(W1030-03-21) Improved Model Development for Accelerated Colon Polyp Growth in Pirc Rats

Purpose: Familial adenomatous polyposis (FAP) is an inherited colorectal cancer (CRC) syndrome characterized by the development of many precancerous polyps in the colon and rectum already at a young age, caused primarily by germline mutations in the APC gene¹. Exposure to dietary toxins and a high-fat diet (HFD) can promote CRC by inducing chronic inflammation, oxidative stress, and alterations in the gut microbiota, all of which contribute to epithelial DNA damage and tumor initiation³. Animal models, particularly genetically engineered rodent models such as the Pirc (Apc^Pirc/+) rat, have been instrumental in elucidating the mechanisms underlying FAP and testing preventive and therapeutic strategies². Ongoing efforts aim to develop improved models that more closely mimic human FAP pathophysiology but also accelerated polyp growth models needed as a platform for high-throughput efficacy screening of drugs for FAP treatment since significant polyp development in Pirc rats takes 26/32 weeks in males/females. Therefore, the aim of this study was to develop an inflammation driven non-colitis accelerated colon polyp growth animal model in Pirc rat that includes the combined treatment with carcinogen Dextran Sodium Sulfate (DSS) and HFD. This model is designed to mimic mild, chronic inflammation and epithelial barrier disruption, a subclinical damage contributing to CRC development to reflect real-life, long-term toxic and diet/lifestyle exposures in combination with genetic predispositions, that might not cause immediate symptoms but promote pro-tumorigenic conditions.

Methods: Optimization of DSS concentration for the accelerated polyp formation in Pirc rats was tested by introducing DSS in drinking water at 1% or 2% in two cycles (5 and 3 days, with 9 days of rest in between). Then, the effect of HFD was established by feeding Pirc rats with commercial diet with 60 kcal% fat, and lastly, the combined effect of 2% DSS and HFD was tested. Control Pirc rats of both sexes were fed with regular rodent diet. Animal body weight, fecal and body condition scores were recorded during 10 weeks of experiment. At the end of experiment, the animals were euthanized, and their colons were harvested for collecting data on polyp counts and size to estimate the polyp burden (volume).

Results: Body condition scores were normal in all groups and diarrhea occurrence was seen only in groups with no HFD, whereas consumption of HFD induced constipation, more severe in females. Body weight loss was recorded only during DSS treatment and was below 5%. Administration of 1% DSS did not increase the polyp growth, but 2% DSS did. There was a clear sex difference in polyp growth in control rats and in rats receiving DSS and HFD. As compared to control rats, in females 2% DSS, HFD and their combination increased the number (3.5-4.6-fold) and burden (1.6-2.4-fold) of polyps, whereas the combination had the most pronounced effect on polyp growth, resulting in highest total polyp number (9.2±4.6) especially the large ones (2±1 polyps 4-5 mm diameter). In male rats, 2% DSS alone and its combination with HFD increased the polyp number (2.6-2.7-fold) and burden (1.52-4.58-fold), especially the number of medium (3.5-7.8 polyps of 2-3 mm) and large ones (1.2-8 polyps of >5 mm), as compared to control male rats. Colon polyp size distribution in male (A) and female (B) Pirc rats is presented in Figure 1.

Conclusion: With the aim to design a platform for testing the long-term efficacy of drugs for FAP treatment we have established an animal model using male and female juvenile Pirc rats starting at an early age of 6.5 weeks (equivalent to early adolescence human age) ending the study at 16.5 weeks (10-week study). Based on the results obtained, only 2% DSS significantly increased the number of polyps in colon of Pirc rats without causing colitis, therefore it was chosen for further development of accelerated colon polyp growth model in combination with high fat diet. The combined effect of 2 cycles of 2% DSS treatment and 10 weeks of high fat diet consumption resulted in significant accelerated polyp growth shown by increased number and size of polyps compared to the control rats or treated with carcinogen or HFD separately.

References: 1. Groden J, Thliveris A, Samowitz W, Carlson M, Gelbert L, Albertsen H, Joslyn G, Stevens J, Spirio L, Robertson M, et al. Identification and characterization of the familial adenomatous polyposis coli gene. Cell. 1991, 9;66(3):589-600. PMID: 1651174.
2. Moser AR, Pitot HC, Dove WF. A dominant mutation that predisposes to multiple intestinal neoplasia in the mouse. Science. 1990, 247(4940):322-4. PMID: 2296722.
3. Nguyen LH, Goel A, Chung DC. Pathways of Colorectal Carcinogenesis. Gastroenterology. 2020, 158(2):291-302. PMID: 31622622.

Acknowledgements: This research was funded by CIPRIT RP240401 award. Rashim Singh is supported by the National Center for Advancing Translational Sciences (NCATS) of the National Institutes of Health under award number K12TR004522.

Colon polyp size distribution in male (A) and female (B) Pirc control rats and Pirc rats treated with 1 and 2% DSS, HFD and combination of 2% DSS and HFD