A novel approach for assessment of cancer predisposing roles of GSTM1 and GSTT1 genes: use of putatively cancer resistant elderly tumor-free smokers as the referents

Association between glutathione S-transferase T1 null genotype and risk of lung cancer: a meta-analysis of 55 studies

The relationship between glutathione S-transferase T1 (GSTT1) gene polymorphism and the risk of lung cancer from the published reports are still conflicting. This study was conducted to evaluate the relationship between GSTT1 polymorphism and the risk of lung cancer. A comprehensive research was conducted through the databases, and 55 studies were recruited into this meta-analysis for the association of null genotype of GSTT1 with lung cancer susceptibility, consisting of 15,140 patients with lung cancer and 16,662 controls. There was a significant association between GSTT1 null genotype and lung cancer risk in the overall populations (OR = 1.138, 95% CI = 1.032-1.255, P heterogeneity = 0.000, P = 0.009). Furthermore, GSTT1 null genotype was associated with the lung cancer risk in Asians (OR = 1.469, 95% CI = 1.228-1.757, P heterogeneity = 0.000, P = 0.000). However, GSTT1 null genotype was not associated with the risk of lung cancer in Caucasians and Africans. In conclusion, GSTT1 null genotype is associated with the lung cancer in overall populations and in Asians.

A meta-analysis of the relationship between glutathione S-transferase T1 null/presence gene polymorphism and the risk of lung cancer including 31802 subjects

The relationship between glutathione S-transferase T1 (GSTT1) null/presence gene polymorphism and the risk of lung cancer from the published reports are still conflicting. This study was conducted to evaluate the relationship between GSTT1 null/presence gene polymorphism and the risk of lung cancer using meta-analysis method. The association studies were identified from PubMed, and Cochrane Library on July 1, 2012, and eligible investigations were included and synthesized using meta-analysis method. 51 reports were recruited into this meta-analysis for the association of null genotype of GSTT1 with lung cancer susceptibility, consisting of 15,140 patients with lung cancer and 16,662 controls. There was a marked association between GSTT1 null genotype and lung cancer risk in overall populations (OR = 1.15, 95 % CI 1.04-1.27, P = 0.007). Furthermore, GSTT1 null genotype was associated with the lung cancer risk in Asians (OR = 1.47, 95 % CI 1.23-1.76, P < 0.0001). However, GSTT1 null genotype was not associated with the risk of lung cancer in Caucasians, Brazilian population and Africans. In conclusion, GSTT1 null genotype is associated with the lung cancer in overall populations and in Asians.

Assessment of cumulative evidence for the association between glutathione S-transferase polymorphisms and lung cancer: application of the Venice interim guidelines

OBJECTIVE

There is an overwhelming abundance of genetic association studies available in the literature, which can often be collectively difficult to interpret. To address this issue, the Venice interim guidelines were established for determining the credibility of the cumulative evidence. The objective of this report is to evaluate the literature on the association of common glutathione S-transferase (GST) variants (GSTM1 null, GSTT1 null and GSTP1 Ile105Val polymorphism) and lung cancer, and to assess the credibility of the associations using the newly proposed cumulative evidence guidelines.

METHODS

Information from the literature was enriched with an updated meta-analysis and a pooled analysis using data from the Genetic Susceptibility to Environmental Carcinogens database.

RESULTS

There was a significant association between GSTM1 null and lung cancer for the meta-analysis (meta odds ratio=1.17, 95% confidence interval: 1.10-1.25) and pooled analysis (adjusted odds ratio=1.10, 95% confidence interval: 1.04-1.16), although substantial heterogeneity was present. No overall association between lung cancer and GSTT1 null or GSTP1 Ile105Val was found. When the Venice criteria was applied, cumulative evidence for all associations were considered 'weak', with the exception of East Asian carriers of the G allele of GSTP1 Ile105Val, which was graded as 'moderate' evidence.

CONCLUSION

Despite the large amounts of studies, and several statistically significant summary estimates produced by meta-analyses, the application of the Venice criteria suggests extensive heterogeneity and susceptibility to bias for the studies on association of common genetic polymorphisms, such as with GST variants and lung cancer.

