Abstract #2879: Inhibition of mammalian target of rapamycin as a therapeutic strategy in the management of bladder cancer

Inhibition of mammalian target of rapamycin as a therapeutic strategy in the management of bladder cancer Purpose. mTOR (mammalian target of rapamycin) is located downstream of nutrients and growth signalling pathways and plays a central role in the regulation of cell growth and proliferation. mTOR helps cells respond to environmental changes and growth conditions by coordinating mRNA translation and proteins synthesis that regulate mechanism of cell growth, proliferation and biogenesis. Dysregulation of PI3K/Akt/mTOR pathway generates a favourable oncogenic environment and has been documented in a variety of human tumours including bladder cancer. Promising preclinical data have led to rapid translation of mTOR inhibitors as anticancer therapy into the clinical setting. We examined whether mTOR inhibition by RAD001 (everolimus) could be therapeutically efficacious in the treatment of bladder cancer. Experimental Design. We evaluated the response of nine urothelial carcinoma cell lines to mTOR inhibition by cell viability assay, western blot, and cell cycle analyses. In vitro effects on angiogenesis were measure using the vascular endothelial growth factor ELISA kit before and after treatment. In vivo, we also determined the effect of RAD001 on tumor growth and malignancy using xenograft nude mice inoculated with human bladder cancer cells. Tumor cell proliferation was determined by PNCA immunostaining. Tumor cell apoptosis was detected by using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling and tumor angiogenesis was investigated by using microvessel density. Results. RAD001 markedly inhibited cell proliferation of all bladder cancer cell lines in a dose-dependent manner which involves a G0/G1 phase arrest (IC50 ranged from 0.5 nmol/L to 100nmol/L). 48 hours after treatment, FACS analysis showed that RAD001 induced a G0/G1 phase in all cell lines without induction of apoptosis. RAD001 significantly inhibited the phosphorylation of downstream S6 and VEGF production in all cell lines. Mice treated with RAD001 were significantly smaller than mice treated with placebo. Tumor tissue from mice treated with RAD001 had a significant decrease in cell proliferation whereas there was no significant effect on apoptosis. Conclusions. Inhibiting mTOR signaling demonstrated remarkable antitumor activity both in vitro and in vivo bladder cancer models. These results indicate that RAD001 could be exploited as a potential therapeutic strategy in bladder cancer.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 2879.