Preclinical antitumor activity of orally administered platinum (IV) complexes.

Several novel platinum (IV) mixed ammine/amine dicarboxylate dichlorides of general structure [Pt(IV)Cl2(OCOY)2NH3(XNH2)], where Y is aliphatic or aromatic and X is alicyclic or aliphatic, known to be particularly well absorbed following oral administration, were evaluated by that route for their antitumor activity. Testing of the Pt(IV) derivatives took place concomitantly with i.v. administered cisplatin and carboplatin in two s.c. staged tumor models, the murine M5076 sarcoma and human A2780 ovarian carcinoma. Based upon repetitive experiments which included an evaluation of different vehicles and treatment schedules, each of the orally administered Pt(IV) dicarboxylates was reproducibly active in the M5076 tumor, producing mean maximum gross log cell kill (LCK) values of between 1.5 and 2.0, and lifespan increases, reflected by mean maximum treated/control median survival (T/C) values, of 139-151%. Cisplatin and carboplatin given i.v. yielded mean maximum LCK of 3.5 and 2.5, respectively, as well as mean maximum T/C values of 166% and 164%, respectively, in the same tumor model. The best of the derivatives in the M5076 experiments, JM-216 [ammine/cyclohexylamine diacetato dichloride Pt(IV)], produced LCK values that averaged only 0.5 lower than that of carboplatin, and increases in lifespan not significantly different than that of carboplatin. Against the A2780 tumor, the Pt(IV) dicarboxylates produced individual best effects of between 0.8-1.1 LCK, based on data from two or three experiments. The mean maximum LCK values for cisplatin and carboplatin were 1.8 and 2.2 LCK, respectively. JM-225, ammine/cyclopentylamine diacetato dichloride Pt(IV), was active in two of three experiments, including one result comparable to that of carboplatin. The Pt(IV) mixed ammine/amine dicarboxylate dichlorides represent a novel class of Pt derivative capable of expressing oral antitumor activity in both murine and human tumor models.

Experimental tumor inhibitory and toxic properties of the mitomycin A analogue 7-(2-hydroxyethoxy) mitosane (BMY-25551).

BMY-25551, 7-(2-hydroxyethoxy)mitosane, was selected from a series of mitomycin A (MMA) analogues for more detailed study. As with other members of this class, it was shown to be 8 to 20 times more potent than mitomycin C (MMC) in cytotoxicity to murine and human tumor cell lines in vitro, in causing DNA cross links in vitro, and in dose levels for tumor inhibition in vivo. BMY-25551 appeared to be more effective in tumor inhibition than MMC against P388 leukemia and B16 melanoma in mice and comparable to MMC against L1210 leukemia and Madison 109 lung carcinoma. BMY-25551 was also comparable to MMC in hematologic depression in mice. Factors affecting its possible utility in humans are discussed.

Antitumor and DNA-binding properties of a group of oligomeric complexes of Pt(II) and Pt(IV).

The antitumor and DNA-binding properties of a group of oligomeric platinum(II) and platinum(IV) complexes are described. The compounds, having the stoichiometry [cis-PtII(X)2(mu-OH)]2(NO3)2, where X is NH3, NH2CH2CH3, and NH2CH(CH3)2, were found to be inactive or only weakly active against L-1210 leukemia. In vitro studies involving PM2-DNA show that these compounds bind to and unwind closed circular DNA in a manner similar to cis-PtII-(NH3)2Cl2. The Pt(IV) complexes produced by hydrogen peroxide oxidation of the Pt(II) dimers are inactive as antitumor agents and are incapable of unwinding PM2-DNA. The cyclotrimer [cis-PtII(RR-DACH)(mu-OH)]3(NO3)3, where RR-DACH is (R,R)-1,2 diaminocyclohexane, exhibits potent antitumor activity against L-1210 leukemia and modest activities with B-16 and M5076 tumor lines. This compound platinates DNA, causing DNA unwinding and mobility shifts.

Experimental antitumor activity of BMY-28175 a new fermentation derived antitumor agent.

