Liver metastasis is a major clinical problem because 45 percent of patients with colorectal carcinoma (CRC) still die of their disease while 75 percent of these develop liver metastasis at some point. Carcinoembryonic antigen (CEA), a 180 kDa glycoprotein tumor marker, is associated with liver metastasis because serum levels of CEA are increased in most patients with metastases. Pretreatment of nude mice with an intravenous injection of CEA or expression of CEA in CRC promotes colonization of the liver by human CRC cells injected into the spleen. This experimental metastasis model is clinically relevant because colonization of the livers of nude mice by freshly isolated human CRC is associated with recurrence in patients. This model also demonstrates that: (1) CRC implant in periportal venules and hepatic sinusoids, (2) more highly than weakly metastatic CRC cells survive 24 hours after implantation, and (3) systemic pretreatment with CEA increases the survival of weakly metastatic CRC cells within the liver. During the previous period of support, the hypothesis that CEA acts as an intercellular adhesion molecule to enhance experimental metastasis was rejected because CEA does not mediate adhesion to hepatic venules. The applicant's data suggest that CRC cells die because they induce microscopic areas of ischemia reperfusion (I/R) injury with production of reactive oxygen species (ROS) as they arrest and occlude hepatic sinusoids. In addition, weakly metastatic CRC appear to be more sensitive to ROS than highly metastatic CRC, possibly because they produce less Manganese Superoxide Dismutase (MnSOD). The current hypothesis is that circulating CEA promotes metastasis by inducing Kupffer cells, the resident macrophages of the liver, to produce IL-10 that inhibits production of toxic ROS that kill weakly metastatic CRC. The applicant will test his postulate by assessing the following specific aims: (1) determine the importance of peroxynitrite in killing CRC within 24 hours of arrest in the liver; (2) identify which subpopulations of liver cells of athymic nude mice kill CRC in I/R injury; (3) determine whether the anti-inflammatory cytokine IL-10 enhances CRC survival in mouse liver; and (4) determine whether expression of MnSOD in either liver or tumor cells enhances the metastatic potential of CRC and induces resistance to death from ROS. The results from these studies should demonstrate the role of both IL-10 and MnSOD in experimental metastasis and provide new approaches to the management of liver metastasis.
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