Abstract 972: Direct activation of pro-apoptotic BAX as a novel strategy for cancer therapy

BCL-2 family proteins are essential regulators of cellular life and death and, when deregulated, contribute to the development, maintenance, and chemoresistance of human cancer. Anti-apoptotic members contribute to cancer pathogenesis by sequestering the α-helical BH3 death domains of their pro-apoptotic counterparts such as BAX. The anti-apoptotic groove that binds and neutralizes BH3 helices has been successfully targeted by small molecules and stapled peptides in an effort to “inhibit the inhibitors” of apoptosis. Using a Stabilized Alpha-Helix of BCL-2 domain (SAHB) modeled after the BIM BH3 helix, we previously identified a geographically distinct BH3-binding groove that mediates the direct activation of BAX, suggesting a new strategy for inducing apoptosis by flipping BAX9s “on switch”. Engagement of the novel site by BIM SAHB directly activates BAX (Gavathiotis et al. Nature, 2008), unleashing a succession of key conformational changes that culminates in the formation of toxic mitochondrial pores (Gavathiotis et al. Mol Cell, 2010). Here, we demonstrate that BIM SAHB effectively overcomes the apoptotic blockades of a series of diverse hematologic cancer cells by broadly targeting inhibitory anti-apoptotic complexes and directly activating BAX. Importantly, BIM SAHB induces dose-responsive caspase 3/7 activation and the morphologic features of apoptosis. To identify a BAX-selective agent, we further performed a computational screen to identify BAX activator molecules (BAMs) capable of directly engaging the BAX trigger site. We demonstrate by competitive fluorescence polarization binding assays and NMR analyses that BAM7 engages the BAX trigger site and, as a result, promotes the functional oligomerization of BAX. Strikingly, the molecule does not interact with the canonical BH3 binding pocket of anti-apoptotic proteins and induces cell death in a BAX-selective fashion. These first stapled peptide and small molecule gain-of-function modulators of a BCL-2 family protein highlight a new pharmacologic paradigm for induction of cancer cell apoptosis through direct activation of BAX. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 972. doi:1538-7445.AM2012-972