> 419, 403,</td><td> 347,</td><td> 303, 213,</td><td> 179,</td>

112.

Preparation of [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] carbonide dihydrazide

Compound 11 (0.34 g, 0.68 mmol) was stirred with ice-cold TFA (5 mL) for min for 10 min without further cooling. The TFA was evaporated as much as possible and the residue was chromatographed on silica gel using methylene chloride: methanol: concentrated NH₄OH solvent system (100: 5: 0.5). The appropriate fractions were combined and compound 11a was obtained after evaporation as a hygroscopic foam (0.2 g, quantitative yield). Compound 11a was characterized as follows: IR (film) 3330, 2964, 2929, 1698, 1660, 1576, 1486, 1231, 1045, 759 cm -1¹. NMR (CDCl 3)₃Δ 8.50, 7.56, 7.10 (d, m, m, 4H, Py), 3.52 (q, 2H, CH₂N), 2.91 (t, 2H, Cfl₂SS), 8.87, 8.85, 4.19, 3.78 (D₂With 0 alternating protons, NH). MS (m / e) 303 (corresponding to [M + H] +), 213, 112.

Adriamycin hydrochloride carbazone derivative and

Preparation of 2 - [[[2 - [(2-pyridinyl) dithio] ethyl] amino] carbonyl] carbonide dihydrazide Adriamycin hydrochloride (356 mg, 0.6 mmol) and 11a (0.2 g, 0.68 mmol) were stirred overnight. in methanol (50 mL) containing 2-3 drops of TFA. A clear solution was obtained, and HPLC (methanol: 0.01 M ammonium phosphate solution-solvent system, 70:30, pH 4.5) indicated that more than 90% of the adriamycin had been converted to semicarbazone. Therefore, the solvent was evaporated, and the residue was chromatographed on a C-18 column using a methanol: water-solvent system (60:40) containing 0.3% ammonium acetate. fractions were monitored by reverse phase TLC (same solvent system but 3% ammonium acetate) and / or HPLC and fractions lacking adriamy100718 sine were pooled. Most of the methanol was evaporated under reduced pressure. The aqueous solution was lyophilized and the red residue was dissolved in a small volume of methanol. The solution was filtered and added to stirred acetonitrile (1 L). The clear solution was concentrated to about one-third of its volume, and the resulting solid was collected by centrifugation and dried to give ADM carbazone (Compound 4) (160 mg). A second crop (85 mg) was obtained by concentrating the solution to 100 ml, diluting with ether and collecting the solid by centrifugation (total yield 49%). This carbazone derivative was characterized as follows: IR (KBr): 3346, 2975, 2936, 1711, 1668, 1618, 1578, 1286, 1210, 1083, 1015, 765 cm -1¹. NMR (CD₃0D) &amp; 8.43, 7.89, 7.77, 7.52, 7.21, (py, phenyl-H), 5.15 (anomeric H), 4.57 (CH₂0H), 4.25 (CH₃£ U), 3.99 (OCH₃), 3.53 (SSCH₂), 3.17 (CH₂-, ring), 3.05 (CH₂NN =), 2.38 (-CH₂-, ring), 1.29 (CH £ H₃). MS (m / e) 828 (corresponding to [M + H]), 699, 572, 537, 377, 346, 289, 213.

Example 3

Preparation of bifunctional compound 12 and thiosemicarbazone derivative of ADM

This example illustrates the preparation of bifunctional compound 12, and a thiosemicarbazone derivative of ADM having a thiosemicarbazone bond at the C-13 position of ADM. In this example, a thio analog of the semicarbazide (Compound 10) described in Example 1 above was prepared as shown schematically in Figure 4. With 2 - [(2-pyridinyl) dithio] ethanamine, elimination of 2-mercaptopyridine could be observed, which could be seen in the increased nucleophilicity of the next thiosemicarbazide group in the last previous product step. This problem could be avoided by using a trans-2-butene group as shown in Fig. 4.

Preparation of 1-bromo-4- (N-phthalimido) -2-butene

To a solution of 1,4-dibromo-2-butene (8.4 g, 40 mmol) in DMF (200 mL) was added potassium phthalimide (4.62 g, 24 mmol) in portions over 1 h. After stirring overnight, the solvent was evaporated and the residue partitioned between water and methylene chloride. The organic layer was washed with water several times, dried and the solvent was evaporated. The residue was crystallized from 2-propanol to give the desired product, 1-bromo-4- (N-phthalimido-2-butene) (3.95 g, 59%), which was characterized as follows: m.p. 101-102 ° C. IR (KBr) 1775, 1711, 1466, 1436, 1393, 723 cm -1¹. NMR (CDCl 3)₃) fi 7.81, 7.73 (m, m 4H, phenyl), 5.88, 5.81 (m, m 2H, 2 = £ H-), 4.30 (d, 2H CH₂-N), 3.90 (d, 2H CH₂Br). MS (m / e) 280 (corresponding to [M + H] &amp; lt; + &amp; gt;), 200.

