Relative biological effectiveness and neural stem cell fate in carbon ion-irradiated human brain organoids.

Abstract

Heavy ion therapy offers a promising approach for treating brain tumors due to the high precision of ion beams and biological effectiveness. However, the mechanisms underlying contrast-enhanced brain lesions, which occur more frequently after ions than conventional X-rays, remain to be elucidated. Cerebral organoids were generated from human embryonic stem cells and exposed to high-energy carbon-ions at early (day 20) and late (day 80) developmental stages. Analyses of gene expression were performed using RT-PCR analysis, and protein expression was assessed using immunofluorescence staining. We demonstrate that exposure to high-energy carbon (C)-ions induces the formation of ectopic choroid plexus (CP)-like structures in human cerebral organoids. RT-PCR analyses revealed that C-ion exposure alters the differentiation trajectories of neuroepithelial stem cells, driven by dysregulation of key developmental signaling pathways including NOTCH, WNT, and BMP. Moreover, we observed increased expression of CP-associated markers AQP1 and CLDN3. The relative biological effectiveness (RBE) of C-ions for the formation of fluid-filled cavities associated with CP-like tissue was calculated as 2.0 after both 60 and 100 days of differentiation. Our findings indicate that aberrant CP development is a central mechanism underlying post-radiation contrast-enhanced brain lesions, and that an RBE of 2 should be considered when determining dose thresholds for normal tissue tolerance in carbon ion therapy for brain tumors.