title: Physiological oxygen concentration alters glioma cell malignancy and responsiveness to photodynamic therapy in vitro.
abstract: OBJECTIVE
  The partial pressure of oxygen (pO2) in brain tumors ranges from 5 to 15%. Nevertheless, the majority of in vitro experiments with glioblastoma multiforme (GBM) cell lines are carried out under an atmospheric pO2 of 19 to 21%. Recently, 5-aminolevulinic acid (5-ALA), a precursor of protoporphyrin IX (PpIX), has been introduced to neurosurgery to allow for photodynamic diagnosis and photodynamic therapy (PDT) in high-grade gliomas. Here, we investigate whether low pO2 affects GBM cell physiology, PpIX accumulation, or PDT efficacy.
  
  
  METHODS
  GBM cell lines (U-87 MG and U-251 MG) were cultured under atmospheric (pO2  =  19%) and physiological (pO2  =  9%) oxygen concentrations. PpIX accumulation and localization were investigated, and cell survival and cell death were observed following in vitro PDT.
  
  
  RESULTS
  A physiological pO2 of 9% stimulated GBM cell migration, increased hypoxia-inducible factor (HIF)-1 alpha levels, and elevated resistance to camptothecin in U-87 MG cells compared to cultivation at a pO2 of 19%. This oxygen reduction did not alter 5-ALA-induced intracellular PpIX accumulation. However, physiological pO2 changed the responsiveness of U-87 MG but not of U-251 MG cells to in vitro PDT. Around 20% more irradiation light was required to kill U-87 MG cells at physiological pO2, resulting in reduced lactate dehydrogenase (LDH) release (one- to two-fold) and inhibition of caspase 3 activation.
  
  
  CONCLUSIONS
  Reduction of oxygen concentration from atmospheric to a more physiological level can influence the malignant behavior and survival of GBM cell lines after in vitro PDT. Therefore, precise oxygen concentration control should be considered when designing and performing experiments with GBM cells.
authors.forename: Ina
authors.initials: I
authors.lastname: Albert
authors.forename: Martin
authors.initials: M
authors.lastname: Hefti
authors.forename: Vera
authors.initials: V
authors.lastname: Luginbuehl
mesh_terms: D000368:Aged; D000622:Aminolevulinic Acid / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D002166:Camptothecin / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D018929:Cell Culture Techniques / Q000379:methods*; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D002465:Cell Movement; D002470:Cell Survival; D016326:Extracellular Matrix Proteins / Q000494:pharmacology; D005260:Female; D005909:Glioblastoma / Q000378:metabolism* / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010778:Photochemotherapy; D011524:Protoporphyrins / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D016326:Extracellular Matrix Proteins; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; D053148:Caspase 3; D010100:Oxygen; D002166:Camptothecin
keywords: 5-Aminolevulinic acid,; Glioblastoma,; Migration,; Photodynamic therapy,; Physiological oxygen concentration