A Homogeneous Polysaccharide from Fructus Schisandra chinensis (Turz.) Baill Induces Mitochondrial Apoptosis through the Hsp90/AKT Signalling Pathway in HepG2 Cells

According to the potential anti-hepatoma therapeutic effect of Schisandra chinensis polysaccharides presented in previous studies, a bioactive constituent, homogeneous Schisandra chinensis polysaccharide-0-1 (SCP-0-1), molecular weight (MW) circa 69.980 kDa, was isolated and purified. We assessed the efficacy of SCP-0-1 against human hepatocellular liver carcinoma (HepG2) cells to investigate the effects of its antitumour activity and molecular mechanisms. Anticancer activity was evaluated using microscopy, 3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyltetrazolium bromide (MTT) assay, Hoechst 33258 staining, acridine orange (AO) staining, flow cytometry (FCM), and cell-cycle analysis. SCP-0-1 inhibited the HepG2 cells' growth via inducing apoptosis and second gap/mitosis (G2/M) arrest dose-dependently, with a half maximal inhibitory concentration (IC50) value of 479.63 µg/mL. Western blotting of key proteins revealed the apoptotic and autophagic potential of SCP-0-1. Besides, SCP-0-1 upregulated Bcl-2 Associated X Protein (Bax) and downregulated B-cell leukemia/lymphoma 2 (Bcl-2) in the HepG2 cells. The expression of caspase-3, -8, and -9; poly (ADP-ribose) polymerase (PARP); cytochrome c (Cyt C); tumor protein 53 (p53); survivin; sequestosome 1 (p62); microtubule-associated protein 1 light chain-3B (LC3B); mitogen-activated protein kinase p38 (p38); extracellular regulated protein kinases (ERK); c-Jun N-terminal kinase (JNK); protein kinase B (AKT); and heat shock protein 90 (Hsp90) were evaluated using Western blotting. Our findings demonstrate a novel mechanism through which SCP-0-1 exerts its antiproliferative activity and induces mitochondrial apoptosis rather than autophagy. The induction of mitochondrial apoptosis was attributed to the inhibition of the Hsp90/AKT signalling pathway in an extracellular signal-regulated kinase-independent manner. The results also provide initial evidence on a molecular basis that SCP-0-1 can be used as an anti-hepatocellular carcinoma therapeutic agent in the future.