Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that have been linked to certain human cancers. The fjord region PAH dibenzo[a,l]pyrene exhibits the highest levels of carcinogenic activity of all PAH as yet tested in rodent tumor models. Another hexacyclic aromatic hydrocarbon, dibenzo[c,p]chrysene (DBC), is a unique PAH that possesses one bay region and two fjord regions within the same molecule. Due to its structure, which is a merger of the fjord region PAHs benzo[c]phenanthrene, benzo[c]chrysene, and benzo[g]chrysene, DBC is of considerable research interest. In order to investigate the pathway of regioselective metabolism we have studied the cytotoxicity, metabolic activation and DNA adduct formation of DBC in human mammary carcinoma MCF-7 cells in culture. The cytotoxicity assay indicated undisturbed cell proliferation even at concentrations as high as 4.5 μM (1.5 μg/ml) DBC. Concurrently, DNA adducts were detected in MCF-7 cells treated with DBC only in low amounts (0.6 pmol adducts/mg DNA). On the contrary, exposure to anti-DBC-1,2-diol-3,4-epoxide and anti-DBC-11,12-diol-13,14-epoxide, two putatively genotoxic metabolites of DBC, resulted in high levels of DNA adducts (33 and 51 pmol adducts/mg DNA, respectively). Although DBC was not efficiently transformed into DNA-reactive metabolites in MCF-7 cells in culture, the results from our study indicate that the two fjord region diol-epoxide derivatives of DBC may serve as ultimate genotoxic metabolites once they are enzymatically generated under certain circumstances in vitro or in vivo.
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