Abstract 1993: Cytosolic BAX dimerization as a mechanism of resistance to apoptosis and a novel target to potentiate BAX activation and apoptosis
Authors: Gitego Nadege , Agianian Bogos , Mak Oi Wei , MV Vasantha Kumar , Cheng Emily , Gavathiotis Evripidis 
Published: March 2024

Abstract
BCL-2 family proteins are master regulators of cellular life and death and have become drug targets for the development of therapeutic agents to overcome the apoptotic blockade of cancer. BAX is a pro-apoptotic BCL-2 member that is a crucial mediator of apoptosis induced by diverse stimuli including various chemotherapeutic and targeted agents. BAX predominantly resides in the cytosol in a quiescent state and upon stress, it undergoes conformational activation and mitochondrial translocation leading to mitochondrial outer membrane permeabilization, a critical event in apoptosis execution. While cytosolic BAX is typically considered an inactive monomer, we previously reported structural and cell-based evidence of a cytosolic BAX dimer. However, it remains unclear how this regulates BAX. Moreover, we found that specific BAX mutants such as P168G and G67R formed inactive BAX dimers and mutations of P168A and G67R have been identified in AML patients and found to have impaired apoptotic activity and notably the BAX P168A mutant appeared in AML patients acquiring resistance to the BCL-2 inhibitor Venetoclax. Here, we investigated the role of the inactive BAX dimer in regulating apoptosis and pro-apoptotic drug treatments in various hematologic and solid tumor cancer cells. Surprisingly, cancer cell lines express cytosolic inactive BAX dimers and/or monomers. Expression of inactive dimers, results in reduced BAX activation, translocation and apoptosis upon pro-apoptotic drug treatments such as BH3 mimetics and chemotherapy drugs. Our findings support the notion that formation of the inactive BAX dimer is a mechanism adopted by cancer cells to further suppress BAX activation and gain survival advantage. Using the inactive BAX dimer crystal structure, we designed a pharmacophore-based drug screen, and identified a small-molecule modulator, BDM19 that binds and activates cytosolic BAX dimers and prompts cells to apoptosis alone or in combination with BCL-2/BCL-XL inhibitors. Moreover, we validated interactions of BDM19 and BAX, using structural, biochemical and cellular methods, critical for BAX activation. Our findings provide mechanistic insights into the regulation of BAX and resistance to apoptosis in cancer through inactive BAX dimerization. Further, we demonstrate a rational strategy to target BAX dimer for therapeutic modulation of BAX and overcoming resistance to apoptosis by pro-apoptotic agents.
Citation Format: Nadege Gitego, Bogos Agianian, Oi Wei Mak, Vasantha Kumar MV, Emily Cheng, Evripidis Gavathiotis. Cytosolic BAX dimerization as a mechanism of resistance to apoptosis and a novel target to potentiate BAX activation and apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1993.