Abstract
Clinical outcomes of vincristine therapy, both neurotoxicity and efficacy, are unpredictable, and the reported pharmacokinetics of vincristine have considerable interindividual variability. In vitro and in vivo data support a dominant role for CYP3A enzymes in the elimination of vincristine. Consequently, genetic polymorphisms in cytochrome P450 (P450) expression may contribute to the interindividual variability in clinical response, but the contributions of individual P450s and the primary pathways of vincristine metabolism have not been defined. In the present study, vincristine was incubated with a library of cDNA-expressed P450s, and the major oxidative metabolites were identified. CYP3A4 and CYP3A5 were the only P450s to support substantial loss of parent drug and formation of the previously unidentified, major metabolite (M1). The structure of M1, arising as a result of an oxidative cleavage of the piperidine ring of the dihydro-hydroxycatharanthine unit of vincristine, was conclusively established after conversion to suitable derivatives followed by spectroscopic analysis, and a new pathway for vincristine metabolism is proposed. CYP3A5 was more efficient in catalyzing the formation of M1 compared with CYP3A4 (9- to 14-fold higher intrinsic clearance for CYP3A5). The formation of M1 was stimulated (3-fold) by the presence of coexpressed cytochrome b5, but the relative efficiencies of M1 formation by CYP3A4 and CYP3A5 were unaffected. Our findings demonstrate that in contrast to most CYP3A biotransformations, the oxidation of vincristine is considerably more efficient with CYP3A5 than with CYP3A4. We conclude that common genetic polymorphisms in CYP3A5 expression may contribute to the interindividual variability in the systemic elimination of vincristine.
Footnotes
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This study was funded by the National Institutes of Health (1 K23 RR019956-01). J.B.D. and P.K. contributed equally to this work.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.106.009902.
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ABBREVIATIONS: ALL, acute lymphoblastic leukemia; P450, cytochrome P450; DQFCOSY, double-quantum filtered correlation spectroscopy; HPLC, high performance liquid chromatography; HMBC, heteronuclear multiple bond correlation; HSQC, heteronuclear single-quantum coherence; LC, liquid chromatography; MS, mass spectrometry; MS/MS, tandem mass spectrometry; TOCSY, total correlation spectroscopy; 1D ZQFTOCSY, one-dimensional zero-quantum filtered total correlation spectroscopy; b5, cytochrome b5; NFV, N-formylvindoline; DHC, dihydrohydroxycatharanthine; OH, hydroxy.
- Received February 26, 2006.
- Accepted May 3, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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