Glioblastoma: therapeutic challenges, what lies ahead.

Glioblastoma (GBM) is one of the most aggressive human cancers. Despite current advances in multimodality therapies, such as surgery, radiotherapy and chemotherapy, the outcome for patients with high grade glioma remains fatal. The knowledge of how glioma cells develop and depend on the tumor environment might open opportunities for new therapies. There is now a growing awareness that the main limitations in understanding and successfully treating GBM might be bypassed by the identification of a distinct cell type that has defining properties of somatic stem cells, as well as cancer-initiating capacity - brain tumor stem cells, which could represent a therapeutic target. In addition, experimental studies have demonstrated that the combination of antiangiogenic therapy, based on the disruption of tumor blood vessels, with conventional chemotherapy generates encouraging results. Emerging reports have also shown that microglial cells can be used as therapeutic vectors to transport genes and/or substances to the tumor site, which opens up new perspectives for the development of GBM therapies targeting microglial cells. Finally, recent studies have shown that natural toxins can be conjugated to drugs that bind to overexpressed receptors in cancer cells, generating targeted-toxins to selectively kill cancer cells. These targeted-toxins are highly effective against radiation- and chemotherapy-resistant cancer cells, making them good candidates for clinical trials in GBM patients. In this review, we discuss recent studies that reveal new possibilities of GBM treatment taking into account cancer stem cells, angiogenesis, microglial cells and drug delivery in the development of new targeted-therapies.

Tenascin-C in the extracellular matrix promotes the selection of highly proliferative and tubulogenesis-defective endothelial cells.

The extracellular matrix (ECM) contains important cues for tissue homeostasis and morphogenesis. The matricellular protein tenascin-C (TN-C) is overexpressed in remodeling tissues and cancer. In the present work, we studied the effect of different ECM-which exhibited a significant diversity in their TN-C content-in endothelial survival, proliferation and tubulogenic differentiation: autologous (endothelial) ECM devoid of TN-C, but bearing large amounts of FN; fibroblast ECM, bearing both high TN-C and FN contents; and finally, glioma-derived matrices, usually poor in FN, but very rich in TN-C. HUVECs initially adhered to the immobilized matrix produced by U373 MG glioma cells, but significantly detached and died by anoikis (50 to 80%) after 24h, as compared with cells incubated with endothelial and fibroblast matrices. Surviving endothelial cells (20 to 50%) became up to 6-fold more proliferative and formed 74-97% less tube-like structures in vitro than cells grown on non-tumoral matrices. An antibody against the EGF-like repeats of tenascin-C (TN-C) partially rescued cells from the tubulogenic defect, indicating that this molecule is responsible for the selection of highly proliferative and tubulogenic defective endothelial cells. Interestingly, by using defined substrata, in conditions that mimic glioma and normal cell ECM composition, we observed that fibronectin (FN) modulates the TN-C-induced selection of endothelial cells. Our data show that TN-C is able to modulate endothelial branching morphogenesis in vitro and, since it is prevalent in matrices of injured and tumor tissues, also suggest a role for this protein in vascular morphogenesis, in these physiological contexts.

Osteoarthritic Synovial Fluid and TGF-ß1 Induce Interleukin-18 in Articular Chondrocytes.

OBJECTIVE: Synovial fluid (SF) plays an important role in the maintenance of articular cartilage. SF is a dynamic reservoir of proteins derived from cartilage and synovial tissue; thus, its composition may serve as a biomarker that reflects the health and pathophysiological condition of the joint. The purpose of the current study was to evaluate the osteoarthritic synovial fluid (OASF) and transforming growth factor-ß1 (TGF-ß1) activity in articular chondrocytes catabolic and inflammatory responses. DESIGN: Chondrocytes were seeded at passage 2 and cultured for 72 hours under different conditions. Human chondrocytes were subjected to OASF while rat chondrocytes were subjected to either healthy synovial fluid (rSF) or TGF-ß1 and then assigned for cell viability analysis. In addition, the effects of OASF and TGF-ß1 on chondrocytes metalloprotease (MMP)-3 and MMP-13 and interleukin-18 (IL-18) expression were evaluated by immunocytochemistry, ELISA, and reverse transcriptase-polymerase chain reaction. RESULTS: SF from osteoarthritic patients significantly induced MMP-3, MMP-13, and IL-18 receptor expression in chondrocytes. To put in evidence the inflammatory activity of OASF, healthy chondrocytes from rat were cultured with TGF-ß1. In the presence of TGF-ß1 these cells started to express MMP-3, MMP-13, and IL-18 genes and attached to each other forming a chondrocyte aggregated structure. Healthy SF was able to maintain a typical monolayer of rounded chondrocytes with no inflammatory response. CONCLUSION: In summary, these observations demonstrated that TGF-ß1, one of the components of OASF, has a dual effect, acting in chondrocyte maintenance and also inducing inflammatory and catabolic properties of these cells.

