Different mechanisms for inhibition of human cytochromes P450 1A1, 1A2, and 1B1 by polycyclic aromatic inhibitors.

We have previously shown that several polycyclic aromatic hydrocarbons (PAHs) strongly inhibit their own and other PAH metabolism catalyzed by cytochrome P450 (P450) 1A1, 1A2, and 1B1 [Shimada, T., and Guengerich, F. P. (2006) Chem. Res. Toxicol. 19, 288-294]. In the present study, we examined mechanisms of how PAHs inhibit these P450 enzymes by using 7-ethoxyresorufin O-deethylation (EROD) as a model reaction. First, we examined mechanisms of inhibition of P450 1A1, 1A2, and 1B1 by the synthetic model inhibitors 1-(1-propynyl)pyrene (1PP), 1-ethynylpyrene (1EP), 2-ethynylpyrene (2EP), and 4-(1-propynyl)biphenyl (4Pbi). Both 1PP and 1EP inhibited P450 1A1 in a mechanism-based manner, but P450 1B1 and 1A2 were directly inhibited by 1PP and 1EP. Interestingly, P450 1B1 inactivated 1PP and 1EP to products that were not inhibitory to P450 1B1. 4Pbi was a mechanism-based inhibitor of P450 1A1 and 1B1, but 2EP directly inhibited these P450s. All four of the inhibitors directly inhibited P450 1A2. We also found that benzo[a]pyrene and seven other PAH compounds tested inhibited P450 1A2 in a mechanism-based manner, but fluoranthene directly inhibited P450 1A2. All of the nine PAHs examined were direct inhibitors of P450 1A1 and P450 1B1. These results suggest different mechanisms of inhibition of P450 1A1, 1A2, and 1B1 by PAHs and related chemicals and that interactions between P450 enzymes and PAH inhibitors are involved in differences in inhibition of the enzymes.

[1]  T. Shimada,et al.  Inhibition of human cytochrome P450 1A1-, 1A2-, and 1B1-mediated activation of procarcinogens to genotoxic metabolites by polycyclic aromatic hydrocarbons. , 2006, Chemical research in toxicology.

[2]  Y. Chun,et al.  Discovery of cytochrome P450 1B1 inhibitors as new promising anti‐cancer agents , 2003, Medicinal research reviews.

[3]  T. Shimada,et al.  Cytochrome P450 1B1: a target for inhibition in anticarcinogenesis strategies. , 2003, Mutation research.

[4]  T. Shimada,et al.  Arylhydrocarbon receptor-dependent induction of liver and lung cytochromes P450 1A1, 1A2, and 1B1 by polycyclic aromatic hydrocarbons and polychlorinated biphenyls in genetically engineered C57BL/6J mice. , 2002, Carcinogenesis.

[5]  H. Rubin.  Synergistic mechanisms in carcinogenesis by polycyclic aromatic hydrocarbons and by tobacco smoke: a bio-historical perspective with updates. , 2001, Carcinogenesis.

[6]  F. Guengerich,et al.  A new selective and potent inhibitor of human cytochrome P450 1B1 and its application to antimutagenesis. , 2001, Cancer research.

[7]  T. Shimada,et al.  Metabolic activation of polycyclic aromatic hydrocarbons and other procarcinogens by cytochromes P450 1A1 and P450 1B1 allelic variants and other human cytochromes P450 in Salmonella typhimurium NM2009. , 2001, Drug metabolism and disposition: the biological fate of chemicals.

[8]  J. Ferguson,et al.  Effect of a complex environmental mixture from coal tar containing polycyclic aromatic hydrocarbons (PAH) on the tumor initiation, PAH-DNA binding and metabolic activation of carcinogenic PAH in mouse epidermis. , 2001, Carcinogenesis.

[9]  T. Perfetti,et al.  The composition of cigarette smoke: a retrospective, with emphasis on polycyclic components , 2000, Human & experimental toxicology.

