ESTRO 2024 - Abstract Book

S5396

Radiobiology - Tumour biology

ESTRO 2024

Christopher Kessler 1 , Francheska Cadacio 1 , Carlo Maurer 2,3 , Arlett Schäfer 2,3 , Daniela Schilling 1,4 , Ihsan E. Demir 5 , Katja Steiger 6,7,8 , Roland M. Schmid 2 , Maximilian Reichert 2,9,3 , Stephanie E. Combs 1,4,8 , Sophie Dobiasch 1,4,8 1 Klinikum rechts der Isar, Technical University of Munich (TUM), Department of Radiation Oncology, Munich, Germany. 2 Klinikum rechts der Isar, Technical University Munich (TUM), Medical Clinic and Polyclinic II, Munich, Germany. 3 Klinikum rechts der Isar, Technical University Munich (TUM), Translational Pancreatic Cancer Research Center, Medical Clinic and Polyclinic II, Munich, Germany. 4 Helmholtz Zentrum München, Institute of Radiation Medicine (IRM), Neuherberg, Germany. 5 Klinikum rechts der Isar, Technical University of Munich (TUM), Department of Surgery, Munich, Germany. 6 Technical University of Munich (TUM), Institute of Pathology, Munich, Germany. 7 Technical University of Munich (TUM), Comparative Experimental Pathology, Munich, Germany. 8 German Cancer Consortium, (DKTK), Munich, Germany. 9 Technical University of Munich (TUM), Center for Organoid Systems (COS), Garching, Germany Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest types of cancer, with a 5-year survival rate of less than 10% [1]. Locally advanced and borderline resectable tumors achieve sufficient downsizing and secondary resectable tumor stage in about one-third of cases following neoadjuvant radio(chemo)therapy. The role of radiotherapy (RT) in this context remains controversial due to heterogeneous tumor radioresponse [1]. To address the high heterogeneity of radioresistance, personalized therapy is necessary. Patient-derived organoids (PDOs) of PDAC were used to highly personalize the prediction of clinical responses to chemotherapy [2]. In our previous data, we have shown that the response of PDOs to RT reflects the heterogeneity of clinical radioresistance and could be sub-grouped according to their response to irradiation.Intracellular hypoxia reduces the effectiveness of RT. Apart from glycolysis, mitochondrial oxidative phosphorylation (OXPHOS) is the most crucial cellular pathway for ATP production. OXPHOS consumes O2 as the terminal electron acceptor, thus reducing intracellular O2. Inhibition of OXPHOS in PDAC cells was demonstrated leading to chemosensitization [3]. Therefore, we hypothesize that OXPHOS inhibition and the resulting increased intracellular O2 availability can lead to radiosensitization of PDAC PDOs. Purpose/Objective: Nine different PDO lines were screened for their response to RT by 3D cell viability assay and further characterized by gene set enrichment analysis using RNA- sequencing data. To display hypoxia immunohistochemical staining for HIF-1a was performed. After PDOs reached about 80 % confluency they were irradiated with 0 Gy, 4 Gy and 8 Gy and fixed 24 h afterwards for staining. To overcome radioresistance, PDOs were treated with the respiratory chain inhibitor Oligomycin A 24 h hours after seeding. Firstly, 6 different inhibitor concentrations were used to determine the concentration for the further irradiation experiments. Doses were adapted from the literature and adapted to the 3D model in a range from 0.1 μg/ml to 6.4 μg/ml [4]. After finding of appropriate concentrations, a combined approach with irradiation (0 Gy, 4 Gy, and 8 Gy) 1.5 h and 24 h after adding of Oligomycin A using the CellRad system (Faxitron Bioptics, LLC, USA) was performed. Medium was changed 48h after irradiation. To assess the response of the combination treatment a microscopic analysis (BZ-X800, Keyence, Japan) of the morphology and an ATP-dependent viability assay (CellTiter Glo® 3D Cell Viability Assay, Promega, US) was conducted 7 days post-irradiation. Material/Methods: