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Antiprogestin-Mediated Inactivation of Cytochrome P450 3A4

Antiprogestin-Mediated Inactivation of Cytochrome P450 3A4 Based on previous observations of very short periods of linearity for antiprogestin metabolite formation and the presence of a common tertiary amine moiety in each compound as the principal site of their metabolism, we hypothesized that mifepristone, lilopristone and onapristone are oxidized by cytochrome P450 (CYP) 3A4 to reactive nitroso species that complex the heme of the enzyme, thereby inactivating it. Upon preincubation with human liver microsomes in the presence (but not the absence) of NADPH, mifepristone inhibited midazolam 1′-hydroxylation, a marker of CYP3A4 catalytic activity, very potently (IC<sub>50</sub> ∼3.5 µmol/l) and extensively (by ∼87%). Lilopristone and onapristone also displayed NADPH and time-dependent inactivation of CYP3A4 with characteristics very similar to mifepristone. These data support antiprogestin-mediated inactivation of CYP3A4 and suggest the potential for drug-drug interactions and time-dependent nonlinearities in pharmacokinetics upon their long-term administration. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Pharmacology Karger

Antiprogestin-Mediated Inactivation of Cytochrome P450 3A4

Pharmacology , Volume 56 (3): 8 – Mar 1, 1998

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References (31)

Publisher
Karger
Copyright
© 1998 S. Karger AG, Basel
ISSN
0031-7012
eISSN
1423-0313
DOI
10.1159/000028193
Publisher site
See Article on Publisher Site

Abstract

Based on previous observations of very short periods of linearity for antiprogestin metabolite formation and the presence of a common tertiary amine moiety in each compound as the principal site of their metabolism, we hypothesized that mifepristone, lilopristone and onapristone are oxidized by cytochrome P450 (CYP) 3A4 to reactive nitroso species that complex the heme of the enzyme, thereby inactivating it. Upon preincubation with human liver microsomes in the presence (but not the absence) of NADPH, mifepristone inhibited midazolam 1′-hydroxylation, a marker of CYP3A4 catalytic activity, very potently (IC<sub>50</sub> ∼3.5 µmol/l) and extensively (by ∼87%). Lilopristone and onapristone also displayed NADPH and time-dependent inactivation of CYP3A4 with characteristics very similar to mifepristone. These data support antiprogestin-mediated inactivation of CYP3A4 and suggest the potential for drug-drug interactions and time-dependent nonlinearities in pharmacokinetics upon their long-term administration.

Journal

PharmacologyKarger

Published: Mar 1, 1998

Keywords: Cytochrome P450 3A4; Antiprogestins; Mifepristone; Lilopristone; Onapristone; Enzyme inactivation

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