Genetic polymorphisms of drug-metabolizing enzymes and susceptibility to head-and-neck squamous-cell carcinoma

Genic-intergenic polymorphisms of CYP1A genes and their clinical impact

The humancytochrome P450 1A (CYP1A) subfamily genes, CYP1A1 and CYP1A2, encoding monooxygenases are critically involved in biotransformation of key endogenous substrates (estradiol, arachidonic acid, cholesterol) and exogenous compounds (smoke constituents, carcinogens, caffeine, therapeutic drugs). This suggests their significant involvement in multiple biological pathways with a primary role of maintaining endogenous homeostasis and xenobiotic detoxification. Large interindividual variability exist in CYP1A gene expression and/or catalytic activity of the enzyme, which is primarily due to the existence of polymorphic alleles which encode them. These polymorphisms (mainly single nucleotide polymorphisms, SNPs) have been extensively studied as susceptibility factors in a spectrum of clinical phenotypes. An in-depth understanding of the effects of polymorphic CYP1A genes on the differential metabolic activity and the resulting biological pathways is needed to explain the clinical implications of CYP1A polymorphisms. The present review is intended to provide an integrated understanding of CYP1A metabolic activity with unique substrate specificity and their involvement in physiological and pathophysiological roles. The article further emphasizes on the impact of widely studied CYP1A1 and CYP1A2 SNPs and their complex interaction with non-genetic factors like smoking and caffeine intake on multiple clinical phenotypes. Finally, we attempted to discuss the alterations in metabolism/physiology concerning the polymorphic CYP1A genes, which may underlie the reported clinical associations. This knowledge may provide insights into the disease pathogenesis, risk stratification, response to therapy and potential drug targets for individuals with certain CYP1A genotypes.

Homozygotes NAT2*5B slow acetylators are highly associated with hepatotoxicity induced by anti-tuberculosis drugs

BACKGROUND

Distinct N-acetyltransferase 2 (NAT2) slow acetylators genotypes have been associated with a higher risk to develop anti-tuberculosis drug-induced hepatotoxicity (DIH). However, studies have not pointed the relevance of different acetylation phenotypes presented by homozygotes and compound heterozygotes slow acetylators on a clinical basis.

OBJECTIVES

This study aimed to investigate the association between NAT2 genotypes and the risk of developing DIH in Brazilian patients undergoing tuberculosis treatment, focusing on the discrimination of homozygotes and compound heterozygotes slow acetylators.

METHODS/FINDINGS

The frequency of NAT2 genotypes was analysed by DNA sequencing in 162 patients undergoing tuberculosis therapy. The mutation analyses revealed 15 variants, plus two new NAT2 mutations, that computational simulations predicted to cause structural perturbations in the protein. The multivariate statistical analysis revealed that carriers of NAT2*5/*5 slow acetylator genotype presented a higher risk of developing anti-tuberculosis DIH, on a clinical basis, when compared to the compound heterozygotes presenting NAT2*5 and any other slow acetylator haplotype [aOR 4.97, 95% confidence interval (CI) 1.47-16.82, p = 0.01].

CONCLUSION

These findings suggest that patients with TB diagnosis who present the NAT2*5B/*5B genotype should be properly identified and more carefully monitored until treatment outcome in order to prevent the occurrence of anti-tuberculosis DIH.

Association of N-acetyltransferases 1 and 2 Polymorphisms with Susceptibility to Head and Neck Cancers-A Meta-Analysis, Meta-Regression, and Trial Sequential Analysis

Background and objective:N-acetyltransferases 1 and 2 (NAT1 and NAT2) genes have polymorphisms in accordance with slow and rapid acetylator phenotypes with a role in the development of head and neck cancers (HNCs). Herein, we aimed to evaluate the association of NAT1 and NAT2 polymorphisms with susceptibility to HNCs in an updated meta-analysis. Materials and methods: A search was comprehensively performed in four databases (Web of Science, Scopus, PubMed/Medline, and Cochrane Library until 8 July 2021). The effect sizes, odds ratio (OR) along with 95% confidence interval (CI) were computed. Trial sequential analysis (TSA), publication bias and sensitivity analysis were conducted. Results: Twenty-eight articles including eight studies reporting NAT1 polymorphism and twenty-five studies reporting NAT2 polymorphism were involved in the meta-analysis. The results showed that individuals with slow acetylators of NAT2 polymorphism are at higher risk for HNC OR: 1.22 (95% CI: 1.02, 1.46; p = 0.03). On subgroup analysis, ethnicity, control source, and genotyping methods were found to be significant factors in the association of NAT2 polymorphism with the HNC risk. TSA identified that the amount of information was not large enough and that more studies are needed to establish associations. Conclusions: Slow acetylators in NAT2 polymorphism were related to a high risk of HNC. However, there was no relationship between NAT1 polymorphism and the risk of HNC.

Polygenic Panels Predicting the Susceptibility of Multiple Upper Aerodigestive Tract Cancer in Oral Cancer Patients

Head and neck cancer was closely related with habitual use of cigarette and alcohol. Those cancer patients are susceptible to develop multiple primary tumors (MPTs). In this study, we utilized the single nucleotide polymorphisms (SNPs) array (Affymetrix Axion Genome-Wide TWB 2.0 Array Plate) to investigate patients' risks of developing multiple primary cancers. We recruited 712 male head and neck cancer patients between Mar 1996 and Feb 2017. Two hundred and eighty-six patients (40.2%) had MPTs and 426 (59.8%) had single cancer. Four hundred and twelve normal controls were also recruited. A list of seventeen factors was extracted and ten factors were demonstrated to increase the risks of multiple primary cancers (alcohol drinking, rs118169127, rs149089400, rs76367287, rs61401220, rs141057871, rs7129229, older age, rs3760265, rs9554264; all were p value < 0.05). Polygenic scoring model was built and the area under curve to predict the risk developing MPTs is 0.906. Alcohol drinking, among the seventeen factors, was the most important risk factor to develop MPT in upper aerodigestive tract (OR: 7.071, 95% C.I.: 2.134-23.434). For those with high score in polygenic model, routine screening of upper digestive tract including laryngoscope and esophagoscope is suggested to detect new primaries early.

Analytical Study of Etiopathological Factors Responsible for Oral Squamous Cell Cancer in Bihar Population

Background

Squamous cell carcinoma (SCC) of maxillofacial region is the most usual form of neoplasia causing malignancies in India and Asian continent. An increased prevalence of mortality rate by cancer of maxillofacial region was observed in various parts of the world.

Objectives

Our aim was to correlate age and gender with etiopathological factors contributing to oral squamous cell carcinoma (OSCC) in the urban population of Patna in 2 years.

Materials and Methods

Data were extracted from hospital records. A total of 236 cases of histologically confirmed mild to advance stage of OSCC in either gender of 15-80 years of age range were evaluated.

Results

Out of 236 histopathologically confirmed patients with OSCC, 172 were male and 64 were female. Insignificant difference was found in all age-groups and in all locations. Most common site was found to be buccal mucosa in both genders. Bony invasion was found to be least common. In our study, it was found that habits of chewing areca nuts, nicotine smoke addiction, consumption of alcohol, combination of chewing nuts and nicotine smoke addiction, and combination of alcohol and nicotine smoke addiction are significantly related to the development of OSCC. No significant association was found between histopathological conclusion and gender in all the four groups, and the prevalence was directly proportional to advancement of age.

Conclusion

We concluded that the OSCC do not have any significant relation with the age and gender. The habit of nicotine and areca nut chewing, nicotine smoke addiction, and combination of nicotine smoke addiction and alcohol and chewing nut and nicotine smoke addiction has significant relationship in the development of OSCC.

