Jenabian_2004_J.Clin.Oncol_22_2065

2065 Background: The carboxylesterase 2 (CES2) is a key enzyme for irinotecan bioactivation. The aims of this work were i) to search for genetic polymorphisms in promoter, coding sequence and intron-exon junctions of CES2, ii) to characterize the reported SNPs in data bases and iii) to study the functional consequences of these polymorphisms.
METHODS: First we analysed the coding and the promoter region of CES2 by direct sequencing in a set of 60 human liver DNA. Second, the CES2 activity was measured in the cytosols and in the microsomes of the same set of human liver by spectrophotometry with the 4-Methylumbelliferyl acetate which is a human CES2 specific substrate. CES2 RNA expression was also quantified by real time PCR from RNA extracted from a subset of 31 human livers.
RESULTS: No SNP was found in the coding sequence and in intron-exon boundaries of the CES2 gene. However, 5 SNPs were identified in non coding regions: -1050 C>T, -1035 G>A, -363 C>G, 7555 G>A, 8772 A>G (allelic frequencies were respectively 2.5%, 4.2%, 10%, 11%, 3.3%). All of these SNPs were in linkage disequilibrium. The overall CES2 activity was on average 7 fold more important in cytosols than in microsomes. The range of CES2 activity in cytosols was 1 to 8.3 fold. Although a significant association was found between the -363 C/G genotype and the 7555 G/A genotype and a low level of CES2 RNA expression, no significant difference in CES2 activity was observed among the different genotypes.
CONCLUSIONS: The level of CES2 activity appears to be variable between individuals but this variability is not explained by genetic polymorphisms. The study of irinotecan metabolism should continue by using a polygenic pharmacogenetic approach of other implicated enzymes. No significant financial relationships to disclose.