Abstract
Boceprevir (SCH 503034), a protease inhibitor, is under clinical development for the treatment of human hepatitis C virus infections. In human liver microsomes, formation of oxidative metabolites after incubations with [14C]boceprevir was catalyzed by CYP3A4 and CYP3A5. In addition, the highest turnover was observed in recombinant CYP3A4 and CYP3A5. After a single radiolabeled dose to human, boceprevir was subjected to two distinct pathways, namely cytochrome P450-mediated oxidation and ketone reduction. Therefore, attempts were made to identify the enzymes responsible for the formation of carbonyl-reduced metabolites. Human liver S9 and cytosol converted ∼28 and ∼68% of boceprevir to M28, respectively, in the presence of an NADPH-generating system. Screening of boceprevir with recombinant human aldo-keto reductases (AKRs) revealed that AKR1C2 and AKR1C3 exhibited catalytic activity with respect to the formation of M+2 metabolites (M28 and M31). The formation of M28 was inhibited by 100 μM flufenamic acid (80.3%), 200 μM mefenamic acid (83.7%), and 100 μM phenolphthalein (86.1%), known inhibitors of AKRs, suggesting its formation through carbonyl reduction pathway. Formation of M28 was also inhibited by 100 μM diazepam (75.1%), 1 mM ibuprofen (70%), and 200 μM diflunisal (89.4%). These data demonstrated that CYP3A4 and CYP3A5 are primarily responsible for the formation of oxidative metabolites and the formation of M28 and M31, the keto-reduced metabolites, are most likely mediated by AKR1C2 and AKR1C3. Because the biotransformation and clearance of boceprevir involves two different enzymatic pathways, boceprevir is less likely to be a victim of significant drug-drug interaction with concomitant medication affecting either of these pathways.
Footnotes
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.110.036996.
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ABBREVIATIONS:
- HCV
- hepatitis C virus
- HPLC
- high-performance liquid chromatography
- LC
- liquid chromatography
- MS
- mass spectrometry
- P450
- cytochrome P450
- NSAID
- nonsteroidal anti-inflammatory drug
- mAb
- monoclonal antibody
- FSA
- flow scintillation analysis
- MS/MS
- tandem MS
- BNPP
- bis(4-nitrophenyl)-phosphate
- HEK
- human embryonic kidney
- HSD
- hydroxysteroid dehydrogenase
- AKR
- aldo-keto reductase
- CBR
- carbonyl reductase
- MAO
- monoamine oxidase.
- Received October 29, 2010.
- Accepted December 1, 2010.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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