The effect of drugs on tumor cell radiosensitivity. (A) U251 Cells were seeded as a single-cell suspension and with a specified number of cells. After allowing cells time to attach (4 h), 17 DMAG or the vehicle control was added (50 nmol/L) and the plates were irradiated 16 h later. Ten to twelve days after seeding, survival curves were generated after normalizing for the cytotoxicity generated by 17 DMAG alone. Data presented are the mean ± SE from at least three independent experiments. (B) Identical experimental conditions as (A) followed by the MSD assay. (C) The non-radiosensitizing effect of perifosine carried out by the MSD assay. U251 cells were treated with perifosine (9 μmol/L) alone and the combination of perifosine and IR.