Antitumour imidazotetrazines--VIII. Uptake and decomposition of a novel antitumour agent mitozolomide (CCRG 81010; M and B 39565; NSC 353451) in TLX5 mouse lymphoma in vitro.

The uptake and incorporation of 8-carbamoyl-3-(2-chloroethyl)(6-14C-imidazo)[5,1-d]-1,2,3,5-tetrazin+ ++-4-(3H)- one (Mitozolomide) into TLX5 mouse lymphoma cells has been studied in vitro. Uptake was rapid, reaching a cell/medium distribution of approximately unity in 1 min at 37 degrees and 10 min at 4 degrees, directly proportional to drug concentration and was unaffected by metabolic inhibitors. These results are consistent with a simple diffusion mechanism. No difference in uptake was observed between drug sensitive and resistant TLX5 lymphoma cells. Cellular radioactivity was found to be progressively accumulated into acid-insoluble material. Acid hydrolysis of this precipitate followed by hplc analysis of the DNA and RNA bases showed that the radioactivity was associated solely with adenine and guanine bases. Mitozolomide was unstable in tissue culture medium and over a 24 hr period about 80% of the drug was converted into 5-aminoimidazole-4-carboxamide (AIC). Non-radioactive AIC suppressed the incorporation of radioactivity into nucleic acids, but had no effects on the initial rate of uptake of mitozolomide into the cell. These results suggest that the radioactivity in nucleic acids arises as a result of salvage of AIC, formed by intracellular decomposition of mitozolomide.