title: Small interfering RNA targeting HIF-1α reduces hypoxia-dependent transcription and radiosensitizes hypoxic HT 1080 human fibrosarcoma cells in vitro.
abstract: BACKGROUND
  Hypoxia inducible factor-1 has been identified as a potential target to overcome hypoxia-induced radioresistance The aim of the present study was to investigate whether selective HIF-1 inhibition via small interfering RNA (siRNA) targeting hypoxia-inducible factor 1α (HIF-1α) affects hypoxia-induced radioresistance in HT 1080 human fibrosarcoma cells.
  
  
  METHODS
  HIF-1α expression in HT 1080 human fibrosarcoma cells in vitro was silenced using HIF-1α siRNA sequence primers. Quantitative real-time polymerase chain reaction assay was performed to quantify the mRNA expression of HIF-1α. HIF-1α protein levels were studied by Western blotting at 20% (air) or after 12 hours at 0.1% O2 (hypoxia). Cells were assayed for clonogenic survival after irradiation with 2, 5, or 10 Gy, under normoxic or hypoxic conditions in the presence of HIF-1α-targeted or control siRNA sequences. A modified oxygen enhancement ratio (OER´) was calculated as the ratio of the doses to achieve the same survival at 0.1% O(2) as at ambient oxygen tensions. OER´ was obtained at cell survival levels of 50%, 37%, and 10%.
  
  
  RESULTS
  HIF-1α-targeted siRNA enhanced radiation treatment efficacy under severely hypoxic conditions compared to tumor cells treated with scrambled control siRNA. OER was reduced on all survival levels after treatment with HIF-1α-targeted siRNA, suggesting that inhibition of HIF-1 activation by using HIF-1α-targeted siRNA increases radiosensitivity of hypoxic tumor cells in vitro.
  
  
  CONCLUSIONS
  Inhibition of HIF-1 activation by using HIF-1α-targeted siRNA clearly acts synergistically with radiotherapy and increase radiosensitivity of hypoxic cells in vitro.
authors: Department of Radiation Oncology, University of Würzburg, Würzburg, Germany. adrian.staab@psi.ch
authors: Adrian
authors: A
authors: Staab
authors: Markus
authors: M
authors: Fleischer
authors: Juergen
authors: J
authors: Loeffler
authors: Harun M
authors: HM
authors: Said
authors: Astrid
authors: A
authors: Katzer
authors: Christian
authors: C
authors: Plathow
authors: Herrmann
authors: H
authors: Einsele
authors: Michael
authors: M
authors: Flentje
authors: Dirk
authors: D
authors: Vordermark
mesh_terms: D015687:Cell Hypoxia / Q000235:genetics*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005354:Fibrosarcoma / Q000473:pathology*; D020868:Gene Silencing; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000235:genetics*; D014407:Tumor Cells, Cultured / Q000528:radiation effects*; D014410:Tumor Stem Cell Assay
chemical_list: C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger