Characterization and functional analysis of two common human cytochrome P450 1B1 variants

New Perspectives of CYP1B1 Inhibitors in the Light of Molecular Studies

Human cytochrome P450 1B1 (CYP1B1) is an extrahepatic heme-containing monooxygenase. CYP1B1 contributes to the oxidative metabolism of xenobiotics, drugs, and endogenous substrates like melatonin, fatty acids, steroid hormones, and retinoids, which are involved in diverse critical cellular functions. CYP1B1 plays an important role in the pathogenesis of cardiovascular diseases, hormone-related cancers and is responsible for anti-cancer drug resistance. Inhibition of CYP1B1 activity is considered as an approach in cancer chemoprevention and cancer chemotherapy. CYP1B1 can activate anti-cancer prodrugs in tumor cells which display overexpression of CYP1B1 in comparison to normal cells. CYP1B1 involvement in carcinogenesis and cancer progression encourages investigation of CYP1B1 interactions with its ligands: substrates and inhibitors. Computational methods, with a simulation of molecular dynamics (MD), allow the observation of molecular interactions at the binding site of CYP1B1, which are essential in relation to the enzyme’s functions.

Single-nucleotide polymorphisms and mRNA expression of CYP1B1 influence treatment response in triple negative breast cancer patients undergoing chemotherapy

Triple negative breast cancer (TNBC) is typically associated with poor and interindividual variability in treatment response. Cytochrome P450 family 1 subfamily B1 (CYP1B1) is a metabolizing enzyme, involved in the biotransformation of xenobiotics and anticancer drugs. We hypothesized that, single-nucleotide polymorphisms (SNPs), CYP1B1 142 C>G, 4326 C>G and 4360 A>G, and CYP1B1 mRNA expression might be potential biomarkers for prediction of treatment response in TNBC patients. CYP1B1 SNPs genotyping (76 TNBC patients) was performed using allele-specific polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism methods and mRNA expression of CYP1B1 (41 formalin-fixed paraffin embeddedblocks) was quantified using quantitative reverse transcription PCR. Homozygous variant genotype (GG) and variant allele (G) of CYP1B1 4326C>G polymorphism showed significantly higher risk for development of resistance to chemotherapy with adjusted odds ratio (OR): 6.802 and 3.010, respectively. Whereas, CYP1B1 142 CG heterozygous genotype showed significant association with goodtreatment response with adjusted OR: 0.199. CYP1B1 142C-4326G haplotype was associated with higher risk for chemoresistance with OR: 2.579. Expression analysis revealed that the relative expression of CYP1B1 was downregulated (0.592) in cancerous tissue compared with normal adjacent tissues. When analysed for association with chemotherapy response, CYP1B1 expression was found to be significantly upregulated (3.256) in cancerous tissues of patients who did not respond as opposed to those of patients who showed response to chemotherapy. Our findings suggest that SNPs together with mRNA expression of CYP1B1 may be useful biomarkers to predict chemotherapy response in TNBC patients.

Indistinguishable gene expression between healthy eyes and eyes with unilateral exfoliative glaucoma

Background

Glaucoma is an optic neuropathy associated with visual field loss. There are different types of glaucoma, among them exfoliative glaucoma. Glaucoma can present as unilateral or bilateral. The present study aimed to show the association between gene expression and exfoliation in unilateral glaucoma cases.

Methods

Included patients were suffering from exfoliative glaucoma in one eye, meanwhile the other eye was healthy and used as a control. Lens capsule and conjunctival biopsies were taken from both eyes. Gene expression was analyzed.

Results

Both groups were completely different at baseline regarding intraocular pressure, visual acuity before the operation, visual field damage, optic nerve damage, etc. As for gene expression, the only significant difference was found in CYP1B1 from lens capsules. None of the other genes studied showed differential expression in either lens capsules or conjunctival biopsies.

Conclusion

No difference in gene expression was found between eyes with and without exfoliative glaucoma. Exfoliative glaucoma seems to be a bilateral disease, though the phenotype is not always clinically present.

Cancer Activation and Polymorphisms of Human Cytochrome P450 1B1

Human cytochrome P450 enzymes (P450s, CYPs) are major oxidative catalysts that metabolize various xenobiotic and endogenous compounds. Many carcinogens induce cancer only after metabolic activation and P450 enzymes play an important role in this phenomenon. P450 1B1 mediates bioactivation of many procarcinogenic chemicals and carcinogenic estrogen. It catalyzes the oxidation reaction of polycyclic aromatic carbons, heterocyclic and aromatic amines, and the 4-hydroxylation reaction of 17β-estradiol. Enhanced expression of P450 1B1 promotes cancer cell proliferation and metastasis. There are at least 25 polymorphic variants of P450 1B1 and some of these have been reported to be associated with eye diseases. In addition, P450 1B1 polymorphisms can greatly affect the metabolic activation of many procarcinogenic compounds. It is necessary to understand the relationship between metabolic activation of such substances and P450 1B1 polymorphisms in order to develop rational strategies for the prevention of its toxic effect on human health.

Cytochrome 1A1 and 1B1 gene diversity in the Zanzibar islands

Amodiaquine (AQ) is a 4-aminoquinoline widely used in the treatment of malaria as part of the artemisinin combination therapy (ACT). AQ is metabolised towards its main metabolite desethylamodiaquine mainly by cytochrome P450 2C8 (CYP2C8). CYP1A1 and CYP1B1 play a minor role in the metabolism but they seem to be significantly involved in the formation of the short-lived quinine-imine. To complete the genetic variation picture of the main genes involved in AQ metabolism in the Zanzibar population, previously characterised for CYP2C8, we analysed in this study CYP1A1 and CYP1B1 main genetic polymorphisms. The results obtained show a low frequency of the CYP1A1*2B/C allele (2.4%) and a high frequency of CYP1B1*6 (approximately 42%) followed by CYP1B1*2 (approximately 27%) in Zanzibar islands. Genotype data for CYP1A1 and CYP1B1 show a low incidence of fast metabolisers, revealing a relatively safe genetic background in Zanzibar's population regarding the appearance of adverse effects.

