A platycoside-rich fraction from the root of Platycodon grandiflorum enhances cell death in A549 human lung carcinoma cells via mainly AMPK/mTOR/AKT signal-mediated autophagy induction

The root of Platycodon grandiflorum (PG), commonly known as Kilkyong in Korea, Jiegeng in China, and Kikyo in Japan, has been extensively used as a traditional anti-inflammatory medicine in Asia for the treatment of respiratory conditions, such as bronchitis, asthma, and tonsillitis. Platycosides isolated from PG are especially well-known for their anti-cancer effects. We investigated the involvement of autophagic cell death and other potential molecular mechanisms induced by the platycoside-containing butanol fraction of PG (PGB) in human lung carcinoma cells. PGB-induced growth inhibition and cell death were measured using a 5-diphenyl-tetrazolium bromide (MTT) assay. The effects of PGB on autophagy were determined by observing microtubule-associated protein 1 light chain 3 (LC3) redistribution with confocal microscopy. The PGB-mediated regulation of autophagy-associated proteins was investigated using Western blotting analysis. Furthermore, the anti-cancer mechanism of PGB was confirmed using chemical inhibitors. A high-performance liquid chromatography (HPLC)-DAD system was used to analyze the platycosides in PGB. In A549 cells, PGB induced significant autophagic cell death. Specifically, PGB upregulated LC3-II in a time- and dose-dependent manner, and it redistributed LC3 via autophagosome formation in the cytoplasm. PGB treatment increased the phosphorylation of AMP-activated protein kinase (AMPK) and subsequently suppressed the AKT/mammalian target of the rapamycin (mTOR) pathway. Furthermore, PGB inhibited cell proliferation by regulating the mitogen-activated protein kinase (MAPK) pathways. In this study, six types of platycosides were identified in the PGB using HPLC. PGB efficiently induced cancer cell death via autophagy and the modulation of the AMPK/mTOR/AKT and MAPK signaling pathways in A549 cells. Therefore, PGB may be an efficacious herbal anti-cancer therapy. [Display omitted]