title: A nucleoside anticancer drug, 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (TAS106), sensitizes cells to radiation by suppressing BRCA2 expression.
abstract: BACKGROUND
  A novel anticancer drug 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (ECyd, TAS106) has been shown to radiosensitize tumor cells and to improve the therapeutic efficiency of X-irradiation. However, the effect of TAS106 on cellular DNA repair capacity has not been elucidated. Our aim in this study was to examine whether TAS106 modified the repair capacity of DNA double-strand breaks (DSBs) in tumor cells.
  
  
  METHODS
  Various cultured cell lines treated with TAS106 were irradiated and then survival fraction was examined by the clonogenic survival assays. Repair of sublethal damage (SLD), which indicates DSBs repair capacity, was measured as an increase of surviving cells after split dose irradiation with an interval of incubation. To assess the effect of TAS106 on the DSBs repair activity, the time courses of γ-H2AX and 53BP1 foci formation were examined by using immunocytochemistry. The expression of DNA-repair-related proteins was also examined by Western blot analysis and semi-quantitative RT-PCR analysis.
  
  
  RESULTS
  In clonogenic survival assays, pretreatment of TAS106 showed radiosensitizing effects in various cell lines. TAS106 inhibited SLD repair and delayed the disappearance of γ-H2AX and 53BP1 foci, suggesting that DSB repair occurred in A549 cells. Western blot analysis demonstrated that TAS106 down-regulated the expression of BRCA2 and Rad51, which are known as keys among DNA repair proteins in the homologous recombination (HR) pathway. Although a significant radiosensitizing effect of TAS106 was observed in the parental V79 cells, pretreatment with TAS106 did not induce any radiosensitizing effects in BRCA2-deficient V-C8 cells.
  
  
  CONCLUSIONS
  Our results indicate that TAS106 induces the down-regulation of BRCA2 and the subsequent abrogation of the HR pathway, leading to a radiosensitizing effect. Therefore, this study suggests that inhibition of the HR pathway may be useful to improve the therapeutic efficiency of radiotherapy for solid tumors.
authors.affiliation: Laboratory of Radiation Biology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, 060-0818, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Meike
authors.forename: Tohru
authors.initials: T
authors.lastname: Yamamori
authors.forename: Hironobu
authors.initials: H
authors.lastname: Yasui
authors.forename: Masato
authors.initials: M
authors.lastname: Eitaki
authors.forename: Akira
authors.initials: A
authors.lastname: Matsuda
authors.forename: Masami
authors.initials: M
authors.lastname: Morimatsu
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukushima
authors.forename: Yasundo
authors.initials: Y
authors.lastname: Yamasaki
authors.forename: Osamu
authors.initials: O
authors.lastname: Inanami
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D024682:BRCA2 Protein / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D003562:Cytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D059765:Homologous Recombination / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D006801:Humans; D008954:Models, Biological; D009369:Neoplasms / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy; D009705:Nucleosides / Q000494:pharmacology; D011836:Radiation Tolerance / Q000187:drug effects / Q000235:genetics; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: C103084:1-(3-C-ethynylribopentofuranosyl)cytosine; D000970:Antineoplastic Agents; D024682:BRCA2 Protein; D009705:Nucleosides; D011838:Radiation-Sensitizing Agents; D003562:Cytidine