RETRACTED ARTICLE: Inhibition of autophagic flux differently modulates cannabidiol-induced death in 2D and 3D glioblastoma cell cultures

Vladimir N Ivanov,Peter W Grabham,Cheng-Chia Wu,Tom K Hei

doi:10.1038/s41598-020-59468-4

Abstract

Radiotherapy combined with chemotherapy is the major treatment modality for human glioblastoma multiforme (GBM). GBMs eventually relapse after treatment and the average survival of GBM patients is less than two years. There is some evidence that cannabidiol (CBD) can induce cell death and increases the radiosensitivity of GBM by enhancing apoptosis. Beside initiation of death, CBD has been demonstrated as an inducer of autophagy. In the present study, we address the question whether CBD simultaneously induces a protective effect in GBM by upregulating autophagy. Addition of chloroquine that suppressed autophagic flux to 2D GBM cultures increased CBD-induced cell death, presenting proof for the protective autophagy. Blockage of autophagy upregulated radiation-induced cytotoxicity but only modestly affected the levels of cell death in CBD- or CBD/γ-irradiated 3D GBM cultures. Furthermore, CBD enhanced the pro-apoptotic activities of JNK1/2 and MAPK p38 signaling cascades while partially downregulated the pro-survival PI3K-AKT cascade, thereby changing a balance between cell death and survival. Suppression of JNK activation partially reduced CBD-induced cell death in 3D GBM cultures. In contrast, co-treatment of CBD-targeted cells with inhibitors of PI3K-AKT-NF-κB, IKK-NF-κB or JAK2-STAT3 pathways killed surviving GBM cells in both 2D and 3D cultures, potentially improving the therapeutic ratio of GBM.

Highlights

Radiotherapy combined with chemotherapy is the major treatment modality for human glioblastoma multiforme (GBM)
Specificity, and safety of the treatment, we address in the present study the question whether autophagy could play a protective role in the survival of CBD/γ-irradiation-treated GBM cells and, correspondingly, if upregulation of CBD-induced death can be enhanced by repression of the lysosomal/ autophagic function in GBM cells
Some experiments were performed with adherent U87MG cells grown as 2D monolayer cultures in cell media supplemented with 5% FBS that could promote autophagy

Summary

Introduction

Radiotherapy combined with chemotherapy is the major treatment modality for human glioblastoma multiforme (GBM). Addition of chloroquine that suppressed autophagic flux to 2D GBM cultures increased CBD-induced cell death, presenting proof for the protective autophagy. The standard care for GBM includes surgical resection followed by concurrent external beam radiotherapy (with a total dose of 60 Gy) together with temozolomide (TMZ), as a supplemental DNA-methylating agent It is followed by one year of adjuvant treatment with TMZ2. Specificity, and safety of the treatment, we address in the present study the question whether autophagy could play a protective role in the survival of CBD/γ-irradiation-treated GBM cells and, correspondingly, if upregulation of CBD-induced death can be enhanced by repression of the lysosomal/ autophagic function in GBM cells. Non-psychogenic CBD, a powerful inducer of intracellular oxidative stress[15,27], was previously demonstrated as an initiator of both apoptotic and autophagic signaling pathways in several types of cancer cells including GBM12,28–30. A challenging problem is to further elucidate interference between apoptosis and autophagy during GBM cell death (especially, using of 3D GBM cultures) to find optimal and safe conditions for cancer treatment

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