PO-488 Activation of Wnt signalling in temozolomide (TMZ) treated glioma cells: mechanism and implications in TMZ chemoresistance

Abstract

IntroductionGlioblastoma (GBM) is a malignant brain tumour. The treatment strategies include the maximal safe surgical resection of the tumour, followed by radiotherapy and chemotherapy (TMZ). In spite, the median survival for the GBM patients remains less than 15 months and recurrence happens in almost all the GBM cases. The objective of this study was to investigate the changes in the signalling pathways in glioma after exposure to TMZ.Material and methodsIn order to find out the signalling pathways which are altered in glioma after TMZ treatment, the changes in the transcriptome of U87 glioma cell line was profiled after 24 hours of treatment with either DMSO or TMZ. The RNA was subjected to microarray profiling through Human HT-12 v4 Expression BeadChip platform (illumina).Results and discussionsInterestingly, pathway analysis using DAVID and gene set enrichment analysis (GSEA) of the differentially expressed genes revealed a positive significant enrichment of both pro-apoptotic and anti-apoptotic signalling pathways in TMZ treated cells. We focused our attention on Wnt signalling pathway because of its significant positive enrichment in TMZ treated cells in spite of the fact that this pathway is a major anti-apoptotic pathway. We confirmed the activation of Wnt signalling by the increased phospho GSK3β ser9 and decreased phospho β-catenin ser33/37/41 levels in TMZ treated cells. The nuclear localization of β-catenin after TMZ treatment was confirmed by confocal microscopy. Further, inhibition of activated Wnt signalling by FH535, a small molecule inhibitor of Wnt signalling or β-catenin knockdown by small interfering RNA increased apoptosis in TMZ treated cells and made glioma cells sensitive to TMZ.ConclusionTMZ treatment results in the activation of anti-apoptotic Wnt pathway in glioma cell lines. We are carrying out in-depth investigation on the mechanism behind activation of Wnt signalling in TMZ-treated cells and testing the impact of inhibition of Wnt signalling in TMZ sensitivity using mouse glioma models.