Heat shock proteins 90 (Hsp90) are chaperones that play a crucial role in stabilizing and activating numerous proteins, including certain oncoproteins essential for cancer cell growth and survival. Due to the increased expression of Hsp90 isoforms (Hsp90α, Hsp90β, Grp94, and TRAP1) in various types of cancer, the Hsp90 family represents a promising therapeutic target, as modulating its function can destabilize key proteins in cancer cells, ultimately leading to their death. Most past research focused on developing inhibitors targeting the N-terminal domain of Hsp90; however, clinical development was largely halted due to toxicity and the survival-inducing heat shock response, rendering the therapy ineffective. Modern research on Hsp90 modulation is primarily directed toward developing C-terminal domain (CTD) inhibitors and isoform-selective inhibitors.
In the experimental part, we synthesized various analogs of N-benzylpiperidine inhibitors
targeting the C-terminal domain of Hsp90. The goal was to develop inhibitors that would halt the growth and proliferation of cancer cells, particularly in aggressive cancers such as Ewing sarcoma and breast cancer. By modifying the structure of starting inhibitors from this structural class, we aimed to improve the anticancer activity of compounds. The work also describes an attempt to synthesize selective inhibitors of the TRAP1 isoform. This was attempted by attaching a mitochondrial-targeting group to the C-terminal domain inhibitors.
Results from the MTS assay on the SK-N-MC Ewing sarcoma model and the MDA-MB-231 triple-negative breast cancer model demonstrated that the compounds affect cancer cell viability, providing indirect evidence of their anticancer activity. We found that replacing the dichlorophenyl fragment with a larger aromatic substituent maintains or improves compound activity in cancer cells, whereas introducing an aliphatic substituent reduces potency.
The findings of this work contribute to the development of new Hsp90 C-terminal domain
inhibitors by providing further insight into the structure-activity relationship of this structural class. Future research should focus on developing an alternative synthetic route for attaching the mitochondrial-targeting group to Hsp90 C-terminal domain inhibitors, thereby achieving selective activity on the TRAP1 isoform.
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