Ouabain suppresses the growth and migration abilities of glioma U-87MG cells through inhibiting the Akt/mTOR signaling pathway and downregulating the expression of HIF-1α

Glioma is one of the most malignant forms of brain tumor, and has been of persistent concern due to its high recurrence and mortality rates, and limited therapeutic options. As a cardiac glycoside, ouabain has widespread applications in congestive heart diseases due to its positive cardiac inotropic effect by inhibiting Na(+)/K(+)-ATPase. Previous studies have demonstrated that ouabain has antitumor activity in several types of human tumor, including glioma. However, the exact underlying mechanism remains to be elucidated. The purpose of present study was to elucidate the effect of ouabain on human glioma cell apoptosis and investigate the exact mechanism. U-87MG cells were treated with various concentrations of ouabain for 24 h, following which cell viability and survival rate were assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The dynamic changes and cell motility were observed using digital holographic microscopy. Additionally, western blot analysis and high-content screening assays were used to detect the protein expression levels of phosphorylated (p-)Akt, mammalian target of rapamycin (mTOR), p-mTOR and hypoxia-inducible factor (HIF)-1α, respectively. Compared with the control group, ouabain suppressed U-87MG cell survival, and attenuated cell motility in a dose-dependent manner (P<0.01). The downregulation of p-Akt, mTOR, p-mTOR and HIF-1α were observed following treatment with 2.5 and 25 µmol/l of ouabain. These results suggested that ouabain exerted suppressive effects on tumor cell growth and motility, leading to cell death via regulating the intracellular Akt/mTOR signaling pathway and inhibiting the expression of HIF-1α in glioma cells. The present study examined the mechanism underlying the antitumor property of ouabain, providing a novel potential therapeutic agent for glioma treatment.