Glutathione S-transferasesP1 AA (105Ile) allele increases oral cancer risk, interacts strongly with c-Jun Kinase and weakly detoxifies areca-nut metabolites

The Glutathione S-transferases (GSTs) protects cellular DNA against oxidative damage. The role of GSTP1 polymorphism (A313G; Ile105Val) as a susceptibility factor in oral cancer was evaluated in a hospital-based case-control study in North-East India, because the habit of chewing raw areca-nut (RAN) with/without tobacco is common in this region. Genetic polymorphism was investigated by genotyping 445 cases and 444 controls. Individuals with the GSTP1 AA-genotype showed association with the oral cancer (OR = 3.1, 95% CI = 2.4–4.2, p = 0.0002). Even after adjusting for age, sex and habit the AA-genotype is found to be significantly associated with oral cancer (OR = 2.4, 95% CI = 1.7–3.2, p = 0.0001). A protein-protein docking analysis demonstrated that in the GG-genotype the binding geometry between c-Jun Kinase and GSTP1 was disrupted. It was validated by immunohistochemistry in human samples, showing lower c-Jun-phosphorylation and down-regulation of pro-apoptotic genes in normal oral epithelial cells with the AA-genotype. In silico docking revealed that AA-genotype weakly detoxifies the RAN/tobacco metabolites. In addition, experiments revealed a higher level of 8-Oxo-2′-deoxyguanosine induction in tumor samples with the AA-genotype. Thus, habit of using RAN/tobacco and GSTP1 AA-genotype together play a significant role in predisposition to oral cancer risk by showing higher DNA-lesions and lower c-Jun phosphorylation that may inhibit apoptosis.

Multiple logistic regression analysis predicts cancer risk among tobacco usage with glutathione S-transferase p1 genotyping in patients with head and neck cancer

INTRODUCTION

Numerous studies have been investigated to understand the association between glutathione S-transferase P1 (GSTP1) polymorphism and risk of head and neck cancer (HNC) but yielded contradictory results, and no studies could confirm polymorphism in GSTP1 and that tobacco usage increases the risk of HNCs. Therefore, this study aimed to understand the association of GSTP1 Ile105Val polymorphism with or without tobacco usage in carcinogenesis and clinicopathological characteristics of patients with HNC.

MATERIALS AND METHODS

Binary logistic regression analysis was performed to predict HNC risk with tobacco use and GSTP1 genotyping. Five predictor variables such as gender, age, tobacco usage, familial, and GSTP1 genotypes were included in the model.

RESULTS

The results of the logistic regression analysis show that the full model which considered all the five independent variables together was statistically significant, log-likelihood = -111.820, and all slopes are zero: G = 74.297, degree of freedom (DF) = 5, P = 0.000. The strongest predictor in this model is tobacco usage (odds ratio = Z = -5.16, P = 0.000).

CONCLUSION

The study concludes that multiple logistic regression analysis model could predict the risk factors in case-control studies where control samples are compromised.

The multifaceted role of glutathione S-transferases in cancer

Glutathione S-transferases (GSTs) are phase II detoxifying enzymes involved in the maintenance of cell integrity, oxidative stress and protection against DNA damage by catalyzing the conjugation of glutathione to a wide variety of electrophilic substrates. Though enzymes of the glutathione synthesis and salvage pathways have been well characterized in the past, there is still a lack of comprehensive understanding of their independent and coordinate regulatory mechanisms in carcinogenesis. The present review discusses implication of GST in cancer development and progression, gene polymorphism, drug resistance, signaling and epigenetic regulation involving their role in cancer. It is anticipated that GST especially the GSTP1 class can be developed as a biomarker either used alone or in combination with other biomarkers for early cancer detection and/or diagnosis as well as for future targeted preventive and therapeutic interventions with dietary agents.

Association of cytochrome P450 1B1 haplotypes with head and neck cancer risk

Genetic polymorphisms have been reported in several cytochrome P450 (CYP) genes, including CYP1B1 which metabolically activates procarcinogens present in tobacco to carcinogenic intermediates. This study used a case-control approach in North Indian population to determine associations between genetic variants in CYP1B1 and risk of Head and Neck Squamous Cell Carcinoma (HNSCC). We examined the genotype and haplotype frequencies at various single-nucleotide polymorphisms (SNPs), including SNPs previously reported in the promoter region and intron 1 of CYP1B1 in Caucasians. Using cycle sequencing, 9 SNPs were identified in the promoter region, intron 1, and exons 2 and 3. Haplotype analysis revealed that 5 SNPs (those in the promoter region, intron, and Arg48Gly and Ala119Ser in exon 2) were in strong linkage disequilibrium (LD). Cases with the T-A-T-G-T haplotype were significantly associated with increased risk of HNSCC. Interestingly, qRT-PCR studies revealed a significant increase in mRNA expression of CYP1B1 in peripheral blood isolated from cases with the T-A-T-G-T haplotype compared with cases with the C-G-C-C-G haplotype, and in cases compared to controls for both main haplotypes. The data thus provide evidence that CYP1B1 haplotypes could be more effective in predicting HNSCC risk. Environ. Mol. Mutagen. 58:443-450, 2017. © 2017 Wiley Periodicals, Inc.

GSTM1 polymorphism is related to risks of nasopharyngeal cancer and laryngeal cancer: a meta-analysis

Background

Accumulating data have reported that GSTM1 polymorphism may be related to nasopharyngeal cancer (NPC) and laryngeal cancer (LC). This meta-analysis was performed to investigate the relationship between GSTM1 polymorphism and risks of NPC and LC.

Methods

Pubmed, Embase, and China National Knowledge Infrastructure (CNKI) databases were searched for potential articles. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to evaluate the relationship of GSTM1 polymorphism with the risks of NPC and LC. I²>50% or P<0.05 indicates significant heterogeneity. When heterogeneity existed, the random-effects model was used to pool data, otherwise, the fixed-effects model was adopted. Publication bias was detected by Begg’s funnel plot and Egger’s regression. Quality of each study was evaluated by Newcastle-Ottawa Scale.

Results

Thirty-two eligible articles were included. Pooled outcome suggested the significant relationship of GSTM1 null genotype with increased risk of LC (OR =1.28, 95% CI =1.05–1.54). Compared with hospital-based (HB) population, GSTM1 null genotype was also related to increased risk of LC (OR =1.38, 95% CI =1.06–1.80). Positive relationship of GSTM1 null genotype with enhanced risk of NPC was observed (OR =1.43, 95% CI =1.26–1.63). A similar trend was also observed in the subgroup analysis by source of control (population-based [PB]: OR =1.39, 95% CI =1.18–1.63; HB: OR =1.52, 95% CI =1.22–1.89).

Conclusion

GSTM1 null genotype is related to increased risk of NPC and LC.

Does CYP2E1 RsaI/PstI polymorphism confer head and neck carcinoma susceptibility?: A meta-analysis based on 43 studies

BACKGROUND

Previous reports showed that CYP2E1 RsaI/PstI polymorphism may be a risk factor for cancers. Published meta-analyses in 2010 and 2011, respectively, on the relationship of CYP2E1 RsaI/PstI polymorphisms with the susceptibility to head and neck carcinoma (HNC) have generated inconsistent results. Thus, this study aimed to conduct an updated meta-analysis involving published studies up to Nov 2015 to get a more confidential result.

METHODS

Eligible studies up to Nov 2015 were retrieved and screened. Data were extracted and a quantitative meta-analysis was conducted. Subgroup analyses on ethnicity, source of controls, sample size, genotyping method, smoking status, and drinking status were also performed.

RESULTS

Forty-one publications including a total of 43 case-control studies were selected for analysis. The overall data under a homozygote comparison model indicated a significant association of CYP2E1 RsaI/PstI polymorphisms with HNC risk (c2c2 vs c1c1: odds ratio [OR] = 1.97; 95% confidence interval [CI] = 1.53-2.53). Similar results were observed in the Asian subgroup (c2c2 vs c1c1: OR = 1.98; 95%CI = 1.51-2.60; c2 vs c1: OR = 1.20; 95%CI = 1.03-1.39) and mixed population (c2 vs c1: OR = 1.41; 95%CI = 1.06-1.86) when the data were stratified by ethnicities. Interestingly, increased cancer risk only was shown among never-smokers (c2c2+c1c2 vs c1c1: OR = 1.44; 95%CI = 1.05-1.98) but not ever-smokers.

CONCLUSION

CYP2E1 RsaI/PstI polymorphisms may modify the susceptibility to HNC, particularly among Asians, mixed population, and never-smokers. Future large and well-designed studies are needed to verify this conclusion.

