Dexamethasone Interferes with Autophagy and Affects Cell Survival in Irradiated Malignant Glioma Cells

Abstract

Objective : Radiation is known to induce autophagy in malignant glioma cells whether it is cytocidal or cytoprotective. Dexamethasone is frequently used to reduce tumor-associated brain edema, especially during radiation therapy. The purpose of the study was to determine whether and how dexamethasone affects autophagy in irradiated malignant glioma cells and to identify possible intervening molecular pathways. Methods : We prepared p53 mutant U373 and LN229 glioma cell lines, which varied by phosphatase and tensin homolog (PTEN) mutational status and were used to make U373 stable transfected cells expressing GFP-LC3 protein. After performing cell survival assay after irradiation, the IC 50 radiation dose was determined. Dexamethasone dose (10 µM) was determined from the literature and added to the glioma cells 24 hours before the irradiation. The effect of adding dexamethasone was evaluated by cell survival assay or clonogenic assay and cell cycle analysis. Measurement of autophagy was visualized by western blot of LC3-I/LC3-II and quantified by the GFP-LC3 punctuated pattern under fluorescence microscopy and acridine orange staining for acidic vesicle organelles by flow cytometry. Results : Dexamethasone increased cell survival in both U373 and LN229 cells after irradiation. It interfered with autophagy after irradiation differently depending on the PTEN mutational status : the autophagy decreased in U373 (PTEN-mutated) cells but increased in LN229 (PTEN wild-type) cells. Inhibition of protein kinase B (AKT) phosphorylation after irradiation by LY294002 reversed the dexamethasone-induced decrease of autophagy and cell death in U373 cells but provoked no effect on both autophagy and cell survival in LN229 cells. After ATG5 knockdown, radiation-induced autophagy decreased and the effect of dexamethasone also diminished in both cell lines. The diminished autophagy resulted in a partial reversal of dexamethasone protection from cell death after irradiation in U373 cells; however, no significant change was observed in surviving fraction LN229 cells. Conclusion : Dexamethasone increased cell survival in p53 mutated malignant glioma cells and increased autophagy in PTENmutant malignant glioma cell but not in PTEN-wildtype cell. The difference of autophagy response could be mediated though the phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin signaling pathway.

Riluzole Reverses a Number of Undesirable Effects of Dexamethasone in Glioblastoma Cells

“…As Dex did not interfere with GBM cell death induced by Ril (Figure 4), combined treatment with Ril and Dex could be beneficial for patients receiving Dex treatment for GBM oedema. Although previous research reported that Dex protects GBM cells from TMZ-induced apoptosis (22) and irradiation-induced autophagy (23), we detected no such negative effect of Dex in this study. This variable effect of Dex is potentially due to different experimental settings or cell lines.…”

“Vanishing” glioblastoma: A case report and review of the literature

“…Other research studies have however indicated that the concurrent administration of DEX with radiotherapy has been associated with a reduction in cell death among cancer cells. This suggests a potential role of DEX in promoting radioresistance [25] .…”

Expression and activation of nuclear hormone receptors result in neuronal differentiation and favorable prognosis in neuroblastoma

“…Dexamethasone (DEX) is commonly used together with chemotherapy against certain types of cancer [ 57 – 59 ] as well as for treating edema in children [ 60 ]. Previously, we showed that GR activation by glucocorticoids drives sympathetic neuronal differentiation in mice.…”