Association of CYP2A6*4 with susceptibility of lung cancer: a meta-analysis

Genetic Polymorphism of Cyp2a6 and Cyp2a13 Genes and Environmental Tobacco Smoke Induced Lung Cancer Risk in Indonesian Female Never Smokers

BACKGROUND: The presence of nicotine metabolite in the urine of subjects exposed to tobacco smoke represents the nicotine metabolism activity in environmental tobacco smokers. CYP2A6 and CYP2A13 are known as the main enzymes responsible for nicotine metabolism and xenobiotic activity in tobacco smoke-related lung cancer. AIM: The aim of this study is to analyze the relationship between genetic polymorphism of CYP26 and CYP2A13 genes and environmental tobacco smoke-induced lung cancer risk in Indonesian females never smoker. METHODS: This is a case-control study with two-stage of distinguishing polymorphism detection. Restriction fragment length polymorphism polymerase chain reaction from venous blood extraction was performed to examine the CYP2A6 and CYP2A13 polymorphism. Logistic regression test in Epi Info-7 software was carried out to examine genetic polymorphism of CYP2A6 and CYP2A13 genes and environmental tobacco smoke-induced lung cancer risk in Indonesian female never smokers. RESULTS: A total of 203 participants enrolled in this study with the first stage of CYP2A6 polymorphism involved 101 subjects showed no significant correlation between the genotypes of CYP2A6 and the incidence of lung cancer. On the other hand, there was a significant correlation between genotypes of CYP2A13 and the incidence of lung cancer (p < 0.05). People with the genotype CT have a 2.7 higher risk for developing lung cancer compare with genotype CC. Allele *1B was the most common allele in CYP2A6. Allele C has more frequencies and has 0.62 times the risk for developing lung cancer compared with allele T with a wide range of confidence intervals (0.73–3.52). CONCLUSIONS: There was a significant correlation between polymorphism CYP213 with the incidence of lung cancer among female lung cancer never smoker. However, the results show no significant relationship between CYP2A6 genetic polymorphism and lung cancer incidence.

Novel Association of Genetic Markers Affecting CYP2A6 Activity and Lung Cancer Risk

Metabolism of nicotine by cytochrome P450 2A6 (CYP2A6) is a suspected determinant of smoking dose and, consequently, lung cancer risk. We conducted a genome-wide association study (GWAS) of CYP2A6 activity, as measured by the urinary ratio of trans-3'-hydroxycotinine and its glucuronide conjugate over cotinine (total 3HCOT/COT), among 2,239 smokers in the Multiethnic Cohort (MEC) study. We identified 248 CYP2A6 variants associated with CYP2A6 activity (P < 5 × 10-8). CYP2A6 activity was correlated (r = 0.32; P < 0.0001) with total nicotine equivalents (a measure of nicotine uptake). When we examined the effect of these variants on lung cancer risk in the Transdisciplinary Research in Cancer of the Lung (TRICL) consortium GWAS dataset (13,479 cases and 43,218 controls), we found that the vast majority of these individual effects were directionally consistent and associated with an increased lung cancer risk. Two hundred and twenty-six of the 248 variants associated with CYP2A6 activity in the MEC were available in TRICL. Of them, 81% had directionally consistent risk estimates, and six were globally significantly associated with lung cancer. When conditioning on nine known functional variants and two deletions, the top two SNPs (rs56113850 in MEC and rs35755165 in TRICL) remained significantly associated with CYP2A6 activity in MEC and lung cancer in TRICL. The present data support the hypothesis that a greater CYP2A6 activity causes smokers to smoke more extensively and be exposed to higher levels of carcinogens, resulting in an increased risk for lung cancer. Although the variants identified in these studies may be used as risk prediction markers, the exact causal variants remain to be identified. Cancer Res; 76(19); 5768-76. ©2016 AACR.

Application of a pharmacokinetic/pharmacogenetic approach to assess the nicotine metabolic profile of smokers in the real-life setting

The nicotine metabolite ratio, i.e., the ratio 3-hydroxycotinine/cotinine, is used to assess the nicotine metabolic status and has been proven to predict the response to smoking cessation treatments in randomized clinical trials. In the current study, a pharmacokinetic-pharmacogenetic integrated approach is described, based on the development of a liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for nicotine metabolite ratio assay in plasma and a real-time PCR analysis for fast genotyping of CYP2A6. The pharmacokinetic-pharmacogenetic approach was validated in 66 subjects with different smoking status. The LC/MS/MS assay was rapid and sensitive enough to detect plasma cotinine levels also in second-hand exposed abstainers. In the cohort of patients of the present study the following results were obtained: (i) the frequencies of CYP2A6 genetic variants were comparable with those from clinical trials carried out in Caucasian populations; (ii) all the subjects carrying the CYP2A6 deficient allele also had a slow metabolizer phenotype; (iii) slow metabolizers had mean nicotine metabolite ratio approximately 50% of that of the normal/fast metabolizers; (iv) women had higher nicotine metabolite ratio than men; and (v) salivary nicotine metabolite ratio measures were comparable to plasma levels. Overall, the findings of the current study demonstrate that the simultaneous assessment of nicotine metabolite ratio and CYP2A6 genotype from human blood samples is feasible and accurate and could be used in a smoking cessation program to optimize treatments and identify those smokers who inherit metabolically deficient CYP2A6 alleles.

