Redefining the Phenotype of Heat Shock Protein 90 (Hsp90) Inhibitors

The phenotypes produced when cells are treated with the heat shock protein 90 (Hsp90) inhibitors AUY922 or 17-AAG (classical inhibitors) are different to those produced when cells are knocked down with Hsp90α. Pull-down assays using classical inhibitors suggest that these molecules bind to multiple targets other than Hsp90. Classical inhibitors also induce similar protein markers as other anti-cancer therapies cisplatin and bortezomib that do not target Hsp90. Together these data suggest that AUY922 and 17-AAG acts on multiple targets and likely kills cells through multiple mechanisms. Comparing these classical inhibitors to the effects seen when treating cells with C-terminal Hsp90 modulators reveals that C-terminal modulators effectively bind to Hsp90, and induce phenotypic markers consistent with the Hsp90α CRISPR knockdown data. Our findings challenge the current interpretation of Hsp90 inhibitors and suggest that a large body of literature that describes the Hsp90 phenotype and inhibitors is re-examined in this context.