It is well known that chronic inflammation of the colon and rectum is associated with an increased risk of colorectal cancer. However, the mechanisms by which inflammation promotes malignant transformation remain undefined. Several studies suggest that certain phagocytic leukocyte- derived metabolites may promote mutagenesis and possibly carcinogenesis in vivo. Studies from our laboratory demonstrate that extravasated phagocytic leukocytes (neutrophils,macrophages) produce large amounts of the free radical nitric oxide (NO). Nitric oxide is extremely unstable in oxygenated solutions and will rapidly and spontaneously decompose to yield potent N-nitrosating agents. These nitrosating species are known to promote the nitrosative deamination of DNA bases resulting in the formation of mutagenic base substitutions. Our central hypothesis is that the phagocytic leukocytes (e.g. neutrophils, macrophages) known to accumulate within the chronically inflamed colon produce large amounts of NO-derived nitrosating agents which mediate mutagenesis and possibly malignant transformation via their ability to promote mutagenic base substitutions. In order to test this hypothesis we intend to: 1) Characterize the neutrophil (PMN) and macrophage-mediated, NO-dependent deamination of deoxyribonucleosides and intact DNA in an environment that more closely mimics the intestinal interstitial space, 2) Assess the mutagenic activity of extravasated PMNs and macrophages using both prokaryotic and eukaryotic tester strains, 3) Quantify the ability of extravasated phagocytic leukocytes to induce malignant transformation in a mammalian cell line, and 4) Determine whether inflammation of the distal colon promotes mutations of a specific target gene incorporated into the genome of colonic epithelial cells of transgenic mice. Data obtained from these studies should provide new insight into the mechanisms by which inflammatory leukocytes mediate mutagenic and carcinogenic alterations. Hopefully, these data may provide the basis for the design of drug therapies to prevent or attenuate endogenous carcinogen formation in vivo.