Fig. 2.

Crucial role of p53 in the synergistic effect of VPA/5′-DFUR combination treatment with RT. a Clonogenic assay shows the long-term effects of combination treatment VPA/5′-DFUR plus 2 Gy RT on CRC cell lines in HCT-116 and HCT-116 p53^−/− collected 12–14 days after RT. A photograph of one well in a representative experiment is shown for each treatment; bar graphs show the area of colony with diameter > 250 μm (mean ± SD of 2 or more separate experiments each one with technical triplicate). * = p < 0.05; ** = p < 0.006; *** = p < 0.0005. b DNA damage was analyzed in HCT-116 and HCT-116 p53^−/− cell lines by visualizing DSB marker γH2AX foci. Cells treated for 24 h with or without VPA and/or 5′-DFUR at the indicated concentration, corresponding to IC₃₀ at 96 h and then with or without 2 Gy RT, were collected 24 h after RT. Cells were fixed, stained for γH2AX (green) and DAPI for nuclei (blue) and observed by microscope. Representative images show γH2AX-positive nuclear foci cells with 63× magnification