Oxygenation and response to irradiation of organotypic multicellular spheroids of human glioma

Purpose: Investigation of the oxygenation status Of organotypic multicellular spheroids (OMS) and their response to irradiation. Materials and Methods: Tumour specimens of glioblastoma multiforme patients (n = 16) were initiated as OMS. Following 20 Gy gamma- irradiation, the cell migratory capacity was evaluated. Spheroid oxygenation was determined by microelectrode pO(2) measurements and pimonidazole immunostaining. Spheroids prepared from established human glioma cell lines were used as a reference. Results: Irradiation inhibited spheroid outgrowth by 12 to 88 % relative to the non-irradiated controls. A large interpatient variation was noticed. Oxygen measurements revealed a gradual decrease in PO2 level from the periphery to the core of the spheroids, but the PO2 values remained within an oxygenated range. However, in the cell line spheroids an intermediate layer of hypoxia surrounding the central core was observed. Conclusion: Cell line spheroids with a hypoxic cell fraction and well-oxygenated OMS both show high resistance to irradiation, indicating that hypoxia may not be the biological factor determining the radioresistance of glioma spheroids in vitro.