Abstract B27: MTORC1/2 inhibition as a treatment strategy for PIK3CA mutant colorectal cancer

Abstract

Abstract Colorectal cancer (CRC) is a leading cause of cancer-related death. PIK3CA mutations are common, leading to a constitutively active phosphoinositide-3 kinase (PI3K). An effective means to target this pathway has yet to be identified. We investigated the use of a panel of inhibitors targeting the PI3K pathway including copanlisib (dual PI3K/mTOR), BYL-719 (alpha isomer specific PI3K), GDC-0941 (pan PI3K), and TAK-228 (MTORC1/2). To test the efficacy of these inhibitors in CRC, murine organotypic cancer spheroids (MDOCS) were generated from the invasive adenocarcinomas of Apc and Pik3ca transgenic mice. These inhibitors were investigated at clinically relevant doses (100-400nM). Copanlisib and TAK-228 were the only inhibitors to result in a significant reduction in the size of the MDOCS (200nM; 27% p-value<0.001, 18% p-value<0.001, respectively). This result correlated with a decrease in the phosphorylation of AKT (ser473), RPS6, and 4EBP1. Minimal induction of apoptosis was observed using these inhibitors alone as measured by cleaved PARP and cleaved caspase 3. These results were confirmed in vivo using transgenic mice with TAK-228 (1mg/kg/day) and copanlisib (10mg/kg q2d x5) resulting in a reduction in lumen occlusion of the colon tumors. Persistent BCL-2 and BCL-xL signaling was hypothesized to be preventing the induction of apoptosis. To determine if inhibition of these BCL-2 family members would further sensitize these MDOCS to copanlisib and TAK-228, these inhibitors were tested in combination with navitoclax (ABT-263; BCL-2 family inhibitor). A dramatic enhanced sensitivity was observed in MDOCS (30% p-value<0.001, 23% p-value<0.001, respectively). This correlated with an induction of apoptosis as measured by cleaved caspase 3. Next a panel of eight CRC patient-derived organotypic cancer spheroids (PDOCS) were treated with the combination of TAK-228 and navitoclax. Differential sensitivity was observed across the panel (25% resistant, 37.5% intermediate, and 37.5% highly sensitive) owing to the importance of mutational profile with targeted therapies. These studies indicate the benefit of MTORC1/2 for the treatment of PIK3CA mutant CRC and with enhanced activity of the combination of MTORC1/2 inhibition in combination with BCL-2 family inhibition. These therapies deserve further investigation for the treatment of patients with PIK3CA mutant CRC. Citation Format: Rebecca A. DeStefanis, Susan N. Payne, Devon Miller, Cheri A. Pasch, Christopher Babiarz, Alyssa DeZeeuw, Stephanie L. Fricke, Carley Sprackling, Alexander E. Yueh, Demetra P. Korkos, Dana R. Van De Hey, Gioia Sha, Aurora Greane, Jeremy D. Kratz, Linda Clipson, Kristina A. Matkowskyj, Michael A. Newton, Dustin A. Deming. MTORC1/2 inhibition as a treatment strategy for PIK3CA mutant colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr B27.