AZD 8330 is a selective allosteric inhibitor of MEK1/2 (IC50 = 7 nM). It blocks phosphorylation of ERK1/2 and inhibits proliferation of certain cancer cells. AZD 8330 is orally bioavailable, inhibits ERK phosphorylation in vivo, and reduces tumor growth in a Calu-6 nude rat xenograft model.