Crucial Involvement Of Tumor-Associated Neutrophils (TAN) In The Regulation Of Chronic Colitis-Associated Carcinogenesis In Mice

[Background]Chronic inflammation is a major driving force in the development of cancer in many tissues. Ulcerative colitis (UC) is one of the major forms of chronic inflammatory bowel disease (IBD) in humans. The risk of colorectal cancer (CRC) development is higher than in the general population, which is related to the duration, extent, and severity of inflammatory disease. The molecular mechanisms underlying this neoplastic transformation are poorly understood, but immune cells that infiltrate the local tissue and produce tumor-promoting cytokines are thought to take a major contribution to colon cancer development. Several studies suggested that the combined treatment with AOM and DSS induced the intracolonic expression of TNF-a, IL-la, and IL-6, which in turn regulated the trafficking inflammatory cells. Furthermore, CCL2axis is crucially involved in the progression phage of colon carcinogenesis by regulating macrophage infiltration. However, the evidence in neutrophils is scant.[Purpose I To understand the involvement of TAN (tumor-associated neutrophils) in the regulation of chronic colitis-associated carcinogenesis, we used a mouse model of UC whereby administration of azoxymethane (AOM) followed by repeated dextran sulfate sodium (DSS) ingestion causes severe colonic inflammation and the subsequent development of multiple tumors.[Methods] Pathogen-free6-to8-week old female BALB/C mice were divided into2groups at random. The first group was induced with AOM and DSS. Mice were injected i.p. with12mg/kg body weight of AOM dissolved in physiological saline. Five days after AOM administration,2%DSS was given in the drinking water for7consecutive days, which was followed by14days regular water. The total21days were recognized as a cycle and repeated3times. The second group was control group, which was treated with physiological saline instead of AOM and DSS. During the course of the experiment, mice were monitored for body weight2times per week. The animals were sacrificed at the indicated time intervals for macroscopical inspection, total RNA and protein extraction, and histological analysis.(Results] We found that a chemokine, CXCL2, was increased in the treating mice with AOM and DSS, together with an infiltration of neutriphils expressing CXCR2, a specific receptor for CXCL2, in the lamina propria and submucosal regions of the colon. This was followed by the development of multiple colonic tumors. Moreover, mice treated with AOM and DSS, enhanced intracolonic matrix metalloproteinase (MMP)-9expression by neutrophils, accompanied by the neovascularization. Furthermore, expression of neutrophil elastase (NE) and Akt Phosphorylation (Ser473) was enhanced, followed by promoting cell proliferation, eventually inducing tumor formation. Finally, in vitro neutrophil chemotaxis analysis showed that neutrophils could migrate in response to CXCL2, and CXCL2stimulated neutrophils to express MMP-9and NE.[Conclusion] These observations would indicate that CXCL2-CXCR2axis appears to regulate intratumoral trafficking of neutrophils, as well as MMP-9and NE expression, and as a consequence to accelerate neovascularization and cell proliferation, subsequent colon carcinogenesis. Thus, targeting the CXCL2-CXCR2axis may be effective for the treatment of colon cancer in individuals with UC.