Elemental analysis₁₂B₁₀Brno₂: lie:

Calculated: C, 51.45; H, 3.60; N, 5.00.

Found: C, 52.35; H, 3.47; N, 4.80.

Preparation of 1- (acetylthio) -4- (N-phthalimido) -2-butene

A mixture of 1-bromo-4- (N-phthalimido) -2-butene (3.95 g; 14 mmol) and potassium thioacetate (1.77 g, 15.5 mmol) in absolute ethanol (50 mL) was heated to reflux. For 1/2 hour. The solvent was evaporated and the residue was extracted with methylene chloride. The solvent was evaporated to give a crystalline residue (3.85 g, 99%) which was used as such in the next step. An analytical sample was prepared by crystallization from 2-propanol, m.p. 69-71 ° C. This compound was characterized as follows: IR (KBr) 1769, 1713, 1688, 1427, 1391, 1114, 958 cm -1¹. NMR (CDCl 3) δ 7.80, 7.73 (m, m 4H Ph), 5.70 (m, 2H, 2 = CH-), 4.24 (d, 2H, E 2 H-N), δ, 48 (t, 2H CH 2 S), 2.29 (s, 3H, C-CH 3). MS (m / e) 276 (corresponding to [M + H]⁺ : aa), 234, 200. Elemental analysis for C 14 H₁₃WELL₃S: lie:

Calculated: C, 61.07; H, 4.76; N, 5.09.

Found: C, 61.29; H, 4.82; N, 5.21.

Preparation of 1-amino-4 - [(2-pyridinyl) dithio] -2-butene hydrochloride

A solution of 1-acetylthio-4- (N-phthalimido) -2-butene (6.5 g, 23.6 mmol) in absolute ethanol (150 mL) and hydrazine (1.74 g, 54 mmol) was heated to reflux. The reaction was monitored by TLC, and in the absence of starting material, the solution was cooled in ice and treated with 6N HCl (10 mL). A large precipitate formed and was identified as phthalhydrazide (NMR, MS) and filtered off. The filtrate was concentrated to 10 mL and diluted with water. The solid was filtered off and the filtrate was washed with ether (2X) and methylene chloride (IX), filtered through celite and lyophilized. The solid was dissolved in a small amount of methanol and the solution was filtered through celite, the solvent was evaporated and the residue was kept under vacuum overnight. A waxy, hygroscopic material was obtained, which was characterized as follows: NMR (DMSO / D₂0) δ 5.83, 5.60 (m, m 2H, 2 = CH-), 3.40 (d, 2H CH₂NH₂), 3.16 (d 2H, CH₂SH) MS (m / e) 104 (corresponding to [M + H] +), 87, 70. This waxy material was dissolved in HPLC grade methanol (75 mL). The solution was stirred and treated with methoxycarbonylsulfenyl chloride (3 g, 23.7 mmol). After 1/2 hour, no starting material was detected by TLC. The solvent was evaporated and the residue was redissolved in methanol (75 ml). The solution was stirred and treated with 2-mercaptopyridine (2.7 g, 24 mmol). After 2 hours the solvent was evaporated and the residue was evaporated under high vacuum. The residue was then dissolved in a mixture of 0.01 N HCl and methanol (90:10, 130 mL). The cloudy solution was washed with methylene chloride, filtered through celite and lyophilized to give 1-amino-4C (2-pyridinyl) dithio] -2-butene hydrochloride as a highly hygroscopic flocculant (4 g, 68%), which was characterized as follows: IR (KBr) 3433 , 2959, 2884, 1607, 1576, 1447, 1418, 1118, 767 cm -1¹. NMR (D₂0) δ 8.51, 8.13, 8.02, 7.54 (m 4H, Py) 5.87, 5.72 (m, m 2H, 2 = £ H-), 3.54 (d 2H , CH₂-NH₂), 3.43 (d 2H, £ H₂-S). MS (m / e) 213 (corresponding to [M + H]⁺: aa), 196, 112.

Preparation of N- [4 - [(2-pyridinyl) dithio] -2-butenyl] hydrazinecarbothioamide 1-Amino-4 - [(2-pyridinyl) dithio] -2-butene hydrochloride (1.5 g, 6 mmol) was suspended in stirred methylene chloride. (30 ml). TEA (1.46 g, 14.6 mmol) was added followed by di-2-pyridylthionocarbonate (Kim and Yi, Tetrahedron Lett. 26 (1985) 1661-1664), (1.4 g, 6 mmol). A clear solution was obtained and TLC showed no starting material. T-Butyl carbazate (0.8 g, 6 mmol) was added and the solution was stirred for 1 hour. The solution was washed with water and the solvent was evaporated. The residue was chromatographed on silica gel using a methylene chloride: methanol solvent system (100: 2) and rechromatographed using a hexane: ethyl acetate solvent system (75:25) to give a foam which was N- [4 - [(2-pyridinyl) dithio] - 2-butenyl] hydrazinecarbothioamide tboc derivative (1.4 g, 58%), which was characterized as follows: IR (KBr) 3238, 2971, 2930, 1718, 1544, 1418, 1156, 762 cm¹. NMR (CDCl 3)₃/ D₂O) δ 8.43, 7.65, 7.08 (m, m, m 4H, py) 5.57 (m 2H, 2 = £ H), 4.12 (d 2H, £ H)₂-N), 3.45 (d 2H CH₂S), 1.46 (s 9H, 3 CH₃). MS (m / e) 387 (corresponding to [M + H] +) 355, 287, 276, 112.

