Abstract 2455: BAM38 is a potent and selective pro-apoptotic BAX activator molecule that restores apoptosis in cancer cells.

Abstract

Abstract Targeting key apoptosis regulators to overcome the apoptotic resistance of cancer cells is a highly attractive therapeutic strategy. The BCL-2 protein family includes both pro- and anti-apoptotic proteins that form a complex interaction network and regulate the critical balance between cellular life and death. BAX is a pro-apoptotic BCL-2 member that, when activated, undergoes a structural transformation, which converts BAX from an inactive conformation into a lethal one, creating mitochondrial pores. Although inactivating mutations in BAX have been identified with a very small frequency in tumors, cancer cells commonly ensure survival by overexpression of anti-apoptotic BCL-2 members, a feature that contributes to tumorigenesis and chemoresistance. Therefore, the vast majority of cancer cells contain functional but suppressed BAX. Our discovery of the BAX trigger site and BAX activator molecule 7 (BAM7), which directly triggers BAX activation and selective BAX-mediated cell death, provides a new opportunity for rational drug design to target BAX and promote cell death in tumors. Using an in silico structural similarity approach and a competitive fluorescence polarization assay, we identified a novel small molecule activator of BAX, BAM38, that has ten-fold improved binding potency compared to BAM7 and retains selectivity over anti-apoptotic BCL-2 proteins. NMR and molecular docking analysis demonstrates that BAM38 engages the BAX trigger site using increased complementary interactions. Biochemical assays indicate that BAM38 has correspondingly improved potency in triggering BAX conformational activation and BAX-mediated membrane permeabilization. In a panel of acute myeloid leukemia (AML) cells that overexpress distinct combinations of anti-apoptotic BCL-2 family proteins, BAM38 overcomes apoptotic blockade through induction of BAX-mediated apoptosis. We observe dose-dependent AML cell death that coincides with BAX translocation, cytochrome c release and caspase 3/7 activation. BAM38 synergizes with the BCL-2/BCL-XL inhibitor ABT-737 in resistant AML cells, highlighting the therapeutic potential of combined direct pharmacologic activation of BAX with targeted inhibition of anti-apoptotic BCL-2 and BCL-XL. Thus, our data suggest a novel small molecule approach to restoring cancer cell death by directly targeting BAX, and provides a lead molecule for further development into a next generation cancer therapeutic. Citation Format: Denis E. Reyna, Loren D. Walensky, Evripidis Gavathiotis. BAM38 is a potent and selective pro-apoptotic BAX activator molecule that restores apoptosis in cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2455. doi:10.1158/1538-7445.AM2013-2455 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.