title: Mechanism-Based Inhibition of CYP3A4 by Podophyllotoxin: Aging of an Intermediate Is Important for in Vitro/in Vivo Correlations.
abstract: An in vitro observation of time-dependent inhibition (TDI) of metabolic enzymes often results in removing a potential drug from the drug pipeline. However, the accepted method for predicting TDIs of the important drug metabolizing cytochrome P450 enzymes often overestimates the drug interaction potential. Better models that take into account the complexities of the cytochrome P450 enzyme system will lead to better predictions. Herein we report the use of our previously described models for complex kinetics of podophyllotoxin. Spectral characterization of the kinetics indicates that an intermediate MI complex is formed, which slowly progresses to an essentially irreversible MI complex. The intermediate MI complex can release free enzyme during the time course of a typical 30 min TDI experiment. This slow rate of MI complex conversion results in an overprediction of the kinact value if this process is not included in the analysis of the activity versus time profile. In vitro kinetic experiments in rat liver microsomes predicted a lack of drug interaction between podophyllotoxin and midazolam. In vivo rat pharmacokinetic studies confirmed this lack of drug interaction.
authors.affiliation: Department of Chemistry, Washington State University , Pullman, Washington 99164, United States.
authors.forename: Carlo
authors.initials: C
authors.lastname: Barnaba
authors.affiliation: Department of Pharmaceutical Sciences, Temple University School of Pharmacy , Philadelphia, Pennsylvania 19140, United States.
authors.forename: Jaydeep
authors.initials: J
authors.lastname: Yadav
authors.affiliation: Department of Pharmaceutical Sciences, Temple University School of Pharmacy , Philadelphia, Pennsylvania 19140, United States.
authors.forename: Swati
authors.initials: S
authors.lastname: Nagar
authors.affiliation: Department of Pharmaceutical Sciences, Temple University School of Pharmacy , Philadelphia, Pennsylvania 19140, United States.
authors.forename: Ken
authors.initials: K
authors.lastname: Korzekwa
authors.affiliation: Department of Chemistry, Washington State University , Pullman, Washington 99164, United States.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Jones
mesh_terms: D000818:Animals; D001559:Benzhydryl Compounds / Q000494:pharmacology; D002853:Chromatography, Liquid; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D008962:Models, Theoretical; D011034:Podophyllotoxin / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D001559:Benzhydryl Compounds; D051544:Cytochrome P-450 CYP3A; D011034:Podophyllotoxin
keywords: carbene; mechanism-based inhibition; methylenedioxyphenyl compounds; podophyllotoxin; time-dependent inhibition