2.2. Cell viability assay

The cytotoxic effects of TMZ (Sigma‐Aldrich, St. Louis, MO, USA) and FM19G11 (Sigma‐Aldrich) were measured using the CellTiter 96 AQueous Non‐Radioactive Cell Proliferation Assay (Promega Corp., Madison, WI, USA) following the manufacturer's protocol. In brief, GBM‐XD and T98G cells were seeded in 96‐well flat‐bottom plates at 5000 cells/well, cultured in DMEM supplemented with 10% FBS, and then treated with TMZ and/or FM19G11, or DMSO as a control. A mixture of 100 μL phenazine methosulfate (PMS) and 2 mL of [3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxyphenyl)‐2‐(4‐sulfophenyl)‐2H‐tetrazolium (MTS) reagent was freshly prepared. Next, 20 μL of MTS/PMS mix reagent was added to 100 μl of media per well, and the cells were incubated at 37°C for 2 hours. The optical density (OD) was measured at 490 nm with a spectrophotometer. Relative cell viability was expressed as the ratio of the OD of TMZ and/or FM19G11‐treated cells to the OD of control cells.