Cytochrome 450 1B1 (CYP1B1) polymorphisms associated with response to docetaxel in Castration-Resistant Prostate Cancer (CRPC) patients

Background

The selection of patients according to key genetic characteristics may help to tailor chemotherapy and optimize the treatment in Castration-Resistant Prostate Cancer (CRPC) patients. Functional polymorphisms within the cytochrome P450 1B1 (CYP1B1) gene have been associated with alterations in enzymatic expression and activity and may change sensitivity to the widely used docetaxel regimen.

Methods

CYP1B1 genotyping was performed on blood samples of 60 CRPC patients treated with docetaxel, using TaqMan probes-based assays. Association between CYP1B1-142C>G (leading to the 48ArgGly transition), 4326C>G (432LeuVal), and 4390A>G (453AsnSer) polymorphisms and treatment response, progression-free-survival (PFS) and overall-survival (OS) was estimated using Pearson χ² test, Kaplan-Meier curves and Log-rank test.

Results

Patients carrying the CYP1B1-432ValVal genotype experienced a significantly lower response-rate (P = 0.014), shorter progression-free-survival (P = 0.032) and overall-survival (P < 0.001). Multivariate analyses and correction for multiple comparisons confirmed its prognostic significance for OS. No significant associations were found among other polymorphisms and both response and clinical outcome.

Conclusions

CYP1B1-4326C>G (432LeuVal) polymorphism emerged as possible predictive marker of response and clinical outcome to docetaxel in CRPC patients and may represent a potential new tool for treatment optimization. Larger prospective trials are warranted to validate these findings, which might be applied to the future practice of CRPC treatment.

Frequency of CYP1B1 homozygous genotype 355T/T in prostate cancer families from Poland

A group of 98 families were analyzed for CYP1B1 gene 355T/T homozygous genotype frequency because of prostate cancer history. Molecular investigations were performed using the restriction fragment length polymorphism-PCR method. 355T/T genotype was detected in 14 of the 98 prostate cancer patients (14.3%). Among them, it was found in one man (7.1%) from a family suspected of hereditary prostate cancer (his age at prostate cancer diagnosis was 57 years) and in 13 men (92.9%) originating from families that did not strictly fulfill hereditary prostate cancer criteria (the median age at prostate cancer diagnosis was 60.1 years). Among 14 355T/T genotype-positive families, in 10 (71.4%) other types of cancers, for example, breast, uterus, stomach, colon, ovary, lung, larynx, bladder, pancreas and melanoma other than prostate cancer, were present, and in four (28.6%) only one cancer type, that is, prostate cancer, occurred. In the Polish population, the CYP1B1 355T/T genotype seems to be associated with prostate cancer; the frequency of this genotype was 5.9% higher in prostate cancer patients than in the general population (8.4%). However, it is not associated with prostate cancer family history.

Comparative docking studies of CYP1b1 and its PCG-associated mutant forms

Molecular docking has been used to compare and contrast the binding modes of oestradiol with the wild-type and some disease-associated mutant forms of the human CYP1b1 protein.The receptor structures used for docking were derived from molecular dynamics simulations of homology-modelled structures. Earlier studies involving molecular dynamics and principal component analysis indicated that mutations could have a disruptive effect on function,by destabilizing the native properties of the functionally important regions, especially those of the haem-binding and substrate-binding regions,which constitute the site of catalytic activity of the enzyme.In order to gain more insights into the possible differences in substrate-binding and catalysis between the wild-type and mutant proteins,molecular docking studies were carried out. Mutants showed altered protein -ligand interactions compared with the wild-type as a consequence of changes in the geometry of the substrate-binding region and in the position of haem relative to the active site. An important difference in ligand -protein interactions between the wild-type and mutants is the presence of stacking interaction with phenyl residues in the wild-type,which is either completely absent or considerably weaker in mutants.The present study revealed essential differences in the interactions between ligand and protein in wild-type and disease mutants,and helped in understanding the deleterious nature of disease mutations at the level of molecular function.

Polymorphisms in genes involved in sex hormone metabolism, estrogen plus progestin hormone therapy use, and risk of postmenopausal breast cancer

Hormone therapy, estrogen plus progestin (E+P) particularly, is associated with increased risk of breast cancer. Functionally relevant polymorphisms in genes involved in sex hormone metabolism may alter exposure to exogenous sex hormones and affect risk of postmenopausal breast cancer. We evaluated associations of common polymorphisms in genes involved in estrogen and/or progesterone metabolism, E+P use, and their interactions with breast cancer risk in a case-control study of postmenopausal women (324 cases; 651 controls) nested within the VITAL cohort. None of the polymorphisms studied was, by itself, statistically significantly associated with breast cancer risk. E+P use was significantly associated with increased breast cancer risk (> or =10 years versus never; odds ratio, 1.9; 95% confidence interval, 1.3-2.8; P(trend) = 0.0002). Statistically significant interactions between CYP1A1 Ile(462)Val (P(interaction) = 0.04), CYP1A1 MspI (P(interaction) = 0.003), CYP1B1 Val(432)Leu (P(interaction) = 0.007), CYP1B1 Asn(453)Ser (P(interaction) = 0.04) and PGR Val(660)Leu (P(interaction) = 0.01), and E+P use were observed. The increased risk of breast cancer associated with E+P use was greater among women with at least one rare allele of the CYP1A1 Ile(462)Val, CYP1A1 MspI, CYP1B1 Asn(453)Ser, and PGR Val(660)Leu polymorphisms than among women homozygous for the common allele of these polymorphisms. Risk of breast cancer increased little with increasing years of E+P use among women with at least one CYP1B1 Val(432) allele; a large increase in risk was seen among women homozygous for CYP1B1 Leu(432). Our results support the hypothesis that specific polymorphisms in genes involved in sex hormone metabolism may modify the effect of E+P use on breast cancer risk.

