[1725] Mammalian Target of Rapamycin (mTOR) Regulates Cellular Proliferation and Tumor Growth in Urothelial Carcinoma

DE Hansel, E Platt, M Orloff, J Harwalker, S Sethu, JL Hicks, A De Marzo, R Steinle, E Hsi, D Theodorescu, C Eng. Cleveland Clinic, Cleveland, OH; Johns Hopkins Hospital, Baltimore, MD; University of Virginia, Charlottesville, VA

Background: Mammalian target of rapamycin (mTOR) signaling has been associated with aggressive tumor growth in many cancer models, although its role in urothelial carcinoma (UCC) has not been explored in detail.
Design: We evaluated expression of phosphorylated mTOR (P-mTOR) and a downstream target, ribosomal S6 protein (P-S6), in 121 cases of UCC by immunohistochemical analysis. We next determined the effects of mTOR inhibition via rapamycin administration on cell proliferation in UCC cell lines RT4, T24, J82 and UMUC3, all of which expressed mTOR signaling components with the exception of PTEN in UMUC3 cells. Mouse studies were performed using T24-xenografted mice subjected to intraperitoneal vehicle (n=9) or 2.5 mg/kg rapamycin administration (n=9) twice weekly for 4 weeks to evaluate bladder tumor growth.
Results: Phosphorylated mTOR and phosphorylated S6 was identified in 74% (90/121) and 55% (66/121) of UCCs, respectively. P-mTOR intensity and %positive cells were associated with reduced disease-specific survival (p=0.041, p=0.078, respectively) and P-mTOR intensity corresponded to increased pathologic stage (p<0.001). Rapamycin treatment resulted in a dose-dependent reduction in proliferation to 12% of control and was significant at 1 nM in J82, T24 and RT4 cells (p=0.002, p=0.002, p=0.03, respectively) and at 10 nM in UMUC3 cells (p=0.03). Reduced proliferation corresponded with reduced P-S6 levels by western blot. Administration of rapamycin to T24-xenografted mice resulted in a 55% reduction in tumor volume (p=0.03) and a 40% reduction in proliferation index (p<0.01) as compared to vehicle-injected mice.
Conclusions: These findings indicate that mTOR pathway activation frequently occurs in UCC and that inhibition of this pathway suggests a potential means by which to reduce urothelial tumor cell growth.
Category: Pathobiology

Tuesday, March 23, 2010 2:30 PM

Platform Session: Section H, Tuesday Afternoon

 

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