GDC-0623 is a potent, ATP-uncompetitive inhibitor of MEK1 (Ki = 0.13 nM in the presence of ATP). It inhibits the proliferation of A375 BRAF(V600E) and HCT116 KRAS(G13D)-mutant cancer cell lines with EC50 values of 7 and 42 nM, respectively. GDC-0623 inhibits ERK and BIM phosphorylation resulting in upregulation and stabilization of pro-apoptotic BIM protein in KRAS mutant and wild-type HCT116 cells and in KRAS mutant GW620 cells.