Abstract
Administration of delavirdine, an HIV-1 reverse transcriptase inhibitor, to rats or monkeys resulted in apparent loss of hepatic microsomal CYP3A and delavirdine desalkylation activity. Human CYP3A catalyzes the formation of desalkyl delavirdine and 6′-hydroxy delavirdine, an unstable metabolite, while CYP2D6 catalyzes only desalkyl delavirdine. CYP2D6 catalyzed desalkyl delavirdine formation was linear with time (up to 30 min) but when catalyzed by cDNA expressed CYP3A4 or human liver microsomes the reaction rate declined progressively with time. Coincubation with triazolam showed that delavirdine caused a time- and NADPH-dependent loss of CYP3A4 activity in human liver microsomes as measured by triazolam 1′-hydroxylation. The catalytic activity loss was saturable and was characterized by aKi of 21.6 ± 8.9 μM and a kinact of 0.59 ± 0.08 min−1. An apparent partition ratio of 41 was determined with cDNA expressed CYP3A4, based on the substrate depletion method. Incubation of [14C]delavirdine with microsomes from several species resulted in irreversible association with an approximately 50 kDa protein, as demonstrated by SDS-PAGE/autoradiography. Binding to the protein was NADPH dependent, glutathione insensitive, proportional to the level of CYP3A expression and was inhibited by ketoconazole, a specific CYP3A inhibitor. NADPH-dependent irreversible binding to human and rat total microsomal protein was demonstrated following exhaustive extraction of microsomal protein. Binding was decreased in the presence of glutathione and appeared to be related to expression level of CYP3A. These results suggest that delavirdine can inactivate CYP3A and has the potential to slow the metabolism of coadministered CYP3A substrates.
Footnotes
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Send reprint requests to: Dr. Richard L. Voorman, Drug Metabolism Research B 300–3, Pharmacia and Upjohn, 301 Henrietta St., Kalamazoo, MI 49007. E-mail: Richard.L.Voorman{at}am.pnu.com
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↵1 This work was presented in part at the 9th International Conference on Cytochrome P450, Zurich, Switzerland, 1995.
- Abbreviations:
- HIV-1
- human immunodeficiency virus type-1
- AIDS
- acquired immune deficiency syndrome
- API
- atmospheric pressure ionization
- ELISA
- enzyme linked immunosorbent assay
- MS
- mass spectrometry
- PCN
- pregnenolone 16α-carbonitrile
- SDS-PAGE
- sodium dodecyl sulfate-polyacrylamide gel electrophoresis
- Received March 5, 1998.
- Accepted May 19, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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