USE OF ACID-SENSITIVE ORGANO- TRANSITION METAL COMPOUNDS IN CANCER TREATMENT

Abstract: This invention relates to the use of organometallic compounds of transition metals in the treatment of cancer. The organometallic compounds of the invention generate active radical species in mildly acidic conditions characteristic of tumors. The active radical species generated by said compounds are capable of cleaving and damaging biomolecules, including nucleic acids and cellular structures in tumors. Hence, the organometallic compounds of the invention can be used in the treatment of cancer. In addition, these compounds have increased anti-cancer efficacy when administered in conjunction with factors which intensify glycolysis, such as hyperglycemia and/or hyperthermia, or when used in conjunction with anti-cancer agents and/or radiotherapy.

Description: USE OF ACID-SENSITIVE ORGANO- TRANSITION METAL COMPOUNDS IN CANCER TREATMENT FIELD OF THE INVENTION This invention relates to a method of treating cancer. Specifically, organometallic compounds of transition metals are administered. These compounds generate active chemical species at mildly acidic pH, which is characteristic of tumors. These active species damage tumor biomolecules and cellular structures. The reactivity of these compounds with tumors can be enhanced by increasing tumor acidity. Thus, the organometallic compounds of the invention are pH-dependent, and, as described herein, generate active chemical species in conditions typical of tumors. BACKGROUND OF THE INVENTION It is well known in the art that tumor tissues differ from normal tissues. For example, tumor tissues have reduced pH levels, .reduced p0 2 levels, and have lower rates of blood flow. The lower pH (increased acidity) levels of malignant tumors is caused by intensive glycolysis, which is characteristic of malignant tumors (see Warburg et al . , The Metabolism of Tumors. Constable, London (1930) ) . The difference in pH between tumor and normal tissues, which is typically about 0.2-0.5 pH units, can be increased by artificial intensification of the glycolysis. Glycolysis intensification can be performed by glucose infusion (see Vaupel et al . , Biological Basis of Qncoloσic Thermotherapy, Springer, Berlin - Heidelberg - New York 73-134 (1990)) . Glucose infusion causes pH of tumors to fall to a ' level of about 5.5. Although it is known to infuse glucose in order to increase tumor acidity, to date, no organometallic compounds are known which are both acid-sensitive within physiological ranges of pH and temperature, and have anti-tumor activity in vivo. Further, it is well known in the art that transient free radicals cleave or damage biomolecules, including nucleic acids (see Sonntag, The Chemical Basis of Radiation Bioloσy. Taylor & Fransis, London (1987) and Riordan et al. , J. Amer. Che . Soc■ , 116:2189-2191 (1994)) . Therefore, it would be beneficial to develop tumor-specific sources of active free radicals. The inventors of the instant application have discovered pH-dependent compounds which generate active radical species. These free radical species are tumor- specific, and can be used in the treatment of cancer. SUMMARY OF THE INVENTION This invention is directed to a method of treating a tumor-bearing subject. An organo- transition metal compound which generates active chemical species in mildly acidic conditions is administered to said subject. The organometallic compounds of the invention can be administered alone, or can be administered while increasing glycolysis of the tumor. Glycolysis can be increased, for example, by provoking hyperglycemia or hyperthermia. The organometallic compounds of the invention can also be administered in conjunction with a known anti-cancer agent and/or with radiation. BRIEF DESCRIPTION OF THE DRAWINGS The above brief description, as well as further objects and features of the present invention, will be more fully understood by reference to the following detailed description of the presently preferred, albeit illustrative, embodiments of the present invention when taken in conjunction with the accompanying drawings wherein: Figure 1 represents the kinetics of homolytic decomposition of two organocobalt complexes of the invention under quasi-physiological conditions; Figures 2A and 2B represent structures depicting some of the organocobalt complexes of the invention; Figure 3 represents structures depicting specific examples of the organocobalt complexes of the invention; Figure 4 shows ligands, substitutents and anions in formulae depicting some of the organocobalt complexes of the invention; and Figure 5 depicts features of the cancer therapy method of the invention, based on pH-dependent selective generation of active radical species in comparison with another method also based on generation of active radical species, photodynamic therapy. DETAILED DESCRIPTION OF THE INVENTION This invention is directed to the use of organometallic compounds of transition metals for the treatment of tumor-bearing subjects. Such transition metals include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum and gold. The compounds of the invention generate active chemical species in mildly acid conditions which are typical of solid tumors. The active species can be carbon- centered or oxygen-centered free radicals. The formation of the active chemical species occurs in tumors, which are slightly acidic. These species cause cleavage of or damage to tumor biomolecules, including nucleic acids and cellular structures. The formation of the active chemical species occurs smoothly and rapidly