title: Accumulation of DNA double-strand breaks in normal tissues after fractionated irradiation.
abstract: OBJECTIVE
  There is increasing evidence that genetic factors regulating the recognition and/or repair of DNA double-strand breaks (DSBs) are responsible for differences in radiosensitivity among patients. Genetically defined DSB repair capacities are supposed to determine patients' individual susceptibility to develop adverse normal tissue reactions after radiotherapy. In a preclinical murine model, we analyzed the impact of different DSB repair capacities on the cumulative DNA damage in normal tissues during the course of fractionated irradiation.
  
  
  METHODS
  Different strains of mice with defined genetic backgrounds (SCID(-/-) homozygous, ATM(-/-) homozygous, ATM(+/-)heterozygous, and ATM(+/+)wild-type mice) were subjected to single (2 Gy) or fractionated irradiation (5 x 2 Gy). By enumerating gammaH2AX foci, the formation and rejoining of DSBs were analyzed in organs representative of both early-responding (small intestine) and late-responding tissues (lung, kidney, and heart).
  
  
  RESULTS
  In repair-deficient SCID(-/-) and ATM(-/-)homozygous mice, large proportions of radiation-induced DSBs remained unrepaired after each fraction, leading to the pronounced accumulation of residual DNA damage after fractionated irradiation, similarly visible in early- and late-responding tissues. The slight DSB repair impairment of ATM(+/-)heterozygous mice was not detectable after single-dose irradiation but resulted in a significant increase in unrepaired DSBs during the fractionated irradiation scheme.
  
  
  CONCLUSIONS
  Radiation-induced DSBs accumulate similarly in acute- and late-responding tissues during fractionated irradiation, whereas the whole extent of residual DNA damage depends decisively on the underlying genetically defined DSB repair capacity. Moreover, our data indicate that even minor impairments in DSB repair lead to exceeding DNA damage accumulation during fractionated irradiation and thus may have a significant impact on normal tissue responses in clinical radiotherapy.
authors.affiliation: Department of Radiation Oncology, Saarland University, Kirrbergerstr. Geb. 49/ 51, 66421 Homburg/Saar, Germany. claudia.ruebe@uks.eu
authors.forename: Claudia E
authors.initials: CE
authors.lastname: Rübe
authors.forename: Andreas
authors.initials: A
authors.lastname: Fricke
authors.forename: Juliane
authors.initials: J
authors.lastname: Wendorf
authors.forename: Annika
authors.initials: A
authors.lastname: Stützel
authors.forename: Martin
authors.initials: M
authors.lastname: Kühne
authors.forename: Mei Fang
authors.initials: MF
authors.lastname: Ong
authors.forename: Peter
authors.initials: P
authors.lastname: Lipp
authors.forename: Christian
authors.initials: C
authors.lastname: Rübe
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D019583:Dose Fractionation, Radiation; D006321:Heart / Q000528:radiation effects; D006579:Heterozygote; D006657:Histones / Q000235:genetics; D006720:Homozygote; D007421:Intestine, Small / Q000528:radiation effects; D007668:Kidney / Q000528:radiation effects; D008168:Lung / Q000528:radiation effects; D051379:Mice; D016513:Mice, SCID; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics*; D025521:Tumor Suppressor Proteins / Q000235:genetics
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D006657:Histones; D025521:Tumor Suppressor Proteins; C475961:gamma-H2AX protein, mouse; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases