Abstract 3945: Inefficient nucleotide excision repair of the N-(dG-8-yl)-6-AC adduct derived from 6-nitrochrysene, an environmental mammary carcinogen, in human cell extracts

Abstract

Abstract Ubiquitous environmental agents [e.g. polynuclear aromatic hydrocarbons (PAH), and their nitrated derivatives (NO2-PAH) as well as the food derived heterocyclic aromatic amines (HAA)] that are known to induce mammary cancer in rodents must be regarded as potential human risk factors for inducing analogus human cancers. Although 6-nitrochrysene (6-NC) is less abundant than other NO2-PAH in the environment, it is the most potent mammary carcinogen in the rat; its carcinogenic potency is not only higher than the carcinogenic PAH, benzo[a]pyrene but also of the well-known carcinogenic HAA, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). The presence of bulky DNA adducts in human breast tissues and blood, support the notion that environmental carcinogens play an important role in the etiology of breast cancer. Studies in rats and in vitro assays have indicated that 6-NC can be activated by simple nitroreduction leading to the formation of the corresponding 6-hydroxylaminochrysene (6-NHOH-C); this metabolite yielded three major DNA adducts: N-(dG-8-yl)-6-AC. 5-(dG-N2-yl)-6-AC, N-(dI-8-yl)-6-AC. The second (major) pathway proceeds via a combination of ring oxidation and nitroreduction leading to the formation of 1,2-dihydroxy-1,2-dihydro-6-hydroxylaminochrysene (1,2-DHD-6-NHOH-C); this metabolite yielded 5-(dG-N2-yl)-1,2-DHD-6-AC and N-(dI-8-yl)-1,2-DHD-6-AC. These DNA lesions are likely to cause mutations if they are not removed by cellular defense mechanisms before DNA replication occurs. However nothing is known about the susceptibility of these adducts to nucleotide excision repair (NER), the major cellular repair system that removes bulky DNA lesions. In order to address this issue, we initially synthesized the N-(dG-8-yl)-6-AC lesion and inserted it into 135-mer DNA duplexes. These constructs were incubated with NER-competent nuclear extracts from human HeLa cells. The efficiencies of repair of these 6-NC-derived lesions was compared to the repair of the dG-C8 adduct derived from PhIP. The PhIP-dG-C8 adduct was readily removed by the NER system with efficiencies approaching those of the well-known pyrimidine (6-4) pyrimidone T-T dimer UV photoproduct. In contrast, the N-(dG-8-yl)-6-AC lesion in the identical sequence context was significantly more resistant to repair with 5 - 6 times lower NER efficiencies. These results suggest that the N-(dG-8-yl)-6-AC lesion derived from the metabolic activation of 6-NC may be more persistent in mammalian tissues than the PhIP lesion which may account for the high tumorigenic activity of 6-NC. Support (R01 CA35519). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3945.