Abstract A60: Late stage intestinal polyps in ApcMin/+ mice are resistant to treatment with retinoids and TRAIL due to up-regulation of pro-survival proteins

The purpose of this study is to determine the mechanism of apoptotic resistance observed in advanced polyps in a mouse model of Familial Adenomatous Polyposis (FAP). FAP is an autosomal dominantly inherited disorder caused by mutations in the tumor suppressor Apc (adenomatous polyposis coli) gene, which results in the formation of hundreds to thousands of polyps, predominantly in the colon and rectum. Left untreated, these polyps will form colorectal adenocarcinomas. Although surgical removal of the colon eliminates the colon cancer risk, these individuals are also at increased risk for other primary cancers, including tumors of the small intestine and stomach. Systemic chemopreventive interventions to specifically remove the pre-cancerous cells in these individuals could greatly improve their outcomes and quality of life. Recently, we have developed a new method based on the ability of combined retinoid and TRAIL (tumor necrosis factor related apoptosis inducing ligand) treatment to induce apoptosis and regression of intestinal polyps in ApcMin/+ mice, a mouse model of FAP. Treatment of these mice with retinoid causes an increase in TRAIL death receptors DR4 and DR5 as well as a concomitant decrease in the decoy receptors. APC deficiency leads to a decreased level of the anti-apoptotic protein FLIP (flice-like inhibitory protein). Thus, the combination of TRAIL and retinoid specifically targets APC deficient cells for apoptosis. We have further determined that early stage intestinal polyps in the ApcMin/+ mouse respond readily to this treatment combination, while late stage polyps are resistant to this treatment. Following up on these findings, we have tested the hypothesis that late stage adenomas of the intestine are resistant to TRAIL and retinoid treatment due to increased inflammatory signaling, resulting in increased anti-apoptotic signaling. We used ApcMin/+ mice at either two months of age or five-six months of age. Adenomas from young mice and older mice were subjected to immunoblot and immunohistochemistry comparing the levels of anti-apoptotic proteins as well as markers of inflammation. Results: Polyps from older mice expressed markedly increased levels of the anti-apoptotic proteins FLIP (flice-like inhibitory protein), XIAP (x-linked inhibitor of apoptosis) and Bcl-2. These polyps also exhibited increased staining for the pro-inflammatory protein cox-2 (cyclooxygenase-2) and the transcription factor NFκB (nuclear factor kappa B). Conclusion: The increased inflammation known to occur in older ApcMin/+ mice leads to an increase in pro-survival proteins that inhibits induction of apoptosis. This suggests that pre-treatment with an anti-inflammatory agent such as sulindac might sensitize adenomas in older mice to retinoid and TRAIL treatment for the induction of apoptosis. Citation Format: Jennifer S. Davis, Shaoyi Huang, Xiaoyang Ren, Zhengming Xu, Ernest Hawk, Xiangwei Wu. Late-stage intestinal polyps in ApcMin/+ mice are resistant to treatment with retinoids and TRAIL due to upregulation of prosurvival proteins. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A60.