Casticin suppresses self-renewal and invasion of lung cancer stem-like cells from A549 cells through down-regulation of pAkt

A subpopulation of cancer stem cells is recognized as the cause of tumorigenesis and spreading. To investigate the effects of casticin (5,3'-dihydroxy-3,6,7,4'-tetramethoxyflavone), derived from Fructus Viticis Simplicifoliae, on lung cancer stem cells, we isolated and identified a subpopulation of lung cancer stem-like cells (LCSLCs) from non-small-cell lung carcinoma A549 cells with the features including self-renewal capacity and high invasiveness in vitro, elevated tumorigenic activity in vivo, and high expression of stemness markers CD133, CD44, and aldehyde dehydrogenase 1 (ALDH1), using serum-free suspension sphere-forming culture method. We then found that casticin could suppress the proliferation of LCSLCs in a concentration-dependent manner with an IC50 value of 0.4 μmol/L, being much stronger than that in parental A549 cells. In addition, casticin could suppress the self-renewal and invasion of LCSLCs concomitant with decreased CD133, CD44, and ALDH1 protein expression and reduced MMP-9 activity. Further experiments showed that casticin suppressed self-renewal and invasion at least partly through down-regulation of Akt phosphorylation. In conclusion, casticin suppressed the characteristics of LCSLCs, suggesting that casticin may be a candidate compound for curing lung cancer via eliminating cancer stem cells.