title: The radiosensitising effect of gemcitabine and its main metabolite dFdU under low oxygen conditions is in vitro not dependent on functional HIF-1 protein.
abstract: BACKGROUND
  Regions within solid tumours often experience oxygen deprivation, which is associated with resistance to chemotherapy and irradiation. The aim of this study was to evaluate the radiosensitising effect of gemcitabine and its main metabolite dFdU under normoxia versus hypoxia and to determine whether hypoxia-inducible factor 1 (HIF-1) is involved in the radiosensitising mechanism.
  
  
  METHODS
  Stable expression of dominant negative HIF-1α (dnHIF) in MDA-MB-231 breast cancer cells, that ablated endogenous HIF-1 transcriptional activity, was validated by western blot and functionality was assessed by HIF-1α activity assay. Cells were exposed to varying oxygen environments and treated with gemcitabine or dFdU for 24 h, followed by irradiation. Clonogenicity was then assessed. Using radiosensitising conditions, cells were collected for cell cycle analysis.
  
  
  RESULTS
  HIF-1 activity was significantly inhibited in cells stably expressing dnHIF. A clear radiosensitising effect under normoxia and hypoxia was observed for both gemcitabine and dFdU. No significant difference in radiobiological parameters between HIF-1 proficient and HIF-1 deficient MDA-MB-231 cells was demonstrated.
  
  
  CONCLUSIONS
  For the first time, radiosensitisation by dFdU, the main metabolite of gemcitabine, was demonstrated under low oxygen conditions. No major role for functional HIF-1 protein in radiosensitisation by gemcitabine or dFdU could be shown.
authors.affiliation: Center for Oncological Research Antwerp, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium. An.Wouters@uantwerpen.be.
authors.forename: An
authors.initials: A
authors.lastname: Wouters
authors.forename: Bea
authors.initials: B
authors.lastname: Pauwels
authors.forename: Natalie
authors.initials: N
authors.lastname: Burrows
authors.forename: Marc
authors.initials: M
authors.lastname: Baay
authors.forename: Vanessa
authors.initials: V
authors.lastname: Deschoolmeester
authors.forename: Trung Nghia
authors.initials: TN
authors.lastname: Vu
authors.forename: Kris
authors.initials: K
authors.lastname: Laukens
authors.forename: Paul
authors.initials: P
authors.lastname: Meijnders
authors.forename: Dirk
authors.initials: D
authors.lastname: Van Gestel
authors.forename: Kaye J
authors.initials: KJ
authors.lastname: Williams
authors.forename: Danielle
authors.initials: D
authors.lastname: Van den Weyngaert
authors.forename: Jan B
authors.initials: JB
authors.lastname: Vermorken
authors.forename: Patrick
authors.initials: P
authors.lastname: Pauwels
authors.forename: Marc
authors.initials: M
authors.lastname: Peeters
authors.forename: Filip
authors.initials: F
authors.lastname: Lardon
mesh_terms: D001943:Breast Neoplasms; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D015687:Cell Hypoxia / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003857:Deoxyuridine / Q000031:analogs & derivatives / Q000494:pharmacology*; D005260:Female; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D066298:In Vitro Techniques; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D000093542:Gemcitabine
chemical_list: C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011838:Radiation-Sensitizing Agents; D003841:Deoxycytidine; D003857:Deoxyuridine; D000093542:Gemcitabine