Chemical modulation of cytosolic BAX homodimer potentiates BAX activation and apoptosis

The Bcl-2 Family protein Bax is a major regulator of physiological and pathological cell death. 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. Previous studies reported two inactive conformations of cytosolic Bax, a monomer and a dimer, however, it remains unclear how they regulate Bax. Here we show that, 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. Using the inactive Bax dimer structure and a pharmacophore-based drug screen, we identify a small-molecule modulator, BDM19 that binds and activates cytosolic Bax dimers and prompts cells to Apoptosis either alone or in combination with Bcl-2/Bcl-xL Inhibitor Navitoclax. Our findings underscore the role of the cytosolic inactive Bax dimer in resistance to Apoptosis and demonstrate a strategy to potentiate BAX-mediated Apoptosis.