Abstract 4058: DNA damage and tumour burden in mouse colon is increased in response to carcinogen exposure after induction of chronic inflammation - a more disease relevant model of colitis-associated colorectal cancer

Chronic inflammation (CI) such as inflammatory bowel disease increases the risk of developing colorectal cancer (CRC). Tumorigenesis is supported by inflammatory cytokines through increased cell proliferation and inhibiting apoptosis of neoplastic cells. The classic mouse model of colitis-associated CRC (CA-CRC) requires treatment with a mutagen (azoxymethane, AOM) followed by induction of inflammation through ingestion of a luminal irritant (dextran sulfate sodium, DSS). AOM is metabolized by colonic epithelium causing DNA damage through formation of mutagenic DNA adducts. Although the AOM + DSS model of CA-CRC is a valuable research model, it “reverses” events that take place in humans where CI typically precedes CRC. We hypothesise that CI sensitises colonic epithelium to DNA damage and predisposes the epithelium to neoplastic transformation. In order to investigate this we reversed the AOM + DSS model to more accurately represent the disease process in humans. Using two experimental approaches we treated wildtype (WT) mice with AOM alone or with DSS then AOM and collected colonic tissue after 6 and 48 hours (short-term) or colonic tumours (long-term). Tumour number and size were quantified. Immunohistochemistry was used to analyse DNA damage, apoptosis, and proliferation. Formation of the DNA adduct O6MeG was measured by a modified method of HPLC, and qPCR was used to analyse expression of DNA damage signalling pathway components. Compared with an AOM challenge alone, prior CI induction by DSS treatment increased DNA damage, reduced apoptosis, and increased tumour number and tumour size. This data reveals how prior CI modulates the colonic epithelial response to mutagen exposure in the short-term and how it promotes tumour formation in the long-term. In addition, this data demonstrates that the “reverse” model of CA-CRC can be successfully used as a more appropriate experimental framework to better understand the molecular mechanisms underpinning CA-CRC and will allow us to further investigate the relationship between prior CI, DNA damage, and tumour development. Citation Format: Tamsin RM Lannagan, Mark T. Mano, Richard J. Head, Trevor Lockett, Matthias Ernst, Leah J. Cosgrove. DNA damage and tumour burden in mouse colon is increased in response to carcinogen exposure after induction of chronic inflammation - a more disease relevant model of colitis-associated colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American A