Abstract 3456: Characterization of dibenzo[a,l]pyrene-trans-11,12-diol glucuronidation by UDP-glucuronosyltransferases

Abstract

Abstract A procarcinogen found most notably in tobacco smoke is dibenzo[a,l]pyrene (DB[a,l]P), which can be further metabolized into its epoxide, diol, and carcinogenic diol-epoxide forms. DB[a,l]P metabolites are some of the most potent carcinogens of the polycyclic aromatic hydrocarbon (PAH) family of compounds due to a structural feature called the fjord region. The activated metabolites of DB[a,l]P bind mostly to deoxyadenosine in DNA to form stable adducts, which can potentially lead to DNA damage. UDP-glucuronosyltransferase (UGT) enzymes mediate the attachment of a UDP-glucuronic acid to a wide variety of endogenous and exogenous substrates including several carcinogens, resulting in increases in water solubility and elimination of the carcinogen from the body. The focus of the current study was to examine the detoxification of the carcinogenic diol form (DB[a,l]P-trans-11,12-diol) by glucuronidation. In order to understand the metabolism of this potent PAH by human UGT enzymes, HEK293 cell lines over-expressing individual UGTs were screened for glucuronidation activity toward DB[a,l]P-11,12-diol. Glucuronide products were quantified using an ultra-performance liquid chromatography (UPLC) method. Six UGTs (UGTs 1A1, 1A7, 1A8, 1A9, 1A10 and UGT2B7) were found to be highly active. Three glucuronide conjugates were observed in activity assays with UGT1A1 and 1A10, while only two glucuronides were formed with UGTs 1A7, 1A8, 1A9, and 2B7. Enzyme kinetic analysis indicated that UGT1A9 is the most active isoform among all the UGTs, exhibiting the highest Vmax/Km for the two glucuronide products it formed. These results suggest that multiple UGTs are involved in stereospecific glucuronidation of DB[a,l]P metabolites in humans. In addition to the further characterization of (DB[a,l]P-trans-11,12-diol) glucuronide conjugates, studies examining the role of polymorphisms in active UGTs on cancer risk are currently on-going. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3456.