Genetic determinants of cytochrome P450 2A6 activity and biomarkers of tobacco smoke exposure in relation to risk of lung cancer development in the Shanghai cohort study

Cytochrome P450 2A6 (CYP2A6) catalyzes nicotine metabolism and contributes to the metabolism of the tobacco-specific lung carcinogen, NNK. Genetic variation in CYP2A6 may affect smoking behavior and contribute to lung cancer risk. A nested case-control study of 325 lung cancer cases and 356 controls was conducted within a prospective cohort of 18,244 Chinese men in Shanghai, China. Quantified were 4 allelic variants of CYP2A6 [*1(+51A), *4, *7, and *9] and urinary total nicotine, total cotinine, total trans-3'-hydroxycotinine (3HC) and total NNAL (an NNK metabolite). Calculated were total nicotine equivalents (TNE), the sum of total nicotine, total cotinine and total 3HC and the total 3HC:total cotinine ratio as a measure of CYP2A6 activity. The nicotine metabolizer status (normal, intermediate, slow and poor) was determined by CYP2A6 genotypes. The smoking-adjusted odds ratios (95% confidence intervals) of lung cancer for the highest vs lowest quartile of total nicotine, total cotinine, total 3HC, TNE and total NNAL were 3.03 (1.80-5.10), 4.70 (2.61-8.46), 4.26 (2.37-7.68), 4.71 (2.61-8.52), and 3.15 (1.86-5.33) (all Ptrend  < 0.001), respectively. Among controls CYP2A6 poor metabolizers had a 78% lower total 3HC:total cotinine ratio and 72% higher total nicotine (Ptrend ≤ 0.002). Poor metabolizers had an odds ratio of 0.64 (95% confidence interval = 0.43-0.97) for lung cancer, which was statistically nonsignificant (odds ratio = 0.74, 95% confidence interval = 0.48-1.15) after adjustment for urinary TNE and smoking intensity and duration. The lower lung cancer risk observed in CYP2A6 poor metabolizers is partially explained by the strong influence of CYP2A6 genetic polymorphisms on nicotine uptake and metabolism.

Genetic determinants of CYP2A6 activity across racial/ethnic groups with different risks of lung cancer and effect on their smoking intensity

Genetic variation in cytochrome P450 2A6 (CYP2A6) gene is the primary contributor to the intraindividual and interindividual differences in nicotine metabolism and has been found to influence smoking intensity. However, no study has evaluated the relationship between CYP2A6 genetic variants and the CYP2A6 activity ratio (total 3-hydroxycotinine/cotinine) and their influence on smoking intensity [total nicotine equivalents (TNE)], across five racial/ethnic groups found to have disparate rates of lung cancer. This study genotyped 10 known functional CYP2A6 genetic or copy number variants in 2115 current smokers from the multiethnic cohort study [African Americans (AA) = 350, Native Hawaiians (NH) = 288, Whites = 413, Latinos (LA) = 437 and Japanese Americans (JA) = 627] to conduct such an investigation. Here, we found that LA had the highest CYP2A6 activity followed by Whites, AA, NH and JA, who had the lowest levels. Adjusting for age, sex, race/ethnicity and body mass index, we found that CYP2A6 diplotypes were predictive of TNE levels, particularly in AA and JA (P trend < 0.0001). However, only in JA did the association remain after accounting for cigarettes per day. Also, it is only in this population that the lower activity ratio supports lower TNE levels, carcinogen exposure and thereby lower risk of lung cancer. Despite the association between nicotine metabolism (CYP2A6 activity phenotype and diplotypes) and smoking intensity (TNE), CYP2A6 levels did not correlate with the higher TNE levels found in AA nor the lower TNE levels found in LA, suggesting that other factors may influence smoking dose in these populations. Therefore, further study in these populations is recommended.

