Abstract 385: mTORC1/2 inhibition as a treatment strategy for subtypes of colorectal cancer
Authors: Fricke Stephanie , Pasch Cheri , Payne Susan , Yueh Alexander , Foley Tyler , Korkos Demetra , Van De Hey Dana , Clipson Linda , Deming Dustin 
Published: July 2016

BACKGROUND Colorectal cancer (CRC) remains the second leading cause of cancer-related deaths in the United States. Several key mutations in CRC include APC (80%), TP53 (50%), and PIK3CA (20-30%). Mutations in the PIK3CA gene, resulting in a constitutively active PI3K, often occur concomitantly with loss of the APC gene in human CRCs. Our lab has developed a murine model system where a constitutively active PI3K and loss of APC occur simultaneously in the colon (AK3K) as well as concomitant loss of p53 (AK3KTO). Colon tumors from these models are cultured as three-dimensional spheroids and treatment studies. METHODS AK3K and AK3KTO spheroids were treated with a dual PI3K/mTOR inhibitor, NVP-BEZ235, or a mTORC1/2 inhibitor, MLN0128. Images were taken both pre- and post-treatment and changes in spheroid diameter were measured. Parallel treatment studies were performed on a primary human colon cancer tumor cell line, SW48, which carries a mutant FBXW7 and also on a cell line transfectedwith a PIK3CA mutation (SW48PK). RESULTS Treatment with NVP-BEZ235 and MLN0128 resulted in a significant treatment response as measured by marked change in spheroid diameter in the AK3K spheroids at 100, 200 and 400nM (p&lt;0.01), with MLN0128 eliciting a greater treatment response. There were no significant differences between drugs in the AK3KTO spheroids. Comparing across cell lines, there were highly significant differences when treated with NVP-BEZ235, as the treatment was much more effective in the AK3KTO cell line at 100, 200, and 400nM (p&lt;0.01). There were no significant differences between cell lines for MLN0128. Immunoblotting further demonstrated a dramatic inhibition of the PI3K/mTOR pathway in both spheroids following treatment with 200nM MLN0128 and 200nM NVP-BEZ235. Treatment of SW48 and SW48PK cells with NVP-BEZ235 and MLN0128 showed highly significant differences between the drugs in both cell lines, with MLN0128 being more effective at 1, 10, and 50nM (p&lt;0.01). At higher drug concentrations (100, 200, and 400nM), there were highly significant differences between drugs for the SW48PK cell line (p&lt;0.01) but no significant differences in the SW48 cells. Comparing across cell lines, there were highly significant differences when treated with MLN0128 at 100, 200, and 400nM (p&lt;0.01), with MLN0128 being more effective in the SW48PK cell line. Immunoblotting demonstrated a reduction in activation of the PI3K/mTOR pathway following treatment with 10nM MLN0128 but this inhibition was not seen when treated with 10nM NVP-BEZ235. CONCLUSIONS mTOR inhibition is sufficient to induce responses in PIK3CA and APC mutated CRCs and concomitant loss of TP53 does not lead to resistance and potentially increases sensitivity. In a cell line predisposed to PI3K/mTOR signaling sensitivity, mTOR inhibition remains sufficient and the addition of a PIK3CA mutation further increases sensitivity

Citation Format: Stephanie Fricke, Cheri Pasch, Susan Payne, Alexander Yueh, Tyler Foley, Demetra Korkos, Dana Van De Hey, Linda Clipson, Dustin Deming. mTORC1/2 inhibition as a treatment strategy for subtypes of colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 385.