Alkyl and vinyl halides are of interest because of their high volumes of production, extensive human exposure, and known genotoxicity and carcinogenicity. Continuing studies are directed toward bifunctional electrophiles in this group (including oxidation products) and the related compound butadiene diepoxide, an oxidation product of another commodity chemical (1,3-butadiene). The proposed studies are focused on thiol- dependent activation mechanisms of 1,2-dibromoethane (ethylene dibromide) and butadiene diepoxide, particularly by glutathione (GSH) transferases (GSTs) and the DNA repair protein O6-alkylguanine DNA- alkyltransferase (AGT). The first Specific Aim involves the characterization of mechanisms of mutation of DNA-AGT crosslinks derived from 1,2-dibromoethane and butadiene diepoxide. Further characterization of crosslinks other than the N7-guanyl ones will be done, and a major hypothesis is that peptides derived from AGT are the mutagenic adducts. The second Specific Aim involves the GSH conjugate of butadiene diepoxide and the hypothesis that this is a prominent electrophilic species involved in DNA alkylation and genotoxicity of butadiene diepoxide (as opposed to a detoxication product). An approach is also proposed to evaluate the AGT and GST pathways for these chemicals in rodents in vivo. The third Specific Aim utilizes a new chemical approach to the synthesis of DNA adducts with unstable glycosidic bonds, including several derived from alkyl and vinyl halides, especially N7-(2-oxoethyl)-guanine, S-[N7-(2-guanylethyl)]glutathione, and N2,3-etheno(5)guanine. Our hypothesis is that these adducts are miscoding. The miscoding potentials of these and other unstable adducts will be evaluated with several microbial and human DNA polymerases, and comparisons will be made. Collectively these studies should provide new mechanistic insight into the toxicity and carcinogenicity of these adducts and important information that may alter paradigms in risk assessment.
We propose a research plan that should produce valuable information related to 1,2-dibromo- and 1,2- dichloroethane, butadiene, and other bis-electrophiles or chemicals that can produce bis-electrophiles, which have practical significance in human health considerations. The work with peptides linked to DNA has basic mechanistic importance and fills a scientific need. The new approaches we propose to study involve labile DNA adducts that should allow us to address several long-standing questions about mutagenesis.
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