Loss of p53 function is an early event in colitis-associated neoplasia in humans. We assessed the role of p53 in a mouse model of colitis-associated neoplasia. Colitis was induced in p53 ^−/− , p53 ^+/− and p53 ^+/+ mice using three or four cycles of dextran sulfate sodium (DSS) followed by 120 days of water. Mice were examined for incidence, multiplicity and types of neoplastic lesions. Lesions were examined for mutations in β-catenin (exon 3), K-ras (codons 12/13) and p53 (exons 5–8) by sequencing and for cellular localization of β-catenin by immunohistochemistry. The incidence of neoplastic lesions was 57, 20 and 20% in p53 ^−/− , p53 ^+/− and p53 ^+/+ mice, respectively ( P = 0.013). p53 ^−/− mice had a greater number of total lesions ( P < 0.0001), cancers ( P = 0.001) and dysplasias ( P = 0.009) per mouse than either p53 ^+/− or p53 ^+/+ mice. Flat lesions were associated with the p53 ^−/− genotype, whereas polypoid lesions were associated with the p53 ^+/− and p53 ^+/+ genotypes ( P < 0.0001). β-Catenin mutations were present in 75% of lesions of p53 ^+/+ mice and absent in lesions from p53 ^−/− mice ( P = 0.055). Nuclear expression of β-catenin was seen only in polypoid lesions (91%). No K-ras or p53 mutations were detected. These data indicate that loss of p53 enhances the induction of colitis-associated neoplasia, particularly flat lesions, and dysregulation of β-catenin signaling plays an important role in the formation of polypoid lesions in this mouse model. As observed in humans, p53 plays a protective role in colitis-associated neoplasia in the DSS model.

Objective: The response of subjects to preventive intervention is heterogeneous. The goal of this study was to determine if the efficacy of a chemopreventive agent differs in non-tumour-bearing animals versus those with colorectal tumours. Sulindac and/or atorvastatin was administered to Apc^+/Min-FCCCmice with known tumour-bearing status at treatment initiation.Design: Male mice (6–8 weeks old) underwent colonoscopy and received control chow or chow with sulindac (300 ppm), atorvastatin (100 ppm) or sulindac/atorvastatin. Tissues were collected from mice treated for 14 weeks (histopathology) or 7 days (gene expression). Cell cycle analyses were performed on SW480 colon carcinoma cells treated with sulindac, atorvastatin or both.Results: The multiplicity of colorectal adenomas in untreated mice bearing tumours at baseline was 3.6-fold higher than that of mice that were tumour free at baseline (P=0.002). Atorvastatin completely inhibited the formation of microadenomas in mice that were tumour free at baseline (P=0.018) and altered the expression of genes associated with stem/progenitor cells. Treatment of tumour-bearing mice with sulindac/atorvastatin led to a 43% reduction in the multiplicity of colorectal adenomas versus untreated tumour-bearing mice (P=0.049). Sulindac/atorvastatin increased the expression ofHoxb13andRprmsignificantly, suggesting the importance of cell cycle regulation in tumour inhibition. Treatment of SW480 cells with sulindac/atorvastatin led to cell cycle arrest (G0/G1).Conclusions: The tumour status of animals at treatment initiation dictates response to therapeutic intervention. Atorvastatin eliminated microadenomas in tumour-free mice. The tumour inhibition observed with Sul/Atorva in tumour-bearing mice was greater than that achieved with each agent.

Purpose: The purpose of this study was to assess the effect of folic acid (FA) supplementation on colitis-associated colorectal cancer (CRC) using the azoxymethane/dextran sulfate sodium (AOM/DSS) model. Methods: Mice were fed a chow containing 2 mg/kg FA at baseline and randomized after the first DSS treatment to receive 0, 2, or 8 mg/kg FA chow for 16 weeks. Colon tissue was collected for histopathological evaluation, genome-wide methylation analyses (Digital Restriction Enzyme Assay of Methylation), and gene expression profiling (RNA-Seq). Results: A dose-dependent increase in the multiplicity of colonic dysplasias was observed, with the multiplicity of total and polypoid dysplasias higher (64% and 225%, respectively) in the 8 mg FA vs. the 0 mg FA group (p < 0.001). Polypoid dysplasias were hypomethylated, as compared to the non-neoplastic colonic mucosa (p < 0.05), irrespective of FA treatment. The colonic mucosa of the 8 mg FA group was markedly hypomethylated as compared to the 0 mg FA group. Differential methylation of genes involved in Wnt/β-catenin and MAPK signaling resulted in corresponding alterations in gene expression within the colonic mucosa. Conclusions: High-dose FA created an altered epigenetic field effect within the non-neoplastic colonic mucosa. The observed decrease in site-specific DNA methylation altered oncogenic pathways and promoted colitis-associated CRC.