Fig. 4

Colony formation assay. (A) Representative results of the colony formation assay: stained Petri dishes with Detroit 562 after 10 days of incubation. Cells were treated with vehicle control (DMSO), 2 Gy of IR, or combined treatment (30 µM SCR130 + 2 Gy). (B) Surviving fraction (SF) of different HPV-negative and HPV-positive HNSCC cell lines and healthy fibroblasts after treatment. Cells were treated with 15 or 30 µM SCR130; half of the samples additionally received 2 Gy IR 3 h afterwards. Vehicle controls were treated with the same volume DMSO as used for 15 and 30 µM SCR130 (0 Gy) respectively and were used for calculating the SF. 2 Gy data were normalized to the vehicle control that received the same volume DMSO as used for 30 µM SCR130. Statistically significant differences were calculated between 2 Gy and 30 µM SCR130 + 2 Gy by one-tailed Mann-Whitney test to evaluate the radiosensitizing effect of SCR130. Each value represents mean ± SD (n ≥ 4). *p = 0.029, **p = 0.001.