Casticin suppresses the carcinogenesis of small cell lung cancer H446 cells through activation of AMPK/FoxO3a signaling

Casticin, a natural polymethoxyflavone isolated from A. annua, V. trifolia, and V. agnus‑castus induces apoptosis in cancer cells by activating FoxO3a. However, whether casticin inhibits in vitro carcinogenesis and cancer stem cell (CSC) characteristics, and whether casticin activates FoxO3a in small cell lung cancer (SCLC) cells remain unclear. We here demonstrated that casticin decreased sphere‑ and colony‑formation capabilities, and downregulated uPAR and CD133 in second‑generation spheres, which were considered as lung cancer stem‑like cells (LCSLCs), from SCLC H446 cells, in a concentration‑dependent manner. In addition, casticin dose‑dependently elevated the phosphorylation levels of AMPK and ACC, and reduced p‑FoxO3a expression. The above effects were attenuated by AMPK knockdown with small interfering RNAs (siRNAs). FoxO3a silencing resulted in decreased protein expression of FoxO3a, increased in vitro carcinogenesis and CSC characteristics, with no appreciable effects on AMPK and ACC phosphorylation, and displayed similar activities to those neutralizing the effects of casticin on in vitro carcinogenesis and CSC characteristics. These findings reveal a novel mechanism for regulating AMPK/FoxO3a signaling in response to casticin, suggesting a new strategy for SCLC therapy by targeting cancer stem‑like cells.