USE OF CLONED AND EXPRESSED HUMAN LIVER UDP-GLUCURONOSYLTRANSFERASES FOR ANALYSIS OF DRUG GLUCURONIDE FORMATION AND ASSESSMENT OF DRUG TOXICITY

Five clond human hepatic UDP-glucuronsyltransferease (UGT) cDNAs were stably expressed in tisse culture cell lines. More than 100 drugs and xenobiotics were used as substrates for glucuronidation catalyzed by t he cloned human transferases to determine the chemical structures acce pted as substrates. UGT-HP1 exhibited a limited substrate specificity for planar phenolic compounds, whereas UGT-HP4 was more accepting of n onplanar phenols, anthraquinones, flavones, alphatic alcohols, aromati c carboxylic acids, steroids and many drugs of Varied structure. UGT-H P3 (bilirubin UGT) catalyzed the glucuronidation of ethinylestradiol. UGT-H6 and UGT-H25 (steroid/bile acid UGTs) also catalyzed the glucuro nidation of some xenobiotics. Levels of UGT-HP4 activity towards some substrates were sufficient to allow determination of kinetic parameter s for the enzyme reaction. Further, metabolism of drugs could be studi ed by addition to the recombinant cell lines in culture and extraction of the media allowed analysis of glucuronide formation. The protectio n afforded against cytotoxic drugs was observed. The data presented he re demonstrate the potential of using these recombinant cell lines for investigation of phase II metabolism by human UGTs and subtle differe nces in protein structure which affect their specificity.