Abstract 3799:Rhodiola rosea extracts, salidroside, and metformin decrease the growth of bladder cancer cell lines via inhibition of TSC- mediated translation initiation and induction of autophagy

Bladder cancer well illustrates the association between aging and cancer, with over 71% of first diagnoses and 85.5% of deaths occurring in patients after 65 years of age. Since cancer and aging share a number of disruptions in molecular pathways and regulatory mechanisms, we examined whether agents with potential anti-aging properties could be useful in bladder cancer chemoprevention. Rhodiola rosea has been in use for centuries in many traditional medicinal practices to increase physical and mental performances, and Rhodiola rosea extracts (RRE) has been the agent in many clinical studies with no reported side effects or drug interactions. Metformin, a commonly prescribed oral and well-tolerated antidiabetic drug, is an insulin-sensitizer. Both RRE and metformin have been reported to have anti-aging effects in model organisms such as Drosophila. In bladder cancer prevention studies, we demonstrated that RRE, one of its active components, salidroside, or metformin significantly inhibit the growth of human urinary bladder cancer cell lines (including RT4, 5637, UMUC3, T24, HT1376, TCCSUP, J82, 253J-P, 253J-BV and 5637), with a minimal effect on normal bladder epithelial cells (TEU-2). In addition, RRE, salidroside and metformin are more effective in the reduction of colony formation of UMUC3 cells in soft agar than in two dimension culture, which suggests their potentials for inhibiting in vivo tumor growth. Using the primary mouse embryo fibroblasts tuberous sclerosis (TSC)-1 or TSC2 knockout and wild-type cells, we showed that TSC2 protein was, at least in part, required for the growth inhibitory effect of RRE, salidroside and metformin. Further study showed that RRE, salidroside and metformin reduce the phosphorylation of the S6 kinase and 4EBP1 which increase the binding of 4EBP1 to m7GTP to stop translation initiation in TSC-positive. UMUC3 but not in TSC-negative RT4 cells. In UMUC3 cells with stably overexperessed EGFP-LC3, we also observed that RRE, salidroside and metformin all significantly increase the percentage of cells with punctuate EGFP-LC3 fluorescence within four to eight hours of treatment, suggesting induction of autophagy. The autophagysome formation by these treatments was further confirmed by vital staining with acridine orange and western blotting analysis of LC3-II cleavage. In summary, our results indicate that RRE, salidroside and metformin share some similar molecular mechanisms in their anti-bladder cancer activity in vitro by involvement of TSC tumor suppressors-mediated inhibition of translational initiation, and by induction of autophagy. Further animal experiments are needed to examine the comparative efficacy of these agents in chemoprevention of bladder carcinogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3799.