DNA repair inhibitors as radiosensitizers in human lung cells

Abstract The aim of this study was to compare the effects of DNA repair inhibitors in the context of radio-sensitization of human lung cells. The radio-sensitizing effects of NU7441 (1 mM), an inhibitor of DNA-dependent protein kinase (DNA-PK); KU55933 (10 μM), an inhibitor of ataxia-telangiectasia mutated kinase (ATM); and VE-821 (10 μM), an inhibitor of ATM-related kinase (ATR) were tested by the xCELLigence system for monitoring proliferation, fluorescence microscopy for DNA damage detection, flow-cytometry for cell cycle and apoptosis analysis and western blotting and ELISA for determination of DNA repair proteins. We employed normal human lung fibroblasts (NHLF, p53-wild-type) and non-small cell lung cancer cells (H1299, p53-negative). DNA-PK inhibition (by NU7441) in combination with ionizing radiation (IR) increased the number of double strand breaks (DSB), which persisted 72 h after irradiation in both cell lines. Additionally, NU7441 and KU55933 in combination with IR caused G2-arrest. ATR inhibitor (VE-821) together with IR markedly inhibited proliferation and induced G2/M arrest accompanied by apoptosis in H1299, but not in NHLF cells, and thus diminished DNA-repair of tumour cells but not normal lung fibroblasts. Our findings indicate that ATR inhibition could be a promising therapeutic strategy in p53-deficient lung tumours.