DC-0623 is an orally active, selective and ATP-uncompetitive MEK inhibitor with potential antineoplastic activity. GDC-0623 specifically inhibits mitogen-activated protein kinase kinase (MEK or MAP/ERK kinase), resulting in inhibition of growth factor-mediated cell signaling and tumor cell proliferation. In a panel of mutant cancer cell lines, GDC-0623 inhibits cellular proliferation with EC50 values in the low nanomolar range. In vivo, GDC-0623 (40 mg/kg, p.o.) causes potent tumor growth inhibition (TGI) in mouse MiaPaCa-2 (120%), A375 (102%) and HCT116 (115%) xenografts. GDC-0623 had been in phase I clinical trials by Genentech, Inc. for the treatment of Advanced or Metastatic Solid Tumors. However, the clinical development of GDC-0623 was discontinued.