Selective inactivation by chlorofluoroacetamides of the major phenobarbital-inducible form(s) of rat liver cytochrome P-450.
Five N-monosubstituted chlorofluoroacetamides have been tested as potential specific irreversible inhibitors of the major phenobarbital-inducible form of rat liver cytochrome P-450 (P450IIB1). In vitro, N-(2-phenethyl)chlorofluoroacetamide was ineffective in causing a time-dependent loss of P450IIB1-mediated androstenedione 16 beta-hydroxylase activity in liver microsomes from phenobarbital-treated rats. However, addition of a nitro or bromo substitutent at the para position of the phenyl group or addition of a second phenyl group at the 1- or 2-position on the phenethyl side chain yielded compounds that caused a selective time-dependent decrease in androstenedione 16 beta-hydroxylase activity relative to four other P-450 form-specific androstenedione or progesterone hydroxylase activities monitored. The two compounds that were the most effective in inactivating P450IIB1 in vitro, N-(2-p-bromophenethyl) and N-(2-p-nitrophenethyl)chlorofluoroacetamide were also administered ip to phenobarbital-treated rats, and inhibition of cytochromes P-450 was assessed by in vitro assays of steroid and R- and S-warfarin hydroxylation in subsequently prepared hepatic microsomes. Both compounds selectively inhibited P450IIB1, and at a dose (200 mg/kg) of N-(2-p-nitrophenethyl)chlorofluoroacetamide that reduced androstenedione 16 beta-hydroxylase activity to approximately one-third of the control level, only two other activities, both attributable to P450IIB1, were decreased. In contrast, steroid and warfarin hydroxylase activities indicative of at least five other cytochromes P-450 were unaffected by the compound. These results indicate the feasibility of an empirical approach to the design of specific cytochrome P-450 inactivators.
Halpert
J
J
Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721.
Jaw
J Y
JY
Balfour
C
C
Kaminsky
L S
LS
D000081:Acetamides / Q000494:pharmacology*; D000818:Animals; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis; D004790:Enzyme Induction / Q000187:drug effects; D006846:Hydrocarbons, Halogenated / Q000494:pharmacology*; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D014859:Warfarin / Q000378:metabolism
D000081:Acetamides; D065607:Cytochrome P-450 Enzyme Inhibitors; D006846:Hydrocarbons, Halogenated; D014859:Warfarin; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D010634:Phenobarbital