The association of the CYP1A1 Ile462Val polymorphism with head and neck cancer risk: evidence based on a cumulative meta-analysis

Objective

The aim of this study was to address the association between the Ile462Val polymorphism in the gene encoding cytochrome P450 1A1 (CYP1A1) and the risk of head and neck cancer (HNC).

Materials and methods

The Medline/PubMed, EMBASE, and Web of Science databases were searched. The strength of the association was evaluated by calculating the odds ratio (OR) with a 95% confidence interval (CI).

Results

Overall, we observed an increased risk of HNC in patients with the Ile/Val+Val/Val genotype compared to those with the Ile/Ile genotype among the 6,367 cases and 6,395 controls evaluated in the 34 eligible studies, with a pooled OR of 1.284 (95% CI: 1.119–1.473). In addition, we observed an increased risk of HNC in patients with the Ile/Val+Val/Val genotype compared to those with the Ile/Ile genotype in the subgroup analyses (OR =1.362, 95% CI: 1.102–1.685 for laryngeal cancer; OR =1.519, 95% CI: 1.253–1.843 for pharyngeal cancer; OR =1.371, 95% CI: 1.111–1.693 for Asians; and OR =1.329, 95% CI: 1.138–1.551 for patients in studies using hospital-based controls).

Conclusion

This cumulative meta-analysis suggests that the CYP1A1 Ile462Val polymorphism might contribute to the risk of HNC, particularly for pharyngeal cancer and laryngeal cancer.

CYP1A1 rs1048943 and rs4646903 polymorphisms associated with laryngeal cancer susceptibility among Asian populations: a meta-analysis

Many studies have investigated the association between CYP1A1 rs1048943 and rs4646903 polymorphisms and laryngeal cancer risk, but their results have been inconsistent. The PubMed and CNKI were searched for case–control studies published up to 01 July 2015. Data were extracted and pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated. In this meta‐analysis, we assessed 10 published studies involving comprising 748 laryngeal cancer cases and 1558 controls of the association between CYP1A1 rs1048943 and rs4646903 polymorphisms and laryngeal cancer risk. For CYP1A1 rs1048943 of the homozygote G/G and G allele carriers (A/G + G/G) versus A/A, the pooled ORs were 1.77 (95% CI = 1.28–2.81, P = 0.007 for heterogeneity) and 1.86 (95% CI = 1.45–2.40, P = 0.000 for heterogeneity). For CYP1A1 rs4646903 of the homozygote G/G and G allele carriers (A/G + G/G) versus A/A, the pooled ORs were 1.53 (95% CI = 1.31–2.21, P = 0.012 for heterogeneity) and 1.33(95% CI = 1.04–1.71, P = 0.029 for heterogeneity). In the stratified analysis by ethnicity, the significantly risks were found among Asians for both the G allele carriers and homozygote G/G. However, no significant associations were found in Caucasian population all genetic models. These results from the meta‐analysis suggest that CYP1A1 rs1048943 and rs4646903 polymorphisms contribute to risk of laryngeal cancer among Asian populations.

Association between CYP1A1 Ile462Val Polymorphism and Oral Squamous Cell Carcinoma Susceptibility: Evidence from 13 Investigations

CYP1A1 Ile462Val polymorphism might play a key role in pathogenesis of oral squamous cell carcinoma (OSCC). Many case-control studies have investigated the association between CYP1A1 Ile462Val polymorphism and OSCC susceptibility. However, the conclusions are inconsistent. To aim a convincible conclusion, we carried out a meta-analysis to systematically evaluate the association of CYP1A1 Ile462Val polymorphism with OSCC susceptibility. We searched Pubmed, Web of Science, Ovid and Embase databases for available publications. The odds ratio (OR) with the corresponding 95% confidence interval (95% CI) was carried out to estimate the association. A total of 13 papers including 1468 cases and 2183 controls were included, a significant increased OSCC risk was observed in recessive model (OR=1.64, 95% CI=1.08-2.49), but not other genetic models. Our results suggest that the homozygous variant of CYP1A1 Ile462Val might be a risk factor of OSCC.

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

The polymorphism of CYP2E1 Rsa I/Pst I gene and susceptibility to respiratory system cancer: a systematic review and meta-analysis of 34 studies

The purpose of this articles is to determine whether the cytochrome P450 2E1 (CYP2E1) Rsa I/Pst I gene polymorphism is correlated with respiratory system cancers. Respiratory system cancers included lung cancer, laryngeal cancer, nasopharyngeal cancer, and cancers of other respiratory organs, which are the most common malignant tumors worldwide; the significant relationship between CYP2E1 Rsa I/Pst I gene polymorphism and some respiratory system cancer have been reported, but results of some other studies are controversial. The pooled odds ratio (OR) with 95% confidence interval (CI) was calculated to assess the association. PubMed, EMBASE, Cochrane Library Databases, China National Knowledge Infrastructure, and Wanfang Database (up to July 20, 2014) were searched for all case-control studies those mainly studied the relationship between CYP2E1 Rsa I/Pst I gene polymorphism and the susceptibility of respiratory system cancer. A total of 332 articles were collected, among which 34 studies that involved 7028 cases and 9822 controls fulfilled the inclusion criteria after being assessed by 2 reviewers. When stratified by cancer site, the C2/C2 polymorphism could increase the risk of nasopharyngeal cancer under the homozygote model (C2C2 vs C1C1: OR = 1.85, 95% CI = 1.20-2.85, P = 0.005) and recessive model (C2C2 vs C1C2/C1C1: OR = 1.89, 95% CI = 1.23-2.89, P = 0.003). Protection effect was found in lung cancer in heterozygote model (C1C2 vs C1C1: OR = 0.82, 95% CI = 0.74-0.91, P < 0.001), dominant model (C1C2/C2C2 vs C1C1: OR = 0.83, 95% CI = 0.76-0.90, P < 0.001), and allele contrast model (C2 vs C1: OR = 0.85, 95% CI = 0.73-1.00, P = 0.045). With regard to ethnicity subgroup analysis, there was significant association in Asian population in heterozygote model (C1C2 vs C1C1: OR = 0.85, 95% CI = 0.78-0.94, P = 0.001), dominant model (C1C2/C2C2 vs C1C1: OR = 0.88, 95% CI = 0.81-0.95, P = 0.001), and recessive model (C2C2 vs C1C2/C1C1: OR = 1.25, 95% CI = 1.01-1.53, P = 0.036). CYP2E1 Rsa I/Pst I gene polymorphism may reduce the risk of respiratory system cancer. Furthermore, significant association was also found in Asian populations.

Meta-analyses of the effect of CYP1A1 and CYP2D6 polymorphisms on the risk of head and neck squamous cell carcinoma

BACKGROUND

CYP1A1 and CYP2D6 are important genes encoding enzymes involved in the metabolism of toxic chemicals and carcinogens. However, inconclusive results for the association between CYP1A1 and CYP2D6 polymorphisms and the risk of head and neck squamous cell carcinoma (HNSCC) have been reported. We conducted a meta-analysis to evaluate the association of CYP1A1 and CYP2D6 polymorphisms with the risk of HNSCC.

METHODS

A database search yielded 19 relevant studies. 3 polymorphisms were included in the meta-analysis: CYP1A1, CYP2D6*4 and CYP2D6*10. Random or fixed effect models were used in the analysis.

RESULTS

The CYP1A1 polymorphism was associated with HNSCC (for m1m1 vs. m1m2: odds ratio (OR) = 1.26, 95% confidence interval (CI) = 1.030-1.542, pheterogeneity = 0.025; for the recessive model: OR = 1.316, 95% CI = 1.065-1.625, pheterogeneity = 0.001). The analysis showed evidence for association between the CYP2D6*4 polymorphism and HNSCC in Asian populations; however, negative results were also observed in other models. A significant association was also observed between CYP2D6*10 polymorphism and HNSCC risk.

CONCLUSIONS

The current study demonstrates that the CYP1A1 and CYP2D6 polymorphisms are associated with susceptibility to both development and progression of HNSCC.

