Abstract
Human liver microsomes catalyze the oxidation of sulfinpyrazone sulfide (SPZS) to a variable mixture of sulfinpyrazone (SPZ) enantiomers and two minor phenolic metabolites. In one, the thiophenyl ring is hydroxylated, whereas in the second an N-phenyl ring is hydroxylated. SPZ is further oxidized to sulfinpyrazone sulfone (SPZO) and a minor polar metabolite that also has anN-phenyl ring hydroxylated. Determination of the metabolism of SPZ and SPZS under modified incubation conditions of prior heat treatment, higher pH, and the presence of detergent indicated that the formation of SPZ was cytochrome P450 (P450)- but not flavin monooxygenase-dependent. Specific P450 inhibitors (sulfaphenazole, quinidine sulfate, coumarin, diethyldithiocarbamic acid, troleandomycin, and furafylline) and specific cDNA-expressed P450s were used to identify the major isoforms responsible for the oxidation of SPZS to SPZ and SPZ to SPZO. Both P450 2C9 and P450 3A4 were responsible for the oxidation of SPZS to SPZ, whereas P450 3A4 alone catalyzed the further oxidation of SPZ to SPZO. SPZS was found to be metabolized by P450 2C9 to SPZ with a high degree of enantiomeric selectivity (9:1) and a Km comparable with its previously determined Ki for inhibition of the P450 2C9-dependent 7-hydroxylation of (S)-warfarin (WARF). In contrast, the P450 3A4-catalyzed oxidation of SPZS to SPZ proceeded with the same enantioselectivity but to a much lesser degree (58:42). These results provide evidence that the metabolism of both (S)-WARF and SPZS is mediated by a common enzyme, P450 2C9, which is central to understanding the WARF-SPZ interaction and SPZS-mediated drug interactions in general.
Footnotes
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Send reprint requests to: Dr. William F. Trager, Department of Medicinal Chemistry, Box 357610, School of Pharmacy, University of Washington, Seattle, WA 98195. E-mail:trager{at}u.washington.edu
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↵1 Current address: Drug Metabolism and Disposition, Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285.
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This study was supported in part by the National Institutes of Health Grant GM 32165.
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↵3 Direct determination of theKm for the P450 2C9-catalyzed oxidation of SPZS to SPZ could not be achieved because of contamination by SPZ, presumably because of the ease of the nonenzymatic atmospheric oxidation of SPZS particularly when exposed to incubation conditions.
- Abbreviations used are::
- SPZ
- sulfinpyrazone
- CUM
- coumarin
- DDC
- diethyldithiocarbamic acid
- FUR
- furafylline
- FMO
- flavin monooxygenase
- P450
- cytochrome P450
- QUI
- quinidine sulfate
- Rt
- retention time
- SFZ
- sulfaphenazole
- SPZO
- sulfinpyrazone sulfone
- SPZS
- sulfinpyrazone sulfide
- TAO
- troleandomycin
- WARF
- warfarin
- HPLC
- high-performance liquid chromatography
- MS/MS
- mass spectrometry/mass spectrometry
- Received December 6, 2000.
- Accepted January 16, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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