A novel Hsp90 inhibitor to disrupt Hsp90/Cdc37 complex against pancreatic cancer cells

Pancreatic cancer is an aggressive disease with multiple biochemical and genetic alterations. Thus, a single agent to hit one molecular target may not be sufficient to treat this disease. The purpose of this study is to identify a novel Hsp90 inhibitor to disrupt protein-protein interactions of Hsp90 and its cochaperones for down-regulating many oncogenes simultaneously against pancreatic cancer cells. Here, we reported that celastrol disrupted Hsp90-Cdc37 interaction in the superchaperone complex to exhibit antitumor activity in vitro and in vivo. Molecular docking and molecular dynamic simulations showed that celastrol blocked the critical interaction of Glu³³ (Hsp90) and Arg¹⁶⁷ (Cdc37). Immunoprecipitation confirmed that celastrol (10 μmol/L) disrupted the Hsp90-Cdc37 interaction in the pancreatic cancer cell line Panc-1. In contrast to classic Hsp90 inhibitor (geldanamycin), celastrol (0.1-100 μmol/L) did not interfere with ATP binding to Hsp90. However, celastrol (1-5 μmol/L) induced Hsp90 client protein degradation (Cdk4 and Akt) by 70% to 80% and increased Hsp70 expression by 12-fold. Celastrol induced apoptosis in vitro and significantly inhibited tumor growth in Panc-1 xenografts. Moreover, celastrol (3 mg/kg) effectively suppressed tumor metastasis by more than 80% in RIP1-Tag2 transgenic mouse model with pancreatic islet cell carcinogenesis. The data suggest that celastrol is a novel Hsp90 inhibitor to disrupt Hsp90-Cdc37 interaction against pancreatic cancer cells.