Antitumor effect of FP3 in combination with cetuximab on patient-derived tumor tissue xenograft models of primary colon carcinoma and related lymphatic and hepatic metastases

FP3 is an engineered protein which contains the extracellular domain 2 of vascular endothelial growth factor (VEGF) receptor 1 (Flt-1) and the extracellular domain 3 and 4 of VEGF receptor 2 (Flk-1, KDR) fused to the Fc portion of human immunoglobulin G1. Previous studies have demonstrated its antiangiogenic effects in vitro and in vivo, and its antitumor activity in vivo. Cetuximab is a monoclonal antibody against epidermal growth factor (EGF) receptor. Combined inhibition of VEGF and EGF signaling may act additively or synergistically. In this study, patient-derived tumor tissue (PDTT) xenograft models of primary colon carcinoma and lymphatic and hepatic metastases were established for assessment of the antitumor activity of FP3 in combination with cetuximab. Xenografts were treated with FP3 and cetuximab, alone or in combination. After tumor growth was confirmed, volume and microvessel density in tumors were evaluated. Levels of VEGF, EGFR and PCNA in the tumor were examined by immunohistochemical staining, and levels of related cell signaling pathway proteins were examined by western blotting. FP3 in combination with cetuximab showed significant antitumor activity in three xenograft models (primary colon carcinoma, lymphatic metastasis and hepatic metastasis). The microvessel density in tumor tissues treated with FP3 in combination with cetuximab was lower compared to that of the control. Antitumor activity of FP3 in combination with cetuximab was significantly higher than that of each agent alone in two xenograft models (colon carcinoma lymphatic metastasis and hepatic metastasis). This study indicated that addition of FP3 to cetuximab significantly improved tumor growth inhibition in the PDTT xenograft models of colon carcinoma lymphatic and hepatic metastases. Combination anti-VEGF (FP3) and anti-EGFR (cetuximab) therapies may represent a novel therapeutic strategy for the management of metastatic colon carcinoma.