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The in vitro cytotoxicity, stability, and metabolism of the 8-(N,N-dimethylcarboxamide) and 8-(N-methylcarboxamide) analogues of the experimental antitumor drug mitozolomide have been investigated in conjunction with their in vivo murine pharmacokinetics and metabolism. When tested against the TLX5 lymphoma in vitro the ID50 values for dimethylmitozolomide, methylmitozolomide, and mitozolomide were 14.6, 3.0, and 2.3 microM, respectively. The cytotoxicity of dimethylmitozolomide was dramatically increased when it was incubated with murine hepatic microsomes. There was no significant difference in the in vitro stabilities of dimethylmitozolomide and methylmitozolamide with half-lives of 43.5 and 45.8 min, respectively, in RPMI at 37 degrees C. The in vitro microsomal incubation of dimethylmitozolomide produced significant amounts of methylmitozolomide, which suggests that methylmitozolomide contributed to the cytotoxicity of dimethylmitozolomide in the presence of microsomes. The pharmacokinetics of both dimethylmitozolomide and methylmitozolomide, given i.p. at 10 mg/kg, were investigated in CBA/Ca mice bearing the s.c. solid TLX5 lymphoma. Methylmitozolomide was absorbed rapidly with maximum plasma and tumor concentrations of 10.66 mg/liter and 8.01 mg/kg, respectively, achieved 0.17 h following dosing. Dimethylmitozolomide was also rapidly absorbed with maximum plasma and tumor concentrations of 9.34 mg/liter and 5.00 mg/kg, respectively, achieved within 0.18 h of dosing. Following administration of dimethylmitozolomide, methylmitozolomide was found in both plasma and tumor tissue. The plasma and tumor area under the curves of methylmitozolomide were 87.7% and 120.8%, respectively, of those seen when mice were dosed with authentic methylmitozolomide. By comparison of the area under the curves and clearance values, it was demonstrated that 89% of the administered dimethylmitozolomide was metabolized via methylmitozolomide.

8-Carbamoyl-3-(2-chloroethyl)imidazo[5,1-d]-1,2,3,5-tetrazin-4(3H) -one (mitozolomide) demonstrates curative action against a range of murine tumor model systems. At single doses of between 20 and 40 mg/kg, the latter of which approximates the 10% lethal dose value in mice, the compound elicited cures against the L1210 and P388 leukemias irrespective of the route of tumor and/or drug administration; in these tests, animals receiving 10(5) cells i.p. survived greater than 60 days after treatment. Potent effects were also observed against the TLX5 lymphoma (s.c.) and B16 melanoma (i.p.). In other experiments, 7 of 10 animals implanted with 2 X 10(5) Lewis lung carcinoma cells survived greater than 60 days while 10 of 10 animals survived greater than 60 days after implantation of the Colon 26 tumor. Potent inhibition of the solid tumor models was also observed with complete cures of the Colon 38, M5076 sarcoma, and ADJ/PC6A plasmacytoma. In cross-resistance studies, the compound was ineffective against an L1210 leukemia made resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea and against a TLX5 lymphoma resistant to dimethyltriazenes but cured animals bearing the L1210 leukemia with derived resistance to cyclophosphamide.