Binding of benzo(a)pyrene (BP) metabolites to DNA was studied in the mouse embryo fibroblast 10T½ cell line. The cells metabolized BP to its diastereoisomeric 7,8-dihydrodiol-9,10-oxides, (±)-7β, 8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene and (±)-7β,8α-dihydroxy-9β,10β-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, which formed covalent adducts with cellular DNA. Detailed analysis by high-pressure liquid chromatography indicated that a deoxyguanosine adduct, N2-(10S-[7R,8S,9R-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene]yldeoxyguaninosine, was the predominant DNA adduct formed in cells exposed to BP. This adduct is also the major one found in human tissues exposed to BP. Exposure of cells to (±)-7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene and (±)-7β,8α-dihydroxy-9β,10β-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, rather than to BP, produced several additional adducts on DNA. During a 68-hr posttreatment incubation, about 50 to 70% of the adducts were removed from the cellular DNA. No major differences between the relative rates of excision from cellular DNA of the individual (±)-7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene and (±)-7β,8α-dihydroxy-9β,10β-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene adducts were found. These results provide evidence that when 10T½ cells are exposed to BP there is stereoselective synthesis and covalent binding of BPDE mainly to the N2 group of deoxyguanosine. This similarity with results obtained in human tissues makes the 10T½ cell an attractive model system for studying the action of BP and related polycyclic hydrocarbons.
This investigation was supported by Grant EPA-R-805482010 from the Environmental Protection Agency and Grant CA 13696 from the National Cancer Institute, NIH.