ESTRO 2025 - Abstract Book

S3889

Radiobiology - Immuno-radiobiology

ESTRO 2025

Spheroids were generated using GL261 glioblastoma cells, MEF fibroblast and RAW264 macrophages. A two-step approach was employed: a stable core was generated using GL261 and MEF cells in a specific ratio, followed by the addition of RAW264 macrophages 24 hours later. X-ray radiotherapy (5, 15, 25 Gy) was applied, and spheroid morphology, stability and size were monitored and analyzed over time (0,1,4 days), through immunofluorescence. Results: The co-culture system showed an increased level of death in GL261 cells when macrophages were added prior the treatment. Compared to a death of 55% in GL261 and RAW264 non treated, there is an increase when treated, arriving to 75% for MBRT and 77% for CRT (Figure 1). In the spheroid system the sequential addition of macrophages improved the stability of the spheroid, enhancing their aggregation. The irradiation increased RAW264 distribution on the pre-formed spheroid, avoiding spreading, maintaining a more spherical morphology, which was not observed in the control group (Figure 2).

Conclusion: The results highlight that radiotherapy not only affects macrophage localization and activation but also improves the structural integrity, sphericity of spheroids, controlling their size, leading to tumor control through macrophages activity. These findings have implications for the preclinical evaluation of tumor-immune interactions and the efficacy of radiotherapy in glioblastoma models. Irradiation of spheroids with MBRT is now under investigation to compare its benefit with CRT. We are exploring the usage of a combination of MBRT and CRT as it has been seen