ACTIVATION OF CHEMICALLY DIVERSE PROCARCINOGENS BY HUMAN CYTOCHROME-P-450 1B1

A human cytochrome P-450 (P450) 1B1 cDNA was expressed in Saccharomyce s cerevisiae, and the microsomes containing P450 1B1 were used to exam ine the selectivity of this enzyme in the activation of a variety of e nvironmental carcinogens and mutagens in Salmonella typhimurium TA1535 /pSK1002 or NM2009 tester strains, using the SOS response as an end po int of DNA damage. We also determined and compared these activities of P450 1B1 with those catalyzed by recombinant human P450s 1A1 and 1A2, which were purified from membranes of Escherichia coli. The carcinoge nic chemicals tested included 27 polycyclic aromatic hydro carbons and their dihydrodiol derivatives, 17 heterocyclic and aryl amines and am inoazo dyes, three mycotoxins, two nitroaromatic hydrocarbons, N-nitro sodimethylamine, vinyl carbamate, and acrylonitrile. Among the three P 450 enzymes examined here, P450 1B1 was found to have the highest cata lytic activities for the activation of 11,12-dihydroxy-11,12-dihydrodi benzo[a,l]pyrene, 1,2-dihydroxy-1,2-dihydro-5-methylchrysene, (+)-7,8- dihydroxy-7,8-dihydrobenzo[a]pyrene, 11,12-dihydroxy-11,12-dihydrobenz o[g]chrysene, 3,4-dihydroxy-3,4-dihydrobenzo[c]phenanthrene, 3-amino-1 ,4-dimethyl-5H-pyrido[4,3-b]indol, 2-aminoanthracene, 3-methoxy-4-amin oazobenzene, and 2-nitropyrene. P450 1B1 also catalyzed the activation of 2-amino-3,5-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethyli midazo[4,5-f]quinoxaline, 2-amino-3-methylimidazo[4,5-f]quinoline, 2-a minofluorene, 6-aminochrysene and its 1,2-dihydroxy, (-)-7,8-dihydroxy -7,8-dihydrobenzo[a]pyrene, 1,2-dihydroxy-1,2-dihydrochrysene, 1-2-dih ydroxy-1,2-dihydro-5,6-dimethylchrysene, 2,3-dihydroxy-2,3-dihydrofluo ranthene, ydroxy-3,4-dihydro-7,12-dimethylbenz[a]anthracene, and 6-nit rochrysene to appreciable extents, However, P450 1B1 did not produce g enotoxic products from benzo[a]pyrene, trans-3,4-dihydroxy-3,4-dihydro benzo[a]anthracene, trans-8,9-dihydroxy-8,9-dihydrobenzo[a]anthracene, 7,12-dimethylbenz[a]anthracene and its cis-5,6-dihydrodiol, 5-methyl- chrysene, 1,12-dihydroxy-11,12-dihydro-3-methylcholanthrene, 1,2-dihyd roxy-1,2-dihydro-6-methylchrysene, benzo[c]phenanthrene, 2-amino-6-met hyldipyrido[1,2-a:3',2'-d]imidazole, 2-acetylaminofluorene, 2-naphthyl amine, aflatoxin B-1, aflatoxin G(1), sterigmatocystin, N-nitrosodimet hylamine, vinyl carbamate, or acrylonitrile in this assay system. P450 1B1 is expressed constitutively in extrahepatic organs, including fet al tissue samples, and is highly inducible in various organs by 2,3,7, 8-tetrachlorodibenzo-p-dioxin and related compounds in experimental an imal models. Thus, activation of procarcinogens by P450 1B1 may contri bute to human tumors of extrahepatic origin.