BMY-28175 is a novel antitumor antibiotic produced in fermentation by Actinomadura verrucosospora. The cytotoxic effects of BMY-28175 were determined using murine and human tumor cell lines in vitro. Following 72 hour exposure, the drug had IC50 values 1.5 to 13.5 ng/ml in a microtiter assay. BMY-28175 was evaluated for antitumor activity against several experimental murine and human tumor models. The drug administered ip was active against ip implanted P388 leukemia, L1210 leukemia, B16 melanoma, M109 lung carcinoma, C26 colon carcinoma, M5076 sarcoma and Lewis lung carcinoma. In addition, BMY-28175 administered iv was active against iv implanted P388 and L1210 leukemias. BMY-28175 was active against sc implanted B16 melanoma (increased lifespan and/or inhibition of primary tumor growth) in about 60% of the tests. The growth of sc implanted M109 was inhibited by BMY-28175 in a single experiment. BMY-28175 was also active against the MX-1 human mammary xenograft implanted in the subrenal capsule of nude mice. The optimal dose for BMY-28175 in these various studies ranged from 0.16 micrograms/kg per injection with consecutive daily (qd1-9) administration, to 51.2 micrograms/kg with single dose administration. The results of these studies indicate that BMY-28175 is one of the most potent antitumor agents yet observed, with a broad spectrum of activity against tumors of murine and human origin and activity against tumors located distal to the site of drug administration.

cis-diamineplatinum (II) complexes containing phosphono carboxylate ligands as antitumor agents.

A series of platinum complexes of the form cis-M[PtA2(PC)] (I) has been prepared and tested for antitumor activity in mice. Compounds in this series contain either two monodentate amine ligands (A), such as NH3 or isopropylamine, or one bidentate diamine (A2), such as ethylenediamine, 1,2-diaminopropane, or 1,2-diaminocyclohexane. The PC ligand is a bidentate, O-bound, phosphono carboxylate chelate of the form -O2C(CR1R2)nPO3-, where n = 0 or 1 and R1 and R2 are chosen from H, methyl, ethyl, propyl, butyl, phenyl, or pentanoic acid substituents. The resulting complexes (I) were prepared as the free acids (M = H) or as sodium salts (M = Na). Members of this series have demonstrated good activity in a number of tumor screens. A total of 18 platinum-phosphono carboxylate (Pt-PC) complexes were tested against Sarcoma 180 ascites (S180a) in CFW mice, with 13 analogues showing activity above the 50% ILS level. Antitumor activity was also observed vs L1210 leukemia in CDF1 mice, where six of the 12 compounds tested gave ILS values in the 60-160% range, and vs M5076 reticulum cell sarcoma (sc tumor, iv drug), where four of the four compounds tested gave ILS and T-C values comparable to that of cisplatin. Each of the Pt-PC complexes was characterized by NMR (195Pt, 13C, and 31P), HPLC, and elemental analysis. These compounds, which are anionic at neutral pH, display excellent solubility and stability in aqueous media, such as phosphate-buffered saline and fetal calf serum. On the basis of a comparative study of BUN and serum creatinine levels in treated mice, representative complexes from this series are also less kidney toxic than cisplatin. The results of these studies demonstrate that the platinum-phosphono carboxylate complexes are a promising new class of antitumor agents.

Antitumor activity and toxicity in animals of N-7[2-(4-nitrophenyldithio) ethyl] mitomycin C (BMY-25067).

BMY-25067, N-7[2-(4-nitrophenyldithio)-ethyl] mitomycin C was selected from a number of disulfide derivatives of the highly active compound RR150, N-7(thioethyl) mitomycin C for further study. BMY-25067 had tumor inhibitory effects equivalent to mitomycin C (MMC) against ascitic P388 and L1210 leukemias and M109 lung carcinoma in mice with i.p. treatment. However, it demonstrated superior activity against B16 melanoma with a high percentage of cures when both tumors and drug were given i.p. Additionally, in separate tests against B16 melanoma implanted s.c. with treatment i.v., BMY-25067 was also consistently superior to MMC. This activity was observed when therapy was initiated either one day post-tumor implant or delayed until the ninth day post-tumor implant. Slight activity was seen against a line of L1210 partially resistant to MMC and none against a line of P388 completely resistant to MMC. Against s.c. M109, BMY-25067 inhibited tumor growth but did not prolong survival with the treatment schedule used. At their respective maximum non-lethal doses in mice, BMY-25067 was less neutropenic than MMC. This was confirmed in ferrets which were also examined for the compound's effects on platelets. BMY-25067 appeared to have much less effect on platelets than MMC; the nadir for BMY-25067 was 3.8 x 10(5) platelets/cmm compared to 7 x 10(4) platelets/cmm for MMC when the drugs were compared at a dose ratio of 2:1, BMY-25067:MMC (determined to represent their relative potencies). This initial evidence of superior antitumor effectiveness particularly to a solid tumor separated from site of treatment and reduced hematologic toxicity suggest that BMY-25067 may be a worthwhile candidate for clinical trial.

