Mammary carcinogenesis and molecular analysis of in vivo cII gene mutations in the mammary tissue of female transgenic rats treated with the environmental pollutant 6-nitrochrysene

We determined the mutant fractions (MF) and mutational specificities in the cII gene in histologically confirmed normal, non-involved and tumor mammary tissues of female transgenic (Big Blue F344 × Sprague-Dawley)F₁ rats treated with the environmental pollutant 6-nitrochrysene (6-NC). At 30 days of age, three groups were set up for oral treatment with 6-NC dissolved in trioctanoin, or trioctanoin alone once a week for 8 weeks. Two dose levels of 6-NC (100 and 200 μmol/rat) were selected on the basis of our previous carcinogenicity bioassays with CD rats. The rats were decapitated 32 weeks after the last carcinogen dose. Both incidence and multiplicity of mammary adenocarcinomas were significantly elevated in the high dose (36%, 0.57, P < 0.01) group but at the low dose these outcomes (16%, 0.23, P < 0.1) were not significantly different from those of control rats (3%, 0.03). The MF in normal, non-involved and tumor tissues from the mammary glands of 6-NC-treated rats were comparable. At the high and low doses, respectively (4.8 ± 2.0, 3.2 ± 2.1) the MF of 6-NC-treated rats, were significantly higher (P < 0.05) than that observed in control rats (1.2 ± 0.6). Control mutants consisted primarily of GC → AT transitions, whereas 6-NC-induced mutants were comprised of several major classes of mutations with GC → TA, GC → CG, AT → GC and AT → TA as the most prevalent. Further studies indicated that the structures of 6-NC-DNA adducts in the mammary tissue are consistent with the mutational specificities. This is the first report that defines the relationship between carcinogenesis and mutagenesis, as well as between structures of 6-NC-DNA adducts and mutation characteristics in the target organ in vivo.