Regulation of human glioblastoma cell death by combined treatment of cannabidiol, γ-radiation and small molecule inhibitors of cell signaling pathways.

Vladimir N Ivanov,Tom K Hei,Jinhua Wu

doi:10.18632/oncotarget.18240

Abstract

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. The challenging problem in cancer treatment is to find a way to upregulate radiosensitivity of GBM while protecting neurons and neural stem/progenitor cells in the brain. The goal of the present study was upregulation of the cytotoxic effect of γ-irradiation in GBM by non-psychotropic and non-toxic cannabinoid, cannabidiol (CBD). We emphasized three main aspects of signaling mechanisms induced by CBD treatment (alone or in combination with γ-irradiation) in human GBM that govern cell death: 1) CBD significantly upregulated the active (phosphorylated) JNK1/2 and MAPK p38 levels with the subsequent downregulation of the active phospho-ERK1/2 and phospho-AKT1 levels. MAPK p38 was one of the main drivers of CBD-induced cell death, while death levels after combined treatment of CBD and radiation were dependent on both MAPK p38 and JNK. Both MAPK p38 and JNK regulate the endogenous TRAIL expression. 2) NF-κB p65-P(Ser536) was not the main target of CBD treatment and this transcription factor was found at high levels in CBD-treated GBM cells. Additional suppression of p65-P(Ser536) levels using specific small molecule inhibitors significantly increased CBD-induced apoptosis. 3) CBD treatment substantially upregulated TNF/TNFR1 and TRAIL/TRAIL-R2 signaling by modulation of both ligand and receptor levels followed by apoptosis. Our results demonstrate that radiation-induced death in GBM could be enhanced by CBD-mediated signaling in concert with its marginal effects for neural stem/progenitor cells and astrocytes. It will allow selecting efficient targets for sensitization of GBM and overcoming cancer therapy-induced severe adverse sequelae.

Highlights

External beam radiation therapy alone or in combination with chemotherapy is the main treatment procedure for brain tumors including glioblastoma [1, 2]
Since U87MG glioblastoma cells contained a normal variant of p53 while U118MG had mutated p53, we expected a different response of these cell lines to combined treatment, due to decreased activity of the mitochondrial apoptotic pathway in U118MG cells
We further demonstrated that SB203580 (20 μM) effectively down-regulated apoptosis induced by CBD (10–20 μM) in both U87MG and U118MG cells (48 h after treatment), while SP600125 (20 μM) showed only moderate negative effects on CBD-induced apoptosis in U87MG cells (Figure 5D, 5E), highlighting a probable leading role of mitogen-activated protein kinase (MAPK) p38-P for regulation of CBDinduced apoptosis in both glioma cell lines

Summary

Introduction

External beam radiation therapy alone or in combination with chemotherapy (using Temozolomide, a DNA methylating agent with DNA damage activity) is the main treatment procedure for brain tumors including glioblastoma [1, 2]. Such treatment causes severe damage to normal brain tissues. While normal glial cells exhibit a substantial degree of radioresistance, adult neurons and endothelial cells could be significantly injured by ionizing radiation. Oligodendrocyte precursor cells (OPC), neural stem and progenitor cells (NSC/NPC) having significant proliferative capacities are highly sensitive to radiation therapy alone or especially in combination with chemotherapy. Clinical observations and experiments with animals further demonstrated that cranial irradiation for brain tumor treatment may result in encephalopathy, as well as strong cognitive and memory deficits [3,4,5,6,7,8,9,10].

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