under very mild conditions, e.g., at a pH level of about 5 to 7, and at a temperature range of about 0-50°C. The compounds of the invention are administered, and the active chemical species they generate act directly on tumors. The anti-tumor activity of these compounds is enhanced if they are administered under conditions which result in increased glycolysis of the tumor (i.e., lower pH of the tumor) . This increased glycolysis can be achieved by creating conditions of hyperglycemia and/or hypothermia. In addition, the compounds of the invention have greater anti- tumor activity when combined with known anti-cancer agents and/or radiation. Further, when such anti-cancer agents and/or radiation are combined with the compounds of the invention, lower doses of the anti-cancer agents and/or radiation can be utilized to obtain enhanced anti-cancer activity and/or to reduce side effects caused by anti-cancer agents. The compounds of the invention include alkylcobalt chelates with tridentate Schiff bases, in particular compounds I-VIII shown in Figure 2A. Such compounds have the general formula These compounds are stable when stored in crystalline form. The active chemical species produced by these compounds have activity which can be defined by the following equation: H* RCo m - → R " + Co 11 - The kinetics of the pH-dependent decomposition of the compounds of the invention and of the formation of alkyl free radicals are shown in Figure 1. Figure 1 shows the first-order rate constant of decay of complex Vb as a function of pH under quasi-physiological conditions, namely in H 2 0-EtOH 9:1 (v/v) solutions with I (ionic strength) = 1 M at 25°C (see Levitin et al . , Metallorganicheskava Khimia, 3:865-875 (1990) and Levitin et al . , Orσanometal . Chem. in the U.S.S.R.. 3:442- 448 (1990) ) . Further, cobalt-containing products of the homolytic decomposition have been shown to catalyze autoxidation of biogenic substrates and intermediate formation of active oxygen. Thus, the compounds of the invention can be regarded as double-action sources of active radical species, both alkyl free radicals and active oxygen species. Resulting active radical species cause cleavage of or damage to biomolecules, e.g. nucleic acids and cellular structures. Thus, these complexes display a cytostatic effect . Since the homolytic decomposition of compounds of the invention and, hence, the generation of active radical species is triggered by mild acidification, their cytostatic effect is tumor-specific due to reduced pH values in malignant neoplasm. The selectivity can be greatly increased by artificially intensifying glycolysis in the tumor by means of induced hyperglycemia and/or hyperthermia. Therefore the complexes can be administered in conjunction with glucose infusion and/or local microwave heating. Furthermore, the compounds of the invention have greater efficiency when combined with radiation and/or other anti-cancer agents. Moreover, if a known anti-cancer agent is combined with the complexes, lower doses of the former can be administered to obtain the same and even enhanced therapeutic results. Thus, the use of the compounds of the invention allow for reduced side effects of known anti-cancer agents. As discussed herein, the organometallic compounds of the invention include organocobalt complexes, such as organocobalt chelates with tridentate Schiff bases. Figures 2A and 2B and Figure 3 represent structures depicting some of the organocobalt complexes of the invention. Figure 4 represents examples of organocobalt complexes of the invention. The compounds of the invention are also referred to herein as "complexes". These complexes are administered, preferably in the presence of enhanced hyperglycemia or hyperthermia (increased glycolysis) , and/or in conjunction with radiation and/or other anti-cancer agents, to treat cancerous tumors . Figure 5 depicts the features of the cancer therapy method of the invention, based on pH-dependent selective generation of active chemical species, as compared with another method also based on the generation of active chemical species, photodynamic therapy. The Examples set forth below describe treatment of different types of tumors utilizing the compounds of the invention, either alone or in conjunction with increased glycolysis (caused by hyperglycemia and/or hyperthermia) or in conjunction with radiation or known anti-cancer agents. EXAMPLES In the following Examples, the organocobalt complexes depicted in Figure 4 are utilized. The methods of therapy referred to in Tables 1-7 are as follows: (a) Injection of organocobalt complex alone; (b) Injection of organocobalt complex in combination with introduction of 20% glucose solution; (c) Injection of organocobalt complex in combination with introduction of the chemotherapeutic agent cis- DDP; (d) Injection of organocobalt complex in combination with local hyperthermia; (e) Injection of organocobalt complex in combination with the chemotherapeutic agent cis-DDP and local hyperthermia; and (f) Injection of organocobalt complex in combination with high-energy irradiation. Example 1 Rats bearing transplanted Guerin carcinoma were treated with organocobalt complex #2 depicted in Figure 4 (lb of Figure 3) alone; cis-DDP alone; hyperthermia alone; organocobalt complex plus cis-DDP; organocobalt complex plus hyperglycemia; organocobalt complex plus hyperthermia; or organocobalt complex plus hyperthermia and cis-DDP. The initial size of the tumors in the rats was 1.5-2.0 cm 3 . The dose of cis-DDP, in combination with the organocobalt complex, was half of that used when cis-DDP