Metabolism of efavirenz and 8-hydroxyefavirenz by P450 2B6 leads to inactivation by two distinct mechanisms

Namandje N Bumpus, Ute M. Kent, Paul F. Hollenberg

Research output: Contribution to journalArticle

Abstract

Efavirenz is a non-nucleoside human immunodeficiency virus (HIV)-1 reverse transcriptase inhibitor used in combination therapy to treat HIV-1. Efavirenz metabolism is catalyzed primarily by the polymorphic enzyme P450 2B6. Metabolism of efavirenz by P450 2B6 and the naturally occurring P450 2B6.4 mutant led to the formation of 8-hydroxyefavirenz. Efavirenz inactivated the 7-ethoxy-4-(trifluoromethyl)coumarin activity of the wildtype P450 2B6 enzyme in a time-, concentration-, and NADPH-dependent manner. However, the P450 2B6.4 variant was not inactivated by efavirenz. The ability of efavirenz to inactivate both enzymes was investigated using cyclophosphamide and bupropion, two structurally unrelated substrates of P450 2B6, as probes. Preincubations with efavirenz decreased the ability of the wild-type enzyme to hydroxylate both substrates to similar extents but had no effect on the activities of the mutant enzyme. Interestingly, the inactivation of the wild-type enzyme was completely reversible after 24 h of dialysis as determined by heme, reduced CO spectra, and activity loss. In contrast, 8-hydroxyefavirenz, a metabolite of efavirenz, was able to inactivate both enzymes irreversibly. These data suggest that incubations of P450 2B6 and P450 2B6.4 with either the parent compound efavirenz or the metabolite 8-hydroxyefavirenz in the reconstituted system result in the formation of two different reactive intermediates that lead to losses in enzymatic activity by two different mechanisms, one reversible and one irreversible.

Original languageEnglish (US)
Pages (from-to)345-351
Number of pages7
JournalJournal of Pharmacology and Experimental Therapeutics
Volume318
Issue number1
DOIs
StatePublished - 2006
Externally publishedYes

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efavirenz
Enzymes
Cytochrome P-450 Enzyme System
8-hydroxyefavirenz
Bupropion
Reverse Transcriptase Inhibitors
Carbon Monoxide

ASJC Scopus subject areas

  • Pharmacology

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Metabolism of efavirenz and 8-hydroxyefavirenz by P450 2B6 leads to inactivation by two distinct mechanisms. / Bumpus, Namandje N; Kent, Ute M.; Hollenberg, Paul F.

In: Journal of Pharmacology and Experimental Therapeutics, Vol. 318, No. 1, 2006, p. 345-351.

Research output: Contribution to journalArticle

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abstract = "Efavirenz is a non-nucleoside human immunodeficiency virus (HIV)-1 reverse transcriptase inhibitor used in combination therapy to treat HIV-1. Efavirenz metabolism is catalyzed primarily by the polymorphic enzyme P450 2B6. Metabolism of efavirenz by P450 2B6 and the naturally occurring P450 2B6.4 mutant led to the formation of 8-hydroxyefavirenz. Efavirenz inactivated the 7-ethoxy-4-(trifluoromethyl)coumarin activity of the wildtype P450 2B6 enzyme in a time-, concentration-, and NADPH-dependent manner. However, the P450 2B6.4 variant was not inactivated by efavirenz. The ability of efavirenz to inactivate both enzymes was investigated using cyclophosphamide and bupropion, two structurally unrelated substrates of P450 2B6, as probes. Preincubations with efavirenz decreased the ability of the wild-type enzyme to hydroxylate both substrates to similar extents but had no effect on the activities of the mutant enzyme. Interestingly, the inactivation of the wild-type enzyme was completely reversible after 24 h of dialysis as determined by heme, reduced CO spectra, and activity loss. In contrast, 8-hydroxyefavirenz, a metabolite of efavirenz, was able to inactivate both enzymes irreversibly. These data suggest that incubations of P450 2B6 and P450 2B6.4 with either the parent compound efavirenz or the metabolite 8-hydroxyefavirenz in the reconstituted system result in the formation of two different reactive intermediates that lead to losses in enzymatic activity by two different mechanisms, one reversible and one irreversible.",
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