The protected carbothioamide (0.86 g, 2.2 mmol) was dissolved in ice-cold TFA. The solution was kept on ice for 10 min (under nitrogen) and an additional 10 min without cooling. The excess acid was evaporated as much as possible under high vacuum and the residue was chromatographed on silica gel using methylene chloride: methanol: concentrated NH₄OH solvent system (100: 5: 0.5). The appropriate fractions were combined to give compound 12 as a gum (0.39 g, 63%), which was characterized as follows: IR (film) 3322, 3198, 2974, 1626, 1574, 1560, 1538, 1448, 1418, 1224, 760 cm '¹. NMR (CDCl 3)₃/ D₂O) δ 8.41, 7.63, 7.11 (mmm 4H, Py) 5.64 (m 2H, 2 = £ H), 4.20 (d 2H, £ H)₂N), 3.41 (d 2H, CH₂S). MS (m / e) 287 (corresponding to [M + H] +), 225, 221, 144, 112.

Preparation of adriamycin hydrochloride thiosemicarbazone derivative and N- [4 - [(2-pyridinyl) dithio] -2-butenyl] hydrazinecarbothioamide

To a stirred suspension of adriamycin hydrochloride (350 mg, 0.6 mmol) in HPLC grade methanol (50 mL) was added a solution of compound 12 (350 mg, 1.2 mmol) in HPLC grade methanol (25 mL). TFA (3-4 drops) was added and the mixture was stirred overnight. A clear solution was obtained and no free adriamycin was detected by HPLC or TLC. The solution was concentrated to a small volume (5 mL) which was added to acetonitrile (600 mL). A precipitate formed which was collected in the refrigerator after cooling by centrifugation and dried under high vacuum (275 mg, 54%). The thiosemicarbazone derivative was characterized as follows: IR (KBr) 3418, 2934, 1616, 1578, 1534, 1414, 1284, 1208, 1012, 986 cm -1¹. NMR (CD₃OD) δ 8.30, 7.80, 7.74, 7.52, (Py, phenyl 7H), 5.60 (2 = CH), 5.40 (anomeric H) 4.67 (£ H₂OH), 4.22 (CH₃CH), 4.09 (CH₂N), 4.02 (0 £ H₃), 3.5-1.88 (group absorption including CH 2 -SS, -E 2 H 2 -E H), 1.30 (CH 3 -CH). MS (m / e) 812 (corresponding to [M + H] +), 701, 683, 669, 572, 554, 540, 536, 522,

504. HRMS calcd for C₃₇B₄₂OF₅O₁₀S₃: lie: 812.2094; The resulting

812,2087.

Example 4

Preparation of Bifunctional Compound 13 and ADM Carboxylate Hydrazone Derivative

This example describes the preparation of a novel bifunctional compound 13 and a carboxylate hydrazone derivative of ADM. The bifunctional carboxylate hydrazine compound is prepared starting from mercaptoethanol, which was derivatized to pyridinyldithioethanol as shown in Figure 5. This compound was then converted to an activated carbonyl derivative which was condensed with hydrazine.

Preparation of [(2-pyridinyl) dithioethylhydrazinecarboxylate

To a cooled (0 ° C) solution of chlorocarbonylsulfenyl chloride (1.24 g, 9.45 mmol) in CH₂Cl₂(10 mL), 2-mercaptoethanol, (737 mg, 9.45 mmol) was added dropwise. The mixture was stirred for 30 min at 0-15 ° C, cooled to 0 ° C and treated with a solution of 2-mercaptopyridine (1.05 g, 9.45 mmol) in CH₂Cl₂in (15 ml). The mixture was stirred for 1 hour at 0 ° C, and then for 16 hours at room temperature. After addition of ammonium carbonate solution (1.0 g in 20 ml of H₂O), the layers were separated and the organic layer was washed with water, dried and concentrated in vacuo to give crude 2- (2-pyridinyldithio) ethanol (1.75 g) as a colorless oil. Carbonyldiimidazole (648 mg, 4 mmol) was added to a solution of 2- (2-pyridinyldithio) ethanol (714 mg, 3.8 mmol) in CH₂Cl₂in (10 mL). The mixture was stirred for 20 hours and then cooled to -20 ° C and treated with hydrazine (122 mg, 3.8 mmol). The mixture was obtained for 16 hours at -5 ° C, and then concentrated in vacuo. The residue was chromatographed on silica gel using a methylene chloride: methanol solvent system (100: 1-3) to give compound 13, 2 - [(2-pyridinyldithio) ethylhydrazinecarboxylate (340 mg, 37%) as a colorless oil, which was characterized as follows: NMR (CDCl 3).₃) δ 8.46 (1H), 7.62 (2H), 7.08 (1H), 5.92 (1H), 4.35 (t, 2H), 3.70 (s, 2H), 3, 01 (t, 2H), 1.56 (s, 2H). MS (m / e) 246 (corresponding to [M + H] +), 142, 103.

