title: Dichloromethyl compounds as mechanism-based inactivators of rat liver cytochromes P-450 in vitro.
abstract: Twenty dichloromethyl compounds have been tested as potential mechanism-based inactivators of the major phenobarbital-inducible isozyme of rat liver cytochrome P-450 (PB-B) in a reconstituted system. With the exception of dichloromethane and dichloroacetamide, all the compounds decreased the ethoxycoumarin deethylase activity of the enzyme in a time- and NADPH-dependent manner. The inhibitory compounds could be divided into two classes according to whether the loss of monooxygenase activity was accompanied by a decrease in spectrally detectable cytochrome P-450. N-Monosubstituted dichloroacetamides in which the side-chain consisted of a phenyl or n-octyl group were able to mimic the action of chloramphenicol and inactivate the PB-B without destroying the heme moiety. In contrast, dichloroacetamides containing an n-hexyl, n-butyl, or methyl substituent caused a significant loss of heme, as did the five non-amides tested: 1,1,2,2-tetrachloroethane, 1,1-dichloroacetone, methyl dichloroacetate, alpha,alpha-dichlorotoluene, and alpha,alpha-dichloroacetophenone. Representative compounds were also examined as inactivators of the major beta-naphthoflavone-inducible isozyme of rat liver cytochrome P-450 (BNF-B), using a reconstituted system, as well as of constitutive cytochromes P-450, using intact liver microsomes from untreated rats. These studies suggested a marked difference in isozyme selectivity between certain of the compounds. For example, of the isozymes monitored, only the PB-B was affected by alpha,alpha-dichlorotoluene in an NADPH-dependent manner, whereas N-octyl dichloroacetamide inactivated not only the PB-B and BNF-B, but also certain constitutive cytochromes, as evidenced by decreases in microsomal S-warfarin hydroxylase activities. These studies help delineate the structural requirements for the use of dichloromethyl compounds as probes of cytochrome P-450 function and as potential isozyme-selective inhibitors.
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D002701:Chloramphenicol / Q000031:analogs & derivatives / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D004980:Ethane / Q000031:analogs & derivatives / Q000494:pharmacology; D006843:Hydrocarbons, Chlorinated / Q000494:pharmacology*; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008752:Methylene Chloride / Q000494:pharmacology; D009249:NADP / Q000378:metabolism
chemical_list: D000081:Acetamides; D065607:Cytochrome P-450 Enzyme Inhibitors; D006843:Hydrocarbons, Chlorinated; C015530:1,1,2,2-tetrachloroethane; D009249:NADP; D008752:Methylene Chloride; D002701:Chloramphenicol; C032619:2,2-dichloroacetamide; D004980:Ethane