Abstract
PURPOSE: Statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, purportedly exert anti-tumoral effects on breast cancer by increasing apoptosis and decreasing proliferation. However, the biologic mechanisms for these actions are not fully elucidated. The aim of this study was to explore the effects of simvastatin on apoptosis, proliferation and commonly abrogated PI3K/Akt/mTOR pathway in a window-of-opportunity breast cancer trial and breast cancer cell lines.
EXPERIMENTAL DESIGN: A total of 16 female patients with newly diagnosed primary breast cancer were recruited into a preoperative window-of-opportunity trial. Patients received simvastatin for 10-28 days at a dose of 20mg daily before definitive breast cancer surgery. Pre- and post-treatment tumor biopsies were obtained for immunohistochemistry staining for cleaved caspase 3, Ki67, Pten, phospho-Akt and phospho-S6 ribosomal protein, and the changes between paired pre- and post-treatment tumors compared. For in vitro functional studies, apoptosis and proliferation assays were performed on breast cancer cell lines MCF7 and MDA-MB-231 48 hours after treatment with simvastatin. Using Western blots, the effects of simvastatin on apoptosis protein caspase 3, cell cycle proteins of c-myc, cyclin D1, p21 and p27, and of PI3K/Akt/mTOR pathway through phosphorylation of Akt, mTOR, p70S6K, S6 ribosomal protein and 4EBP1, were assessed.
RESULTS: In the prospective clinical trial, simvastatin treatment led to significant increase in apoptosis in post-treatment tumors, as determined by positive cleaved caspase 3 (23.4±24.3 vs 8.9±7.4, p=0.002). Decreased trend for proliferation was also observed in post-treatment tumors (57.7±35.2 vs 74.6±59.9 for Ki67, p=0.245). Moreover, simvastatin treatment markedly suppressed PI3K/Akt/mTOR signalling pathway by activating Pten (66.1±65.2 vs 30.0±46.6, p=0.005) and by dephosphorylating Pten downstream effectors, Akt and S6 ribosomal protein (9.0±19.5 vs 93.0±87.4, p=0.002 for phospho-Akt; 63.7±51.6 vs 108.6±67.7, p=0.033 for phospho-S6 ribosomal protein). In MCF7 and MDA-MB-231 cells, simvastatin treatment similarly induced apoptosis and inhibited cell proliferation, with decrease in expression of c-myc and cyclin D1 and increase in cell cycle suppressor p21 and p27 at a dose dependent manner. Moreover, simvastatin treatment, at 20uM for MCF7 and 400nM for MDA-MB-231 cells, strongly suppressed sequential phosphorylation of PI3K/Akt/mTOR pathway cascades including Akt, mTOR, p70S6K, S6 ribosomal protein and 4EBP1.
CONCLUSION: The clinical trial and in vitro functional studies concordantly showed simvastatin to promote apoptosis, suppress proliferation and dephosphorylate sequential signalling cascades of PI3K/Akt/mTOR pathway of breast cancer. These findings shed light on the biological and potential anti-tumor effects of simvastatin in breast cancer.
Citation Format: Tingting Wang, Serena Seah, Ching-Wan Chan, Mikael Hartman, Nyein Nyein Thaw Dar, Philip Iau, Boon-Cher Goh, Soo-Chin Lee. Simvastatin induced apoptosis and suppressed proliferation of breast cancer through deactivating PI3K/Akt/mTOR pathway. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2630. doi:10.1158/1538-7445.AM2014-2630
