Blockade of the MAP kinase pathway suppresses growth of colon tumors in vivo

The mitogen-activated protein kinase pathway is thought to be essential in cellular growth and differentiation. Here we report the discovery of a high ly potent and selective inhibitor of the upstream kinase MEK that is orally active. Tumor growth was inhibited as much as 80% in mice with colon carci nomas of both mouse and human origin after treatment with this inhibitor. E fficacy was achieved with a wide range of doses with no signs of toxicity, and correlated with a reduction in the levels of activated mitogen-activate d protein kinase in excised tumors. These data indicate that MEK inhibitors represent a promising, noncytotoxic approach to the clinical management of colon cancer.