Specificity of cDNA-expressed human and rodent cytochrome P450s in the oxidative metabolism of the potent carcinogen 7,12-dimethylbenz a anthracene

Specificity of cDNA-expressed human and rodent cytochrome P450s in the oxidative metabolism of the potent carcinogen 7,12-dimethylbenz a anthracene

Shou M G; Korzekwa K R; Krausz K W; Buters J T M; Grogan J; Goldfarb I; Hardwick J P; Gonzalez F J; Gelboin H V

Molecular Carcinogenesis

1996

1996-12

7,12-Dimethylbenz[a]anthracene (DMBA), a potent carcinogen, requires metabolic activation by cytochrome P450s (P450s) to electrophilic metabolites that result in DNA modification, mutagenicity, and carcinogenicity. In this study, we used eight human forms, four rodent forms, and one rabbit form of P450 expressed from recombinant vaccinia or baculovirus vectors to define their specificity for metabolizing DMBA. Of the eight human P450s, 1A1 was the most active (specific activity = 14.7 nmol/min/nmol of P450) in total metabolism of DMBA and showed approximately 6- to 33-fold more activity than other P450s. 2B6, 2C9, and 1A2 were also capable of metabolizing DMBA (2.0-2.5 nmol/min/nmol of P450), whereas 2C8, 2E1, 3A4, and 3A5 exhibited relatively low activities. Among animal P450s, mouse 1A1 exhibited activity similar to that of human 1A1 and had 5.0- to 37-fold more activity than other rodent and rabbit P450s. In regard to enzyme regioselectivity, most human and rodent P450s predominantly formed the 8,9-diol, but human 2B6 and rat 2B1 preferentially formed the 5,6-diol. In the production of monohydroxymethyl metabolites, all the enzymes yielded more 7-hydroxymethyl-12-methylbenz[a]anthracene (7HOM12MBA) than 12-hydroxymethyl-7-methylbenz[a]anthracene (7M12HOMBA), except for human 1A1, which presented the reverse selectivity. Human liver microsomes from 10 organ donors were shown to metabolize DM BA and in most circumstances generated the meta belie profile DM BA trans-8,9-d dihydrodiol > 7HOM12MBA greater than or equal to DMBA trans-5,6-dihydrodiol greater than or equal to 7,12-dihydroxymethylbenz[a]anthracene > 7M12HOMBA > DMBA trans-3,4-dihydrodiol. Thus, the combined activity of hepatic microsomal 2C9, 1A2, and 2B6 may contribute to the metabolic activation and the metabolism of DMBA in normal human liver. (C) 1996 Wiley-Liss, Inc.

12-dimethylbenz(a)anthracene; 12-dimethylbenz(a)anthracene; 12-dimethylbenzanthracene metabolites; 7; binding; Biochemistry & Molecular Biology; cDNA expression; chromatography; cytochrome P450; high-performance liquid; human-tissues; hydrocarbons; liver; lung-cancer; metabolism of polycyclic aromatic; microsomes; mouse skin; Oncology; purification; rat; vaccinia virus

Journal Article

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