Gene-gene interactions of drug metabolizing enzymes and transporter protein in the risk of upper aerodigestive tract cancers among Indians.

BACKGROUND: The combined genetic effects of single nucleotide polymorphisms may additively or synergistically contribute to the increased cancer risk. The interactions associated with xenobiotic metabolizing enzymes and transporter protein involved in the biotransformation and transport of xenobiotics could determine the functional outcomes over the independent effects of a single susceptibility gene in the risk of upper aerodigestive tract cancers. METHODS: The hospital-based case-control study evaluated CYP1A1 (*2A and *2C), CYP2E1 (*1B, *5B, and *6), GST (M1, T1, and P1) and ABCB1 3435C>T polymorphisms among 408 histopathologically confirmed cases and 220 controls using polymerase chain reaction based methods in an Indian population. RESULTS: The multivariate logistic regression analyses demonstrated potentially high risk gene-gene interactions with the concurrent deletions of the GSTT1 and GSTM1 genes and GSTP1 variant genotypes (OR 5.81; 95% CI 1.01-40.28), the deletions of GSTT1 and GSTM1 genotypes with variant genotypes of CYP1A1*2A (OR 8.21; 95% CI 1.91-49.48), GSTT1 and GSTM1 deficient genotypes along with CYP2E1*1B variant genotypes (OR 6.73; 95% CI 1.32-22.81), the polymorphic genotypes of ABCB1 and deficient GSTT1 (OR 6.08; 95% CI 2.21-16.76) and an enhanced risk with the combined variant genotypes of CYP1A1*2A, GSTT1 and ABCB1 (OR 11.14; 95% CI 2.70-46.02). CONCLUSION: The findings indicate that the interactions associated with various drug metabolizing enzymes and transporter protein exhibit high risk for UADT cancers than that ascribed to a single susceptible gene. This was particularly established among the polymorphic carriers of CYP1A1*2A, GSTT1 and ABCB1 genes in the population investigated.

Gene-environment interactions associated with CYP1A1 MspI and GST polymorphisms and the risk of upper aerodigestive tract cancers in an Indian population.

PURPOSE: Genetic risk to tobacco related cancers are associated with polymorphisms in CYP1A1 and GST, which are involved in the metabolic activation and detoxification of carcinogens. The genetic variations in these drug-metabolizing enzymes may alter the susceptibility to UADT cancers triggered by environmental exposures. The hospital-based case-control study evaluated the impact of combined CYP1A1 MspI and GST (M1 & T1) polymorphisms among the individuals exposed to environmental risk factors as modulators in the risk of UADT cancers in Tamilians, a population of south India. METHODS: The unrelated histopathologically confirmed 408 cases and 220 population-based controls matched by age and gender were genotyped for CYP1A1 MspI, GSTM1 and GSTT1 polymorphisms using PCR based methods. To investigate the potential gene-environment interactions, analyses were carried out stratifying by smoking and tobacco chewing status using SPSS software. RESULTS: The combination of genes and environment interactions by stratified analyses revealed significant interactions among the habitual tobacco smokers (CYP1A1 MspI & GSTM1 null: OR 14.06; 95% CI 3.90-50.68, CYP1A1 MspI & GSTT1 null: OR 33.28; 95% CI 4.24-261.19) and tobacco chewers (CYP1A1 MspI & GSTM1 null: OR 20.51; 95% CI 6.77-62.13, CYP1A1 MspI & GSTT1 null: OR 79.35; 95% CI 10.40-605.55) on the multiplicative scale. CONCLUSION: Our findings have indicated that the individuals polymorphic for CYP1A1 MspI either with GSTM1 null or with GSTT1 null genotypes revealed an increased risk for UADT cancers than that ascribed to a single susceptible gene among the tobacco users in the population [single gene risk among smokers and chewers, respectively, for CYP1A1 MspI (OR 6.43; 95% CI 3.69-11.21); (OR 10.24; 95% CI 5.95-17.60), GSTM1*0 (OR 3.77; 95% CI 1.94-7.37); (OR 7.97 95% CI 4.10-15.76) and GSTT1*0 (OR 6.95 95% CI 2.88-16.77); (OR 25.83 95% CI 7.78-85.76).

A single-nucleotide polymorphism in the MDR1 gene as a predictor of response to neoadjuvant chemotherapy in breast cancer.

BACKGROUND: The single-nucleotide polymorphism (SNP) 3435C > T in exon 26 of the MDR1 gene has been shown to correlate with the functioning of P-glycoprotein. We studied the frequency of SNP in exon 26 of the MDR1 gene in breast cancer and its role in predicting response to neoadjuvant chemotherapy in breast cancer. PATIENTS AND METHODS: Ninety-six patients with locally advanced breast carcinoma were enrolled. Genotyping of exon 26 of the MDR1 gene was performed, and computed tomography scans were performed before and after neoadjuvant chemotherapy. Response to 3 cycles of the 5-fluorouracil/doxorubicin/ cyclophosphamide (FAC) regimen was assessed. The prevalence of SNP was compared with that of historical controls. Association of the response was compared with the genotypes. RESULTS: The frequency of genotypes was different from that of healthy sex-matched historical controls. Prevalence of TT genotype was significantly increased in breast cancer patients (P = .025). The patients with TT genotype had 2.26 times the chance of responding to neoadjuvant chemotherapy when compared with patients with the CC genotype (P = .44). CONCLUSION: Significantly higher prevalence of 3435TT genotype in exon 26 of the MDR1 gene in patients with breast cancer might suggest the possibility of increased breast cancer susceptibility. The genotypes did not show any significant association to response to chemotherapy in the population studied.

