Discovery of 5-aryl-3-thiophen-2-yl-1H-pyrazoles as a new class of Hsp90 inhibitors in hepatocellular carcinoma

Although hepatocellular carcinoma (HCC)-related mortality has increased over the past decades, treatment options are still very limited, underlining the need for developing new therapeutic strategies. The molecular chaperone heat shock protein 90 (Hsp90) plays a key role in post-translational maturation of many oncogenic client proteins that are important for survival and proliferation of cancer cells. Thus, inhibitors of Hsp90 are promising targets for many cancer types. In this study, 15 diarylpyrazole compounds were screened against MCF7 and HepG2 cell lines. Compound 8, which contained a thiophene group, demonstrated the highest antiproliferative activity against HepG2 cells having an IC50, of 0.083 mu M. Four additional diarylpyrazoles, each containing a thiophene group, were prepared and screened for antiproliferative activity. None of these four compounds exhibited superior activity to compound 8 on HepG2 cells. Therefore, compound 8 was selected for further in vitro assays. Cell cycle arrest was observed at the G2 phase in compound 8-treated cells. Compound 8 also caused a 7.7-fold increase in caspase-3. These results confirm the apoptotic effect of compound 8 on HepG2 cells. Moreover, compound 8 inhibited Hsp90 (IC50, = 2.67 +/- 0.18 mu M) in an in vitro assay and caused a 70.8% reduction in Hsp90 levels in a HepG2 cell-based assay. Additionally, compound 8 caused significant reduction in the levels of Hsp90 client proteins (Akt, c-Met, c-Raf, and EGFR) and a 1.57-fold increase in Hsp70. Molecular docking studies were also performed to predict the binding mode of compound 8 and followed by molecular dynamics simulations to give further insights into the binding mode of 8.