Abstract 5476: Small molecule activation of BAX-mediated apoptosis through direct engagement of the BAX trigger site

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Abstract BCL-2 family proteins are key regulators of the mitochondrial apoptotic pathway in health and disease. Anti-apoptotic members such as BCL-2 and BCL-XL have been implicated in the initiation, progression, and chemoresistance of human cancer. The anti-apoptotic BCL-2/BCL-XL groove that binds and sequesters pro-apoptotic BH3 death helices has been successfully targeted by small molecules and peptides. Such compounds induce tumor cell apoptosis and are being advanced in clinical trials as promising next-generation cancer therapeutics. We recently localized a distinct BH3 binding groove on pro-apoptotic BAX and demonstrated that engagement of the novel site by a triggering BIM BH3 helix directly activates BAX (Gavathiotis et al. Nature, 2008), unleashing a succession of key conformational changes that culminates in the formation of a toxic mitochondrial pore (Gavathiotis et al. Mol Cell, 2010). Here we applied these new structural insights in a computational screen to identify small molecules capable of directly engaging the BAX trigger site for therapeutic induction of BAX-mediated apoptosis in human cancer. We confirmed by NMR analysis that a series of identified small molecules indeed bound to the BAX trigger site and in fluorescence polarization assays were strikingly selective for the BH3-binding groove of BAX as compared to that of anti-apoptotic targets. We demonstrate that molecular binding triggers dose-responsive BAX activation, as assessed by in vitro oligomerization, membrane permeabilization, and cell death assays. Importantly, the small molecule BAX activators induce apoptosis of cancer cells in a BAX-dependent manner, highlighting both the selectivity and pharmacologic potential of direct BAX activation as a novel strategy for cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5476. doi:10.1158/1538-7445.AM2011-5476