NK4, an HGF antagonist, prevents hematogenous pulmonary metastasis by inhibiting adhesion of CT26 cells to endothelial cells

Hepatocyte growth factor (HGF) plays a definitive role in invasive, angiogenic, and metastatic activities of tumor cells by binding to the c-Met receptor. NK4, a competitive antagonist for HGF and the c-Met receptor, prevents tumor cell growth and metastasis via its bifunctional properties to act as an HGF antagonist and angiogenesis inhibitor. In the present study, we investigated the inhibitory effectiveness of NK4 on hematogenous pulmonary metastasis of the CT26 murine colon cancer cell line, focusing on tumor cell adhesion to endothelial cells. In an in vitro adhesion assay, HGF facilitated adhesion of CT26 cells to a murine endothelial cell line (F-2) in a dose-dependent manner. Furthermore, the enhancing effect of HGF on CT26-F-2 cell interaction was blocked by NK4 as well as by anti-HGF antibody. Similarly, HGF-induced phosphorylation of focal adhesion kinase (FAK), downstream of integrin signaling, was reduced by NK4 and by anti-HGF antibody. However, distinct integrin expression on the surface of CT26 cells was not altered by HGF. In an in vivo experimental pulmonary metastasis assay, stable NK4 expression potently decreased the number of pulmonary metastatic foci. The NK4-induced suppression of pulmonary metastasis was partially reversed when HGF was intraperitoneally administered in an adhesive phase. These results suggest that NK4 could act on tumor cells to inhibit CT26 adhesion to endothelial cells by reducing FAK phosphorylation, which is regulated by inside-out HGF/c-Met signaling, and thereby suppress hematogenous pulmonary metastasis.