Abstract B43: Reversible linkage of two distinct small molecule inhibitors of MYC generates a more potent and selective dimeric inhibitor that is active in cancer cell lines over-expressing MYC

Up to 70% of all human cancers have deregulated or elevated levels of MYC, making MYC a high profile cancer drug target. The disordered structure of the MYC protein has made identifying small molecule inhibitors of this target very challenging, however recent reports have identified molecules that bind to MYC and block its function. Here we describe the successful application of a novel approach for generating selective dimeric MYC inhibitors by modifying and reversibly linking two previously described small molecule inhibitors of MYC (10058-F4 and 10074-G5) that bind to distinct sites in the bHLHZip domain of the protein. We synthesized two directed libraries of monomers based on each of these molecules to identify the optimal dimer configuration required to inhibit MYC activity. Each monomer contains one of the respective ligands, a connector of varying length, and a bioorthogonal linker element that allows reversible dimerization. We identified specific combinations of monomers (termed active dimers), which displayed synergistic inhibition of MYC in biochemical and cellular assays. Through SPR, ELISA and EMSA we demonstrate that these dimers directly bind to MYC, block its interaction with Max and thus its binding to DNA, respectively. These dimeric inhibitors have superior anti-proliferative activity in MYC over-expressing cell lines compared to their monomeric components, and this activity is correlated with a decrease in MYC protein levels and an inhibition of MYC-dependent gene expression. Control combinations that lack a linker element, and thus are unable to form a dimer, do not show any synergistic effects in these assay systems. Collectively, these data validate our new approach to generate selective inhibitors of MYC assembled from smaller, lower affinity components. This approach provides an opportunity for developing novel therapeutics against MYC and other challenging intracellular drug target classes. Citation Format: Jutta Wanner, Darlene Romashko, Douglas S. Werner, Earl W. May, Yue Peng, Ryan Schulz, Kenneth W. Foreman, Suzanne Russo, Lee D. Arnold, Maneesh Pingle, Donald E. Bergstrom, Francis Barany, Stuart Thomson. Reversible linkage of two distinct small molecule inhibitors of MYC generates a more potent and selective dimeric inhibitor that is active in cancer cell lines over-expressing MYC. [abstract]. In: Proceedings of the AACR Special Conference on Myc: From Biology to Therapy; Jan 7-10, 2015; La Jolla, CA. Philadelphia (PA): AACR; Mol Cancer Res 2015;13(10 Suppl):Abstract nr B43.