title: Adaptive response and its variation in human normal and tumour cells.
abstract: OBJECTIVE
  Adaptive responses in mammalian cells appear to be highly variable. Six human cell lines were used to evaluate whether adaptive response could be related to radiation sensitivity or tumour versus normal cell lines.
  
  
  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 cell lines. The AR was observed at 2 h and persisted for up to 24 h. It was observed for doses as low as 0.2 and 0.5 Gy and declined with higher doses. In 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 response is variable among cell lines and appears not to be related to radiosensitivity nor differences between tumour and normal cell lines.
authors.affiliation: Ottawa Regional Cancer Centre, Ontario, Canada. graaphorst@cancercare.on.ca
authors.forename: G P
authors.initials: GP
authors.lastname: Raaphorst
authors.forename: S
authors.initials: S
authors.lastname: Boyden
mesh_terms: D000222:Adaptation, Physiological; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D009369:Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy*; D011836:Radiation Tolerance / Q000502:physiology*; D011853:Radiobiology; D013997:Time Factors; D014407:Tumor Cells, Cultured