title: Stereochemical specificity in the metabolic activation of benzo(c)phenanthrene to metabolites that covalently bind to DNA in rodent embryo cell cultures.
abstract: Benzo(c)phenanthrene (BcPh) has only weak carcinogenic activity in rodent bioassays. However, bay-region diol-epoxides of BcPh have the highest tumor-initiating activities of all hydrocarbon diol-epoxides tested to date. To determine whether BcPh is metabolically activated to bay-region diol-epoxides that bind to DNA in cells, Sencar mouse, Syrian hamster, and Wistar rat embryo cell cultures were exposed to [5-3H]-BcPh, and the BcPh-deoxyribonucleoside adducts formed were analyzed by immobilized boronate chromatography and reverse-phase high-performance liquid chromatography. Greater than 74% of the BcPh-deoxyribonucleoside adducts formed in all 3 species resulted from reaction of (4R,3S)-dihydroxy-(2S,1R)-epoxy-1,2,3,4-tetrahydro-BcPh [(-)-BcPhDE-2] with DNA to yield deoxyadenosine and deoxyguanosine adducts in a ratio of 3:1. A much smaller proportion of BcPh-deoxyribonucleoside adducts were formed by reaction of (4S,3R)-dihydroxy-(2S,1R)-epoxy-1,2,3,4-tetrahydro-BcPh [(+)-BcPhDE-1] with deoxyadenosine. No BcPh-deoxyribonucleoside adducts arising from either (+)-BcPhDE-2 or (-)-BcPhDE-1 were detected. The absence of adducts from these isomers of BcPhDE was not due to failure of these isomers to react with DNA in cells, for reaction of (+/-)-BcPhDE-1 or (+/-)-BcPhDE-2 with DNA in solution or in hamster embryo cell cultures resulted in the formation of DNA adducts from both the (+)- and (-)-enantiomers of each BcPhDE. These results indicate that both the (+)- and (-)-3,4-dihydrodiols of BcPh are formed and that their metabolic activation to diol-epoxides occurs with high stereospecificity in cells from all 3 species of rodents. The finding that the major DNA-binding metabolite is (-)-BcPhDE-2, the diol-epoxide with the (R,S)-diol-(S,R)-epoxide absolute configuration that is associated with high carcinogenic activity of diol-epoxides of other hydrocarbons, demonstrates that these cells are able to activate BcPh to an ultimate carcinogenic metabolite. The fact that a high proportion of the BcPh-DNA adducts are deoxyadenosine adducts suggests that BcPh has DNA-binding properties similar to those of the potent carcinogen 7,12-dimethylbenz(a)anthracene. The stereospecificity observed in the metabolic activation of BcPh to DNA-binding metabolites and the reaction of these metabolites with both deoxyguanosine and deoxyadenosine suggest that studies of the interactions of BcPh with DNA in vivo may be a valuable approach for establishing the role of specific activation pathways and DNA adducts in tumor induction.
mesh_terms: D000818:Animals; D001711:Biotransformation; D002478:Cells, Cultured; D006224:Cricetinae; D004247:DNA / Q000187:drug effects*; D004249:DNA Damage; D008647:Mesocricetus; D051379:Mice; D010616:Phenanthrenes / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D010616:Phenanthrenes; D004247:DNA; C002615:benzo(c)phenanthrene