Selective MEK1 and MEK2 inhibitor. Inhibits MEK activity in mouse colon 26 cells (IC50 = 0.33 nM). Inhibits the growth of melanoma cell lines in vitro and in vivo; induces G1-phase cell cycle arrest and apoptosis in a mouse xenograft model. Also inhibits production of proangiogenic cytokines such as VEGF. Orally active.