Polymorphisms in drug-metabolizing enzymes and risk to head and neck cancer: evidence for gene-gene and gene-environment interaction

A case-control study involving 750 cases with squamous-cell carcinoma of the head and neck (HNSCC) and an equal number of healthy controls was initiated to investigate the association of polymorphisms in the drug metabolizing genes cytochrome P450 1A1 (CYP1A1), CYP1B1, CYP2E1 and glutathione S-transferase M1 (GSTM1) with the risk of developing cancer. Attempts were also made to identify the role and nature of gene-gene and gene-environment interactions in modifying the susceptibility to HNSCC. Polymorphisms in drug metabolizing CYPs or GSTM1 showed modest associations with cancer risk. However, cases carrying haplotypes with variant alleles of both CYP1A1*2A and *2C or CYP1B1*2 and *3 or CYP2E1*5B and *6 were at significant risk of developing HNSCC. Likewise, cases carrying a combination of variant genotypes of CYPs and GSM1 (null) were at higher risk (up to 5-fold) of developing HNSCC. HNSCC risk also increased several-fold in cases carrying variant genotypes of CYPs who were regular tobacco smokers (8-18-fold), tobacco chewers (3-7-fold), or alcohol users (2-4-fold). Statistical analysis revealed a more than multiplicative interaction between combinations of the variant genotypes of CYPs and GSTM1 (null) and between variant genotypes and tobacco smoking or chewing or alcohol consumption, in both case-control and case-only designs. The data thus suggest that although polymorphisms in carcinogen-metabolizing CYPs may be a modest risk factor for developing HNSCC, gene-gene, and gene-environment interactions play a significant role in modifying the susceptibility to HNSCC.

N-acetyltransferase 2 genetic variants confer the susceptibility to head and neck carcinoma: evidence from 23 case-control studies

Previous evidence indicated that N-acetyltransferase 2 (NAT2) polymorphisms might be a risk factor for several cancers. A number of studies have been conducted on the association between NAT2 polymorphisms and head and neck cancer (HNC) risk. Nevertheless, the results were conflicting. Published meta-analysis on this issue has generated inconclusive results. Thus, we aimed to derive a more precise estimation of the relationship by conducting an updated meta-analysis. Published data prior to August 2013 have been searched and screened. Subgroup analysis on ethnicity, source of controls, sample size, and genotyping method were also performed. As a result, a total of 23 case-control studies including 4,028 cases and 4,872 controls were selected for analysis. Interestingly, the results showed that NAT2 polymorphisms might increase HNC risk for the overall data (OR 1.23, 95% CI 1.01-1.49). Moreover, in subgroup analyses according to ethnicity, data showed that slow acetylators might increase HNC susceptibility among Asians (OR 1.78, 95% CI 1.27-2.49), but not among Caucasians or mixed ethnicities. In conclusion, NAT2 polymorphism might be a low-penetrant risk factor for HNC among Asians.

Polymorphisms in the human cytochrome P450 and arylamine N-acetyltransferase: susceptibility to head and neck cancers

The occurrence of head and neck cancer (HNC) is associated with smoking and alcohol drinking. Tobacco smoking exposes smokers to a series of carcinogenic chemicals. Cytochrome P450 enzymes (CYP450s), such as CYP1A1, CYP1B1, and CYP2D6, usually metabolize carcinogens to their inactive derivatives, but they occasionally convert the chemicals to more potent carcinogens. In addition, via CYP450 (CYP2E1) oxidase, alcohol is metabolized to acetaldehyde, a highly toxic compound, which plays an important role in carcinogenesis. Furthermore, two N-acetyltransferase isozymes (NATs), NAT1 and NAT2, are polymorphic and catalyze both N-acetylation and O-acetylation of aromatic and heterocyclic amine carcinogens. Genetic polymorphisms are associated with a number of enzymes involved in the metabolism of carcinogens important in the induction of HNC. It has been suggested that such polymorphisms may be linked to cancer susceptibility. In this paper, we select four cytochrome P450 enzymes (CYP1A1, CYP1BA1, CYP2D6, and CYP2E1), and two N-acetyltransferase isozymes (NAT1 and NAT2) in order to summarize and analyze findings from the literature related to HNC risk by focusing on (i) the interaction between these genes and the environment, (ii) the impact of genetic defect on protein activity and/or expression, and (iii) the eventual involvement of race in such associations.

Polymorphic variation of CYP1A1 and CYP1B1 genes in a Haryana population

Cytochrome P450 (CYP) 1A1 and CYP1B1 are important phase I xenobiotic metabolizing enzymes involved in the metabolism of numbers of toxins, endogenous hormones, and pharmaceutical drugs. Polymorphisms in these phase I genes can alter enzyme activity and are known to be associated with cancer susceptibility related to environmental toxins and hormone exposure. Their genotypes may also display ethnicity-dependent population frequencies. The present study was aimed to determine the frequencies of commonly known functional polymorphisms of CYP1A1 and CYP1B1 genes in a Haryana state population of North India. The allelic frequency of CYP1A1 polymorphism m1 (MspI) was 29.65% and m2 (Ile(462)Val) was 24.85%. The frequency of CYP1B1 polymorphism m1 (Val(432)Leu) was 45.85% and m2 (Asn(453)Ser) was 16.2%. We observed inter- and intra-ethnic variation in the frequency distribution of these polymorphisms. Analysis of polymorphisms in these genes might help in predicting the risk of cancer. Our results emphasize the need for more such studies in high-risk populations.

Functional CYP1A1 genetic variants, alone and in combination with smoking, contribute to development of head and neck cancers

CYP1A1 plays an essential role in pathogenesis of head and neck cancers. Functional CYP1A1 Ile462Val and MspI single nucleotide polymorphisms (SNP) are considered to have significant effects on risk of head and neck cancers. Several case-control studies have examined how these genetic polymorphisms are involved in development of this group of malignancies, but the conclusions are inconsistent. Therefore, we conducted this meta-analysis to systematically examine the associations between these functional genetic variants and head and neck cancer risk. A total of 28 studies are eligible for CYP1A1 Ile462Val SNP (4639 patients and 4701 controls), and 22 studies for MspI SNP (4168 patients and 4638 controls). Pooled odds ratios (ORs) and the 95% confidence interval (95% CI) were appropriately calculated using either fixed-effect model or random-effect model. There was no association between Ile462Val polymorphism and head and neck cancer risk (OR = 1.23, 95% CI = 0.99-1.53, P = 0.062). However, in a stratified analysis, a statistically significant correlation between this SNP and pharyngeal cancer risk was observed (OR = 1.76, 95% CI = 1.32-2.33, P < 0.001). For MspI SNP, our data indicated that carriers of TC and CC genotypes had a 34% increased risk to develop head and neck cancers compared to TT carriers (95% CI = 1.15-1.57, P < 0.001). This effect was even more pronounced in smokers (OR = 2.98, 95% CI = 1.69-5.26, P < 0.001), demonstrating that gene-smoking interaction intensifying carcinogenesis may exist. These findings reveal that the functional CYP1A1 MspI genetic variant, alone and in combination with smoking, plays a more important role in pathogenesis of head and neck cancers.

Glutathione S-transferase P1 Ile105Val polymorphism and oral cancer risk: a meta-analysis

Objective The glutathione S-transferase P1 (GSTP1) gene has been suggested to play an important role in the pathogenesis of oral cancer. However, the results have been inconsistent. In this study, we performed a meta-analysis to clarify the association of GSTP1 Ile105Val polymorphisms with oral cancer risk. Methods Published literature from PubMed and EMBASE were retrieved. Pooled odds ratio (OR) with 95% confidence interval (CI) was calculated using fixed- or random-effects model. Results 13 studies (1803 oral cancer cases and 2998 controls) for GSTP1 Ile105Val polymorphism were included in the meta-analysis. The results indicated that there was no significant association between GSTP1 Ile105Val polymorphism and oral cancer in the overall population (OR=1.30, 95%CI=0.92-1.38, I(2)=48.0%, p for heterogeneity=0.027). Further subgroup analysis by ethnicity suggested that GSTP1 Ile105Val polymorphism was significantly associated with oral cancer only in East Asians (OR=1.64, 95%CI=1.16-2.31, I(2)=0.0%, p for heterogeneity=0.525), but not in Caucasians (OR=1.16, 95%CI=0.73-1.82, I(2)=7.5%, p for heterogeneity=0.299), Africans (OR=1.10, 95%CI=0.37-3.28), South Asians (OR=1.20, 95%CI=0.69-2.08, I(2)=74.3%, p for heterogeneity=0.021) and mixed population (OR=0.91, 95%CI=0.70-1.20, I(2)=39.7%, p for heterogeneity=0.174). Conclusions The present meta-analysis has limited evidence to support the association of GSTP1 Ile105Val polymorphism with HCC risk in the overall population. However, GSTP1 Ile105Val polymorphism might be associated with risk of oral cancer in East Asians.