CYP1B1 variants are associated with prostate cancer in non-Hispanic and Hispanic Caucasians

Cytochrome P450 1B1 (CYP1B1) is involved in the activation of many carcinogens and in the metabolism of steroid hormones. We compared allele, genotype and haplotype frequencies of six single-nucleotide polymorphisms (SNPs) within CYP1B1 among non-Hispanic Caucasians (496 cases and 498 controls) and Hispanic Caucasians (153 cases and 240 controls). In the Hispanic Caucasians, the GG genotype for rs1056836 decreased the risk for prostate cancer (PCa) when compared with the CC genotype [odds ratio (OR) = 0.31, P = 0.04, 95% confidence interval (CI) = 0.10–0.96]. Among non-Hispanic Caucasian men with more aggressive PCa, the prevalence of several SNPs (rs2567206, rs2551188, rs2617266, rs10012 and rs1056836) was significantly associated with the disease status. A common C-G-C-C-G-A haplotype for rs2567206-rs2551188-rs2617266-rs10012-rs1056836-rs1800440 showed an inverse association with PCa risk in Hispanic Caucasians (OR = 0.19, P = 0.04, 95% CI = 0.04–0.95) and with aggressive disease status (i.e. Gleason score ≥7) in non-Hispanic Caucasian cases (OR = 0.64, P = 0.008, 95% CI = 0.47–0.89). In the non-Hispanic Caucasian cases, a second major haplotype T-A-T-G-C-A was positively associated with the high-grade disease status (OR = 1.77, P = 0.002, 95% CI = 1.24–2.53). Our findings suggest that genetic polymorphisms in CYP1B1 may modify the risk for PCa and support the role of CYP1B1 as a candidate gene for PCa.

Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by human CYP1B1 genetic variants

Human cytochrome P450 1B1 (CYP1B1) plays a critical role in the metabolic activation of a variety of procarcinogens, including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). The existence of human CYP1B1 missense genetic variants has been demonstrated, but their activities in metabolizing PhIP are unknown. In this study, we expressed 15 naturally occurring CYP1B1 variants (with either single or multiple amino acid substitutions) and determined their activity changes in metabolizing PhIP to its two major metabolites, 2-hydroxyamino-PhIP and 4'-hydroxy-PhIP. Although the PhIP-metabolizing activities of four variants (Ala(119)Ser, Pro(379)Leu, Ala(443)Gly, Arg(48)Gly/Leu(432)Val) were comparable with that of the expressed wild-type CYP1B1, five variants (Trp(57)Cys, Gly(61)Glu, Arg(48)Gly/Ala(119)Ser, Arg(48)Gly/Ala(119)Ser/Leu(432)Val, Arg(48)Gly/Ala(119)Ser/Leu(432)Val/Ala(443)Gly) exhibited more than 2-fold decrease in activity and a reduction in the catalytic efficiency (V(max)/K(m)) for both N- and 4-hydroxylation of PhIP. Six variants (Gly(365)Trp, Glu(387)Lys, Arg(390)His, Pro(437)Leu, Asn(453)Ser, Arg(469)Trp) showed little activity in PhIP metabolism, but the molecular mechanisms involved are apparently different. The microsomal CYP1B1 protein level was significantly decreased for the Trp(365), Lys(387), and His(390) variants and was not detectable for the Ser(453) variant. In contrast, there was no difference between the Trp(469) variant and the wild-type in the microsomal CYP1B1 protein level and P450 content but the Trp(469) variant totally lost its metabolic activity toward PhIP. The Leu(437) variant also had a substantial amount of CYP1B1 protein in the microsomes, but there was a lack of detectable P450 peak and activity. Our results should be useful in selecting appropriate CYP1B1 variants as cancer susceptibility biomarkers for human population studies related to PhIP exposure.

Single nucleotide polymorphisms and haplotypes of the genes encoding the CYP1B1 in Korean women: no association with advanced endometriosis

OBJECTIVE

To investigate whether single nucleotide polymorphisms and its haplotypes of gene encoding CYP1B1 are associated with the risk of advanced endometriosis in Korean women.

METHODS

We investigated 221 patients with histopathologically confirmed endometriosis rAFS stage III/IV and 188 control group women who were surgically proven to have no endometriosis. The genetic distribution of four different CYP1B1 polymorphisms at Ala119Ser, Leu432Val, Asp(449)(C>T), Asn453Ser were analyzed by polymerase chain reaction (PCR) and restriction fragment length polymorphism of PCR products. Haplotype analysis was also performed.

RESULTS

We found no overall association between each individual CYP1B1 genotype or haplotype and the risk of endometriosis. Also, the odds ratio of each haplotypes of CYP1B1 showed no association with the risk of endometriosis.

CONCLUSIONS

These results suggest that CYP1B1 genetic polymorphism may not be associated with development of advanced endometriosis in Korean women.

