Humans are exposed to nitrosamines either directly or as a result of their formation in vivo; however, epidemiological studies indicating that a particular type of human cancer is causally associated with exposure to nitrosamines are not available. This difficulty in relating the measurement of environmental nitrosamines to an observed increased rate of a cancer may be overcome by the development of methods that permit the measurement of past exposure at the individual level. Nitrosamines are enzymatically converted into metabolites which bind covalently to DNA and various DNA adducts have been identified. The present studies have the specific aims of 1) developing immunological methods using monoclonal and/or polyclonal antibodies to quantitate certain of these DNA adducts in human tissues 2) assessing the value of this approach as a method for determining human exposure to environmental alkylating agents. Antibodies against 7-methyldeoxyguanosine (7-medG), O4-methyldeoxythymidine (O4-medT) and phosphotriesters will be developed and characterized for their sensitivity and specificity. These antibodies and those already available against O6-methyldeoxyguanosine (O6-medG) and O6-ethyldeoxyguanosine (O6-etdG) will be used in immunoassays to detect these adducts in DNA from human surgical tissue specimens of oesophagus or stomach obtained from populations at differential risk of cancer at either or both of these sites and for which some evidence of exposure to environmental nitrosamines exists. DNA is extracted from the tissues, hydrolyzed, fractionated chromatographically and the isolated DNA adducts are quantitated by immunoassay using the appropriate antibodies. Using this methodology with the antibody for O6-medG and a 2 mg sample of DNA levels of modification approaching one adduct in 10-8 of the corresponding normal nucleoside can be detected. In preliminary studies of oesophageal and stomach tissue samples from one of the proposed study populations from Linxian County in People's Rep. of China significant levels of O6-medG have already been detected. The capacity of the same tissues to repair O6-alkyldG and O4-medT will also be examined in conjunction with determination of adduct levels. In parallel, experimental studies in rats are planned to examine the presence of DNA adducts in peripheral blood cells following nitrosamine exposure. These experiments are designed to assess the potential of this approach as an alternative method of assessing human exposure to environmental nitrosamines.
