The primary goal has been the elucidation of the structures of reactive metabolites responsible for the carcinogenic, cytotoxic and mutagenic activity of drugs, polycyclic aromatic hydrocarbons and other environmental chemicals. The approach taken consists of: i) study of the metabolism of the chemicals with liver microsomes and with purified cytochromes P450 and epoxide hydrolase, ii) synthesis of oxidative metabolites, iii) evaluation of the mutagenicity and tumorigenicity of the synthetic metabolites, iv) elucidation of the roles of the cytochrome P450 system and epoxide hydrolase in modulating the mutagenicity of these metabolites, v) determination of the rates and products of reactions of arene oxides and diol epoxides with biopolymers and model compounds, and vi) search for agents capable of preventing the tumorigenicity of reactive metabolites. Work during the past year has focused in two areas. i) Studies of the reaction mechanisms of K-region arene oxides have elucidated the role of the intrinsic chemical reactivity at each epoxide carbon. Conformational factors play a key role in the determination of rates and products of solvolytic cleavage and epoxide hydrolase-catalyzed hydrolysis. Our results also suggest that the transition state for nucleophilic attack of methoxide ion on the K-region arene oxides (a model for attack of water catalyzed by epoxide hydrolase) involves a partial positive charge on the carbon that undergoes nucleophilic substitution. ii) Synthetic studies have produced biologically significant oligonucleotides containing specific diol epoxide adducts. An adduct corresponding to trans opening of the (1R,2S)-diol (3S,4R)-epoxide of phenanthrene by the exocyclic amino group of deoxyadenosine (dA) was incorporated into a nonanucleotide comprising codons 60-62 of the human K-ras b oncogene. In duplexes formed by this adducted oligonucleotide, substitution of deoxyguanosine for thymidine in the complementary strand opposite the modified dA had almost no effect on the melting temperature. This result suggests a possible role for such base-pair """"""""mismatches"""""""" in mutations caused by diol epoxide adduct formation.
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