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Poster presentations: Basic Science 2020

P036 A novel p53-mediated mouse model of inflammatory bowel disease-associated colorectal cancer

A.M. Churchhouse1, C.V. Billard1, M.J. Arends2, K.B. Myant1

1The Institute of Genetics and Molecular Medicine, The University of Edinburgh, Edinburgh, UK, 2Division of Pathology, Centre for Comparative Pathology, Cancer Research UK Edinburgh Centre, The Institute of Genetics and Molecular Medicine, The University of Edinburgh, Edinburgh, UK

Background

Current mouse models of colitis-associated cancer often utilise a combination of APC mutation, Dextran sulphate sodium (DSS) and azoxymethane administration. However, only 13% of human inflammatory bowel disease (IBD)-associated cancers is associated with an APC mutation1. Instead, they are frequently associated with mutation of p53 (occurring in 63% of human cancers1). Whilst some models of IBD-associated cancer using either global p53 loss or mutant p53 have been described, we felt that a more pathophysiologically relevant model would be represented using p53 loss solely in the colonic epithelium.

Methods

Colonic epithelial p53 floxing in Vil-CreERT2p53fl/fl mice was achieved through intraperitoneal injection of 120 and 80 mg/kg tamoxifen on two consecutive days. After 16 days, mice were started on a chronic DSS treatment protocol. Chronic DSS-induced colitis involved three 5-day cycles of low-dose DSS (1.5% initially and subsequently 1% for the remaining two cycles), interspersed with normal drinking water for 2 weeks to facilitate recovery. After three cycles of DSS, mice were aged to 164 days.

Results

At 164 days post induction of DSS, 100% of mice had developed adenomata with low-grade dysplasia (n = 4). Adenomata in 50% of these mice (n = 2) also had features of high-grade dysplasia. There were between one and three adenomata in each animal. No features of invasive adenocarcinoma were demonstrated. There was partial β-catenin nuclear localisation in these tumours. Background chronic colitis was evident, even though the experiment ended over 3 months after the DSS treatment finished.

Conclusion

To the best our knowledge, this is the first mouse model of colitis-associated cancer using p53 loss in the colonic epithelium together with chronic colitis induction using DSS. The experiment ended over 3 months after the DSS treatment finished, showing that the resultant chronic colitis can persist long after the initial insult is given. The fact that β-catenin is partially, but not fully nuclear localised suggests an alternative pathway to tumour formation in this p53fl/fl model, and may therefore be more pathophysiologically relevant to human IBD-associated colorectal cancers. Further work is now being carried out to both validate and further evaluate this novel mouse model, including assessment of stem cell dynamics in response to colitis in the context of p53 loss.

Reference:

Robles, A. I. et al. Whole-Exome Sequencing Analyses of Inflammatory Bowel Disease-Associated Colorectal Cancers. Gastroenterology 150, 931–943 (2016).