Preparation of adriamycin hydrochloride hydrazone derivative and [(2-pyridinyl) dithio] ethyl hydrazinecarboxylate

To a suspension of adriamycin hydrochloride (290 mg, 0.5 mmol) in anhydrous methanol (4 mL) was added a solution of 13 (170 mg, 6.9 mmol) in methanol (4 mL) and CF₃C/O₂H (6 mg) in methanol (1 mL). After stirring for 24 hours, the mixture was concentrated to about 1 mL, and acetonitrile (50 mL) was added to this solution. The product was isolated by centrifugation. The solid was dissolved in water / methanol and then lyophilized to give the hydrazone derivative of adriamycin (354 mg, 88%) as a dark red solid which

<td colspan="8">was characterized as follows: NMR (CD₃OD) δ 8.34 (1H), 7.93</td>

<td>(d, 1 H), 7.81</td><td>(M,</td><td>3H), 7.54</td><td>(D,</td><td>1H);</td><td> 7,17</td><td>(M,</td><td>1H), 5.49</td>

<td>(m, 1H), 5.19</td><td>(S,</td><td>1H), 4.59</td><td>(M,</td><td>2H);</td><td> 4,37</td><td>(M,</td><td>2H), 4.25</td>

<td>(m, 1H), 4.01</td><td>(S,</td><td>3H), 3.63</td><td>(M,</td><td>1H);</td><td> 3, 54</td><td>(M.</td><td>1H), 3.10</td>

<td>(t, 3H), 2.37</td><td>(M,</td><td>2H), 2.03</td><td>(M,</td><td>1H);</td><td> 1,89</td><td>(M,</td><td>1H), 1.29</td>

<td colspan="2">(d, 3 H). MS (m / e):</td><td colspan="3">771 (corresponding to [M + H] *:</td><td colspan="2">aa), 642.</td><td></td>

Example 5

Preparation of bifunctional compound 15 and arylhydrazone derivative of ADM

This example describes a process for preparing a novel bifunctional compound, Compound 15, and an arylhydrazone derivative of ADM having an arylhydrazone bond at the C-13 position of ADM. Compound 15 is prepared using 4-NBoc-hydrazinobenzoic acid, and attaching a 2- (2-pyridinyldithio) ethanamine group as shown in Figure 6.

4- (N-boc-hydrazino) benzoic acid p-Hydrazinobenzoic acid (760 mg, 5 mmol) was dissolved in dioxane (10 mL), water (5 mL), and 1 N NaOH solution (5 mL). Di-t-butyl pyrocarbonate (1.31 g, 6 mmol) was added at 0 ° C, and the reaction mixture was stirred for 1 hour at 0 ° C and 30 min at room temperature. After this period, the volume of the solution was halved and the solution was adjusted to acidic pH with 0.5% HCl and extracted with EtOAc. The combined EtOAc solution was washed with brine and dried over Na₂SO₄:with. The solvent was removed to give a slightly brown solid which was recrystallized from EtOAc and hexane (950 mg, 75%) and characterized as follows:

NMR (CD 3 OD) δ 7.84 (d, 2H, J = 8.5 Hz), 6.75 (d, 2H, J = 8.5 Hz), 1.4® (s, 9H); IR (KBr) 3316, 1688, 1607, 1298 cm -1¹.

Preparation of N- [2 - [(2-pyridinyl) dithio] ethyl-4- (N-boc-hydrazino) benzamic acid

4- (N-boc-hydrazino) benzoic acid (252 mg, 1 mmol), N-hydroxysuccinimide (115 mg, 1 mmol) and dicyclohexylcarbodiimide (DCC) (247 mg, 1.2 mmol) in dimethylformamide (DMF) (5 ml) was stirred overnight at room temperature. The dicyclohexylurea (DCU) was filtered off and the filtrate was evaporated. The residue was crystallized by adding Et₂O to give 4- (N-boc-hydrazino) benzoic acid N-hydroxysuccinimide ester (300 mg). This material (250 mg, 0.72 mmol) and 2- (2-pyridinyl) dithio) ethylamine hydrochloride (167 mg, 0.75 mmol) were dissolved in DMF (4 mL). After addition of TEA (0.125 mL, 0.9 mmol), the mixture was stirred overnight at room temperature. The DMF was removed and the residue was chromatographed on SiO₂(2% MeOH / CH₂Cl₂) to give a foam (217 mg, 52%) which was characterized as follows: NMR (CDCl 3₃Δ 8.37 (d, 1H, J = 5.1 Hz), 8.01 (bt, 1H), 7.78 (d, 2H, J = 8.7Hz), 7.57 (m, 1H), 7.46 (d, 1H, J = 8.1 Hz), 7.09 (m, 1H), 6.84 (d, 2H, J = 8.7Hz), 7.40 (bs, 1H), 5, 92 (bs, 1H), 3.70 (m, 2H), 2.98 (t, 2H, J = 5.8 Hz), 1.45 (s, 9H); IR (KBr) 3303, 1714, 1610, 1505 cm-1¹; ms m / e (M + H), 365, 321, 421 112, HRMS calcd for C₁₉B₂₅OF₄O₃S₂: 421.1368, found 421.1358.

