Glutathione S-transferase and cytochrome-P-450 polymorphism as risk factors for squamous cell carcinoma of the larynx

Glutathione S-transferase theta 1 (GSTT1) deletion polymorphism and susceptibility to head and neck carcinoma: a systematic review with five analyses

Glutathione S-transferase theta 1 (GSTT1) enzyme plays a key role in the neutralization of electrophilic compounds such as carcinogens. Herein, we aimed to evaluate GSTT1 deletion polymorphism and susceptibility to head and neck carcinoma (HNC) according to 107 articles in a systematic review with five analyses. The databases of PubMed/Medline, Web of Science, Scopus, and Cochrane Library from the beginning of each database until June 21, 2023, with no restrictions to identify pertinent articles. The RevMan 5.3 software was used to calculate the effect sizes, which were displayed as the odds ratio (OR) along with a 95% confidence interval (CI). Both the publication bias and sensitivity analyses were performed using the CMA 3.0 software. A trial sequential analysis (TSA) was conducted. Of the 1966 records retrieved from four databases, 107 articles were included in the analysis. The combined analysis revealed that the pooled OR was 1.28 (95% CI: 1.14 to 1.44; p-value < 0.0001). The pooled OR was highest in mixed ethnicity. Nasopharyngeal cancer had the highest OR (1.84), followed by oral cancer (OR = 1.20), and laryngeal cancer (OR = 1.17). Studies with less than 200 samples had a higher OR compared to those with 200 or more samples. The studies with a quality score of 7 or more had a higher OR compared to those with a score of less than 7. When both age and sex are considered, while the OR of 1.42 is significant, the high heterogeneity suggests caution in interpreting these results. There is no evidence of publication bias. TSA reported that the study does not have sufficient statistical power. This comprehensive meta-analysis revealed a significant association between the GSTT1 null genotype and an increased risk of HNC, with variations based on factors such as ethnicity, cancer type, sample size, control source, and quality score.

Gene polymorphisms and risk of head and neck squamous cell carcinoma: a systematic review

Background

Exposure to the same environmental factors in different people have resulted in different susceptibility to head and neck squamous cell carcinoma (HNSCC), which suggests genetic variation may be a risk factor for the development of HNSCC. So, the aim was to review literatures on the association between gene polymorphisms and risk of HNSCCs.

Materials and methods

This systematic review included all articles on the impact of gene polymorphisms on risk and susceptibility to HNSCC published till September 2021 using PubMed, Web of science, SCOPUS, Google Scholar and Cochrane library databases.

Results

Of 1163 initial searched articles, 77 articles were eligible to include in this review. Studies were categorized based on gene functions. In each category, studied gene polymorphisms related to growth control genes, cell cycle control, apoptosis, DNA repair genes, carcinogen-metabolizing enzymes, alcohol-metabolizing genes, antioxidant gene, inflammatory cytokine, transcription factor, tumor immunity, folate metabolism, and tumor suppressor gene were discussed separately. Among the polymorphisms that are often significantly associated with HNSCC risk are: GSTM1 null, GSTT1 null, CYP2D6 *4, XRCC1 Arg194Trp and Arg399Gln, ERCC1 C8092A, XPD Lys751Gln, XRCC3 Thr241Met, P53 codon 72 and MTHFR C677T polymorphisms.

Conclusion

Varied and contradictory results have been reported in different studies regarding the association of gene polymorphisms with HNSCC risk. To conclude about this association and to overcome these contradictions, it is necessary to use the results of existing meta-analyses or to perform new or updated meta-analyses.

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.

Association of GSTO2 (N142D), GSTT1, and GSTM1 Polymorphisms With Graft-Versus-Host Disease in Allogeneic Hematopoietic Stem Cell Transplant Recipients

OBJECTIVES

Graft-versus-host disease is a major problem after bone marrow transplant. GSTM1, GSTT1, and GSTO2 are important genes that interfere with xenobiotic and drug metabolism. Polymorphisms of these genes may influence the metabolism of immunosuppressive drugs given for inhibition of graft-versus-host disease and may influence their susceptibility to diseases, which bone marrow transplant could alleviate.

MATERIALS AND METHODS

We examined the polymorphisms of 2 groups: The first group was composed of 88 patients who had undergone a bone marrow transplant and 100 otherwise healthy persons; the second group was composed of 54 patients without graft-versus-host disease and 34 patients with graft-versus-host disease. We used polymerase chain reaction-restriction fragment length polymorphism method for genotyping GSTO2 and also for multiplexing polymerase chain reactions for GSTT1 and GSTM1 genotypes.

RESULTS

No significant association existed between the genotypes GSTO2 (DD: P = .458, OR 0.422), GSTM1 (P = .349, OR 1.52), or GSTT1 (P = .887, OR 1.086), and the incidence of GVHD. Moreover, we saw no association between these polymorphisms and the problems that lead to bone marrow transplant (GSTO2: DD, P = .181, OR 0.465; GSTM1: P = .699, OR 0.892; GSTT1: P = .656, OR 0.845). We showed that men have more bone marrow transplants than do women (P = .019, OR 2.034).

CONCLUSIONS

Our results show that these poly-morphisms may have no effect on the metabolism of drugs used to treat graft-versus-host disease and also, may play no significant role in creating the problems that lead to bone marrow transplant.

GSTM1 and GSTM5 Genetic Polymorphisms and Expression in Age-Related Macular Degeneration

PURPOSE

Previously, two cytosolic antioxidant enzymes, Glutathione S-transferase Mu 1 (GSTM1) and Mu 5 (GSTM5), were reduced in retinas with age-related macular degeneration (AMD). This study compared genomic copy number variations (gCNV) of these two antioxidant enzymes in AMD versus controls.

METHODS

Genomic copy number (gCN) assays were performed using Taqman Gene Copy Number Assays (Applied Biosystems, Darmstadt, Germany) in technical quadruplicate for both GSTM1 and GSTM5. Peripheral leukocyte RNA levels were compared with controls in technical triplicates. Statistical comparisons were performed in SAS v9.2 (SAS Institute Inc., Cary, NC).

RESULTS

A large percentage of patients in both AMD and age-matched control groups had no copies of GSTM1 (0/0). The mean gCN of GSTM1 was 1.40 (range 0-4) and 1.61 (range 0-5) for AMD and control, respectively (p = 0.29). A greater percentage of control patients had > 3 gCNs of GSTM1 compared with AMD, respectively (15.3% versus 3.0%, p = 0.004). The gCN of GSTM5 was 2 in all samples except one control sample. The relative quantification of GSTM1 and GSTM5 mRNA from peripheral blood leukocytes in patients showed significant differences in relative expression in AMD versus control (p < 0.05). Peripheral blood leukocyte mRNA and gCN were not significantly correlated (p = 0.27).

CONCLUSION

Since high copy numbers of GSTM1 are found more frequently in controls than in AMD, it is possible that high copy number leads to increased retinal antioxidant defense. Genomic polymorphisms of GSTM1 and GSTM5 do not significantly affect the peripheral blood leukocyte mRNA levels.

Gene-environment interactions in determining differences in genetic susceptibility to cancer in subsites of the head and neck

Genetic differences in susceptibility to cancer in subsites of the head and neck were investigated in a case-control study involving 750 cases of cancers of the oral cavity, larynx, or pharynx, and an equal number of healthy controls. The prevalence of variant genotypes of cytochrome P450 (CYP) 1A1, 1B1, 2E1, or glutathione-S-transferase M1 (null) in cases suggests that polymorphisms in drug metabolizing enzymes (DMEs) modify cancer risk within subsites of the head and neck. Tobacco or alcohol use was found to increase the risk in cases of laryngeal, pharyngeal, or oral cavity cancers. Interaction between genetic variation in DMEs and tobacco smoke (or smoking) exposures conferred significant risk for laryngeal cancer. Likewise, strong associations of the polymorphic genotypes of DMEs with cases of pharyngeal and oral cavity cancer who were tobacco chewers or alcohol users demonstrate that gene-environment interactions may explain differences in genetic susceptibility for cancers of the oral cavity, larynx, and pharynx.

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.

GSTM3 A/B polymorphism and risk for head and neck cancer: a meta-analysis

Background

Glutathione S-transferase M3 (GSTM3) is an important member of the GSTs that plays a critical role in the development of head and neck cancer (HNC). Several studies have investigated between the GSTM3 A/B polymorphism and risk of HNC, however, the results remain controversial. The aim of this meta-analysis is to evaluate the association between the GSTM3 A/B polymorphism and the risk of HNC.

Methods

All eligible case-control studies published up to July 2013 were identified by searching PubMed and Web of Science. The HNC risk associated with the GSTM3 A/B polymorphism was estimated for each study by odds ratios (OR) together with its 95% confidence interval (CI), respectively.

Results

Fourteen studies from ten publications with 2110 patients and 2259 controls were included. Overall, the GSTM3 A/B polymorphism was associated with a decreased risk of HNC using the dominant model, homozygote comparison model and heterozygote comparison model (OR = 0.82, 95%CI: 0.71–0.94; OR = 0.67, 95%CI: 0.49–0.94; and OR = 0.84, 95%CI: 0.73–0.97, respectively); besides, in stratification analyses by ethnicity, similar results were observed in Caucasian populations. Stratification by tumor site indicated that the GSTM3 polymorphism was associated with a decreased risk of laryngeal cancer under recessive model and homozygote comparison (OR = 0.52, 95%CI: 0.30–0.89; and OR = 0.50, 95%CI: 0.29–0.87, respectively); By stratifying source of control, decreased cancer risk was observed in hospital-based population under all genetic models (OR = 0.67, 95%CI: 0.56–0.81 for the dominant model; OR = 0.66, 95%CI: 0.46–0.95 for the recessive model; OR = 0.55, 95%CI: 0.37–0.83 for the homozygote comparison model, and OR = 0.70, 95%CI: 0.58–0.84 for the heterozygote comparison model).

Conclusions

This meta-analysis suggests that the GSTM3 A/B polymorphism may be an important protective factor for HNC, especially of laryngeal cancer and Caucasian populations.

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.

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.

DNA methylation is associated with altered gene expression in AMD

PURPOSE

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. Evidence suggests oxidative stress plays a role in the disease. To assess the potential contribution of epigenetic regulation of antioxidant genes relevant to AMD pathogenesis, we evaluated DNA methylation, a tissue-specific genetic modulation that affects gene expression.

METHODS

Using the Infinium HumanMethylation27 Illumina platform, we performed DNA bisulfite sequencing to compare the methylation status in postmortem retina pigment epithelium (RPE)/choroid between patients with AMD and age-matched controls. Gene expression was assessed with the Affymetrix Exon Array. TaqMan gene expression assays were used for relative quantification (RT-PCR) confirmation of the expression array results: Glutathione S-transferase isoform mu1 (GSTM1) and mu5 (GSTM5) promoter methylation was confirmed by CpG island bisulfite pyrosequencing. To assess protein levels and localization, we used Western analysis, immunohistochemistry, and immunofluorescence with murine and human samples.

RESULTS

The mRNA levels of GSTM1 and GSTM5 were significantly reduced in AMD versus age-matched controls in RPE/choroid and neurosensory retina (NSR), which corresponded to hypermethylation of the GSTM1 promoter. mRNA and protein levels were decreased (RPE to a greater extent than NSR) in AMD postmortem samples, irrespective of age. Immunohistochemistry and immunofluorescence confirm the presence of the enzymes in the NSR and RPE.

CONCLUSIONS

Comparison of DNA methylation, together with mRNA levels, revealed significant differences between AMD versus normal retinas. The evidence presented suggests that GSTM1 and GSTM5 undergo epigenetic repression in AMD RPE/choroid, which may increase susceptibility to oxidative stress in AMD retinas.

Lack of association between glutathione S-transferase T1 gene polymorphism and laryngeal cancer susceptibility: a meta-analysis based on 2,124 cases and 2,059 controls

Studies investigating the association between glutathione S-transferase T1 (GSTT1) gene polymorphism and laryngeal cancer susceptibility have reported conflicting results. The aim of the present study was to conduct a meta-analysis assessing the possible association of GSTT1 gene polymorphism with laryngeal cancer risk. The relevant studies were identified through a search of PubMed, Embase, ISI Web of Knowledge and Chinese National Knowledge Infrastructure until May 2011. Twelve studies were included in the present meta-analysis, which described a total of 2124 laryngeal cancer cases and 2059 controls. The overall odds ratio (OR) for GSTT1 null genotype was 1.40 (95% CI=0.90-2.16). When stratifying for race, the pooled ORs for GSTT1 null genotype were 1.07 (95% CI=0.81-1.41) in Caucasians and 5.63 (95% CI=1.00-31.83) in Asians. The pooled ORs for GSTT1 null genotype were 1.03 (95% CI=0.71-1.49) in population-based studies and 2.39 (95% CI=0.73-7.86) in hospital-based studies, stratifying for study design. This meta-analysis suggested that there was lack of association between GSTT1 gene polymorphism and laryngeal cancer risk. However, larger scale primary studies are still required to further evaluate the interaction of GSTT1 gene polymorphism with laryngeal cancer risk.

Glutathione S-transferases: an overview in cancer research

IMPORTANCE OF THE FIELD

The Glutathione S-transferases (GSTs) have advanced beyond the classic view of their role in metabolism and are encouraging scientists to assess new approaches to cancer risk characterization and chemotherapy resistance and are opening up exciting possibilities in drug discovery.