Experimental antitumor activity of BMY-28090, a new antitumor antibiotic.

BMY-28090 is a novel actinomycete fermentation derived antitumor agent. The cytotoxic effect of BMY-28090 was evaluated in two murine and eight human tumor cell lines in vitro. Following 72-hour exposures, BMY-28090 was cytotoxic for all of these cell lines with IC50 values of less than 0.02 to 3.25 micrograms/ml. BMY-28090 was evaluated for in vivo antitumor activity in a variety of experimental murine tumor and human tumor xenograft models. Initial testing against the murine tumor models was performed using BMY-28090 as the water insoluble free base whereas subsequent antitumor tests were performed using water soluble lactate or succinate salts. BMY-28090 administered ip demonstrated good, reproducible antitumor activity against ip implanted P388 leukemia, L1210 leukemia, B16 melanoma and M5076 sarcoma. The water soluble preparations of BMY-28090 were active iv against sc implanted B16 melanoma and M5076 sarcoma as well as subrenal capsule (src) M5076 sarcoma; activity against src implanted B16 was marginal. BMY-28090 lactate was also evaluated for activity against src implanted MX-1 human mammary tumor xenografts in nude mice and the HCT116 human colon tumor xenografts in immune-suppressed BDF1 mice. At maximum tolerated doses administered ip, BMY-28090 was active against the MX-1 xenograft in two of three tests, causing greater than 90% inhibition of tumor growth. BMY-28090 administered iv at maximally tolerated doses had marginal activity against the HCT116 xenografts, producing 61% and 68% inhibition of tumor growth in two tests. The results of these studies demonstrated that BMY-28090 has a broad spectrum of in vitro cytotoxicity against both murine and human tumor cell lines.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of in vitro cytotoxicity with preclinical in vivo antitumor activity.

Several human and murine tumor cell lines were evaluated in an in vitro cytotoxicity assay as prescreens for fermentation extracts and pure materials subsequently tested in vivo against P388 leukemia or B16 melanoma. Each material, regardless of its in vitro cytotoxicity, was evaluated in vivo. At the criteria levels of in vitro positivity and in vivo activity invoked, a highly significant relationship between these two endpoints was demonstrated for each cell line. When cell lines were compared, most of them performed in a similar manner, with HCT-116 human colon carcinoma cells providing a modest advantage predicting for P388 activity in some comparisons. Using the data from any two cell lines in concert did not improve the acuity of the prescreen beyond that associated with the better cell lines used singularly and only a minority of active materials was predicted for uniquely. Overall, the in vitro cytotoxicity assay provided a useful prescreen for selecting P388 and B16 in vivo active materials.

The search for more active and less toxic mitomycin and etoposide analogs.

Mitomycin C has broad-spectrum activity, but clinical utility is limited by cumulative myelosuppression. VP-16 also has broad-spectrum activity and, although myelosuppression is the dose-limiting toxicity, unlike mitomycin C it is predictable and reversible. Using toxicity reduction as a target for analog selection with mitomycin C has not yet resulted in a more clinically effective agent. Another goal would be to look for more rapid recovery and reversibility of myelosuppression, or compounds with greater antitumor activity or a different antitumor profile. With VP-16, analog evaluation is in an early stage, but selection based upon increased activity not reduced toxicity appears to be the avenue of choice and has resulted in the preliminary identification of analogs which in initial studies have superior activity to the parent compound.

Comparative antitumor studies on platinum(II) and platinum(IV) complexes containing 1,2-diaminocyclohexane.

The synthesis and characterization of a group of platinum(IV) compounds containing the various isomeric forms of 1,2-diaminocyclohexane (DACH) are described. Antitumor tests with the new complexes, as well as with other platinum(II) compounds containing the DACH ligand, revealed that trans,cis-PtIV(SS-DACH)(OH)2Cl2, 7, is more active than its mirror image, trans,cis-PtIV(RR-DACH)(OH)2Cl2, 6, against L1210 leukemia implanted in mice. However, activity is dependent on the tumor model, and against B16 melanoma implanted in mice, the activities of the two enantiomers are reversed, with 6 being more active than 7. The results of the tests are discussed in light of the mechanism by which Pt(IV) compounds are believed to express their antitumor effects.

