EO inhibits the autophagy level of glioblastoma cells and increases the sensitivity of glioblastoma cells to TMZ. (A and B) RT-PCR analysis of the mRNA levels of lysosomal genes normalized relative to GAPDH in glioblastoma cells LN229 (A) and U87 (B) treated with DMSO, 5 µM EO, and 10 µM EO, respectively. HPRT is a housekeeping control gene. Error bars represent the SDs of four repeats. Student’s t test (unpaired); P** < 0.01; P*** < 0.001; P**** < 0.0001, and no significant (n.s.). (C and D) Cytotoxicity of EO (0, 5, 10, and 20 µM) in combination with gradient TMZ (0 to 800 µM) on glioblastoma cells U87 (C) and LN229 (D) were assessed with the cell counting kit-8 assay. The cell viabilities were normalized relative to untreated samples. Error bars represent the SDs of five repeats. (E and F) Bliss model of EO (0, 5, 10, and 20 µM) and gradient TMZ (0 to 800 µM) synergy in U87 (E) and LN229 (F) cells. A positive score represents a synergistic effect.