Lack of functional normalisation of tumour vessels following anti-angiogenic therapy in glioblastoma.

Neo-angiogenesis represents an important factor for the delivery of oxygen and nutrients to a growing tumour, and is considered to be one of the main pathodiagnostic features of glioblastomas (GBM). Anti-angiogenic therapy by vascular endothelial growth factor (VEGF) blocking agents has been shown to lead to morphological vascular normalisation resulting in a reduction of contrast enhancement as seen by magnetic resonance imaging (MRI). Yet the functional consequences of this normalisation and its potential for improved delivery of cytotoxic agents to the tumour are not known.

Glutamine synthetase activity fuels nucleotide biosynthesis and supports growth of glutamine-restricted glioblastoma.

L-Glutamine (Gln) functions physiologically to balance the carbon and nitrogen requirements of tissues. It has been proposed that in cancer cells undergoing aerobic glycolysis, accelerated anabolism is sustained by Gln-derived carbons, which replenish the tricarboxylic acid (TCA) cycle (anaplerosis). However, it is shown here that in glioblastoma (GBM) cells, almost half of the Gln-derived glutamate (Glu) is secreted and does not enter the TCA cycle, and that inhibiting glutaminolysis does not affect cell proliferation.

Engraftment of Human Glioblastoma Cells in Immunocompetent Rats through Acquired Immunosuppression.

Transplantation of glioblastoma patient biopsy spheroids to the brain of T cell-compromised Rowett (nude) rats has been established as a representative animal model for human GBMs, with a tumor take rate close to 100%. In immunocompetent littermates however, primary human GBM tissue is invariably rejected. Here we show that after repeated passaging cycles in nude rats, human GBM spheroids are enabled to grow in the brain of immunocompetent rats.

Bevacizumab treatment induces metabolic adaptation toward anaerobic metabolism in glioblastomas.

Anti-angiogenic therapy in glioblastoma (GBM) has unfortunately not led to the anticipated improvement in patient prognosis. We here describe how human GBM adapts to bevacizumab treatment at the metabolic level. By performing (13)C6-glucose metabolic flux analysis, we show for the first time that the tumors undergo metabolic re-programming toward anaerobic metabolism, thereby uncoupling glycolysis from oxidative phosphorylation.

A co-culture model with brain tumor-specific bioluminescence demonstrates astrocyte-induced drug resistance in glioblastoma.

Background: Although several studies suggest that stromal fibroblasts mediate treatment resistance in several cancer types, little is known about how tumor-associated astrocytes modulate the treatment response in brain tumors. Since traditionally used metabolic assays do not distinguish metabolic activity between stromal and tumor cells, and since 2-dimensional co-culture system does not recreate the formidable complexity of the microenvironment within 3-dimensional structures such as solid tumor tissue, we instead established a glioblastoma (GBM) cell-specific bioluminescent assay for direct measurements of tumor cell viability in the treatment of clinical relevant drugs.

Methods: Using lentiviral transfection, we established a panel of human GBM cell lines constitutively expressing a fusion transgene encoding luciferase and the enhanced green fluorescence protein (eGFP).

Bevacizumab treatment for human glioblastoma. Can it induce cognitive impairment?

Recent results from 2 double-blind, placebo-controlled phase III trials (RTOG 0825) and (AVAglio) for first-line treatment of glioblastoma patients with the VEGF antibody bevacizumab, showed similar results, related to overall and progression-free survival. The RTOG 0825 trial indicated, opposed to the AVAglio trial, that patients treated with bevacizumab showed a decline in global neurocognitive function compared to untreated patients, -a decline that was most obvious after prolonged treatment. At present, there is a considerably controversy related to these observations.

A novel, diffusely infiltrative xenograft model of human anaplastic oligodendroglioma with mutations in FUBP1, CIC, and IDH1.

Oligodendroglioma poses a biological conundrum for malignant adult human gliomas: it is a tumor type that is universally incurable for patients, and yet, only a few of the human tumors have been established as cell populations in vitro or as intracranial xenografts in vivo. Their survival, thus, may emerge only within a specific environmental context. To determine the fate of human oligodendroglioma in an experimental model, we studied the development of an anaplastic tumor after intracranial implantation into enhanced green fluorescent protein (eGFP) positive NOD/SCID mice.

EGFR wild-type amplification and activation promote invasion and development of glioblastoma independent of angiogenesis.

Angiogenesis is regarded as a hallmark of cancer progression and it has been postulated that solid tumor growth depends on angiogenesis. At present, however, it is clear that tumor cell invasion can occur without angiogenesis, a phenomenon that is particularly evident by the infiltrative growth of malignant brain tumors, such as glioblastomas (GBMs). In these tumors, amplification or overexpression of wild-type (wt) or truncated and constitutively activated epidermal growth factor receptor (EGFR) are regarded as important events in GBM development, where the complex downstream signaling events have been implicated in tumor cell invasion, angiogenesis and proliferation.

In vivo animal models for studying brain metastasis: value and limitations.

Brain metastasis is associated with a particular poor prognosis. Novel insight into the brain metastatic process is therefore warranted. Several preclinical models of brain tumor metastasis have been developed during the last 60 years, and they have in part revealed some of the mechanisms underlying the metastatic process.

In vivo models of primary brain tumors: pitfalls and perspectives.

Animal modeling for primary brain tumors has undergone constant development over the last 60 years, and significant improvements have been made recently with the establishment of highly invasive glioblastoma models. In this review we discuss the advantages and pitfalls of model development, focusing on chemically induced models, various xenogeneic grafts of human cell lines, including stem cell-like cell lines and biopsy spheroids. We then discuss the development of numerous genetically engineered models available to study mechanisms of tumor initiation and progression.

Expression of the progenitor marker NG2/CSPG4 predicts poor survival and resistance to ionising radiation in glioblastoma.

Glioblastoma (GBM) is a highly aggressive brain tumour, where patients respond poorly to radiotherapy and exhibit dismal survival outcomes. The mechanisms of radioresistance are not completely understood. However, cancer cells with an immature stem-like phenotype are hypothesised to play a role in radioresistance.

Glioma cell populations grouped by different cell type markers drive brain tumor growth.

Although CD133 has been proposed as a marker for brain tumor-initiating cells, studies show that a tumorigenic potential exists among CD133(-) glioma cells as well. However, it is not established whether the ability of CD133(-) cells to form tumors is a property confined to a small subpopulation, rather than a common trait associated with most glioma cell types. Thus, we used lentiviral vectors expressing green fluorescent protein under lineage-specific promoters to identify CD133(-) glioma cells expressing Nestin, glial fibrillary acidic protein (GFAP), and neuron-specific enolase (NSE).

A reproducible brain tumour model established from human glioblastoma biopsies.

Background: Establishing clinically relevant animal models of glioblastoma multiforme (GBM) remains a challenge, and many commonly used cell line-based models do not recapitulate the invasive growth patterns of patient GBMs. Previously, we have reported the formation of highly invasive tumour xenografts in nude rats from human GBMs. However, implementing tumour models based on primary tissue requires that these models can be sufficiently standardised with consistently high take rates.

Hyperoxic treatment induces mesenchymal-to-epithelial transition in a rat adenocarcinoma model.

Tumor hypoxia is relevant for tumor growth, metabolism and epithelial-to-mesenchymal transition (EMT). We report that hyperbaric oxygen (HBO) treatment induced mesenchymal-to-epithelial transition (MET) in a dimethyl-alpha-benzantracene induced mammary rat adenocarcinoma model, and the MET was associated with extensive coordinated gene expression changes and less aggressive tumors. One group of tumor bearing rats was exposed to HBO (2 bar, pO(2) = 2 bar, 4 exposures à 90 minutes), whereas the control group was housed under normal atmosphere (1 bar, pO(2) = 0.

Highly infiltrative brain tumours show reduced chemosensitivity associated with a stem cell-like phenotype.

Aims: Cancer stem-like cells might have important functions in chemoresistance. We have developed a model where highly infiltrative brain tumours with a stem-like phenotype were established by orthotopic transplantation of human glioblastomas to immunodeficient rats. Serial passaging gradually transformed the tumours into a less invasive and more angiogenic phenotype (high-generation tumours).

