Abstract 3152: Identification and characterization of inhibitors SHOC2-MRAS-PP1C complex assembly

Abstract Inhibition of SHOC2 function by either genetic ablation or protein degradation potently sensitizes RAS-driven cells to MEK inhibition and impairs RTK-mediated adaptive reactivation of MAPK signaling induced by a MEK inhibitor (MEKi). The SHOC2-MRAS-PP1C (SMP) complex is responsible for full activation of RAF via dephosphorylation of the phosphoserine in conserved region 2 (CR2-pS). Based on the SMP complex’s critical role in RAF activation and SHOC2 synthetic lethal interaction with MEKi, the SMP complex represents an attractive target for the development of novel therapeutic agents that could prevent adaptive resistance to MEKi. We have conducted a systematic DNA encoding library (DEL) screening campaign against the purified intact SMP complex and all three individual components using the HitGen OpenDEL kit. A series of SHOC2 selective hits were identified and profiled using direct binding and biochemical assays. The lead compounds bind to full-length SHOC2 protein with KDs in the low nM range, inhibit SMP complex formation, and block dephosphorylation of BRAF CR2-pS peptide. Hydrogen/deuterium exchange mass spectroscopy (HDX-MS) analysis of SHOC2 in complex with a lead compound identified a putative binding site, consistent with biochemical studies and supporting the MRAS competitive nature of the lead compounds. To our knowledge, these compounds represent first-in-class examples of direct modulators of the SMP complex, via SHOC2 engagement, that have the potential for optimization as either PPI modulators or selective degraders. Citation Format: Alexei Brooun, Patrick Fagan, Simon Bergqvist, Oleksii Hrabovsky, Fang Fang, Yecenia Peraza, Yin Wu, Dongming Quan, Meiying Cui, Liang Huang, Yujie Chen, Huihui Zhu, Ping Chen, Adriana Irimia, Peter Chua, Mykola Protopopov, Yurii Moroz, Olga Tarkhanova, Jean-Michel Vernier, Robert Shoemaker. Identification and characterization of inhibitors SHOC2-MRAS-PP1C complex assembly [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3152.