MTA combined with irradiation. (A) Combination index (CI) plots of radiation (RT) immediately followed by 24 h incubation with various concentrations of MTA in A549 cells. The plots represent the mean of at least three independent experiments. (B-C) Radiation dose-response curves of CAL-27 (B) and A549 (C) cells treated with 24 h MTA followed by different time intervals (24, 8, 4, 1, 0 h) and subsequent irradiation. Survival values from combination experiments were normalised to MTA cytotoxicity (see table 1 for the cytotoxic effect of MTA alone). Data points represent mean values from at least three independent experiments; bars, SD.