Induction of ROS-dependent apoptotic cell death by platycodin D in human prostate cancer PC3 cells

Background and objective: Platycodin D (PD), a triterpenoid saponin isolated from an edible and medicinal plant Platycodon grandiflorum, possesses multiple pharmacological properties. The purpose of this study is to investigate the effect of PD on the growth of PC3 human prostate cancer cells and the underlying molecular mechanisms.

Materials and methods: Cell viability, apoptosis and mitochondrial membrane potential (MMP) were measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, nuclear staining and flow cytometry analysis. To investigate the mechanism of anti-cancer activity of PD, expression of apoptosis regulatory protein, caspase activity, and generation of intracellular reactive oxygen species (ROS) were determined.

Results: PD treatment reduced PC3 cell proliferation, which was associated with induction of apoptosis, and accompanied by increased expression of Fas, Fas-ligand (FasL) and pro-apoptotic Bax, and decreased expression of anti-apoptotic Bcl-2 and truncation of Bid. PD also inhibited expression of c-FLIP and members of inhibitor of apoptosis protein family, and activated caspases, resulting in an increase in poly (ADP-ribose) polymerase cleavage. However, in the presence of a pan-caspase inhibitor, PD-mediated growth inhibition and apoptosis were significantly protected. PD also destroyed the integrity of mitochondria due to the loss of MMP, leading to cytosolic release of cytochrome c. Moreover, the levels of ROS were markedly increased by PD treatment, which was significantly attenuated by the ROS scavenger N-acetyl-L-cysteine (NAC). Furthermore, NAC fully suppressed PD-induced apoptotic events and cytotoxicity.

Conclusions: The results of this study show that PD had chemopreventive potential through the induction of ROS-dependent apoptosis in PC3 cells, and that this compound could be useful for developing an effective and selective natural source to inhibit cancer cell proliferation.

Platycodin D; Prostate cancer cells; Apoptosis; Caspase; Reactive oxygen species

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