Preparation of N- [2 - [(2-pyridinyl) dithio] ethyl] -4-hydrazinobenzamide

The compound prepared above (200 mg, 0.48 mmol) was treated with TFA (1.5 mL) at 0 ° C for 1 h. After this period, the TFA was evaporated and the residue was triturated with Et₂O to give about 200 mg of N- [2 - [(2-pyridinyl) dithio] ethyl] -4-hydrazinobenzamide (Compound 15) as an oil, which was characterized as follows: NMR (CD₃0D) δ 8.38 (d, 1H, J = 4.5Hz), 7.81 (m, 4H), 7.22 (t, 1H, J = 5.8Hz), 6.97 (d, 2H, J = 8.8Hz), 3.67 (t, 2H, J = 6.6Hz), 3.06 (t, 2H, J = 6.6Hz); IR (film) 3278, 1674, 1613 cm¹; MS m / e 321 (M &amp; lt; + &amp; gt; H).

Preparation of arylhydrazone derivative of adriamycin and N- (2 - [(2-pyridinyldithio) ethyl] -4-hydrazinobenzamide

Compound 15 and adriamycin hydrochloride (250 mg, 0.43 mmol) were dissolved in MeOH (15 mL) and stirred for 2 days in the dark. The solvent was removed and the residue was chromatographed on C-18 reverse phase SiO₂: 11a. Eluted with MeOH: H₂With O (2: 1) containing 0.3% NH₄0Ac to give hydrazone compound 7 as an orange powder (30 mg, 8%), which was characterized as follows: NMR (CD₃0D) δ 8.33

<td>(D.</td><td>1H, J =</td><td>4.8 Hz), 7.85 (d, 1 H,</td><td>J = 7.9 Hz), 7.74 (t,</td><td>1H,</td>

<td>J = 8</td><td>.0 Hz)</td><td>, 7.66 (m, 4 H), 7.41</td><td>(d, 1H, J = 8.5 Hz),</td><td> 7,14</td>

<td>(M,</td><td>1H), 7</td><td>.02 (d, 2H, J = 8.8 Hz)</td><td>, 5.46 (bs, 1 H), 5.16</td><td>(M,</td>

<td>1H);</td><td> 4, 60</td><td>(s, 2 H), 4.23 (m, 1 H)</td><td>, 3.91 (s, 3 H), 3.62</td><td>(M,</td>

<td>4H),</td><td> 3,02</td><td>(m, 4H), 2.61 (m, 1 H)</td><td>, 2.38 (m, 1 H), 1.97</td><td>(M,</td>

<td>2H);</td><td> 1,32</td><td colspan="3">(d, 3H, J = 6.5 Hz); IR (KBr) 3206, 1708, 1607,</td>

<td> 1578</td><td>cm '¹;</td><td>MS m / e 846 (M + H),</td><td colspan="2">737, 717, HRMS calcd</td>

^C4i^B44^OF5 ° II^S2^for 846.2479, found 846.2380.

Eluted with MeOH: H₂With O (3: 1) containing 0.3% NH₄0Ac to give the anhydro derivative as a blue solid (120 mg, 34%). NMR (CD₃OD) δ 8.40 (d, 1H, J = 4.1 Hz), 7.77 (m, 5H), 7.42 (m, 1H), 7.22 (m, 1H), 7.16 ( m, 2H), 5.35 (bs, 1H), 5.26 (m, 1H), 4.65 (s, 2H), 4.00 (m, 1H), 3.93 (s, 3H), 3.67 (t, 2H, J = 6.5 Hz), 3.44 (m, 1H), 3.08 (t, 2H, J = 6.5 Hz), 2.49 (m, 1H), 1.88 (m, 1H), 1.63 (m, 1H), 1.19 (d, 3H, J = 6.5 Hz); MS m / e 828 (M + H) 699, 681, 495; HRMS calcd for C₄₁B₄₁OF₅O_loS₂828.2372, found 828.2300.

