8,9-Dihydroxy-8,9-dihydrodibenzo[a, l]pyrene is a potent morphological cell-transforming agent in C3H10T1/2C18 mouse embryo fibroblasts in the absence of detectable stable covalent DNA adducts

Abstract

The comparative genotoxic effects of racemic trans-8,9-dihydroxy-8,9-dihydrodibenzo[a, l]pyrene (trans-DB[a, l]P-8,9-diol), the metabolic K-region dihydrodiol of dibenzo[a, l]pyrene (DB[a, l]P) (dibenzo[def, p]chrysene) and DB[a, l]P in transformable mouse embryo C3H10T 1/2 C18 (C3H10T 1/2) fibroblasts was investigated. The C3H10T 1/2 mouse embryo morphological cell-transforming activities of these polycyclic aromatic hydrocarbons (PAHs) were assayed using concentration-response studies. At concentrations of 33 nM and above both trans-DB[a, l]P-8,9-diol and DB[a, l]P produced significant (and similar) numbers of type II and III foci per dish and numbers of dishes with type II and II foci. Concomitant cytotoxicity studies revealed a reduction in colony survival of ˜25% up to 198 nM for both PAHs. DNA adducts of trans-DB[a, l]P-8,9-diol and DB[a, l]P in C3H10T 1/2 cells were analyzed by a 32P-post-labeling TLC/HPLC method. No adducts were observed in the DNA of C3H10T 1/2 cells treated with trans-DB[a, l]P-8,9-diol at concentrations that induced morphological cell transformation. Under the same exposure and chromatographic conditions, DNA adducts of deoxyadenosine and deoxyguanosine derived from the fjord region anti-DB[a, l]P-11,12-diol-13,14-epoxide and syn-DB[a, l]P-11,12-diol-13,14-epoxide were observed in the DNA of DB[a, l]P-treated cells. These results indicate that trans-DB[a, l]P-8,9-diol has intrinsic genotoxic activity equal to that of DB[a, l]P, based on morphological cell transformation of mouse embryo fibroblasts. The activity of trans-DB[a, l]P-8,9-diol is apparently not associated with the formation of observable stable covalent DNA adducts. These results suggest that under appropriate conditions, trans-DB[a, l]P-8,9-diol may serve as an intermediate in the genotoxicity of DB[a, l]P.