Possible future issues in the treatment of glioblastomas: special emphasis on cell migration and the resistance of migrating glioblastoma cells to apoptosis

Present and potential future adjuvant issues in high-grade astrocytic glioma treatment

Despite major advances in the management of malignant gliomas of which glioblastomas represent the ultimate grade of malignancy, they remain characterized by dismal prognoses. Glioblastoma patients have a median survival expectancy of only 14 months on the current standard treatment of surgical resection to the extent feasible, followed by adjuvant radiotherapy plus temozolomide, given concomitantly with and after radiotherapy. Malignant gliomas are associated with such dismal prognoses because glioma cells can actively migrate through the narrow extra-cellular spaces in the brain, often travelling relatively long distances, making them elusive targets for effective surgical management. Clinical and experimental data have demonstrated that invasive malignant glioma cells show a decrease in their proliferation rates and a relative resistance to apoptosis (type I programmed cell death) as compared to the highly cellular centre of the tumor, and this may contribute to their resistance to conventional pro-apoptotic chemotherapy and radiotherapy. Resistance to apoptosis results from changes at the genomic, transcriptional and post-transcriptional level of proteins, protein kinases and their transcriptional factor effectors. The PTEN/ PI3K/Akt/mTOR/NF-kappaB and the Ras/Raf/MEK/ERK signaling cascades play critical roles in the regulation of gene expression and prevention of apoptosis. Components of these pathways are mutated or aberrantly expressed in human cancer, notably glioblastomas. Monoclonal antibodies and low molecular-weight kinase inhibitors of these pathways are the most common classes of agents in targeted cancer treatment. However, most clinical trials of these agents as monotherapies have failed to demonstrate survival benefit. Despite resistance to apoptosis being closely linked to tumorigenesis, tumor cells can still be induced to die by non-apoptotic mechanisms such as necrosis, senescence, autophagy (type II programmed cell death) and mitotic catastrophe. Temozolomide brings significant therapeutic benefits in glioblastoma treatment. Part of temozolomide cytotoxic activity is exerted through pro-autophagic processes and also through the induction of late apoptosis. Autophagy, type II programmed cell death, represents an alternative mechanism to overcome, at least partly, the dramatic resistance of many cancers to pro-apoptotic-related therapies. Another way to potentially overcome apoptosis resistance is to decrease the migration of malignant glioma cells in the brain, which then should restore a level of sensitivity to pro-apoptotic drugs. Recent series of studies have supported the concept that malignant gliomas might be seen as an orchestration of cross-talks between cancer cells, microenvironment, vasculature and cancer stem cells. The present chapter focuses on (i) the major signaling pathways making glioblastomas resistant to apoptosis, (ii) the signaling pathways distinctly activated by pro-autophagic drugs as compared to pro-apoptotic ones, (iii) autophagic cell death as an alternative to combat malignant gliomas, (iv) the major scientific data already obtained by researchers to prove that temozolomide is actually a pro-autophagic and pro-apoptotic drug, (v) the molecular and cellular therapies and local drug delivery which could be used to complement conventional treatments, and a review of some of the currently ongoing clinical trials, (vi) the fact that reducing the levels of malignant glioma cell motility can restore pro-apoptotic drug sensitivity, (vii) the observation that inhibiting the sodium pump activity reduces both glioma cell proliferation and migration, (viii) the brain tumor stem cells as a target to complement conventional treatment.

Pharmacotherapy for adults with tumors of the central nervous system

Tumors of the adult central nervous system are among the most common and most chemoresistant neoplasms. Malignant tumors of the brain and spinal cord collectively account for approximately 1.3% of all cancers and 2.2% of all cancer-related deaths. Novel pharmacological approaches to nervous system tumors are urgently needed. This review presents the current approaches and challenges to successful pharmacotherapy of adults with malignant tumors of the central nervous system and discusses novel approaches aimed at overcoming these challenges.

Resistance of human glioblastoma multiforme cells to growth factor inhibitors is overcome by blockade of inhibitor of apoptosis proteins

Multiple receptor tyrosine kinases (RTKs), including PDGFR, have been validated as therapeutic targets in glioblastoma multiforme (GBM), yet inhibitors of RTKs have had limited clinical success. As various antiapoptotic mechanisms render GBM cells resistant to chemo- and radiotherapy, we hypothesized that these antiapoptotic mechanisms also confer resistance to RTK inhibition. We found that in vitro inhibition of PDGFR in human GBM cells initiated the intrinsic pathway of apoptosis, as evidenced by mitochondrial outer membrane permeabilization, but downstream caspase activation was blocked by inhibitor of apoptosis proteins (IAPs). Consistent with this, inhibition of PDGFR combined with small molecule inactivation of IAPs induced apoptosis in human GBM cells in vitro and had synergistic antitumor effects in orthotopic mouse models of GBM and in primary human GBM neurospheres. These results demonstrate that concomitant inhibition of IAPs can overcome resistance to RTK inhibitors in human malignant GBM cells, and suggest that blockade of IAPs has the potential to improve treatment outcomes in patients with GBM.

