ESTRO 2025 - Abstract Book

S3883

Radiobiology - Immuno-radiobiology

ESTRO 2025

[3]Zhang P, Wang B, Chen X, et al. Local Tumor Control and Normal Tissue Toxicity of Pulsed Low-Dose Rate Radiotherapy for Recurrent Lung Cancer[J]. Dose-Response, 2015, 13(2): 1559325815588507.

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Digital Poster Enhancing antitumor immunity by targeting cancer associated fibroblasts with radiation and ATM inhibition Sissel Hauge 1 , Chloé A E Müller 1 , Turid Hellevik 2 , Inigo Martinez-Zubiaurre 3 , Randi G Syljuåsen 1 1 Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway. 2 Department of Radiation Oncology, University Hospital of Northern Norway, Tromsø, Norway. 3 Department of Clinical Medicine, Faculty of Health Sciences, UiT-The Arctic University of Norway, Tromsø, Norway Purpose/Objective: Radiotherapy combined with immune checkpoint inhibitors holds promise for treating non-small cell lung cancer (NSCLC). However, treatment efficacy can be limited by the tumor microenvironment. Cancer associated fibroblasts (CAFs) are prominent constituents of the tumor microenvironment and are known to promote cancer cell survival and immune suppression. This study aimed to induce an immune-stimulating phenotype in CAFs by combining radiation with cell cycle checkpoint inhibitors. We previously demonstrated that such inhibitors can increase type I interferon (IFN-I) signaling in irradiated tumor cells, likely through immune sensing of cytosolic DNA from ruptured micronuclei. Given the critical role of the IFN-I response in mediating radiation-induced antitumor immunity, we investigated whether this approach could induce an IFN-I response in CAFs and shift their phenotype towards supporting antitumor immunity. Material/Methods: Patient-derived CAFs from four NSCLC donors were examined. Expression of CAF markers was validated by immunoblotting. Cells were treated with radiation (2, 6 or 18 Gy) and inhibitors targeting ATR (VE-822), ATM (AZD1390), CHK1 (LY2606368) and WEE1 (AZD1775). IFN-I responses were assessed 3-8 days post-treatment using IFN-β ELISA and immunoblotting in recipient cells after medium transfer. Mechanisms were investigated using flow cytometry for cell cycle analysis and siRNA knockdown of cGAS, RIG-I and CDKNA1. Co-culture experiments of CAFs with NSCLC cell lines (A549, H460) were also conducted. Live-cell flow cytometry was employed to measure MHC-I expression on cancer cells (which can be increased by IFN-I). Results: Combining radiation with ATM inhibition induced IFN-I release from CAFs, with response magnitudes varying in a donor-dependent manner. Co-culturing CAFs with NSCLC cell lines synergistically amplified this response. ATM inhibition abrogated the radiation-induced G1 checkpoint in CAFs, and a similar IFN-I enhancement was observed following radiation combined with CDKNA1 depletion, which disrupts the G1 checkpoint by an independent method. These results clearly linked the IFN-I response to aberrant cell cycle entry post-irradiation. Furthermore, the IFN-I response partially depended on the cytosolic DNA sensor cGAS and RNA sensor RIG-I. Radiation combined with ATM inhibition markedly increased MHC-I surface expression on cancer cells, especially when they were co cultured with CAFs. Conclusion: This study demonstrates that combining radiation with ATM inhibition can effectively target CAFs, inducing an IFN-I response. Beyond the well-established radiosensitizing effects of ATM inhibition, our findings reveal a potential novel role for ATM inhibitors in reprogramming NSCLC-CAFs into an immune-activating phenotype. This dual mechanism represents a promising approach to enhance radiotherapy-immunotherapy synergies by reducing the immunosuppressive influences of the tumor microenvironment.

Keywords: CAFs, ATM inhibition, Type I interferon