was administered alone. When local hyperthermia was induced with or without organocobalt complex, the temperature employed was 41°C and 43°C, respectively. Results are shown in terms of delay in tumor growth, complete tumor regression and complete cure. As shown in Table 1, below, the organocobalt complex of the invention, when used either alone or in combination with cis- DDP or cis-DDP plus hyperthermia, resulted in greater delay of tumor growth, as well as the highest level of both complete tumor regression and complete cure. TABLE 1 Therapy control complex complex + induced hyperglycemia chemotherapy (cis-DDP) * complex + cis-DDP local hyperthermia complex + local hyperthermia complex + local hyperthermia + cis-DDP 55.0 ± 5.5 55 55 Here and below cis-DDP was used as the platidiam preparation produced by Lachema (Czechia) Example 2 Organocobalt complexes 1-14 of Figure 4 were utilized in therapy methods a-e described in Example 1. Again, the therapy methods and organocobalt complexes were used to treat rat Guerin carcinoma. Table 2, below, shows the results in terms of delay of tumor growth (in days) /complete tumor regression (in %) . The same conditions as described in Example 1 were used. As shown in Table 2, the organocobalt complexes of the invention had increased anti-tumor efficacy when used in conjunction with local hyperthermia and chemotherapy. Example 3 Organocobalt complex #2 of Figure 4 (complex lb of Figure 3) was utilized in the treatment of rat sarcoma 45, under the conditions described in Example 1. As shown in Table 3 below, again, the organocobalt complex of the invention caused increased delay in tumor growth, increased complete tumor regression and increased cure when administered in conjunction with local hyperthermia and chemotherapy. TABLE 3 Therapy Delay in Complete Complete tumor growth (days) regression (%) cure (%) control complex lb 2.5 ± 0.5 complex lb + induced hyperglycemia ± 0.8 chemotherapy (cis-DDP) 11 + 1 30 27.5 complex lb + cis-DDP 10.5 + 0.5 25 25 local hyperthermia ± 1 complex lb + local hyperthermia 7.5 ± 0.8 complex lb + local hyperthermia + cis-DDP 27.5 + 2.5 35 30 Example 4 Organocobalt complex #2 of Figure 4 (lb of Figure 3) was utilized in conjunction with X-ray (190 kV) local irradiation to treat sarcoma 45 under the conditions described in Example 1. Table 4 below, shows the anti-tumor efficacy of the complex in conjunction with radiotherapy in the treatment of rats bearing sarcoma 45. Tumor size was determined on the 28th day after treatment. The results show that the combination of the complex and radiotherapy was effective in slowing down tumor growth. TABLE 4 Therapy Tumor Size (cm 3 ) Control 30.7 ± 2.3 Irradiation 10 Gy 15.4 ± 4.1 15 Gy 13.7 ± 3.3 20 Gy 6.0 + 1.9 Complex lb + 7.9 ± 2.7 irradiation 10 Gy Example 5 Organocobalt complex #2 of Figure 4 (lb of Figure 3) was utilized in conjunction with cis-DDP to treat rats bearing Walker 256 carcinoma, under the conditions described in Example 1. Table 5, below, shows that the use of the complex of the invention allows an efficient reduction in dose of cis- DDP. TABLE 5 Therapy Tumor growth Complete tu delay (days) regression control 0 cis-DDP, 3mg/kg 15.5 ± 1.0 90 1.5 10.0 ± 0.5 80 0.75 7.0 ± 0.7 55 Complex lb + cis-DDP, 1.5 mg/kg 15.0 + 1.0 80 Complex lb + cis-DDP, 0.75 mg/kg 10.0 ± 0.5 85 Example 6 Organocobalt complex #2 of Figure 4 (complex lb of Figure 3) was utilized in conjunction with cis-DDP to treat mouse ascite leukemia L1210, as described in Example 1. 10 5 tumor cells were implanted intraperitoneally. Table 6, below, shows the amount of organocobalt complex and/or cis-DDP injected into the mice. Results are shown in terms of mouse survival time (in days) . "*" indicates that toxicity resulted. Parenthetical percentages indicate the percentage of animals that survived 90 days. As shown in Table 6, the greatest survival time was observed in mice treated with the organocobalt complex alone, and in mice treated with decreased doses of both the organocobalt complex and cis-DDP. These examples demonstrate that the organocobalt complexes of the invention significantly increase the antineoplastic action of a known cytostatic agent. The use of these complexes allowed for a significantly decreased dose of chemotherapeutic agent (cis-DDP) and a decrease in the intensity of physical means (local hyperthermia and radiation) in order to obtain enhanced anti-cancer activity. No side effects were observed with the organocobalt complexes which would require discontinuation of treatments with the organocobalt complex. Thus, the organocobalt complexes of the invention can be utilized to decrease toxic action of known cytostatic agents. TABLE 6 Therapy Dose (mg/kg) Times Survival time (days) cis-DDP Complex Used control 9.0 ± 0.25 complex 50 2 10.0 ± 0.2 100 2 12 ± 1 100 3 14.5 1 15 5 12.5 ± 0.5 complex 2.5 20 12.5 ± 0.5 (28%) cis-DDP Example 7 Acute toxicity (LD 50 ) values and endurability (curable dose/LD 50 ) characteristics of organocobalt complex lb (Figure 3) were determined and compared with known anti-cancer agents. The complex was administered in both mice and rats intraperitoneally. As shown in Table 7, below, complex lb showed relatively low toxicity and good endurability in both mice and rats, as compared with the known anti-cancer agents. Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of various aspects of the invention. Thus, it is to be understood that numerous modifications may be made in the illustrative embodiments and other arrangements may be devised without departing from the spirit and scope of the invention.