Ovarian Cancer Risk and Polymorphisms Involved in Estrogen Catabolism

Polymorphisms within genes responsible for estrogen catabolism could alter cellular levels of genotoxic 4-hydroxylated catechol estrogens and antiangiogenic 2-methoxyestradiol, thus influencing risk of developing ovarian cancer. We carried out a population-based case-control study of 310 epithelial ovarian cancer cases and 585 controls in African-American and Caucasian women ages 35 to 54 years from Seattle, Atlanta, and Detroit metropolitan areas. Subjects were interviewed and genotyped for CYP1A1 m1, m2, m3, and m4; CYP1B1 Arg(48)Gly, Ala(119)Ser, Val(432)Leu, and Asn(453)Ser; COMT Val(158)Met; UGT1A1 A(TA)nTAA; and SULT1A1 Arg(213)His polymorphisms. Unconditional logistic regression was used to calculate odds ratios (OR). Haplotypes were inferred and analyzed using models based on expectation-maximization with progressive ligation and Bayesian coalescence theory. CYP1B1 Leu(432) carriers were at increased risk of ovarian cancer, with an adjusted OR of 1.5 (95% confidence interval, 1.1-2.3) compared with Val(432) homozygotes. The most common CYP1B1 haplotype was Arg(48)-Ala(119)-Val(432)-Asn(453). All other haplotypes with frequencies >5% contained the Leu(432) allele. In diplotype analyses, relative to women homozygous for Arg(48)-Ala(119)-Val(432)-Asn(453), women with diplotypes containing at least one Leu(432) allele had adjusted ORs ranging from 1.3 to 2.2. Among women homozygous for COMT Met(158), carriers of CYP1B1 Leu(432) had a 2.6-fold increase in risk relative to CYP1B1 Val(432) homozygotes (95% confidence interval, 1.1-5.9). This latter result is opposite in direction from a similar analysis conducted by other investigators in a different study population. No association of ovarian cancer risk was observed with any of the other polymorphisms examined, either alone or in combination.

CYP1A1 and CYP1B1 genetic polymorphisms, smoking and breast cancer risk in a Finnish Caucasian population

We investigated the associations between two CYP1A1 polymorphisms (Ile462Val and Thr461Asn) and one CYP1B1 polymorphism (Leu432Val) and breast cancer risk. The study population consisted of 483 breast cancer patients and 482 healthy population controls, all of homogenous Finnish origin. No statistically significant overall associations were found between the CYP1A1 and CYP1B1 genotypes and breast cancer risk. However, a significant increase in the breast cancer risk was seen for women who had smoked 1-9 cigarettes/day and carried the CYP1B1 432Val allele; the OR was 2.6 (95% CI 1.07-6.46) for women carrying the Leu/Val genotype and 5.1 (95% CI 1.30-19.89, P for trend 0.005) for women with the Val/Val genotype compared to similarly smoking women homozygous for the 432Leu allele. Furthermore, when CYP1B1 genotypes were combined with the previously analyzed N-acetyl transferase (NAT2) genotypes, a significant increase in breast cancer risk was found among women who had at least one CYP1B1 432Val allele together with the NAT2 slow acetylator genotype (OR 1.52; 95% CI 1.03-2.24) compared to women carrying a combination of CYP1B1 Leu/Leu and NAT2 rapid acetylator genotypes. This risk was seen to be confined to ever smokers; the OR was 2.46 (95% CI 1.11-5.45) for ever smokers carrying at least one CYP1B1 432Val allele together with the NAT2 slow acetylator genotype compared to ever smokers with the CYP1B1 Leu/Leu and NAT2 rapid acetylator genotype combination. Our results suggest that the CYP1B1 polymorphism may be an important modifier of breast cancer risk in Finnish Caucasian women who have been exposed to tobacco smoke and/or carry the NAT2 slow acetylator genotype.

Cytochrome P450 interactions in human cancers: new aspects considering CYP1B1

Molecular epidemiological studies are now a powerful tool to determine differential genetic susceptibilities to cancer-causing agents, and to obtain information on potential mechanisms. Cytochrome P450 (CYP) allelic variants are considered biomarkers of susceptibility to cancer. Such variants have an influence on the bioactivation and thereby on the potency of chemical carcinogens. This is very much straight forward for tobacco smoke-related human cancers. A new aspect is the implication of CYP1B1 in tobacco smoke-related cancers at several organ sites. On this basis, the present review is focused on lung, breast, urinary bladder and head and neck cancer. The CYP profile of the human lung includes CYP1A1, -1B1, -2A6, -2A13, -2B6, -2C18, -2E1, -2F1, -3A5 and -4B1. Polycyclic aromatic hydrocarbons (PAHs) and nitrosamines, as active components of tobacco smoke, appear as primary chemical factors for lung malignancies. For human mammary cancer, the use of hormone replacement therapy (HRT) has been shown to be associated with an increase of breast cancer risk, and there seems to be a link between risks caused by HRT use and modifying polymorphisms of drug/xenobiotic enzymes. Specifically, an association of the CYP1B1*3/*3 genotype with increased breast cancer risks has been postulated. Cigarette smoking is a major cause of human urinary bladder cancer. Arylamines, PAHs and nitrosamines are locally activated within the urothelium. Important CYPs in the bladder epithelium of experimental animals and man are CYP1B1 and -4B1. Alcohol consumption and tobacco smoking are known as the major causes of head and neck cancers. Recently, it appears that a polymorphic variant CYP1B1*3/*3 relates significantly to the individual susceptibility of smokers to head and neck cancer, supporting the view that PAH are metabolically activated through CYP1B1. It appears that CYP1B1 plays a key role for the activation of carcinogens at several organ targets, with a likelihood of complex gene-environment interactions implying Phase II enzymes.

