A radiosensitizing effect of artesunate in glioblastoma cells is associated with a diminished expression of the inhibitor of apoptosis protein survivin

Abstract

Background and purpose: Novel strategies to overcome an irradiation resistant phenotype may help to increase therapeutic efficacy in glioblastoma multiforme. The present study aimed to elucidate radiation sensitizing properties of artesunate, a semi synthetic derivate of artemisinin and to assess factors involved in this effect.

Materials and methods: LN229 and U87MG cells were treated with various concentrations of artesunate and radiation response was determined by a colony forming assay. Cell numbers, apoptosis induction, cell cycle distribution, and DNA repair following combined modality treatment were monitored by MTT-, caspase 3/7 assay, cytofluorometry, and γ-H2AX foci formation. Expression of survivin, survivin-GFP fusion protein, XIAP, cellular (c)IAP1 and cIAP2 was monitored by Western immunoblotting.

Results: Treatment of glioma cells with artesunate and irradiation resulted in an increased apoptotic fraction, pronounced G2/M arrest and increased DNA damage as demonstrated by an elevated amount of γ-H2AX foci/nucleus. Incubation with artesunate lowers survivin expression in a time and dose-dependent manner, whereas expression of XIAP, cIAP1 and cIAP2 was not affected. In clonogenic assays, treatment with artesunate revealed a significantly reduced surviving fraction, whereas stable over expression of a survivin-GFP protein reversed artesunate-mediated radiosensitization.

Conclusion: Artesunate selectively down regulates survivin that contributes to a radio-sensitization of glioma cells by an increased induction of apoptosis, cell cycle arrest, and a hampered DNA damage response.