In vivo characterization of P388 leukemia resistant to mitomycin C.

A line of P388 leukemia resistant to mitomycin C (MMC) was successfully developed in vivo by treating mice bearing parental P388 (P388/0) with MMC followed by serial passage of the surviving leukemic cells. From this P388/MMC line, a subline was derived by not treating the passage mice with MMC (P388/MMC-NP); resistance to MMC was stable for as many as 56 weeks of transplantation. The chemosensitivities of each P388 line to assorted anticancer drugs were compared in vivo. Both P388/MMC and P388/MMC-NP had similar patterns of drug cross-resistance and collateral sensitivity. With respect to alkylating agents (e.g. cyclophosphamide, Platinol and chlorambucil), there was generally a partial degree of cross-resistance, sometimes only detectable at suboptimal dose levels. With respect to DNA binders or intercalators (e.g. actinomycin D, luzopeptin A, amsacrine, doxorubicin), the extent of cross-resistance varied from none (dihydoxyanthraquinone) to marked (doxorubicin). Antimitotic inhibitors (vinblastine and vincristine) were completely cross-resistant, as were some miscellaneous natural agents (rebeccamycin, VP-16, sesbanimide, and elsamicin, a chartreusin analog). Antimetabolites (e.g. methotrexate and 6-thioguanine) showed no cross-resistance and even demonstrated some occasional evidence of collateral effectiveness.

The mouse as a model for predicting the myelosuppressive effects of anticancer drugs.

We evaluated 17 clinically used anticancer drugs for their effects on total WBC and absolute neutrophil counts in BDF1 mice. These drugs were selected from three categories, based on their myelosuppressive effects in man: myelosuppression is dose-limiting; myelosuppression occurs but is not dose-limiting; or myelosuppression does not occur. The ability of each drug to cause myelosuppression in mice was determined by its effect on the neutrophil count 4 days after single-dose treatment. The neutropenic effect of the maximum tolerated dose (LD0-20) of each drug was characterized as marked (greater than 65% decreases), moderate (35%-65% decreases), or minimal (less than 35% decreases) to correspond with the three clinical categories of myelosuppression. The neutropenic effects in mice correctly predicted (true + or true -) the myelosuppressive effects in man for 13 of the 17 drugs (76%). Marcellomycin and the platinum complexes cisplatin, carboplatin, and spiroplatin did not cause neutropenia at maximum tolerated doses. These represent false-negative predictions, since the drugs are myelosuppressive in man. The results with the platinum complexes indicate that this method is not suitable as a means of screening these agents for myelosuppression. Excluding the platinum complexes, the predictions were correct for 12 of 13 drugs (92%). Therefore, this model is considered a good predictor for the myelosuppressive effects of anticancer drugs in man (except platinum complexes) and can be used effectively to screen drugs for this toxicity. However, it is important that drugs identified by this system as being less myelosuppressive than the reference agent(s) be evaluated further, since all the incorrect predictions were false negatives.

Evaluation of cis-diamminedichloroplatinum(II) combined with metoclopramide or sodium thiosulfate on L1210 leukemia in vitro and in vivo.

A microtiter assay was developed to monitor cytotoxic activity of drugs alone and in combination at varying ratios on a single plate. Combinations of metoclopramide or sodium thiosulfate with cis-diamminedichloroplatinum(II) (cisplatin) were evaluated in vitro and in vivo for cisplatin cytotoxicity to murine leukemia L1210. The in vitro assay indicated that metoclopramide did not interfere with cisplatin-induced cytotoxicity and confirmed previously reported inhibition of cisplatin activity by sodium thiosulfate. The drug combinations were also evaluated in vivo for antitumor activity and the results of these studies corroborated the in vitro results.

Antitumor activity and toxicity in animals of BMY-25282, a new mitomycin derivative.

