Human glioblastoma (U87) cells grown in 3D culture showed a radio-resistance to X-ray and proton radiation.

Glioblastoma multiforme is the most malignant brain tumor and is resistant to conventional radiotherapy. Proton radiotherapy utilizes accelerated proton beams to irradiate deep-seated tumors with minimum ionization in the entrance channel, thanks to its inverted dose profile. This work aims to investigate the response of human glioma (U87) cells cultured in a 3D culture after X-ray and proton irradiation. U87 cells have been cultured in 3D bio-phantom where cells were grown in Matrigel matrix inside a 96-well plate. The morphology of U87 cells in 3D culture has been observed for 48 h, and cells have grown in their natural shape. The response of cells in 3D bio-phantom was evaluated by exposing the cells to 6 MV X-ray and 70 MeV monoenergetic proton beams. Post-irradiation, the surviving cells were determined by a colony formation assay, and the survival curve of cells in 3D culture was compared with the cells grown in 2D monolayer culture. The response of cells in the 3D bio-phantom following X-ray and proton radiation demonstrated an increased survival fraction in the high-dose region than those in 2D monolayer. However, U87 cells showed more sensitivity towards proton irradiation compared to X-rays, regardless of the culture setup. Finally, we obtained the RBE value of 1.15 for cells in 3D bio-phantom and 1.29 for cells in 2D monolayer. Therefore, U87 cells grown in our 3D culture setup demonstrate radio-resistant behavior and exhibit higher sensitivity towards proton irradiation compared to X-ray irradiation in our clonogenic assay.