The etiology of most breast cancers remains obscure. A significant portion of breast cancer incidence in the U.S. is related to environmental factors and lifestyle, including diet. An example of a class of environmental mammary carcinogens is the nitropolynuclear aromatic hydrocarbons (NO2-PAH). The National Agency for Research on Cancer listed some NO2-PAH as possibly carcinogenic to humans. However, the actual risk associated with human exposure to NO2-PAH has not been clearly defined. In order to evaluate risks, we focused our efforts on understanding the mechanistic basis for tumor induction by 6-nitrochrysene (6-NC) and mono-nitropyrene (mono-NP) isomers (1-, 2- and 4-NP). Studies proposed in the present application are a logical extension of our findings. Accordingly, we formulated the following hypotheses and the Specific Aims to test them. (1) We hypothesize that 1,2-dihydroxy- 1,2-dihydro-6-nitrochrysene (l,2-DHD-6-NC) or 1,2-dihydroxy-1,2-dihydroxy-6-aminochrysene (1,2-DHD-6-AC) is the proximate mammary carcinogen and 1,2-dihydroxy-1,2-dihydro-6-hydroxylamino-chrysene (1,2-DHD-6-NHOH) is the ultimate carcinogenic form. To test our hypothesis, we will carry out the following: (a) synthesis of DNA adducts derived from 1,2-DHA-6-NHOH, (b) synthesis of ample materials of metabolites derived from 6-NC and comparison of their relative potency as mammary carcinogens by intramammary administration in rats, (c) determine the type and frequency of mutations in the p53 gene in rat mammary tumors. (2) We have shown that NO2-PAH derived DNA adduct formation is necessary but is not sufficient for carcinogenesis. Clearly, there are gaps in our understanding of the role of DNA adducts in mammary carcinogenesis. Thus, we will determine the relationships between: (a) the nature and levels of DNA adducts, (b) mutation frequency and spectra and (c) mammary carcinogenicity induced by 6-NC using rats harboring the lacI reporter gene. Our hypothesis is that the major DNA adduct derived from l,2-DHD-6-NHOH is responsible for the type and frequency of mutations in both the lacI gene and in the p53 gene. (3) To translate our ongoing studies of NO2-PAH in rodents, we propose to pursue similar studies in cultured human mammary tissues. We propose to employ normal (MCF-1OA) and cancer cell lines (MCF-7) to determine: (a) the metabolic capacity of the target organ (human breast tissues) and (b) the form of P450 isozymes involved in the activation of these carcinogens. The proposed study will also provide an experimental approach to the identification of relevant DNA adducts detected in humans; toward this end a pilot study will be initiated to determine the possible presence of NO2-PAH-derived DNA adducts in human breast tissues. (4) The hypothesis to be tested here is that certain covalent modification of genomic DNA by ultimate carcinogenic metabolites derived from 6-NC and mono-NP represents a type of cellular damage that can be responsible for an increased expression of the tumor suppressor protein p53.