Hispidulin potentiates the antitumor effect of sunitinib against human renal cell carcinoma in laboratory models.

The aim of the study was to evaluate the effect of the hispidulin, a naturally occurring flavonoid, in combination with a new multi-targeted oral medication, sunitinib on renal cell carcinoma (RCC) cell proliferation in vitro and on tumor growth in vivo. After treatment with hispidulin or sunitinib, either alone or in combination, MTT assay was used to examine cell viability and flow cytometry analysis was employed to examine cell cycle distribution and apoptosis of the RCC cell lines 786-0 and Caki-1. Western blotting was employed to examine the expression of proteins related to pStat3 signaling pathway. Furthermore, a xenograft mouse model was applied to study the antitumor efficacy of sunitinib or hispidulin alone or in combination, with immunohistochemistry to detect expression of proteins related to xenograft growth and angiogenesis. Hispidulin dose-dependently inhibited proliferation and induced apoptosis in both of the tested RCC cell lines when used alone; when combined with sunitinib, relatively low concentration of hispidulin enhanced the antitumor activity of the latter. The antitumor activity of hispidulin and its enhancement of the antitumor activity of sunitinib correlated with the suppression of pStat3 signaling and the consequent downregulation of Bcl-2 and survivin. Moreover, combination of hispidulin and sunitinib inhibited the growth and angiogenesis of xenografts generated from Caki-1 significantly. Immunohistochemistry indicated decreased expression of proteins promoting xenograft growth and angiogenesis after combination treatment of hispidulin and sunitinib. Our results showed that hispidulin, by inhibiting pStat3 signaling, exhibited antitumor activity and the joint use of hispidulin and sunitinib could provide greater antitumor efficacy compared to either drug alone. Therefore, combination treatment with hispidulin and sunitinib might offer a novel therapeutic option for patients with RCC.