Association of GSTP1 Ile105Val polymorphism and risk of head and neck cancers: a meta-analysis of 28 case-control studies

BACKGROUND AND AIMS

The Glutathione S-transferase P1 (GSTP1) polymorphism have been considered a risk modifier for developing head and neck cancer (HNC) in many studies; however, the results of such studies are inconsistent. The aim of this study was to evaluate the possible association between the GSTP1 Ile105Val polymorphism and risk of HNC.

METHOD

We performed a search in the relevant electronic database and a meta-analysis based on 28 published case-control studies that included 6,404 cases and 6,523 controls. To take into account the possibility of heterogeneity across the studies, a Chi-square based I(2)-statistic test was performed. Crude pooled odds ratios (ORs) with 95% confidence intervals (CIs) were assessed using both fixed-effects and random-effects models.

RESULTS

The results of this meta-analysis showed that the GSTP1 Ile105Val polymorphism was not significantly associated with risk of HNC in the overall study population (pooled OR 1.00, 95% CI 0.92-1.09) or in subgroup analyses stratified by ethnicity, sample size, tumor site or publication year. Moreover, substantial evidence of heterogeneity among the studies was observed. Publication year was identified as the main cause of heterogeneity.

CONCLUSION

This meta-analysis does not support a significant association between the GSTP1 Ile105Val polymorphism and risk of HNC.

Association between GSTM1 and GSTT1 allelic variants and head and neck squamous cell cancinoma

Backgrounds

GSTM1 and GSTT1 are involved in the detoxification of carcinogens such as smoking by-products, and polymorphisms in these two genes with a result of loss of enzyme activity may increase risk of carcinogenesis. Although many epidemiological studies have investigated the association between GSTM1 or GSTT1 null genotype and head and neck squamous cell carcinoma (HNSCC), the results remain conflicting. To elucidate the overall association of GSTM1, GSTT1 and HNSCC, we included all available studies and performed this meta-analysis.

Methodology/Principal Findings

A dataset including 42 articles for GSTM1, 32 articles for GSTT1, and 15 articles for GSTM1 and GSTT1 in combination were identified by a search in PubMed. Associations beween HNSCC and polymorphisms of GSTM1 and GSTT1 alone and in combination were analysed by software RevMan 5.1. Stratification analysis on ethnicity and smoking status, sensitivity analysis, heterogeneity among studies and their publication bias were also tested. Association was found in overall analysis between HNSCC and GSTM1 and GSTT1 null genotype. Stratified by ethnicity, we found increased risks of HNSCC in carriers with GSTM1 null genotype in Asian, GSTT1 null genotype in South American, and dual null genotype in European and Asian. When stratified by smoking, a more significant association of GSTM1 null genotype with HNSCC risk was observed in smokers.

Conclusions/Significance

This meta-analysis presented additional evidence of the association between GSTM1 and GSTT1 polymorphisms and HNSCC risk.

Quantitative assessment of the association between GSTM1 null genotype and laryngeal cancer risk

Previous studies investigating the association between glutathione S-transferase M1 (GSTM1) null genotype and laryngeal cancer risk reported controversial results. Thus, a meta-analysis was performed to clarify the effect of GSTM1 null genotype on laryngeal cancer risk. A literature search was performed for all possible studies. We estimated summary odd ratio (OR) with its 95 % confidence interval (95 % CI) to assess the association. Subgroup analyses were performed by ethnicity or the sample size. 24 individual case-control studies involving a total of 2,809 laryngeal cancer cases and 4,478 controls were finally included into this meta-analysis. Meta-analyses of total 24 studies showed the GSTM1 null genotype was significantly associated with increased laryngeal cancer risk (random-effects OR = 1.44, 95 % CI 1.19-1.73, P < 0.001). Subgroup analyses by ethnicity showed that the GSTM1 null genotype was associated with increased laryngeal cancer risk in both Caucasians (fixed-effects OR = 1.17, 95 % CI 1.04-1.33, P = 0.012) and Asians (random-effects OR = 1.89, 95 % CI 1.28-2.77, P = 0.001). Also, subgroup analyses by sample size also further identified this association above. The cumulative meta-analyses showed a trend of more obvious association between GSTM1 null genotype and increased risk of laryngeal cancer as information accumulated by year. Meta-analysis of available data suggests that GSTM1 null genotype contributes to increased laryngeal cancer risk in both Caucasians and East Asians.

Glutathione S-transferase M1 gene polymorphism and laryngeal cancer risk: a meta-analysis

BACKGROUND AND OBJECTIVES

Studies investigating the association between glutathione S-transferase M1 (GSTM1) gene polymorphism and laryngeal cancer risk have reported conflicting results. The aim of the present study was to conduct a meta-analysis assessing the possible associations of GSTM1 gene polymorphism with laryngeal cancer risk.

METHODS

The relevant studies were identified through a search of PubMed, Embase, ISI Web of Knowledge and Chinese National Knowledge Infrastructure until May 2011 and selected on the basis of the established inclusion criteria for publications, then a meta-analysis was performed to quantitatively summarize association of GSTM1 polymorphism with laryngeal cancer susceptibility.

RESULTS

Seventeen studies were included in the present meta-analysis (2,180 cases and 2,868 controls). The combined results based on all studies showed that GSTM1 null genotype was associated with increased laryngeal cancer risk (OR = 1.17, 95% CI = 1.04∼1.31). When stratifying for race, GSTM1 null genotype exhibited increased laryngeal cancer risk in Caucasians (OR = 1.15, 95% CI = 1.01∼1.31), while no significant association was detected in Asians (OR = 1.25, 95% CI = 0.80∼1.96). In the subgroup analysis based on source of controls, significant associations were observed in the population-based studies (OR = 1.15, 95% CI = 1.01∼1.31) yet not in the hospital-based studies (OR = 1.25, 95% CI = 0.93∼1.67). Furthermore, in the subgroup analysis based on sample size, significant associations were also found in studies with at least 50 cases and 50 controls (OR = 1.15, 95% CI = 1.02∼1.30) but not in studies with fewer than 50 cases or 50 controls (OR = 1.46, 95% CI = 0.87∼2.46).

CONCLUSIONS

This meta-analysis supported that the GSTM1 gene polymorphism was associated with laryngeal cancer, particularly in Caucasians, and these associations varied in different subgroup, which indicated that population-based study with larger sample size was more appropriate in design of future study.

Cytochrome P450 1A1 Ile462Val polymorphism and oral carcinoma risk: an updated meta-analysis including 1,515 cases and 2,233 controls

Cytochrome P450 (CYP) 1A1 Ile462Val (exon7) polymorphism has been suggested to be a risk factor for several cancers. Published data on its association with oral cancer risk have generated conflicting results. Our previous meta-analysis containing data from prior to Jan 2008 regarding this issue failed to find a significant association between CYP1A1 Ile462Val variation and oral cancer susceptibility. An updated meta-analysis with eligible studies for the period up to May 2012 was conducted. Separate analyses on ethnicity and source of controls were also performed. A total of 13 case-control studies comprising 1,515 cases and 2,233 controls were lastly selected for analysis. Compared with the previous meta-analysis, the overall data also failed to indicate a significant association of CYP1A1 Ile462Val polymorphism with oral cancer risk (Val/Val vs. Ile/Ile--OR = 1.46; 95 % CI = 0.96-2.24; dominant model--OR = 1.01; 95 % CI = 0.81-1.25; and recessive model--OR = 1.46; 95 % CI = 0.96-2.23). However, in the subgroup analysis by ethnicity, increased cancer risk was observed among Asians under the additive and recessive models (Val/Val vs. Ile/Ile--OR = 1.74; 95 % CI = 1.04-2.90 and recessive model-OR = 1.73; 95 % CI = 1.04-2.87), inconsistent with the previous meta-analysis. Collectively, the data of the present study suggest that CYP1A1 variant Val/Val alleles might modify the susceptibility to oral cancer among Asians. Further well-designed investigations with large sample sizes are required to confirm this conclusion.

NAT2 polymorphisms with oral carcinoma susceptibility: a meta-analysis

Published data have implicated NAT2 polymorphisms as risk factors for various cancers. A number of studies have focused on the association of NAT2 polymorphisms with susceptibility to oral carcinoma and have yielded inconclusive results. The aim of the present study was to derive a more precise estimation of the relationship. We first carried out a deliberate search in the databases without a language limitation, covering all papers published up to Dec 2011. A total of seven case-control studies including 1,379 cases and 1,868 controls were selected and the relevant data were extracted for systematic meta-analyses. No significant association was found for the overall data (OR: 1.04, 95 % CI: 0.79-1.39). In subgroup analyses according to ethnicity, slow acetylators might increase oral cancer risk among Asians (OR: 1.38, 95 % CI: 1.04-1.82) but not Caucasians or Mixed races. The data suggested that NAT2 polymorphisms might be a low-penetrant risk factor for oral carcinoma in Asians.

An unlikely role for the NAT2 genotypes and haplotypes in the oral cancer of south Indians

The arylamine N-acetyltransferase 2 (NAT2) enzyme detoxifies a wide spectrum of naturally occurring xenobiotics including carcinogens and drugs. Acetylation catalysed by the NAT2 is an important process in metabolic activation of arylamines to electrophilic intermediates that initiate carcinogenesis. Polymorphism in N-acetyltransferase 2 gene was reported to be associated with the susceptibility of various cancers.

OBJECTIVE

The aim of our study was to determine whether there is any association between the susceptibility to oral cancer amongst the variations of NAT2 genotypes.

DESIGN

This study was carried out in 157 patients with oral cancer. The control group consisted of 132 healthy volunteers. The most common polymorphisms rs1799929, rs1799930 and rs1799931 on the NAT2 gene were screened for the genotypes using TaqMan allelic discrimination.

RESULTS

All the three SNPs were polymorphic with minor allele frequency of 0.339, 0.372 and 0.061 for rs1799929, rs1799930 and rs1799931, respectively. None of the polymorphic site deviated from HWE in controls. There were no significant differences in genotype or allele frequencies of three SNPs between controls and cases with oral cancer. Risk of oral cancer development for the carriers of the individual deduced phenotypes was also not statistically significant. Of the 3 studied polymorphisms, 2 were in strong LD and form one haplotype block. None of the haplotype had shown significant association with the oral cancer.

CONCLUSIONS

Our study concludes that the NAT2 genotypes, phenotypes and haplotypes are not involved in the susceptibility to oral cancer in South Indian subjects.

Association of NAT2 phenotype with risk of head and neck carcinoma: A meta-analysis

N-acetyltransferase 2 (NAT2) is a key enzyme involved in the metabolism of xenobiotics and plays a significant role in the detoxification of numerous potential carcinogens. According to its acetylation status, NAT2 acetylator may be classified into two phenotypes, rapid and slow. Numerous studies have demonstrated that the polymorphisms of NAT2 were correlated with individual susceptibility to several malignant neoplasms, including head and neck carcinomas (HNC). However, the associations between the acetylator phenotypes and HNC risk in each study were not entirely consistent. To assess these associations more comprehensively, we performed a meta-analysis. In this meta-analysis, 16 eligible studies including 2,965 cases with HNC and 3,919 controls were identified by searching the databases of PubMed, Medline and the ISI Web of Knowledge. Odds ratios (ORs) with 95% confidence intervals (95% CIs) were used to evaluate the association. No significant associations between the rapid acetylator phenotype in NAT2 and HNC risk were found either in the overall analysis (OR=0.98; 95% CI 0.83, 1.15; I(2)=57%; P(heterogeneity)=0.003) or in the subgroup analysis by ethnicity (for the Caucasian population, OR=1.03, 95% CI 0.85, 1.24, I(2)=63%, P(heterogeneity)=0.002; for other mixed populations, OR=0.78, 95% CI=0.61, 1.00, I(2)=0%, P(heterogeneity)=0.47). In conclusion, this meta-analysis suggested that there is no association between the NAT2 phenotype and the risk of HNC.

Joint effects of alcohol consumption and polymorphisms in alcohol and oxidative stress metabolism genes on risk of head and neck cancer

BACKGROUND

Single-nucleotide polymorphisms (SNP) in alcohol metabolism genes are associated with squamous cell carcinoma of the head and neck (SCCHN) and may influence cancer risk in conjunction with alcohol. Genetic variation in the oxidative stress pathway may impact the carcinogenic effect of reactive oxygen species produced by ethanol metabolism. We hypothesized that alcohol interacts with these pathways to affect SCCHN incidence.

METHODS

Interview and genotyping data for 64 SNPs were obtained from 2,552 European- and African-American subjects (1,227 cases and 1,325 controls) from the Carolina Head and Neck Cancer Epidemiology Study, a population-based case-control study of SCCHN conducted in North Carolina from 2002 to 2006. We estimated ORs and 95% confidence intervals (CI) for SNPs and haplotypes, adjusting for age, sex, race, and duration of cigarette smoking. P values were adjusted for multiple testing using Bonferroni correction.

RESULTS

Two SNPs were associated with SCCHN risk: ADH1B rs1229984 A allele (OR = 0.7; 95% CI, 0.6-0.9) and ALDH2 rs2238151 C allele (OR = 1.2; 95% CI, 1.1-1.4). Three were associated with subsite tumors: ADH1B rs17028834 C allele (larynx, OR = 1.5; 95% CI, 1.1-2.0), SOD2 rs4342445 A allele (oral cavity, OR = 1.3; 95% CI, 1.1-1.6), and SOD2 rs5746134 T allele (hypopharynx, OR = 2.1; 95% CI, 1.2-3.7). Four SNPs in alcohol metabolism genes interacted additively with alcohol consumption: ALDH2 rs2238151, ADH1B rs1159918, ADH7 rs1154460, and CYP2E1 rs2249695. No alcohol interactions were found for oxidative stress SNPs.

CONCLUSIONS AND IMPACT

Previously unreported associations of SNPs in ALDH2, CYP2E1, GPX2, SOD1, and SOD2 with SCCHN and subsite tumors provide evidence that alterations in alcohol and oxidative stress pathways influence SCCHN carcinogenesis and warrant further investigation.

Possible association of NAT2 polymorphism with laryngeal cancer risk: an evidence-based meta-analysis

PURPOSE

N-acetyltransferase 2 (NAT2) plays an important role in the metabolism of various potential carcinogens, which can be subdivided into rapid and slow acetylation phenotype according to the different genotypes. A number of studies have been devoted to the association of NAT2 polymorphism with susceptibility to laryngeal carcinoma; however, the results were inconsistent and inconclusive. The aim of the present study was to conduct a meta-analysis assessing the possible association of NAT2 polymorphism with laryngeal cancer risk.

METHODS

The relevant studies were identified through a search of PubMed, Embase, ISI Web of Knowledge, and Chinese National Knowledge Infrastructure until February 2011 and selected on the basis of the established inclusion criteria for publications, and then a meta-analysis was performed to quantitatively summarize the association of NAT2 polymorphism with laryngeal cancer susceptibility.

RESULTS

Seven studies were included in the present meta-analysis, which described a total of 980 laryngeal cancer cases and 1,487 controls. The overall odds ratio (OR) for NAT2 slow and rapid acetylators was 0.99 (95% CI = 0.71-1.38) and 1.01 (95% CI = 0.72-1.40), respectively. When stratifying for race, the pooled ORs for NAT2 slow acetylator were 1.99 (95% CI = 1.10-3.63) in Asians and 0.85 (95% CI = 0.62-1.15) in Caucasians, and the pooled ORs for NAT2 rapid acetylator were 0.50 (95% CI = 0.28-0.91) in Asians and 1.18 (95% CI = 0.87-1.60) in Caucasians.

