Abstract 1608: Silibinin synergizes with histone deacetylase (HDAC) inhibitors in upregulating E-cadherin expression in non-small lung cancer (NSCLC) cells

Abstract

Abstract Lung cancer is the leading cause of cancer-related mortalities, and the 5-year survival rate of this malignancy remains at 15%. This feature is attributed primarily to the early metastasis of the disease within the organ and to distant sites that involves the epithelial-to-mesenchymal transition (EMT) of lung cancer cells. Aggressive cancer cells with EMT are characterized by loss of cell adhesion, repression of E-cadherin expression and increased cell mobility. NSCLC cells widely differ in their basal level of E-cadherin expression, which is epigenetically silenced in most of them due to deacetylation by histone deactylases. This suggests that inhibitors of HDACs would be useful in NSCLC control. Several HDAC inhibitors (HDACi) have shown potential in this regard, and are in clinical trials; however, their toxicity and cancer cell resistance are the limiting factors. Silibinin (Sb), a non-toxic chemopreventive agent, has shown strong efficacy against epithelial cancers including NSCLC, and previously, we have demonstrated that Sb alters HDAC enzymatic activity and protein levels in a total cellular extract of H1299 cells. Herein, we sought to determine the putative role of Silibinin, either alone or in combination with other HDACi in modulating E-cadherin levels in NSCLC cell lines including H1299 cells (epigenetically silent E-cadherin levels). Treatment with HDAC inhibitors, Trichostatin A [TSA] (0.33-1 µM) or SAHA (0.5-5 µM) led to a dose-dependent induction of E-cadherin expression levels. Furthermore, the combinations of TSA (0.5 µM) with low doses of Sb (3.75-25 µM) in H1299 cells, significantly increased E-cadherin protein levels (24h), which remained sustained at later time points (48-72h) longer than with TSA alone treatments. Also, at these time points, Zeb1, a major transcriptional repressor of E-cadherin, was inversely down-modulated with the combination treatments. Substantial inhibition of invasion/migration of H1299 cells with similar treatment conditions further emphasized the biological significance of E-cadherin restoration. Unlike H1299 cells, treatment of H322 and H358 cells (with detectable E-cadherin level) with Sb (3.75-25 µM) alone was sufficient to consistently increase the basal levels of E-cadherin, with concomitant reduction of Zeb1 levels, which also led to inhibition of migratory potential of these cells. Overall these findings demonstrate that Sb alone or in combination with HDAC inhibitors upregulates E-cadherin expression levels in NSCLC cell lines, and this consequently leads to inhibition of invasion/migratory phenotype of these cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1608. doi:1538-7445.AM2012-1608