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P003. Tumour microenvironment differs between murine sporadic and inflammation-associated colorectal tumourigenesis

S.K. Fu1, F. Lloyd1, C. Forrest2, I. Lawrance1, B. Klopcic1

1University of Western Australia, Centre for Inflammatory Bowel Diseases, Medicine and Pharmacology, Perth, Australia; 2University of Western Australia, School of Pathology and Laboratory Medicine, Perth, Australia

Background: Colorectal cancer (CRC) is common, but human sporadic and colitis-associated CRC (CAC) have different pathogeneses. The aim of this study was to identify differences in gene expression levels and inflammatory cell infiltration of tumours from mice models of sporadic and CAC.

Methods: Mice used in this study are on a FVB background. Sporadic CRC tumourigenesis was mimicked by giving 6 weekly intraperitoneal (IP) injections of azoxymethane (AOM). CAC was modelled by a single AOM IP injection prior to two cycles of 7 days of dextran sodium sulphate (DSS) in the drinking water followed by 14 days of plain water. Tumours of similar size were harvested from both models at weeks 13 (AOM-alone) and 8 (AOM/DSS) respectively and processed for further analysis. Histological and immunofluorescent (IF) assessment of CD4, CD8a, F4/80, and Ly6G was performed on tumours. Whole-genome microarray (Illumina BeadChip, MouseRef 8 v2) was used to compare gene expression in tumours from both models. Gene ontology analysis was performed using the Database for Annotation, Visualisation and Integrated Discovery.

Results: The majority of tumours were polypoid and all were dysplastic. Unlike AOM/DSS, the AOM-alone protocol induced high-grade dysplasic polyps (21% [4/19] vs 0% [0/9]) and 2 flat lesions, one with invading CRC. Microarray analysis identified that 665 genes were differentially expressed between the tumours (p < 0.05), and 398 had increased expression levels in the AOM-alone tumours and included genes associated with cytokine activity, cell division, and the regulation of apoptosis. 267 genes were reduced and were associated with immune response, the lysosome and positive regulation of the immune system. IF assessment of the inflammatory cell infiltrates showed the presence of CD4-positive, CD8a-positive, F4/80-positive and Ly6G-positive cells in all tumours without any significant differences in the cell numbers between the models.

Conclusions: AOM and AOM/DSS tumours are histologically different with marked gene-expression differences suggesting a different pathogenesis. All AOM-alone tumours displayed inflammatory cell infiltration suggesting a crucial role for the immune cells in the progression of tumours in both models once tumourigenesis is initiated. Further work is required to confirm histological differences between AOM and AOM/DSS tumours.