Studies On The Antiangiogenic Activity And Mechanism Of Tanshinone I

Objective: Angiogenesis is critical to tumor growth and metastasis. Nowadays, Angiogenesis inhibition has become an important strategy for cancer therapy. Tanshinone-1, a major active principle of Salvia miltiorrhiza(Danshen), has been shown to overcome tumor drug resistance and metastasis. This study is designed to investigate the antiangiogenic activity and mechanism of tanshinone-1. Methods: We used the in vitro proliferation, migration and tube formation models of vascular endothelial cells to detect the impact of tanshinone-1 on angiogenesis at its initiation stage. We used the aortic ring sprouting and the chick chorioallantoic membrane models to investigate whether tanshinone-1 inhibited angiogenesis ex vivo and in vivo. Finally, we using Westen blotting, Real-time q PCR, ELISA and RNAi interference techniques to explore the antiangiogenic mechanisms of tanshinone-1. Results: Tanshinone-1 inhibited the proliferation of endothelial cells in a concentration-dependent manner with the 72-h IC50 of 7.75 μM. Tanshinone-1 also inhibited migration and tube formation of vascular endothelial cells in a concentration-dependent manner, and the inhibition rates at 50 μM reached about 58% and 94%, respectively. Moreover, tanshinone-1 inhibited the rat aortic ring sprouting and the neovascularization of the chick chorioallantoic membrane at as low as 1.25 μM and 0.1 μM, respectively. Mechanistic studies showed that in endothelial cells, tanshinone-1 almost completely inhibited phosphorylation of Stat3 at Tyr705 regardless of hypoxia or normoxia but only slightly decreased the hypoxia-induced HIF-1α accumulation. In tumor cells, contrastively, tanshinone-1 could not only make phosphorylation of Stat3 at Tyr705 disappear but also reduce the hypoxia-induced accumulation of HIF-1α to its baseline levels at normoxia. Consequently, VEGF secretion from tumor cells was reduced, which could potentiate the direct inhibition of tanshinone-1 on endothelial cells.Conclusion: Tanshinone-1 inhibits tumor angiogenesis in both direct and indirect ways. Tanshinone-1 directly suppresses proliferation, migration and tube formation(differentiation) of endothelial cells, which could be amplified indirectly by its reducing the secretion of VEGF from tumor cells. Reduction of p-705-Stat3 and HIF-1α accumulation contribute to the antiangiogenic activity of tanshinone-1. Together with its good safety and excellent characteristics in overcoming tumor drug resistance and metastasis, our findings could distinguish tanshinone-1 and its improved derivatives from present antiangiogenesis agents, especially those used in the clinic.