Suppression of lymphangiogenesis in human lymphatic endothelial cells by simultaneously blocking VEGF-C and VEGF-D/VEGFR-3 with norcantharidin.

Lymph node metastasis of tumors is a crucial early step in the metastatic process. Tumor lymphangiogenesis plays an important role in promoting tumor metastasis to regional lymph nodes. Norcantharidin (NCTD) has been reported to possess potent anti-angiogenesis and antitumor properties in several cell lines and xenograft tumor models. However, its role in tumor-associated lymphangiogenesis and lymphatic metastasis remains unclear. Here, we investigated the effect of NCTD on proliferation, apoptosis, migration, invasion and the lymphatic tube formation, lymphangiogenesis, of human lymphatic endothelial cells (HLECs) in vitro by MTT, proliferation assay, Hoechst staining and flow cytometry, scraping line method, Matrigel invasion assay, inverted or fluorescence microscope and transmission electron microscope. Moreover, the underlying mechanisms, such as VEGF-C, VEGF-D, VEGFR-3 at protein and mRNA levels in lymphangiogenesis using 3-dimensional (3-D) culture of HLECs were measured by immunohistochemistry, western blotting and real-time polymerase chain reaction (RT-PCR). It was shown that NCTD inhibited proliferation, migration, invasion and lymphatic tube formation (forming-lymphatic and/or formed-lymphatic) of HLECs, induced HLEC apoptosis (all P<0.01) significantly, in a dose- and time-dependent manner (IC50 6.8 µg/ml); and downregulated the expression of VEGF-C, VEGF-D and VEGFR-3 at protein or/and mRNA levels (P<0.01) in HLEC lymphatic tube formation. Thus, we identified for the first time that NCTD inhibited HLEC lymphangiogenesis by simultaneously blocking VEGF-C and VEGF-D/VEGFR-3 in vitro. The present findings may be of importance to explore the therapeutical target or strategy of NCTD for tumor lymphangiogenesis and lymphatic metastasis.