P088 TLR3 ameliorates colitis-associated colon tumourigenesis in mice

Abstract Background Toll-like receptor 3 (TLR3) signalling regulates innate and adaptive immune systems by the recognition of dsRNA. Activation of TLR3 signalling by poly(I:C) attenuates dextran sodium sulphate (DSS)-induced murine colitis. However, little information is available on the role of TLR3 signalling in the development of colitis-associated colon tumourigenesis. Methods Wild-type (WT) and TLR3-deficient (TLR3−/−) mice were intraperitoneally injected azoxymethane (AOM) 12.5 mg/kg on day 0 followed by three cycles of 2% DSS for 5 days and 2 weeks of free water consumption. Clinical indices such as weight change, colon length, the number of tumours, and the histologic severity of colitis were evaluated in each experiment. Immunohistochemical or immunofluorescence analyses for phospho-IκB kinase (IKK) and β-catenin were performed in colon tissues. To elucidate the antitumourigenic mechanism by colon inflammation, poly(I:C) or PBS was intraperitoneally injected in the AOM/DSS-induced tumourigenesis model in WT mice. To evaluate direct antitumor effect on tumourigenesis, as first experimental model, both WT and TLR3−/− mice were intraperitoneally injected AOM weekly for 12 weeks without DSS treatment. As the second experimental model, WT and TLR3−/− mice were received 2% DSS mixed with drinking water three times for 5 days every 2 weeks after one intraperitoneal AOM injection. Results TLR3−/− mice exhibited a higher tumour burden compared with wild-type mice. Body weight loss was greater in TLR3−/− mice than in WT mice. However, here was no significant difference in colon length and the severity of colitis between the two groups. Immunoreactivity for β-catenin was markedly increased in TLR3−/− mice. However, there was no difference in IKK expression. Activation of TLR3 by poly(I:C) was not associated with the reduced tumour development in WT mice. However, repeated AOM injections without DSS resulted in greater body weight loss in TLR3−/− mice than in WT mice, which was associated with the increased tumour development in TLR3−/−mice. Conclusion TLR3 signalling attenuated colitis-associated colon cancer development. Based on our experiments, TLR3 signalling inhibits colon tumourigenesis by direct antitumor activity rather than anti-inflammatory effect of colitis.