DIFFERENTIAL MUTAGENICITY AND CYTOTOXICITY OF (+ -)-BENZO[A]PYRENE-TRANS-7,8-DIHYDRODIOL AND -BENZO[A]PYRENE-TRANS-7,8-DIHYDRODIOL-9,10-EPOXIDE IN GENETICALLY-ENGINEERED HUMAN FIBROBLASTS/

DNA repair-deficient (xeroderma pigmentosum group A (XPA)) and DNA rep air-proficient (normal) human skin fibroblasts were genetically engine ered by transformation with a controllable human cytochrome P450 (CYP) 1A1 expression vector. Induction of CYP1A1 enabled these cells to meta bolize (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol (BPD) into a potent cytotoxicant and mutagen. The XPA cells were more susceptible than the normal cells to the cytotoxic effects of both CYP1A1-metabolized BPD and exogenously supplied (+/-)-anti benzo[a]pyrene-trans-7,8-dihydrodi ol-9,10-epoxide (BPDE). Furthermore, the differential cytotoxicity bet ween XPA and normal cells induced by CYP1A1-metabolized BPD was 8.4-fo ld greater than that induced by exogenously supplied BPDE. The two cel l lines had similar CYP1A1 activities, suggesting that a difference in metabolic potential was not the cause of the differential response to BPD. At comparable cytotoxicity in both XPA and normal cells, BPD tre atment induced more mutants and more DNA adducts than BPDE treatment d id. At similar levels of DNA adducts in XPA cells, the levels of cytot oxicity induced by CYP1A1-metabolized BPD and exogenously supplied BPD E were similar, but CYP1A1-metabolized BPD induced a threefold higher hypoxanthine phosphoribosyltransferase mutation frequency. In contrast , at similar levels of adducts in CYP1A1-expressing normal cells, BPD induced less cytotoxicity and a lower mutation frequency. DNA adducts were identified and quantified by P-32-postlabeling analyses. The prin cipal adduct formed by both CYP1A1-metabolized BPD and exogenously sup plied BPDE was 10-beta-(deoxyguanosin-N-2-yl)-7 beta,8 alpha,9 lpha-tr ihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene, indicating that the differ ential effects of BPD- and BPDE-induced adducts were not due to a diff erence in the types of adducts formed. The results of these studies su ggest that CYP1Al-metabolized BPD may form adducts preferentially in t ranscriptionally active genes or that the intracellular concentration of BPDE may influence the balance between cytotoxicity and mutagenicit y (or both). (C) 1995 Wiley-Liss, Inc.