AREAS COVERED IN THIS REVIEW

In this review, the most recent knowledge about the impact of GST genetic polymorphisms in human's cancer susceptibility, ethnic differences in the effects of risk factors and the rise of the GSTs as important targets for drug development are presented. In this context, the ethnic distribution of GST alleles in different populations, which is an important concept that is being incorporated in epidemiologic studies of cancer risk and environmental exposure, was also evaluated. We present up-to-date information about the new generation of GST-activated cytotoxic prodrugs based on GST overexpression in tumor-acquired drug resistance and the newest results of clinical trials.

WHAT THE READER WILL GAIN

A critical approach of the major advances in research of GST, underlining the new advances of GST genes polymorphisms in cancer susceptibility and target for therapeutic intervention.

TAKE HOME MESSAGE

Although polygenic factors are involved in increased risk of cancer, the interindividual GST variability plays a central role in reduce cells exposure to carcinogens.

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.

Genetic and environmental factors in head and neck cancer genesis

Head and neck squamous cell carcinoma (HNSCC) include squamous cell carcinomas of the oral cavity, pharynx, and larynx. Epidemiologic data suggest that the etiology and pathogenesis of HNSCC are influenced by environmental and lifestyle-related factors, such as tobacco use, ethanol consumption, papilloma virus infection, dietary factors and exposure to toxic substances. DNA repair systems and carcinogen-metabolizing enzymes can increase the risk for HNSCC but no definite causal mechanism has been demonstrated. There are several well-characterized entities that are associated with risk and prognosis of head and neck cancer, including Lynch-II syndrome, Bloom syndrome, Fanconi's anemia, xeroderma pigmentosum, ataxia telangiectasia, and Li-Fraumeni syndrome. This review aims to present the current status in our understanding of HNSCC and highlight controversies relating to the role of several factors in the genesis of the cancer.

Epidemiology of carcinogen metabolism genes and risk of squamous cell carcinoma of the head and neck

The risk association between tobacco and alcohol use with squamous cell carcinoma of the head and neck (SCCHN) is well recognized. However, clearly not all individuals who smoke or drink develop SCCHN. Individual genetic susceptibility differences in carcinogen-metabolizing enzyme function, mutagen sensitivity, apoptosis, and chromosomal aberrations either alone or in combination have been theorized to modify the risk of SCCHN. Nearly all carcinogens and procarcinogens require activation by metabolizing enzymes. Similarly, detoxifying enzymes exist and deactivate carcinogens as well as their intermediate by-products. Together these enzymes are termed xenobiotic-metabolizing enzymes; genetic polymorphisms of these enzymes can modify an individual's response to carcinogens and hence the carcinogenic potential of such exposures. In this review, we explore the available evidence in recent literature regarding the risk association between SCCHN and various xenobiotic-metabolizing enzymes, including cytochrome P450s, glutathione S-transferases, N-acetyltransferases, NAD(P)H:quinone oxidoreductase 1, alcohol dehydrogenase, and aldehyde dehydrogenase.

Chemoprevention of squamous cell carcinoma of the head and neck

PURPOSE OF REVIEW

The aim of this article is to summarize progress in understanding of the biology of squamous cell carcinoma of the head and neck and of trials to prevent malignant conversion of oral premalignant lesions and the development of second primary tumors in those already treated for squamous cell carcinoma of the head and neck.

RECENT FINDINGS

The understanding of squamous cell carcinoma of the head and neck biology is rapidly evolving. Clinical trials for chemoprevention are involving more diverse regimens, following disappointing results of retinoid monotherapy. In-vitro and animal studies form the rationale for the next generation of studies, employing combination, synergistic treatments.

SUMMARY

Based on trial data to date, no recommendation for intervention with a chemopreventive agent can be made. It is clear, however, that smoking cessation is an effective intervention for preventing oral premalignant lesions and second primary tumors. Promising trials are being conducted and designed currently. The future of this area of study will involve rational choice of multidrug regimens based on current understanding of the biology of squamous cell carcinoma of the head and neck.

Evaluation of glutathione S-transferase polymorphisms and mutagen sensitivity as risk factors for the development of second primary tumors in patients previously diagnosed with early-stage head and neck cancer

BACKGROUND

The objective of this study was to evaluate the effects of polymorphisms in 2 genes in the glutathione S-transferase (GST) family and the mutagen-sensitivity phenotype on the risk of second primary tumors (SPTs) in patients with previously diagnosed early-stage head and neck squamous cell carcinoma. Data were available for 303 patients who were enrolled in a placebo-controlled chemoprevention trial of low-dose 13-cis-retinoic acid to reduce the occurrence of SPTs.

METHODS

A Cox proportional hazards model and survival tree analysis were used to evaluate the association between specified genetic variations and the development of SPTs. The average number of bleomycin-induced chromatid breaks per cell was used to quantify mutagen sensitivity as an individual patient's degree of sensitivity to genotoxicity.

RESULTS

The GST-M1 null genotype was associated with an increased risk for any SPTs (hazard ratio [HR], 1.99; 95% confidence interval [95% CI], 1.11-3.56) and for tobacco-related SPTs (HR, 2.16; 95% CI, 1.01-4.62) after adjusting for covariates. The GST-T1 null genotype and bleomycin-induced chromatid breaks were not associated with a statistically significant increased risk for SPTs or tobacco-related SPTs after similar adjustment. Simultaneous nonnull status for both GST genotypes was associated with a decreased risk for any SPTs (HR, 0.52; 95% CI, 0.28-0.96) and tobacco-related SPTs (HR, 0.50; 95% CI, 0.22-1.11) compared with null status for GST-M1 accompanied by nonnull status for GST-T1.

CONCLUSIONS

An association was observed between the development of SPTs and the GST-M1 null genotype after successful treatment for early-stage head and neck squamous cell carcinoma. The GST-T1 null genotype and bleomycin-induced chromatid breaks were not associated with an increased risk, and no significant interactions were identified.

Genetic polymorphism of N-acetyltransferase 2 in the susceptibility to laryngeal squamous cell carcinoma

BACKGROUND

The purpose of this study was to investigate whether polymorphism of N-acetyltransferase 2 (NAT2) genotypes are associated with the risk of laryngeal squamous cell carcinoma (SCC).

