Survival of irradiated glia and glioma cells studied with a new cloning technique.

A method allowing cloning of monolayer cultured cells with a low plating efficiency was developed. Cells were grown in several small palladium squares to obtain a high cell density. These squares were surrounded by non-adhesive agarose to prevent large distance migration and thereby mixing of the clones. By using easily-cloned hamster cells for comparison it was found that the survival curves were similar to the curves obtained with conventional cloning. The new method was used to compare the radiosensitivity of cultured human glia and glioma cells which both have a low plating efficiency (less than 5 per cent) when seeded sparsely. The survival curves for the glioma cells had high Do-values (1.5--2.5 Gy) and large shoulders (extrapolation numbers around 5) indicating that they were rather resistant and had a high capacity for accumulation of sublethal damage. The survival curves for glia cells had lower Do-values (1.3--1.5 Gy) and no shoulders at all, indicating that they were more sensitive than the glioma cells.