Glioblastoma Stem Cells: A Neuropathologist's View

Glioblastoma (WHO Grade IV) is both the most common primary brain tumor and the most malignant. Advances in the understanding of the biology of the tumor are needed in order to obtain a clearer picture of the mechanisms driving these tumors. To neuropathologists, glioblastoma is a tumor that represents a complex system of migrating pleomorphic tumor cells, proliferating blood vessels, infiltrating inflammatory cells, and necrosis. This review will highlight how the glioma stem cell concept brings these elements together into a collective whole, interacting with microenvironmental influences in complex ways. Borrowing from chaos theory a vocabulary of “self organizing systems” and “complex adaptive systems” that seem useful in describing these pathologic features, a new paradigm of glioblastoma biology will be proposed that genetic changes should be understood in a three dimensional framework as they relate not only to the tumor cells themselves but also to the multicellular hierarchical unit, not isolated from, but responsive to, its local milieu. In this way we will come to better appreciate the impact our therapeutic interventions have on the regional phenotypic heterogeneity that exists within the tumor and the intercellular communications directing adaptation and progression

Cancer stem cells in gliomas: identifying and understanding the apex cell in cancer’s hierarchy.

ABSTRACT Neuro-oncology research has rediscovered a complexity of nervous system cancers through the incorporation of cellular heterogeneity into tumor models with cellular subsets displaying stem-cell characteristics. Self-renewing cancer stem cells (CSCs) can propagate tumors and yield nontumorigenic tumor bulk cells that display a more differentiated phenotype. The ability to prospectively isolate and interrogate CSCs is defining molecular mechanisms responsible for the tumor maintenance and growth. The clinical relevance of CSCs has been supported by their resistance to cytotoxic therapies and their promotion of tumor angiogenesis. Although the field of CSC biology is relatively young, continued elucidation of the features of these cells holds promise for the development of novel patient therapies.

c-Myc Is Required for Maintenance of Glioma Cancer Stem Cells

Malignant gliomas rank among the most lethal cancers. Gliomas display a striking cellular heterogeneity with a hierarchy of differentiation states. Recent studies support the existence of cancer stem cells in gliomas that are functionally defined by their capacity for extensive self-renewal and formation of secondary tumors that phenocopy the original tumors. As the c-Myc oncoprotein has recognized roles in normal stem cell biology, we hypothesized that c-Myc may contribute to cancer stem cell biology as these cells share characteristics with normal stem cells.Based on previous methods that we and others have employed, tumor cell populations were enriched or depleted for cancer stem cells using the stem cell marker CD133 (Prominin-1). We characterized c-Myc expression in matched tumor cell populations using real time PCR, immunoblotting, immunofluorescence and flow cytometry. Here we report that c-Myc is highly expressed in glioma cancer stem cells relative to non-stem glioma cells. To interrogate the significance of c-Myc expression in glioma cancer stem cells, we targeted its expression using lentivirally transduced short hairpin RNA (shRNA). Knockdown of c-Myc in glioma cancer stem cells reduced proliferation with concomitant cell cycle arrest in the G(0)/G(1) phase and increased apoptosis. Non-stem glioma cells displayed limited dependence on c-Myc expression for survival and proliferation. Further, glioma cancer stem cells with decreased c-Myc levels failed to form neurospheres in vitro or tumors when xenotransplanted into the brains of immunocompromised mice.These findings support a central role of c-Myc in regulating proliferation and survival of glioma cancer stem cells. Targeting core stem cell pathways may offer improved therapeutic approaches for advanced cancers

Tgf-b and a specific tgf-b inhibitor regulate pericentrin b and myh9 in glioma cell lines

