Inhibitor of mitogen-activated protein kinase kinase (MAPKK / MEK). Acts by binding to the inactivated form of MEK, thereby preventing its phosphorylation by cRAF or MEK kinase (IC50 = 2-7 μM). Inhibits cell growth and proliferation in acute myelogenous leukemia (AML) cell lines; causes G1 arrest by blocking p53-dependent p21 induction. Also available as part of the MAPK Cascade Inhibitor Tocriset™ and MAPK Inhibitor Tocriset™.