The DNA adductome of lung carcinogenesis

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SUMMARY Lung cancer is the most common cancer worldwide, accounting for 1.6 million deaths in 2012 and for 158,000 deaths in the US in 2015. Despite the clear role of cigarette smoke in this epidemic, the precise mechanisms through which this cancer develops remain unclear. Despite anti-smoking campaigns, in 2014 there were still 40 million smokers in the U.S. and over 1 billion worldwide. More effective strategies for prevention and treatment of this disease, demand better tools to understand the mechanisms of lung cancer etiology and development. Numerous studies have shown that chemicals present in tobacco smoke induce DNA modifications (DNA adducts) which if not repaired, can lead to mutations ultimately resulting in loss of normal cellular growth control mechanisms and lung cancer. Many of these studies, using relatively non-specific techniques such as immunoassay and 32P-postlabelling, have clearly shown that DNA adduct levels are higher in the lungs of smokers than non-smokers, which is consistent with the multiple mutations found in the lungs of smokers. However, use of these non-specific techniques has not resulted in the positive structural characterization of any DNA adduct, and thus on a clear identification of the mechanisms involved in their formation. Other studies targeted at specific DNA adducts, have resulted in the identification of a few chemically characterized DNA adducts, but these results do not explain those found using the more general non-specific approaches. A precise characterization of the DNA damage during lung carcinogenesis that is both precise and comprehensive remains elusive. We have developed a new mass spectrometry based DNA adductomic approach performing comprehensive high resolution analysis of DNA adducts and providing information on their fragmentation allowing for structural elucidation. Our long-term goal is to determine the DNA damage profile characterizing lung carcinogenesis to identify a DNA adductome that may be ultimately used for early detection prevention and treatment. Our hypothesis is that with our method will combine the screening ability of the non-specific methods used in the past with the specific chemical characterization of the various modifications detected, resulting in a specific adductomic profile. The objectives of this application are: 1. to characterize the lung DNA adductome in animal models using the tobacco specific nitrosamine NNK to induce lung cancer and identify the driver adducts by enhancing its effects by co-exposure to the pro-inflammatory agent lipopolysaccharide (LPS); 2. to characterize the evolution of the DNA adductome in these models over time, clarifying the contribution of inflammation and endogenous processes; 3. to characterize the DNA adductome in smokers' lung DNA comparing it to non-smokers and to the profile identified in the animal models. Collectively our results will characterize the adductome associated with NNK and NNK+LPS induced lung carcinogenesis and the adductome in the lung DNA of smokers, setting the stage for the identification of molecular signatures for the investigation of cancer etiology in human molecular epidemiology studies. 1