MAPK1 and cancer: In a cell viability screen of 474 human cancer cell lines the calculated GI50 values for GDC-0994 and cobimetinib were strongly correlated, with BRAF mutant cell lines showing the strongest sensitivity and BRAF/RAS-wild type (WT) and RAS mutant lines showed more variable and modest potency, suggesting redundancy and overlapping pharmacological effects of MEK and ERK inhibitors (Fig 1a).