Polycyclic aromatic amines, heterocylic amines and nitroarenes are environmental carcinogens that are present in many cooked and broiled foods, notably meats, products of fuel combustion such as diesel exhaust, tobacco smoke, cooking oil fumes, coffee, tea and spices, and polluted air and water. Cancer is initiated when metabolites of these chemicals form DNA lesions that cause mutations during replication. Among the plethora of DNA adducts, it is essential to identify the most hazardous ones for purposes of biomonitoring and assessing the exposure risk of individuals to environmental carcinogens. Biomonitoring will be greatly improved by concentrating on those adducts that are the most persistent ones in vivo. We are focusing on a group of aromatic amine-, heterocyclic amine- and nitroarene-derived DNA adducts of varying sizes and shapes that stem from these metabolically activated environmental carcinogens. They have been identified in human cells and fluids, and in animal cells and tissues. We will investigate DNA adducts to dG-N2 that have been largely overlooked, but are often persistent in animal studies and adducts to dG-C8, for which animal studies suggest repair susceptibility in a number of cases. Our central hypothesis is that those adducts that entirely escape nucleotide excision repair (NER) are critical ones, as they will gradually accumulate in our DNA and cause cancer-initiating mutations. Our long-term goal is to determine the properties of adducts that govern repair resistance and susceptibility, and identify those adducts that resist NER. Our three Specific Aims test the hypothesis that the linkage site to guanine, the size and shape of the aromatic ring system and the sequence context of the adducts are the key factors that determine their NER susceptibility. We will utilize innovative molecular modeling approaches to elucidate the properties of the DNA lesions and determine the characteristics responsible for repair resistance or susceptibility. We will work hand-in-hand with our long-term collaborator N. Geacintov, who will perform NER studies with human HeLa cell extracts for our adducts. Our underlying hypothesis is that lesion-induced local stabilization of the DNA duplexes is the fundamental property that determines the NER resistance of a given lesion. Prior work has demonstrated, using melting points of duplexes as indicators of stability, that repair resistant adducts either cause minor stability decreases or stabilize modified double-stranded DNA. In contrast, DNA lesions that elicit NER are thermally destabilizing. We will investigate the adducts in uncomplexed DNA as well as when complexed with histone proteins in nucleosomes, the fundamental DNA-organization unit in the cellular environment. Our studies will provide the next-generation of biomarkers for exposure and risk of developing cancer, facilitate design of better NER-resistant chemotherapeutics through our gained understanding of NER mechanisms, and advance our capability for genotoxic screening of adducts derived from the polycyclic aromatic amines, heterocylic amines and nitroarenes present in our environment.
Our work will advance cancer prevention: it will yield novel capability for efficient screening of aromatic amines, heterocyclic amines and nitroarenes to determine their carcinogenic potency;furthermore, it will provide the next-generation of exposure biomarkers that will serve as much more powerful signals of cancer susceptibility in individuals. In addition, the design of more effective cancer chemotherapeutic agents will be facilitated through the enhanced understanding of NER lesion-recognition mechanisms that will emerge from our work.
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