METHODS

The study group consisted of 45 white patients with laryngeal SCC (42 men, with a mean age of 54 years [range, 37-70 years] and three women, with a mean age of 47 years [range, 32-55 years]) and 104 control subjects (68 men and 36 women; mean age, 50 years; range, 28-73 years). All of the patients were primarily treated with surgical intervention. Blood samples (5 mL) were obtained before surgery or from the patients under follow-up to 5 years after surgery (mean follow-up, 27 months; range, 6-48 months). DNA was extracted from the lymphocytes by high pure template preparation kit. NAT2*5A, NAT2*6A, NAT2*7A/B, and NAT2*14A were detected by use of LightCycler-NAT2 mutation detection kit by real-time polymerase chain reaction with Light Cycler instruments. The association between NAT2 polymorphisms and laryngeal SCC was prospectively modeled through multivariate logistic regression analysis.

RESULTS

We found that the risk of laryngeal SCC was 7.3-fold higher in individuals with NAT2*5 mutant allele, 3.8-fold higher in subjects with NAT2*6 heterozygote allele, and 38.3-fold higher in NAT2*6 mutant allele. We also found that individuals with NAT2*7 heterozygote allele had a 0.2-fold less risk for the development of laryngeal SCC (p = .018).

CONCLUSION

In this population, patients with NAT2*5 mutant and *6 heterozygous and mutant genotypes had a significantly higher risk for development of laryngeal SCC.

Glutathione S-transferase T1 null polymorphism and the risk for head and neck cancer

CONCLUSIONS

Inter-regional differences in the distribution of genetic polymorphisms in glutathione S-transferases (GSTs) exist, which may have significant effect on the outcome of other GST polymorphism studies. The GSTT1 null genotype appears to be involved in modulation of the risk for head and neck squamous cell carcinoma (HNSCC).

BACKGROUND

The risk of HNSCC is strongly associated with smoking of cigarettes and consumption of alcohol, resulting in a load of toxins/carcinogens. Detoxification of such exogenous harmful compounds often occurs by phase II enzymes such as GSTs. Proper functioning of these enzymes may be deficient due to the presence of particular genetic polymorphisms in these GSTs, and this may increase the risk for HNSCC. We compared the GSTT1, GSTM1 and GSTP1 genotype frequencies in two groups of healthy blood donors, collected from different but adjacent regions in the Netherlands, with those of a group of patients with HNSCC.

SUBJECTS AND METHODS

The GSTM1,GSTT1 and GSTP1 genotype frequencies in two Dutch Caucasian control populations (n = 207 and n = 285) from different but adjacent geographical regions (Maastricht and Nijmegen; distance, 125 km) and 185 patients with HNSCC from the Maastricht region were determined by PCR-related methods.

RESULTS

For the occurrence of the GSTT1 null genotype we found a significant difference (p=0.003) between the two control groups (20.3% vs 33.0% null genotype in the Nijmegen and Maastricht control groups, respectively). Since the HNSCC patients were collected from the Maastricht area, comparison with the Maastricht controls reveals a significant difference for GSTT1 null rates, which are lower in patients vs controls (OR = 0.49, CI = 0.32-0.76).

Cytochrome P-450 1A1 gene polymorphisms and risk of breast cancer: a HuGE review

Cytochrome P-450 (CYP) 1A1 plays a key role in phase I metabolism of polycyclic aromatic hydrocarbons and in estrogen metabolism. It is expressed predominantly in extrahepatic tissues, including the breast. Four CYP1A1 gene polymorphisms (3801T --> C, Ile462Val, 3205T --> C, and Thr461Asp) have been studied in relation to breast cancer. The 3801C variant is more common than the Val variant. Both variants occur more frequently in Asians than in White populations. The 3205T --> C polymorphism has been observed in African Americans only. Little data are available on the geographic/ethnic distribution of the Thr461Asp polymorphism. The functional significance of the polymorphisms is unclear. In 17 studies, no consistent association between breast cancer and CYP1A1 genotype was found. Meta-analysis found no significant risk for the genotypes 1) 3801C/C (relative risk (RR) = 0.97, 95% confidence interval (CI): 0.52, 1.80) or 3801T/C (RR = 0.91, 95% CI: 0.70, 1.19) versus 3801T/T, 2) Val/Val (RR = 1.04, 95% CI: 0.63, 1.74) or Ile/Val (RR = 0.92, 95% CI: 0.76, 1.10) versus Ile/Ile, or 3) Asp/Asp (RR = 0.95, 95% CI: 0.20, 4.49) or Thr/Asp (RR = 1.12, 95% CI: 0.87, 1.43) versus Thr/Thr. Future studies should explore possible interactions between CYP1A1 and sources of polycyclic aromatic hydrocarbons, markers of estrogen exposure, other lifestyle factors influencing hormonal levels, and other genes involved in polycyclic aromatic hydrocarbon metabolism or hormonal biosynthesis.

Glutathione S-transferase polymorphisms and survival from head and neck cancer

BACKGROUND

The purpose of this study was to evaluate the prognostic ability of polymorphisms of three genes involved in the metabolism of tobacco carcinogens (GSTT1, GSTM1, GSTP1) and one polymorphism of a DNA repair gene (XRCC1) for patients diagnosed with squamous cell carcinoma (SCC).

METHODS

Cox proportional hazard models were used to estimate risk of death for a prospective cohort of 190 patients.

RESULTS

Individuals with the GSTT1 functional genotype were twice as likely to die from any cause (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.13-4.97) and were three times as likely to die from SCC (HR, 3.4; 95% CI, 1.33-8.41) after adjustment for age, primary therapy, and stage of disease. The XRCC1 399 Gln genotype was predictive of disease recurrence.

CONCLUSIONS

Our findings, from one of the first studies to examine this research question, suggest that genomic markers of carcinogen metabolism and DNA repair capability may serve as prognostic indicators of disease recurrence and death.

Expression-Based Discovery of Variation in the Human Glutathione S-Transferase M3 Promoter and Functional Analysis in a Glioma Cell Line Using Allele-Specific Chromatin Immunoprecipitation

Discovery and functional evaluation of biologically significant regulatory single nucleotide polymorphisms (SNP) in carcinogen metabolism genes is a difficult challenge because the phenotypic consequences may be both transient and subtle. We have used a gene expression screening approach to identify a functional regulatory SNP in glutathione S-transferase M3 (GSTM3). Anttila et al. proposed that variation in GSTM3 expression was affected by exposure to cigarette smoke and inheritance of the GSTM1-null genotype. To investigate the mechanism of GSTM3 expression was affected by exposure to cigarette smoke and inheritance of the GSTM1-null genotype. To investigate the mechanism of GSTM3 expression variation, we measured GSTM3 expression in lymphoblast cells from a human Centre d'Etude du Polymorphisme Humain family and observed a low expression phenotype. Promoter sequencing revealed two novel GSTM3 promoter SNPs: A/C and A/G SNPs, 63 and 783 bp upstream of the codon 1 start site, respectively. In this pedigree, the two children homozygous for the −63C/C genotype had 8-fold lower GSTM3 expression relative to the two children with the −63A/A genotype, with no association between A−783G SNP and GSTM3 expression. Further evaluation using genotyped glioma cell lines and with luciferase reporter constructs showed that the −63C allele was associated with lower GSTM3 expression (P &lt; 0.0001 and P &lt; 0.003). RNA pol II chromatin immunoprecipitation was combined with quantitative probed-based allelic discrimination genotyping to provide direct evidence of a 9-fold reduced RNA pol II binding capacity for the −63C allele. These results show that the GSTM3 −63C allele strongly affects gene expression in human cell lines and suggests that individuals who carry the low expression allele may be deficient in glutathione transferase catalyzed biological functions.

