HSP90 inhibition: two-pronged exploitation of cancer dependencies.

The early clinical hypothesis for inhibiting HSP90 in cancers was based on the dependence of certain key client proteins in malignant cells--including a host of well-characterized oncoproteins--on the activity of HSP90 for their function and stability. The additional concept has been established that cancer cells have heightened dependence on the efficient maintenance of intracellular proteomic homeostasis, central components of which are HSP90 and other heat shock proteins. We evaluate the evidence that inhibiting HSP90 in cancer exploits both of these biological vulnerabilities very effectively, we review the current status of the discovery and development of HSP90 inhibitors and we identify routes to improve their clinical efficacy, based on emerging knowledge.