Targeting NRF2, Regulator of Antioxidant System, to Sensitize Glioblastoma Neurosphere Cells to Radiation-Induced Oxidative Stress

Abstract

The presence of glioma stem cells (GSCs), which are enriched in neurospheres, may be connected to the radioresistance of glioblastoma (GBM) due to their enhanced antioxidant defense and elevated DNA repair capacity. The aim was to evaluate the responses to different radiation qualities and to reduce radioresistance of U87MG cells, a GBM cell line. U87MG cells were cultured in a 3D model and irradiated with low (24 mGy/h) and high (0.39 Gy/min) dose rates of low LET gamma and high LET carbon ions (1-2 Gy/min). Thereafter, expression of proteins related to oxidative stress response, extracellular 8-oxo-dG, and neurospheres were determined. LD50 for carbon ions was significantly lower compared to LD50 of high and low dose rate gamma radiation. A significantly higher level of 8-oxo-dG was detected in the media of cells exposed to a low dose rate as compared to a high dose rate of gamma or carbon ions. A downregulation of oxidative stress proteins was also observed (NRF2, hMTH1, and SOD1). The NRF2 gene was knocked down by CRISPR/Cas9 in neurosphere cells, resulting in less self-renewal, more differentiated cells, and less proliferation capacity after irradiation with low and high dose rate gamma rays. Overall, U87MG glioma neurospheres presented differential responses to distinct radiation qualities and NRF2 plays an important role in cellular sensitivity to radiation.

1-O-Hexyl-2,3,5-Trimethylhydroquinone Ameliorates the Development of Preeclampsia through Suppression of Oxidative Stress and Endothelial Cell Apoptosis

“…Nrf2 is a transcription factor and protects cells against oxidative stress, electrophiles, and carcinogenic substances [ 43 , 44 ]. Under regular conditions, Nrf2 is bound to Kelch-like ECH-associated protein 1 (Keap1) in the cytosol and forms an E3 ubiquitin ligase complex, which leads to ubiquitination and proteasomal degradation of Nrf2 [ 45 , 46 ].…”

Therapeutic Potential of Curcumin for the Treatment of Malignant Gliomas

“…NRF2 is a leucine zipper protein that is responsible for regulation of oxidative stress; it is normally bound to KEAP1, in an inactive state. Upon exposure to insults such as toxins or radiation, NRF2 dissociates from KEAP1 and accumulates within the cell' s nucleus, ultimately resulting in antioxidant gene activation and resistance to oxidative stress (27). This is an important effect and suggests that curcumin may play a protective role in normal tissues that also receive systemic treatment or ionizing radiation.…”

“…This is an important effect and suggests that curcumin may play a protective role in normal tissues that also receive systemic treatment or ionizing radiation. Curcumin is a known activator of NRF2 (27). Interestingly, NRF2 is upregulated in glioblastoma and is possibly responsible for glioblastoma survival in an environment under increased oxidative stress (27).…”

Antitumor Activity of Curcumin in Glioblastoma

“…NRF2 is usually bound to KEAP1, until cellular exposure to chemical toxins and radiation causes its disassociation and intranuclear accumulation resulting in activation of genes related to antioxidant response and detoxification, ultimately increasing resistance to oxidative stress [ 41 ]. NRF2 has been postulated to increase GBM survival, especially given the elevated oxidative stress in the GBM microenvironment secondary to peroxisome activity, glucose metabolism, mitochondrial dysfunction, and oncogene activity [ 41 ]. NRF2 has also been associated with reduced ferroptosis in GBM [ 42 ].…”

“…NRF2 has also been associated with reduced ferroptosis in GBM [ 42 ]. Knockdown of NRF2 in U87MG GBM cell lines that were subsequently treated with radiation resulted in downregulation of oxidative stress proteins as well as decreased proliferative and self-renewal capacity compared to control groups that did not have an NRF2 knockdown [ 41 ]. Patients with GBM and upregulated NRF2 have reduced overall survival compared to patients with normal NRF2 levels [ 42 ].…”