Ethanolic extract of Cordyceps cicadae exerts antitumor effect on human gastric cancer SGC-7901 cells by inducing apoptosis, cell cycle arrest and endoplasmic reticulum stress

Cordyceps cicadae (Miq.) Massee is a traditional Chinese medicine that has been used for approximately 1600 years in China. C. cicadae, a member of the Cordyceps genus, exerts a therapeutic effect on many diseases, such as cancer. This study aimed to evaluate the antineoplasmic activity of C. cicadae and to identify its molecular mechanism of cell death. The toxicity of the ethanolic extract of C. cicadae (EEC) against different cancer cell lines was determined through MTT assay. Human gastric cancer SGC-7901 cells were treated with EEC for 48 h. Cell morphology was examined by using an Olympus phase-contrast microscope. The cell apoptosis was quantified through Annexin V-FITC/PI staining. Cells were stained with PI and then subjected to flow cytometry for the investigation of cell cycle status. Cells were subjected to mitochondrial membrane potential (MMP) assay after incubation with JC-1 probes and to intracellular Ca2+ measurement through flow cytometry after incubation with Fluo-3 AM fluorescent probes. Western blot analysis was conducted to quantify the expression of proteins related to apoptosis, cell cycle and endoplasmic reticulum stress. High-performance liquid chromatography (HPLC) analysis was performed to analyse the biological activity components of EEC. EEC suppressed the proliferation of SGC-7901 cells and induced the development of abnormal morphological features in a dose-dependent manner. Flow cytometry results indicated that EEC treatment caused cell apoptosis and arrested the cell cycle in the S phase. In addition, EEC treatment triggered MMP depolarization and Ca2+ overloading in the cytosol of SGC-7901 cells. Western blot analysis demonstrated that EEC increased Bax, AIF, caspase-8, caspase-6 and caspase-3 activities and decreased Bcl-2 activity. The release of cytochrome c from mitochondria was associated with mitochondrial dysfunction, which was caused by the activation of the cell surface receptor Fas and the cleavage of PARP. EEC-induced S phase arrest was associated with the up-regulation of E2F1, cyclin A2, cyclin E and p53 expression levels and the down-regulation of CDK2 expression. In addition, EEC increased the expression of endoplasmic reticulum stress-related proteins, such as calpain-1, caspase-12 and caspase-9. HPLC assay results suggested that EEC contained adenine, uridine, adenosine and N6-(2-Hydroxyethyl)-adenosine. EEC inhibited the proliferation of SGC-7901 cells by inducing caspase-dependent apoptosis, arresting the cell cycle in the S phase and increasing endoplasmic reticulum stress. This study revealed that C. cicadae is a potential natural source of anticancer drugs.