title: Role of cytochrome P450 1a1 and 1b1 in the metabolic activation of 7,12-dimethylbenz[a]anthracene and the effects of naturally occurring furanocoumarins on skin tumor initiation.
abstract: The current study was designed to determine the mechanistic basis for differences in the effects of naturally occurring furanocoumarins on skin tumor initiation by 7,12-dimethylbenz[a]anthracene (DMBA). Female SENCAR mice were pretreated topically with bergamottin, imperatorin, or isopimpinellin (100-3200 nmol), 7,8-benzoflavone (7,8-BF, 5-40 nmol, a known inhibitor of DMBA skin carcinogenesis in mice), or acetone (vehicle control) 5 min prior to topical treatment with DMBA (10 nmol). Imperatorin, isopimpinellin, and 7,8-BF, but not bergamottin, significantly blocked total DMBA-DNA adduct formation. HPLC analysis of DNA adducts revealed that bergamottin preferentially inhibited formation of anti-DMBA diol-epoxide (DMBADE) derived DNA adducts, imperatorin, and isopimpinellin inhibited both anti- and syn- derived adducts, whereas 7,8-BF showed some selectivity for reduction of syn-DMBADE-DNA adducts. Mouse embryo fibroblast C3H/10T1/2 (10T1/2) cells, and mouse hepatoma-derived 1c1c7 (Hepa-1) cells, which preferentially express P450 1b1 and P450 1a1, respectively, were co-incubated with 2 microM bergamottin, imperatorin, isopimpinellin, and 7,8-BF, and with DMBA (2 microM). Hepa-1 cells (P450 1a1) formed mainly anti-DMBADE-DNA adducts. In contrast, 10T1/2 cells (P450 1b1) formed mainly syn-DMBADE-DNA adducts. Bergamottin inhibited DMBA metabolism to DMBA-3,4-diol and blocked DNA adduct formation in Hepa-1 cells, but had little effect in 10T1/2 cells. In contrast, 7,8-BF completely blocked DMBA metabolism and DNA adduct formation in 10T1/2 cells, but had little effect in Hepa-1 cells. Imperatorin and isopimpinellin inhibited DMBA bioactivation in both cell lines. These results indicate that bergamottin is a more selective inhibitor of P450 1a1 and overall a less effective inhibitor of the metabolic activation of DMBA in mouse epidermis. In contrast, imperatorin, isopimpinellin, and especially 7,8-BF, which block metabolic activation of DMBA in mouse epidermis, appear more selective for P450 1b1. On the basis of our studies using 10T1/2 cells and Hepa-1 cells, it appears that P450 1a1 is primarily responsible for converting DMBA-3,4-diol to anti-DMBADE, whereas P450 1b1 is primarily responsible for converting DMBA-3,4-diol to syn-DMBADE. These data demonstrate the role of P450 1a1 and 1b1 in the metabolic activation of DMBA in mouse epidermis and provide a mechanistic explanation for the differential effects of naturally occurring furanocoumarins (and 7,8-BF) on polycyclic aromatic hydrocarbon skin carcinogenesis.
authors.affiliation: University of Texas MD Anderson Cancer Center, Science Park-Research Division, Department of Carcinogenesis, P.O. Box 389, Smithville, Texas 78957, USA.
authors.forename: Heather E
authors.initials: HE
authors.lastname: Kleiner
authors.forename: Suryanarayana V
authors.initials: SV
authors.lastname: Vulimiri
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Reed
authors.forename: Ann
authors.initials: A
authors.lastname: Uberecken
authors.forename: John
authors.initials: J
authors.lastname: DiGiovanni
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000378:metabolism* / Q000633:toxicity; D000818:Animals; D016588:Anticarcinogenic Agents / Q000627:therapeutic use; D001189:Aryl Hydrocarbon Hydroxylases; D002273:Carcinogens / Q000378:metabolism* / Q000633:toxicity; D002478:Cells, Cultured; D003374:Coumarins / Q000494:pharmacology / Q000627:therapeutic use*; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism*; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D018736:DNA Adducts / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D011564:Furocoumarins / Q000627:therapeutic use; D051379:Mice; D018632:Mice, Inbred SENCAR; D010936:Plant Extracts / Q000627:therapeutic use; D012878:Skin Neoplasms / Q000139:chemically induced / Q000517:prevention & control*
chemical_list: D016588:Anticarcinogenic Agents; D002273:Carcinogens; D003374:Coumarins; D018736:DNA Adducts; D011564:Furocoumarins; D010936:Plant Extracts; C015304:isopimpinellin; D015127:9,10-Dimethyl-1,2-benzanthracene; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585498:Cyp1b1 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; C068337:bergamottin; C031534:imperatorin