Selection of extreme phenotypes: the role of clinical observation in translational research

Systematic collection of phenotypes and their correlation with molecular data has been proposed as a useful method to advance in the study of disease. Although some databases for animal species are being developed, progress in humans is slow, probably due to the multifactorial origin of many human diseases and to the intricacy of accurately classifying phenotypes, among other factors. An alternative approach has been to identify and to study individuals or families with very characteristic, clinically relevant phenotypes. This strategy has shown increased efficiency to identify the molecular features underlying such phenotypes. While on most occasions the subjects selected for these studies presented harmful phenotypes, a few studies have been performed in individuals with very favourable phenotypes. The consistent results achieved suggest that it seems logical to further develop this strategy as a methodology to study human disease, including cancer. The identification and the study with high-throughput techniques of individuals showing a markedly decreased risk of developing cancer or of cancer patients presenting either an unusually favourable prognosis or striking responses following a specific treatment, might be promising ways to maximize the yield of this approach and to reveal the molecular causes that explain those phenotypes and thus highlight useful therapeutic targets. This manuscript reviews the current status of selection of extreme phenotypes in cancer research and provides directions for future development of this methodology.

Investigation of glutathione S-transferase M1 and T1 deletions in lung cancer

Glutathione S-transferases (GSTs) M1 and T1 are known to be polymorphic in humans. Both polymorphisms are due to gene deletions which are responsible for the existence of null genotypes. Previous studies have suggested that GST genotypes may play a role in determining susceptibility to a number of unrelated cancers, including lung cancer. The GSTM1 and GSTT1 polymorphisms were determined by PCR-based analysis in 75 lung cancer patients and 55 controls. The unconditional logistic regression analysis was used to calculate ORs and 95% CI. The frequencies of GSTM1 and GSTT1 null genotypes were 37.3 and 22.7% in lung cancer patients and 27.3 and 16.4% in controls, respectively. When analyzed by histology the GSTM1 null genotype was more prevalent in squamous-cell carcinoma and adenocarcinoma patients. Whereas, GSTT1 null genotype frequency was lower in small-cell lung cancer patients than controls. But these differences were not statistically significant. According to smoking status, null genotype for both gene are associated with an increase in risk for lung cancer. Our results suggest that GSTM1 and GSTT1 polymorphisms may play a role in the development of lung cancer for some histological subtypes and modifies the risk of smoking-related lung cancer.

Genome-wide profile of pleural mesothelioma versus parietal and visceral pleura: the emerging gene portrait of the mesothelioma phenotype

BACKGROUND

Malignant pleural mesothelioma is considered an almost incurable tumour with increasing incidence worldwide. It usually develops in the parietal pleura, from mesothelial lining or submesothelial cells, subsequently invading the visceral pleura. Chromosomal and genomic aberrations of mesothelioma are diverse and heterogenous. Genome-wide profiling of mesothelioma versus parietal and visceral normal pleural tissue could thus reveal novel genes and pathways explaining its aggressive phenotype.

METHODOLOGY AND PRINCIPAL FINDINGS

Well-characterised tissue from five mesothelioma patients and normal parietal and visceral pleural samples from six non-cancer patients were profiled by Affymetrix oligoarray of 38 500 genes. The lists of differentially expressed genes tested for overrepresentation in KEGG PATHWAYS (Kyoto Encyclopedia of Genes and Genomes) and GO (gene ontology) terms revealed large differences of expression between visceral and parietal pleura, and both tissues differed from mesothelioma. Cell growth and intrinsic resistance in tumour versus parietal pleura was reflected in highly overexpressed cell cycle, mitosis, replication, DNA repair and anti-apoptosis genes. Several genes of the "salvage pathway" that recycle nucleobases were overexpressed, among them TYMS, encoding thymidylate synthase, the main target of the antifolate drug pemetrexed that is active in mesothelioma. Circadian rhythm genes were expressed in favour of tumour growth. The local invasive, non-metastatic phenotype of mesothelioma, could partly be due to overexpression of the known metastasis suppressors NME1 and NME2. Down-regulation of several tumour suppressor genes could contribute to mesothelioma progression. Genes involved in cell communication were down-regulated, indicating that mesothelioma may shield itself from the immune system. Similarly, in non-cancer parietal versus visceral pleura signal transduction, soluble transporter and adhesion genes were down-regulated. This could represent a genetical platform of the parietal pleura propensity to develop mesothelioma.

CONCLUSIONS

Genome-wide microarray approach using complex human tissue samples revealed novel expression patterns, reflecting some important features of mesothelioma biology that should be further explored.

