RT Journal Article SR Electronic T1 In Vitro Biotransformation and Identification of Human Cytochrome P450 Isozyme-Dependent Metabolism of Tazofelone JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1383 OP 1388 VO 25 IS 12 A1 Surapaneni, Sekhar S. A1 Clay, Michael P. A1 Spangle, Larry A. A1 Paschal, Jonathan W. A1 Lindstrom, Terry D. YR 1997 UL http://dmd.aspetjournals.org/content/25/12/1383.abstract AB Tazofelone is a new inflammatory bowel disease agent. The biotransformation of tazofelone in human livers and the cytochrome P450 responsible for the biotransformation has been studied. Two metabolites of tazofelone were formed in vitro. A sulfoxide metabolite was identified by cochromatography with authentic standards, and a quinol metabolite of tazofelone was identified by mass spectrometry and proton NMR. Sulfoxidation was catalyzed by a single enzyme system while formation of the quinol metabolite was catalyzed by a two enzyme system. The Km andVmax values for sulfoxidation were 12.4 μM and 0.27 nmol/min/mg protein, respectively. The high affinityKm and Vmaxvalues for the formation of the quinol metabolite were 7.5 μM and 0.17 nmol/min/mg protein, respectively. Tazofelone was incubated at 20 μM concentration with human microsomes to determine which of the cytochrome P450 isozyme(s) is involved in the oxidation of tazofelone. A strong correlation was found between the immunoquantified concentrations of CYP3A and the rates of formation of the sulfoxide and quinol metabolites of tazofelone. Similarly, significant correlations were observed between the formation of midazolam 1′-hydroxylation and the rates of formation of both metabolites of tazofelone. Inhibition studies have indicated that triacetyloleandomycin, a CYP3A specific inhibitor, almost completely inhibited the formation of both of these tazofelone metabolites. Incubations with specific cDNA expressed microsomes indicated that the formation of both the sulfoxide and quinol metabolites was highest with CYP3A4 containing microsomes. The correlation data was confirmed by inhibition studies and cDNA expressed cytochrome P450 systems demonstrating that the biotransformation of tazofelone to its metabolites is primarily mediated by CYP3A. The American Society for Pharmacology and Experimental Therapeutics