Basic questions concerning the invasiveness of gliomas, such as whether their invasiveness increases with histological grade9,16,20,22,25 or whether all gliomas of the same grade and type invade the brain to a similar degree,16,40 still remain unanswered. One reason for these uncertainties is purely technical.32 Over the years, several attempts have been made to design reliable methods to evaluate the invasiveness of gliomas that have been removed at biopsy.9,16,20,40 Investigations of monolayer migration9,20,28 and filter-based transmigration,43 as well as studies in which glioma spheroids are confronted with various invasion substrates,13,15,16,40 have highlighted isolated aspects of glioma cell motility and invasiveness.32,47 None of these methods combines technical simplicity, reliability, and precision of the estimate. Moreover, some results have brought into question the very relevance of these studies to circumstances in vivo.32
In an attempt to design an ex vivo system to be used reliably to analyze the invasiveness of individual human gliomas removed at biopsy, we have turned to cultures of organotypical brain slices as recipients for implanted glioma cells. Such brain slices have been shown to survive in culture for several weeks at least, preserving tissue architecture and composition (see Discussion and references listed in the study by Gähwiler, et al.21). Recently, organotypical slices of rodent36,41 and human brain31 were successfully used to measure and modulate the invasiveness of established glioma cell lines in experiments lasting from 2 to 7 days. Results of preliminary study have indicated that such short experimental protocols do not permit the researcher sensitively to detect differences in the invasiveness of gliomas retrieved at biopsy. To validate the use of the ISIS in longer term studies we first implanted various GBM cell lines of different known in vivo invasion potentials and followed their evolution for up to 29 days. In a second step, the method was adapted to analyze tumor tissue obtained at biopsy from 27 consecutive patients. The results indicate that the ISIS is an ex vivo system that permits the precise characterization of the invasiveness of individual gliomas.
We thank Dr. A. Perzelova for providing the 8-MG-BA GBM cell line. In addition we thank Drs. P. Decp and M. Djindjian for providing tumor specimens. Doctor Christov and Ms. de Boüard contributed equally to this study.
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This work was supported by Institut Nationale de la Santé et de la Recherche Médicale, Association pour la Recherche sur le Cancer (to Dr. Lefrançois, 9032), Ligue Nationale contre le Cancer, and fellowships from Association Française de Recherche Génétique (to Ms. de Boüard).