Benzo[a]pyrene-DNA adduct formation in target and activator cells in a Wistar rat embryo cell-mediated V79 cell...

To determine the relationship of the benzo[a]pyrene (BaP)-DNA adducts formed in the activator cells of a cell-mediated mutation assay to the adducts formed in the target cells and to mutation induction, irradiated second passage Wistar rat embryo (WRE) cells and V79 Chinese hamster lung cells were exposed to [3H]BaP for 5, 24 and 48 h under the conditions of a cell-mediated mutation assay. The V79 target cells were separated from the WRE activator cells by an immunoseparation procedure; the resulting V79 cell pellet contained less than 7% WRE cells. The percentage of the BaP-DNA adducts containing cis vicinal hydroxyl groups and the h.p.l.c profile of individual adducts in the V79 target cells were similar to those of the WRE activator cells for each time point. The transfer of reactive BaP metabolites from the activator cells to the target cell DNA was detectable after only 5 h of exposure to BaP, however, exposure for this length of time did not result in significant mutation induction. The (+)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BaPDE)-deoxyguanosine (dGuo) adduct was essentially absent after 5 h of exposure, but the amount of this adduct increased at longer times of exposure as did the mutation frequency. The complex mixture of BaP-DNA adducts formed in the WRE cells was also present in the V79 cells after all three times of exposure to BaP, a result which demonstrates the value of this cell-mediated mutation assay for investigating the role of species-specific differences in the activation of BaP. The correlation between the increase in mutation induction and the relative amount of the (+)-anti-BaPDE-dGuo adduct present in V79 cell DNA suggests the importance of this adduct in mutation induction by BaP.