Figure 1. VE-821 radiosensitizes pancreatic tumor cells. (A) Western blot analysis of Chk1 inhibition. Cells were treated with 100 nM gemcitabine and 1 µM VE-821 1 h prior to irradiation at 6 Gy as indicated in the graphical representation. Drugs were left for the duration of the experiment and cells were lysed at 2 h post-irradiation and subjected to western blot analysis. (B) Effect of VE-821 on cell viability of pancreatic cancer cells with and without radiation treatment. PSN-1, PANC-1, and MiaPaCa-2 cells were treated with increasing concentrations of VE-821 for 72 h. Cells were irradiated at 4Gy 1h after VE-821 addition. Cell viability was measured after 10 d and shown as normalized to DMSO-treated cells. (C) Scheduling of VE-821 affects radiosensitivity. PSN-1 cells were plated as single cells, treated with 1 µM VE-821 at different time points in relation to 4 Gy irradiation and assessed for colony formation after 10 d as indicated in the graphical representation. The survival fraction at 4 Gy for each of the treatment schedules was determined by taking into account the relevant plating efficiency of unirradiated cells (see Fig. S1B). (D) Clonogenic survival of pancreatic cancer cells, MiaPaCa-2, PSN-1, PANC-1 and primary cancer cells PancM in response to irradiation and VE-821 treatment. Cells were treated according to the 72h VE-821 treatment regime described in (C) with 1 µM VE-821 added at 1 h prior to irradiation and removed 72 h post-irradiation and colony-forming ability being assessed after 10 to 21 d. N = 3; *p < 0.05; **p < 0.01 over DMSO-treated control.