Abstract 2471: Chemical optimization of direct and selective molecular activators of pro-apoptotic BAX for cancer therapy.

BAX is a pro-apoptotic BCL-2 family member that lies dormant in the cytosol until triggered by cellular stress to translocate to the mitochondria and form toxic oligomeric pores. The majority of cancer cells retain wild-type BAX and instead neutralize the death pathway by overexpressing anti-apoptotic BCL-2 family proteins. Thus, direct activation of BAX represents a pharmacologic opportunity to lower the apoptotic threshold in the setting of chemoresistance. Using a Stabilized Alpha-Helix of BCL-2 domain (SAHB) modeled after the BIM BH3 helix, we previously identified the “trigger site” for direct BAX activation at the confluence of alpha-helices 1 and 6. In silico screening for small molecule modulators of BAX led to our identification of BAX activator molecule 7 (BAM7), which selectively engages the trigger site and promotes BAX-mediated cell death (Gavathiotis et al, Nat Chem Biol, 2012). Here, we applied BAM7 to a panel of acute lymphoblastic leukemia cells and observe dose-responsive killing in the micromolar range. To improve the potency of anti-ALL activity, we undertook a systematic medicinal chemistry-based iteration of BAM7’s molecular features. A series of analogs demonstrate improved BAX binding activity based on a FITC-BIM SAHB/BAX competitive fluorescence polarization assay. The most potent binders were advanced to testing in a cellular model of anti-apoptotic protein-dependent chemoresistance. Whereas select BAM7 derivatives exhibited a potency similar to or greater than the BCL-2/BCL-X L inhibitor ABT-737 in a BCL-X L -dependent ALL cell line, the compounds significantly outperformed ABT-737 in the isogenic MCL-1-dependent ALL cells. Preliminary studies revealed favorable pharmacokinetic profiles for lead BAM7 derivatives, including oral bioavailability and central nervous system penetration. These early encouraging structure-activity relationship and pharmacokinetic data on chemically-optimized BAM7 analogs suggest that direct and selective activation of BAX may be a viable strategy for therapeutic induction of apoptosis in the context of cancer chemoresistance. Citation Format: Joseph A. Bellairs, Denis Reyna, Divakaramenon Sethumadhavan, Madhavi Neelagiri, Alex Broadhead, Christopher Baccei, Brian Koss, Joseph T. Opferman, Evripidis Gavathiotis, Loren D. Walensky. Chemical optimization of direct and selective molecular activators of pro-apoptotic BAX for cancer therapy. [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 2471. doi:10.1158/1538-7445.AM2013-2471