Common variants in glucuronidation enzymes and membrane transporters as potential risk factors for colorectal cancer: a case control study.

BACKGROUND: Associations between polymorphisms of UDP-glucuronosyltransferases (UGTs) or efflux transporters (e.g., P-glycoprotein and MRP2) and different types of cancer have been described, whereas the role of influx transporters (e.g. OATP1B1 and OATP2B1) has been seldom explored. The GenColon study investigated potential associations between variant alleles of UGTs, efflux and influx transporters and CRC. METHODS: Three hundred CRC cases were matched with 300 controls for age, sex and enrolment site. Fifteen SNPs in UGT1A6-9, UGT2B7, ABCB1, ABCC2, SLCO1B1 and SLCO2B1 genes were characterized using Taqman® PCR. Using multivariate conditional logistic regression, we investigated the relationships between CRC and "environmental" risk factors (physical activity, housing and working areas, consumption of red meat, tobacco, alcohol); genetic polymorphisms, in the study population and in the subgroups with "environmental" risk factors. RESULTS: No significant association was observed for the analyzed SNPs (or haplotypes). However, an increased CRC risk was found in carriers of the UGT1A8 rs1042597-G variant allele (additive risk OR = 3.39[1.29-8.89], p = 0.02951) in the subgroup of meat-consumers (n = 84), and in carriers of the ABCB1 rs1045642-T (exon26) variant allele (additive risk; OR = 1.89[1.10-3.39], p = 0.0257) in the "never alcohol consumption subgroup" (n = 125). In addition, as previously reported, the following CRC risk factors were identified: absence of physical activity (OR = 6.35[3.70-10.9], p < 0.0001), living or working in rural or mix area (OR = 2.50[1.48-4.23], p = 0.0006 and OR = 2.99[1.63-5.48], p = 0.004, respectively) and tobacco exposure >30 years (3.37[1.63-6.96], p = 0.0010). CONCLUSIONS: Variant genotypes of influx transporters (OATP1B1 and 2B1) were not associated with CRC. This study confirmed the influence of lifestyle factors, but not the previously reported detrimental effect of SNPs in intestinal UGTs or efflux transporters, except for a UGT1A8 variant in subjects consuming meat and the exon 26 SNP of ABCB1 in the never alcohol consumption subgroup. TRIAL REGISTRATION: Registered in Direction Générale de la Santé the 1st July 2008 under the number DGS2008-0144.

Simultaneous evaluation of six human glucuronidation activities in liver microsomes using liquid chromatography-tandem mass spectrometry.

This article describes the development of a procedure for the simultaneous evaluation of the activity of six different uridine diphosphate (UDP)-glucuronyltransferases (UGTs) in human liver microsomes (HLMs). The method consists of incubations of probe substrates for UGT1A1 (etoposide), UGT1A3 (chenodeoxycholic acid), UGT1A4 (trifluoperazine), UGT1A6 (serotonin), UGT1A9 (mefenamic acid), and UGT2B7 (azidothymidine) with HLMs. The six substrates were divided into three different incubations (etoposide + mefenamic acid; chenodeoxycholic acid + serotonin + azidothymidine; and trifluoperazine alone), the media of which were pooled before analysis. Glucuronide formation rates were determined in a single run of 20 min using a validated liquid chromatography-tandem mass spectrometry method. No significant difference was observed between glucuronidation activities measured using the current procedure and individual incubations of the probes. The method was used successfully for the determination of UGT activities in 44 individual HLM preparations and for the phenotyping of preparations predicted to have altered UGT1A1 and UGT2B7 activities because of known genetic polymorphisms.

CYP3A5 genotype does not influence everolimus in vitro metabolism and clinical pharmacokinetics in renal transplant recipients.

BACKGROUND: CYP3A5 genotyping might be useful to guide tacrolimus and sirolimus dosing. The aim of this study was to assess the influence of CYP3A5 polymorphism on everolimus metabolism and pharmacokinetics. METHODS: We investigated the effect of CYP3A5 6986A>G polymorphism (CYP3A5*1/*3 alleles) on the pharmacokinetics of everolimus in 28 renal transplant patients and on its in vitro hepatic metabolism using a bank of genotyped human liver microsomes (n=49). We further evaluated in vitro the contribution of CYP3A4, CYP3A5, and CYP2C8 to everolimus hepatic metabolism using recombinant enzymes. RESULTS: We found no association between CYP3A5 polymorphism and everolimus pharmacokinetics in renal transplant patients. On the other hand, no effect of CYP3A5 polymorphism was observed on the intrinsic clearance of everolimus by human liver microsomes, whereas that of tacrolimus (positive control) was 1.5-fold higher in microsomes carrying the CYP3A5*1 allele than in noncarriers. In vitro data showed that CYP3A4 is a better catalyst of everolimus metabolism than CYP3A5, whereas the opposite was observed for tacrolimus. CONCLUSIONS: This study provides direct and indirect evidence that CYP3A5 genotyping cannot help improve everolimus therapy.