The covalent binding of genotoxins to DNA to form DNA adducts is considered by many to be the first step in chemically induced carcinogenesis. Measurement of DNA adducts in cells provides direct evidence for exposure and a means for assessing human health risk. However, the relationship between DNA adduct formation and cancer development in humans has only been established for a few carcinogens. This is, in part, because of the low levels at which adducts occur in affected tissues and organs, the limited amounts of DNA available, and the difficulties associated with the analysis. In order to address these analytical problems, we have been exploring the use of capillary separation methods (liquid chromatography (LC) and capillary electrophoresis (CE)) coupled to mass spectrometry (MS) for the unequivocal detection and characterization of DNA adducts. Using animal models, our research has demonstrated the capability of capillary LC-MS/MS for the detection and quantification of DNA adducts at levels similar to those encountered in human exposure. Our work has focused on aromatic amines such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 4-aminobiphenyl (ABP), 2-amino-1- methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), found in cigarette smoke and formed during the grilling of fish or beef. Lung, colon, breast, pancreas and other tissues contain enzymes capable of activating these carcinogens into reactive forms that can bind to DNA bases. We propose to capitalize on our successful animal studies to examine lung and other human tissues with emphasis on the comparison of DNA adduct content between smokers and non-smokers. We will further examine the sequence recognition patterns of carcinogens by reacting them with synthetic oligonucleotides that mimic p53 gene sequences known to display specific mutations associated with lung cancer. We expect that the data generated in this program will help define the relationship between cigarette smoke and lung cancer and the value of DNA adducts as indicators for genotoxic cancer.
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