Small-molecule inhibitor of C‑terminal HSP90 dimerization modulates autophagy and functions synergistically with mTOR inhibition to kill cisplatin-resistant cancer cells.

A major obstacle for the successful treatment of cancer is the presence or development of resistance mechanisms toward therapeutic intervention. In urothelial cancer, cisplatin-based regimens are still routinely employed, and multiple pathways contribute to chemoresistance. Since the identification of heat shock protein 90 (HSP90) as potential cancer target, various HSP90 inhibitors have been developed and evaluated in clinical trials. However, limited efficacy has been observed, mainly caused by dose-limiting toxicity and the concomitant induction of a cytoprotective heat shock response (HSR). To avoid this effect, inhibitors targeting the C-terminal domain (CTD) of HSP90 that do not elicit an HSR have been put forward. Additionally, the crosstalk between autophagy and HSP90 is currently being explored, since both processes work together in proteostasis, and the modulation of autophagy might be helpful in order to improve the efficacy of HSP90 inhibitors. We demonstrate that the second-generation small-molecule inhibitor VWK147 targeting HSP90 CTD dimerization induces cell death in both cisplatin-sensitive and cisplatin-resistant urothelial carcinoma cells. The treatment with VWK147 in these cells led to the destabilization of classical HSP90 client proteins without triggering an HSR. Additionally, we observe that VWK147 re-sensitizes resistant urothelial carcinoma cells to cisplatin and-in combination with mTOR inhibition-synergistically kills cisplatin-sensitive and -resistant cells, in contrast to what is observed upon treatment with the N-terminal domain-targeting HSP90 inhibitor 17-AAG. This synergy may be explained by VWK147-mediated inhibition of late autophagy events, and thus a blockade of autophagic flux. Finally, we also observed that VWK147 induces non-canonical LC3 lipidation, indicating that this compound exerts a broader effect on ion balance or pH of the endolysosomal system. VWK147 is a promising inhibitor that targets the C-terminal dimerization of HSP90 and simultaneously exhibits autophagy-modulating effects. This compound could potentially be an effective option for improving anti-cancer therapies and/or overcoming treatment resistance.