Abstract 374: Discovery and targeting MKK3-MYC protein-protein interaction for therapeutic interrogation in cancer

Protein-protein interactions (PPIs) dictate the signal transduction and regulate diverse physiological programs, including cell death and survival. Recently we have developed a PPI high-throughput screening platform to detect the PPIs between cancer-associated proteins in the context of cancer cells. Characterization of ~3,500 PPIs tested for a set of lung-cancer related proteins resulted in a network of high-confidence direct PPIs, termed OncoPPi. To enable streamlined and integrated analysis of PPI datasets, we have developed the OncoPPi Portal, a web-based resource that integrates the network of experimentally detected cancer-associated PPIs with cancer genomics, pharmacological, and protein structural data to support cancer research. The analysis of the OncoPPi network revealed a new connectivity between transcription factor MYC and Mitogen-Activated Protein Kinase Kinase 3 (MKK3) known an activator of p38 signaling pathway. MYC is frequently amplified across the vast majority of cancer types, and extensive clinical and biological studies have established MYC as a highly attractive therapeutic target in cancer. However, currently, there are no FDA-approved MYC inhibitors, and novel therapeutic strategies to control MYC-dependency are urgently needed. We found that in contrast to other MYC-regulating kinases, such as ERK, MKK3 enhances MYC protein stability and transcriptional activity in a phosphorylation-independent manner. The biochemical studies guided by computational molecular modeling have revealed specific domains of MKK3 and MYC that are responsible for their interaction. Furthermore, we found that MKK3-MYC PPI can be disrupted by a short 27 amino acid residue fragment derived from MYC helix-loop-helix domain. Overexpression of this peptide was correlated with the cell growth inhibition and induction of apoptosis in multiple cancer cell lines. To identify small molecule chemical probes to test MKK3-MYC dependency in cancer, we have developed a time-resolved fluorescence resonance energy transfer (TR-FRET) assay to monitor the interaction of MKK3 and MYC in mammalian cells. We have further optimized the assay for ultra-high-throughput screening (uHTS) in 1536-well plate format. A pilot screening with a library of 3,280 compounds has identified several positive hits that were further validated in orthogonal affinity pull-down PPI inhibition assays. In summary, the integration of experimentally determined OncoPPi network with bioinformatics approaches has established a new biological role for MKK3 as a direct regulator of MYC-driven cell growth and proliferation. Our HTS PPI inhibitor platform has revealed first small molecule inhibitors for MKK3-MYC PPI. Together, this data defines the MKK3/MYC interface as a new potential therapeutic target to control MYC-driven tumorigenesis. Citation Format: Xuan Yang, Yuhong Du, Haian Fu, Andrey A. Ivanov. Discovery and targeting MKK3-MYC protein-protein interaction for therapeutic interrogation in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 374.