The epidemiology of laryngeal cancer in Brazil

The city of São Paulo exhibits one of the highest incidences of laryngeal cancer in world and Brazil presents remarkable occurrence, compared with other Latin American countries. Around 8,000 new cases and 3,000 deaths by laryngeal cancer occur annually in the Brazilian population. In the city of São Paulo, incidence rates for laryngeal cancer among males have been decreasing since the late 1980s while, among females, the rates have shown a stable trend. This phenomenon is probably the expression of changes in gender behavior related to tobacco smoking. Several risk factors are involved in the genesis of laryngeal cancer. The most important are tobacco smoking and alcohol intake, but occupational hazards have also been associated with the disease, such as asbestos, strong inorganic acids, cement dust and free crystalline silica. Additionally, salted meat and total fat intake have been linked to elevated risk of laryngeal cancer. Conversely, several studies have confirmed that fruits, raw leaf vegetables and legumes protect against this cancer. Some researchers have postulated a possible association between laryngeal squamous cell carcinoma and human papilloma virus (HPV), but this is not universally accepted. Gastroesophageal reflux disease is weakly, but consistently correlated with laryngeal cancer. Familial cancer clusters, particularly of head and neck tumors, seem to increase the risk of laryngeal cancer. Some genetic polymorphisms, such as of genes that code for xenobiotic-metabolizing enzymes, have shown elevated risk for laryngeal cancer according to recent studies. Public health policies regarding the control of tobacco smoking and alcohol consumption, and also surveillance of carcinogen exposure in occupational settings, could have an impact on laryngeal cancer. No proposals for screening have been recommended for laryngeal cancer, but one diagnostic goal should be to avoid treatment delay when suspected symptoms have been observed.

Glutathione S-transferase M1, T1, and P1 gene polymorphism in laryngeal squamous cell carcinoma

PURPOSE

To investigate the influence of the glutathione S-transferase (GST) M1, T1, and P1 genotypes on the laryngeal squamous cell carcinoma risk.

MATERIAL AND METHODS

The study group consisted of 42 white patients with laryngeal squamous cell carcinoma (39 of them were male, mean age: 53, range: 37-67 and 3 of them were female, mean age: 47, range: 32-55) and 89 control subjects (nonsmokers = 47, smokers = 42) (58 male and 31 female, mean age: 51, range: 30-72). DNA samples were isolated from blood samples using high pure polymerase chain reaction (PCR) Template Preparation Kit. The detection of GST T1, GST M1, and P1 polymorphisms were detected by using real-time PCR.

RESULTS

Gene polymorphisms at GST M1 and P1 were not significantly different in patient and control groups. However, GST T1 null type significantly increased in laryngeal cancer patients when compared with the nonsmoking controls (P =.04).

CONCLUSIONS

There was a significant association between GST T1 null genotype and laryngeal squamous cell carcinoma. However the potential role of GSTs as markers of susceptibility to laryngeal carcinoma needs further studies in a larger number of patients.

Association of cytochrome P450 2E1 polymorphisms and head and neck squamous cell cancer

The development of head and neck squamous cell cancer (HNSCC) is known to be strongly associated with tobacco use. One of the main enzymes for bioactivation of tobacco-related substances is the cytochrome 450 (CYP)2E1, of which different genetic variants are described. Analyzing a correlation between certain neoplasia and alteration of the CYP2E1 gene, most studies focus on the polymorphisms -1053C>T and 7632T>A, but recently another polymorphism, named -71G>T, with enhanced transcriptional activity, has been identified. In the current case-control study we investigate the putative association of the mentioned CYP2E1 polymorphisms on the risk of HNSCC. Comparing 312 German individuals with HNSCC to 299 controls we found a significantly enhanced risk for the development of that neoplasia in smoking carriers of -71G>T heterozygosity, while in -1053C>T and 7632T>A polymorphisms a corresponding correlation was absent. Since a coincidence of an aberrant p53 gene and CYP2E1 mutations has been described, we choose a subgroup of 140 patients with HNSCC for analyzing an association of mutations in these two genes. However, no such association could be found in either of the mentioned polymorphisms. Further studies have to focus on the -71G>T polymorphism and its possible linkage to cancers, in which smoking is a known risk-factor, as well as its functional relevance concerning the bioactivation of tobacco-related substances.

Polymorphisms of GSTT1 and related genes in head and neck cancer risk

BACKGROUND

Glutathione S-transferase T1 detoxifies some environmental carcinogens while activating others and is deleted in 15% to 38% of humans. We sought to determine whether GSTT1 genotype and genotypes of several related genes are associated with risk of squamous cell carcinoma of the head and neck (HNSCC).

METHODS

Somatic genotypes for GSTT1, GSTM1, GSTP1, and CYP1A1 were determined in 283 individuals with HNSCC and 208 population-based controls.

RESULTS

The OR for presence of GSTT1 was 1.6 (CI, 1.1-2.5, p = 0.03). HNSCC risk was not associated with GSTM1 null genotype, the presence of the GSTP1 Val/Val genotype, or the Val/Val homozygous genotype for CYP1A1. Stratified analysis revealed disparate ORs for women (OR, 3.0; CI, 1.5-6.3) and men (OR, 1.2; CI, 0.7-2.1) for the presence of GSTT1.

CONCLUSIONS

In this population, the presence of GSTT1 gene was associated with a significant increase in the risk of HNSCC. This association was particularly robust in women.

High-throughput detection of glutathione s-transferase polymorphic alleles in a pediatric cancer population

Polymorphisms of glutathione S-transferase (GST) enzymes have been correlated with altered risk of several cancers, as well as altered response and toxicity from cancer chemotherapy. We report a low cost, highly reproducible and specific PCR-based high-throughput assay for genotyping different GSTs designed for use in large clinical trials. In comparison to an alternative genotyping method (single nucleotide extension), the sensitivity and specificity of the high throughput assay was shown to be 92 and 97%, respectively, depending on the source of genomic DNA. Using the high-throughput assay, we demonstrate by multivariate analysis an increased risk of acute lymphoblastic leukemia, glial brain tumors, and osteosarcoma for patients carrying nonnull alleles of GSTM1 and/or GSTT1.

