TY - JOUR T1 - Identification of the Human UDP-Glucuronosyltransferases Involved in the Glucuronidation of Combretastatin A-4 JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1141 LP - 1146 DO - 10.1124/dmd.109.031435 VL - 38 IS - 7 AU - Silvio Aprile AU - Erika Del Grosso AU - Giorgio Grosa Y1 - 2010/07/01 UR - http://dmd.aspetjournals.org/content/38/7/1141.abstract N2 - The stilbenic compound (Z)-combretastatin A-4 (CA-4) has been described as a potent tubulin polymerization inhibitor. In vivo, CA-4 binds to tubulin and inhibits microtubule depolymerization, which results in morphological changes in proliferating endothelial cells. Combretastatin A-4 prodrug phosphate is a leading vascular disrupting agent and is currently being evaluated in multiple clinical trials as a treatment for solid tumors. The aim of this study was to identify and characterize the UDP-glucuronosyltransferase (UGT) isoforms involved in CA-4 glucuronidation by incubation with human liver microsomes and a panel of nine liver-expressed recombinant UGT Supersomes (1A1, 1A3, 1A4, 1A6, 1A9, 2B4, 2B7, 2B15, and 2B17). As we observed, the high rate of formation of CA-4 glucuronide (Vmax = 12.78 ± 0.29 nmol/min/mg protein) and the low Km (6.98 ± 0.65 μM) denoted that UGT1A9 was primarily responsible for the in vitro glucuronidation of CA-4. UGT1A6 was also a significant contributor to CA-4 glucuronidation (Vmax = 3.95 ± 0.13 nmol/min/mg protein and S50 = 44.80 ± 3.54 μM). Furthermore, we demonstrated that the kinetics of CA-4 glucuronidation with liver microsomes but also with a panel of recombinant UGTs is atypical as it fits two different models: the substrate inhibition and also the sigmoidal kinetic model. Finally, experiments conducted to inhibit the glucuronosyltransferase activity in the human liver microsomes assay showed that phenylbutazone, trifluoperazine, propofol, and 1-naphthol effectively inhibited CA-4 glucuronidation. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics ER -