Characterization of glioma cell invasion: towards novel therapeutic targets

The aggressive potential of glioblastoma (GBM) is partially due to its highly invasive behaviour. Since invasive cells cannot be easily removed by surgery or irradiation, this tumour always recurs and is eventually lethal. Therefore it is crucial to elucidate the process of invasion in GBM to identify the key genes underlying the invasive capacity and may represent new therapeutic targets for GBM patients.The invasive behaviour of patient-derived glioma cell lines grown as neurospheres was characterized using different in vitro invasion assays. To target candidate genes responsible for invasion a whole genome library shRNA screen was performed. Furthermore, the in vivo invasive behaviour of glioma cell lines was investigated in orthotopic xenografts in mice and in slice cultures of adult mouse brain. Immunohistochemical analyses of xenografts were assessed at different time points of tumour development. Immunofluorescent staining against proliferating and invasive cells in xenografts were performed.Glioma cell lines grown as 3D neurospheres displayed variable degrees of invasion in vitro and in vivo, and their invasive potential in vivo was reflected in their in vitro behaviour. E.g. the cell line, which developed a circumscribed, angiogenic phenotype in vivo showed the least invasion, while the cell lines with invasive phenotypes in vivo also displayed highest invasive scores in vitro. In addition, different developmental steps of tumour invasion were identified in orthotopic xenografts and the ratio of proliferating versus invasive cells was determined. Preliminary data on invasion-essential genes identified from shRNA interference screen will be presented.The in vitro invasive behaviour of patient-derived glioma cell lines mirrors their in vivo invasive characteristics. Our data show that cells can proliferate and migrate at the same time, indicating a ‘go-and-grow’ process. Whole genome shRNA interference screen is a powerful tool to identify novel candidates to target the invasion process in GBM.