title: Impact of dose-rate on the low-dose hyper-radiosensitivity and induced radioresistance (HRS/IRR) response.
abstract: OBJECTIVE
  To ask whether dose-rate influences low-dose hyper- radiosensitivity and induced radioresistance (HRS/IRR) response in rat colon progressive (PRO) and regressive (REG) cells.
  
  
  METHODS
  Clonogenic survival was applied to tumorigenic PRO and non-tumorigenic REG cells irradiated with (60)Co γ-rays at 0.0025-500 mGy.min(-1). Both clonogenic survival and non-homologous end-joining (NHEJ) pathway involved in DNA double-strand breaks (DSB) repair assays were applied to PRO cells irradiated at 25 mGy.min(-1) with 75 kV X-rays only.
  
  
  RESULTS
  Irrespective of dose-rates, marked HRS/IRR responses were observed in PRO but not in REG cells. For PRO cells, the doses at which HRS and IRR responses are maximal were dependent on dose-rate; conversely exposure times during which HRS and IRR responses are maximal (t(HRSmax) and t(IRRmax)) were independent of dose-rate. The t(HRSmax) and t(IRRmax) values were 23 ± 5 s and 66 ± 7 s (mean ± standard error of the mean [SEM], n = 7), in agreement with literature data. Repair data show that t(HRSmax) may correspond to exposure time during which NHEJ is deficient while t(IRRmax) may correspond to exposure time during which NHEJ is complete.
  
  
  CONCLUSIONS
  HRS response may be maximal if exposure times are shorter than t(HRSmax) irrespective of dose, dose-rate and cellular model. Potential application of HRS response in radiotherapy is discussed.
authors: Institut National de la Santé et de la Recherche Médicale (INSERM) U 1052, groupe de radiobiologie , Lyon.
authors: Charles
authors: C
authors: Thomas
authors: Jennifer
authors: J
authors: Martin
authors: Clément
authors: C
authors: Devic
authors: Elke
authors: E
authors: Bräuer-Krisch
authors: Michel
authors: M
authors: Diserbo
authors: Juliette
authors: J
authors: Thariat
authors: Nicolas
authors: N
authors: Foray
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003037:Cobalt Radioisotopes; D003106:Colon / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004260:DNA Repair / Q000528:radiation effects; D005720:Gamma Rays / Q000627:therapeutic use; D006801:Humans; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000528:radiation effects*; D051381:Rats; D014965:X-Rays
chemical_list: D003037:Cobalt Radioisotopes