Pharmacogenetics and regulation of human cytochrome P450 1B1: implications in hormone-mediated tumor metabolism and a novel target for therapeutic intervention

Several of the hormone-mediated cancers (breast, endometrial, ovarian, and prostate) represent major cancers in both incidence and mortality rates. The etiology of these cancers is in large part modulated by the hormones estrogen and testosterone. As advanced disease develops, the common treatment for these cancers is chemotherapy. Thus, genes that can alter tissue response to hormones and alter clinical response to chemotherapy are of major interest. The cytochrome P450 1B1 (CYP1B1) may be involved in disease progression and modulate the treatment in the above hormone-mediated cancers. This review will focus on the pharmacogenetics of CYP1B1 in relation to hormone-mediated cancers and provide an assessment of cancer risk based on CYP1B1 polymorphisms and expression. In addition, it will provide a summary of CYP1B1 gene regulation and expression in normal and neoplastic tissue.

Risk of Testicular Germ Cell Cancer in Relation to Variation in Maternal and Offspring Cytochrome P450 Genes Involved in Catechol Estrogen Metabolism

The incidence of testicular germ cell carcinoma (TGCC) is highest among men ages 20 to 44 years. Exposure to relatively high circulating maternal estrogen levels during pregnancy has long been suspected as being a risk factor for TGCC. Catechol (hydroxylated) estrogens have carcinogenic potential, thought to arise from reactive catechol intermediates with enhanced capability of forming mutation-inducing DNA adducts. Polymorphisms in maternal or offspring genes encoding estrogen-metabolizing enzymes may influence prenatal catechol estrogen levels and could therefore be biomarkers of TGCC risk. We conducted a population-based, case-parent triad study to evaluate TGCC risk in relation to maternal and/or offspring polymorphisms in CYP1A2, CYP1B1, CYP3A4, and CYP3A5. We identified 18- to 44-year-old men diagnosed with invasive TGCC from 1999 to 2004 through a population-based cancer registry in Washington State and recruited cases and their parents (110 case-parent triads, 50 case-parent dyads). Maternal or offspring carriage of CYP1A2 -163A was associated with reduced risk of TGCC [maternal heterozygote relative risk (RR), 0.6; 95% confidence interval (95% CI), 0.2-1.7; offspring heterozygote RR, 0.7; 95% CI, 0.3-1.5)]. Maternal CYP1B1 (48)Gly homozygosity was associated with a 2.7-fold increased risk of TGCC (95% CI, 0.9-7.9), with little evidence that Leu(432)Val or Asn(453)Ser genotypes were related to risk. Men were also at increased risk of TGCC if they carried the CYP3A4 -392G (RR, 7.0; 95% CI, 1.6-31) or CYP3A5 6986G (RR, 2.4; 95% CI, 1.1-5.6) alleles. These results support the hypothesis that maternal and/or offspring catechol estrogen activity may influence sons' risk of TGCC.

Characterization of common CYP1B1 variants with different capacity for benzo[a]pyrene-7,8-dihydrodiol epoxide formation from benzo[a]pyrene

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 (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol from benzo[a]pyrene as indicated by lower intrinsic clearance (Vmax/Km). 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.

Estrogen-metabolizing gene polymorphisms and age at natural menopause in Caucasian women

BACKGROUND

Lifestyle parameters, personal history and genetic factors are thought to affect the timing of natural menopause in humans. Based on their biological function, estrogen-metabolizing gene polymorphisms have been regarded as candidate genes for early menopause.

METHODS

In the present cross-sectional, multi-centre study, we analysed nine single nucleotide polymorphisms of six estrogen-metabolizing genes [three estrogen-synthesizing genes, i.e. 17-beta-hydroxysteroid dehydrogenase type 1 (17-beta HSD), cytochrome P-450 (CYP) 17 and CYP19; and three estrogen-inactivating genes, i.e. catechol-O-methyltransferase (COMT), CYP1A1 and CYP1B1] by sequencing-on-chip-technology in 1360 Caucasian women with natural menopause. Women's lifestyle parameters, reproductive and personal histories were ascertained.

RESULTS

Carriage of at least one mutant allele of the CYP1B1-4 Asn453Ser A--> G polymorphism (P = 0.004) and the number of full-term pregnancies (P < 0.001) were found to be independently associated with age at natural menopause. Women with at least one polymorphic allele of CYP1B1-4 experienced natural menopause earlier than non-carriers of the polymorphism [mean (SD) 48.6 (5.0) versus 49.4 (4.3) years]. Women with no, one, two and three or more full-term pregnancies experienced natural menopause at 48.5 (5.0), 48.8 (4.8), 49.5 (4.2) and 49.6 (4.6) years, respectively.

CONCLUSION

We present the most comprehensive data on estrogen-metabolizing gene polymorphisms and timing of natural menopause to date. The number of full-term pregnancies and the CYP1B1-4 polymorphism are significant predictors of timing of natural menopause in Caucasian women.

CYP1A1 and CYP1B1 genotypes, haplotypes, and TCDD-induced gene expression in subjects from Seveso, Italy

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is highly toxic in experimental animals, and is known to induce cytochrome P450 (CYP) gene expression. We investigated the effect of CYP1A1 and CYP1B1 variant genotypes and haplotypes on CYP1A1 and CYP1B1 mRNA expression and ethoxyresorufin-O-deethylase (EROD) activity in lymphocytes from 121 subjects from the Seveso population, Italy, accidentally exposed to TCDD in 1976. The 3'UTR 3801T>C and I462V variants of CYP1A1 were present in 16% and 6% of the subjects, respectively. The frequency of CYP1B1 variants was 85.2% for L432V, 49.6% for R48G and A119S, and 28.7% for N453S. There was complete linkage disequilibrium (LD) among the CYP1B1 variant loci (D'=-1) and high LD among the CYP1A1 loci (D'=0.86). Gene expression measured by RT-PCR did not vary by CYP1B1 genotype in uncultured lymphocytes. However, when lymphocytes were treated in vitro with 10 nM TCDD, CYP1B1 and CYP1A1 mRNA expression was strongly induced and modified by CYP variant alleles. Specifically, the CYP1B1*3 haplotype (L432V) was associated with increased CYP1B1 mRNA expression (P=0.03), following an additive model; the CYP1A1 I462V polymorphism was positively, although not significantly, associated with CYP1A1 expression. The CYP1B1*3 variant may have affected CYP1B1 expression in subjects highly and acutely exposed to dioxin at the time of the accident. Although based on small number of subjects, a slight increase in eczema (P=0.05, n=8) and urticaria (P=0.02, n=2) was observed 20 years after the accident in subjects carrying the CYP1B1*3 allele. Genetic variation in cytochrome P450 induction may identify subjects with variable responsiveness to TCDD and potentially increased risk of disease.

