Metformin delayed repair of IR-induced DNA damage in p53-deficient cells compared with p53 wild-type cells.

HCT116 p53^+/+ and p53^-/- cells were pretreated with 2.5 mM metformin for 24 h, and then irradiated with 6 Gy. (A) Immunofluorescence staining at 6 and 24 h after IR, showed γ-H2AX, a marker for DNA damage; Rad51, a marker of DNA repair; and nuclear DNA stained with DAPI using image analysis in three (green/red/blue) fluorescence channels. (B) For quantitative analysis, γ-H2AX or Rad51 foci-positive cells were counted in at least 100 cells from randomly captured images. Values are mean ± S.E.M, *p < 0.001. IR, ionizing radiation; γ-H2AX, γ-H2A histone family, member X.