Hyperoxia resensitizes chemoresistant human glioblastoma cells to temozolomide

Abstract

OBJECTIVE: Temozolomide (TMZ) is the standard chemotherapy for glioblastoma multiforme (GBM). Intratumoral hypoxia is common in GBM and is associated with TMZ-resistance. We investigated whether and how induced hyperoxia may resensitize chemoresistant GBM cells to TMZ. STUDY DESIGN: In vitro study on the effects of atmospheric oxygen at different concentrations on TMZ-sentivity in GBM cells. MATERIALS AND METHODS: TMZ-sensitive human GBM cells (D54-S and U87-S) were chronically treated with TMZ to develop isogenic subclones of TMZ-resistant cells (D54-R and U87-R). Cells were then exposed to different concentrations of oxygen – hypoxia (1%), normoxia (20%) and hyperoxia (80%) - under ambient atmospheric pressure with or without concomitant TMZ treatment. Chemosensitivity was measured using sulforhodamine B assay. Apoptotic and mitogen-activated protein kinase (MAPK)-related pathways were also studied. RESULTS: TMZ-sensitivity was enhanced by hyperoxia especially in chemoresistant cells. Under hyperoxia, D54-R/U87-R cells regained the same responses towards TMZ as D54-S/U87-S cells under normoxia through caspase-dependent pathway. Both TMZ and hyperoxia were associated with increased phosphorylation of MAPK, but to lesser extents in D54-R cells. The findings suggested that MAPK activities may have a protective role against hyperoxia. This effect appeared to be downregulated in chemoresistant cells, rendering them more susceptible to hyperoxic stress. CONCLUSION: Induced hyperoxia may resensitize chemoresistant GBM to TMZ. The role of MAPK-related pathway in response to oxidative stress in GBM remains to be explored. Further in vivo study is required to investigate the potential application and mechanism of hyperoxia as a chemotherapy adjunct for GBM.