CONCLUSIONS

This meta-analysis suggested that there was overall lack of association between NAT2 polymorphism and laryngeal cancer risk; however, NAT2 slow acetylation may contribute to a risk factor for laryngeal cancer in Asians but not in Caucasians.

CYP2E1 Rsa I/Pst I polymorphism contributes to oral cancer susceptibility: a meta-analysis

Previous data on association between CYP2E1 Rsa I/Pst I polymorphism and oral cancer risk were controversial. To investigate the association between CYP2E1 Rsa I/Pst I polymorphism and oral cancer risk. We performed a meta-analysis to assess the relationship between oral cancer and genotype with English language until June 2010. Twelve published case-control studies of 1259 patients with oral cancer and 2262 controls were acquired. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of the association in codominant and dominant models. Overall, the pooled ORs indicated a significant association between CYP2E1 Rsa I/Pst I polymorphism and oral cancer risk (for c1/c2 vs. c1/c1: OR=1.30, 95% CI=1.04-1.62, Pheterogeneity=0.57; for (c1/c2+c2/c2) vs. c1/c1: OR=1.32, 95% CI=1.07-1.64, Pheterogeneity=0.57, respectively). In subgroup analysis by race, the same significant risks were found among Asian (for c1/c2 vs. c1/c1: OR=1.41, 95% CI=1.05-1.91, Pheterogeneity=0.92; for (c1/c2+c2/c2) vs. c1/c1: OR=1.43, 95% CI=1.08-1.88, Pheterogeneity=0.97, respectively). In conclusion, this meta-analysis demonstrates that CYP2E1 Rsa I/Pst I c2 allele may be a biomarker for oral cancer, especially among Asian populations.

Meta-analyses of the effect of cytochrome P450 2E1 gene polymorphism on the risk of head and neck cancer

Many studies have investigated the association between the CYP2E1 5'-flanking region (RsaI/PstI) polymorphism and head and neck cancer susceptibility, but the results were conflicting. In this meta-analysis, we assessed 24 published studies involving 12,562 subjects of the association between CYP2E1 RsaI/PstI polymorphism and head and neck cancer risk. Using the fixed effects model, we found significant association between PstI/RsaI polymorphism and head and neck cancer risk [OR=1.11 (95%CI: 1.00-1.22) for c2 allele (P=0.04) and OR=1.57 (95% CI: 1.14-2.15) for c2 homozygous (P=0.006) compared with wild type homozygote]. Significant results were also found in East Asians and Mix populations when stratified by ethnicity. However, no significant associations were found for Caucasians in all genetic models. Stratified analyses according to source of controls, significant associations were found only in hospital base controls. In the subgroup analyses by tumor types, significant association was detected only in oral cancer group, while no significant associations among laryngeal- or pharyngeal- cancer subgroup. This meta-analysis suggests that the CYP2E1 RsaI/PstI polymorphism may be a risk factor for head and neck cancer in Asians and Mix population, and that different carcinogenic processes involved in the genesis of various tumor types may exist.

The PstI/RsaI and DraI polymorphisms of CYP2E1 and head and neck cancer risk: a meta-analysis based on 21 case-control studies

BACKGROUND

CYP2E1 encodes a member of the cytochrome P450 superfamily of enzymes which play a central role in activating and detoxifying many carcinogens and endogenous compounds thought to be involved in the development of cancer. The PstI/RsaI and DraI polymorphism are two of the most commonly studied polymorphisms of the gene for their association with risk of head and neck cancer, but the results are conflicting.

METHODS

We performed a meta-analysis using 21 eligible case-control studies with a total of 4,951 patients and 6,071 controls to summarize the data on the association between the CYP2E1 PstI/RsaI and DraI polymorphism and head and neck cancer risk, especially by interacting with smoking or alcohol.

RESULTS

Compared with the wild genotype, the OR was 1.96 (95% CI: 1.33-2.90) for PstI/RsaI and 1.56 (95% CI: 1.06-2.27) for DraI polymorphism respectively. When stratified according to ethnicity, the OR increased in the Asians for both polymorphisms (OR = 2.04, 95% CI: 1.32-3.15 for PstI/RsaI; OR = 2.04, 95% CI: 1.27-3.29 for DraI), suggesting that the risk is more pronounced in Asians.

CONCLUSION

Our meta-analysis suggests that individuals with the homozygote genotypes of PstI/RsaI or DraI polymorphism might be associated with an increased risk of head and neck cancer, especially in Asians.

CYP1A1 and CYP3A4 polymorphic variations in Delhi population of Northern India

Cytochrome P450 (CYP) 1A1 and CYP3A4 are important phase I xenobiotic metabolizing enzymes involved in the metabolism of numbers of toxins, endogenous hormones and pharmaceutical drugs. Polymorphisms in these phase I genes can alter enzyme activity and are known to be associated with cancer susceptibility related to environmental toxins and hormone exposure. Their genotypes may also display ethnicity dependent population frequencies. The present study was aimed to determine the frequencies of commonly known functional polymorphisms of CYP1A1 and CYP3A4 in North Indian population. Allelic frequency of CYP1A1 polymorphisms, m1, m2 and m4 were observed to be 40.3, 31.2 and 0% respectively. Frequency of CYP3A4*1B polymorphism was 0%. We observed inter as well as intra ethnic variation in the distribution of frequency of these polymorphisms. Analysis of polymorphisms in these genes might help in predicting the risk of cancer. Our results emphasize the need for more such studies in "high risk populations".

GSTT1, GSTM1, GSTM3 and NAT2 polymorphisms in laryngeal squamous cell carcinoma in a Greek population

OBJECTIVE

It is well known that laryngeal squamous cell carcinoma is strongly related to tobacco and alcohol consumption. Accumulating evidence suggests that alterations of detoxification enzymes, such as glutathione S-transferases and N-acetyltransferases, influence the risk of cancers associated with tobacco smoke and alcohol.

METHODS

This was a retrospective case-control study. The study group consisted of 88 Greek patients with laryngeal squamous cell carcinoma; there were also 102 control subjects. Frequencies of the genotypes GSTT1, GSTM1, GSTM3 and NAT2 were evaluated by polymerase chain reaction restriction fragment polymorphism.

RESULTS

The distribution of overall genotypes was 55.68 per cent rapid acetylator and 44.32 per cent slow acetylator in patients, and 36.27 per cent rapid acetylator and 63.72 per cent slow acetylator in controls. The odds ratio for rapid acetylator status in cases versus controls was 2.207 (95 per cent confidence interval 1.23-3.95, p = 0.0087).

CONCLUSION

This study demonstrated a significant relationship between rapid acetylator genotypes and laryngeal squamous cell carcinoma in a Greek population.

Oral cancer and polymorphism of ethanol metabolising genes

Oral cancer is the sixth most common cancer worldwide and a major health problem in some parts of the world. Epidemiological studies have shown that habitual alcohol consumption could be a risk factor in oral carcinogenesis, although the true involvement of alcohol is unknown. Via alcohol dehydrogenase (ADH) and cytochrome P450 oxidase (CYP) alcohol is metabolized to acetaldehyde, a highly toxic compound, which plays an important role in carcinogenesis. Subsequently, and during the metabolizing process, acetaldehyde becomes acetate by acetaldehyde dehydrogenase (ALDH). Therefore, acetaldehyde levels are determined mainly by the action of ADH, CYP and ALDH. Recently, several studies have found that certain polymorphisms of genes encoding these enzymes confer a higher or lower metabolic activity and therefore different risk for certain malignancies such as oral cancer. In this review, we analyze the polymorphisms of alcohol metabolising enzymes in relation susceptibility to an oral cancer.

