Synthetic Lethal Interaction of SHOC2 Depletion with MEK Inhibition in RAS-Driven Cancers

Abstract

Graphical Abstract Highlights d RTK-RAS-MAPK pathway members score strongly in genome-scale MEKi modifier screens d Depletion of SHOC2 potently sensitizes RAS-driven cells to MEK inhibition d SHOC2 loss impairs RTK-mediated adaptive reactivation of MAPK signaling induced by MEKi d A model of SHOC2 degradation suggests a combination therapeutic strategy with MEKi SUMMARY The mitogen-activated protein kinase (MAPK) pathway is a critical effector of oncogenic RAS signaling, and MAPK pathway inhibition may be an effective combination treatment strategy. We performed genome-scale loss-of-function CRISPR-Cas9 screens in the presence of a MEK1/2 inhibitor (MEKi) in KRAS-mutant pancreatic and lung cancer cell lines and identified genes that cooperate with MEK inhibition. While we observed heterogeneity in genetic modifiers of MEKi sensitivity across cell lines, several recurrent classes of synthetic lethal vulnerabilities emerged at the pathway level. Multiple members of receptor tyrosine kinase (RTK)-RAS-MAPK pathways scored as sensitizers to MEKi. In particular, we demonstrate that knockout, suppression, or degradation of SHOC2, a positive regulator of MAPK signaling, specifically cooperated with MEK inhibition to impair proliferation in RAS-driven cancer cells. The depletion of SHOC2 disrupted survival pathways triggered by feedback RTK signaling in response to MEK inhibition. Thus, these findings nominate SHOC2 as a potential target for combination therapy. 118 Cell Reports 29, 118-134, October 1, 2019 ª 2019 The Author(s). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).(A) Schematic of pooled CRISPR-Cas9 screening strategy. (B-D) Genome-scale screen results in pancreatic cancer, CFPAC-1 (B), and lung cancer lines, A549 (C) and NCI-H23 (D). Red points have FDR < 0.25 (STARS algorithm). Mean trametinib sensitivity (x axis) is calculated as the difference in the log2(fold-change) in sgRNA representation between cells treated with trametinib for 14 days and the initial pool of sgRNAs. Differential sensitivity indicates the difference log2(fold-change) in sgRNA representation between the trametinib-treated and DMSO-treated arms of the screen. Scores represent the average of all guides for a given gene. (E) Venn diagram summarizes the overlap of genes that are depleted in all three screens with an FDR < 0.25.

MEK inhibitor resistance mechanisms and recent developments in combination trials

“…Inhibition of SHP2 was able to block ERK reactivation following MEK inhibition and prevent adaptive resistance in multiple cancer models [90]. Similarly, depletion of SHOC2, a scaffolding protein responsible for allowing the activation of RAF through MRAS, was found to play a critical role in disrupting survival pathways activated by RTKs following MEK inhibition [52,91]. In particular, SHOC2 inhibition was found to sensitize RAS-driven cancers in vitro to MEK inhibition and was found to play a remarkably similar role to SHP2 in RTK signaling [52].…”

“…For example, despite combination therapy of BRAF and MEK inhibition's improving patient survival in BRAF-mutant melanoma, tumors often recur around 13 months of treatment [51]. Studies are beginning to show a plethora of ways that tumor cells come to evade MEK inhibition, and this often involves a re-wiring of the MAPK pathway to reactivate ERK signaling, showing that many cancer cells have a dependence on this pathway for survival and proliferation [23,52]. In addition, other cell signaling pathways, such as the PI3K/AKT pathway, may show upregulation following MEKi treatment, revealing other mechanisms by which tumor cells confer resistance to MAPK inhibition [18,24].…”

Molecular alterations and targeted therapy in pancreatic ductal adenocarcinoma

“…SHP2 inhibition (by SHP099) and SHOC2 suppression (by gene knockout) were performed to confirm the effectiveness of this strategy in murine models. The combined application of trametinib and SHP099 or trametinib and SHOC2 knockout resulted in tumour stasis [67,68]. In addition to the direct cytostatic effect on the tumour, MEK inhibitors also exert an inhibitory effect on several immunosuppressive immune cells, indicating potential synergy with immunotherapy.…”

Rapid and direct control of target protein levels with VHL-recruiting dTAG molecules

“…This interaction leads to exclusive degradation of the FKBP12 F36V -tagged protein. Studies degrading diverse targets including oncoproteins, transcription factors, chromatin regulators, and kinases illustrate the utility of the dTAG system for drug target validation and discovery 6,[12][13][14][15][16][17][18][19][20][21][22][23] . Despite this broad applicability, we observed context-specific and protein-specific differences in the effectiveness of dTAG-13 for inducing target protein degradation.…”