Physiological oxygen concentration alters glioma cell malignancy and responsiveness to photodynamic therapy in vitro

• Published in: Neurological research (New York) 2014-11, Vol.36 (11), p.1001-1010
• Main Authors: Albert, Ina, Hefti, Martin, Luginbuehl, Vera
• Format: Article
• Language: English
• Subjects: 5-Aminolevulinic acid; Aged; Aminolevulinic Acid - metabolism; Antineoplastic Agents, Phytogenic - pharmacology; Camptothecin - pharmacology; Caspase 3 - metabolism; Cell Culture Techniques - methods; Cell Hypoxia; Cell Line, Tumor; Cell Movement; Cell Survival; Extracellular Matrix Proteins - pharmacology; Female; Glioblastoma; Glioblastoma - metabolism; Glioblastoma - physiopathology; Glioblastoma - therapy; Humans; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; Male; Migration; Oxygen - metabolism; Photochemotherapy; Photodynamic therapy; Physiological oxygen concentration; Protoporphyrins - metabolism
• ISSN: 0161-6412; 1743-1328
• DOI: 10.1179/1743132814Y.0000000401

Objectives: The partial pressure of oxygen (pO 2 ) 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 pO 2 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 pO 2 affects GBM cell physiology, PpIX accumulation, or PDT efficacy. Methods: GBM cell lines (U-87 MG and U-251 MG) were cultured under atmospheric (pO 2  =  19%) and physiological (pO 2  =  9%) oxygen concentrations. PpIX accumulation and localization were investigated, and cell survival and cell death were observed following in vitro PDT. Results: A physiological pO 2 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 pO 2 of 19%. This oxygen reduction did not alter 5-ALA-induced intracellular PpIX accumulation. However, physiological pO 2 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 pO 2 , resulting in reduced lactate dehydrogenase (LDH) release (one- to two-fold) and inhibition of caspase 3 activation. Discussion: 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.