title: In vitro exploration of potential mechanisms of toxicity of the human hepatotoxic drug fenclozic acid.
abstract: The carboxylic acid NSAID fenclozic acid exhibited an excellent preclinical safety profile and promising clinical efficacy, yet was withdrawn from clinical development in 1971 due to hepatotoxicity observed in clinical trials. A variety of modern in vitro approaches have been used to explore potential underlying mechanisms. Covalent binding studies were undertaken with [(14)C]-fenclozic acid to investigate the possible role of reactive metabolites. Time-dependent covalent binding to protein was observed in NADPH-supplemented liver microsomes, although no metabolites were detected in these incubations or in reactive metabolite trapping experiments. In human hepatocytes, covalent binding was observed at lower levels than in microsomes and a minor uncharacterizable metabolite was also observed. In addition, covalent binding was observed in incubations undertaken with dog and rat hepatocytes, where a taurine conjugate of the drug was detected. Although an acyl glucuronide metabolite was detected when liver microsomes from human, rat and dog were supplemented with UDPGA, there was no detectable UDPGA-dependent covalent binding. No effects were observed when fenclozic acid was assessed for P450-dependent and P450-independent cytotoxicity to THLE cell lines, time-dependent inhibition of five major human cytochrome P450 enzymes, inhibition of the biliary efflux transporters BSEP and MRP2 or mitochondrial toxicity to THLE or HepG2 cells. These data suggest that Phase 1 bioactivation plays a role in the hepatotoxicity of fenclozic acid and highlight the unique insight into mechanisms of human drug toxicity that can be provided by investigations of biotransformation and covalent binding to proteins.
authors.affiliation: Molecular and Clinical Pharmacology, MRC Centre for Drug Safety Science, Sherrington Building, University of Liverpool, Ashton Street, Liverpool, L69 3GE, UK.
authors.forename: Alison V M
authors.initials: AV
authors.lastname: Rodrigues
authors.forename: Helen E
authors.initials: HE
authors.lastname: Rollison
authors.forename: Scott
authors.initials: S
authors.lastname: Martin
authors.forename: Sunil
authors.initials: S
authors.lastname: Sarda
authors.forename: Timothy
authors.initials: T
authors.lastname: Schulz-Utermoehl
authors.forename: Simone
authors.initials: S
authors.lastname: Stahl
authors.forename: Frida
authors.initials: F
authors.lastname: Gustafsson
authors.forename: Julie
authors.initials: J
authors.lastname: Eakins
authors.forename: J Gerry
authors.initials: JG
authors.lastname: Kenna
authors.forename: Ian D
authors.initials: ID
authors.lastname: Wilson
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002461:Cell Line, Transformed; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004285:Dogs; D056945:Hep G2 Cells / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000166:cytology / Q000187:drug effects; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000378:metabolism; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D013844:Thiazoles / Q000378:metabolism / Q000493:pharmacokinetics* / Q000633:toxicity*; D018675:Toxicity Tests / Q000379:methods*
chemical_list: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D013844:Thiazoles; C093491:ABCB11 protein, human; C000715087:ABCC2 protein, human; C490548:Abcb11 protein, rat; C100273:fenclozic acid