Cancer Biology and Signal Transduction MEK Inhibitor for Gastric Cancer withMEK1 Gene Mutations

The prognosis for patients with unresectable advanced or recurrent gastric cancer remains poor. The identification of additional oncogeneswith influences similar to those of epidermal growth factor receptor gene mutations, upon which the growth of cancer cells is dependent, is needed. In this study, we evaluated sensitivity toMEK inhibitors (GSK1120212 andPD0325901) in several gastric cancer cell lines in vitro and found three poorly differentiated gastric cancer cell lines that were hypersensitive to the inhibitors. The sequence analyses in these three cell lines revealed that one cell line had a novelMEK1mutation, while the other two had previously reported KRAS andMEK1mutations, respectively; the gene statuses of the other resistant cell lines were all wild-type. Experiments using MEK1 expression vectors demonstrated that the MEK1 mutations induced the phosphorylation of ERK1/2 and had a transforming potential, enhancing the tumorigenicity. The MEK inhibitor dramatically reduced the phosphorylation of ERK1/2 and induced apoptosis in the cell lines with MEK1 mutations. In vivo, tumor growth was also dramatically decreased by an inhibitor. One of the 46 gastric cancer clinical samples that were examined had a MEK1 mutation; this tumor had a poorly differen-tiated histology. Considering the addiction of cancer cells to activeMEK1 mutations for proliferation, gastric cancer with such oncogenic MEK1 mutations might be suitable for targeted therapy with MEK inhibitors. Mol Cancer Ther; 13(12); 3098–106. 2014 AACR