Abstract 4598: Silibinin targets fibronectin-integrin interaction and actin remodeling towards inhibiting motility and proliferation of human prostate carcinoma PC3 cells

Abstract

Abstract Prostate cancer (PCA) is the 2nd leading cause of cancer-related deaths in US men. Patients with localized PCA have a very high 5-year survival rate; however, in patients with clinically detectable metastatic disease, median survival is reduced to 12-15 months. Therefore, preventing or inhibiting metastasis through non-toxic agents could be a useful approach for lowering high mortality among PCA patients. We have shown recently that silibinin possess strong anti-metastatic efficacy against PCA, but mechanism of its action still remains largely unknown. The first major event during PCA metastasis is replacement of cell-cell interaction with integrins based cell-matrix interaction which then controls motility, invasiveness and survival as well as confers chemoresistance to PCA cells. Accordingly, here we examined silibinin effect on cell-matrix interaction using advanced human PCA PC3 cells and extracellular matrix (ECM) component fibronectin. Fibronectin (5-15 microgram/ml) strongly induced motile morphology in PC3 cells within 1 hr of plating and significantly enhanced cell proliferation measured after 24 hrs compared to cells plated on BSA. Silibinin (50-200 microM) significantly inhibited fibronectin-induced motile morphology by 24-83% and cell proliferation by 34-82%. Cell detachment assay clearly showed that PC3 cells plated on fibronectin are attached through strong interactions and silibinin (50-200 microM) significantly inhibits these interactions in a dose-dependent manner. To rule out the possibility that silibinin physically affects cell-fibronectin interaction, we performed studies where PC3 cells were pre-treated with silibinin for 48 hrs, and then cells collected and plated on fibronectin. Under these experimental conditions too, silibinin significantly inhibited fibronectin-induced motile morphology and proliferation of PC3 cells. Next, we performed wound healing assay to study silibinin effect on cell migration, and our results clearly showed that silibinin (50-200 microM, 6 hrs) inhibits fibronectin-induced motility in PC3 cells. Integrins, over-expressed by metastatic PCA cells, primarily interact with fibronectin and transduce signals related to proliferation and motility through actin remodeling. Accordingly, next we studied silibinin effect on these critical signaling molecules and found that it strongly decreases the basal protein levels of integrin beta 3, cortactin and ARP2 (actin-related protein) as well as fibronectin-induced integrin beta 3 and ARP2 expression in PC3 cells. Together, these results, for the first time, showed that silibinin targets PCA cells’ interaction with ECM, thereby inhibiting their motility and survival. These observations further support silibinin use in PCA intervention including metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4598. doi:10.1158/1538-7445.AM2011-4598