title: Metabolism of benzo[a]pyrene and benzo[a]pyrene-7,8-dihydrodiol in human mammary epithelial cells: feedback inhibition by 7-hydroxybenzo[a]pyrene.
abstract: The metabolism of benzo[a]pyrene (B[a]P) and (-)-transbenzo[a]pyrene-7,8-dihydrodiol (B[a]P-diol) was compared in human mammary epithelial cells (HMEC) grown in serum-free medium, MCDB-170. Conversion of B[a]P-diol to the carcinogen (+)-benzo[a]pyrene-7,8-dihydroxy-9,10-epoxide (BPDE), as measured by analysis of their tetraol hydrolysis products, occurred much more efficiently in cultures incubated with [3H]B[a]P-diol than in cultures incubated with [3H]B[a]P. In cultures pretreated with unlabeled B[a]P (24 h, 400 nM), the conversion of [3H]-B[a]P-diol to [3H]tetraols is inhibited 49%, while the conversion of [3H]B[a]P to [3H]B[a]P-diol- is not affected. These observations led to the identification of a major B[a]P-derived metabolite as 7-hydroxybenzo[a]pyrene (B[a]P-7-ol), which was found to be an extremely potent and selective inhibitor of the conversion of B[a]P-diol to BPDE, with a KI estimated at 3-12 nM. Thus B[a]P activation in HMEC appears to be significantly limited by a feedback inhibition pathway induced by B[a]P-7-ol. The potency and selectivity of the B[a]P-7-ol-induced inhibition suggests that the diol to diolepoxide conversion is affected by a selective oxygenase in HMEC, rather than a non-enzymatic, peroxy radical-induced mechanism. B[a]P-7-ol should prove to be a valuable tool in the study of B[a]P carcinogenesis.
authors.affiliation: Division of Cell and Molecular Biology, Lawrence Berkeley Laboratory, Berkeley, CA 94720.
authors.forename: A N
authors.initials: AN
authors.lastname: Tischler
authors.forename: G A
authors.initials: GA
authors.lastname: Levine
authors.forename: J C
authors.initials: JC
authors.lastname: Bartley
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism / Q000493:pharmacokinetics; D001564:Benzo(a)pyrene / Q000378:metabolism* / Q000493:pharmacokinetics; D001711:Biotransformation; D001940:Breast / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002273:Carcinogens / Q000378:metabolism / Q000493:pharmacokinetics; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004101:Dihydroxydihydrobenzopyrenes / Q000378:metabolism* / Q000493:pharmacokinetics; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006801:Humans
chemical_list: D002273:Carcinogens; D004101:Dihydroxydihydrobenzopyrenes; C017228:benzo(a)pyrene 7,8-dihydrodiol; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide