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Introduction
Although there has been progress in treatment in the recent decade, patients with glioblastoma (GBM) still only have a median survival of 9 months and 5-year survival rate of 9.8% (1). Exploration of glioma-initiating cells (GICs) impelled us to recognize the biological behavior of glioma from a new perspective. GICs are identified to be the root of tumorigenesis, invasion, angiogenesis and treatment resistance (2). It is also regarded as the important target to treat malignant glioma (3). Further investigation of GICs in vitro and in vivo may promote the effective strategies and methods to treat glioma.
The correct GICs sources and the suitable experimental animal models are necessary for research on GICs in vivo (4). It has been reported that GICs could be isolated from human primary glioma samples and glioma cell lines (5–7). A number of implanted models based on the injection of GICs into immunodeficient or immunocompetent mice are being used to investigate GICs in vivo (7–9). However, whether these implanted models can reflect malignant biological behavior of GICs accurately is unclear.
Although human primary glioma cells preserve the majority of glioma characteristics, the heterogeneous mesenchymal microenvironment and the deficiency of immunological elements may induce the large discrepancy of biological features between human primary glioma and xenograft in immunodeficient animal. Murine malignant glioma cell line GL261 was created by intracranial injection of 3-methylcholantrene into C57/BL6 mice and widely used in glioma research (10). In order to confirm a reliable experimental animal model for research on GICs, we isolated neurosphere-like tumor cells from GL261 (GL261-NS) and primary human glioma specimens (PGBM-NS), injected GL261-NS into C57/BL6 mice brain to establish a syngeneic orthotopically transplanted model and injected PGBM-NS into NOD/SCID mouse brain to establish a xenograft model. We detected the different tumorigenic characteristics of GICs and analyzed the tumor inflammatory microenvironment in the two models.
Materials and methods
Patients and specimens
Tumor tissues were obtained from the Neurosurgery Department of Daping Hospital. Five patients with primary GBM underwent curative resection between 2008 and 2009 and samples from these patients were used for primary glioma cell culture (Table I). The protocol was approved by the institutional Research Ethics Board at Daping Hospital, Chongqing, China.
Cell cultures
GL261 cell line was obtained from American Type Culture...