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/
Th. Quan et al., 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/, Molecular carcinogenesis, 12(2), 1995, pp. 91-102
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.