Question: What is the role of Hsp90 inhibition in cancer therapy?

Context:
Geldanamycin (GA) can be considered a relatively new component with a promising mode of action against human malignancies. It specifically targets heat shock protein 90 (Hsp90) and interferes with its function as a molecular chaperone.
In toto, we have evinced the dose-dependent and cell line-specific actions of geldanamycin on cell cycle progression, survival and motility of human bladder cancer cells, due to downregulation of critical Hsp90 clients and subsequent disruption of signaling -oncogenic- integrity.
Low-dose Hsp90 inhibitors tumor-selectively sensitize bladder cancer cells to chemoradiotherapy
Hsp90 inhibitors at low concentrations, which did not exert cytocidal effects but inactivated key anti-apoptotic proteins including erbB2, Akt, and NF-κB, efficiently sensitized bladder cancer cells (T24, 5637 and UM-UC-3 cells) to in vitro CRT by enhancing apoptosis.
In mice UM-UC-3 tumor xenografts model, Hsp90 inhibitors successfully potentiated anti-tumor activity of CRT.
The Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG), which simultaneously inactivated both Akt and ERK signaling at noncytocidal concentrations, synergistically potentiated the cytotoxicity of CDDP against BCICs by enhancing CDDP-induced apoptosis in vitro.
We have demonstrated that, upon 17-AAG treatment, bladder cancer cells are arrested in the G1 phase of the cell cycle and eventually undergo apoptotic cell death in a dose-dependent manner. Furthermore, 17-AAG administration was shown to induce a pronounced downregulation of multiple Hsp90 protein clients and other downstream effectors, such as IGF-IR, Akt, IKK-α, IKK-β, FOXO1, ERK1/2 and c-Met, resulting in sequestration-mediated inactivation of NF-κB, reduced cell proliferation and decline of cell motility.
In total, we have clearly evinced a dose-dependent and cell type-specific effect of 17-AAG on cell cycle progression, survival and motility of human bladder cancer cells, due to downregulation of multiple Hsp90 clients and subsequent disruption of signaling integrity.
Low dose geldanamycin inhibits hepatocyte growth factor and hypoxia-stimulated invasion of cancer cells
GA downregulated Met by inhibiting new protein maturation, thereby dampening HGF signaling.
HGF and chemical hypoxia with CoCl2 cooperatively 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.
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.
upon geldanamycin treatment, bladder cancer cells are prominently arrested in the G1 phase of cell cycle and eventually undergo programmed cell death via combined activation of apoptosis and autophagy.
geldanamycin administration proved to induce prominent downregulation of several Hsp90 protein clients and downstream effectors, such as membrane receptors (IGF-IR and c-Met), protein kinases (Akt, IKKα, IKKβ and Erk1/2) and transcription factors (FOXOs and NF-κΒ), therefore resulting in the impairment of proliferative -oncogenic- signaling and reduction of cell motility
17-Allylamino-17-demethoxygeldanamycin (17-AAG), a benzoquinone ansamycin antibiotic, specifically targets heat shock protein 90 (Hsp90) and interferes with its function as a molecular chaperone that maintains the structural and functional integrity of various protein clients involved in cellular signalin

Answer: Hsp90 inhibition is followed by G1/S cell cycle arrest, downregulation of key signalling proteins such as IGF-IR, Akt, IKK-α, IKK-β, FOXO1, ERK1/2 and c-Met, and sequestration-mediated inactivation of NF-κB, resulting in disruption of oncogenic signalling integrity, reduced cell proliferation, decline of cell motility, enhanced apoptotic cell death, and finally, sensitization of cancer cells to additional chemotherapy and/or radiotherapy.