Project Summary/Abstract: Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease due to the lack of early detection and effective therapies. Therefore, there is an urgent need to develop novel treatment strategies. PDAC has a well- defined mutational landscape, with mutations in KRAS being the most frequently found in the vast majority of clinical cases. Accordingly, effective targeted therapies against KRAS and its downstream pathways have been highly sought after. Among these targets, downstream MEK1/2 inhibition has been shown to be a promising strategy against pancreatic cancer. However, intrinsic and acquired mechanisms of resistance to MEK inhibitors (MEKi) have been reported. To better enhance MEK inhibition in KRAS mutant cancers, we conducted a series of unbiased genome- scale depletion screens to identify novel targets that enhance KRAS mutant cancer cells to MEKi treatment (trametinib). Among these targets, we identified SHOC2 as a consistent and effective selective dependency by which genetic deletion led to MEK sensitization. Further functional validation studies revealed SHOC2 knockout (KO) in combination with MEKi treatment led to ablation of tumor growth in xenograft mice. SHOC2 is a scaffolding protein that facilitates RAS signaling by binding to RAS, RAS effectors (RAF1/PI3K) and other downstream regulators. Based on our findings, we hypothesize that SHOC2 is a novel, potent target to sensitize KRAS mutant pancreatic cancer cells to MEK inhibitors through mechanisms downstream of RAS signaling. To test this hypothesis and better understand the functional role of SHOC2 in mediating MEKi sensitivity, we propose to: (1) Determine the functional role of SHOC2 on the downstream effectors of KRAS signaling in PDAC; (2) Determine SHOC2 protein interactions and functional domains that regulate MEKi sensitivity; (3) Evaluate the therapeutic relevance of SHOC2 depletion in clinically relevant models of PDAC. The proposed studies will open new avenues for enhancing MEK inhibitor therapy to improve the survival outcome of pancreatic cancer patients.