[10]  H. Yamazaki,et al.  Selectivity of polycyclic inhibitors for human cytochrome P450s 1A1, 1A2, and 1B1. , 1998, Chemical research in toxicology.

[11]  P. Hollenberg,et al.  A role for threonine 302 in the mechanism-based inactivation of P450 2B4 by 2-ethynylnaphthalene. , 1996, Archives of biochemistry and biophysics.

[12]  H. Yamazaki,et al.  Activation of chemically diverse procarcinogens by human cytochrome P-450 1B1. , 1996, Cancer research.

[13]  P. Hollenberg,et al.  Mechanism-based inactivation of cytochrome P450 2B1 by 2-ethynylnaphthalene: identification of an active-site peptide. , 1993, Chemical research in toxicology.

[14]  M. Foroozesh,et al.  Suicide inhibitors of cytochrome P450 1A1 and P450 2B1. , 1992, Biochemical pharmacology.

[15]  T. Shimada,et al.  Human liver microsomal cytochrome P-450 enzymes involved in the bioactivation of procarcinogens detected by umu gene response in Salmonella typhimurium TA 1535/pSK1002. , 1989, Cancer research.

[16]  L. Gan,et al.  1-Ethynylpyrene, a suicide inhibitor of cytochrome P-450 dependent benzo[a]pyrene hydroxylase activity in liver microsomes. , 1984, Biochemistry.

[17]  A. Conney,et al.  Induction of microsomal enzymes by foreign chemicals and carcinogenesis by polycyclic aromatic hydrocarbons: G. H. A. Clowes Memorial Lecture. , 1982, Cancer research.

[18]  D. Nebert,et al.  Metabolism of polycyclic aromatic hydrocarbons: etiologic role in carcinogenesis. , 1982, Pharmacological reviews.

[19]  H. Gelboin.  Benzo[alpha]pyrene metabolism, activation and carcinogenesis: role and regulation of mixed-function oxidases and related enzymes. , 1980, Physiological reviews.

[20]  T. Slaga,et al.  The effects of weak or non-carcinogenic polycyclic hydrocarbons on 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene skin tumor-initiation. , 1979, Cancer letters.

[21]  P. Ortiz de Montellano,et al.  Self-catalyzed destruction of cytochrome P-450: covalent binding of ethynyl sterols to prosthetic heme. , 1979, Proceedings of the National Academy of Sciences of the United States of America.

[22]  B. L. Van Duuren,et al.  Cocarcinogenic agents in tobacco carcinogenesis. , 1973, Journal of the National Cancer Institute.

[23]  T. Omura,et al.  THE CARBON MONOXIDE-BINDING PIGMENT OF LIVER MICROSOMES. I. EVIDENCE FOR ITS HEMOPROTEIN NATURE. , 1964, The Journal of biological chemistry.

[24]  Oliver H. Lowry,et al.  Protein measurement with the Folin phenol reagent. , 1951, The Journal of biological chemistry.

[25]  Tsutomu Shimada,et al.  Xenobiotic-metabolizing enzymes involved in activation and detoxification of carcinogenic polycyclic aromatic hydrocarbons. , 2006, Drug metabolism and pharmacokinetics.

[26]  S. Amin,et al.  Effect of artificial mixtures of environmental polycyclic aromatic hydrocarbons present in coal tar, urban dust, and diesel exhaust particulates on MCF‐7 cells in culture , 2004, Environmental and molecular mutagenesis.

[27]  F. Guengerich,et al.  Oxidation of benzo[a]pyrene by recombinant human cytochrome P450 enzymes. , 1995, Chemical research in toxicology.

[28]  T. Slaga,et al.  Anticarcinogenic and cocarcinogenic effects of benzo[e]pyrene and dibenz[a,c]anthracene on skin tumor initiation by polycyclic hydrocarbons. , 1982, Carcinogenesis.