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.

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.

We applied an alternative approach to assess the controversial evidence for the role of GSTM1 and GSTT1 deficiencies (null genotypes) in cancer susceptibility. In this study setting, the prevalence of GSTM1 and GSTT1 null genotypes in the lung cancer patients (LCs, n = 167) were compared with those in the group of putatively cancer resistant individuals, i.e. elderly tumor-free donors (EDs, n = 324). Healthy middle-aged donors (HDs, n = 339) were used as another comparison group. Our results support the previous conclusions of a modest protective effect associated with presence of at least one functional copy of GSTM1 gene; the prevalence of GSTM1 deficiency in LCs (54%) did not differ from that observed in HDs (54%), but showed a significant increase when compared with EDs (45%) (OR = 1.46, 95% CI = 1.00-2.12). Furthermore, in agreement with mechanistic considerations, the GSTM1 null genotypes were more prevalent in squamous cell carcinoma patients (58%) and in lung cancer patients with seemingly low cumulative carcinogen exposure dose (non-smokers: 63%; patients aged below 50 years: 76%). Contrary to GSTM1, no significant effect in the lung cancer proneness was observed for the GSTT1 genotypes. The results of this study are thus in good agreement with the body of literature data, including several published meta-analyses. Consequently, the suggested study design involving additional "cancer resistant" group of non-affected subjects appears to provide highly demonstrative data and to be well suited for pilot investigations and for resolving controversial issues.

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.