The activation of epidermal growth factor (EGF) through its receptor, EGFR, is one of the major mechanisms that mediate renal cell carcinoma (RCC) metastasis. Silibinin, a natural flavonoid antioxidant with pleiotropic anticancer capability, has shown anti-metastatic effects in a variety of cancers. However, the mechanism by which silibinin inhibits EGFR signal-induced migration and invasion of RCC cells is not clear. Here, we evaluated the potential roles of EGFR signaling cascade that affects

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... RCC progression, and also investigated the inhibitory effect of silibinin on the EGFR signal-induced migration and invasion abilities of RCC cells. Our data indicated that silibinin inhibited migration and invasion of RCC cells in a dosedependent manner via blocking the EGFR signal, especially in the EGFR highly expressing RCC cells. Silibinin inhibited phosphorylation of EGFR and its downstream molecules ERK1/2 but did not affect phosphorylation of other downstream molecules, STAT3 and Akt, in human RCC cell lines. Moreover, our data suggested that silibinin significantly reduced the MMP-9 expression and its activity that was promoted by the EGFR signal, and also suppressed MMP9-dependent migration and invasion abilities of RCC cells. Taken together, this study clearly demonstrated that silibinin inhibited EGFR induced migration and invasion of RCC cells via blockade of EGFR/MMP-9 signaling. Thus, we suggest that silibinin could be used as a potential effective drug for the inhibition of RCC metastasis. Abbreviations: EGFR, epidermal growth factor receptor; MMP-9, matrix metallopeptidase 9; SB, silibinin; RCC, renal cell carcinoma; ERK, extracellular signal-regulated kinase