Targeting Annexin II Function with Small Molecule Natural Products as a Novel Anti-Cancer Strategy

Abstract

The establishment and dissemination of cancers is dependent not only on the dysregulation of cell autonomous processes, but also on the ability of tumor cells to establish an adequate blood supply in their host environment (neoangiogenesis) and escape local tissue constraints (metastasis). The key proteins that mediate each of these processes are highly sought after as potential therapeutic targets. Annexin AII (AII) is a cellular protein that plays a critical role in multiple cancer relevant processes such as metastasis, angiogenesis, and mitogenic signal transduction. Studies have correlated elevated levels of AII with aggressive tumors. However, the multiple roles of AII have made it difficult to define specific mechanisms by which the protein can contribute to a malignant phenotype. Using a cell-based reporter assay, we have identified Withaferin A (WA) from Withania somnifera, a plant with medicinal uses that date back to over 3,000 years in Ayurvedic medicine, as a small molecule natural product that interacts with the AII protein. Work in our laboratory has shown that WA disrupts F-actin organization via a covalent interaction with AII that results in concentration-dependent cytotoxicity and marked anti-invasive activity in tumor cells. We also determined the effects of WA on AII-dependent endothelial cell plasmin generation and network formation. In vivo mouse xenograft models utilizing WA against Ewing's sarcoma were performed to further characterize the anti-tumor activity of WA. Our findings indicate that WA is a potent anti-tumor agent, resulting in decreased endothelial cell plasmin generation, tumor growth inhibition and reduced blood vessel formation both in vitro and in vivo.The potent anti-tumor activity of WA suggests that AII represents a previously unexploited target for therapeutic intervention by small molecule drugs. Our in vitro findings and animal studies indicate that WA therapy has potent anti-tumor effects and supports the notion of WA serving as lead for the synthesis of new compounds that target AII function. Furthermore, as a small molecule modulator of AII function, WA provides a tool to study the complex cellular functions of AII.