Coding polymorphisms in Casp5, Casp8 and DR4 genes may play a role in predisposition to lung cancer

Apoptosis plays a role in the elimination of DNA-damaged cells thus protecting the host from cancer development. Some data indicate that normal variations within the sequence of apoptotic genes may lead to suboptimal apoptotic capacity and therefore increased cancer risk. We tested 19 coding apoptotic gene SNPs in 2-stage molecular epidemiological study. For the preliminary sorting of SNP candidates, we employed a "comparison of extremes" approach, where 111 patients with highly pronounced LC susceptibility (non-smokers or young-onset light smokers) were analyzed against 110 subjects with the evidence for LC tolerance (elderly tumor-free heavy smokers). Three genotypes demonstrated possible association with LC risk (Leu/Leu-homozygotes for Casp5 Val318Leu versus other genotypes: OR=2.47 (95% CI: 1.07-5.69), p=0.03; His-carriers for Casp8 His302Asp: OR=2.26 (95% CI: 1.18-4.31), p=0.02; Arg-carriers for DR4 Lys441Arg: OR=1.89 (95% CI: 1.05-3.40), p=0.03), and therefore were selected for the validation. The extended study included 2 case-control series, namely subjects from Russia (351 LC cases and 538 controls) and Moldova (296 LC cases and 295 controls). Interestingly, all three candidate genotypes consistently demonstrated OR above 1 both in Russian and in Moldovian groups. Although the combined Mantel-Haenszel analysis yet failed to reach statistical significance (OR=1.22 (95% CI: 0.90-1.65), p=0.21; OR=1.17 (95% CI: 0.92-1.50), p=0.21; OR=1.19 (95% CI: 0.95-1.51), p=0.14, respectively), the obtained data indicate that Casp5, Casp8 and DR4 gene polymorphisms may deserve consideration in large-scale case-control studies of LC risk modifiers.

Glutathione S-transferase M1 (GSTM1) polymorphisms and lung cancer: a literature-based systematic HuGE review and meta-analysis

Multiple genes have been studied for potential associations with lung cancer. The gene most frequently associated with increased risk has been glutathione S-transferase M1 (GSTM1). The glutathione S-transferase enzyme family is known to catalyze detoxification of electrophilic compounds, including carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress. In this review, the authors summarize the available evidence associating lung cancer with the GSTM1 gene. They describe results from an updated meta-analysis of 98 published genetic association studies investigating the relation between the GSTM1 null variant and lung cancer risk including 19,638 lung cancer cases and 25,266 controls (counting cases and controls in each study only once). All studies considered, the GSTM1 null variant was associated with an increased risk of lung cancer (odds ratio (OR) = 1.22, 95% confidence interval (CI): 1.14, 1.30), but no increase in risk was seen (OR = 1.01, 95% CI: 0.91, 1.12) when only the five largest studies (>500 cases each) were considered. Furthermore, while GSTM1 null status conferred a significantly increased risk of lung cancer to East Asians (OR = 1.38, 95% CI: 1.24, 1.55), such a genotype did not confer increased risk to Caucasians. More data regarding the predictive value of GSTM1 genetic testing are needed before population-based testing may be reasonably considered.

Dose effects in gene environment interaction: an enzyme kinetics based approach

There have been many observations of different forms of the effect of dose in toxicological and pharmacological research into gene environment interactions. In one form, the effect of genetic variation is seen to be more potent at lower doses, while in the other, the genetic variant has a stronger effect at higher doses of exposure. The application of principles of classical enzyme kinetics to this problem has led to a hypothesis that for any gain of function polymorphism, a low exposure gene (LEG) or low dose effect will always be observed, while for any loss of function polymorphism, the high exposure gene (HEG) effect will always be seen. Furthermore the dose effect is found to be independent of any effects on Vmax, but is related to effects on Km of the gene product. The hypothesis is derived from the Michaelis-Menten equation, and if supported by experimental evidence, could lead to important implications for drug dosage and toxicological risk analysis in the context of individual differences in genetic profiles.

Five glutathione s-transferase gene variants in 23,452 cases of lung cancer and 30,397 controls: meta-analysis of 130 studies

BACKGROUND

Glutathione S-transferases (GSTs) are known to abolish or reduce the activities of intracellular enzymes that help detoxify environmental carcinogens, such as those found in tobacco smoke. It has been suggested that polymorphisms in the GST genes are risk factors for lung cancer, but a large number of studies have reported apparently conflicting results.