Overexpression and altered subcellular localization of autophagy-related 16-like 1 in human oral squamous-cell carcinoma: correlation with lymphovascular invasion and lymph-node metastasis

Autophagy is a dynamic process of subcellular degradation, which has recently sparked great interest because it is involved in various developmental processes and various diseases including cancer. Autophagy-related 16-like 1 is a component of a large protein complex essential for autophagosome formation. We previously applied proteomic methods to characterize differentially expressed proteins in oral squamous cell carcinoma cells and detected significantly high expression levels of autophagy-related 16-like 1 in oral squamous cell carcinoma-derived cell lines compared to human normal oral keratinocytes. In the current study, to further determine the potential involvement of autophagy-related 16-like 1 in oral squamous cell carcinoma, we evaluated the state of autophagy-related 16-like 1 protein expression in human oral premalignant lesions and primary oral squamous cell carcinomas, and correlated the results with clinicopathologic variables. Autophagy-related 16-like 1 immunoreaction was predominant in a variety of subcellular components of oral squamous cell carcinoma tissues, including the cytoplasm and plasma membrane of malignant cells (45% and 39%, respectively) and peritumoral and intratumoral stroma (52%), whereas all of the components in normal tissues had no or faint autophagy-related 16-like 1 expression. In addition, high stromal expression of autophagy-related 16-like 1 was associated significantly with lymphovascular invasion of tumor cells (P = .037) and positive lymph node status (P = .015). Furthermore, cytoplasmic and plasma membranous autophagy-related 16-like 1 were also expressed in abundance in the oral premalignant lesion cells (74% and 32%, respectively). Our finding suggests that dysregulation of autophagy-related 16-like 1 protein expression is a frequent and early event during oral carcinogenesis and could affect the malignant behavior of oral squamous cell carcinoma cells.

Active ras triggers death in glioblastoma cells through hyperstimulation of macropinocytosis

Expression of activated Ras in glioblastoma cells induces accumulation of large phase-lucent cytoplasmic vacuoles, followed by cell death. This was previously described as autophagic cell death. However, unlike autophagosomes, the Ras-induced vacuoles are not bounded by a double membrane and do not sequester organelles or cytoplasm. Moreover, they are not acidic and do not contain the autophagosomal membrane protein LC3-II. Here we show that the vacuoles are enlarged macropinosomes. They rapidly incorporate extracellular fluid-phase tracers but do not sequester transferrin or the endosomal protein EEA1. Ultimately, the cells expressing activated Ras detach from the substratum and rupture, coincident with the displacement of cytoplasm with huge macropinosome-derived vacuoles. These changes are accompanied by caspase activation, but the broad-spectrum caspase inhibitor carbobenzoxy-Val-Ala-Asp-fluoromethylketone does not prevent cell death. Moreover, the majority of degenerating cells do not exhibit chromatin condensation typical of apoptosis. These observations provide evidence for a necrosis-like form of cell death initiated by dysregulation of macropinocytosis, which we have dubbed "methuosis." An activated form of the Rac1 GTPase induces a similar form of cell death, suggesting that Ras acts through Rac-dependent signaling pathways to hyperstimulate macropinocytosis in glioblastoma. Further study of these signaling pathways may lead to the identification of other chemical and physiologic triggers for this unusual form of cell death.

Enhanced expression of NADPH oxidase Nox4 in human gliomas and its roles in cell proliferation and survival

Reactive oxygen species (ROS) have been attracting attention as mediators of various cell-signaling pathways. Nox-family NADPH oxidases have proven to be a major source of ROS production in various cell types and have crucial roles in various physiological and pathological processes. In this study, we show that Nox4, a member of Nox family, is prominently expressed in various neuroepithelial tumors by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical studies. We quantified Nox4 mRNA expression by real-time PCR in tumor specimens from 58 patients with astrocytomas and found that the expression levels of Nox4 mRNA in glioblastomas (WHO grade IV) were significantly higher than those in other astrocytomas (WHO grade II and III). In addition, we show that specific knockdown of Nox4 expression by RNA interference results in cell-growth inhibition and enhances induction of apoptosis by chemotherapeutic agents, such as cisplatin, in cultured glioma cell lines. Based on these observations, enhanced expression of Nox4 appears to be involved in cell proliferation and survival in glioma cells.