A genome-wide association study identifies risk loci for spirometric measures among smokers of European and African ancestry

BACKGROUND

Pulmonary function decline is a major contributor to morbidity and mortality among smokers. Post bronchodilator FEV1 and FEV1/FVC ratio are considered the standard assessment of airflow obstruction. We performed a genome-wide association study (GWAS) in 9919 current and former smokers in the COPDGene study (6659 non-Hispanic Whites [NHW] and 3260 African Americans [AA]) to identify associations with spirometric measures (post-bronchodilator FEV1 and FEV1/FVC). We also conducted meta-analysis of FEV1 and FEV1/FVC GWAS in the COPDGene, ECLIPSE, and GenKOLS cohorts (total n = 13,532).

RESULTS

Among NHW in the COPDGene cohort, both measures of pulmonary function were significantly associated with SNPs at the 15q25 locus [containing CHRNA3/5, AGPHD1, IREB2, CHRNB4] (lowest p-value = 2.17 × 10(-11)), and FEV1/FVC was associated with a genomic region on chromosome 4 [upstream of HHIP] (lowest p-value = 5.94 × 10(-10)); both regions have been previously associated with COPD. For the meta-analysis, in addition to confirming associations to the regions near CHRNA3/5 and HHIP, genome-wide significant associations were identified for FEV1 on chromosome 1 [TGFB2] (p-value = 8.99 × 10(-9)), 9 [DBH] (p-value = 9.69 × 10(-9)) and 19 [CYP2A6/7] (p-value = 3.49 × 10(-8)) and for FEV1/FVC on chromosome 1 [TGFB2] (p-value = 8.99 × 10(-9)), 4 [FAM13A] (p-value = 3.88 × 10(-12)), 11 [MMP3/12] (p-value = 3.29 × 10(-10)) and 14 [RIN3] (p-value = 5.64 × 10(-9)).

CONCLUSIONS

In a large genome-wide association study of lung function in smokers, we found genome-wide significant associations at several previously described loci with lung function or COPD. We additionally identified a novel genome-wide significant locus with FEV1 on chromosome 9 [DBH] in a meta-analysis of three study populations.

The allele frequency of CYP2A6*4 in four ethnic groups of China

The CYP2A6*4 allele, characterized as the whole deletion of this gene, is closely associated with nicotine dependence, cancer susceptibility, and drug responsiveness. The frequency of this molecular variant differs across populations. Although genetic polymorphisms of CYP2A6*4 and its functional results have been reported in Chinese Han population, the allele frequency of CYP2A6*4 was largely unknown in other Chinese ethnic population. In this study, we investigated the allele frequency of CYP2A6*4 in four main ethnic groups of China based on our newly developed quantitative real-time PCR assay. The frequencies of the CYP2A6*4 allele were 7.9%, 15%, 0% and 2% in Han (N=120), Uighur (N=100), Bouyei (N=100) and Tibetan (N=100) (P<0.0001), respectively. This work greatly expanded our understanding of the distribution of CYP2A6*4 in Chinese population and provided more information of different ethnic population's smoking behavior and also in disease susceptibility and drug response.

The contribution of common genetic variation to nicotine and cotinine glucuronidation in multiple ethnic/racial populations

BACKGROUND

The lung cancer risk of smokers varies by race/ethnicity even after adjustment for smoking. Evaluating the role of genetics in nicotine metabolism is likely important in understanding these differences, as disparities in risk may be related to differences in nicotine dose and metabolism.

METHODS

We conducted a genome-wide association study in search of common genetic variants that predict nicotine and cotinine glucuronidation in a sample of 2,239 smokers (437 European Americans, 364 African Americans, 453 Latinos, 674 Japanese Americans, and 311 Native Hawaiians) in the Multiethnic Cohort Study. Urinary concentration of nicotine and its metabolites were determined.

RESULTS

Among 11,892,802 variants analyzed, 1,241 were strongly associated with cotinine glucuronidation, 490 of which were also associated with nicotine glucuronidation (P < 5×10(-8)). The vast majority were within chromosomal region 4q13, near UGT2B10. Fifteen independent and globally significant SNPs explained 33.2% of the variation in cotinine glucuronidation, ranging from 55% for African Americans to 19% for Japanese Americans. The strongest single SNP association was for rs115765562 (P = 1.60 × 10(-155)). This SNP is highly correlated with a UGT2B10 splice site variant, rs116294140, which together with rs6175900 (Asp67Tyr) explains 24.3% of the variation. The top SNP for nicotine glucuronidation (rs116224959, P = 2.56 × 10(-43)) was in high LD (r(2) = 0.99) with rs115765562.

CONCLUSIONS

Genetic variation in UGT2B10 contributes significantly to nicotine and cotinine glucuronidation but not to nicotine dose.

IMPACT

The contribution of genetic variation to nicotine and cotinine glucuronidation varies significantly by racial/ethnic group, but is unlikely to contribute directly to lung cancer risk.