gms | German Medical Science

Objective: Stem-like Brain Tumour Initiating Cells (BTICs) appear to be a key cellular component of the invasive phenotype and resistance of malignant gliomas to radiotherapy. The molecular mechanisms of radioresistance in BTICs are largerly undefined. The aim of this study was to assess transcriptional profiles of non-irradiated BTICs and their radioresistant derivatives.

Methods: BTICs were derived from human GBMs and propagated as neurosphere cultures. To select radioresistant populations BTICs were subjected to repetitive rounds of radiation (2,5 Gy single treatment) over six consecutive passages. The analysis of the global transcriptional profiles were performed using GeneChip Human Gene 1.0 ST arrays (Affymetrix). The differentially expressed genes were categorized by change in expression level and biological function (GeneOntology). The tumorigenic potential and radio resistance were evaluated in an orthotopic glioma mouse model. Nude mice bearing BTIC-induced tumours were treated with 15 Gy radiation total dose (6x2.5 Gy/d). Histology was performed on formalin-fixed, paraffin-embedded samples.

Results: Ten long-term neurosphere cultures were established from GBM and characterized in vitro and in vivo. Five (50%) showed a propensity for continuous regeneration in vitro after repetitive exposures to radiation and gave rise to tumours with radioresistant phenotype in vivo. A microarray-based analysis of the transcription profile identified more than 1000 genes differentially expressed in BTICs and their radioresistant derivative (FDR P <0.05 correction). Out of all differentially regulated genes the majority (69%) were down-regulated in radioresistant BTICs. In the group of the strongest up-regulation (logFC ≥1.0), genes with functions in cell adhesion/migration were represented by 16,1%. 18.9% of the genes from the down-regulated group (logFC ≤–1.0) were with functions in DNA metabolism or nucleic acid binding. Genes differentially expressed in radio resistant BTICs included those involved in the regulation of glioma core pathways (TCGA research network, Nature 2008).

Conclusions: Molecular alterations associated with glioma radiorestance involve stable radiation-induced changes in the transcriptome. Signaling pathways associated with recurrent GBM, including those involved in the regulation of cell adhesion, migration and DNA metabolism, are the major targets for radiation-induced alterations in the transcriptome of radioresistant glioma.