Polymorphism in cytochrome P450 2A6 and glutathione S-transferase P1 modifies head and neck cancer risk and treatment outcome

A case control study was carried out to investigate the association of functionally important polymorphism in cytochrome P450 2A6 (CYP2A6) and glutathione S-transferase P1 (GSTP1) genes with head and neck squamous cell carcinoma (HNSCC) and treatment response in cases receiving a combination of chemo-radiotherapy. The study group consisted of 350 males suffering from HNSCC and an equal number of male controls. Multivariate logistic regression analysis revealed statistically significant decrease in risk to HNSCC in cases with variant genotypes (CYP2A6*1B and CYP2A6*4C) of CYP2A6 (OR: 0.78; 95% CI: 0.43-1.22; P=0.04) or GSTP1 (OR: 0.71; 95% CI: 0.51-1.00; P=0.05). The risk associated with these variant genotypes was found to be further decreased in cases carrying a combination of variant genotypes of CYP2A6 and GSTP1 (OR: 0.40; 95% CI: 0.25-0.65; P=0.00). A similar decrease in risk was observed in cases with variant genotypes of CYP2A6 (OR: 0.59; 95% CI: 0.40-0.86; P=0.00) or GSTP1 (OR: 0.62; 95% CI: 0.42-0.91; P=0.01) and who were regular tobacco users (cigarette smokers or tobacco chewers). Interestingly, only 27% of the cases carrying the variant forms of CYP2A6 (*1A/*4C+*1B/*4C+*4C/*4C) responded to the treatment for HNSCC when compared to those with wild-type genotype (69%). However with GSTP1, cases with homozygous mutant genotype (Val/Val) showed a superior treatment response (75%) when compared to cases with wild-type genotype (25%). Further, cases carrying a combination of variant genotype of CYP2A6 and wild-type genotype of GSTP1 exhibited a very poor treatment response demonstrating that polymorphisms in CYP2A6 and GSTP1 not only modified the risk to HNSCC but also played a major role in determining the chemotherapeutic response.

Polymorphism in cytochrome P4501A1 is significantly associated with head and neck cancer risk

A case control study was undertaken to investigate the association of polymorphisms in cytochrome P4501A1 (CYP1A1) with squamous cell carcinoma of head and neck (HNSCC) in North Indian population. The variant genotypes of CYP1A1*2A and CYP1A1*2C were found to be overrepresented in cases when compared to controls. The HNSCC risk also increased several folds in cases with combination of variant genotypes of CYP1A1*2A or CYP1A1*2C with null genotype of glutathione-S-transferase M1 (GSTM1), a phase II enzyme, particularly in cases who were tobacco users (smokers and tobacco chewers), demonstrating the role of gene-gene and gene-environment interactions in the development of HNSCC.

Polymorphisms of CYP1A1 and GSTM1 and laryngeal cancer risk: evidence-based meta-analyses

PURPOSE

Previous evidence implicates CYP1A1 and GSTM1 polymorphisms as risk factors for various cancers. A number of studies have been devoted to the association of CYP1A1 or GSTM1 polymorphism with susceptibility to laryngeal carcinoma, with the results inconsistent and inconclusive. The aim of the present study was to assess the possible associations of laryngeal cancer risk with CYP1A1 genetic variation and GSTM1 null genotype respectively.

METHODS

The associated literature was acquired through deliberate searching and selected based on the established inclusion criteria for publications, then the extracted data were further analyzed using systematic meta-analyses.

RESULTS

The results showed that the overall odds ratio (OR) was 1.32 (95% CI = 1.08-1.61) for CYP1A1 Mspl polymorphism. Using subgroup analysis, the pooled ORs were 1.38 (95% CI = 0.98-1.95) in Asians and 1.29 (95% CI = 1.01-1.65) in Caucasians. For CYP1A1 exon7 polymorphism, the overall OR was 1.38 (95% CI = 0.98-1.95). The overall OR was 1.24 (95% CI = 1.03-1.49) for GSTM1 polymorphism and the pooled ORs were 1.36 (95% CI = 0.75-2.48) in Asians, 1.16 (95% CI = 0.94-1.44) in Caucasians and 1.52 (95% CI = 1.05-2.19) in Turkey population.

CONCLUSIONS

The data suggest CPY1A1 MspI polymorphism as a risk factor for laryngeal cancer in Caucasians but not in Asians. However, the results suggest a marked correlation of GSTM1 polymorphism with laryngeal cancer risk in Turkey population but not Caucasians and Asians.

Case-control study of oral and oropharyngeal cancer in whites and genetic variation in eight metabolic enzymes

BACKGROUND

Genetic variation in xenobiotic metabolizing enzymes may explain differing susceptibilities to the cancer causing effects of tobacco and alcohol.

METHODS

We compared 203 oral squamous cell carcinoma cases and 416 controls for single nucleotide polymorphisms (SNPs) in 8 genes (CYP1A1, CYP2E1, MPO, mEH, GSTM1, GSTT1, GSTP1, and NAT2). Except for NAT2, genotype frequencies were similar in the 2 groups. We classified subjects as fast or slow NAT2 acetylators genotyping 13 NAT2 SNPs.

RESULTS

Fast acetylators were overrepresented in cases (53.7%) compared with controls (43.9%; odds ratio (OR) 1.55, 95% confidence interval (CI) 1.08-2.20; p value = .03). Gene-gene interaction testing suggested several cancer-NAT2 associations, with association strongest among persons without a CYP1A1 variant (*2C or *4) allele (OR 1.77, 95% CI 1.20-2.60, p value = .03) or with a variant MPO (463A) allele (OR 2.38, 95% CI 1.34-4.21, p value = .05).

CONCLUSION

These results implicate fast NAT2 acetylation as a risk factor for oral cancer.

Meta-analysis and pooled analysis of GSTM1 and CYP1A1 polymorphisms and oral and pharyngeal cancers: a HuGE-GSEC review

The association of GSTM1 and CYP1A1 polymorphisms and oral and pharyngeal cancers was assessed through a meta-analysis of published case-control studies and a pooled analysis of both published and unpublished case-control studies from the Genetic Susceptibility to Environmental Carcinogens database (http://www.upci.upmc.edu/research/ccps/ccontrol/index.html ). Thirty publications used in the meta-analysis included a total of 7783 subjects (3177 cases and 4606 controls); 21 datasets, 9397 subjects (3130 cases and 6267 controls) were included in the pooled analysis. The GSTM1 deletion was 2-fold more likely to occur in African American and African cases than controls (odds ratio: 1.7, 95% confidence interval: 0.9-3.3), although this was not observed among whites (odds ratio: 1.0, 95% confidence interval: 0.9-1.1). The meta-analysis and pooled analysis showed a significant association between oral and pharyngeal cancer and the CYP1A1 MspI homozygous variant (meta-ORm2/m2: 1.9, 95% confidence interval: 1.4-2.7; Pooled ORm2m2: 2.0, 95% confidence interval: 1.3-3.1; ORm1m2 or [infi]m2m2: 1.3, 95% confidence interval: 1.1-1.6). The association was present for the CYP1A1 (exon 7) polymorphism (ORVal/Val: 2.2, 95% confidence interval: 1.1-4.5) in ever smokers. A joint effect was observed for GSTM1 homozygous deletion and the CYP1A1 m1m2 variant on cancer risk. Our findings suggest that tobacco use and genetic factors play a significant role in oral and pharyngeal cancer.

Pharmacogenomics of anti-TB drugs-related hepatotoxicity

Anti-TB drug (ATD)-related hepatotoxicity is a worldwide serious medical problem among TB patients. Apart from acting on the bacteria, isoniazid, the principal ATD, is also metabolized by human enzymes to generate toxic chemicals that might cause hepatotoxicity. It has been proposed that the production and elimination of the toxic metabolites depends on the activities of several enzymes, such as N-acetyl transferase 2 (NAT2), cytochrome P450 oxidase (CYP2E1) and glutathione S-transferase (GSTM1). There is now evidence that DNA sequence variations or polymorphisms at these loci (NAT2, CYP2E1 and GSTM1) could modulate the activities of these enzymes and, hence, the risk of hepatotoxicity. Since the prevalence of polymorphisms is different in worldwide populations, the risk of ATD hepatotoxicity varies in the populations. Thus, the knowledge of polymorphisms at these loci, prior to medication, may be useful in evaluating risk and controlling ATD hepatotoxicity.