Background: The major determining factor of prognosis of oral squamous cell carcinoma is cervical lymph node metastasis. 6,8-Diprenylgenistein (6,8-DG), an isoflavonoid isolated from Cudrania tricuspidata has been reported to have anti-microbial and anti-obesity activities. However, its effects on lymphangiogenesis and lymph node metastasis in oral cancer have not yet been reported.
Methods: To investigate the in vitro inhibitory effects of 6,8-DG on VEGF-A-induced lymphangiogenesis, we performed the proliferation, tube formation, and migration assay using human lymphatic microvascular endothelial cells (HLMECs). RT-PCR, Western blot, immunoprecipitation, ELISA and co-immunoprecipitation assays were used to investigate the expression levels of proteins, and mechanism of 6,8-DG. The in vivo inhibitory effects of 6,8-DG were investigated using an oral cancer sentinel lymph node (OCSLN) animal model.
Results: 6,8-DG inhibited the proliferation, migration and tube formation of rhVEGF-A treated HLMECs. In addition, the in vivo lymphatic vessel formation stimulated by rhVEGF-A was significantly reduced by 6,8-DG. 6,8-DG inhibited the expression of VEGF-A rather than other lymphangiogenic factors in CoCl2-treated SCCVII cells. 6,8-DG inhibited the expression and activation of VEGFR-2 stimulated by rhVEGF-A in HLMECs. Also, 6,8-DG inhibited the activation of the lymphangiogenesis-related downstream signaling factors such as FAK, PI3K, AKT, p38, and ERK in rhVEGF-A-treated HLMECs. Additionally, 6,8-DG inhibited the expression of the hypoxia-inducible factor (HIF-1α), which is involved in the expression of VEGF-A in CoCl2-treated SCCVII cells, and 6,8-DG inhibited VEGF-A signaling via interruption of the binding of VEGF-A and VEGFR-2 in HLMECs. In the VEGF-A-induced OCSLN animal model, we confirmed that 6,8-DG suppressed tumor-induced lymphangiogenesis and SLN metastasis.
Conclusion: These data suggest that 6,8-DG inhibits VEGF-A-induced lymphangiogenesis and lymph node metastasis in vitro and in vivo. Furthermore, the inhibitory effects of 6,8-DG are probably mediated by inhibition of VEGF-A expression in cancer cells and suppression of the VEGF-A/VEGFR-2 signaling pathway in HLMEC. Thus, 6,8-DG could be novel and valuable therapeutic agents for metastasis prevention and treatment of oral cancer.
Keywords: 6,8-diprenylgenistein; VEGF-A-induced lymphangiogenesis; oral cancer; sentinel lymph node metastasis.