A series of aryl acetylenes and aryl olefins have been examined as substrates and inhibitors of cytochrome P-450 dependent monooxygenases in liver microsomes from 5,6-benzoflavone or phenobarbital pretreated rats. 1-Ethynylpyrene (EP), 3-ethynylperylene (EPL), cis- and trans-1-(2-bromo-vinyl)pyrene (c-BVP and t-BVP), and 1-allylpyrene (AP) serve as mechanism-based irreversible inactivators (suicide inhibitors) of benzo(a)pyrene (BP) hydroxylase, while 1-vinyl-pyrene (VP) and phenyl 1-pyrenyl acetylene (PPA) do not cause a detectable suicide inhibition of the BP hydroxylase. The mechanism-based loss of BP hydroxylase activity caused by the aryl acetylenes is not accompanied by a corresponding loss of the P-450 content of the microsomes (suicide destruction). In the presence of NADPH, ('3)H-labeled EP covanlently attached to P-450 isozymes with a measured stoichiometry of one mole of EP per mole of the P-450 heme. The fact that closely associated proteins such as P-450 reductase and cytochrome b(,5) are not labeled by EP under these conditions indicates the labeling is selective for P-450 proteins and is indicative of a process involving a reactive inter-mediates produced during the catalytic cycle The results of the effects of these aryl derivatives in the mammalian cell-mediated mutagenesis assay and toxicity assay show that none of the compounds examined nor any of their metabolites produced in the incubation system are cytotoxic to V79 cells. When tested as a modifier of the epidermal keratinocyte-mediated DMBA mutagenesis and cytotoxicity, EP, t-BVP, c-BVP, and EPL were found effective at preventing both mutations and cytotoxicity in the coincubated V79 cells. These inhibitors therefore block the metabolic conversion of DMBA to cytotoxic and mutagenic derivatives by P-450 dependent monooxygenases present in the mouse skin keratinocytes Because of the special effects of EP and related compounds upon the microsomal BP hydroxylase activities, these compounds may prove to be a useful addition to the list of selective monooxygenase inhibitors available to the investigators in this field. In addition, since cytochrome P-450 dependent oxidations of BP and other polycyclic arylhydrocarbons are critical steps in the conversion of these procarcinogens into their ultimate carcinogenic metabolites, EP or related structures may eventually be useful anticancer agents. (Abstract shortened with permission of author.)
