Fig. 2

Effect of radiation on TMZ-sensitive and -resistant U87MG cells in both in vitro and in vivo. (A) Analysis of the relative number of cell clones in TMZ-sensitive and -resistant cells following exposure to varying radiation doses (0, 2, 4, 6 Gy). The median effective dose (ED50) was calculated and expressed as a percentage relative to the unirradiated control. (B) The cell viability expressed as optical density (OD) measurements at 450 nm for TMZ-sensitive and -resistant cells under different radiation conditions (0 Gy and 2 Gy) within 96 h. (C) Representative fluorescence microscopy images of DAPI/γH2AX staining in TMZ-sensitive and -resistant cells at 0–6 h after 4 Gy radiation exposure are presented. The fluorescence of DAPI (blue) and γH2AX (red) indicate the presence of nucleus DNA damage and repair foci, respectively. (D) A quantitative assessment of the DNA damage response in TMZ-sensitive and -resistant cells at 0–6 h after 4 Gy radiation exposure was expressed by the mean tail moment of the comet assay. (E) In vivo imaging of tumors in response to radiation in tumor-bearing mice that had been injected with either TMZ-sensitive or TMZ-resistant cells. All data from more than three independent experiments are presented as SD. A two-tailed t-test was used for comparisons between the two indicated groups (** p < 0.01, *** p < 0.001)