Proteasomal Degradation of Human CYP1B1: Effect of the Asn453Ser Polymorphism on the Post-Translational Regulation of CYP1B1 Expression

Allelic variations in CYP1B1 are reported to modulate the incidence of several types of cancer. To provide a mechanistic basis for this association, we investigated the impact of nonsilent allelic changes on the intracellular levels and post-translational regulation of CYP1B1 protein. When transiently expressed in COS-1 cells, either in the presence or absence of recombinant cytochrome P450 reductase, the cellular level of the CYP1B1.4 allelic variant (containing a Ser at the amino acid position 453; Ser453) was 2-fold lower compared with the other four allelic CYP1B1 proteins (containing Asn453), as analyzed by both immunoblotting and ethoxyresorufin O-deethylase activity. This difference was caused by post-translational regulation; as in the presence of cycloheximide, the rate of degradation of immunodetectable and enzymatically active CYP1B1.4 was distinctly faster than that of CYP1B1.1. Pulse-chase analysis revealed that the half-life of CYP1B1.4 was a mere 1.6 h compared with 4.8 h for CYP1B1.1. The presence of the proteasome inhibitor MG132 [N-benzoyloxycarbonyl (Z)-Leu-Leuleucinal] increased the stability not only of immunodetectable CYP1B1, but also--unexpectedly given the size of the proteasome access channel--increased the stability of enzymatically active CYP1B1. The data presented herein also demonstrate that CYP1B1 is targeted for its polymorphism-dependent degradation by polyubiquitination but not phosphorylation. Our results importantly provide a mechanism to explain the recently reported lower incidence of endometrial cancer in individuals carrying the CYP1B1*4 compared with the CYP1B1*1 haplo-type. In addition, the mechanistic paradigms revealed herein may explain the strong overexpression of CYP1B1 in tumors compared with nondiseased tissues.

Cytochrome P450 1B1 Gene Polymorphisms and Postmenopausal Endometrial Cancer Risk

Estrogen unopposed by progestins is a key factor in endometrial cancer etiology. Cytochrome P450 1B1 (CYP1B1), responsible for the 4-hydroxylation of estrogen, may be important in endometrial carcinogenesis, either as a regulator of estrogen availability or as a producer of potentially genotoxic estrogen metabolites. We investigated the association of CYP1B1 genotype and endometrial cancer risk in a population-based case-control study of postmenopausal Swedish women. We used the Expectation-Maximization algorithm to estimate the haplotype frequencies in the population and calculated odds ratios and 95% confidence intervals from conditional logistic regression models. In stratified analysis, we investigated the possible effects of CYP1B1 genotype on endometrial cancer risk in subgroups defined primarily by menopausal hormone use and also by body mass index, smoking, use of combined oral contraceptives, and family history. We genotyped 689 cases and 1,549 controls for the CYP1B1 single nucleotide polymorphisms m2, m3, and m4 and estimated the haplotype frequencies among controls to 0.086, 0.291, 0.452, and 0.169 for the CYP1B1*1, CYP1B1*2, CYP1B1*3, and CYP1B1*4 alleles, respectively. We found no evidence for an overall association between CYP1B1 genotype and endometrial cancer risk, nor was there any clear indication of gene-environment interaction.

Polymorphisms in the CYP1B1 gene are associated with increased risk of prostate cancer

CYP1B1 has been evaluated as a candidate gene for various cancers because of its function in activating environmental procarcinogens and catalysing the conversion of oestrogens to genotoxic catechol oestrogens. To test the hypothesis that genetic polymorphisms in the CYP1B1 gene may associate with the risk for prostate cancer (CaP), we compared the allele, genotype, and haplotype frequencies of 13 single nucleotide polymorphisms (SNPs) of CYP1B1 among 159 hereditary prostate cancer (HPC) probands, 245 sporadic CaP cases, and 222 unaffected men. When each of the SNPs was analysed separately, marginally significant differences were observed for allele frequencies between sporadic cases and controls for three consecutive SNPs (−1001C/T, −263G/A, and −13C/T, P=0.04–0.07). Similarly, marginally significant differences between sporadic cases and controls in the frequency of variant allele carriers were observed for five consecutive SNPs (−1001C/T, −263G/A, −13C/T, +142C/G, and +355G/T, P=0.02–0.08). Interestingly, when the combination of these five SNPs was analysed using a haplotype approach, a larger difference was found (P=0.009). One frequent haplotype (C-G-C-C-G of −1001C/T, −263G/A, −13C/T, +142C/G, and +355G/T) was associated with an increased risk for CaP, while the other frequent haplotype (T-A-T-G-T) was associated with a decreased risk for CaP. These findings suggest that genetic polymorphisms in CYP1B1 may modify the risk for CaP.

