Cisplatin-mediated radiosensitization of non-small cell lung cancer cells is stimulated by ATM inhibition

Abstract

Background and purpose: Cisplatin activates ataxia-telangiectasia-mutated (ATM), a protein with roles in DNA repair, cell cycle progression and autophagy. We investigated the radiosensitizing effect of cisplatin with respect to its effect on ATM pathway activation.

Material and methods: Non-small cell lung cancer cells (NSCLC) cell lines (A549, H460) and human fibroblast (ATM-deficient AT5, ATM-proficient 1BR3) cells were used. The effects of cisplatin combined with irradiation on ATM pathway activity, clonogenicity, DNA double-strand break (DNA-DSB) repair and cell cycle progression were analyzed with Western blotting, colony formation and γ-H2AX foci assays as well as FACS analysis, respectively.

Results: Cisplatin radiosensitized H460 cells, but not A549 cells. Radiosensitization of H460 cells was not due to impaired DNA-DSB repair, increased apoptosis or cell cycle dysregulation. The lack of radiosensitization demonstrated for A549 cells was associated with cisplatin-mediated stimulation of ATM (S1981) and AMPKα (T172) phosphorylation and autophagy. However, in both cell lines inhibition of ATM and autophagy by KU-55933 and chloroquine diphosphate (CQ) respectively resulted in a significant radiosensitization. Combined treatment with the AMPK inhibitor compound-C led to radiosensitization of A549 but not of H460 cells. As compared to the treatment with KU-55933 alone, radiosensitivity of A549 cells was markedly stimulated by the combination of KU-55933 and cisplatin. However, the combination of CQ and cisplatin did not modulate the pattern of radiation sensitivity of A549 or H460 cells. In accordance with the results that cisplatin via stimulation of ATM activity can abrogate its radiosensitizing effect, ATM deficient cells were significantly sensitized to ionizing radiation by cisplatin.

Conclusion: The results obtained indicate that ATM targeting can potentiate cisplatin-induced radiosensitization.

Keywords: ATM; Autophagy; Cisplatin; Ionizing radiation; NSCLC.