Characterization of the Selectivity and Mechanism of Human Cytochrome P450 Inhibition by the Human Immunodeficiency Virus-Protease Inhibitor Nelfinavir Mesylate

摘要: In vitro studies with human liver microsomes and P450 probe substrates were performed to characterize selectivity mechanism of cytochrome inhibition by nelfinavir mesylate. At therapeutic concentrations (steady-state plasma ≈4 μM), was found be a competitive inhibitor only testosterone 6β-hydroxylase (CYP3A4) aKiconcentration 4.8 μM. supratherapeutic concentrations, competitively inhibited dextromethorphan O-demethylase (CYP2D6),S-mephenytoin 4-hydroxylase (CYP2C19), phenacetinO-deethylase (CYP1A2) Kiconcentrations 68, 126, 190 μM, respectively. Nelfinavir did not appreciably inhibit tolbutamide (CYP2C9), paclitaxel 6α-hydroxylase (CYP2C8), or chlorzoxaxone (CYP2E1) activities. The inhibitory potency toward CYP3A4 suggested the possibility in vivo this isoform, whereas other P450s considered unlikely. one-sequence crossover study 12 healthy volunteers, elimination CYP3A substrate terfenadine carboxylate metabolite terfenadine. 24-hr urinary recoveries 6β-hydroxycortisol reduced an average 27% during treatment, consistent nelfinavir. Inhibition vitrowas NADPH-dependent requiring catalytic formation metabolic intermediate. catechol (M3) unlikely responsible for as addition O-methyl transferase,S-adenosyl methionine, ascorbic acid preincubation mixture protect against loss activity. Also, M3 CYP3A4. Although incubations showed time- concentration-dependent activity, partial complete recovery enzyme activity upon dialysis indicated that reversible. Microsomal NADPH result spectral content compared control. Glutathione, N-acetylcysteine, catalase attenuate Collectively, these results suggest probable is transient intermediate stable coordinates tightly but reversibly heme moiety P450.