Human drug metabolising cytochrome P450 enzymes: properties and polymorphisms

The cytochrome P450s are responsible for about 75% of phase I dependent drug metabolism and for the metabolism of a huge amount of dietary constituents and endogenous chemicals. The human has 59 active genes, and 6 of those encode important drug metabolising enzymes. About 40% of cytochrome P450 dependent drug metabolism is catalysed by polymorphic enzymes and such drug P450 interactions are frequently seen in adverse drug reaction reports. In this contribution an update of human cytochrome P450 enzymology and pharmacogenetics is given with particular emphasis on CYP1B1, CYP2B6, CYP2E1 and CYP3As.

Single amino acid mutations, but not common polymorphisms, decrease the activity of CYP1B1 against (-)benzo[a]pyrene-7R-trans-7,8-dihydrodiol

Genetic differences that underlie inter-individual variation in the metabolism of common carcinogens are important potential sources of cancer susceptibility. Cytochrome P450 1B1 (CYP1B1), a central enzyme in the activation of the ubiquitous environmental carcinogen benzo[a]pyrene (B[a]P), has several genetic variants. This study investigated six rare mutations and four common polymorphisms for their effects on B[a]P metabolism. Five missense mutations associated with congenital glaucoma (Gly61Glu, Gly365Trp, Asp374Asn, Pro437Leu and Arg469Tryp) dramatically decreased the capacity of CYP1B1 to convert (-)benzo[a]pyrene-7R-trans-7,8-dihyrodiol (B[a]P-7,8-diol) to (+/-)benzo[a]pyrene-r-7,t-8-dihydrodiol-9,10-epoxides. These five mutations resulted in enzymes with 3-12% of normal activity when assayed in vitro using an Saccharomyces cerevisiae microsomal expression system. A 10 bp deletion mutation produced no detectable protein or activity. In contrast, proteins containing all possible combinations of four common single nucleotide polymorphisms (Arg48Gly, Ala199Ser, Val432Leu, Asn453Ser) had modest effects on B[a]P-7,8-diol metabolism. Michaelis-Menten analysis suggested that two alleles, Arg48, Ala119, Val432, Ser453 (RAVS) and Arg48, Ala119, Leu432, Ser453 (RALS), have KM values 2-fold lower than Arg48, Ala119, Val432, Ser453 (RAVN): 1.4+/-0.3 and 1.3+/-0.4 microM, respectively, compared with 2.8+/-0.8 microM (P<0.05). However, these differences could not be confirmed with direct measurements of rate at low substrate concentration. There were no significant differences for either of two other kinetic parameters, kcat or kcat/KM. Allele frequency analysis in three populations reveals the Ser453 variant is rare among those of Asian (<1%) and African ancestry (<4%), and more common in individuals of European ancestry (16%). Haplotypes containing the Ser453 variant were uncommon; only RALS was detectable in our small populations. The RALS allele occurred between 0.5% in Asians and 15% in Europeans. Our study demonstrates that rare, disease-associated mutations in CYP1B1 significantly decrease the enzyme's metabolism of B[a]P-7,8-diol; however, our results do not identify any major differences in this metabolism due to four common single amino acid polymorphisms.

Molecular modelling of human CYP1B1 substrate interactions and investigation of allelic variant effects on metabolism

Molecular modelling of human CYP1B1 based on homology with the mammalian P450, CYP2C5, of known three-dimensional structure is reported. The enzyme model has been used to investigate the likely mode of binding for selected CYP1B1 substrates, particularly with regard to the possible effects of allelic variants of CYP1B1 on metabolism. In general, it appears that the CYP1B1 model is consistent with known substrate selectivity for the enzyme, and the sites of metabolism can be rationalized in terms of specific contacts with key amino acid residues within the CYP1B1 heme locus. Furthermore, a mode of binding interaction for the inhibitor, alpha-naphthoflavone, is presented which accords with currently available information. The current paper shows that a combination of molecular modelling and experimental determinations on the substrate metabolism for CYP1B1 allelic variants can aid in the understanding of structure-function relationships within P450 enzymes.

Markers of genetic susceptibility in human environmental hygiene and toxicology: the role of selected CYP, NAT and GST genes

Inherited genetic traits co-determine the susceptibility of an individual to a toxic chemical. Special emphasis has been put on individual responses to environmental and industrial carcinogens, but other chronic diseases are of increasing interest. Polymorphisms of relevant xenobiotic metabolising enzymes may be used as toxicological susceptibility markers. A growing number of genes encoding enzymes involved in biotransformation of toxicants and in cellular defence against toxicant-induced damage to the cells has been identified and cloned, leading to increased knowledge of allelic variants of genes and genetic defects that may result in a differential susceptibility toward environmental toxicants. "Low penetrating" polymorphisms in metabolism genes tend to be much more common in the population than allelic variants of "high penetrating" cancer genes, and are therefore of considerable importance from a public health point of view. Positive associations between cancer and CYP1A1 alleles, in particular the *2C I462V allele, were found for tissues following the aerodigestive tract. Again, in most cases, the effect of the variant CYP1A1 allele becomes apparent or clearer in connection with the GSTM1 null allele. The CYP1B1 codon 432 polymorphism (CYP1B1*3) has been identified as a susceptibility factor in smoking-related head-and-neck squameous cell cancer. The impact of this polymorphic variant of CYP1B1 on cancer risk was also reflected by an association with the frequency of somatic mutations of the p53 gene. Combined genotype analysis of CYP1B1 and the glutathione transferases GSTM1 or GSTT1 has also pointed to interactive effects. Of particular interest for the industrial and environmental field is the isozyme CYP2E1. Several genotypes of this isozyme have been characterised which seem to be associated with different levels of expression of enzyme activity. The acetylator status for NAT2 can be determined by genotyping or by phenotyping. In the pathogenesis of human bladder cancer due to occupational exposure to "classical" aromatic amines (benzidine, 4-aminodiphenyl, 1-naphthylamine) acetylation by NAT2 is regarded as a detoxication step. Interestingly, the underlying European findings of a higher susceptibility of slow acetylators towards aromatic amines are in contrast to findings in Chinese workers occupationally exposed to aromatic amines which points to different mechanisms of susceptibility between European and Chinese populations. Regarding human bladder cancer, the hypothesis has been put forward that genetic polymorphism of GSTM1 might be linked with the occurrence of this tumour type. This supports the hypothesis that exposure to PAH might causally be involved in urothelial cancers. The human polymorphic GST catalysing conjugation of halomethanes, dihalomethanes, ethylene oxide and a number of other industrial compounds could be characterised as a class theta enzyme (GSTT1) by means of molecular biology. "Conjugator" and "non-conjugator" phenotypes are coincident with the presence and absence of the GSTT1 gene. There are wide variations in the frequencies of GSTT1 deletion (GSTT1*0/0) among different ethnicities. Human phenotyping is facilitated by the GST activity towards methyl bromide or ethylene oxide in erythrocytes which is representative of the metabolic GSTT1 competence of the entire organism. Inter-individual variations in xenobiotic metabolism capacities may be due to polymorphisms of the genes coding for the enzymes themselves or of the genes coding for the receptors or transcription factors which regulate the expression of the enzymes. Also, polymorphisms in several regions of genes may cause altered ligand affinity, transactivation activity or expression levels of the receptor subsequently influencing the expression of the downstream target genes. Studies of individual susceptibility to toxicants and gene-environment interaction are now emerging as an important component of molecular epidemiology.

