Akt inhibition / Glioblastoma multiforme / Malignant gliomas / PI3K-Akt pathway
P. Sminia C.A. Fedrigo, R.S. Narayan, L.J.A. Stalpers, B.G. Baumert, G.J. Peters, B.J. Slotman VU University Medical Center, Radiation Oncology, Amsterdam Netherlands; Academic Medical Center, Radiation Oncology, Amsterdam Netherlands; MediClin Robert-Janker-Clinic & University of Bonn Medical Centre, Cooperation Unit Neurooncology, Bonn Germany; VU University Medical Center, Medical Oncology, Amsterdam Netherlands
Background: Glioblastoma multiforme (GBM) is the most common, invasive and deadly primary type of malignant brain tumor. The Phosphatidylinositol-3-Kinase-Akt pathway is commonly overexpressed in GBM and has been associated with resistance to therapy. The aim of the study was to investigate the cytotoxic and radiosensitizing effects of the Akt inhibitor MK-2206 on human malignant glioma cells and spheroids in vitro.
Materials and Methods: Experiments were performed on a panel of five GBM cell lines (U251, T98, D384, U87, VU122). Cells were treated with the allosteric Akt inhibitor MK-2206 alone and in combination with irradiation (0–8 Gy). Endpoints: cell survival (clonogenic assay), cell invasion (transwell Boyden chamber technique) and expression of the proteins PTEN, Akt and pAkt (Western blot). U87 multicellular spheroids were analysed in a growth – volume – assay following the combination treatment of MK-2206 (1microM), fractionated irradiation (5 x 2 Gy) and repeated administration of temozolomide (TMZ; 5 x 5microM).
Results: MK-2206 reduced the expression of the phospho-Akt key protein of the PI3Kinase-Akt pathway. The drug was cytotoxic for all glioma cells in the dose range between 1 and 10mM for 24 hours, but no radiosensitizing effect was found on clonogenic cell survival. The invasion capacity was assessed at doses between 1 and 10 microM MK-2206 for 16 hours. A dose-dependent inhibition of invasion was observed for all but one of the cell lines. Irradiation (4 Gy) alone increased the expression of pAkt, which was inhibited (30min, 1 h, 2 h and 4 h) following pre-incubation with MK-2206 (1microM and 10microM for 1 h). When the drug was administered additional to irradiation, a further inhibition of cell migration and invasion was observed, which was not found after irradiation alone. The radio-enhancing effect of MK-2206 was most pronounced in inhibition of the growth of glioma spheroids in the fractionated irradiation regimen.
Conclusion: Targeting of the PI3K-Akt pathway enhanced the effect of radiation and TMZ in a series of in vitro assays, in particular regarding cell invasion and migration, and on spheroid growth. Taken together, Akt pathway inhibition yields promising perspective in the therapy of GBM patients.
No conflict of interest.
Quelle: Sminia et al. Proceedings of the European Cancer Congress, 27 sept. – 1 okt. Amsterdam, the Netherlands. Abstract # 711