Abstract 298: Identifying mechanisms of anti-apoptotic adaptation to enhance BAX activation and overcome resistance to apoptosis
Authors: Andrea G. Lopez-Arroyo, Evripidis Gavathiotis
Journal: Cancer Research (2018)

Abstract The BCL-2 protein family includes both pro- and anti-apoptotic proteins, which have a central role in regulating apoptosis during tumor formation and in response to chemotherapy. Cancer cells can evade apoptosis through upregulation of the BCL-2 anti-apoptotic proteins and/or the downregulation or inhibition of the BCL-2 pro-apoptotic proteins. BAX is a crucial pro-apoptotic BCL-2 family protein that upon activation translocates from the cytosol to the mitochondria to execute mitochondrial outer membrane permeabilization, the “point of no return” for mitochondrial apoptosis. BH3 mimetics, small molecules that have been developed to bind specific anti-apoptotic BCL-2 proteins, such as Venetoclax, have shown efficacy in hematologic cancers but generally are less effective in solid tumors. Here we explored a panel of non-small cell lung cancer (NSCLC) cell lines for elucidating their mechanism of anti-apoptotic adaptation and identify novel therapeutic strategies to overcome resistance to apoptosis. We used the BH3 profiling approach in NSCLC cell lines, as a tool to understand addiction to specific BCL-2 family members, and identified cells that depend on one or more anti-apoptotic proteins for their survival. Furthermore, these cell lines have low expression levels of the activators BH3-only proteins suggesting that downregulation of BH3-only proteins could be a second apoptotic block. Using size-exclusion chromatography of cytosolic cellular extracts we found that NSCLC cell lines contain BAX in dimeric conformation, which is previously characterized to provide resistance to BAX activation, suggesting that this could be a third factor increasing the apoptotic threshold. Our laboratory recently developed a lead BAX activator small molecule, BTSA1, that mimics BIM BH3 helix and interacts with the BAX activation site inducing apoptosis in vitro and in vivo in hematological cancers. We hypothesized that availability of increased amounts of cytosolic BAX monomers in addition to direct BAX activation by BTSA1 would be sufficient to broadly overcome resistance to apoptosis in NSCLC cells. To systematically identify such mechanisms, we have performed combinatorial high-throughput screens using a library of FDA-approved and investigational chemotherapeutic drugs. We identified drugs that significantly enhanced apoptosis when are combined with direct BAX activation. Our work highlights three different mechanisms of anti-apoptotic adaptation and resistance in NSCLC and provides novel pharmacological strategies that may lead to effective therapies for cancer patients. Citation Format: Andrea G. Lopez-Arroyo, Evripidis Gavathiotis. Identifying mechanisms of anti-apoptotic adaptation to enhance BAX activation and overcome resistance to apoptosis [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 298.