Silibinin induces apoptosis through inhibition of the mTOR-GLI1-BCL2 pathway in renal cell carcinoma

The downstream transcriptional factor of the hedgehog (Hh) pathway, GLI family zinc finger 1 (GLI1), plays a crucial role in regulating tumor progression. In the present study, we demonstrated that silibinin, a natural flavonoid antioxidant isolated from extracts of the milk thistle herb, exerts its anticancer capabilities by restraining GLI1 function in renal cell carcinoma (RCC) cells in vitro and in vivo. In the present study, we confirmed that silibinin induced growth inhibition of RCC through caspase-dependent apoptosis and downregulation of GLI1 and BCL2, which could be partially reversed by GLI1 overexpression. Moreover, we determined that the decreased GLI1 expression by silibinin was mediated by the mammalian target of rapamycin (mTOR) pathway. The in vivo mouse xenograft study also showed that silibinin significantly reduced RCC tumor growth and specifically targeted the mTOR-GLI1-BCL2 signaling pathway. In conclusion, our findings demonstrated for the first time that silibinin induces apoptosis of RCC cells through inhibition of the mTOR-GLI1-BCL2 pathway. These findings also indicate that GLI1 is a novel regulator for the potential therapeutic application of silibinin against RCC.