Reinventing Hsp90 Inhibitors: Blocking C-Terminal Binding Events to Hsp90 by Using Dimerized Inhibitors

Heat shock protein 90 (Hsp90) is a molecular chaperone (90 kDa) that functions as a dimer. This protein facilitates the folding, assembly, and stabilization of more than 400 proteins that are responsible for cancer development and progression. Inhibiting Hsp90's function will shut down multiple cancer-driven pathways simultaneously because oncogenic clients rely heavily on Hsp90, which makes this chaperone a promising anticancer target. Classical inhibitors that block the binding of adenine triphosphate (ATP) to the N-terminus of Hsp90 are highly toxic to cells and trigger a resistance mechanism within cells. This resistance mechanism comprises a large increase in prosurvival proteins, namely, heat shock protein 70 (Hsp70), heat shock protein 27 (Hsp27), and heat shock factor 1 (HSF-1). Molecules that modulate the C-terminus of Hsp90 are effective at inducing cancer-cell death without activating the resistance mechanism. Herein, we describe the design, synthesis, and biological binding affinity for a series of dimerized C-terminal Hsp90 modulators. We show that dimers of these C-terminal modulators synergistically inhibit Hsp90 relative to monomers.