Small molecule inhibitors of membrane-bound MCL-1 and BCL-2

Mcl-1 and Bcl-2 are anti-apoptotic members of the Bcl-2 family of proteins. These proteins sequester activators of Bax-Bak oligomerization and inhibit the subsequent mitochondrial depolarization. Knockdown of anti-apoptotic Bcl-2 family proteins has induced apoptosis in a variety of cancers, signifying that these malignancies are dependent on these proteins for survival. Thus, their inhibition by small molecules is an emerging strategy in cancer therapy. While Bcl-2 specific and pan-inhibitors have emerged, there remains a dearth of molecules that effectively inhibit Mcl-1. In fact, increased Mcl-1 expression is a common mechanism of resistance to these therapies.

Previous efforts to identify small molecules that inhibit MCL-1 or BCL-2 function have exploited assays using soluble, truncated, bacterially-expressed recombinant proteins. Since in vivo MCL-1 and BCL-2 exist at full length and are membrane bound, we thought we could improve the identification of biologically active small molecules by screening in a more physiologically relevant environment. It is likely that membrane association affects the structure and access of binding sites. We have therefore developed a screening assay to assess inhibition of full-length Mcl-1 and Bcl-2 in a membrane-bound state. The screen identified compounds that selectively permeabilize membranes whose integrity depends on either MCL-1 or BCL-2. The screen was optimized for high-throughput 384-well format. Positive controls for screening were peptides representing the BH3 domains of Bad and Noxa, known to be selective inhibitors of Bcl-2 and Mcl-1, respectively. We screened >70,000 compound wells. These compounds include an assortment of known bioactives, natural product extract mixtures, and commercial library compounds. We have identified several lead compounds from the primary screen and have validated their performance in biochemical and biological assays.

Citation Format: Luv G. Patel, Ronald M. Paranal, Jeremy Ryan, Kristopher Sarosiek, James E. Bradner, Anthony Letai. Small molecule inhibitors of membrane-bound MCL-1 and BCL-2. [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 4610. doi:10.1158/1538-7445.AM2013-4610

©2013 American Association for Cancer Research
2013