Hsp90 C-Terminal Inhibitors Exhibit Antimigratory Activity by Disrupting the Hsp90α/Ahal Complex in PC3-MM2 Cells

Human Hsp90 isoforms are molecular chaperones that are often up-regulated in malignances and represent a primary target for Hsp90 inhibitors undergoing clinical evaluation. Hsp90 alpha is a stress-inducible isoform of Hsp90 that plays a significant role in apoptosis and metastasis. Though Hsp90 alpha is secreted into the extracellular space under metastatic conditions, its role in cancer biology is poorly understood. We report that Hsp90 alpha associates with the Aha1 co-chaperone and found this complex to localize in secretory vesicles and at the leading edge of migrating cells. Knockdown of Hsp90 alpha resulted in a defect in cell migration. The functional role of Hsp90 alpha/Aha1 was studied by treating the cells with various novobiocin-based Hsp90 C-terminal inhibitors. These inhibitors disrupted the Hsp90 alpha/Aha1 complex, caused a cytoplasmic redistribution of Hsp90 alpha and Aha1, and decreased cell migration. Structure-function studies determined that disruption of Hsp90 alpha/Aha1 association and inhibition of cell migration correlated with the presence of a benzamide side chain, since an acetamide substituted analog was less effective. Our results show that disruption of Hsp90 alpha/Aha1 interactions with novobiocin-based Hsp90 C-terminal inhibitors may limit the metastatic potential of tumors.