Metabolic activation of 4H-cyclopenta[def]chrysene in human mammary carcinoma MCF-7 cell cultures

The tumor initiating activities of 4H-cyclopenta[def]chrysene (C[def]C) and its two putative reactive metabolites. trans-1,2-dihydroxy-anti-3,3a-epoxy -1,2,3,3a-tetrahydro-4H-cyclopenta [def]chrysene (C[def]C-3,3a-DE) and tran s-6,7-dihydroxy-anti-8,9-epoxy-6,7,8,9-tetrahydro-4H-cyclopenta[def]chrysen e (C[def]C-8,9-DE), were evaluated previously in mice [Amin, S., et al. (19 95) Carcinogenesis 16, 2813-2817]. C[def]C-3,3a-DE was the more active indu cer of lung tumors and elicited twice as many tumors as C[def]C-8,9-DE. In this study, the route of metabolism of C[def]C to DNA-reactive metabolites in the human mammary carcinoma cell line (MCF-7) was investigated using the P-32-postlabeling assay. The results show that metabolic activation to DNA -binding species proceeds through the formation of both trans-1,2-dihydrodi ol and trans-6,7-dihydrodiol metabolites of C[def]C. At a 1 mu M dose, addu cts from the methylene-bridged (C[def]C-3,3a-DE) and bay region (C[def]C-8, 9-DE) dihydrodiol epoxides were detected in comparable amounts. In contrast , the majority of the postlabeled adducts recovered from cells exposed to a 10 mu M dose were derived from the bay region dihydrodiol epoxide, C[def]C -8,9-DE. Using markers from reactions of the dihydrodiol epoxides with deox yguanosine 3'-phosphate and deoxyadenosine 3'-phosphate, it was shown that the major radioactive spots formed with both anti-C[def]C-3,3a-DE and anti- C[def]C-8,9-DE chromatographed with deoxyguanosine adduct markers. Thus, th e human cells used in these studies can activate C[def]C to carcinogenic me tabolites.