BMY-25282, 7-N-(dimethylamino methylene)mitomycin C, is one of a novel series of amidino mitomycin derivatives. Some of these were discovered as intermediates in a synthetic program being conducted to find improved procedures for modifying the structure of mitomycin C (MMC). Markedly superior in vivo antitumor effects have been observed with BMY-25282 compared to MMC in initial tests against i.p.-implanted P388 leukemia and B16 melanoma. When administered i.v. to mice bearing s.c. B16 melanoma, BMY-25282 was also superior to MMC. The derivative was fully active against a line of L1210 leukemia which was partially resistant to MMC treatment but had little or no activity against a line of L1210 fully resistant to MMC. It is also 2 to 4 times more potent than MMC based on a comparison of doses required to achieve optimum antitumor effects. The superior antitumor efficacy of BMY-25282 over MMC against both i.p. and s.c. B16 melanoma was maintained when the drug was given in pluronic acid formulation. Against P-388 leukemia, however, the efficacy of the drugs was equivalent when BMY-25282 was administered in the pluronic vehicle. In an in vitro clonogenic assay involving freshly explanted human tumors, BMY-25282 was consistently more potent in cytotoxic effects than MMC. With human colorectal carcinoma samples, BMY-25282 was 13.8 times more potent than MMC. The i.v. 50% lethal dose values of BMY-25282 and MMC in C57BL/6 X DBA/2 F1 mice were 2.1 mg/kg and 8.6 mg/kg, respectively. Leukopenic effects of the drugs in mice were comparable at doses up to their respective 50% lethal dose values. Hematology studies in ferrets revealed a similar pattern of depression and recovery of lymphocytes, neutrophils, and platelets for BMY-25282 and MMC; however, with BMY-25282 there was earlier recovery of platelet counts. BMY-25282 is being further developed toward possible clinical trial.

Preclinical antitumor and toxicologic profile of carboplatin.

Carboplatin, an analog of the antitumor drug Platinol, was selected for clinical evaluation on the basis of its experimental antitumor and toxicologic profile in animal models. Described in this review is a detailed summary of selected preclinical data accumulated on carboplatin as well as data obtained concomitantly using Platinol. The predominant result gleaned from the experimental antitumor data is that of comparability between the two compounds, a finding which we feel best reflects the emerging clinical data. With respect to the preclinical toxicology, carboplatin was found to be less nephrotoxic and less emetic than Platinol. This pattern of toxicity for carboplatin appears to be substantiated in the clinical setting.

Animal models for evaluating the myelosuppressive effects of cancer chemotherapeutic agents.

An important objective of new anticancer drug discovery programs is identification of agents that are less myelosuppressive than those currently available. We have developed several animal models to evaluate these drugs for myelosuppression. Our screening model measures changes in neutrophil counts in mice as an indicator of myelosuppression. This model correctly predicted the myelosuppressive effects of 13 (76%) of 17 known agents. Cisplatin, carboplatin, spiroplatin, and marcellomycin caused no reduction in the neutrophil counts, representing four (24%) of 17 false negatives. Our secondary evaluation system is the more labor-intensive murine CFU-C assay on femoral bone marrow cells from drug-treated mice. Known myelosuppressive drugs such as mitomycin C, doxorubicin, and BCNU, as well as the false negatives from the mouse neutropenia model (cisplatin, carboplatin, spiroplatin, and marcellomycin) caused marked inhibition of colony formation 24 h after dosing; bleomycin was inactive. Advanced evaluations are performed using ferrets in which neutrophil counts can be monitored in the same animal for 28 days after treatment. Mitomycin C, doxorubicin, and BCNU caused significant reductions in the neutrophil counts whereas bleomycin had no effect. Importantly, cisplatin and marcellomycin also caused significant reductions in the neutrophil counts. Although the mouse neutropenia model is a rapid assay, there is potential for false-negative predictions. It is important that other test systems be used for more advanced evaluation of drugs identified by this model as being less myelosuppressive than reference drugs. The mouse CFU-C and ferret hematology models are suitable for this purpose in that they can identify the false-negative predictions as well as identify less myelosuppressive drugs such as bleomycin.

Antitumor activity and toxicity in animals of RR-150 (7-cysteaminomitosane), a new mitomycin derivative.

The experimental antitumor activity of a new mitomycin derivative, 7-cysteaminomitosane (RR-150), was evaluated in mice. When administered i.p. to mice bearing i.p.-implanted tumors, RR-150 was superior to mitomycin C (MMC) in increasing the life span of animals bearing P388 leukemia, B16 melanoma, and a line of L1210 leukemia partially resistant to MMC. RR-150 appeared comparable to MMC in increasing life span of mice bearing Madison 109 lung carcinoma, Colon 26 carcinoma, or parental (nonresistant) L1210 leukemia. Mice immunosuppressed with 550 rads whole-body irradiation prior to i.p. implantation of B16 still benefited (e.g., 40% cure rate) following optimal RR-150 therapy when compared to nonirradiated, B16-implanted mice given RR-150 (e.g., 70% cure rate). RR-150 had inconsistent activity in the treatment of s.c.-implanted tumors. In toxicity evaluations, RR-150 was comparable to MMC in suppression of total while blood cell counts but appeared to be less neutropenic. RR-150 also caused less cumulative leukopenia than did MMC in a weekly chronic dose experiment. Based on serum chemistries, RR-150 did not have significant nephrotoxicity, but there was evidence of possible liver toxicity at doses near the 50% lethal dose. Because of the balance of favorable antitumor and toxicity properties of RR-150, work is under way to prepare a more bioavailable form for advanced evaluation.