Knocking down galectin 1 in human hs683 glioblastoma cells impairs both angiogenesis and endoplasmic reticulum stress responses

Galectin (Gal) 1 is a hypoxia-regulated proangiogenic factor that also directly participates in glioblastoma cell migration. To determine how Gal-1 exerts its proangiogenic effects, we investigated Gal-1 signaling in the human Hs683 glioblastoma cell line. Galectin 1 signals through the endoplasmic reticulum transmembrane kinase/ribonuclease inositol-requiring 1alpha, which regulates the expression of oxygen-regulated protein 150. Oxygen-regulated protein 150 controls vascular endothelial growth factor maturation. Galectin 1 also modulates the expression of 7 other hypoxia-related genes (i.e. CTGF, ATF3, PPP1R15A, HSPA5, TRA1, and CYR61) that are implicated in angiogenesis. Decreasing Gal-1 expression in Hs683 orthotopic xenografts in mouse brains by siRNA administration impaired endoplasmic reticulum stress and enhanced the therapeutic benefits of the proautophagic drug temozolomide. These results suggest that decreasing Gal-1 expression (e.g. through brain delivery of nonviral infusions of anti-Gal-1 siRNA in patients) can represent an additional therapeutic strategy for glioblastoma.

Videomicroscopic extraction of specific information on cell proliferation and migration in vitro

In vitro cell imaging is a useful exploratory tool for cell behavior monitoring with a wide range of applications in cell biology and pharmacology. Combined with appropriate image analysis techniques, this approach has been shown to provide useful information on the detection and dynamic analysis of cell events. In this context, numerous efforts have been focused on cell migration analysis. In contrast, the cell division process has been the subject of fewer investigations. The present work focuses on this latter aspect and shows that, in complement to cell migration data, interesting information related to cell division can be extracted from phase-contrast time-lapse image series, in particular cell division duration, which is not provided by standard cell assays using endpoint analyses. We illustrate our approach by analyzing the effects induced by two sigma-1 receptor ligands (haloperidol and 4-IBP) on the behavior of two glioma cell lines using two in vitro cell models, i.e., the low-density individual cell model and the high-density scratch wound model. This illustration also shows that the data provided by our approach are suggestive as to the mechanism of action of compounds, and are thus capable of informing the appropriate selection of further time-consuming and more expensive biological evaluations required to elucidate a mechanism.

Cdk5-mediated regulation of the PIKE-A-Akt pathway and glioblastoma cell invasion

Isoform A of phosphatidylinositol 3-kinase enhancer (PIKE-A) is a newly identified prooncogenic factor that has been implicated in cancer cell growth. How PIKE-A activity is regulated in response to growth signal is poorly understood. Here, we demonstrate that cyclin dependent kinase 5 (Cdk5), a protein known to function mainly in postmitotic neurons, directly phosphorylates PIKE-A at Ser-279 in its GTPase domain in glioblastoma cells. This phosphorylation event stimulates PIKE-A GTPase activity and the activity of its downstream effector Akt. Growth signal activates Cdk5 and results in a Cdk5-dependent accumulation of phosphorylated PIKE-A and activation of Akt in the nucleus. Furthermore, PIKE-A phosphorylation and Cdk5 are increased in human glioblastoma specimens. Phosphorylation of PIKE-A by Cdk5 mediates growth factor-induced migration and invasion of human glioblastoma cells. Together, these findings identify PIKE as the first Cdk5 target in cancer cells, revealing a previously undescribed regulatory mechanism that mediates growth signal-induced activation of PIKE-A/Akt and tumor invasion.

Expression of coronin-3 (coronin-1C) in diffuse gliomas is related to malignancy

Coronin-3 (coronin-1C), a homotrimeric F-actin binding protein, has been shown to be important for cell migration and brain morphogenesis. Here, we present for the first time a detailed analysis of the expression pattern of coronin-3 in human brain tumours and demonstrate that coronin-3 expression correlates with malignant phenotype in diffuse gliomas. In general, the expression of coronin-3 varies in different brain tumour entities. However, in diffuse gliomas, the number of coronin-3 expressing tumour cells correlates with the degree of malignancy. High-grade gliomas, such as anaplastic astrocytomas, anaplastic oligodendrogliomas, anaplastic oligoastrocytomas and glioblastomas, show high numbers of tumour cells positive for coronin-3, while diffuse low-grade gliomas, such as diffuse astrocytomas, oligodendrogliomas and oligoastrocytomas, exhibit low numbers of coronin-3-positive tumour cells. In order to explore and verify a contribution of coronin-3 to the malignant phenotype of diffuse gliomas, we employed an efficient shRNA-mediated coronin-3 knockdown in U373 and A172 human glioblastoma cells. Coronin-3 knockdown glioblastoma cells exhibited reduced levels of cell proliferation, cell motility and invasion into extracellular matrix compared to control cells. Together, our findings demonstrate evidence for a contribution of coronin-3 expression in the malignant progression of diffuse gliomas.

