Heat shock protein 90 (Hsp90) is a molecular chaperone that ensures the correct folding of its substrates and therefore plays an important role in proteostasis. Since its expression is strongly increased in cancer cells, Hsp90 represents a promising target in cancer therapy. The functional form of Hsp90 consists of two identical monomers, each with three domains: the N-terminal domain (NTD) with ATP-binding site, the middle domain, which binds client proteins and the C-terminal domain (CKD), responsible for dimerization of Hsp90. N-terminal domain inhibitors were discovered first. Although some of the first inhibitors showed anticancer activity in pre-clinical and clinical studies, they were later mostly abandoned due to their side effects and the induction of the heat shock response. The drawbacks associated with Hsp90 NTD inhibition led to the development of C-terminal domain inhibitors, which did not induce the heat shock response.
In the context of this master’s thesis, we synthesized novel Hsp90 C-terminal domain inhibitors, that were based on the previously evaluated compound TJD-337. All eleven newly prepared compounds contain (S)-3,4-dichloro-N-(1-(6-formamidopyridin-3-yl)pyrrolidin-3-yl)benzamide moiety and differ in the basic centre and spacer. By introducing varying basic centers, we examined the effect of amine substitution on the activity. By changing the number of C-atoms in the spacer and cyclizing it, we investigated the effect of the distance between the basic center and the aromatic system and the effect of the rigidity of the spacer. All of the final compounds were biologically assessed using the metabolic activity assay on the MCF-7 breast cancer cells. Compound 21 (0,51 ± 0,07 μM) with a cyclobutyl spacer and a primary amine, showed the most potent inhibitory activity. Comparing the results, we found out that the presence of a basic centre and the optimal distance between the benzamide group and the basic centre are important for inhibitory activity. The long, linear spacer in compound 24 and the absence of the basic center in compound 15 lead to inactivity of those compounds, while in the case of a rigidized cyclic spacer in compound 21, compounds activity is improved. The results are promising for the further development of Hsp90 C-terminal domain inhibitors and for the therapy of triple-negative breast cancer and other cancers.
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