gms | German Medical Science

Objective: Glioblastoma (GBM) is the most common and malignant primary brain tumor in adults. The aggressive properties of GBM were shown to be linked to distinct phenomena such as stemness and dormancy – a reversible growth arrest of tumor cells permitting an escape of common therapies even promoted by the standard chemotherapeutic agent temozolomide (TMZ) used in GBM itself. In the framework of a previously performed microarray-based transcriptome analysis to investigate gene expression during TMZ-promoted cellular dormancy entry and exit, several genes could be identified, being differently involved in GBM progression, namely Chemokine (C-C Motif) Receptor-Like (CCRL)1, Schlafen (SLFN)13, Sloan-Kettering Institute (SKI), Cdk5 And Abl Enzyme Substrate (Cables)1 and Dachsous Cadherin-Related (DCHS)1.

Methods: The genes identified were validated with regard to their regulation under TMZ-induced tumor dormancy in two different human GBM cell lines and primary cultures using qPCR, and a correlation analysis was performed. The gene expression of the identified genes as well as stemness markers were furthermore examined in human GBM ex vivo tissue. Immunofluorescence double staining of GBM ex vivo samples was performed to investigate the cellular localization and connections to tumor stem-like cells. Lastly, stem-like cell lines and primary cultures were examined regarding a potential gene expression of the identified genes via qPCR.

Results: The gene regulation differed between the cell lines and primary cultures, similarities especially among the primary cultures were identified revealing a more homogeneous upregulation of the markers during entry and exit of dormancy. All genes were clearly detectable in human GBM ex vivo tissue. The markers were found to be co-expressed or expressed in close localization with stemness markers and with each other, supporting a correlation of gene expression found via qPCR. Finally, the identified genes were found to be expressed in stem-like cells of GBM cell lines and primary cultures to individual extends.

Conclusion: Our study highlights the connection between tumor progression and dormancy, as well as dormancy and stem cell properties of GBM cells. Only by expanding our knowledge of the processes involved in GBM progression and resistance to therapy it will be possible to significantly prolong patient’s survival or even to cure this disease in the future.