Mitomycin C analogues with aryl substituents on the 7-amino group.

A series of 30 different N7-phenyl-substituted mitomycin C analogues, including 25 new compounds, was prepared from mitomycin A. Seven of these compounds were clearly superior to mitomycin C in activity against P-388 murine leukemia. The para- and the meta-substituted derivatives were subjected to Hansch analysis, which revealed that the lipid-water distribution coefficient pi was the only significant factor in determining antitumor potency (MED). The substituent electronegativity factor sigma was statistically insignificant in determining potency, despite the good correlation of sigma p with the polarographic quinone-reduction potential. These results suggest that diffusion into the tumor cell or access to the receptor is more important than bioreductive activation in determining antitumor potency for this particular group of mitosanes . Fifteen new mitomycin C analogues with heterocycles on the 7-amino group also were prepared. Two of them, containing pyrazolyl and aminopyridyl substituents, were more active than mitomycin C against P-388 murine leukemia. No broad correlations could be made among the antitumor potencies and physicochemical properties for this type of analogue.

Tallysomycin S10b: experimental antitumor activity and toxicity.

Tallysomycin S10b (TLM S10b), a structural analog of bleomycin (BLM), was evaluated and compared with BLM for antitumor activity in several murine tumor systems and for toxic effects in mice and rats. Neither TLM S10b nor BLM was effective against IP P388 and L1210 leukemias, whereas both drugs were active against IP P388/J leukemia (a BLM-sensitive subline). TLM S10b and BLM were both active against murine solid tumors, including SC B16 melanoma, IV Lewis lung carcinoma, SC Madison 109 lung carcinoma, SC CD8F1 mammary carcinoma and SC Colon 38 carcinoma. In human tumor xenograft models, TLM S10b was active against a colon tumor and had slight activity against breast and lung tumors. Compared with TLM S10b, BLM had less activity against the colon tumor, comparable activity against the breast tumor, and no effect against the lung tumor. A consensus of the antitumor data indicated that compared with BLM, TLM S10b had comparable or greater activity and was about twice as potent. TLM S10b and BLM had approximately equivalent LD50 values in mice. TLM S10b had minimal effects on WBC counts, blood urea nitrogen levels, and serum glutamic pyruvic transaminase levels in mice during the time periods monitored. These effects were comparable to or less pronounced than those of BLM. Both drugs caused dose-related increases in the whole-lung hydroxyproline content in mice, but the dose-response curves were not parallel. TLM S10b caused a larger increase than BLM at the lower doses and a smaller increase than BLM at the highest doses. In rats, TLM S10b and BLM caused comparable, significant decreases in lung mechanics; however, histopathological examination of the lungs indicated that TLM S10b caused less evidence of pulmonary toxicity than did BLM at comparable dose levels. TLM S10b was, therefore, generally comparable to BLM in causing pulmonary toxicity in mice and showed possibly less pulmonary toxicity in rats, while demonstrating approximately equivalent to four-fold greater potency, depending on the test system. It also appeared that TLM S10b caused less pulmonary toxicity than BLM in both mice and rats at doses approaching maximally tolerated levels. TLM S10b is currently undergoing phase I clinical evaluation.

Mitomycin C analogues with secondary amines at position 7.

A series of mitomycin C analogues with secondary amines at position 7 was prepared from mitomycin A. Eleven of the 20 new compounds in this series were more active than mitomycin C against P-388 murine leukemia, and 2 of these 11 were significantly less leukopenic. The two substituents conferring these superior properties were 4-formylpiperazine and 2-cyanoaziridine. No quantitative correlations could be made among antitumor activities and physicochemical properties of the analogues, although the relative ease of quinone reduction might be related to the good potencies (minimum effective doses) of many of them.