Characterization of Common CYP1B1 Variants with Different Capacity for Benzo[a]pyrene-7,8-Dihydrodiol Epoxide Formation from Benzo[a]pyrene

Abstract

Cytochrome P450 1B1 (CYP1B1), an extrahepatic enzyme inducible by smoking, is overexpressed in many tumors and catalyzes the metabolic activation of procarcinogens such as polycyclic aromatic hydrocarbons. In human, CYP1B1 is genetically polymorphic and five common missense mutations causing amino acid substitution have been identified. In this study, we have investigated CYP1B1 haplotypes present in a Spanish population and carried out functional analyses of the corresponding enzymes in yeast using benzo [a]pyrene as a substrate. CYP1B1*1, CYP1B1*2, CYP1B1*3, CYP1B1*4, CYP1B1*6, and CYP1B1*7, encoding combinations of the Arg48Gly, Ala119Ser, Leu432Val, Asn453Ser, and Ala443Gly amino acid substitutions, were present at frequencies of 14.3%, 25.5%, 38.8%, 18.1%, 0.4%, and 2.6%, respectively. The variant CYP1B1 forms were heterologously expressed with human reductase in Saccharomyces cerevisiae and kinetic analyses of benzo[a]pyrene metabolism were carried out. CYP1B1.7, having the amino acid substitutions Arg48Gly, Ala119Ser, Leu432Val, and Ala443Gly, exhibited a significantly decreased capacity (P < 0.001) for the formation of (F)-benzo[a]pyrene-trans-7,8-dihydrodiol from benzo[a]-pyrene as indicated by lower intrinsic clearance (V max / K m ). A somewhat decreased clearance was observed for CYP1B1.4, whereas no significant differences in kinetic properties among the remaining variant enzymes were observed as compared with CYP1B1.1. Thus, genetic polymorphism in the CYP1B1 gene, as defined by the haplotypes investigated, might cause interindividual differences in susceptibility (e.g., to lung cancer induced by smoking). The results indicate the necessity to make molecular epidemiologic investigations regarding the association of the specific CYP1B1 haplotypes and cancer risk. (Cancer Res 2005; 65(12): 5105-11)

Ovarian Cancer Risk and Polymorphisms Involved in Estrogen Catabolism

“…If multiple polymorphisms in a single gene affect enzyme function in an epistatic fashion, such an analysis may have a relatively greater ability to identify an association with cancer risk. Prior in vitro enzyme function studies have shown differences in estrogen 4-OH rates across the CYP1B1 haplotypes with conflicting results (25,(31)(32)(33)(34) allele (SULT1A1*2) is associated with f2-fold lower enzyme activity and is less thermostable (38) (9,10,13,14).…”

Cytochrome P450 pharmacogenetics and cancer

“…Five common missense mutations causing amino-acid substitutions in CYP1B1 have been identified and seven haplotypes carrying one or more of these SNPs have been characterized. For one haplotype, the corresponding enzyme CYP1B1.7 was shown to exhibit a significantly decreased capacity to metabolize estradiol (Aklillu et al, 2002) and benzo[a]-pyrene (Aklillu et al, 2005), which suggests a potential role in the interindividual differences in cancer risk or in hormone therapy. With respect to the metabolism of anticancer drugs, McFadyen et al (2001b) showed that a cell line overexpressing CYP1B1 had a significantly decreased sensitivity towards docetaxel and Bournique and Lemarie (2002) showed that the underlying mechanism was the binding of docetaxel to CYP1B1 and an effector action of this enzyme.…”

Metabolism of 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by Human CYP1B1 Genetic Variants

“…In contrast, CYP1B1 is predominantly expressed in extrahepatic tissues, including prostate, mammary gland, and colon (Aklillu et al, 2005). Therefore, metabolic activation of PhIP in situ by CYP1B1 and other extrahepatic enzymes such as CYP1A1 is believed to play a critical role in PhIP-related carcinogenesis in these tissues, such as prostate cancer (Holme et al, 1989;Patterson and Murray, 2002).…”

“…The Gly (CYP1B1*7) exist as common haplotypes in several different populations (Aklillu et al, 2002;Aklillu et al, 2005). During the enzyme kinetic study of the CYP1B1 variants with reduced PhIP-metabolizing activity, the variants Arg Ser variant (CYP1B1.2) showed no K m value change for PhIP N-hydroxylation and in the metabolism of other substrates (Aklillu et al, 2002;Aklillu et al, 2005), it is reasonable to speculate that the K m value changes in the variants Arg Gly substitution in the CYP1B1.7 variant resulted in a further increase in the K m value for PhIP N-hydroxylation, suggesting that the substitution also affects substrate binding.…”

“…Recently, the existence of the genetic variants of human CYP1B1 has been dem-onstrated (Stoilov et al, 1998;McLellan et al, 2000;Aklillu et al, 2002;Tanaka et al, 2002). Functional characterization of several CYP1B1 missense variants has been conducted with carcinogen substrates estradiol, benzo [␣]pyrene, and 7,12-dimethylbenz[␣]anthracene (Li et al, 2000;Shimada et al, 2001;Aklillu et al, 2002;Aklillu et al, 2005). However, the impact of these and other reported CYP1B1 missense variations on PhIP metabolism is yet unknown.…”