Indirect Genotoxicity in Metal Carcinogenesis

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Project Summary Mutations in various oncogenes and tumor-suppressor genes as well as other genome rearrangements are a principal cause of human cancers. Lung tumors have especially high burdens of mutations. Despite this dependence of cancer development on multiple genetic events, many human lung carcinogens are tested as nonmutagenic in standard assays. Our current lack of knowledge about the causes of genetic damage by seemingly nonmutagenic carcinogens negatively impacts public health actions and precludes early detection of this class of dangerous chemicals. Metals is one important group of widespread carcinogens that are largely nonmutagenic, including lung cancer-causing nickel (Ni). Ni is a large-volume industrial metal with inhalation exposures occurring daily among millions of workers. This metal is also a common environmental pollutant that is abundantly released during fossil fuel burning, incineration of municipal waste and many other processes. Ni is found at > 50% of Superfund toxic sites. In this project, we will test a conceptually novel hypothesis that Ni(II) disrupts a unique biochemical process and the resulting metabolic dysfunction causes gross genetic alterations and cancerous transformation of human lung cells. Our main hypothesis will be tested in three complementary aims. The proposed studies will determine (1) mechanisms of Ni(II)-induced changes in cell metabolites, (2) initial and secondary genetic abnormalities resulting from Ni(II)-altered metabolism and protective functions of ATR kinase, and (3) importance of Ni-induced metabolic dysfunction in tumorigenic cell transformation. The completion of the proposed work is expected to establish a novel mechanism for indirect genotoxicity by a major human carcinogen. This mechanism can be applicable to other nonmutagenic carcinogens possessing a specific chemical reactivity. The project should also provide a valuable mechanistic information needed for modeling of cancer risks at low-dose Ni exposures and identify targets for development of potential chemopreventive approaches.