Increased cytotoxic effects via combined treatment of magnetic field and radiation therapy in patient-derived organoids of pancreatic ductal adenocarcinoma

Purpose/Objective Pancreatic ductal adenocarcinoma (PDAC) remains one of the most lethal malignancies, with limited treatment options. Magnetic Resonance-guided Radiotherapy (MRIgRT) combines real-time imaging and irradiation under a static magnetic field (SMF), potentially influencing biological responses beyond its technical advantages. This study aimed to investigate the combined effects of SMF and radiotherapy on patient-derived PDAC organoids (PDOs) to assess whether MRI guidance modulates radiation-induced cytotoxicity. Material/Methods Two PDO lines (PDAC-9 and PDAC-12) were established from treatment-naïve PDAC tissues and cultured in 3D BME matrices. Organoids were exposed to three experimental conditions: (i) untreated control (CTRL), (ii) 10 Gy irradiation using a standard linac (IR), and (iii) 10 Gy irradiation on a 0.35 T MR-Linac with real-time cine-MRI acquisition (IRrtMRI). Organoid viability was assessed by CellTiter-Glo luminescence assay. Morphometric analysis was performed using Bright-field images classifying organoids as small, medium, or large. Cell death was quantified by 7-AAD flow cytometry, while DNA damage and apoptosis were evaluated via western blotting for γH2AX and cleaved-PARP1. Statistical analysis was performed by ANOVA with multiple comparisons (GraphPad Prism 10). Results Both PDO lines exhibited reduced growth and viability after irradiation, with a significantly stronger effect under combined IRrtMRI exposure. The proportion of large organoids decreased to 0%, while small organoids markedly increased in both PDAC-9 and PDAC-12 (p < 0.01). Cell viability assays confirmed enhanced inhibition following IRrtMRI compared to IR alone (p < 0.001). Flow cytometry revealed that apoptotic cells increased from 40% (IR) to 70% (IRrtMRI) in PDAC-12, whereas PDAC-9 showed relative resistance. Western blot analysis demonstrated increased γH2AX phosphorylation in both PDOs and cleaved-PARP1 induction selectively in PDAC-12 under combined treatment, indicating augmented DNA damage and apoptosis. Conclusion Exposure to radiotherapy under a static 0.35 T magnetic field with real-time MRI enhances genotoxic and apoptotic effects in PDAC organoids compared to conventional irradiation. The observed radiosensitization may derive from magnetic field–mediated prolongation of radical lifetimes, absence of CBCT X-ray–induced adaptive responses, and DNA polarization phenomena. These findings suggest a possible biological advantage of MRIgRT beyond improved targeting accuracy, supporting further investigation into its translational and clinical implications in pancreatic cancer.