S2518
Radiobiology – DNA damage repair
ESTRO 2026
a Boyden chamber assay, and immunohistochemical analyses of spheroid sections were performed. Results: ATR inhibition combined with RT enhanced the tumor– immune cell interactions, reflected by sustained or increased T cell proliferation, migration, and spheroid infiltration, along with reduced PD-L1 expression on tumor cells. In contrast, ATM inhibition induced a more immunosuppressive environment, characterized by impaired T cell activity and increased PD-1 expression on T cells and PD-L1 expression on tumor cells. Detailed analysis of T cell activation markers revealed a heterogeneous, cell line–dependent response. Consistently, autologous co-culture experiments using patient-derived HNSCC and T cells confirmed the findings from allogeneic models, underscoring the translational relevance of an ATRi- induced immunostimulatory shift compared to ATMi- mediated suppression. Conclusion: Inhibition of ATR is more effective than ATM blockade in enhancing T cell activity, underscoring the therapeutic promise of ATR inhibitors that is also reflected in clinical trial outcomes. The relatively modest immunostimulatory effects of ATM inhibition—may diminish its clinical relevance at least for stimulating anti-HSNCC tumor responses. Elucidating the mechanisms driving these differences will require further investigation. References: [1] Meidenbauer, J., Wachter, M., Schulz, S. R., Mostafa, N., Zülch, L., Frey, B., Fietkau, R., Gaipl, U. S., & Jost, T. (2024). Inhibition of ATM or ATR in combination with hypo-fractionated radiotherapy leads to a different immunophenotype on transcript and protein level in HNSCC. Frontiers in oncology, 14, 1460150. https://doi.org/10.3389/fonc.2024.1460150.[2] Donaubauer, A., Schäfer, A., Hundsdorfer, S., Fietkau, R., Gaipl, U. S., Jost, T. Analysis of Human T Cell Activity in an Allogeneic Co-Culture Setting of Pre-Treated Tumor Cells. J. Vis. Exp. (217), e67643, doi:10.3791/67643 (2025). Keywords: Radiosensitization, inhibitors, immune modulation
2024;134.doing:10.1172/JC11745874.Zhang X,Wang Y,Li J, et al. NBS1 lactylation is required for efficient DNA repair and chemotherapy resistance. Nature.2024. doi :10.1038/s41586-024-07632-4 Keywords: AARS1,lactylation,nasopharyngeal cancer Digital Poster Highlight 2662 Impact of ATR or ATM kinase blockade and hypofractionated irradiation on the tumor-CD8+ T cell interface in 3D head and neck cancer models Lilli Zülch 1 , Kirsten Lauber 2 , Markus Eckstein 3,4 , Rainer Fietkau 5,4 , Stefanie Corradini 6,2 , Udo S. Gaipl 1,4 , Tina Jost 1,4 1 Department of Radiation Oncology, Translational Radiobiology, Universitätsklinikum, Erlangen, Germany. 2 Department of Radiation Oncology, University Hospital, LMU München, Munich, Germany. 3 Institute of Pathology, Universitätsklinikum Erlangen, Erlangen, Germany. 4 Comprehensive Cancer Center Erlangen-EMN, Universitätsklinikum Erlangen, Erlangen, Germany. 5 Department of Radiation Oncology, Universitätsklinikum, Erlangen, Germany. 6 Department of Radiation Oncology, Universitätsklinikum Erlangen, Erlangen, Germany Purpose/Objective: Particularly HPV-negative head and neck squamous cell carcinoma (HNSCC) is still challenging due to its pronounced radioresistance leading to an unfavourable prognosis and reduced survival. A promising approach to counteract this resistance is the use of DNA damage repair inhibitors (DDRi), targeting centrals proteins of the DNA double-strand break repair, in combination with radiotherapy (RT). To examine how these treatments not only increase tumor cell death [1], but also modulate tumor– immune cell interactions, we established a 3D spheroid tumor cell culture model. The tumor microenvironment was therby mimicked by co- cultivation of HNSCC tumor cells with human CD8+ T cells (healthy donor). Material/Methods: HPV-positive and HPV-negative HNSCC cell lines were seeded into low-attachment U-bottom plates to generate spheroids. After 24 hours, spheroids were treated with the ATM inhibitor AZD0156 (1 µM) or the ATR inhibitor VE-822 (0.1 µM), either alone or in combination with hypofractionated radiotherapy (RT; 2 × 5 Gy). CD8 ⁺ cytotoxic T lymphocytes (CTLs) were isolated from healthy donor blood using magnetic- activated cell sorting (MACS), labeled with CFSE, and pre-activated with CD3/CD28 stimulation for 48 hours. Following co-culture, T cell proliferation and activation marker expression were assessed by flow cytometry after 48 hours [2]. T cell migration was evaluated using
Mini-Oral 3462
CRISPR-based screening identifies novel radiation resistance targets in KRAS mutant lung cancer Ashley Nicholls 1 , Amna Shah 2 , Valentina Quarantotti 2 , Rebecca England 3 , Melanie Lad 3 , Yann Wallez 4 , Vaclav Urban 2 , Joff Jones 2 , Hui Sun Leong 2 , Daniel Barrell 2 , Alex Kalinka 3 , Andy Sayer 3 , David Walter 3 , Gerry Crossan 2 , Laura Rosenberg 2 , Jacob Sporn 1 , Douglas Ross-Thriepland 2 , Lydia Gardner 5 , Stephen McMahon 5 ,
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