AbstractBackgroundColorectal cancer (CRC) is the most common malignancy in the world, and novel molecular targeted therapies for CRC have been vigorously pursued. We searched for novel combination therapies based on the expression patterns of membrane proteins in CRC cell lines.ResultsA positive correlation was observed between the expression of human pidermal growth factor receptor (HER) 3 and mesenchymal‐to‐epithelial transition factor (MET) on the cell surface of CRC cell lines. The brief stimulation of HER3/MET‐high SW1116 CRC cells with both neuregulin‐1 (NRG1) and hepatocyte growth factor enhanced ERK phosphorylation and cell proliferation more than each stimulation alone. In addition, a prolonged NRG1 stimulation resulted in the tyrosine phosphorylation of MET. In this context, the Forkhead Box protein M1 (FOXM1)‐regulated tyrosine phosphorylation of MET by NRG1 was demonstrated, suggesting the existence of a signaling pathway mediated by FOXM1 upon the NRG1 stimulation. Since the co‐expression of HER3 and MET was also demonstrated in in vivo CRC tissues by immunohistochemistry, we investigated whether the co‐inhibition of HER3 and MET could be an effective therapy for CRC. We established HER3‐and/or MET‐KO SW1116 cell lines, and HER3/MET‐double KO resulted in the inhibition of in vitro cell proliferation and in vivo tumor growth in nude mice by SW1116 cells. Furthermore, the combination of patritumab, an anti‐HER3 fully human mAb, and PHA665752, a MET inhibitor, markedly inhibited in vitro cell proliferation, 3D‐colony formation, and in vivo tumor growth in nude mice by SW1116 cellsConclusionThe dual targeting of HER3/MET has potential as CRC therapy.