Discovery of chrysoeriol, a PI3K-AKT-mTOR pathway inhibitor with potent antitumor activity against human multiple myeloma cells in vitro. 
This study was designed to determine the impact of chrysoeriol on proliferation and cell cycle progression in the human multiple myeloma cell lines RPMI 8226 and KM3, and its related molecular mechanisms.  Chryseoriol was identified by using the phosphorylated AKT-specific cytoblot high throughput assay.  CCK-8 assay was employed to examine the growth inhibition rate and IC(50) (48 h) in peripheral blood mononuclear cells (PBMNCs), RPMI 8226 and KM3 cells treated with chrysoeriol at various concentrations.  Cells were labeled with 5-6-carboxyfluorescein diacetate succinimidyl ester (CFSE), and the proliferation dynamics was detected by flow cytometry and analyzed with ModFit software.  The cell cycles of RPMI 8226 and KM3 cells were measured by flow cytometry when the IC(50) concentration of chrysoeriol was adopted.  The alterations in cell-cycle related proteins (Cyclin B1, Cyclin D1, p21) and proteins in PI3K-AKT-mTOR pathway were determined by Western blot analysis.  The results showed the proliferation of multiple myeloma cells was significantly inhibited by chrysoeriol, resulting in cell cycle arrest in G(2)/M phase.  Chrysoeriol could significantly reduce the expression of p-AKT (s473) and p-4eBP1 (t37/46) protein, meanwhile enhanced Cyclin B1 and p21 protein expression.  Similar effects were not observed in PBMNCs from normal donors.  It was concluded that chrysoeriol was a selective PI3K-AKT-mTOR pathway inhibitor.  It restrained the proliferation of human multiple myeloma cells, but didn't affect proliferation of PBMNCs from normal donors.  It might exhibit the cell cycle regulatory effect via the inhibition of PI3K-AKT-mTOR signal pathway.