Figure 2: GSK3β silencing causes radiation resistance in pancreatic cancer cells. Panc-1 (A, C) and AsPC-1 (B, D) cells were transfected using Oligofectamine (Invitrogen) with ns (non-specific) or GSK3β siRNA (60 nM; Dharmacon) and 48 hours post-transfection were treated with ionizing radiation (RT; 0-8 Gy). Twentyfour hours later, cells were seeded in 60-mm dishes in triplicate for clonogenic survival. After 10 to 12 days of growth, colonies with more than 50 cells were scored. C, D, The Sensitization Enhancement Ratio (SER) was calculated from the radiation survival curves (A,B) as the ratio of the mean inactivation dose (according to the methods of Fertil et al. [59]) for ns siRNA-treated cells to siGSK3β-treated cells and are the mean ± SD of n=2 independent experiments. SER values<1 indicate radiation resistance. Cytotoxicity from siGSK3β treatment alone (in the absence of radiation) is expressed as the Surviving Fraction (SF).