Example 6

Characterization of ADM derivatives

The release of ADM at different pH values ​​in the range of 4.5 to 7.4 from the ADM derivatives of the invention prepared as described in Examples 1-5 above was examined using HPLC analysis. Stock solutions (1 mg / ml) of ADM derivatives were prepared in methanol and aliquots were diluted in aqueous buffer to pH 4.5, 5.0 and

7.4 to achieve final concentrations of about 1.6 nmol / ml. Incubations in each buffer were performed at 37 ° C every 24 hours, and aliquots were analyzed by loading onto an HPLC column to determine the amount of unconjugated ADM. The released material was identified as intact ADM based on the retention time in the column and based on the UV profile of the eluted material. Release rates are expressed as a percentage of the maximum amount of ADM and are shown in Figures 10-12.

As illustrated in the figures, the ADM derivatives of the invention had a wide range of release rates. The amount of material released from the ADM derivatives increased as the pH decreased from 7 to 4. The ADM derivatives have an acid-sensitive linking group, followed by the release of ADM from the antibody protein. These results are consistent with the existence of a semicarbazone, carbazone, thiosemicarbazone, carboxylate hydrazone, or arylhydrazone bond linking ADM to the bifunctional compound.

Example 7

Preparation of anthracycline immunoconjugates

This example describes the preparation of the anthracycline immunoconjugates of the invention by conjugating the ADM derivatives described above (Examples 1-5) to a monoclonal antibody.

Preparation of immunoconjugates containing a disulfide bond within a bifunctional compound

The monoclonal antibody used was 5E9 prepared from the hybridoma ATCC No. HB21, available from the American Type Culture Collection ATCC, Rockville, MD. Monoclonal antibody 5E9 is an IgG1 antibody that is reactive with the transferrin receptor in all proliferating human cells and cross-reactive with various histological types of cancer cells. 5E9 was purified from vat100718 lumen fluid produced in BALB / c mice by the method described by Bruck et al .; One-Step Purification of Mouse Monoclonal Antibodies From Ascitic Fluid by DEAE-Affigel Blue Chromatography, J. Immunol. Methods 5b (1982) 313-319).

Prior to reacting the ADM derivative with the selected monoclonal antibody, the antibody was thiolated, i.e., to add reactive sulfhydryl groups to the antibody molecule. Thiolation of the 5E9 monoclonal antibody (MAb) was performed using SPDP essentially as described by Greenfield et al .; above. Briefly, SPDP (Pierce Chemical Co., IL) (50 mM) dissolved in ethanol was added to 5E9-MAb (5-10 mg / ml) in phosphate buffered saline (PBS), pH 7.2, to give a final concentration between 5 -10 mM. The reaction mixture was incubated for 30 min at 30 ° C. Unreacted SPDP was separated from the SPDP-derivatized antibody by gel filtration chromatography using a PD-10 column (Pharmacia). Reactive pyridinyldithio groups were removed by washing with excess DTT. The reduced antibodies were run through a PD-10 column, and antibodies containing free thiols were used for condensation with ADM derivatives.

Reactive thiol groups were also added to the antibody protein using 2-IT. The antibody (5-10 mg / ml in 50 mM TEA, 50 mM NaCl, 1 mM EDTA, pH 8.0) was mixed with 2-IT (Pierce Chemical Co., IL) to a final concentration of 5-10 mM . The reaction was allowed to proceed for 90 min at 4 ° C, and the thiolated antibodies were separated on a PD-10 column equilibrated with 2 M NaCl / PBS.

The number of reactive thiol groups added to the antibody was determined using DTNB (5,5'-dithiobis- (2-nitrobenzoic acid) (E₄₁₂= 14150) by the method described by: Ellman; Arch. Biochem. Biophys. 82 (1959) 70-77).

Each ADM derivative was dissolved in DMF and added to reduced SPDP-thiolated MAb-5E9 in PBS.

The amount of ADM derivative was equal to the number of thiol groups of the antibody. The conjugation reaction was incubated overnight at 4 ° C. After this period, the antibody solution was dialyzed against PBS to remove the unconjugated adriamycin derivative. The antibody solution was then treated overnight with SM-2 BioBeads beads (Bio-Rad Laboratories, Richmond, CA). The amount of conjugated anthracycline bound to Mab was determined by absorbance at 495 nm (E₄₉₅ = 8030). The amount of antibody protein was determined by absorbance at 280 nm (1 mg / ml = 1.4 optical density (OD) units). To correct the ADM absorbance overlap at 280 nm, the following equation was used:

^280 ^- (θ.72 XA_&lt;95 )

Antibody (mg / ml) = —-- 1.4

Immunoconjugates were analyzed for the presence of unconjugated ADM or ADM derivatives using HPLC analysis. HPLC was performed using a Phenomenex column packed with 5 μm IB-SIL C18 beads. Unconjugated drug, ADM derivatives (i.e., ADM derivatives) were added to the column. ADM conjugated to each of the bifunctional compounds prepared as described in Examples 1-5 above) (0.1 pmol), or immunoconjugates containing 0.5 to 5 pmol drug equivalent and eluted with methanol and 10 mM ammonium phosphate, pH 4. , 5 (70:30) at a rate of 1.5 ml / min. The immunoconjugates produced did not contain significant amounts (less than 1%) of unconjugated drug as determined by HPLC analysis.

