title: Resistance of hypoxic cells to ionizing radiation is influenced by homologous recombination status.
abstract: OBJECTIVE
  To determine the role of DNA repair in hypoxic radioresistance.
  
  
  METHODS
  Chinese hamster cell lines with mutations in homologous recombination (XRCC2, XRCC3, BRAC2, RAD51C) or nonhomologous end-joining (DNA-PKcs) genes were irradiated under normoxic (20% oxygen) and hypoxic (<0.1% oxygen) conditions, and the oxygen enhancement ratio (OER) was calculated. In addition, Fanconi anemia fibroblasts (complementation groups C and G) were compared with fibroblasts from nonsyndrome patients. RAD51 foci were studied using immunofluorescence.
  
  
  RESULTS
  All hamster cell lines deficient in homologous recombination showed a decrease in OER (1.5-2.0 vs. 2.6-3.0 for wild-types). In contrast, the OER for the DNA-PKcs-deficient line was comparable to wild-type controls. The two Fanconi anemia cell strains also showed a significant reduction in OER. The OER for RAD51 foci formation at late times after irradiation was considerably lower than that for survival in wild-type cells.
  
  
  CONCLUSIONS
  Homologous recombination plays an important role in determining hypoxic cell radiosensitivity. Lower OERs have also been reported in cells deficient in XPF and ERCC1, which, similar to homologous recombination genes, are known to play a role in cross-link repair. Because Fanconi anemia cells are also sensitive to cross-linking agents, this strengthens the notion that the capacity to repair cross-links determines hypoxic radiosensitivity.
authors.affiliation: Division of Experimental Therapy, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Debbie
authors.initials: D
authors.lastname: Sprong
authors.forename: Hilde L
authors.initials: HL
authors.lastname: Janssen
authors.forename: Conchita
authors.initials: C
authors.lastname: Vens
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Begg
mesh_terms: D000818:Animals; D016466:CHO Cells / Q000502:physiology / Q000528:radiation effects; D002453:Cell Cycle / Q000502:physiology / Q000528:radiation effects; D015687:Cell Hypoxia / Q000235:genetics* / Q000528:radiation effects; D002470:Cell Survival; D006224:Cricetinae; D003412:Cricetulus; D004260:DNA Repair / Q000235:genetics* / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000172:deficiency; D005347:Fibroblasts / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D011836:Radiation Tolerance / Q000235:genetics*; D011995:Recombination, Genetic / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; C448305:RAD51C protein, human; C110901:X-ray repair cross complementing protein 3; C113187:XRCC2 protein, human