title: The effects of protoporphyrin IX-induced photodynamic therapy with and without iron chelation on human squamous carcinoma cells cultured under normoxic, hypoxic and hyperoxic conditions.
abstract: BACKGROUND
  Photodynamic therapy requires the combined interaction of a photosensitiser, light and oxygen to ablate target tissue. In this study we examined the effect of iron chelation and oxygen environment manipulation on the accumulation of the clinically useful photosensitiser protoporphyrin IX (PpIX) within human squamous epithelial carcinoma cells and the subsequent ablation of these cells on irradiation.
  
  
  METHODS
  Cells were incubated at concentrations of 5%, 20% or 40% oxygen for 24h prior to and for 3h following the administration of the PpIX precursors aminolevulinic acid (ALA), methyl aminolevulinate (MAL) or hexylaminolevulinate (HAL) with or without the iron chelator 1,2-diethyl-3-hydroxypyridin-4-one hydrochloride (CP94). PpIX accumulation was monitored using a fluorescence plate reader, cells were irradiated with 37 J/cm(2) red light and cell viability measured using the neutral red uptake assay.
  
  
  RESULTS
  Manipulation of the oxygen environment and/or co-administration of CP94 with PpIX precursors resulted in significant changes in both PpIX accumulation and photobleaching. Incubation with 5% or 40% oxygen produced the greatest levels of PpIX and photobleaching in cells incubated with ALA/MAL. Incorporation of CP94 also resulted in significant decreases in cell viability following administration of ALA/MAL/HAL, with oxygen concentration predominantly having a significant effect in cells incubated with HAL.
  
  
  CONCLUSIONS
  Experimentation with human squamous epithelial carcinoma cells has indicated that the iron chelator CP94 significantly increased PpIX accumulation induced by each PpIX congener investigated (ALA/MAL/HAL) at all oxygen concentrations employed (5%/20%/40%) resulting in increased levels of photobleaching and reduced cell viability on irradiation. Further detailed investigation of the complex relationship of PDT cytotoxicity at various oxygen concentrations is required. It is therefore concluded that iron chelation with CP94 is a simple protocol modification with which it may be much easier to enhance clinical PDT efficacy than the complex and less well understood process of oxygen manipulation.
authors.affiliation: Clinical Photobiology, European Centre for Environment and Human Health, University of Exeter Medical School, University of Exeter, Knowledge Spa, Royal Cornwall Hospital, Truro, Cornwall TR1 3HD, UK.
authors.forename: Emma
authors.initials: E
authors.lastname: Blake
authors.forename: James
authors.initials: J
authors.lastname: Allen
authors.forename: Alison
authors.initials: A
authors.lastname: Curnow
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000378:metabolism*; D045744:Cell Line, Tumor; D004357:Drug Synergism; D006801:Humans; D007502:Iron Chelating Agents; D010100:Oxygen / Q000378:metabolism*; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000008:administration & dosage / Q000493:pharmacokinetics; D011524:Protoporphyrins / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D011728:Pyridones / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D007502:Iron Chelating Agents; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D011728:Pyridones; C068543:1,2-diethyl-3-hydroxypyridin-4-one; C028025:protoporphyrin IX; D010100:Oxygen
keywords: CP94; Iron chelation; Oxygen manipulation; Photodynamic therapy; Protoporphyrin IX