METHODS AND FINDINGS

Literature-based meta-analysis was supplemented by tabular data from investigators of all relevant studies of five GST polymorphisms (GSTM1 null, GSTT1 null, I105V, and A114V polymorphisms in the GSTP1 genes, and GSTM3 intron 6 polymorphism) available before August, 2005, with investigation of potential sources of heterogeneity. Included in the present meta-analysis were 130 studies, involving a total of 23,452 lung cancer cases and 30,397 controls. In a combined analysis, the relative risks for lung cancer of the GSTM1 null and GSTT1 null polymorphisms were 1.18 (95% confidence interval [CI]: 1.14-1.23) and 1.09 (95% CI: 1.02-1.16), respectively, but in the larger studies they were only 1.04 (95% CI: 0.95-1.14) and 0.99 (95% CI: 0.86-1.11), respectively. In addition to size of study, ethnic background was a significant source of heterogeneity among studies of the GSTM1 null genotype, with possibly weaker associations in studies of individuals of European continental ancestry. Combined analyses of studies of the 105V, 114V, and GSTM3*B variants showed no significant overall associations with lung cancer, yielding per-allele relative risks of 1.04 (95% CI: 0.99-1.09), 1.15 (95% CI: 0.95-1.39), and 1.05 (95% CI: 0.89-1.23), respectively.

CONCLUSIONS

The risk of lung cancer is not strongly associated with the I105V and A114V polymorphisms in the GSTP1 gene or with GSTM3 intron 6 polymorphism. Given the non-significant associations in the larger studies, the relevance of the weakly positive overall associations with the GSTM1 null and the GSTT1 null polymorphisms is uncertain. As lung cancer has important environmental causes, understanding any genetic contribution to it in general populations will require the conduct of particularly large and comprehensive studies.

Combined CYP1A1/GSTM1 at-risk genotypes are overrepresented in squamous cell lung carcinoma patients but underrepresented in elderly tumor-free subjects

PURPOSE

Polycyclic aromatic hydrocarbons are activated by cytochrome P450 1A1 (CYP1A1) and inactivated by glutathione S-transferase mu (GSTM1). Therefore, it is expected that a combination of proficient CYP1A1 genotype with deficient GSTM1 variant would result in particularly elevated lung cancer (LC) risk, especially for squamous cell carcinoma (SCC). This study was aimed to validate whether the CYP1A1-C (3801) (CYP1A1*2) allele has an unfavorable significance alone and/or in combination with the GSTM1 deficiency.

METHODS

We compared the distribution of CYP1A1 and GSTM1 genotypes in LC patients (n=141), healthy donors (HD, n=204), and elderly tumor-free smokers and non-smokers (ED, n=246).

RESULTS

CYP1A1*2 allele carriers demonstrated a clear-cut association with SCC: the adjusted odds ratios (OR) were 2.22 (95% CI=1.06-4.63) and 2.27 (95% CI=1.14-4.52) when HD and ED were used as referents, respectively. CYP1A1*2(+)/GSTM1(-) combined genotypes were overrepresented in the SCC patients (14/70, 20.0%) and underrepresented in the ED (19/246, 7.7%) as compared to the intermediate prevalence in the HD (26/204, 12.7%); the adjusted OR for SCC versus ED reached 3.85 (95% CI=1.43-10.33).

CONCLUSIONS

In agreement with some literature data, our results support the concerted role of CYP1A1 and GSTM1 at-risk genotypes in SCC predisposition.

‘Comparison of extremes’ approach provides evidence against the modifying role of NAT2 polymorphism in lung cancer susceptibility

NAT2 (arylamine N-acetyltransferase 2) polymorphism, being a key determinant of individual variations in acetylation capacity, is suspected to modify the risk of carcinogen-related malignancies. As tobacco smoke and other inhaled hazards contain a variety of NAT2 substrates, the relationship between NAT2 phenotype and lung cancer (LC) risk has been a subject of intensive research, however different case-control studies produced controversial data. In the present report, we employed a novel 'comparison of extremes' approach, i.e. we compared the distribution of NAT2 genotypes in lung cancer patients (LC, n=178) not only to the population controls (healthy donors (HD), n=364), but also to the subjects with a putative cancer-resistant constitution (elderly tumor-free smokers and non-smokers (ED), n=351). Frequencies of homozygous rapid, heterozygous rapid and slow acetylators were 6, 39 and 56% in LC, 8, 32 and 60% in HD, and 6, 35 and 59% in ED, respectively. Comparison of the NAT2 genotype frequencies between affected and non-affected individuals did not reveal any statistical deviations, irrespectively of smoking history, gender, age, or histological type of LC. Adjusted odds ratio for rapid vs. slow acetylators was 1.12 (95% confidence intervals (CI): 0.73-1.74) comparing LC vs. HD, and 1.10 (95% CI: 0.74-1.62) comparing LC vs. ED. Similar distribution of NAT2 acetylator genotypes both in tumor-prone and in tumor-resistant groups suggests that, despite the presence of NAT2 carcinogenic substrates in tobacco smoke, NAT2 polymorphism does not play a noticeable role in lung cancer susceptibility.