title: Selective targeting of homologous DNA recombination repair by gemcitabine.
abstract: OBJECTIVE
  Gemcitabine (2',2'-difluoro-2'-deoxycytidine, dFdC) is a potent radiosensitizer. The mechanism of dFdC-mediated radiosensitization is yet poorly understood. We recently excluded inhibition of DNA double-strand break (DSB) repair by nonhomologous end-joining (NHEJ) as a means of radiosensitization. In the current study, we addressed the possibility that dFdC might affect homologous recombination (HR)-mediated DSB repair or base excision repair (BER).
  
  
  METHODS
  DFdC-mediated radiosensitization in cell lines deficient in BER and in HR was compared with that in their BER-proficient and HR-proficient parental counterparts. Sensitization to mitomycin C (MMC) was also investigated in cell lines deficient and proficient in HR. Additionally, the effect of dFdC on Rad51 foci formation after irradiation was studied.
  
  
  RESULTS
  DFdC did induce radiosensitization in BER-deficient cells; however, the respective mutant cells deficient in HR did not show dFdC-mediated radiosensitization. In HR-proficient, but not in HR-deficient, cells dFdC also induced substantial enhancement of the cytotoxic effect of MMC. Finally, we found that dFdC interferes with Rad51 foci formation after irradiation.
  
  
  CONCLUSIONS
  DFdC causes radiosensitization by specific interference with HR.
authors.affiliation: Department of Pulmonary Diseases, University Hospital Groningen, Groningen, The Netherlands. f.m.wachters@int.azg.nl
authors.forename: Floris M
authors.initials: FM
authors.lastname: Wachters
authors.forename: John W G
authors.initials: JW
authors.lastname: van Putten
authors.forename: Jan G
authors.initials: JG
authors.lastname: Maring
authors.forename: Malgorzata Z
authors.initials: MZ
authors.lastname: Zdzienicka
authors.forename: Harry J M
authors.initials: HJ
authors.lastname: Groen
authors.forename: Harm H
authors.initials: HH
authors.lastname: Kampinga
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D016466:CHO Cells; D002470:Cell Survival; D006224:Cricetinae; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006979:Hyperthermia, Induced; D016685:Mitomycin / Q000494:pharmacology; D051135:Rad51 Recombinase; D011836:Radiation Tolerance / Q000235:genetics; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D011853:Radiobiology; D014407:Tumor Cells, Cultured / Q000528:radiation effects; D000093542:Gemcitabine
chemical_list: D000903:Antibiotics, Antineoplastic; D000964:Antimetabolites, Antineoplastic; D004268:DNA-Binding Proteins; D011838:Radiation-Sensitizing Agents; D003841:Deoxycytidine; D016685:Mitomycin; D051135:Rad51 Recombinase; D000093542:Gemcitabine