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Metabolism and Murine Pharmacokinetics of the 8-(N,N-Dimethylcarboxamide) Analogue of the Experimental Antitumor Drug Mitozolomide (NSC353451)¹

Cancer Research Campaign Experimental Chemotherapy Group, Pharmaceutical Sciences Institute, Aston University, Birmingham B4 7ET, England [K. R. H., C. P. Q., J. A. S., A. G., M. F. G. S.] and May & Baker Ltd., Dagenham, Essex RM10 7XS, England [E. L.]

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 µM, 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 methylmitozolomide with half-lives of 43.5 and 45.8 min, respectively, in RPMI at 37°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.

¹ This study was generously supported by Grant SP1518 from the Cancer Research Campaign of Great Britain and also by a CASE studentship (to K. R. H.) from the Science and Engineering Council in collaboration with May & Baker Ltd. This is Part 19 of the series "Antitumor Imidazotetrazines." Part 18 is Ref. 1.

² To whom requests for reprints should be addressed.

Received 8/ 2/88. Revised 1/30/89. Revised 3/29/89. Accepted 6/ 8/89.