Effect of duration of exposure to benzo(a)pyrene diol-epoxide on neoplastic transformation, mutagenesis, cytotoxicity, and total covalent binding to DNA of rodent cells

Abstract

We examined the effect of different durations of exposure (20 sec to 24 hr) to (±) 7-β,8α-dihydroxy-9α, 10α -epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDE I) on the induction of transformation in C3H/10T1/2 cells and of mutations to 6-thioguanine resistance in Chinese hamster ovary cells (CHO), as well as on BPDE I-DNA binding in these two cell lines. A 20-sec exposure of the cells to BPDE I was sufficient to induce mutations and morphological transformation in vitro. However, the transformation frequency in CH3 mouse-embryo-derived 10T1/2 cells increased twofold and the frequency of mutations in CHO cells sixfold when the exposure time to BPDE I was increased from 20 sec to 8 h. Cytotoxicity increased under similar conditions. A large number of BPDE I-DNA adducts were formed in both cell lines within the first 15-min of exposure of the cells to this ultimate carcinogen. The total covalent binding did not increase with longer than 15-min incubation times. These results suggest that in addition to its covalent binding to DNA, BPDE I may influence other cellular mechanism(s) that are responsible for the initiation of transformation and mutagenesis.