A novel functional polymorphism in the uridine diphosphate–glucuronosyltransferase 2B7 promoter with significant impact on promoter activity

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Abstract
To clarify the molecular determinants of the metabolic variability of morphine, we searched for genetic polymorphisms in the gene for uridine diphosphate-glucuronosyltransferase 2B7 (UGT2B7) and evaluated their functional impact in vitro and in patients with cancer receiving long-term morphine therapy. Genetic analysis revealed the existence of 8 single-nucleotide polymorphisms (SNPs), 6 of which are tightly linked and are at positions -1248, -1241, -1054, -842, -268, and -102 relative to the hepatic start site. In contrast, an SNP at position -66 occurs independently, whereas a novel variation at position -79 appears to be in linkage disequilibrium with the codon 268 SNP (UGT2B7*2). At least 4 haplotypes were observed in white subjects included in the initial SNP screening. On functional in vitro characterization, promoter-reporter gene constructs with the -79 variation displayed 2.5- to 7-fold less activity compared with the wild-type construct in Caco-2 colon cells and HepG2 hepatoma cells, respectively (P =.015 and P <.001, respectively). To investigate a possible effect of the -79 variation in vivo, serum morphine and morphine glucuronide concentrations were measured by liquid chromatography-mass spectrometry in patients with cancer who received long-term oral morphine therapy, and subjects were then genotyped for the -79 polymorphism. Among 175 patients with normal hepatic and renal function, 6 were heterozygous for the -79 variation, and the morphine-6-glucuronide (M6G)/morphine and morphine-3-glucuronide (M3G)/morphine ratios versus those in the 169 noncarriers were 5.9 +/- 3.5 versus 7.1 +/- 7.0 for M6G/morphine (P =.96) and 31.2 +/- 17.1 versus 42.9 +/- 31.2 for M3G/morphine (P =.53), respectively. Further studies in larger samples are needed to make conclusions about the possible clinical relevance of the -79 polymorphism in the UGT2B7 gene.

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