Mutations induced by dacarbazine activated with cytochrome P-450.

The mutagenicity of the antitumor drug dacarbazine (DTIC) is due to alkylation of cellular DNA by metabolites resulting from the metabolism of this drug by the mixed function oxidase system. In the present study, we used an in vitro shuttle vector assay to study the base and sequence specificity of mutagenesis by DTIC. The shuttle vector plasmid pSP189 was treated with DTIC (1-2.5 mM) in vitro in a reconstituted cytochrome P-450 system at 37 degrees C for either 30 or 60 min. SupF tRNA gene insert contained in the plasmid was sequenced after replication of the drug-treated plasmid in human Ad 293 cells followed by amplification in indicator bacteria. Mutagenesis of DTIC in this system was dependent upon the presence of the cytochrome P-450 reconstituted system and NADPH. Mutations induced by DTIC included single base substitutions (35%), single base deletions (30.5%), single base insertions (19.4%) and large deletions (13.8%). Among the substitutions, transversions and transitions were in the ratio of 1:0.7. Base pairs 108 and 127 in the SupF tRNA of the pSP189 were identified as mutational hot spots.