A recombinant NH(2)-terminal heparin-binding domain of the adhesive glycoprotein, thrombospondin-1, promotes endothelial tube formation and cell survival: a possible role for syndecan-4 proteoglycan.

Thrombospondin-1 (TSP-1) is a multifunctional protein known to modulate angiogenesis, endothelial cell adhesion and apoptosis. In this study, we have demonstrated that TSP18, a recombinant 18 kDa protein encompassing the N-terminal residues 1-174 of human TSP-1, accelerated the process of tube-like structures formation by human umbilical vein endothelial cells (HUVECs) when included in fibrin matrices at 0.55-2.2 microM concentrations, for times ranging from 24 to 72 h. This effect was specifically inhibited by V58A4, a Mab raised against TSP18. Whole TSP-1 showed a dual effect, weakly enhancing tube formation at 22 nM (10 microg/ml), but causing inhibition at 45 and 90 nM (20 and 40 microg/ml, respectively). In order to investigate the possible effects of TSP18 on cell adhesion and viability, we performed adhesion assays on different protein supports. HUVECs adhered more weakly on TSP-1-coated surfaces, remaining round-shaped, as compared to the well-spread phenotype displayed on fibronectin and gelatin. Cells adhering on TSP18-coated surfaces displayed a well spread phenotype, with this adhesion strongly inhibited by heparin. The binding of TSP18 to endothelial membrane extracts was blocked by a monoclonal IgG directed against the cell surface proteoglycan syndecan-4. The DNA fragmentation patterns and the nuclear morphology were comparable for HUVECs adhering on all proteins, including TSP18, showing minimal cell apoptosis. Our results indicate that the N-terminal region of TSP-1 constitutes a suitable adhesive support for HUVECs, protecting them from apoptosis, possibly mediated by syndecan-4 proteoglycan.

Glioblastoma cells: a heterogeneous and fatal tumor interacting with the parenchyma.

Glioblastomas (GBMs) are considered to be one of the deadliest human cancers, characterized by a high proliferative rate, aggressive invasiveness and insensitivity to radio- and chemotherapy, as well as a short patient survival period. Moreover, GBMs are among the most vascularized and invasive cancers in humans. Angiogenesis in GBMs is correlated with the grade of malignancy and is inversely correlated with patient survival. One of the first steps in tumor invasions is migration. GBM cells have the ability to infiltrate and disrupt physical barriers such as basement membranes, extracellular matrix and cell junctions. The invasion process includes the overexpression of several members of a super-family of zinc-based proteinases, the Metzincin, in particular a sub-group, metalloproteinases. Another interesting aspect is that, inside the GBM tissue, there are up to 30% of microglia or macrophages. However, little is known about the immune performance and interactions of the microglia with GBMs. These singular properties of GBMs will be described here. A sub-population of cells with stem-like properties may be the source of tumors since, apparently, GBM stem cells (GSCs) are highly resistant to current cancer treatments. These cancer therapies, while killing the majority of tumor cells, ultimately fail in GBM treatment because they do not eliminate GSCs, which survive to regenerate new tumors. Finally, GBM patient prognostic has shown little improvement in decades. In this context, we will discuss how the membrane-acting toxins called cytolysins can be a potential new tool for GBM treatment.

Inhibition of MAPK/ERK, PKC and CaMKII signaling blocks cytolysin-induced human glioma cell death.

