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The multidrug resistance gene 1 (MDR1) seems to play a role in the carcinogenesis of colorectal tumors. The importance of MDR1 SNPs 2677GT/A in exon 21 and 3435CT in exon 26 for cancer susceptibility, however, has not yet been clearly defined.Two hundred and eighty-five colorectal cancer patients and 275 controls from five hospitals in the European part of Russia were genotyped for the polymorphisms -129TC (rs3213619) in exon 1b, 2677GT/A (rs2032582), and 3435CT (rs1045642) in this population-based case-control study. Genotype-phenotype analysis was performed with simultaneous consideration of lifestyle risk factors.Our analysis confirmed the preponderate impact of smoking on colorectal cancer development. The risk of heavy smokers (/=60 pack years) to develop colorectal cancer by far exceeded that of lifelong non-smokers (OR = 3.9, 95% CI: 1.4 to 10.6). Smoking is a more potent risk factor than is the genetic influence of MDR1 in our study. However, a smoking and age-stratified analysis, revealed a statistically significant association between MDR1 genotypes and colorectal cancer in life-long non-smokers with an ageor =63 years (the median age in our sample). The association was stronger for rectal cancer than for colon cancer. Patients who carried the genotypes (-129TT; 2677GG; 3435CC) or (-129TT; 2677TT; 3435TT) developed more frequently colorectal cancer than others (OR = 3.9; 95% CI: 2.0 to 7.7).Our results show that the interaction of genetic and lifestyle risk factors should be taken into account to elucidate the genetic influence of MDR1 variability on cancer susceptibility.

The frequency of functionally important mutations and alleles of genes coding for xenobiotic metabolizing enzymes shows a wide ethnic variation. However, little is known of the frequency distribution of the major allelic variants in the Russian population. Using polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) genotyping assays and the real-time PCR with fluorescent probes, the frequencies of functionally important variants of the cytochromes P 450 (CYP) 2C9, 2C19, 2D6, 1A1 as well as arylamine N-acetyltransferase 2 (NAT2) and P-glycoprotein (MDR1) were determined in a sample of 290 Russian volunteers derived from Voronezh area. CYP2C9*2 and *3 alleles were found with allelic frequencies of 10.5% and 6.7%, respectively. The novel intron-2 T>C mutation at exon 2 +73 bp occurred in 24.8% of alleles. CYP2C19*2 and *3 alleles occurred in 11.4% and 0.3%, respectively. Six persons (2.1%) carried two of these CYP2C19 alleles responsible for poor metabolizing activity. Of all subjects, 5.9% were CYP2D6 poor metabolizers, whereas 3.4% were addressed to ultra-rapid metabolizers (CYP2D6*1×2/*1). The CYP1A1*2A allele was found in 4.7%, *2B in 5.0%, *4 in 2.6%, and the 5′-mutations −3219C>T, −3229G>A, and the novel −4335G>A in 6.0%, 2.9% and 26.0% of alleles, respectively. Genotyping of eight different single nucleotide polymorphisms in the NAT2 gene provided in 58.0% a genotype associated with slow acetylation. The MDR1 triple variants G2677T and G2677A in exon 21 had an allelic frequency of 41.9% and 3.3%, respectively, and the variant C3435T in exon 26 one of 54.3%. Frequencies of functionally important haplotypes were calculated. The overview of allele distribution of important xenobiotic-metabolizing enzymes among a Russian population shows similarity to other Caucasians. The data will be useful for clinical pharmacokinetic investigations and for drug dosage recommendations in the Russian population.