ABSTRACT
The purpose of this study was to select the active compounds targeting Hsp90 protein in pancreatic cancer cells through a new dual "target + activity" rapid discovery technique. We combined an in vitro anti-cancer activity screening method with a dual-luciferase reporter gene and multi-chromatography separation technology, for rapid discovery of potential Hsp90 inhibitors from the Chinese herbal medicine Physalis angulata L. The anti-proliferation activity of those compounds was assessed in pancreatic cancer cell line BxPC-3 by MTT assays. The molecular mechanisms of Hsp90 inhibition were explored by Western blot and shRNA knockdown assays. As a result, two withanolides, withanolide E (WE) and 4β-hydroxywithanolide E (HWE), were identified from Physalis angulata L. The half maximal inhibitory concentration (IC50) of WE and HWE were 0.71±0.03 and 1.23±0.10 μmol·L-1 for the growth of BxPC-3 cells in 48 h. Luciferase reporter assay demonstrated that WE and HWE significantly induced heat shock element (HSE) activity in a dose- and time-dependent manner. The molecular mechanism study showed that after exposing to 5 μmol·L-1 WE or HWE for 48 h, the aggregation of Hsp90 dimer was upregulated to 6.5±1.3 and 11.8±2.0 fold, while the expression of Hsp90 client protein Akt was downregulated to 21.7%±2.8% and 9.8%±1.4% of the control group. Moreover, the Hsp90 inhibitory activity of WE or HWE was canceled by shRNA mediated Hsp90 knockdown. Overall, based on the dual "target + active" rapid discovery technique, two new Hsp90 inhibitors WE and HWE were found from Physalis angulata L. The Hsp90 inhibitory mechanism of WE and HWE may be mediated by induction of Hsp90 aggregate dimer and inhibition of Hsp90 client protein Akt expression.