Example 8

Characterization of immunoconjugates

Immunoconjugates prepared as described in Example 7 above consisted of ADM molecules conjugated to the 13-keto position of the bifunctional compound that formed a bond between ADM and MAb-5E9. In addition, the addition of a MAb containing free thiol groups to an ADM derivative containing a reactive pyridinyldithio group resulted in the formation of a disulfide bond in the bifunctional compound combining the ADM with the MAb. Immunoconjugates prepared according to this embodiment include, but are not limited to, 5E9-ADM-semicarbazone [3.42]; 5E9-ADM-carbazone [4.37]; 5E9-ADM-tiosemikarbatsoni- [2.51]; 5E9-ADM-karboksylaattihydratsoni- [2.35]; and 5E9-ADM-arylhydrazone- [2,52], wherein the first part of the name represents the monoclonal antibody used to form the conjugate, the second part represents the anthracycline attached to the antibody, and the number in the name indicates the ADM / antibody molar ratio of the particular conjugate.

The binding activity of the immunoconjugates of the invention was determined in a fluorescence binding assay as described by: Greenfield et al .; In Vitro Evaluation of Immunoconjugates Prepared by Linking Mitomycin C to Monoclonal Antibodies via Polyglutamic Acid Carriers, in Antibody Immunoconjugates and Radiopharmaceuticals, vol. 2, p. 201 (1989). Briefly, immunoconjugates were serially diluted in 100 μl of assay media (RPMI 1640 supplemented with 10% fetal bovine serum and penicillin / streptomycin, Gibco, Gr and Island, NY). CEM hair cells (ATCC no. CCL 119) (1 χ 10⁶ cells) grown in the same medium were collected and washed by centrifugation, and then resuspended (1 χ 10⁶) to a medium containing diluted immunoconjugates. After 1 hour of incubation at 4 ° C, the cells were washed and suspended for an additional 1 hour at 4 ° C in 100 μl of medium containing 1:40 diluted goat anti-mouse IgG-FITC (Cappel, Durham, NC). ). Cells were washed and analyzed using a Coulter Epics V-fluorescence cell analyzer. In each experiment, serially diluted MAb was used as an unconjugated positive binding control. Table 1 shows the protein yield in% (obtained from 100718), the molar ratios (moles of ADM / MAb) and the binding as a percentage of the initial binding.

table 1

<td>5E9 Immunoassay</td><td>protein-</td><td>mole-</td><td>% of original</td>

<td>conjugate</td><td>yield (%)</td><td>relations</td><td>commitment</td>

<td>semicarbazone</td><td> 83</td><td> 3,42</td><td> 97</td>

<td>carbazone</td><td> 74</td><td> 4,37</td><td> 92</td>

<td>thiosemicarbazone</td><td> 61</td><td> 2,51</td><td> 72</td>

<td>carboxylate</td><td></td><td></td><td></td>

<td>hydrazone</td><td> 78</td><td> 2,35</td><td> 97</td>

<td>aryylihydratsoni</td><td> 86</td><td> 2,52</td><td> 91</td>

As shown in Table 1, 5E9 immunoconjugates retained more than 90% of the original binding activity of unconjugated 5E9 (except thiosemicarbazone). This indicates that conjugation of ADM derivatives to 5E9-MAb resulted in a relatively small loss of antibody binding activity. Protein yields indicate that large amounts of protein were maintained throughout the conjugation procedure.

Release of ADM from carbazone immunoconjugate

The release rates of ADM from the carbazone immunoconjugate of the invention at pH 4.5, 5.0 and 7.4 were also examined by HPLC analysis as described above in Example 6 for the ADM derivatives of the invention. As shown in Figure 13, the release rate of ADM from the immunoconjugate is substantially the same as seen with the carbazone derivative of ADM in Example 6. The amount of material released from the ADM immunoconjugate increased as the pH decreased from 7 to 4. This ADM immunoconjugate has an acid-sensitive linking group that results in the release of ADM from the antibody protein. These results are consistent with the presence of a hydrazone bond that connects ADM to the bifunctional compound.

The experimental values ​​described herein indicate that the immunoconjugates of the invention release the ADM moiety under physiological conditions, i.e., under acidic conditions typical of the lysosome environment.

