gms | German Medical Science

Objective: To investigate whether cell lines, which were established under serum-free neural stem cell conditions and maintain stem cell-like properties in vitro (GS cell lines), preserve the expression phenotype of human glioblastomas more adequately than conventional glioma cell lines and express specific genes amenable to therapeutic targeting.

Methods: 75 samples were profiled using Affymetrix HG-U133 Plus 2.0 microarrays, including GS cell lines, original tumor samples, conventional serum-cultured glioma cell lines, and monolayer cultures established from the same tumors as GS-lines. CXCR4 was validated as specific therapeutic target in vitro and in vivo and its regulation was studied.

Results: A subset of GS cell lines that displayed a full stem-like phenotype (GSf) reflected the expression signature of glioblastomas most closely. These lines are tumorigenic and highly invasive in vivo, express CD133, grow spherically in vitro, are multipotent and display a proneural gene expression signature, thus emerging as the most representative model for human glioblastomas both functionally and transcriptionally. In contrast, GS lines with a restricted stem-like phenotype (GSr) exhibited expression signatures resembling conventional glioma cell lines, which are most distant from original tumors by cluster analysis, indicating that the transcriptional resemblance between GS lines and tumors is associated with different degrees of "stemness". We identified CXCR4 as overexpressed in tumors and GSf lines compared with conventional glioma cell lines, thus emerging as a potential therapeutic target. GSf lines contained a small subpopulation of CXCR4high cells, which partially coexpressed CD133, whereas conventional cell lines contained no CXCR4high cells but a major proportion of CXCR4low cells. In vivo, convection-enhanced local treatment with a specific CXCR4 antagonist inhibited the highly invasive growth of GS xenografts, and cell migration but not proliferation was inhibited in vitro.

Conclusions: The group of GSf cell lines represents the most appropriate model for human glioblastomas, reflecting the original tumor gene expression signature most closely and maintaining highly invasive growth in vivo as well as stem cell characteristics in vitro. CXCR4 is an attractive specific target to treat the otherweise therapy-resistant, tumor-initiating glioma stem cells within a narrow enough therapeutic window to make this a safe strategy.