The 90 kDa heat shock proteins (Hsp90) are molecular chaperones that are required for the refolding of denatured proteins and the maturation of nascent polypeptides into their biologically active, three-dimensional structures. In fact, numerous proteins represented in all ten hallmarks of cancer are dependent upon Hsp90 for conformational maturation. Hsp90 inhibition provides a combinatorial attack on multiple pathways responsible for malignant cell growth and proliferation. Consequently, Hsp90 has emerged as a promising target for the development of cancer chemotherapeutics. 

Hsp90 contains two ATP binding sites, and in order to fold nascent polypeptides into biologically active proteins, Hsp90 catalyzes the hydrolysis of ATP. ATP hydrolysis provides the Hsp90 protein folding machinery the requisite energy for folding "client" proteins into their correct three-dimensional conformation. Disruption of this folding process results in the destabilization of Hsp90 "client" protein complexes, which leads to ubiquitinylation and proteasome-mediated degradation of the protein substrate. 

The N-terminal ATP binding site is inhibited by the natural products geldanamycin (GDA) and radicicol (RDC). Numerous (~20) analogs of these natural products have undergone clinical evaluation for the potential treatment of cancer. Unfortunately, the vast majority of these molecules have failed. The current hypothesis is that on-target toxicities are produced when all four Hsp90 isoforms are targeted simultaneously. Therefore, we are working towards the development of the first isoform selective Hsp90 inhibitors based on a structure-based approach.

The C-terminal ATP binding site was identified by one of our collaborators, Len Neckers (National Cancer Institute), who demonstrated that the coumarin antibiotics, including novobiocin, inhibit the C-terminal ATP binding site. We have developed the most potent C-terminal inhibitors of Hsp90 and have demonstrated that these Hsp90 inhibitors can segregate heat shock induction from client protein degradation, offering new methods for the treatment of neurodegeneration (including chemobrain) and cancer.