miR-603 synergizes with IR and TMZ treatment in BT-99, an unmethylated glioblastoma xenograft model. (a) miR-603 synergized with IR (6 Gy) and TMZ treatment (100 µM) in BT-99 in vitro. Limiting dilution assay was performed using BT-99, an MGMT promoter unmethylated glioblastoma line with high MGMT expression, with or without stable miR-603 expression. The frequency of sphere-forming cells in each group was calculated using ELDA analysis. **p < 0.01, ***p < 0.001, n.s.p > 0.05 between indicated groups (one-way ANOVA). (b) miR-603 synergized with IR and TMZ treatment in BT-99 in vivo. Kaplan–Meier survival curves of mice bearing intracranial BT-99 implants with or without ectopic miR-603 expression after various treatments. The mice underwent 5 days of 2 Gy/day radiation and the intraperitoneal administration of TMZ at 50 mg/kg/day starting 7 days after tumor implant.