BACKGROUND: Cytolysins are pore-forming toxins that show anticancer activity by a mechanism hitherto poorly investigated. MATERIALS AND METHODS: To investigate how cytolysins are cytotoxic to resistant cancer cells, proliferation and cell death were evaluated on U87 glioblastoma cells treated with toxin Bc2 or equinatoxin-II (EqTx-II). RESULTS: Toxins Bc2 and EqTx-II decreased cell viability and increased lactate dehydrogenase (LDH) release in a concentration-dependent manner. Swollen, dead or dying cells were negative for TUNEL staining. The pre-treatment with inhibitors of mitogen-activated/extracellular regulated kinase (MEK1), protein kinase C (PKC) or Ca(2+)/calmodulin-dependent kinase II (CaMKII) blocked the toxic effects of toxin Bc2 and EqTx-II, suggesting that calcium entry, activation of MEK1, PKC and CaMKII pathways are involved in the cytotoxicity induced by these cytolysins. CONCLUSION: Cytolysins were shown to be toxic to glioblastoma cells by activating several intracellular signaling pathways and resulting in necrosis-like cell death.

Homocysteine induces cytoskeletal remodeling and production of reactive oxygen species in cultured cortical astrocytes.

Homocysteine (Hcy) is an excitatory amino acid which markedly enhances the vulnerability of neuronal cells to excitotoxicity and oxidative injury. Patients with severe hyperhomocysteinemia exhibit a wide range of clinical manifestations including neurological abnormalities such as mental retardation, cerebral atrophy, and seizures. In this study we treated cortical astrocytes and neurons in culture with 10 and 100 µM Hcy and after 24h exposure cytoskeletal remodeling was analyzed by immunocytochemistry. We observed dramatically altered actin cytoskeleton in astrocytes exposed to 100 µM Hcy, with concomitant change of morphology to fusiform and/or flattened cells with retracted cytoplasm. Moreover, we observed disruption of the glial fibrillary acidic protein (GFAP) meshwork, supporting misregulation of actin cytoskeleton. Induction of reactive oxygen species (ROS) in astrocytes showed fluctuating levels along 24h exposure to both Hcy concentrations. Actin remodeling induced by 100 µM Hcy was prevented by the antioxidants folate (5 µM) or trolox (80 µM). Unlike astrocyte cytoskeleton, results evidence little susceptibility of neuron cytoskeleton until 24h of treatment, since immunocytochemical analysis showed that 10 and 100 µM Hcy-treated neurons presented unaltered neurite arborization. Moreover, alterations in astrocyte and neuron viability were not observed along the 24h of exposure to Hcy. Neuron/astrocyte co-cultures evidence an anchorage dependence for neuronal survival over long exposure to Hcy. Taken together, these findings indicate, that the cytoskeleton of cortical astrocytes, but not of neurons in culture, is a target to Hcy and such effects are mediated by redox signaling. Astrocytes were able to respond to Hcy (100 µM) reorganizing their cytoskeleton, surviving, and protecting neurons from Hcy damage. Moreover our results suggest a protective role for astrocytes remodeling the cytoskelon, and probably generating signals that would assure neuronal survival in response to the damage induced by Hcy.

Interactive properties of human glioblastoma cells with brain neurons in culture and neuronal modulation of glial laminin organization.

The harmonious development of the central nervous system depends on the interactions of the neuronal and glial cells. Extracellular matrix elements play important roles in these interactions, especially laminin produced by astrocytes, which has been shown to be a good substrate for neuron growth and axonal guidance. Glioblastomas are the most common subtypes of primary brain tumors and may be astrocytes in origin. As normal laminin-producing glial cells are the preferential substrate for neurons, and glial tumors have been shown to produce laminin, we questioned whether glioblastoma retained the same normal glial-neuron interactive properties with respect to neuronal growth and differentiation. Then, rat neurons were co-cultured onto rat normal astrocytes or onto three human glioblastoma cell lines obtained from neurosurgery. The co-culture confirmed that human glioblastoma cells as well as astrocytes maintained the ability to support neuritogenesis, but non-neural normal or tumoral cells failed to do so. However, glioblastoma cells did not distinguish embryonic from post-natal neurons in relation to neurite pattern in the co-cultures, as normal astrocytes did. Further, the laminin organization on both normal and tumoral glial cells was altered from a filamentous arrangement to a mixed punctuate/filamentous pattern when in co-culture with neurons. Together, these results suggest that glioblastoma cells could identify neuronal cells as partners, to support their growth and induce complex neurites, but they lost the normal glia property to distinguish neuronal age. In addition, our results show for the first time that neurons modulate the organization of astrocytes and glioblastoma laminin on the extracellular matrix.