Effects of geldanamycin on HIF-1α mediated angiogenesis and invasion in prostate cancer cells

Geldanamycin (GA), a benzoquinone ansamycin, is a naturally occurring inhibitor of heat shock protein (Hsp90), which regulates the transcription activity of hypoxia-inducible factor 1 (HIF-1 alpha). Under hypoxia, HIF-1 alpha is activated in tumor cells, and induces the transcription of vascular endothelial growth factor ( VEGF), which is the prime regulator for angiogenesis. VEGF promotes the formation of new blood vessels by stimulating endothelial cell division and migration. This eventually forms a vascular network that allows for tumor growth and metastasis. In this study, we used GA to inhibit HIF-1 alpha transcription function. Human prostate cancer DU-145 cells were incubated in a hypoxic chamber at 1% O-2 and 37 degrees C for different durations. Both mRNA and protein levels of HIF-1 alpha and VEGF were upregulated under hypoxic conditions. We demonstrated that GA treatment of hypoxic DU-145 cells abolished the induction of HIF-1 alpha protein in a time-dependent manner and decreased VEGF mRNA and its protein levels. The transient transfection of DU-145 cells with luciferase reporter gene construct (5HRE/hCMVmp-luc) showed that the transcriptional activity of HIF-1 alpha was significantly induced in response to hypoxia, but inhibited by GA. In addition, using conditioned medium from GA-treated hypoxic cells led to a significant decrease in cell invasion in comparison with using conditioned medium from nontreated hypoxic cells. These data provide evidence for the important role of GA in inhibition of angiogenesis and also invasion mediated by HIF-1 alpha in prostate cancer cells.