Low dose geldanamycin inhibits hepatocyte growth factor and hypoxia-stimulated invasion of cancer cells

Hepatocyte growth factor (HGF) receptor Met and hypoxia-inducible factor-1 (HIF-1) signaling pathways are commonly activated in aggressive tumors and promote progres sion. Since both Met and HIF-1a proteins are heat shock protein (Hsp) 90 clients, Hsp90 inhibitors might be expected to positively impact tumor progression. Here, we systemati cally evaluated the inhibitory effects of the prototypical Hsp90 inhibitor geldanamycin (GA) on cellular processes involved in invasion and angiogenesis in T24 bladder cancer cells stimulated with HGF and chemical hypoxia. First, we demonstrated the positive feedback loop between Met and HIF-1 pathways, which serves to sustain and amplifies their signaling in T24 cells. GA downregulated Met by inhibiting new protein maturation, thereby dampening HGF signaling. HGF and chemical hypoxia with CoCl2 coopera tively promoted in vitro invasion and vascular endothelial growth factor (VEGF) secretion, while CoCl2 but not HGF activated urokinase-type plasminogen activator and matrix metalloproteinase 2, both of which promote invasion and angiogenesis. Low dose GA (100 nmol/L) inhibited these processes by suppressing both HGF and HIF-1 pathways. Notably, brief GA pretreatment inhibited in vitro invasion and VEGF secretion induced by HGF as effectively as did continuous treatment. Moreover, we found that GA inhibited activation of focal adhesion kinase, focal adhesion assembly, and actin reorganization induced by HGF and integrin engagement by extracellular matrix. Thus, GA widely suppresses extrinsic stimuli-induced signaling that contribute to tumor invasion and angiogenesis in this bladder carcinoma model, suggesting the utility of Hsp90 inhibitors in preventing tumor progression and metastasis.