Abstract 2936: MTORC1/2 inhibition in combination with BCL-2/BCL-xL inhibition in APC and PIK3CA mutant colorectal cancer
Authors: Fricke Stephanie L. , Payne Susan N. , Pasch Cheri A. , Korkos Demetra P. , Sha Gioia , Yueh Alex E. , Babiarz Christopher , Clipson Linda , Matkowskyj Kristina A. , Newton Michael A. , Deming Dustin A. 
Published: August 2018

Background: Intrinsic resistance to agents targeting the PI3K/AKT/mTOR pathway has been commonly encountered in clinical trials of patients with PIK3CA mutant colorectal cancer (CRC). Upregulation of antiapoptotic signaling has been proposed as a mechanism of resistance to these therapies, including upregulation of BCL-2 and BCL-xL. To investigate if inhibition of BCL-2 family members would sensitize Pik3ca mutant cancers to MTORC1/2 inhibition, treatment studies were performed with TAK-228 (MTORC1/2 inhibitor), BEZ235 (dual PI3K/mTOR inhibitor), navitoclax (ABT-263; BCL-2, BCL-xL and BCL-w inhibitor) and the combination of navitoclax with either TAK-228 or BEZ235.

Methods: Therapeutic investigations with 200 nM TAK-228 or 200 nM BEZ235 and 250 nM navitoclax were performed in murine CRC spheroids with loss of APC and a constitutively active PI3K. Images were taken both pre- and post-treatment and changes in spheroid diameter were measured. Parallel treatment studies were performed on patient-derived organotypic CRC spheroids. Additionally, treatment studies were performed in vivo using a novel transgenic mouse model carrying Apc and Pik3ca mutations. The mice were treated with the combination of BEZ235 and navitoclax or with a single agent alone for 7 consecutive days.

Results: Treatment of CRC spheroids with TAK-228 resulted in a reduction of sphere size by 16% while control treated spheres increased by 77% of their size at day 0. No response was seen with navitoclax treatment alone. A profound synergistic treatment response was observed with the combination of TAK-228 and navitoclax (reduction of 26%, p&lt;0.001), with most spheroids undergoing complete collapse. A similar treatment response was observed with BEZ235 and navitoclax. Human CRC spheroids treated with TAK-228 and/or navitoclax demonstrated a variable response with 3 of 5 lines having a greater than 15% reduction in sphere size when treated with the combination of TAK-228 and navitoclax (p&lt;0.001). This enhanced treatment response correlated with an increase in apoptosis as measured by cleaved caspase 3. No enhanced activity was observed with the combination of BEZ235 and ABT-199 (selective BCL-2 inhibitor). In transgenic mice with Apc and Pik3ca mutant cancers, a median change in lumen occlusion of -42% was observed with the combination of BEZ235 and navitoclax compared to -15% with BEZ235 alone (one-sided p&lt;0.03, n=34 mice).

Conclusion: Synergistic activity was seen with the combination of TAK-228 or BEZ235 and navitoclax. This combination deserves further study in future clinical trials.

Citation Format: Stephanie L. Fricke, Susan N. Payne, Cheri A. Pasch, Demetra P. Korkos, Gioia Sha, Alex E. Yueh, Christopher Babiarz, Linda Clipson, Kristina A. Matkowskyj, Michael A. Newton, Dustin A. Deming. MTORC1/2 inhibition in combination with BCL-2/BCL-xL inhibition in APC and PIK3CA mutant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2936.