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* = Presenting author

P062 Critical role of the IL-33/ST2 axis in colitis-associated colorectal cancer

L. R. Lopetuso*1, 2, 3, C. De Salvo3, L. Di Martino3, W. Goodman3, F. Scaldaferri2, A. Gasbarrini2, T. T. Pizarro3

1Catholic University of the Sacread Hearth, Internal Medicine, Gastroenterology Division, Rome, Italy, 2Catholic University of Sacred Heart, Internal Medicine Department, Gastroenterology Division, Rome, Italy, 3Case Western Reserve University, Pathology, Cleveland, United States

Background

Emerging evidence suggests IL-33/ST2 critical role in epithelial proliferation and potential contribution to inflammation-driven tumourigenesis that can lead to colorectal cancer (CRC). The aim was to characterise the precise contribution of IL-33/ST2 axis in the azoxymethane (AOM)/dextran sodium sulfate (DSS) model of colitis-associated CRC.

Methods

C57/BL6 wild-type (WT), IL-33 KO, and ST2 KO mice were given a single dose of AOM, followed by 2 cycles of 3% DSS for 7 d. Aged-matched WT mice, injected with vehicle and given regular drinking water, were used as controls (CT). At 8 wks after AOM injection, mice were sacrificed. IHC, immunofluorescence (IF), and qPCR were done on full-thickness colons for IL-33 and ST2 localisation and identification, and mRNA expression, respectively. FACS analysis was performed on resected, isolated polyps to functionally characterise ST2+ cells.

Results

IL-33, ST2L, and sST2 mRNA transcripts were dramatically elevated in WT vs CT mice. IHC of treated WT mice revealed localisation of IL-33 to the colonic epithelium and to cells within the LP morphologically consistent with tissue macrophages. ST2 staining was localised to the intestinal epithelium in tissues immediately adjacent to tumours, whereas within the tumours themselves, ST2+ cells displayed a spindle/fibroblast-like morphology with a unique distribution throughout the polyps. Little to no staining for both IL-33 and ST2 was present in CT. Using IF, ST2 co-localised with αSMA in polyps; however, ST2 staining was not exclusive for αSMA+ cells. FACS analysis showed a distinct population of CD45+ haematopoietic cells consisting of CD3/CD8+ cytotoxic T-cells (CTLs), CD19+ B-lymphocytes, CD11b+CD11c- and CD11b+CD11c+ myeloid cells. ST2 was mainly expressed by CTLs, and CD11b+CD11c- and CD11b+CD11c+ myeloid cells. Non-haematopoietic cells (CD45-) also expressed ST2. DSS challenge in WT mice resulted in increased body weight loss and DAI vs IL-33 KO and ST2 KO mice. At 5 weeks post AOM injection, experimental mice underwent survival colonoscopy. WT had already developed protruding lesions with abnormal vascular patterns, suggesting pre-tumourous lesions, whereas IL-33 KO and ST2 KO mice showed the absence of pre-tumourous lesions with a more impressive mucosal inflammation, likely due to reduced epithelial proliferation and repair caused by the absence of IL-33 signalling. At sacrifice, increased number and size of polyps were observed in WT vs IL-33KO and ST2KO mice.

Conclusion

Our results suggest that activation of the IL-33/ST2 axis sustains tumourigenesis in the murine model of colitis-associated CRC. Further studies are underway to determine mechanisms of action that support these findings.