Use of patient-derived tumor organoids from head and neck squamous cell carcinoma for the evaluation of the differential effect of carbon ions over X-rays

Background and purpose, Conventional radiotherapy, based on the use of X-rays, remains a standard treatment modality for advanced Head and Neck Squamous Cell Carcinoma (HNSCC), either as a standalone approach or in combination with surgery and/or chemotherapy. Despite its widespread use, approximately 50% of HNSCC patients ultimately experience locoregional recurrence, underscoring the critical need to improve the therapeutic efficacy of radiotherapy. Heavy particles such as carbon ions could lead to better efficiency in treating HNSCC with less side effects. Patient-Derived Tumor Organoids (PDTO) are new 3D in vitro model close to original tumor. However, cancer cell inactivation and/or death induced by carbon ions have not been assessed on PDTO so far or even compared to X-ray. Methods and Materials, Five PDTO lines established from HNSCC patients were exposed to carbon ions and to X-rays and their response to treatments were compared using viability assay, cell cycle analysis and a newly designed clonogenic assay named Organoid Forming Assay (OFA). Results, Viability assays showed a better cell killing effect of carbon ions over X-Rays with a relative biological effect (RBE) ranging from 1.14 to 1.94. OFA revealed a better efficiency of carbon ions over X-rays in a X-ray-resistant PDTO line (RBE at 6.54) compared to a X-ray-sensitive one (RBE at 4.23). These results were confirmed using cell cycle analysis and viability assay. Conclusions, OFA could be a new alternative assay to evaluate different radiotherapy modalities including carbon ions on PDTO models. These results suggest that PDTO may be used to study effects of carbon ions and carbon ions could overcome radioresistance to photons observed in some patients and lead to improvement in management of HNSCC patients.