Genetic variation and haplotype structures of the glutathione S-transferase genes GSTA1 and GSTA2 in Japanese colorectal cancer patients.

Glutathione S-transferases (GSTs) play a vital role in the phase II biotransformation of many chemicals, including anticancer drugs. In this study, to elucidate the haplotype structures of the two closely related alpha-class genes GSTA1 and GSTA2, we screened for genetic variation in 214 Japanese colorectal cancer patients who received oxaliplatin-based chemotherapy. By direct resequencing of the 5'-flanking region, all the exons, and their flanking introns for 107 patients, 29 and 27 variants were identified in GSTA1 and GSTA2, respectively. The known functional single nucleotide polymorphisms (SNPs) -567T>G, -69C>T, and -52G>A in GSTA1*B were found at allele frequencies of 0.140. Of the four major GSTA2 allelic variants reported previously (GSTA2*A, *B, *C, and *E), only GSTA2*B (frequency = 0.154), *C (0.706), and *E (0.140) were detected. Following linkage disequilibrium analysis, haplotypes of both genes were separately estimated. Then, rapid genotyping methods for 7 and 6 SNPs tagging common haplotypes of GSTA1 and GSTA2, respectively, were developed using the single-base extension assay, and an additional 107 patients were genotyped. Finally, haplotype combinations of both genes were classified into 3 major types: GSTA1*A-GSTA2*C, GSTA1*A-GSTA2*B, and GSTA1*B-GSTA2*E. These findings will be useful in pharmacogenomic studies on xenobiotics including anticancer drugs.

Association of carboxylesterase 1A genotypes with irinotecan pharmacokinetics in Japanese cancer patients.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Association of UDP-glucuronosyltransferase 1A1 (UGT1A1) genetic polymorphisms *6 and *28 with reduced clearance of SN-38 and severe neutropenia in irinotecan therapy was demonstrated in Japanese cancer patients. * The detailed gene structure of CES1 has been characterized. * Possible functional SNPs in the promoter region have been reported. WHAT THIS STUDY ADDS * Association of functional CES1 gene number with AUC ratio [(SN-38 + SN-38G)/irinotecan], an in vivo index of CES activity, was observed in patients with irinotecan monotherapy. * No significant effects of major CES1 SNPs on irinotecan PK were detected. AIMS Human carboxylesterase 1 (CES1) hydrolyzes irinotecan to produce an active metabolite SN-38 in the liver. The human CES1 gene family consists of two functional genes, CES1A1 (1A1) and CES1A2 (1A2), which are located tail-to-tail on chromosome 16q13-q22.1 (CES1A2-1A1). The pseudogene CES1A3 (1A3) and a chimeric CES1A1 variant (var1A1) are also found as polymorphic isoforms of 1A2 and 1A1, respectively. In this study, roles of CES1 genotypes and major SNPs in irinotecan pharmacokinetics were investigated in Japanese cancer patients. METHODS CES1A diplotypes [combinations of haplotypes A (1A3-1A1), B (1A2-1A1), C (1A3-var1A1) and D (1A2-var1A1)] and the major SNPs (-75T>G and -30G>A in 1A1, and -816A>C in 1A2 and 1A3) were determined in 177 Japanese cancer patients. Associations of CES1 genotypes, number of functional CES1 genes (1A1, 1A2 and var1A1) and major SNPs, with the AUC ratio of (SN-38 + SN-38G)/irinotecan, a parameter of in vivo CES activity, were analyzed for 58 patients treated with irinotecan monotherapy. RESULTS The median AUC ratio of patients having three or four functional CES1 genes (diplotypes A/B, A/D or B/C, C/D, B/B and B/D; n= 35) was 1.24-fold of that in patients with two functional CES1 genes (diplotypes A/A, A/C and C/C; n= 23) [median (25th-75th percentiles): 0.31 (0.25-0.38) vs. 0.25 (0.20-0.32), P= 0.0134]. No significant effects of var1A1 and the major SNPs examined were observed. CONCLUSION This study suggests a gene-dose effect of functional CES1A genes on SN-38 formation in irinotecan-treated Japanese cancer patients.

Genetic variations and haplotype structures of the glutathione S-transferase genes, GSTT1 and GSTM1, in a Japanese patient population.

Glutathione S-transferases (GSTs) play a vital role in phase II biotransformation of many synthetic chemicals including anticancer drugs. Deletion polymorphisms in GSTT1 and GSTM1 are reportedly associated, albeit controversial, with an increased risk in cancer as well as with altered responses to chemotherapeutic drugs. In this study, to elucidate the haplotype structures of GSTT1 and GSTM1, genetic variations were identified in 194 Japanese cancer patients who received platinum-based chemotherapy. Homozygotes for deletion of GSTT1 (GSTT1(*)0/(*)0 or null) and GSTM1 (GSTM1(*)0/(*)0 or null) were found in 47.4% and 47.9% of the patients, respectively, while 23.2% of the patients had both GSTT1 null and GSTM1 null genotypes. From homozygous (+/+) and heterozygous ((*)0/+) patients bearing GSTT1 and GSTM1 genes, six single nucleotide polymorphisms (SNPs) for GSTT1 and 23 SNPs for GSTM1 were identified. A novel SNP in GSTT1, 226C>A (Arg76Ser), and the known SNP in GSTM1, 519C>G (Asn173Lys, (*)B), were found at frequencies of 0.003 and 0.077, respectively. Using the detected variations, GSTT1 and GSTM1 haplotypes were identified/inferred. Three and six common haplotypes (N> or =10) in GSTT1 and GSTM1, respectively, accounted for most (>95%) inferred haplotypes. This information would be useful in pharmacogenomic studies of xenobiotics including anticancer drugs.