*R. A. Malizia2, *S. P. Sharp2, T. Walrath1, D. Shanti1, C. J. Booth3, E. C. Lee2, S. C. Stain2, W. O’Connor1 1Albany Medical College,Department Of Immunology And Microbial Disease,Albany, NY, USA 2Albany Medical College,Department Of Surgery,Albany, NY, USA 3Yale University School Of Medicine,Department Of Comparative Medicine,New Haven, CT, USA
*Co-First Authors
Introduction:
Chronic intestinal inflammation predisposes patients with Inflammatory Bowel Disease (IBD) to Colitis-Associated Cancer (CAC). Fewer than half of CAC cases are diagnosed early, leading to a high associated morbidity and mortality. Despite continued efforts to improve early detection of high risk, pre-dysplastic regions in IBD patients, current macroscopic and genetic surveillance modalities remain limited. DNA damage repair (DDR) genes and their role in the formation of sporadic colorectal cancer have been well characterized. However, limited data exists regarding these genes in CAC. DDR genes are of paramount importance as they govern microsatellite instability and responsiveness to chemotherapeutic agents. We investigated the regulation of genes controlling DDR during the transition from chronic colitis to CAC in a preclinical model of disease.
Methods:
As recurrent colitic episodes increase the risk for CAC, we utilized the best characterized murine model for CAC to study colitis-associated tumorigenesis in C57BL/6 mice. Mice were separated into four distinct cohorts; unmanipulated controls, Azoxymethane (AOM) only, Dextran Sodium Sulfate (DSS) only, or with the combination of AOM/DSS. Colonic tumors were visualized and graded utilizing high-resolution murine colonoscopy. Upon sacrifice, histopathological analysis was conducted for each cohort. Distal colon segments were analyzed for the presence of dysplasia, adenoma, and adenocarcinoma. Gene expression was evaluated using semi-quantitative RT-PCR.
Results:
Tumors were observed in the AOM/DSS cohort by 5 weeks as expected. No tumor development occurred in the control (0/5), AOM only (0/5), or DSS only (0/5) cohorts, as expected. Exposure to the AOM mutagen was sufficient to significantly induce mRNA expression of DNA repair genes. Colons exposed to DSS were grossly edematous and foreshortened as compared to control. Upon colonic resection, half of the AOM/DSS cohort displayed macroscopically visible tumor (MVT). The remaining population (7/14) was devoid of visible tumor. Importantly, histological evaluation displayed microscopic evidence of dysplasia, and adenocarcinoma. Therefore, this group was denoted as the non-macroscopically visible tumor (NMVT) group. Interestingly, both MVT and NMVT tumor-developing groups showed reduced mRNA expression of mlh1, anapc1, and ercc4 relative to DSS or mutagen alone. Moreover, colitis alone was able to reduce mRNA expression of ercc4.
Conclusion:
In this study, for the first time, ercc4 has been shown to be down-regulated in chronic colitis and marks the early transition to dysplasia in murine colonic tissue. In addition, our results illustrate changes in DDR gene expression are specific and not universal in the progression to neoplasia. This phenomenon has not been previously illustrated in CAC and validates the AOM/DSS model of CAC as a means to further investigate potential markers of early malignant transformation.