Tumorigenicity and genotoxicity of an environmental pollutant 2,7-dinitrofluorene after systemic administration at a low dose level to female rats.

Environmental pollution with nitroaromatic compounds may pose health hazards. We have examined the tumorigenicity in female Sprague-Dawley rats of 2,7-dinitrofluorene (2,7-diNF) and 9-oxo-2,7-diNF administered by intraperitoneal (i.p.) and oral routes at 10 micromol/kg body weight, 3 times per week for 4 weeks. After i.p. treatment, the estimated median latency for the combined malignant and benign mammary tumors was decreased in 2,7-diNF- (p = 0.003) or 9-oxo-2,7-diNF-treated (p = 0.007), relative to vehicle-treated rats (42 or 64 vs. 80 weeks, respectively), whereas after oral dosing, there were no significant differences. At 90 weeks, the malignant mammary tumor incidence in 2,7-diNF-, 9-oxo-2,7-diNF- and vehicle-i.p. treated rats was 44 (p = 0.02 vs. vehicle-treated), 25 and 6%, respectively. Liver and mammary gland DNA was analyzed by HPLC combined with electrospray tandem mass spectrometry for the presence of a deoxyguanosine (dG-2,7-diNF) adduct and a deoxyadenosine (dA-2,7-diNF) adduct derived from 2,7-diNF, and a deoxyguanosine (dG-9-oxo-2,7-diNF) adduct derived from 9-oxo-2,7-diNF. Both dG-2,7-diNF and dA-2,7-diNF were detected in DNA of 2,7-diNF-treated rats, whereas only very low levels of dG-9-oxo-2,7-diNF were detected in DNA of 9-oxo-2,7-diNF-treated rats. After i.p. treatment, the dA-2,7-diNF level was higher (p < 0.01) in the mammary gland than liver (13.6 vs. 7.8 adducts/10(8) nucleotides). In the mammary gland, the dG-2,7-diNF level was higher (p < 0.05) after i.p. than oral dosing and also higher (p < 0.05) than in the liver (36 vs. 8.6 and vs. 9.1 adducts/10(8) nucleotides, respectively). The preferential display of carcinogenicity and genotoxicity in the mammary gland by low doses of 2,7-diNF signifies its potential relevance for environmental breast cancer.