Abstract
It has been demonstrated previously that several 3-trifluoromethyl-3-(4-alkoxyphenyl)diaziridines inhibit the 7-ethoxy-4-(trifluoroethyl)coumarin (7-EFC) O-deethylation activity of P450 2B6 in a mechanism-based manner. In contrast, 3-trifluoromethyl-3-(4-methylthio)phenyl)diaziridine did not have any effect on the activity of P450 2B6. It is interesting that both the alkoxy and the thiophenyl compounds were metabolized by P450 2B6. In this report, the structure-activity relationships for the mechanism-based inactivation of cytochrome P450 2B6 by a series of aryl diaziridines were investigated. Three diaziridines that did not contain a 4-alkoxy-substituent on their phenyl ring, namely, 3-trifluoromethyl-3-(3-methoxyphenyl)diaziridine, 3-trifluoromethyl-3-phenyl diaziridine, and 3-trifluoromethyl-3-(4-chlorophenyl)diaziridine had no effect on the P450 2B6 7-EFC activity. Another analog that did not contain a diaziridine substructure, 3-trifluoromethyl-3-(4-methoxyphenyl)ethanone, also had no effect on the activity of P450 2B6. Glutathione ethyl ester adducts of the phenyldiaziridine reactive intermediates were isolated from reaction mixtures of the inactivated samples and analyzed by liquid chromatography-tandem mass spectrometry. The structures of the conjugates suggested that the electrophilic reactive intermediate in each case was a quinone methide (quinomethane), 4-ethylidene-cyclohexa-2,5-dienone, generated from the 4-alkoxyphenyldiaziridines by removal of both of the diaziridine and the 4-alkyl groups. In conclusion, the determinant factor for the mechanism-based inactivator activity of the aryl diaziridines seems to be the formation of the reactive quinomethane intermediate, which is generated from the 4-alkoxyphenyl diaziridines by a cytochrome P450-catalyzed metabolic reaction.
Footnotes
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This work was supported in part by National Institutes of Health Grant CA 16954, and by Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan.
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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.106.011452.
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ABBREVIATIONS: SAR, structure-activity relationship; P450, cytochrome P450; reductase, NAPDH-cytochrome P450 reductase; 7-EFC, 7-ethoxy-4-(trifluoromethyl)coumarin; MBI, mechanism-based inactivator; LC, liquid chromatography; GC, gas chromatography; HR, high resolution; MS, mass spectrometry; MS/MS, tandem mass spectrometry; ESI, electrospray ionization; GSHEE, glutathione ethyl ester; DMSO, dimethyl sulfoxide; amu, atomic mass unit(s); HPLC, high-performance liquid chromatography; r.t., retention time.
- Received June 12, 2006.
- Accepted September 20, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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