Identification of Enzymes Responsible for Primary and Sequential Oxygenation Reactions of Capravirine in Human Liver Microsomes

Abstract

ABSTRACT:Capravirine, a new non-nucleoside reverse transcriptase inhibitor, undergoes extensive oxygenation reactions, including N-oxidation, sulfoxidation, sulfonation, and hydroxylation in humans. Numerous primary (mono-oxygenated) and sequential (di-, tri-, and tetraoxygenated) metabolites of capravirine are formed via the individual or combined oxygenation pathways. In this study, cytochrome P450 enzymes responsible for the primary and sequential oxygenation reactions of capravirine in human liver microsomes were identified at the specific pathway level. The total oxygenation of capravirine is mediated predominantly (>90%) by CYP3A4 and marginally (<10%) by CYP2C8, 2C9, and 2C19 in humans. Specifically, each of the two major mono-oxygenated metabolites C23 (sulfoxide) and C26 (N-oxide), is mediated predominantly (>90%) by CYP3A4 and slightly (<10%) by CYP2C8, the minor tertiary hydroxylated metabolite C19 by CYP3A4, 2C8, and 2C19, and the minor primary hydroxylated metabolite C20 by CYP3A4, 2C8, and 2C9. However, all sequential oxygenation reactions are mediated exclusively by CYP3A4. Due to their relatively insignificant contributions of C19 and C20 to total capravirine metabolism, no attempt was made to determine relative contributions of cytochrome P450 enzymes to the formation of the two minor metabolites.

Metabolism and Pharmacokinetics of a Novel Src Kinase Inhibitor TG100435 ([7-(2,6-Dichloro-phenyl)-5-methyl-benzo[1,2,4]triazin-3-yl]-[4-(2-pyrrolidin-1-yl-ethoxy)-phenyl]-amine) and Its Active N-Oxide Metabolite TG100855 ([7-(2,6-Dichloro-phenyl)-5-methylbenzo[1,2,4]triazin-3-yl]-{4-[2-(1-oxy-pyrrolidin-1-yl)-ethoxy]-phenyl}-amine)

“…been demonstrated that N-oxidation of tamoxifen in humans was catalyzed by FMO1 and FMO3 (Parte and Kupfer, 2005). On the other hand, N-oxidation of capravirine, a non-nucleoside reverse transcriptase inhibitor, is mediated predominantly by CYP3A4 in human liver microsome (Bu et al, 2006). Our studies indicate that N-oxidation of TG100435 is primarily mediated by FMO (Fig.…”

Evaluation of Capravirine as a CYP3A Probe Substrate: In Vitro and in Vivo Metabolism of Capravirine in Rats and Dogs

“…In a further study, P450 enzymes responsible for the primary and sequential oxygenation reactions of capravirine in human liver microsomes have been identified at the specific pathway level (Bu et al, 2006). The total oxygenation of capravirine is mediated predominantly (Ͼ90%) by CYP3A4 and marginally (Ͻ10%) by CYP2C8, 2C9, and 2C19.…”

“…Capravirine represents a novel non-nucleoside reverse transcriptase inhibitor that had been developed for the treatment of human immunodeficiency virus type 1 (Fujiwara et al, 1998(Fujiwara et al, , 1999Ohkawa et al, 1998;Ren et al, 2000;Bu et al, 2004Bu et al, , 2005Bu et al, , 2006Bu et al, , 2007. In humans, capravirine is predominantly metabolized to a variety of mono-, di-, tri-, and tetraoxygenated metabolites via individual or combined oxygenation reactions of N-oxidation, sulfoxidation, sulfone formation, and hydroxylation (Bu et al, 2004).…”

“…The sequential incubation method should be applicable to mechanistic studies of other compounds involving complicated sequential metabolism when radiolabeled materials are available. We were able to develop the new method largely due to the biotransformation features of capravirine that allow the study of metabolic diversity (i.e., hydroxylation, sulfoxidation, sulfone formation, and N-oxidation) as well as multiplicity (i.e., mono-, di-, tri-, and tetraoxygenations).In a further study, P450 enzymes responsible for the primary and sequential oxygenation reactions of capravirine in human liver microsomes have been identified at the specific pathway level (Bu et al, 2006). The total oxygenation of capravirine is mediated predominantly (Ͼ90%) by CYP3A4 and marginally (Ͻ10%) by CYP2C8, 2C9, and 2C19.…”

“…Because the majority of in vivo oxygenated metabolites of capravirine were observed in liver microsomal incubations, the in vitro models provided good insight into the in vivo oxygenation pathways. In conclusion, the diversity (i.e., hydroxylation, sulfoxidation, sulfone formation, and N-oxidation), multiplicity (i.e., mono-, di-, tri-, and tetraoxygenations), and high enzymatic specificity (>90% contribution by CYP3A4 in humans, CYP3A1/2 in rats, and CYP3A12 in dogs) of the capravirine oxygenation reactions observed in humans, rats, and dogs in vivo and in vitro suggest that capravirine can be a useful CYP3A substrate for probing catalytic mechanisms and kinetics of CYP3A enzymes in humans and animal species.Capravirine represents a novel non-nucleoside reverse transcriptase inhibitor that had been developed for the treatment of human immunodeficiency virus type 1 (Fujiwara et al, 1998(Fujiwara et al, , 1999Ohkawa et al, 1998;Ren et al, 2000;Bu et al, 2004Bu et al, , 2005Bu et al, , 2006Bu et al, , 2007. In humans, capravirine is predominantly metabolized to a variety of mono-, di-, tri-, and tetraoxygenated metabolites via individual or combined oxygenation reactions of N-oxidation, sulfoxidation, sulfone formation, and hydroxylation (Bu et al, 2004).…”