Abstract 2757: Characterization of the glucuronidation of the major nicotine metabolite, 3’-hydroxycotinine: Potential role for knock-out polymorphisms in UGTs 2B17 and 2B10

Abstract

Abstract 3’-Hydroxycotinine (3HC) and its glucuronide (3HC-Gluc) conjugate are major nicotine metabolites excreted in the urine of smokers and other tobacco or nicotine users. Previous studies have demonstrated that human liver microsomes (HLM) were active in catalyzing the formation of both 3HC-O-Gluc and 3HC-N-Gluc. While not all human UDP-glucuronosyltransferases (UGTs) were previously screened, UGTs 2B7, 1A9, 2B4 and 2B15 were shown to be active in the formation of 3HC-O-Gluc and UGT1A4 active in 3HC-N-Gluc formation. In the present study, all known human UGTs except for UGT2B28 were screened for glucuronidation activity against 3HC. Homogenates from cell lines over-expressing UGTs 2B17 and 2B10 exhibited the highest O- and N-glucuronidation activities, respectively for the UGTs tested. Kinetic analysis for the formation of 3HC-O-Gluc demonstrated that the KM for UGT2B17 is 3.7- and 4.2-fold lower than that observed for UGTs 1A9 (p<0.005) and 2B7 (p<0.005); the KM of 3HC-N-Gluc formation was 4.4-fold lower (p<0.05) for UGT2B10 than that observed for UGT1A4. Kinetic analysis demonstrated that HLM from subjects exhibiting the homozygous null UGT2B17 deletion [UGT2B17 (*2/*2)] exhibited a KM for 3HC-O-Gluc formation that was 3.1-fold higher (p<0.001) than that observed in HLM from subjects exhibiting the wild-type UGT2B17(*1/*1) genotype. The KM of 15.6 μM for 3HC-O-Gluc formation in UGT2B17 (*2/*2) HLM was close to that observed for UGT2B17 (8.3 μM). 3HC-N-Gluc formation activity was decreased by 91% (p<0.001) in HLM from subjects with the UGT2B10(*2/*2) knock-out genotype and 39% (p<0.001) in HLM from subjects with the UGT2B10(*1/*2) genotype as compared to that observed for UGT2B10(*1/*1) HLMs. The KM of 13 μM for 3HC-N-Gluc formation in UGT2B10 (*1/*1) HLM (n=6) was close to that observed for UGT2B10 (13 μM). These results demonstrate that UGTs 2B17 and 2B10 play key roles in the hepatic glucuronidation of 3HC and that functional polymorphisms in UGT2B17 and UGT2B10 are associated with significantly reduced glucuronidation activities against 3HC in HLM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2757. doi:10.1158/1538-7445.AM2011-2757