Pharmacogenetics of the major polymorphic metabolizing enzymes

There is increasing information available on the existence of polymorphisms in genes encoding xenobiotic metabolizing enzymes and the functional significance of many of these. In addition to genes long recognized as being polymorphic, such as CYP2D6, CYP2C19 and CYP2C9, there is now information available on the existence of polymorphisms in other cytochrome P450 genes such as CYP2A6, CYP2B6 and CYP2C8. With respect to phase II metabolism, polymorphisms in GSTM1, GSTT1, NAT2 and TPMT are well understood but information is also emerging on other GST polymorphisms and on polymorphisms in the UDP-glucuronosyltransferases and sulfotransferases. The availability of comprehensive information on the occurrence and functional significance of polymorphisms affecting drug metabolism should facilitate their application to pharmacogenomic profiling.

Cytochrome P450 1B1: a target for inhibition in anticarcinogenesis strategies

Cytochrome P450 (P450) 1B1 is expressed in a number of human tissues in which cancers occur (e.g. prostate, ovary, uterus, mammary gland). P450 1B1 activates many environmental mutagens and also catalyzes the 4-hydroxylation of estrogens, considered to be an important step in hormonal carcinogenesis. We have examined the activities of several of the major allelic variants of human P450 1B1 in these reactions. Another interest has been the development of chemical inhibitors of P450 1B1. 2-Ethynylpyrene and alpha-naphthoflavone preferentially inhibit human P450 1B1 compared to P450 1A1, which may be present in the same tissue sites. The natural product resveratrol is also an inhibitor of P450 1B1. Further studies with rhapontigenin and synthetic stilbenes led to the discovery of 2,4,3',5'-tetramethoxystilbene, a selective inhibitor of P450 1B1 relative to other P450s. Inhibition is competitive, with a K(i) value of 3nM, and the inhibitor is resistant to metabolism. In addition to blocking 17beta-estradiol 4-hydroxylation, this stilbene also inhibited the activation of heterocyclic amines to mutagens. 2,4,3',5'-Tetramethoxystilbene also suppressed expression of P450 1B1 and growth of human mammary tumor cells. 3,3',4',5,5'-Pentamethoxystilbene was a selective inhibitor of P450 1A1, showing mixed inhibition, and also suppressed P450 1A1 expression in HepG2 cells. Substituted stilbenes may be useful in preventing cancer caused by estrogens and xenobiotics.

Functional analysis of six different polymorphic CYP1B1 enzyme variants found in an Ethiopian population

Cytochrome P450 1B1 (CYP1B1) is an extrahepatic enzyme of potential importance for the metabolism of estrogen and for metabolic activation of environmental carcinogens. We investigated an Ethiopian population for functional polymorphisms in the CYP1B1 gene using genomic DNA sequencing and detected three novel single nucleotide polymorphisms (SNPs). One of these (4360C-->G in exon 3) is present at a frequency of 7% and causes an Ala443Gly amino acid substitution. In addition, the four described previously missense mutations Arg48Gly, Ala119Ser, Leu432Val, and Asn453Ser were found with frequencies of 51, 50, 53, and 2%, respectively, yielding a total of 32 possible CYP1B1 haplotypes. Allele-specific PCR methods for haplotype analysis were developed and seven different CYP1B1 alleles were found: CYP1B1*1, *2, *3, *4, *5, *6, and *7 with frequencies of 8, 37, 39, 2, 0.7, 6, and 7%, respectively. The functional properties of different forms of CYP1B1, as well as of the Leu432Val + Asn453Ser and Leu432Val + Ala443Gly variants, were evaluated after heterologous expression of the corresponding cDNAs in Saccaromyces cerevisiae. The results revealed that CYP1B1.6 and CYP1B1.7, having the amino acid substitutions Arg48Gly, Ala119Ser, and Leu432Val in common, exhibited altered kinetics with significantly increased apparent K(m) and lowered V(max) values for both the 2- and 4-hydroxylation of 17 beta-estradiol, whereas the other constructs were indistinguishable from the CYP1B1.1 enzyme. The results emphasize the necessity of a complete haplotype analysis of enzyme variants for evaluation of functional consequences in vivo and for analyses of genetic polymorphisms in relation to, for example, cancer incidence.