Survival of Irradiated Glia and Glioma Cells Studied with a New Cloning Technique

Abstract

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.

Cellular repair factors influencing radiocurability of human malignant tumours

“…The human melanoma line C-32, however, is significantly more radioresistant than other tumour lines we have examined. Other investigators have reported some human glioblastoma lines to be radioresistant in vitro, though the frequency of radioresistant cells in vivo is unknown (Gerwick et al, 1977;Nilsson et al, 1980). Inherent cellular radioresistance may thus, in some cases, be an important factor in clinical radiocurability, though results from several laboratories with a wide variety of human tumour lines have shown few apart from the C-32 melanoma, to be unusually radioresistant in vitro (Smith et al, 1978;Weininger et al, 1978;Wells et al, 1977).…”

Failure of betamethasone to alter the radiation response of two cultured human glioma cell-lines

“…The poor results must instead have other explanations, such as a low 'intrinsic' radiosensitivity of the glioma cells [10,11,20,21], presence of hypoxic cells (see review by Hill [22]) or failure to include all tumor cells in the irradiated volume. It is possible that combinations of factors, rather than a single cause, explain the poor treatment of results for patients with malignant gliomas.…”

“…The study by Nederman et al [9] on the effects of betamethasone was very limited while the study by Millar et al [10] on dexamethasone was carried out in more detail. Cultured glioma cells are known to have a low cloning efficiency [10,11] and it is therefore difficult to clone them according to the original description by Puck and Marcus [12]. An alternative method to obtain radiation survival parameters is to use the extrapolation method, which has been previously described to be a reliable and easily handled method [13,14].…”

“…The cells were continuously cultured with different concentrations of betamethasone: • = 0/zg/ml; A = 1 p.g/ml; O = 10/zg/ml; [] = 25/zg/ml. The solid lines are least square fits to the points for the control cultures.Cell survival data for the studied cell-lines from previously published reports using the palladium island technique (dotted lines,[11]) and conventional cloning (dashed lines,[10]) are superimposed.…”

Theory and practice of predictive assays in radiation therapy

“…Petri dishes are layered with a thin film of agarose, anda pattern of 0.3 mm diameter palladium islands are deposited onto the agarose. Cells are unable to grow on agarose but grow on the islands to form colonies [26].…”