Rhodiola rosea extracts and salidroside decrease the growth of bladder cancer cell lines via inhibition of the mTOR pathway and induction of autophagy

Abstract

The incidence of human urinary bladder cancer increases markedly with age, suggesting a mechanistic connection between aging and bladder carcinogenesis and a potential use of anti-aging agents in bladder cancer chemoprevention. Rhodiola rosea, growing in high altitude or cold regions of the world, has been reported to have anti-aging effects in Drosophila. We demonstrated that a R. rosea extract and one of its bioactive components, salidroside, inhibited the growth of bladder cancer cell lines with a minimal effect on nonmalignant bladder epithelial cells TEU-2. Interestingly, the R. rosea extract and salidroside component exhibited a selective ability to inhibit the growth of p53 knockout primary mouse embryo fibroblasts (p53-/- MEFs) compared to their wild-type counterparts. The growth inhibitory effects of the R. rosea extract and salidroside were, however, attenuated in TSC2 and p53 double knock MEFs (TSC2-/-, p53-/- MEFs), suggesting that TSC2 protein is, at least in part, required for the growth inhibitory effects of the R. rosea extract and salidroside. The R. rosea extract and salidroside treatment of UMUC3 cells resulted in an increase of AMP-activated protein kinase (AMPK)-α phosphorylation and a decrease of 4E-BP1 phosphorylation, leading to increased binding of 4E-BP1 to m7 GTP. These results indicate that the R. rosea extract and salidroside inhibit translation initiation. Furthermore, both the R. rosea extract and salidroside treatment of UMUC3 cells caused a significant percentage of cells undergoing autophagy. Therefore, the R. rosea extract and salidroside deserve further study as novel agents for chemoprevention of bladder carcinogenesis.