ROCK1 is a potential combinatorial drug target for BRAF mutant melanoma

Treatment of BRAF mutant melanomas with specific BRAF inhibitors leads to tumor remission. However, most patients eventually relapse due to drug resistance. Therefore, we designed an integrated strategy using (phospho)proteomic and functional genomic platforms to identify drug targets whose inhibition sensitizes melanoma cells to BRAF inhibition. We found many proteins to be induced upon PLX4720 (BRAF inhibitor) treatment that are known to be involved in BRAF inhibitor resistance, including FOXD3 and ErbB3. Several proteins were down‐regulated, including Rnd3, a negative regulator of ROCK1 kinase. For our genomic approach, we performed two parallel shRNA screens using a kinome library to identify genes whose inhibition sensitizes to BRAF or ERK inhibitor treatment. By integrating our functional genomic and (phospho)proteomic data, we identified ROCK1 as a potential drug target for BRAF mutant melanoma. ROCK1 silencing increased melanoma cell elimination when combined with BRAF or ERK inhibitor treatment. Translating this to a preclinical setting, a ROCK inhibitor showed augmented melanoma cell death upon BRAF or ERK inhibition in vitro . These data merit exploration of ROCK1 as a target in combination with current BRAF mutant melanoma therapies. Synopsis An integrated analysis of proteomic and phospho‐proteomic data from BRAF inhibitor‐treated melanoma cells and a functional genomic screen for shRNAs sensitizing melanoma to BRAF inhibitor treatment identifies ROCK1 kinase as a combinatorial drug target. Proteomic and phospho‐proteomic analysis on BRAF inhibitor‐treated melanoma cells identifies proteins involved in melanoma cell survival. A synthetic lethality shRNA screen identifies shRNAs that sensitize melanoma to BRAF/ERK inhibitors. Integrated analysis of the proteomic and genomic data reveals ROCK1 as potential companion target for BRAF mutant melanoma. Graphical Abstract An integrated analysis of proteomic and phospho‐proteomic data from BRAF inhibitor‐treated melanoma cells and a functional genomic screen for shRNAs sensitizing melanoma to BRAF inhibitor treatment identifies ROCK1 kinase as a combinatorial drug target.