MTH1 inhibition disrupts cell cycle and induces apoptosis in osteosarcoma cells. (a) HOS-MNNG and U2OS cells were treated with 100 nM or 500 nM (low dose) and 2 or 8 µM (high dose) TH1579 for 48 h, and the proportion of cells in subG1, G0–G1, S, G2–M was determined by propidium iodide staining and flow cytometry. (b-c) Tumour cells were treated with TH1579 at the indicated concentrations and apoptosis was evaluated by a caspase 3/7 assay and cleaved poly (ADP-ribose) polymerase (PARP) expression using western blotting. (d) U2OS cells were treated with 8 µM TH1579 for 24 h, and modified comet assay was performed to evaluate DNA damage (+/- OGG1). The tail moment was calculated using FiJi and the Open comet plugin. (e) U2OS cells were treated with TH1579 at indicated concentrations for 24 h and 8-oxo-dG incorporation into DNA was evaluated by fluorescence using Alexa488-conjugated Avidin (scale bar 100 μm). (f) gH2AX expression was evaluated by western blot in U2OS cells, after 48 h of treatment with TH1579 at the indicated doses. Error bars show SD. Statistical significativity was assessed by Kruskal–Wallis or Anova. ** p < 0.01, ***p < 0.001.