Flavonoids isolated from Citrus platymamma induced G2/M cell cycle arrest and apoptosis in A549 human lung cancer cells

Citrus platymamma hort. ex Tanaka belongs to the Rutaceae family and is widely used in folk medicines in Korea due to its anti-proliferative, anti-cancer, anti-oxidant, anti-inflammatory and anti-diabetic activities. However, the molecular mechanism of its anti-cancer effect is not well understood. The present study was conducted to elucidate the anti-cancer effect and molecular mechanism of flavonoids from Citrus platymamma (FCP) on A549 cells. FCP displayed concentration-dependent inhibition on A549 cells proliferation. Further, flow cytometry revealed that FCP significantly increased the sub-G1 (apoptotic cell population) and G2/M phase population, and the total number of apoptotic cells, in a dose-dependent manner. Nuclear condensation and fragmentation were also observed upon staining with Hoechst 33342 in FCP-treated A549 cells. Immunoblotting demonstrated a dose-dependent downregulation of cyclin B1, cyclin-dependent kinase 1, cell division cycle 25c, pro-caspases −3, −6, −8 and −9, and poly (adenosine diphosphate-ribose) polymerase (PARP) in FCP-treated A549 cells. In addition, FCP induced caspase-3 activation and subsequent PARP cleavage, and increased the B-cell lymphoma (Bcl)-2-associated X protein/Bcl-extra large ratio in A549 cells. These findings suggest that FCP induced G2/M arrest and apoptosis of A549 cells. The present study provides evidence that FCP may be useful in the treatment of human lung cancer.