title: Contribution of HIF-1 and drug penetrance to oxaliplatin resistance in hypoxic colorectal cancer cells.
abstract: BACKGROUND
  Hypoxia is as an indicator of poor treatment outcome. Consistently, hypoxic HCT116 colorectal cancer cells are resistant to oxaliplatin, although the mechanistic basis is unclear. This study sought to investigate the relative contribution of HIF-1 (hypoxia-inducible factor-1)-mediated gene expression and drug penetrance to oxaliplatin resistance using three-dimensional spheroids.
  
  
  METHODS
  Hypoxia-inducible factor-1alpha function was suppressed by the stable expression of a dominant-negative form in HCT116 cells (DN). Cells were drug exposed as monolayer or multicellular spheroid cultures. Cells residing at differing oxygenation status were isolated from Hoechst 33342-treated spheroids using flow cytometry. Sub-populations were subjected to clonogenic survival assays and to Inductively-Coupled Plasma Mass Spectroscopy to determine oxaliplatin uptake.
  
  
  RESULTS
  In spheroids, a sensitivity gradient (hypoxic<aerobic) was revealed by survival assays and this correlated with levels of platinum-bound DNA. The resistance of hypoxic sub-populations exceeded relative changes in adduct levels, implicating factors other than drug penetrance in cell response. Dominant-negative monolayer cells showed no resistance to oxaliplatin in hypoxia and spheroids; the relative resistance of hypoxic compared with aerobic sub-populations was reduced compared with those from controls.
  
  
  CONCLUSIONS
  Overall, data show that drug penetration, DNA damage levels and HIF-1-dependent processes, all contribute to the resistance of hypoxic cells to oxaliplatin.
authors.affiliation: Paterson Institute for Cancer Research, University of Manchester, Manchester, UK.
authors.forename: D L
authors.initials: DL
authors.lastname: Roberts
authors.forename: K J
authors.initials: KJ
authors.lastname: Williams
authors.forename: R L
authors.initials: RL
authors.lastname: Cowen
authors.forename: M
authors.initials: M
authors.lastname: Barathova
authors.forename: A J
authors.initials: AJ
authors.lastname: Eustace
authors.forename: S
authors.initials: S
authors.lastname: Brittain-Dissont
authors.forename: M J
authors.initials: MJ
authors.lastname: Tilby
authors.forename: D G
authors.initials: DG
authors.lastname: Pearson
authors.forename: C J
authors.initials: CJ
authors.lastname: Ottley
authors.forename: I J
authors.initials: IJ
authors.lastname: Stratford
authors.forename: C
authors.initials: C
authors.lastname: Dive
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D015687:Cell Hypoxia; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D019008:Drug Resistance, Neoplasm; D045325:HCT116 Cells; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000502:physiology*; D009944:Organoplatinum Compounds / Q000493:pharmacokinetics / Q000494:pharmacology*; D000077150:Oxaliplatin; D018874:Spheroids, Cellular
chemical_list: D000970:Antineoplastic Agents; D051793:Hypoxia-Inducible Factor 1; D009944:Organoplatinum Compounds; D000077150:Oxaliplatin