Increased lymphatic vascular density is seen before colorectal cancers reach stage II and growth factor FGF-2 is downregulated in tumor tissue compared with normal mucosa.

Lymphangiogenesis is an important event in progression of colorectal cancer (CRC), and the estimated lymphatic vascular density (LVD) probably indicates facilitated lymphatic tumor cell invasion and metastasis. However, at what time point during tumor progression this process is triggered, is unclear. The aim of this study was twofold.

The progenitor cell marker NG2/MPG promotes chemoresistance by activation of integrin-dependent PI3K/Akt signaling.

Chemoresistance represents a major problem in the treatment of many malignancies. Overcoming this obstacle will require improved understanding of the mechanisms responsible for this phenomenon. The progenitor cell marker NG2/melanoma proteoglycan (MPG) is aberrantly expressed by various tumors, but its role in cell death signaling and its potential as a therapeutic target are largely unexplored.

Expression of the "stem cell marker" CD133 in pancreas and pancreatic ductal adenocarcinomas.

Background: It has been suggested that a small population of cells with unique self-renewal properties and malignant potential exists in solid tumors. Such "cancer stem cells" have been isolated by flow cytometry, followed by xenograft studies of their tumor-initiating properties. A frequently used sorting marker in these experiments is the cell surface protein CD133 (prominin-1).

Cancer stem cells as mediators of treatment resistance in brain tumors: status and controversies.

Malignant primary brain tumors are characterized by a short median survival and an almost 100% tumor-related mortality. Despite the addition of new chemotherapy regimes, the overall survival has improved marginally, and radiotherapy is only transiently effective, illustrating the profound impact of treatment resistance on prognosis. Recent studies suggest that a small subpopulation of cancer stem cells (CSCs) has the capacity to repopulate tumors and drive malignant progression and mediate radio- and chemoresistance.

CD133 negative glioma cells form tumors in nude rats and give rise to CD133 positive cells.

CD133 is a cell surface marker expressed on progenitors of haematopoietic and endothelial cell lineages. Moreover, several studies have identified CD133 as a marker of brain tumor-initiating cells. In this study, human glioblastoma multiforme biopsies were engrafted intracerebrally into nude rats.

Lymphangiogenesis in colorectal cancer--prognostic and therapeutic aspects.

Colorectal cancer (CRC) represents the second most common cause of cancer mortality in the western world. The tumors frequently show metastatic spread which affects different organs such as lymph nodes, liver and lungs. Although the pattern of spread may vary, the initial step usually involves dissemination to regional lymph nodes.

Hyperoxia retards growth and induces apoptosis, changes in vascular density and gene expression in transplanted gliomas in nude rats.

This study describes the biological effects of hyperoxic treatment on BT4C rat glioma xenografts in vivo with special reference to tumor growth, angiogenesis, apoptosis, general morphology and gene expression parameters. One group of tumor bearing animals was exposed to normobaric hyperoxia (1 bar, pO(2) = 1.0) and another group was exposed to hyperbaric hyperoxia (2 bar, pO(2) = 2.

Neural stem cell markers, nestin and musashi proteins, in the progression of human glioma: correlation of nestin with prognosis of patient survival.

Background: The IF protein nestin and the RNA-binding protein musashi are expressed by neural progenitor cells during CNS development. Their expression in glial tumors was evaluated by immunohistochemistry, and the histopathological scores correlated with levels of cysteine cathepsins that are known prognostic markers in several tumors.

Methods: The levels of nestin, musashi, and cathepsins B and L were assessed by immunohistochemical analysis of biopsies from 87 patients with primary CNS tumors.

Angiogenesis-independent tumor growth mediated by stem-like cancer cells.

In this work, highly infiltrative brain tumors with a stem-like phenotype were established by xenotransplantation of human brain tumors in immunodeficient nude rats. These tumors coopted the host vasculature and presented as an aggressive disease without signs of angiogenesis. The malignant cells expressed neural stem cell markers, showed a migratory behavior similar to normal human neural stem cells, and gave rise to tumors in vivo after regrafting.