RADIOSENSITIVITY IN-VITRO OF CLONOGENIC AND NON-CLONOGENIC GLIOBLASTOMA CELLS OBTAINED FROM A HUMAN BRAIN-TUMOR

Cells obtained from a human glioblastoma (G5) were characterized and u sed to develop an assay measuring their radiosensitivity in vitro. Sur viving fractions were estimated 12 days after irradiation by image ana lysis of the total surface occupied by the cells. This report evaluate s 4 experimental factors which may influence the radiosensitivity in v itro of G5 cells : passage number, delay between plating and irradiati on, cell density and clonal heterogeneity The radiosensitivity of the G5 cell line was found to be passage-independent at least between pass ages 12 and 75. Experimental conditions influence the radiosensitivity as surviving fraction at 2 Gy (SF2) range from 90% (5000 cells/well, irradiation 72 h after seeding) to 49% (2500 cells per well, irradiati on 24 h after seeding). The heterogeneity of the radiosensitivity is l arge at the clonal level nr SF2 of six clones isolated from the G5 lin e were 45%, 50%, 72%, 74%, 79% and 84%. Finally, when G5 cell; were ir radiated at low cell density and at the beginning of the growth phase, the radiosensitivity measured with this assay is comparable to that o btained with a standard colony assay. We propose that this assay may b e useful to determine the intrinsic radiosensitivity of cells obtained from human tumours.