Abstract P2-07-01: Simvastatin Prevents Breast Cancer Skeletal Metastasis by Increasing p53 Levels To Increase PTEN and Inhibit CD44 Expression

Abstract

Abstract Bone represents one of the main sites of metastatic spread of breast cancer. The prognosis for the breast cancer patients with bone metastasis is very poor with severely compromised life style associated with extreme bone pain and fracture prevalence. We used heart injection model to test the effect of simvastatin on breast cancer bone metastasis. Simvastatin prevented osteolytic lesions in mice injected with MDA-MB-231 (MDA) human breast cancer cells, indicating that statin attenuates breast cancer metastasis to bone. To investigate the mechanism, MDA cells were used in an in vitro wound-healing assay. Simvastatin significantly inhibited the migration of MDA cells. Transwell invasion assay using collagen-coated discs confirmed the inhibitory effect of simvastatin on breast cancer cell invasion. We have recently shown that simvastatin inhibits primary tumor growth in mice by upregulating the tumor suppressor PTEN. Overexpression of PTEN in MDA cells significantly blocked their ability to migrate and invade. To determine the mechanism of PTEN upregulation, we considered the tumor suppressor protein p53, which is known to regulate PTEN expression. Simvastatin-treated mice tumors showed significantly increased levels of p53. Similarly, simvastatin enhanced the expression of p53 in MDA cells. Additionally, simvastatin increased transcription of the reporter plasmids containing the consensus p53-binding element (p53-Luc) or the PTEN promoter (PTEN-Luc). Cotransfection of p53 with these reporter constructs resulted in similar increase in transcription, indicating a role of p53 in PTEN expression by simvastatin. Recent reports indicate a direct correlation between expression of CD44 in breast cancer and their metastasis to other organs including bone. Levels of CD44 were significantly reduced in the tumors of mice treated with simvastatin. In MDA cells, simvastatin decreased the expression of CD44 protein and its transcription, as determined by CD44 promoter-driven luciferase construct (CD44-Luc). p53 acts as transcriptional activator or transcriptional repressor in a cell-type and context-dependent manner. Presence of non-canonical p53-binding elements has been reported in the CD44 promoter. Cotransfection of p53 with CD44-Luc significantly suppressed the transcription of CD44. Furthermore, expression of p53 markedly reduced the expression of CD44 protein. Finally, downregulation of endogenous CD44 by specific shRNA decreased migration of MDA cells. Together these results uncover a novel action of simvastatin, which targets p53 expression to simultaneously increase PTEN and decrease CD44 thus blocking migration and preventing bone metastasis of the human breast cancer cells. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-07-01.