ESTRO 2025 - Abstract Book

S3990

Radiobiology - Tumour radiobiology

ESTRO 2025

Purpose/Objective: Although there have been significant treatment improvements, 20-40% of HNSCC patients will still have incurable disease, with treatment resistance being a major contributing factor to treatment failure (1, 2). HT acts as a radiosensitiser and immune modulator through various mechanisms (3, 4). IO has significantly transformed the oncology field, and the combination of RT/IO treatment is an actively growing research field (5, 6). This study aims to explore the additive and/or synergistic effects of combining RT, HT, and IO in preclinical models of HNSCC. Material/Methods: Patient-derived organoids (PDOs) were generated from HNSCC tumour samples within the SOTO study (NCT05400239), a prospective clinical study. The effect of RT in combination with HT was assessed in cell lines (MOCL1, SCC9, SCC15) and PDOs using in vitro viability and clonogenic assays. Hyperthermia was delivered at 42 o C for 60 minutes before or after RT exposure. Moreover, we developed a co-culture model involving autologous peripheral blood mononuclear cells (PBMCs) and PDOs to investigate the effects of combining RT, HT, and a PD1 checkpoint inhibitor. We also established and utilised an in-vivo HT delivery model using the WIRA machine, to assess the effect of HT and IO combination in a HNSCC syngeneic murine model. Confocal microscopy was utilised to assess treatment outcomes and quantify apoptosis and flow cytometry was used to analyse changes in the PDOs immunophenotype following treatment Results: The combination of HT and RT led to a statistically significant decrease in cell viability and clonogenic potential across three HNSCC cell lines (MOCL1, SCC9, and SCC15). A dose- and time-dependent reduction in viability was observed. Treatment response varied among different PDO lines and heating techniques. Moreover, the combination treatment significantly increased the expression of immune markers, including PDL1, PDL2, and CD73. After establishing safe delivery of hyperthermia in-vivo with the WIRA machine, the combination of HT and IO resulted in delayed tumour growth. The triple combination of RT, HT, and IO investigated in PDOs significantly reduced the number and size of organoids and increased apoptosis. Conclusion: This project demonstrates that combining HT and RT enhances the treatment efficacy in HNSCC models. The variability across the different PDOs and heating techniques highlights the value of using robust pre-clinical models for treatment investigation. Additionally, a novel method of localised hyperthermia delivery to mice was successfully established, creating a foundation for subsequent in vivo investigations. The triple-modality approach offers a promising strategy to overcome treatment resistance in HNSCC. 1. Pisani P, et al. Metastatic disease in head & neck oncology. Acta Otorhinolaryngol Ital. 2020;40(Suppl. 1):S1-S86. 2. Barker HE, et al. The tumour microenvironment after radiotherapy: mechanisms of resistance and recurrence. Nat Rev Cancer. 2015;15(7):409-25. 3. Horsman MR, Overgaard J. Hyperthermia: a potent enhancer of radiotherapy. Clin Oncol (R Coll Radiol). 2007;19(6):418-26. 4. Frey B, et al. Hyperthermia-induced modulations of the immune system. Int J Hyperthermia. 2012;28(6):528-42. 5. Waldman AD, et al. A guide to cancer immunotherapy: from T cell science to clinical practice. Nat Rev Immunol. 2020;20(11):651-68. 6. Kang J, et al. Current clinical trials testing immunotherapy with radiotherapy. J Immunother Cancer. 2016;4:51. Keywords: hyperthermia, immunotherapy, radiotherapy References: