Interferon signaling is enhanced by ATR inhibition in glioblastoma cells irradiated with X-rays, protons or carbon ions

Abstract Background and purposeInterferon signaling plays an important role in antitumor immune responses. Inhibitors of the DNA damage response, such as ATR inhibitors, can increase interferon signaling upon conventional radiotherapy with X-rays. However, whether such inhibitors also increase interferon (IFN) signaling after high linear energy transfer (LET) particle irradiation is not known. Materials and methodsHuman glioblastoma U-251 and T98G cells were treated with X-rays, protons (linear energy transfer (LET): 7 and 38 keV/μm) and carbon ions (LET: 28 and 73 keV/μm), with and without ATR inhibitor (VE822) or ATM inhibitor (AZD1390). DNA damage signaling and cell cycle distribution were assayed by immunoblotting and flow cytometry, and radiosensitivity by clonogenic survival. IFN-β secretion was measured by ELISA and STAT1 activation by immunoblotting. ResultsHigh-LET protons and carbon ions caused stronger activation of the DNA damage response compared to low-LET protons andX-rays at similar radiation dose. G2 checkpoint arrest was abrogated by the ATR inhibitor and prolonged by the ATM inhibitor after all radiation types. The inhibitors increased radiosensitivity, as measured after X- and carbon-ion-irradiation. ATR inhibition increased IFN signaling after both low-LET and high-LET irradiation in both cell lines. In T98G, IFN signaling was also enhanced by ATM inhibition. Notably, T98G cells secreted markedly more IFN-β when the inhibitors were combined with high-LET compared to low-LET irradiation. ConclusionOur results show that ATR inhibition can increase IFN signaling after both X-, proton- and carbon-ion-irradiation. Additionally, IFN induction is strongly dependent on LET in one of the tested cell lines.