Claims: WE CLAIM : 1. A method of treating a tumor-bearing subject comprising administering to said subject an acid-sensitive organometallic compound which is capable of generating active chemical species in physiological and mildly acidic conditions which are characterisitc of tumors. 2. The method of Claim 1 wherein said active chemical species is a carbon-centered and/or oxygen-centered free radical. 3. The method of Claim 1 wherein said organometallic compound is a derivative of a transition metal. 4. The method of Claim 1 wherein said organometallic compound is an organocobalt complex. 5. The method of Claim 4 wherein said organocobalt complex is an organocobalt chelate having a tridentate Schiff base ligand. 6. The method of Claim 5 wherein said organocobalt chelate having a tridentate Schiff base ligand is an alkylcobalt chelate. 7. The method of Claim 6 wherein said alkylcobalt chelate has the formula: wherein R is an alkyl group. 8. The method of Claim 4 wherein said organocobalt complex is selected from the organocobalt compounds depicted in Figures 2A and 2B. 9. The method of Claim 4 wherein said organocobalt complex is selected from the organocobalt compounds depicted in Figure 3. 10 The method of Claim 4 wherein said organocobalt complex is selected from the organocobalt compounds depicted in Figure 4. 11. The method of Claim 1 wherein said organometallic compound is administered in an aqueous medium. 12. The method of Claim 1 further comprising intensifying glycolysis of said tumor. 13. The method of Claim 12 wherein said glycolysis is intensified by provoking hyperthermia. 14. The method of Claim 12 wherein said glycolysis is intensified by provoking hyperglycemia. 15. The method of Claim 1 further comprising administering, in conjunction with said organometallic compound, at least one other anti-cancer agent. 16. The method of Claim 15 wherein said anti-cancer agent is selected from the group consisting of cis-DDP, mitomycin C, methotrixate and adriamycin. 17. The method of Claim 1 further comprising administering radiotherapy in conjunction with said organometallic compound. 18. A method of treating a tumor-bearing subject comprising generating an active radical species in said tumor utilizing an organometallic compound. 19. The method of Claim 18 further comprising intensifying glycolysis of said tumor. 20. The method of Claim 19 wherein said glycolysis is intensified by provoking hyperthermia. 21. The method of Claim 19 wherein said glycolysis is intensified by provoking hyperglycemia. 22. The method of Claim 18 further comprising administering an anti-cancer agent. 23. The method of Claim 22 wherein said anti-cancer agent is selected from the group consisting of cis-DDP, mitomycin C, methotrixate and adriamycin. 24. The method of Claim 18 further comprising administering radiotherapy. 25. The method of Claim 18 wherein said organometallic compound is an organocobalt compound.

Inventors: BUBNOVSKAYA LARIS, LEVITIN ILIA, OSINSKY SERGEI, TSIKALOVA MARINA, VOL PIN MARK, BUBNOVSKAYA, LARIS, LEVITIN, ILIA, OSINSKY, SERGEI, TSIKALOVA, MARINA, VOL'PIN, MARK
Applicants: BUBNOVSKAYA LARIS, CANCER RES INST, LEVITIN ILIA, OSINSKY SERGEI, TSIKALOVA MARINA, VOL PIN MARK, BUBNOVSKAYA, LARIS, CANCER RESEARCH INSTITUTE, LEVITIN, ILIA, OSINSKY, SERGEI, TSIKALOVA, MARINA, VOL'PIN, MARK
Application year: 1996
Main classification: A61K31
IPC codes: A61K31, A61K33, A61P3, A61P35, A61P43