Los gliomas malignos son tumores vasculares heterogéneos altamente invasivos. El factor de transformación de creci­miento P (TGF-P) es una citoquina multifuncional que es expresada por gliomas de grado III /IV y promueve angiogenesis de tumores, invasión y escape inmunológico. Recientemente se demostró que una pequeña molécula inhibidora (SB-431542) del receptor de TGF-P tipo I (TGF-P-RI), bloquea la señal de transducción mediada por TGF-P, la inducción del factor angiogénico de expresión y la movilidad celular. Ya que las líneas celulares de gliomas mues­tran sensitividad diferencial a TGF-P, se esperaba que también mostrarían impacto diferencial por el bloqueo de la señal de TGF-p. En el presente trabajo se usó un análisis diferencial en gel (DIGE, por sus siglas en inglés: Differential in gel electrophoresis) y espectrometría de masas para determinar los efectos sobre regulación de proteínas por TGF-(3 y SB-431542 en células de gliomas humanos. Se encontró que pericentrina B y miosina no muscular fueron expresa­das diferencialmente en fragmentos, los cuales pueden ser el resultado de la activación de proteasas por el mecanismo de crecimiento del tumor. Estos resultados sugieren que tanto pericentrina B como miosina no muscular, podrían ser usadas como bio-marcadores potenciales de gliomas. Palabras clave: DIGE, proteomica, glioma, TGF-P, espectrometría de masas, miosina no muscular, pericentrina B.Malignant gliomas are heterogeneous, highly invasive vascular tumours. The multifunctional cytokine, transforming growth factor-beta (TGF-P), is expressed by grade III/IV gliomas and promotes tumour angiogenesis, invasión and immune escape. It has been shown previously that a small TGF-P receptor type I (TGF-(3-RI) molecule inhibitor (SB-431542) blocks TGF-(3-mediated signal transduction, induction of angiogenic factor expression and cellular motility. As glioma cell lines display differential sensitivity to TGF-P, it was expected that they would also be differentially impacted by disruption of TGF-P signalling. Differential in gel expression (DIGE) analysis and mass spectrometry was used in this work for determining protein regulation effects of both TGF-P and SB-431542 on human glioma cell lines. It was found that pericentrin B and non muscle myosin were differentially expressed in fragments which likely resulted from protease activation by the tumour growth mechanism. These results suggest that both pericentrin B and non-muscle myosin might be potential glioma biomarkers. Key words: DIGE, proteomics, glioma, TGF-P, mass spectrometry, non muscle myosin, pericentrin B

Direct contact with perivascular tumor cells enhances integrin αvβ3 signaling and migration of endothelial cells

The secretion of soluble pro-angiogenic factors by tumor cells and stromal cells in the perivascular niche promotes the aggressive angiogenesis that is typical of glioblastoma (GBM). Here, we show that angiogenesis also can be promoted by a direct interaction between brain tumor cells, including tumor cells with cancer stem-like properties (CSCs), and endothelial cells (ECs). As shown in vitro, this direct interaction is mediated by binding of integrin αvβ3 expressed on ECs to the RGD-peptide in L1CAM expressed on CSCs. It promotes both EC network formation and enhances directed migration toward basic fibroblast growth factor. Activation of αvβ3 and bone marrow tyrosine kinase on chromosome X (BMX) is required for migration stimulated by direct binding but not for migration stimulated by soluble factors. RGD-peptide treatment of mice with established intracerebral GBM xenografts significantly reduced the percentage of Sox2-positive tumor cells and CSCs in close proximity to ECs, decreased integrin αvβ3 and BMX activation and p130CAS phosphorylation in the ECs, and reduced the vessel surface area. These results reveal a previously unrecognized aspect of the regulation of angiogenesis in GBM that can impact therapeutic anti-angiogenic targeting

Glioblastoma on a microfluidic chip: Generating pseudopalisades and enhancing aggressiveness through blood vessel obstruction events

Background: Glioblastoma (GBM) is one of the most lethal tumor types. Hypercellular regions, named pseudo- palisades, are characteristic in these tumors and have been hypothesized to be waves of migrating glioblastoma cells.These “waves” of cells are thought to be induced by oxygen and nutrient depletion caused by tumor-induced blood vessel occlusion. Although the universal presence of these structures in GBM tumors suggests that they may play an instrumental role in GBM’s spread and invasion, the recreation of these structures in vitro has remained challenging. Methods: Here we present a new microfluidic model of GBM that mimics the dynamics of pseudopalisade forma- tion.To do this, we embedded U-251 MG cells within a collagen hydrogel in a custom-designed microfluidic device. By controlling the medium flow through lateral microchannels, we can mimic and control blood-vessel obstruction events associated with this disease. Results: Through the use of this new system, we show that nutrient and oxygen starvation triggers a strong migratory process leading to pseudopalisade generation in vitro.These results validate the hypothesis of pseudo- palisade formation and show an excellent agreement with a systems-biology model based on a hypoxia-driven phenomenon. Conclusions: This paper shows the potential of microfluidic devices as advanced artificial systems capable of mod- eling in vivo nutrient and oxygen gradients during tumor evolution