Adaptive responses in human glioma cells assessed by clonogenic survival and DNA strand break analysis.

Purpose: Human gliomas are known to be radioresistant and the aim was to determine if this resistance in part could be due to an adaptive response.

Materials And Methods: Human U-87MG glioma cells were used. Three different radiation regimens that could be related to clinical treatments were tested for their ability to cause an adaptive response. Cell survival and DNA double-strand breakage were the measured endpoints.

Results: All three regimens caused an adaptive response in terms of cell survival when given priming doses of radiation. The DNA double-strand break endpoint also showed fewer breaks when the adaptive response occurred.

Conclusions: Using irradiation regimens that closely resembled clinical applications, in vitro data are presented that show an adaptive response in human glioma cells. This effect in part could be responsible for the radioresistance of human gliomas.