PT - JOURNAL ARTICLE AU - Takenaga, Norihiro AU - Ishii, Mikio AU - Kamei, Toshio AU - Yasumori, Toshio TI - Structure-Activity Relationship in<em>O</em>-Glucuronidation of Indolocarbazole Analogs AID - 10.1124/dmd.30.5.494 DP - 2002 May 01 TA - Drug Metabolism and Disposition PG - 494--497 VI - 30 IP - 5 4099 - http://dmd.aspetjournals.org/content/30/5/494.short 4100 - http://dmd.aspetjournals.org/content/30/5/494.full SO - Drug Metab Dispos2002 May 01; 30 AB - The glucuronidation of 6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13-(β-d-glucopyranosyl)5H-indolo[2,3-a]pyrrolo[3,4-c]carbazole-5,7(6H)-dione (compound 1), a potent inhibitor of DNA topoisomerase I, and its related indolocarbazole compounds was studied using human liver microsomes. Compound 1 and its structurally related compounds with the NHCHO moiety at the N-6 position were glucuronidated even if the positions of the phenolic hydroxy moiety were different in these molecules. Compounds that have the NHCH(CH2OH)2moiety at the N-6 position, however, were not glucuronidated. The three-dimensional structure of these substrates was determined by the semiempirical molecular-orbitals calculation method. Computer-modeling studies, however, revealed that the O-glucuronidation of indolocarbazole analogs depended on the molecular size of the substrates. Compounds larger than 14.5 Å in diameter perpendicular to the phenolic hydroxy moiety were not glucuronidated. The chemical reactivity of the hydroxy moiety, evaluated by the atom electron density and the electrostatic potential charges, was very similar in these substrates. These results suggest that a molecular length less than 14.5 Å may be required for a substrate to interact with the active site of UDP-glucuronosyltransferase (UGT). To further characterize the glucuronidation of indolocarbazole analogs, compound 1 was used as a representative compound to assess expressed human UGTs. The glucuronidation of compound 1 was catalyzed by recombinant UGT1A9 and UGT1A10 among UGT isoforms tested. The American Society for Pharmacology and Experimental Therapeutics