1. Supplementary Figure Supplementary Figure U251 cells were not sensitized to radiation by downregulation of P-ERK1/2 with 2 µM of MEK inhibitor, U0126. The activity of the inhibitor was verified by the reduction of colony formation by 20 µM U0126. However, even at this concentration a synergistic effect with radiation was not observed. Thus signalling via MEK does not seem to mediate radioprotection in these cells.