Abstract 1341: Mice expressing activated PI3K develop advanced colon cancer

Abstract

Abstract Background: Mutations in PIK3CA are a common feature of human cancers and multiple new PI3K inhibitors are in clinical development. These mutations are present in 20-30% of colorectal cancers in humans; however, the effects of such mutations on the intestinal mucosa have not been previously studied in animal models. Here we demonstrate that the expression of a dominant active form of the PI3K protein in the mouse intestine results not only in hyperplasia but also advanced neoplasia. Methods: Mice carrying a transgene in which the fatty acid binding protein promoter is fused to Cre recombinase (FC) were crossed to mice carrying a transgene encoding a chimeric protein with the iSH2 domain of the p85 subunit fused to the N-terminus of p110 (PIK3ca*). Progeny carrying both transgenes (FC PIK3ca*) express this constitutively active form of p110 in epithelial cells of the distal small bowel and colon. Results: Invasive mucinous adenocarcinomas develop in the proximal colon by only 50 days of age. These tumors are very aggressive, spreading into the mesentery and adjacent organs, and their histological characteristics are strikingly similar to those of invasive colon cancers in humans. Neoplastic cells exhibit a high rate of cell proliferation as seen by increased Ki67 immunohistochemical staining and phosphorylation of AKT, pS6, and p4E-BP1 by western blot demonstrating downstream signaling of PI3K. Interestingly, these cells did not exhibit perturbations in ERK and WNT signaling. Consistent with the lack of aberrant WNT signaling, no benign polypoid intermediaries were identified. Together, the results indicate that tumors in this model form via a non-canonical mechanism. A cohort of FC PIK3ca* mice were imaged by FDG dual hybrid PET/CT colonography and mice with similar sized tumors were divided into control and experimental arms. The experimental arm was treated with rapamycin (6mg/kg/day) for 14 days. Both groups were re-imaged 14 days later. The full results of the rapamycin treatment will be presented. Conclusion: This unique model of advanced colonic invasive adenocarcinomas has the potential to further our understanding of human disease and facilitate the development of therapeutics, especially inhibitors targeting downstream of PI3K. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1341. doi:1538-7445.AM2012-1341