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 trans-6,7-dihydroxy-anti-8,9-epoxy-6,7,8, 9-tetrahydro-4H-cyclopenta[def]chrysene (C[def]C-8,9-DE), were evaluated previously in mice [Amin, S., et al. (1995) Carcinogenesis 16, 2813-2817]. C[def]C-3,3a-DE was the more active inducer 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 32P-postlabeling assay. The results show that metabolic activation to DNA-binding species proceeds through the formation of both trans-1,2-dihydrodiol and trans-6,7-dihydrodiol metabolites of C[def]C. At a 1 microM dose, adducts 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 microM dose were derived from the bay region dihydrodiol epoxide, C[def]C-8,9-DE. Using markers from reactions of the dihydrodiol epoxides with deoxyguanosine 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, the human cells used in these studies can activate C[def]C to carcinogenic metabolites.