19 ROLE OF IL-33 IN PURINE METABOLISM AND ILC2 ACTIVATION DURING COLITIS-ASSOCIATED CANCER

Abstract UC patients have an increased risk of developing colorectal cancer, however, the immune cells and cytokines that mediate the transition from intestinal inflammation to cancer are poorly understood. Mucosal IL-33 is increased in UC patients, in addition, IL-33 and its receptor, ST2, are expressed in polyps in AOM/DSS models of colitis-associated cancer (CAC). Therefore, several studies have implicated IL-33, which is also an important activator of Innate Lymphoid Cells type 2 (ILC2s), in the formation of tumors. Moreover, it has been shown that ecto-5’-nucleotidase (CD73), critical ectoenzyme in purine metabolism which hydrolyzes extracellular AMP to adenosine, is upregulated in cancerous tissues, and an incompetent purine metabolic pathway has been associated with inflammation and inappropriate resolution in numerous inflammatory diseases, including IBD. In order to induce colitis-associated polyposis, we performed AOM/DSS protocol on 10-wk-old C57BL/6, IL-33KO and CD73KO mice as follow: the carcinogen Azoxymethane (AOM) was injected intraperitoneally (i.p.) on day 0. After two weeks, 3% dextran sodium sulfate (DSS) was administered in drinking water for a week, followed by two weeks of recovery with normal water. DSS administration and recovery was repeated one more time before euthanizing mice for tissue collection and analysis. Flow cytometry analysis showed that all ILC2s, and more specifically CD73 expressing ILC2s were significantly decreased in mesenteric lymph nodes (MLNs) of AOM/DSS treated mice lacking IL-33, compared to WT, on the other hand, CD73 deficient mice displayed a strongly reduced number of polyps compared to WT and flow cytometry revealed an ST2 expressing ILC2 cell population that was markedly reduced in CD73 deficient mice in comparison to WT. We next injected AOM/DSS treated C57BL/6 mice with either inhibitor of CD73 or sodium polyoxotungstate 1 (POM-1) CD39 inhibitor, therefore targeting the key enzymes in the purine metabolism pathway. We injected the mice i.p. with 10 mg per Kg body weight per day of either compounds or PBS, every day during the 2 weeks of DSS, to mimic a possible therapeutic treatment to prevent purine metabolism-depentent CAC. Histologic investigation of colon tissues isolated from mice treated with CD39 or CD73 inhibitors showed a significant decrease in inflammation and polyp numbers compared to vehicle-treated mice. The data so far collected suggest that a cell population of CD73 expressing ILC2s is involved in polyp formation in AOM/DSS-treated mice and that ILC2s expansion and activity depends on IL-33/ST2 and purine metabolism synergy. Therefore the possibility exists that blockade of IL-33/ST2 axis and purine metabolism might be effective in reducing ILC2s expansion and thus be beneficial in preventing or reducing early events promoting CAC.