Formation of 4,4'-methylene-bis(2-chloroaniline)-DNA adducts in yeast expressing recombinant cytochrome P450s.

N-Oxidation of 4,4'-methylene-bis(2-chloroaniline) (MBOCA) may lead to formation of DNA adducts. To determine if cytochrome P450s are involved in the formation of MBOCA derived-DNA adducts, yeast strains expressing rodent P450s were exposed to MBOCA, and 32P-postlabelling of nucleotides from yeast genomic DNA was done. Chromatographic analysis on PEI cellulose showed that, upon exposure to MBOCA for 1 h, nine DNA adducts were formed in yeast expressing phenobarbital-inducible rabbit P450 2B5. With a 4-h-exposure, all adducts increased in parallel. In cell-free experiments, the incubation of MBOCA with phenobarbital-induced rat microsomal fraction followed by incubation with thymus DNA, led to the formation of more than ten DNA adducts. When yeast expressing 3-methylcholanthrene-inducible rat P450 1A1 was exposed to MBOCA, one major and two minor adducts were formed. No adducts were detected in control yeast. These results show that recombinant rabbit P450 2B5 exhibits a potential activation of MBOCA and that rat P450 1A1 has some effect. The use of yeast expressing recombinant P450s and the technique of 32P-postlabelling facilitates a simple search for chemicals with carcinogenic potential.