Chaetoglobosin K inhibits tumor angiogenesis through downregulation of vascular epithelial growth factor-binding hypoxia-inducible factor 1α

Ovarian cancer is the fifth leading cause of cancer deaths for women in America. With no known carcinogens or manageable risk factors, targeted prevention is currently unavailable. Angioprevention is a nonspecific strategy to limit the growth of solid tumors and is especially suitable for ovarian cancers. In search of angiopreventive agents, we examined chaetoglobosin K (ChK), a natural cytochalasan compound from the fungus Diplodia macrospora. We found that ChK significantly inhibits cell viability at concentrations as low as 0.5 μmol/l for A2780/CP70 ovarian cancer cells and 1.0 μmol/l for OVCAR-3 cells. ChK also significantly inhibits the secretion of key angiogenesis mediators, including Akt (which is also known as protein kinase B), hypoxia-inducible factor 1α (HIF-1α), and vascular epithelial growth factor (VEGF) by ovarian cancer cells. More importantly, ChK inhibits in-vitro and in-vivo angiogenesis induced by ovarian cancer cells and reduces the migratory capability of human umbilical vein endothelial cells. Through transfection of HIF-1α plasmids in luciferase assays, we found that ChK executes its VEGF inhibition by mediating the downregulation of HIF-1α. Furthermore, chromatin immunoprecipitation assays using the HIF-1α antibody revealed that ChK inhibits the interaction of HIF-1α with the VEGF promoter. Through transfection of Akt plasmids, we found that inhibition of HIF-1α by ChK occurs through downregulation of Akt. To our knowledge, this is the first report about the potential angioprevention of ChK. Our data suggest that this natural fungal bioactive compound effectively inhibits angiogenesis through downregulation of VEGF-binding HIF-1α and could be an effective agent for cancer treatment.