digitoxin and Glioblastoma

Tissue hypoxia contributes to solid tumor pathogenesis by activating a series of adaptive programs. We previously showed that hypoxia promotes the preferential expansion and maintenance of CD133 positive human glioma stem cells (GSC) in a hypoxia inducible factor 1 alpha (HIF-1α)-dependent mechanism. Here, we examined the activity of digitoxin (DT), a cardiac glycoside and a putative inhibitor of HIF-1α, on human GSC in vitro and in vivo. During hypoxic conditions (1% O2), we observed the effect of DT on the intracellular level of HIF-1α and the extracellular level of vascular endothelial growth factor (VEGF) in human GSC. We found that DT at clinically achievable concentrations, suppressed HIF-1α accumulation during hypoxic conditions in human GSC and established glioma cell lines. DT treatment also significantly attenuated hypoxia-induced expression of VEGF, a downstream target of HIF-1α. Exposure to DT also reduced hypoxia-induced activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. Furthermore, DT potently inhibited neurosphere formation, and decreased CD133 expression even at concentrations that were not overtly cytotoxic. Lastly, treatment with DT reduced GSC engraftment in an in vivo xenograft model of glioblastoma. Intraperitoneal injections of DT significantly inhibited the growth of established glioblastoma xenografts, and suppressed expression of HIF-1α and carbonic anhydrase (CA9), a surrogate marker of hypoxia. Taken together, these results suggest that DT at clinically achievable concentration functions as an inhibitor of HIF-1α, worthy of further investigations in the therapy of glioblastoma.

Topics: AC133 Antigen; Animals; Carbonic Anhydrases; Digitoxin; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Glioblastoma; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Mice; Mice, SCID; Neoplastic Stem Cells; RNA Interference; RNA, Small Interfering; Spheroids, Cellular; Tumor Cells, Cultured; Tumor Hypoxia; Vascular Endothelial Growth Factor A; Xenograft Model Antitumor Assays

Malignant glioma is one type of common malignancy in central nervous system (CNS) tumors which has a very bad influence on the survival quality of the patients. In this regard, lots of studies on improving the therapeutic effects of malignant glioma have been done continuously. This study takes glioma stem cells (GSCs) as the subject and focuses on the sensitization effect of digitoxin (DT) on the apoptosis mediated by TNF-related apoptosis-inducing ligand (TRAIL) to prove that the combination therapy of DT and TRAIL has a more active effect of inducing GSCs apoptosis. This study used cultured GSCs. Comparisons of single drug therapy and combination therapy indicated that DT had a synergistic action with TRAIL to produce a more active effect of inducing the apoptosis of GSCs. This effect was also shown in the changes of expressions of cell apoptosis pathway related protein markers tested by Western Blot method. In conclusion, DT had a sensitization effect on GSCs apoptosis mediated by TRAIL.

Topics: Apoptosis; Brain Neoplasms; Digitoxin; Drug Therapy, Combination; Glioblastoma; Humans; Neoplastic Stem Cells; TNF-Related Apoptosis-Inducing Ligand; Tumor Cells, Cultured

Glioblastoma multiforme is the most lethal and aggressive astrocytoma among primary brain tumors in adults. However, most glioblastoma cells have been reported to be resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Here, we have shown that digitoxin (DT), a clinically approved cardiac glycoside for heart failure, can induce TRAIL-mediated apoptosis of glioblastoma cells. DT in noncytotoxic doses (20 nmol/l) can increase TRAIL-induced apoptosis in TRAIL-resistant U87MG glioblastoma cells. Treatment with DT led to apoptosis and a robust reduction in the levels of the antiapoptotic protein survivin by inducing its proteasomal degradation; however, it did not affect the levels of many other apoptosis regulators. Moreover, silencing survivin with small interfering RNAs sensitized glioma cells to TRAIL-induced apoptosis, underscoring the functional role of survivin depletion in the TRAIL-sensitizing actions of DT. We demonstrate that inactivation of survivin and death receptor 5 expression by DT is sufficient to restore TRAIL sensitivity in resistant glioma cells. Our results suggest that combining DT with TRAIL treatments may be useful in the treatment of TRAIL-resistant glioma cells.

Topics: Apoptosis; Brain Neoplasms; Caspases, Effector; Caspases, Initiator; Cell Line, Tumor; Digitoxin; Down-Regulation; Drug Resistance, Neoplasm; Enzyme Activation; Glioblastoma; Humans; Inhibitor of Apoptosis Proteins; Receptors, TNF-Related Apoptosis-Inducing Ligand; RNA, Small Interfering; Survivin; TNF-Related Apoptosis-Inducing Ligand; Up-Regulation