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.

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.

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.

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.

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.

Antiemetic activity of butorphanol against cisplatin-induced emesis in ferrets and dogs.

The analgesic agent butorphanol was evaluated for its ability to block cisplatin-induced emesis in ferrets and dogs. In ferrets, butorphanol (0.15, 0.3, or 0.45 mg/kg; expressed in terms of the tartrate salt) administered sc 30 minutes prior to cisplatin (8 mg/kg iv) reduced the number of emetic episodes but did not eliminate them. When these doses of butorphanol were administered 30 minutes before and 30 and 90 minutes after cisplatin, they caused a dose-related reduction in the number of emetic episodes; there was complete protection at a dose of 0.45 mg/kg/injection. In dogs, butorphanol (0.185 or 0.37 mg/kg/injection, expressed in terms of the tartrate salt) was administered sc on the same multiple-dose schedule used in the ferrets; this caused a nearly complete elimination of the emetic response to cisplatin (3 mg/kg iv). Butorphanol caused some sedation in both species at effective antiemetic doses but had no effect on the antitumor activity of cisplatin against murine L1210 leukemia. Naloxone blocked the antiemetic effect of butorphanol in ferrets, indicating the involvement of opiate receptors. The results of these studies suggest that butorphanol may be useful clinically in mitigating the emetic effects of cisplatin.

Cisplatin-induced emesis in the Ferret: a new animal model.

The ferret, a carnivore weighing about 1 kg, was evaluated for its potential use in testing drugs for emetic and antiemetic activity. An acute emetic response to apomorphine indicated that the ferret can respond to emetic stimuli and suggested that the ferret has an emetic chemoreceptor trigger zone. Cisplatin produced a dose-related emetic response. Antagonism with metoclopramide provided complete protection from cisplatin-induced emesis. The results of these initial studies indicate that the ferret may be a useful species in emesis research.

A technique for chronic jugular catheterization in the ferret.

A technique was developed to provide an efficient method for blood sampling and intravenous drug administration in the ferret by using an indwelling jugular catheter.

Pharmacokinetics of carminomycin in dogs and humans. Preliminary report.

Carminomycin was administered to four dogs and two human patients as a single intravenous dose. Plasma samples were obtained and assayed for carminomycin and carminomycinol by high pressure liquid chromatography with fluorescence detection. The plasma disappearance of carminomycin could be described by a three-compartment open model. Distribution was rapid and the apparent volume of distribution was greater than 100 l/m2 in both species. The terminal half-life of drug was 86 h in dogs and 20 h in humans. In both dogs and humans carminomycinol concentrations rapidly surpassed carminomycin levels, and terminal half-lives were longer than for the parent compound in the two species. Since carminomycinol has antitumor activity and host toxicity, this metabolite may play an important role in the efficacy and toxicity of carminomycin therapy.

Pharmacokinetics of tallysomycin and bleomycin in the beagle dog.

The pharmacokinetics of tallysomycin, a third-generation bleomycin analog, and bleomycin have been determined and compared in the beagle dog. Both compounds exhibited biphasic plasma elimination characteristics and were extensively absorbed after in injection. The elimination half-lives of tallysomycin after iv and im administration were 1.51 +/- 0.41 hours and 2.40 +/- 0.667 hours respectively. These values were longer than the comparable iv (1.01 +/- 0.19 hours) and im (1.12 +/- 0.39 hours) elimination half-lives for bleomycin. The volume of distribution in the central compartment after iv administration was 0.111 +/- 0.039 liter/kg for tallysomycin and 0.125 +/- 0.0723 liter/kg for bleomycin. The total apparent volumes of distribution were 0.706 +/- 0.255 liter/kg and 0.388 +/- 0.245 liter/kg for tallysomycin and bleomycin respectively after iv injection. These values were significantly different (P less than 0.05). Total urinary recovery in 24 hours for tallysomycin was significantly (P less than 0.05) less than that for bleomycin after both iv and im injections. These observed differences in pharmacokinetic behavior may, in part, account for differences in in vivo antitumor activities and toxic effects which have been reported for these drugs.

Comparative first dose effects of prazosin and tiodazosin (BL-5111) in spontaneously hypertensive rats.

Prazosin produces a "first-dose" phenomenon in man clinically characterized by an exaggerated hypotensive response to the initial dose of the drug, with subsequent doses not producing this exaggerated effect. In spontaneously hypertensive rats (SHR), prazosin (1 mg kg po) produced a similar effect, appreciably reducing systolic blood pressure at 12 hours after the first dose but having little or no effect at 12 hours after the subsequent doses. In contrast, BL-5111, an antihypertensive agent similar in chemical structure and shown in previous studies to be slightly less potent than prazosin but with appreciably less alpha-adrenergic receptor antagonist activity, had no effect on blood pressure at 12 hours after dosing (1 and 2 mg/kg po). Pretreatment of rats with an ineffective blood pressure lowering dose of prazosin (0.03 mg/kg po) significantly attenuated the first dose effect of prazosin, resembling the clinical observations seen in patients. Thus, the SHR may be a useful model for predicting the prazosin-like "first-dose" phenomenon with related analogs.