Immunohistochemical Evidence of Successful inhibition of S6 Kinase Activity by Rapamycin Therapy in Advanced Localized Prostate Cancer
GJ Netto, A Armstrong, L Schultz, R Albadine, AM Demarzo, R Shah, H Fedor, J Hicks, M Carducci. Johns Hopkins University, Duke University and University of Michigan
Background: mTOR pathway activation due to PTEN loss has been associated with adverse pathologic features in men with prostatic carcinoma (PCa). However, the benefit of mTOR inhibition in prostate cancer remains unclear. We aimed to study the inhibition of S6 kinase activity in radical prostatectomy (RRP) following Rapamycin therapy.
Design: We conducted a two-arm open label multicenter prospective clinical trial of Rapamycin Rx in men with localized intermediate to high-risk PCa undergoing RRP. S6 kinase activity was assessed by measuring phosphorylation levels of S6 protein (serine 240/244 ; Cell Signaling) using standard immunohistochemistry. Semi-quantitative scoring was performed (H-score) measuring the percentage of positive cells (0-100%) multiplied by the intensity of staining (0-3+). We similarly assessed expression levels of 4EBP-1, phosphorylated Akt (Serine 473; Cell Signaling), p27 and PTEN (Cell Signaling). Tumor cell proliferation index was assessed using Ki67 while rate of apoptosis was evaluated using anti-cleaved caspase 3.
Results: 32 treated subjects and 10 non treated control PCa pts were accrued from 3 centers. No significant difference in rate of serious adverse events was detected between treated and control groups. Five (50%) of treated men achieved >60% tumor S6 kinase inhibition as assessed by significant reduction of phos S6 immunohistochemical levels in RRP PCa compared to pretreatment biopsy levels (p=0.04). The latter was further validated by lack of significant reduction in phos S6 in RRP compared to pretreatment biopsy in the non treated controls (p=0.67). Treated PCa also demonstrated significant reduction in cytoplasmic p27 immunostaining with shift toward nuclear localization compared to non-treated controls. No significant effect on Akt activity was detected in treated PCa tumors. There was no change in 4EBP-1 activity, Ki-67, or caspase-3 cleavage.
Conclusions: This is the first study to show pharmacodynamic evidence of mTOR inhibition in localized PCa following Rapamycin treatment. Rapamycin successfully and safely inhibited PCa S6 kinase activity leading to decreased phos S6 in PCa. No effect on Akt activation or change in proliferation or apoptosis was observed in our cohort. Additional studies in larger cohort and further analysis to define the mechanisms of mTOR pathway modulation in PCa are needed.
Category: Genitourinary (including renal tumors)
Monday, March 22, 2010 1:00 PM
Poster Session II # 107, Monday Afternoon