Combined Therapy Targeting MET and Pro-HGF Activation Shows Significant Therapeutic Effect Against Liver Metastasis of CRPC

The liver is the most lethal metastatic site in castration-resistant prostate cancer (CRPC). Overexpression of MET protein has been reported in CRPC, and <i>MET</i> is an important driver gene in androgen-independent CRPC cells. Mouse CRPC cell line CRTC2 was established by subcutaneous injection of hormone-sensitive PC cells (TRAMP-C2) in castrated nude mice. CRCT2/luc2 cells were injected into the spleen of castrated nude mice, and liver metastasis was confirmed at 2 weeks post-injection. We administered MET inhibitor (MET-I) and HGF activator inhibitor (HGFA-I) to this liver metastasis model and assessed the therapeutic effect. After intrasplenic injection, CRTC2 showed a higher incidence of liver metastasis whereas no metastasis was observed in TRAMP-C2. Microarray analysis revealed increased expression of <i>HGF</i>, <i>MET</i>, and <i>HPN</i>, <i>HGFAC</i> (encoding HGF activating proteases) in liver metastasis. Proliferation of CRCT2 was significantly inhibited by co-administration of MET-I and HGFA-I by in vitro analysis with HGF-enriched condition. In an analysis of the mouse model, the combination-therapy group showed the strongest reduction for liver metastasis. Immunohistochemical staining also revealed the strongest decrease in phosphorylation of MET in the combination-therapy group. Co-culture with HGF-expressed mouse fibroblasts showed attenuation of the inhibitory effect of MET-I; however, additional HGFA-I overcame the resistance. We established an androgen-independent CRPC cell line, CRTC2, and liver metastasis model in mice. Significant effect was confirmed by combined treatment of MET-I and HGFA-I by in vitro and in vivo analysis. The results suggested the importance of combined treatment with both MET- and HGF-targeting agents in the treatment of HGF-enriched conditions including liver metastasis.