Glutathione S-transferase M1 or T1 null genotype as a risk factor for developing multiple primary neoplasms in the upper aero-digestive tract, in Indian males using tobacco

In this study conducted amongst Indian male tobacco users with upper aero-digestive tract (UADT) squamous carcinoma, 30 patients with multiple primary neoplasms (MPN) were compared with 28 age and sex matched patients with a single primary neoplasm (SPN) for various environmental factors (form of tobacco use, alcohol, radiotherapy for index cancer) and genetic parameters (family history of UADT cancers and GSTT1/GSTM1 genotype). The GSTM1/T1 null genotype, seen in 60% patients with MPN versus 33% patients with SPN (P=0.03) had an odds ratio of 3.7 [CI=1.14-11.99; P=0.03] for developing MPN. Tobacco use in the form of smoking with or without chewing, as opposed to only chewing, and regular alcohol intake were the two other factors with almost three fold increased risk for the development of MPN, although, the effect was not statistically significant. All three patients with a family history of UADT cancer developed MPN, suggesting an inherited predisposition.

Relationship of tobacco smoking with GSTM1 gene polymorphism in laringeal cancer

This paper aimed to analyze the association of polymorphism of GSTM1 0/0 genotype with laryngeal cancer along a hospital based case-control study. Polymorphisms of GSTM1 0/0 of samples from 36 patients with laryngeal cancer and 35 healthy controls were detected by PCR method. The reaction used as GSTM1 primers, using the sequence sense: 5'-CTGCCCTACTTGGATTGATGGG-3' and antisense: 5'-TGGATTGTAGCAGATCATGC-3'. N Acetyl transferase 1 (NAT1) gene using the primers sense: 5'-TAAAAGTAAAATGATTTGCTTTCG-3' and antisense: 5'- GCTTTCTAGCATAAATCACCAA-3' was used as internal positive control. Two sided 2 and multivariation analysis were used to analyse the results. The proportions of GSTM1 deleted genotype in cases and controls were 47.2% and 54.3%, respectively. There was significant increment of GSTM 0/0 genotype frequency in moderate smokers group of patients compared to control (P=0.033, OR= 4.78, 95% CI = 1.30-7.13). We conclude that GSTM1 deleted genotype may be a genetic susceptibility marker for laryngeal cancer whose exposed to low doses carcinogens. The absence of this enzyme seems to have a role in the development of laryngeal cancer, in which the mechanism still needs further investigation.

Genetic susceptibility--molecular epidemiology of head and neck cancer

In parts of the developing world (South Central Asia in particular), squamous cell carcinoma of the head and neck (SCCHN) is one of the most common malignancies encountered. Although tobacco and alcohol are clearly defined as etiologic factors in these malignancies, clinical observations have suggested that inherited genetic factors put some individuals at increased risk for SCCHN. Emerging data (both phenotypic and genotypic) support this concept of genetic susceptibility to SCCHN and point to differences in DNA repair ability, carcinogen metabolism, and cell cycle control as the systems important to the risk of tobacco-induced malignancies. The ability to identify such high-risk individuals will have major influences on the practice of cancer prevention in the future.

Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Epidemiological studies have estimated that approximately 80% of all cancers are related to environmental factors. Individual cancer susceptibility can be the result of several host factors, including differences in metabolism, DNA repair, altered expression of tumor suppressor genes and proto-oncogenes, and nutritional status. Xenobiotic metabolism is the principal mechanism for maintaining homeostasis during the body's exposure to xenobiotics. The balance of xenobiotic absorption and elimination rates in metabolism can be important in the prevention of DNA damage by chemical carcinogens. Thus the ability to metabolize and eliminate xenobiotics can be considered one of the body's first protective mechanisms. Variability in individual metabolism has been related to the enzymatic polymorphisms involved in activation and detoxification of chemical carcinogens. This paper is a contemporary literature review on genetic polymorphisms involved in the metabolism of endocrine disruptors potentially related to cancer development.

Genetic mechanisms in squamous cell carcinoma of the head and neck

This review aims to explore the genetic mechanisms involved in the development of squamous cell carcinoma of the head and neck (SCCHN). The epidemiology of SCCHN is complex due to the multiple molecular events that occur and the number of environmental agents to which individuals may have been exposed. It is clear that the major aetiological agents are tobacco and alcohol but it is also becoming apparent that other factors such as an underlying genetic susceptibility may also be important. An inherited predisposition may occur as a consequence of increased mutagen sensitivity, inability to metabolize carcinogens or pro-carcinogens or repair DNA damage. The current advances in understanding of the roles of somatic mutations, viral infection and angiogenesis are discussed. The final part of this review focuses on the way in which molecular changes may be used for prevention, early diagnosis and treatment of SCCHN.

Genetic polymorphisms of biotransformation enzymes: allele frequencies in the population of the Czech Republic

Polymerase chain reaction-restriction fragment length polymorphism based genotyping assays were used to determine the frequency of polymorphisms in CYP1A1 (3'-flanking region), CYP2E1 (5'-flanking region and intron 6), EPHX (exon 3 and exon 4), GSTM1 (deletion), GSTP1 (exon 5) and GSTT1 (deletion) in a group of 416 Czech individuals. A comprehensive overview of the methodology is also presented. We have found the following frequencies of mutated alleles: CYP1A1-m2, 0.097; CYP2E1-C, 0.077; CYP2E1-c2, 0.023; EPHX(exon 3)-His, 0.381; EPHX(exon 4)-Arg, 0.198; GSTM1-null, 0.51; GSTP1-Val, 0.3; GSTT1-null, 0.164. These values are similar to those presented in the majority of studies on European Caucasians, although a few cases of significant differences in the distribution of genotypes were found. These differences were most probably caused by methodological variations or statistical bias in the analyses of low numbers of samples in the control groups of some authors. Based on the results of EPHX genotyping, the activity of its protein product was deduced and the Czech population was divided into three subgroups with low, medium and high EPHX activity. We found that 43% of the Czech population would fall into the low, 44% into the medium and 13% into the high EPHX activity group. The data obtained may prove to be very useful for epidemiological studies on the influence of genetic polymorphisms of biotransformation enzymes on carcinogenesis or other environment-related diseases.

