An orally bioavailable inhibitor of MEK1/2 (IC50 = 12 nM) that inhibits ERK phosphorylation in various cancer cell lines (IC50s ≥ 5 nM); efficacious in several xenograft tumor models in mice, including those bearing K-Ras or B-Raf mutations, as well as in clinical studies using patients with N-Ras melanoma, non-small cell lung cancer, or biliary tract cancer.