KO-947 blocks ERK signaling and proliferation of tumor cells exhibiting dysregulation of MAPK pathway signaling, including mutations in BRAF, NRAS or KRAS, at low nanomolar concentrations...In cell-line derived xenograft studies, the drug profoundly suppresses ERK signaling for up to five days after a single dose and induces regressions in RAS- and RAF-mutant melanoma, NSCLC and pancreatic cancer models on administration schedules ranging from daily to weekly.