Mammalian class theta GST and differential susceptibility to carcinogens: a review

Glutathione S-transferases (GSTs) are an important part of the cellular detoxification system and, perhaps, evolved to protect cells against reactive oxygen metabolites. Theta is considered the most ancient among the GSTs and theta-like GSTs are found in mammals, fish, insects, plants, unicellular algae, and bacteria. It is thought that an ancestral theta-gene underwent an early duplication before the divergence of fungi and animals and further duplications generated the variety of the other classes of GSTs (alpha, mu, phi, etc.). The comparison of the aminoacidic homologies among mammals suggests that a duplication of an ancient GST theta occurred before the speciation of mammals and resulted in the subunits GSTT1 and GSTT2. The ancestral GST theta has a dehalogenase activity towards several halogenated compounds, such as the dichloromethane. In fact, some aerobic and anaerobic methylotrophic bacteria can use these molecules as the sole carbon and energy source. The mammalian GST theta cannot sustain the growth of bacteria but still retains the dehalogenating activity. Therefore, although mammalian GST theta behaves as a scavenger towards electrophiles, such as epoxides, it acts also as metabolic activator for halogenated compounds, producing a variety of intermediates potentially dangerous for DNA and cells. For example, mice exposed to dichloromethane show a dose-dependent incidence of cancer via the GSTT1-1 pathway. Because GSTT1-1 is polymorphic in humans, with about 20% of Caucasians and 80% of Asians lacking the enzyme, the relationship between the phenotype and the incidence of cancer has been investigated extensively in order to detect GSTT1-1-associated differential susceptibility towards endogenous or exogenous carcinogens. The lack of the enzyme is related to a slightly increased risk of cancer of the bladder, gastro-intestinal tract, and for tobacco-related tumors (lung or oral cavity). More pronounced risks were found in males with the GSTT1-null genotype for brain diseases and skin basal cell carcinomas not related to sunlight exposures. Moreover, there was an increased risk of kidney and liver tumors in humans with the GSTT1-1 positive genotype following exposures to halogenated solvents. Interestingly, the liver and kidney are two organs that express the highest level of GST theta in the human body. Thus, the GSTT1-1 genotype is suspected to confer decreased or increased risk of cancer in relation to the source of exposure; in vitro studies, mostly conducted on metabolites of butadiene, confirm the protective action of GSTT1-1, whereas, thus far, experimental studies prove that the increasing risk is limited.

Influence of GSTM1 genotype on comet assay and chromosome aberrations after induction by bleomycin in cultured human lymphocytes

Investigators have demonstrated that the mutagen sensitivity assay, based on the quantification of bleomycin (BLM)-induced chromatid breaks in short-term cultured peripheral lymphocytes, can be a marker of cancer susceptibility. Although many factors can contribute to variability in human biomonitoring studies, genetic susceptibility (the influence of polymorphic metabolising genes on response to environmental mutagens) should be considered whenever appropriate. Glutathione-S-transferases (GSTs) encode a family of detoxifying phase II enzymes catalysing the conjugation of glutathione to electrophilic compounds. Studies on Caucasians indicate that about 45% of individuals lack the glutathione-S-transferase M1 (GSTM1, null) enzyme, and are therefore, theoretically at a higher risk to the toxic effects of chemicals. The aim of the present study was to investigate this hypothesis further by evaluating whether the GSTM1 genotype influences the background [corrected] level of DNA damage and the induction of chromosomal aberrations by BLM in peripheral-blood lymphocytes. The alkaline comet assay was used to evaluate background levels of DNA damage in unstimulated lymphocytes while standard cytogenetic techniques were used in mitogen-stimulated lymphocytes treated with BLM. Without BLM treatment, individuals with the GSTM1 null genotype had no significant difference in frequencies of damaged cells by comparison to individuals with the GSTM1 genotype. Also, no significant differences between the two groups of individuals (GSTM1 positive and GSTM1 null) were observed for BLM-induced chromosomal aberrations.

Influence of glutathione S-transferase M1 and T1 genotypes on larynx cancer risk among Korean smokers

Glutathione S-transferase (GST) isoenzymes are involved in the detoxification of major carcinogens present in tobacco smoke. It is thus conceivable that deficiency in GST activity due to homozygous deletions of the GSTM1 and GSTT1 genes (the null genotypes) may modulate susceptibility to smoking-induced cancers. The influence of the GSTM1 and GSTT1 null genotypes on larynx cancer risk among the Korean population were evaluated using peripheral blood DNA from 82 larynx cancer patients and 63 healthy controls, all of whom were male current smokers. Increased larynx cancer risk was related to the GSTM1 null genotype (odds ratio (OR)=3.53, 95% confidence interval (CI)=1.27-9.83). The OR associated with the GSTT1 null genotype was also increased, but did not reach statistical significance (OR=1.83, 95% CI=0.70-4.79). Individuals lacking both the GSTM1 and GSTT1 genes were at a significantly higher risk for larynx cancer than individuals with both genes present (OR=4.04, 95% CI=1.33-12.30). These data confirm that the GSTM1 null genotype is an important risk modifier for larynx cancer among Korean smokers and combined GSTM1 and GSTT1 null genotypes could be a useful predictor of genetic susceptibility to larynx cancer.

Polymorphisms of glutathione S-transferase genes (GSTM1, GSTP1 and GSTT1) and breast cancer susceptibility

The glutathione S-transferase (GST) family of enzymes function in the body to detoxify carcinogenic compounds. Several genes that code for these enzymes are polymorphic, with particular genotypes previously shown to confer an increased cancer risk. In this study, we investigated the role of three GST genes (GSTM1, GSTP1 and GSTT1) in the development of sporadic breast cancer. Genotypes were determined in 129 breast cancer affected and 129 age and sex matched control individuals. Results did not support an involvement of these specific GST gene polymorphisms, either independently or in combination, in susceptibility to sporadic breast cancer in the tested Australian Caucasian population.

Glutathione-S-transferase polymorphisms and risk of squamous-cell carcinoma of the head and neck

Differences in genetic susceptibility to tobacco-induced carcinogenesis appear to modulate an individual's risk of squamous-cell carcinoma of the head and neck (SCCHN). Risk for SCCHN may be associated with the null alleles of the carcinogen-metabolizing genes glutathione-S-transferase (GST) T1 and GSTM1. In this study, we evaluated the association between GSTM1 and GSTT1 null genotypes and risk of SCCHN in a matched case-control study of 162 patients with SCCHN and 315 healthy controls. Our results showed that 53.1% of cases and 42.9% of controls were null for GSTM1, whereas 32.7% of cases and 17.5% of controls were null for GSTT1 (p < 0.05 and p < 0.001, respectively). Furthermore, 19.8% of cases but only 7.9% of controls were null for both genes (p < 0.001). Multivariate analysis using logistic regression models, including age, sex, ethnicity, smoking status, alcohol status and GST genotypes, showed that both of these genotypes remained independent risk factors for disease [adjusted odds ratios (ORs) = 1.50 and 2.27, respectively; 95% confidence intervals (CIs) = 1.01-2.23 and 1.43-3.60, respectively). When the genotypes were divided into neither null, either null or both null, there was a dose-response relationship (adjusted OR = 1.50, 95% CI = 0.98-2.30) for the either-null group and (adjusted OR = 3.64, 95% CI = 1.94-6.84) for the both-null group (p < 0.001, trend test). Our findings suggest that the GSTM1 and GSTT1 null genotypes are independent risk factors for SCCHN and markers for genetic susceptibility to tobacco-induced carcinogenesis.