BEHAB/brevican requires ADAMTS-mediated proteolytic cleavage to promote glioma invasion

Malignant gliomas are the most common and deadly primary brain tumors, due to their infiltrative invasion of the normal neural tissue that makes them virtually impossible to completely eliminate. We have previously identified and characterized the proteoglycan BEHAB/brevican in gliomas and have demonstrated that upregulation and cleavage of this CNS-specific molecule promote glioma invasion. Here, we have further investigated if the proteolytic processing of BEHAB/brevican by metalloproteases of the ADAMTS family is a necessary step in mediating its pro-invasive effect in glioma. By generating a site-specific ((396)SRG(398) --> NVY) mutant form resistant to ADAMTS cleavage, we have shown that the predominant proteolytic processing of BEHAB/brevican by glioma cells occurs only at this site. More importantly, "uncleavable" BEHAB/brevican is unable to enhance glioma cell invasion in vitro and tumor progression in vivo. In addition, our results suggest that the full-length protein and its cleavage products may act independently because the mutant form does not exert a dominant negative effect on normal BEHAB/brevican expression or cleavage. These results illustrate how the regulated processing of major components of the neural extracellular matrix has important functional implications in glioma progression. In addition, our findings underscore the relevance of the ADAMTS family of metalloproteases as attractive targets for novel pharmacological approaches in glioma therapy.

Targeting the alpha 1 subunit of the sodium pump to combat glioblastoma cells

OBJECTIVE

Ion transporters play pivotal roles in cancer cell migration in general and in glioblastomas (GBMs) in particular. However, the specific role of Na/K-ATPase (the sodium pump) and, in particular, its alpha1 subunit, has remained unexplored in GBMs.

MATERIALS AND METHODS

The expression of Na+/K+ -ATPase alpha1 in GBM clinical samples, normal brain tissue, and a human GBM cell line has been investigated. Using the novel cardenolide UNBS1450 (Unibioscreen, Brussels, Belgium), which is a ligand of the sodium pump, we have characterized the effects of inhibiting Na+/K+ -ATPase alpha1 in human GBM cells with respect to cell proliferation; morphology; impact on intracellular Na+, Ca2+, and adenosine triphosphate; and changes in the actin cytoskeleton. We have investigated the mechanism by which UNBS1450 overcomes the apoptosis resistance of GBMs and determined its anti-tumor effects in comparative studies in vitro in GBM cell viability assays and in vivo using an orthotopic human GBM xenograft model.

RESULTS

Overall, the alpha1 subunit of Na+/K+ -ATPase is highly expressed in a majority of glioblastomas compared with normal brain tissues, and by binding to this subunit in human U373-MG GBM cells, UNBS1450 impairs cell proliferation and migration via an intracellular adenosine triphosphate decrease-mediated disorganization of the actin cytoskeleton and cytotoxic proautophagic effects. UNBS1450 also significantly increases the in vivo survival of mice orthotopically grafted with U373-MG GBM cells.

CONCLUSION

Inhibition of the Na+/K+ -ATPase alpha1 subunit in human GBM cells impairs both cell migration and cell proliferation.

Phenotypic and genotypic characterization of orthotopic human glioma models and its relevance for the study of anti-glioma therapy

Most human gliomas are characterized by diffuse infiltrative growth in the brain parenchyma. Partly because of this characteristic growth pattern, gliomas are notorious for their poor response to current therapies. Many animal models for human gliomas, however, do not display this diffuse infiltrative growth pattern. Furthermore, there is a need for glioma models that represent adequate genocopies of different subsets of human gliomas (e.g., oligodendrogliomas). Here, we assessed the intracerebral growth patterns and copy number changes [using multiplex ligation-dependent probe amplification (MLPA)/comparative genomic hybridization (CGH)] of 15 human glioma lines in nude mice. Most xenografts present with compact growing lesions intracerebrally. Only the E98 and, to a lesser degree, E106 xenograft lines (propagated through subcutaneous growth) consistently produced intracerebral tumors, displaying diffuse infiltrative growth in the brain parenchyma. In contrast, four xenograft lines (E434, E468, E473 and E478), established by direct intracerebral inoculation of human glioma cells and serially propagated intracerebrally, consistently showed extensive diffuse infiltration throughout the brain. After several passages, the neoplastic cells still carry typical chromosomal aberrations [(-1p/-19q in oligodendroglioma, +7/-10 in glioblastoma multiforme (GBM)]. Especially these latter four models and the E98 line thus represent adequate geno- and phenocopies of human gliomas and form an attractive platform to investigate different therapeutic approaches in a preclinical setting.

