Characterization of the Major Bropirimine Oxidative Metabolites Formed In Vitro
Abstract
Bropirimine (2-amino-5-bromo-6-phenyl-4-pyrimidinone) is a member of a class of antineoplastic agents known as aryl pyrimidinones. In human liver microsomal incubations, bropirimine oxidative metabolism is characterized by the formation of three metabolites. Mass spectrometric analysis of the incubation mixture revealed three bropirimine oxidative metabolites, identified as the bropirimine dihydrodiol,p-hydroxybropirimine, and m-hydroxybropirimine.In vitro studies using human liver microsomes and recombinant cytochrome P450 isoforms were performed to identify the P450 enzyme(s) responsible for bropirimine oxidation. Coincubation with the selective CYP1A2 inhibitor alpha-naphthoflavone abolished bropirimine metabolism in human liver microsomes. Furthermore, when screened against a panel of cDNA expressed cytochrome P450 enzymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4), bropirimine was metabolized to both p- and m-hydroxybropirimine exclusively in incubations with cDNA-expressed CYP1A2 microsomes. Mechanistic studies using cDNA-expressed CYP1A2 microsomes fortified with microsomal epoxide hydrolase revealed that all three bropirimine oxidative metabolites appear to be the result of a common arene oxide, which serves as a substrate for microsomal epoxide hydrolase to generate the dihydrodiol or rearranges to yield p- andm-hydroxybropirimine.
Footnotes
-
Send reprint requests to: Larry C. Wienkers, Drug Metabolism and Disposition Research, Pharmacia & Upjohn, 7265–300-313, 301 Henrietta Street, Kalamazoo, MI 49007.
- Abbreviations used are::
- CYP or P450
- cytochrome P450
- HPLC
- high-performance liquid chromatography
- mEH
- microsomal epoxide hydrolase
- Received January 21, 1998.
- Accepted June 2, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|