Disrupting Redox Balance: A Redox-Based Strategy to Combat Temozolomide Resistance in Glioblastoma

Glioblastoma is an aggressive brain tumor with a median survival of only 15 months despite current therapies. Temozolomide (TMZ) is the standard chemotherapeutic due to its ability to cross the blood-brain barrier; however, acquired resistance limits its efficacy. Oxidative stress, particularly the regulation of Reactive Oxygen Species (ROS), has a dual role in tumor progression and cell death. Cancer cells tightly balance ROS through antioxidant systems fueled by NADPH, which is generated by NADK enzymes, while NADPH oxidases (NOX) produce ROS. Here, the study investigated whether disrupting NADPH homeostasis could enhance oxidative stress and induce cytotoxicity in TMZ-resistant glioblastoma.

The study investigated the effects of Thionicotinamide (TIO) and Sanguinarine (SNG), a NADK2 inhibitor and a NOX5 activator, on cell viability, gene expression, ROS and NADPH levels, apoptosis, and colony formation in glioma cell lines and healthy control HUVECs. Cells were treated for 24 hours with sub-toxic concentrations of SNG (0.5 µM) and TIO (100 µM).

Combined SNG and TIO treatment significantly reduced viability in TMZ-resistant cells (LN18 and TMZresU87-MG), but not in TMZ-sensitive or control cells. Intracellular ROS levels doubled in resistant cells after combined treatment, while NADPH levels decreased 20% in both resistant and sensitive glioma cells. Gene expression analysis revealed that TIO reduced NADK2 expression, and SNG upregulated NOX5 in TMZresistant cells.

These findings suggest that lowering NADPH levels (a necessary catalyst for the cell) and increasing ROS disrupted the cellular homeostasis. Increased oxidative stress in the cell is particularly pronounced in TMZ-resistant cells.

This study provides evidence that co-targeting ROS production and NADPH depletion using SNG and TIO synergistically induces oxidative stress and cytotoxicity in TMZ-resistant glioma, highlighting a promising strategy for overcoming TMZ resistance.