title: Clustered double-strand breaks in heterochromatin perturb DNA repair after high linear energy transfer irradiation.
abstract: High linear energy transfer (LET) radiotherapy offers superior dose conformity and biological effectiveness compared with low-LET radiotherapy, representing a promising alternative for radioresistant tumours. A prevailing hypothesis is that energy deposition along the high-LET particle trajectories induces DNA lesions that are more complex and clustered and therefore more challenging to repair. The precise molecular mechanisms underlying the differences in radiobiological effects between high-LET and low-LET radiotherapies remain unclear.
  
  
  
  Human fibroblasts were irradiated with high-LET carbon ions or low-LET photons. At 0.5h and 5h post exposure, the DNA-damage pattern in the chromatin ultrastructure was visualised using gold-labelled DNA-repair factors. The induction and repair of single-strand breaks, double-strand breaks (DSBs), and clustered lesions were analysed in combination with terminal dUTP nick-end labelling of DNA breaks.
  
  
  
  High-LET irradiation induced clustered lesions with multiple DSBs along ion trajectories predominantly in heterochromatic regions. The cluster size increased over time, suggesting inefficient DSB repair. Low-LET irradiation induced many isolated DSBs throughout the nucleus, most of which were efficiently rejoined.
  
  
  
  The clustering of DSBs in heterochromatin following high-LET irradiation perturbs efficient DNA repair, leading to greater biological effectiveness of high-LET irradiation versus that of low-LET irradiation.
authors.affiliation: Department of Radiation Oncology, Saarland University, Homburg/Saar, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Lorat
authors.affiliation: Department of Radiation Oncology, Saarland University, Homburg/Saar, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Timm
authors.affiliation: Department of Biophysics, GSI Helmholtz Center for Heavy Ion Research, Darmstadt, Germany.
authors.forename: Burkhard
authors.initials: B
authors.lastname: Jakob
authors.affiliation: Department of Biophysics, GSI Helmholtz Center for Heavy Ion Research, Darmstadt, Germany.
authors.forename: Gisela
authors.initials: G
authors.lastname: Taucher-Scholz
authors.affiliation: Department of Radiation Oncology, Saarland University, Homburg/Saar, Germany. Electronic address: claudia.ruebe@uks.eu.
authors.forename: Claudia E
authors.initials: CE
authors.lastname: Rübe
mesh_terms: D002478:Cells, Cultured; D004247:DNA / Q000528:radiation effects*; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D005347:Fibroblasts / Q000528:radiation effects*; D006570:Heterochromatin / Q000235:genetics*; D006801:Humans; D018499:Linear Energy Transfer; D011878:Radiotherapy
chemical_list: D006570:Heterochromatin; D004247:DNA
keywords: Double-strand breaks (dsbs); High-LET irradiation; Ku-heterodimer; Non-homologous end joining (NHEJ); Single-strand breaks (ssbs); Transmission electron microscopy