Cytotoxic activity of immunoconjugates

The cytotoxicity of the immunoconjugates of the invention was determined in in vitro tests using a colony formation assay on soft agar using Daudi (Burkitt's lymphoma) cells (phenotype: 5E9⁺, ATCC no. HB21) as described by: Greenfield et al .; EP Patent Application 328147, supra. Daudi cells were grown in complete medium (RPMI 1640 medium + 10% fetal bovine serum (FCS)). 1 x 10⁵ cells in 1 ml of medium were exposed for 1.5 hours to serially diluted 5E9-ADM immunoconjugates or unconjugated ADM. A three-fold assay was performed on each dilution. Controls consisted of similarly treated cells that were not exposed to drugs. The cells were then washed and suspended in RPMI 1640 medium containing 15% FBS and 0.3% agarose (Marine Colloid, Rockland, ME). Then 1 ml of cell suspension (1 x 10³) was coated on a 0.4% agarose layer in 6-well microtiter plates (Costar, Cambridge, MA). Samples were incubated for 7-10 days at 37 ° C, and the resulting column was stained with 0.5 ml of 1 mg / ml β-iodinitrotetrazolium violet (Sigma Chemical Co., St. Louis, MO) for 48 hours. Colonies were counted using an Optimax 40-10 image analyzer, and inhibition of colony formation was determined by comparing drug-treated or immunoconjugate-treated cells to an untreated control. The results are shown in Table 2 IC below₅₀as (the concentration required to inhibit colony formation by 50%).

Table 2

<td>5E9 immunoconjugate</td><td> -^50-</td><td>LM^a</td>

<td>semicarbazone</td><td> &gt;5,1</td><td>χ 10 '⁷</td>

<td>carbazone</td><td> 4,0</td><td>χ 10 '⁷</td>

<td>thiosemicarbazone</td><td> 3,0</td><td>x 10 '⁷</td>

<td>karboksylaattihydratsoni</td><td> 5,9</td><td>χ 10 '⁷</td>

<td>aryy1ihydratsoni</td><td> &gt;6,4</td><td>χ 10 '⁷</td>

“M = molar concentration of immunoconjugate required to inhibit colony formation by 50% as measured after 24 hours.

As shown in Table 2, in addition to the release of ADM, all pH-sensitive immunoconjugates have significant cytotoxic activity in vitro.

Example 9

Preparation of an anthracycline immunoconjugate containing a thioether bond

This example describes an alternative embodiment for preparing an anthracycline immunoconjugate of the invention in which ADM is conjugated to a monoclonal antibody with one of the ADM derivatives of the invention prepared as described in Examples 1-5 above and having one of the following bonds: semicarbazone, carbazone, thiosemicarbazone, carboxylate hydrazone, and arylhydrazone as its attachment site to the ADM molecule. In addition, the immunoconjugate has a thioether bond as part of its binding to the antibody.

MAb 5E9 (2.5 mg in 2.5 ml PBS) is reacted with SMPB (succinimidyl 4- (p-maleimidophenyl) butyrate 59.5 pg in 100 tetrahydrofuran) at 30 min time. The pH is adjusted to 6.0 with sodium citrate buffer. The mixture is passed through a PD-10 gel filtration column (Pharmacia) to separate the maleimide-containing antibody from the unreacted materials. The ADM derivatives (1 mg) prepared as described above are then dissolved in 1 ml of MeOH / H₂To 0 (9: 1), and 0.5 pmol of each ADM derivative is reacted with 0.5 pmol of tri-n-butylphosphine in 4: 1 acetone: H₂In O to prepare a reduced form of the ADM derivative. After 10 min, 0.1 M sulfur in toluene is added to destroy the remaining phosphine. The reduced ADM derivatives are then mixed with the MAb containing 5E9-maleimide. The immunoconjugates thus prepared are purified by passing through a PD-10 gel filtration column. In cases where the removal of toluene solvent is not complete and the organic solvent layer separates the protein slightly from the floating reaction mixture, a light stream of air is used to remove the solvent, and the denatured protein is removed by rotating the mixture at 16,000 xg for 2 min. The clear supernatant contains immunoconjugates and is gel filtered and analyzed in PBS at pH 7.4. The ADM / antibody molar ratio is determined spectrophotometrically as described above using OD₂₈₀and OD₄₉₅ : S. A typical reaction produces immunoconjugates with molar ratios between 3 and 4.

The binding and cytotoxic activity of the immunoconjugates prepared as described in this example were tested as described above.

The above examples illustrate the preparation of novel N-substituted bifunctional hydrazine compounds, novel N-substituted hydrazone derivatives of ADM prepared with these bifunctional compounds, and novel immunoconjugates in which ADM was conjugated to the antibody via a novel acid-sensitive bond. The bifunctional compounds were readily conjugated to a cytotoxic reagent, ADM, and a cell targeting molecule, a monoclonal antibody. The conjugates retained both antibody binding activity, (i.e., target cell specificity) and cytotoxic drug activity, and released free, modified 100718-ton ADM under acidic conditions typical of the cellular environment of the target cells.

Thus, the novel bifunctional compounds of the invention are promising for conjugating useful molecules, especially for releasing cytotoxic drugs to a target cell population for the preferential killing of these cells in the treatment of diseases such as cancers and other tumors, non-cell killing viral or other pathogenic infections.

Although a number of embodiments of the invention have been shown herein, it will be appreciated that our basic structure may be modified to provide other embodiments using the bifunctional compounds of the invention, derivatives of cytotoxic reagents, conjugates, and methods. It is therefore to be understood that the scope of the invention is defined by the appended claims rather than by the specific embodiments exemplified hereinabove.