CYP1A1 polymorphisms and the risk of upper aerodigestive tract cancers in an Indian population.

BACKGROUND: The inter-individual differences in upper aerodigestive tract (UADT) cancer risk may be partly attributed to the polymorphic variability in the CYP1A1 gene that is involved in the metabolic activation of xenobiotics to carcinogenic reactive metabolites. METHODS: The hospital-based case-control study evaluated CYP1A1*2A and CYP1A1*2C polymorphisms in 408 histopathologically confirmed cases and 220 controls using polymerase chain reaction-restriction fragment length polymorphism methods. RESULTS: The multivariate logistic regression analyses demonstrated that CYP1A1 *1A/*2A (odds ratio [OR] 1.76; 95% Confidence interval [CI] 1.19-2.60) and *2A/*2A (OR 2.83; 95% CI 1.43-5.61) genotypes were significantly associated with increased risk for UADT cancers. The gene-environment interaction analyses revealed a significant interaction among tobacco smokers and chewers carrying CYP1A1*2A mutant genotypes on the multiplicative scale. CONCLUSION: CYP1A1*2A polymorphic genotypes are associated with an enhanced risk to UADT cancers, in particular, among the habitual tobacco smokers and chewers carrying mutant genotypes in the Tamilians of the Indian population.

ABCB1 genetic polymorphism and risk of upper aerodigestive tract cancers among smokers, tobacco chewers and alcoholics in an Indian population.

BACKGROUND AND OBJECTIVE: Upper aerodigestive tract (UADT) cancers are associated with the tobacco use and alcohol consumption. Certain toxins and carcinogens causing UADT cancers are found to be substrates of polymorphic ABCB1 gene encoded P-glycoprotein efflux pump. This study investigates the association between ABCB1 gene polymorphism at exon 26 (3435C>T) and risk to UADT cancers in Tamilians, a population of south India. METHODS: The study included 219 unrelated histopathologically confirmed cases and 210 population-based controls. Genomic DNA was extracted from peripheral leukocytes and genotyped for ABCB1 3435C>T polymorphism by PCR-restriction fragment length polymorphism method. RESULTS: The multivariate logistic regression analyses demonstrated that the homozygous ABCB1 TT genotype was significantly associated with an overall increased risk for developing UADT cancers [odds ratio (OR): 2.53; 95% confidence interval (CI): 1.28-5.02]. Further, the determination of gene-environment interaction by stratified analyses have revealed a significant interaction between the smoking and homozygous TT genotype [(OR: 7.52; CI: 1.50-37.70) and (OR: 16.89; CI: 3.87-73.79) for 11-20 and >20 pack-years, respectively]. The strongest interaction was observed among the regular tobacco chewers (OR: 45.29; CI: 8.94-130.56) homozygous for TT genotype. No suggestion, however, of an interaction between the genotypes and the alcohol consumption on the multiplicative scale was made. CONCLUSION: The ABCB1 gene polymorphism at exon 26 (3435C>T) may be one of the risk factors for susceptibility to UADT cancers. Furthermore, the significant interaction among habitual smokers and tobacco chewers, homozygous for TT genotype modulates the risk to UADT cancers in the Tamilian population of south India.

CYP2C9 and CYP2C19 genetic polymorphisms: frequencies in the south Indian population.

The aim of the study was to establish the frequencies of CYP2C9*1, *2, *3 and CYP2C19*1, *2 and *3 in the south Indian population and to compare them with the inter-racial distribution of the CYP2C9 and CYP2C19 genetic polymorphisms. Genotyping analyses of CYP2C9 and CYP2C19 were conducted in unrelated, healthy volunteers from the three south Indian states of Andhra Pradesh, Karnataka and Kerala, by the polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP). The allele frequencies of the populations of these three states were then pooled with our previous genotyping data of Tamilians (also in south India), to arrive at the distribution of CYP2C9 and CYP2C19 alleles in the south Indian population. Frequencies of CYP2C9 and CYP2C19 alleles and genotypes among various populations were compared using the two-tailed Fisher's exact test. The frequencies of CYP2C9*1, *2 and *3 in the south Indian population were 0.88 (95% CI 0.85-0.91), 0.04 (95% CI 0.02-0.06) and 0.08 (95% CI 0.06-0.11), respectively. The frequencies of CYP2C9 genotypes *1/*1, *1/*2, *1/*3, *2/*2, *2/*3 and *3/*3 were 0.78 (95% CI 0.74-0.82), 0.05 (95% CI 0.03-0.07), 0.15 (95% CI 0.12-0.18), 0.01 (95% CI 0.0-0.02), 0.01 (95% CI 0.0-0.02) and 0.0, respectively. CYP2C19*1, *2 and *3 frequencies were 0.64 (95% CI 0.60-0.68), 0.35 (95% CI 0.31-0.39) and 0.01 (95% CI 0.0-0.03), respectively. As a result of a significant heterogeneity, the data on CYP2C19 genotype frequencies were not pooled. The frequency of CYP2C9*2 mutant alleles in south Indians was higher than in Chinese and Caucasians, while CYP2C9*3 was similar to Caucasians. CYP2C19*2 was higher than in other major populations reported so far. The relatively high CYP2C19 poor-metabolizer genotype frequency of 12.6% indicates that over 28 million south Indians are poor metabolizers of CYP2C19 substrates.