Adaptive response and its variation in human normal and tumour cells

Purpose: Adaptive responses in mammalian cells appear to be highly variable . Six human cell lines were used to evaluate whether adaptive response coul d be related to radiation sensitivity or tumour versus normal cell lines. Materials and methods: Six human cell lines (two fibroblasts, two melanoma, two breast carcinoma) were cultured under identical conditions to plateau phase. The cells were given inducing doses of 0, 0.2, 0.5, 1.0, 2.0 and 4.0 Gy followed after incubation at 37 degrees C by challenge doses to assess radiation response. Results: An adaptive response (AR) was observed in some but not all the cel l lines. The AR was observed at 2 h and persisted for up to 24-h. It was ob served for doses as low as 0.2 and 0.5 Gy and declined with higher doses. I n the resistant melanoma cell line there was no adaptive response; instead it showed sensitization for all inducing doses. Conclusions: Human cells can demonstrate an adaptive response. This respons e is variable among cell lines and appears not to be related to radiosensit ivity nor differences between tumour and normal cell lines.