Drug metabolism polymorphisms as modulators of cancer susceptibility

Recently, several molecular genetic bases of polymorphic enzyme activities involved in drug activation and detoxification have been elucidated. Many molecular epidemiology studies based on these premises have sought to gather information on the association of genetically determined metabolic variants with different risks of environmentally induced cancer. While rare alterations of tumor suppressor genes dramatically raise cancer risk for the single affected subjects, far more common and less dramatic differences in genes encoding for drug metabolism enzymes can be responsible for a relatively small, but rather frequent increase of cancer risk at the population level. This increase could be especially important in specific cases of occupational, pharmacological or environmental exposure. Examination of the current literature reveals that the most extensively investigated metabolic polymorphisms are those of P450 1A1 and P450 2D6 cytochromes, glutathione S-transferases (GSTs; M1 and, to a lesser extent, M3, P1 and T1) and N-acetyltransferases (NATs; NAT1 and NAT2). Making reference to these enzymes, we have assayed the current knowledge on the relations among polymorphisms of human xenobiotic-metabolizing enzymes and cancer susceptibilities. We have found intriguing models of susceptibility toward different types of cancer. We have reviewed and commented these models on light of the complex balance among different enzyme activities that, in each individual, determines the degree of each cancer susceptibility. Moreover, we have found techniques of molecular genetic analysis, more suitable than previous ones on phenotypic expression, now allowing better means to detect individuals at risk of cancer. According to the models presently available, a systematic screening of individuals at risk seems to make sense only in situations of well defined carcinogenic exposures and when performed by the polymorphism analysis of coordinated enzyme activities concurring to the metabolism of the carcinogen(s) in question. Genetic polymorphism analysis can allow for the detection of patients more prone to some types of specific cancers, or to the adverse effects of specific pharmaceutical agents. Considering the increasingly confirmed double-edged sword nature of metabolism polymorphism (both wild-type and variant alleles can predispose to cancer, albeit in different situations of exposure), individual susceptibility to cancer should be monitored as a function of the nature, and mechanism of action, of the carcinogen(s) to which the individual under study is known to be exposed, and with reference to the main target organ of the considered type of exposure.

Combined effect of polymorphic GST genes on individual susceptibility to lung cancer

Glutathione S-transferases (GSTs) are known to take part in detoxification of many potentially carcinogenic compounds. Therefore, polymorphisms of the GST genes have been considered as potentially important modifiers of individual risk of environmentally induced cancers. The association between lack of glutathione S-transferase M1 gene (GSTM1 null genotype) and susceptibility to smoking-related lung cancer has been actively studied, with contradictory results. In contrast, little is known about the more recently found polymorphisms in GSTM3, GSTP1 and GSTT1 genes with respect to individual responses to environmental exposures. In this study, we determined the genotype distribution of all these genes, and their combinations, among 208 Finnish lung cancer patients and 294 population controls. None of the genotypes studied had a statistically significant effect on lung cancer risk, when studied separately. However, a significant association was observed for concurrent lack of the GSTM1 and GSTT1 genes and susceptibility to squamous cell carcinoma. For that cell type, the risk was more than 2-fold when compared with that of individuals having other genotype combinations (OR = 2.3; 95% CI = 1.0-5.3; p = 0.05). Moreover, the risk was mostly attributable to patients with smoking history of 40 pack-years or less (OR = 2.9; 95% CI = 1.1-7.7; p = 0.03). In contrast, this genotype combination did not affect the risk for other histological types of lung cancer, and the other genotype combinations had no effects on individual susceptibility to this malignancy. The overall role of GST polymorphisms in modifying the lung cancer risk may therefore be more limited than has been so far anticipated.

Glutathione S-transferase polymorphisms: influence on susceptibility to cancer

The glutathione S-transferase supergene family includes several loci that demonstrate well characterised polymorphisms. The apparently critical role of these enzymes in cellular protection from the cytotoxic and mutagenic effects of electrophiles suggest that alleles associated with impaired detoxification will confer an increased susceptibility to a wide range of diseases. This hypothesis has been examined in case control studies and while data in some diseases such as lung cancer are conflicting, an increasing body of evidence suggests the importance of several glutathione S-transferase polymorphisms. In particular, GST genotypes have been associated with an increased susceptibility or worse outcome in diseases associated with oxidative stress. For example, both GSTM1 and GSTT1 genotypes are associated with susceptibility and outcome in cutaneous basal cell carcinoma. It still remains unclear however, why particular glutathione S-transferase loci are associated with altered risk in some diseases but not others. Further, the true in vivo substrates of these enzymes is unknown, consequently their mechanism of action remains unclear.

Polymorphism in glutathione S-transferase loci as a risk factor for common cancers

Though a developing body of data indicates polymorphism at GST genes influences cancer susceptibility, it is unclear why a genotype is associated with one cancer but not another. We believe the GST exert a critical role in normal cell house-keeping activities. GSTM1, GSTM3 and GSTT1 influence tumorigenesis because these enzymes utilise the products of UV-induced oxidative stress. Further support for the importance of these genes in the protection of skin from UV comes from studies in systemic lupus erythematosus (Ollier et al, 1996). Thus, GSTM1 null is associated with increased anti-Ro (but not anti-La) antibodies, a phenotype associated with photosensitivity. At present there is no basis for predicting which cancers will be influenced by GST polymorphisms though other studies do indicate that the GSTs are critical in the metabolism of environmental carcinogens. For example, GSTT1 null confers an increased risk of astrocytoma (Hand et al, 1996). While brain tumours are not clearly associated with environmental pollutants, N-methyl-N-nitrosourea, processed meats and occupation have been implicated. Why GSTT1 but not GSTM1 or GSTM3 influences the risk of astrocytoma is unclear. GSTM3 appears a good susceptibility candidate, as some astrocytes demonstrate strong expression (Hand et al, 1996). Susceptibility to squamous cell cancer of the larynx, a pathology associated with chronic consumption of tobacco and alcohol, is also influenced by allelism at GSTM3 (Jahnke et al, 1996). The roles of CYP2D6 and CYP1A1 are even more unclear, though the finding that systemic agents such as arsenic predispose to multiple BCC, suggests that CYP2D6-mediated hepatic detoxification of photosensitizing agents may be important. Importantly, the extent of altered risk conferred by genotypes is generally 2-3 fold and it is necessary to identify which other genes interact with the GST so that haplotypes associated with 10-20 fold increases in risk can be defined.