Heat shock proteins (Hsp) or stress proteins are an evolutionarily conserved family of chaperones that contribute to the maintenance of cellular proteostasis by preventing aggregation and ensuring the correct folding of proteins. Their expression is increased under stress conditions, both in healthy and cancerous cells. In the latter, heat shock proteins, including Hsp90, are particularly important because many oncogenic proteins necessary for cancer cell proliferation are unstable and misfolded. Inhibition of Hsp90 therefore has a therapeutic benefit for cancer therapy. The first Hsp90 inhibitors bound to the N-terminal domain of Hsp90 and thus inhibited ATPase activity. Such a mechanism of Hsp90 inhibition led to a concomitant induction of the heat shock response, which increased the expression of genes for heat shock protein synthesis, making the cell resistant to therapy at the same dose. When the dose was increased, adverse effects occurred, leading to the development of inhibitors of the C-terminal domain of Hsp90 that do not induce the heat shock response.
In this Master's thesis, we therefore prepared 12 different inhibitors based on the 1,2,3-triazole ring that bind to the Hsp90 C-terminal domain. All compounds contain a triazole ring and 7-methoxy-substituted naphthalene moiety and differ in the orientation of the amide group as well as the basic centre and spacer separating them. We divided the compounds into libraries A and B according to the spatial orientation of the amide group, as we wanted to determine how the change in orientation affected the inhibitory activity of the compounds.
The final compounds were biologically assessed using the MTS assay in the MCF-7 breast cancer cell line. The results are reported as the mean inhibitory concentration (IC50). For comparison, we tested the previously synthesised compound TJD-163. Of the inhibitors prepared, only compound 11 showed no activity, which may be attributed to the long and flexible spacer between the amide group and the basic centre. The compounds with the strongest inhibitory activity were 25 (2.4 ± 0.1 μM) and 13 (2.8 ± 0.6 μM). Comparing the other results, we found that the distance between the naphthalene ring and the cationic centre is most important for effective antiproliferative activity. The activity is also enhanced by a lower degree of amine substitution (1° > 2° ⡈ 3°) and the presence of a basic centre (N > O), while the activity can also be influenced to a lesser extent by the orientation of the amide bond. The results obtained thus provide valuable insights into understanding the relationship between the structure of the compounds and their antiproliferative activity.
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