Metabolism and DNA binding of the environmental pollutant 6-nitrochrysene in primary culture of human breast cells and in cultured MCF-10A, MCF-7 and MDA-MB-435s cell lines.

The environmental pollutant 6-nitrochrysene (6-NC) is a potent mammary carcinogen in the rat. To determine if the results obtained in 6-NC-treated rodents can be applicable to humans, we examined its metabolic activation in primary cultures of human breast cells prepared from tissues obtained from reduction mammoplasty from 3 women and in a cultured, immortalized human mammary epithelial cell line (MCF-10A), as well as estrogen-dependent (MCF-7) and estrogen-independent (MDA-MB-435s) human breast cancer cell lines. Metabolites identified following 24 hr incubations of [(3)H]6-NC (2.5, 5.0 and 10 microM) with human breast cells were derived from ring-oxidation (trans-1,2-dihydroxy-1,2-dihydro-6-nitrochrysene [1,2-DHD-6-NC]) and nitro-reduction (6-aminochrysene [6-AC]); chrysene-5,6-quinone (C-5,6-Q) was also detected. Levels of metabolites (pmol/mg protein) varied greatly depending on the concentration of 6-NC and the individual breast tissue used; 1,2-DHD-6-NC, ranged from not detected to 15.6 +/- 1.0; 6-AC, from 11.5 +/- 4.0 to 155 +/- 10.2; C-5,6-Q, from 18.3 +/- 10.8 to 196.7 +/- 15.4. Qualitatively similar metabolic profiles were obtained upon incubation of [(3)H]6-NC with MCF-10A, MCF-7 and MDA-MB-435s. We also detected 1,2-dihydroxy-6-aminochrysene (1,2-DH-6-AC; ranged from not detected to 50.4 +/- 9.8). Some of the metabolites identified in our study are known to be proximate carcinogenic forms of 6-NC in rodents. MCF-7 was the most efficient cell line in catalyzing 6-NC to genotoxic metabolites, and we demonstrated that the major DNA adduct is chromatographically identical to that found in the mammary gland of rats treated by gavage with 6-NC and that obtained from the incubation of [(3)H]1,2-DHD-6-NC with MCF7 cells or from nitro-reduction of 1,2-DHD-6-NC in the presence of 2'-deoxyguanosine 5'-monophosphate in vitro. This is the first report to demonstrate the ability of human breast cells, MCF-10A, and breast cancer cell lines to activate 6-NC to metabolites that can damage DNA. Copyright 2002 Wiley-Liss, Inc.