Stem cells tropism for malignant gliomas

Various studies have demonstrated the tremendous tropism of stem cells for malignant gliomas, making these cells a potential vehicle for delivery of therapeutic genes to disseminated glioma cells. However, little is known about the mechanisms underlying the glioma-induced tropism of stem cells. Soluble factors including chemokines or growth factors released and expressed by glioma cells at least mediate the tropism of stem cells for gliomas. Here we review the possible mechanisms of stem cells tropism for malignant gliomas.

The sodium pump alpha1 subunit as a potential target to combat apoptosis-resistant glioblastomas

PURPOSE

To review the involvement of the ion transporter Na+/K+-ATPase (NaK) in the migration and proliferation of glioma cells. Preliminary studies indicate that NaK alpha1 subunits seem to be upregulated in a proportion of glioblastomas but not in normal brain tissues.

DESIGN

The present review focuses on (1) the natural resistance of migrating malignant glioma cells to apoptosis, (2) autophagic cell death as an alternative to combat malignant gliomas, (3) the fact that reducing the levels of malignant glioma cell motility can restore proapoptotic drug sensitivity,and (4) on the observation that inhibiting the NaK activity reduces both glioma cell proliferation and migration.

RESULTS

The natural ligands of the NaK are the cardiotonic steroids. A hemisynthetic derivative of 2"-oxovoruscharin (UNBS1450), a novel cardenolide, displays unique structural features, making its binding affinity to NaK alpha subunits (including alpha1) 10 to 100 times higher than that of other cardenolides. UNBS1450 markedly decreases intracellular ATP concentration in glioma cells, disorganizes the actin cytoskeleton, and leads to autophagic cell death in NaK alpha1 over-expressing glioma cells.

CONCLUSIONS

Glioblastoma patients who do not respond to chemotherapy and whose tumors over-express NaK alpha1 subunits could benefit from a treatment using ligands with marked binding affinity for the NaK alpha1 subunit.

Proautophagic drugs: a novel means to combat apoptosis-resistant cancers, with a special emphasis on glioblastomas

The therapeutic goal of cancer treatment has been to trigger tumor-selective cell death. Although cell death can be achieved not only by apoptosis (type I programmed cell death) but also by necrosis, mitotic catastrophe, and autophagy, drugs inducing apoptosis remain the main chemotherapeutic agents in medical oncology. However, cancer cells in their relentless drive to survive, hijack cell processes, resulting in apoptosis resistance, which underlies not only tumorigenesis but also the inherent resistance of certain cancers to radiotherapy and chemotherapy. Unlike apoptosis, which is a caspase-dependent process characterized by nuclear condensation and fragmentation, autophagic cell death is a caspase-independent process characterized by the accumulation of autophagic vacuoles in the cytoplasm accompanied by extensive degradation of the Golgi apparatus, the polyribosomes, and the endoplasmic reticulum, which precedes the destruction of the nucleus. The most striking evidence for proautophagic chemotherapy to overcome apoptosis resistance in cancer cells comes from the use of temozolomide, a proautophagic cytotoxic drug, which has demonstrated real therapeutic benefits in glioblastoma patients and is in clinical trials for several types of apoptosis-resistant cancers. A number of potential common targets in autophagy and apoptosis resistance pathways, that is, mammalian target of rapamycin (mTOR), phosphatidylinositol 3' kinase (PI3K), and Akt have been identified. Thus, further success in certain devastating cancers might be achieved by the combination of proautophagic drugs such as temozolomide with mTOR, PI3K, or Akt inhibitors, or with endoplasmic reticulum stress inhibitors as adjuvant chemotherapies.

In vivo tracking of superparamagnetic iron oxide nanoparticle–labeled mesenchymal stem cell tropism to malignant gliomas using magnetic resonance imaging

Object

Mesenchymal stem cells (MSCs) have been shown to migrate toward tumors, but their distribution pattern in gliomas has not been completely portrayed. The primary purpose of the study was to assay the tropism capacity of MSCs to gliomas, to delineate the pattern of MSC distribution in gliomas after systemic injection, and to track the migration and incorporation of magnetically labeled MSCs using 1.5-T magnetic resonance (MR) imaging.

Methods

The MSCs from Fischer 344 rats were colabeled with superparamagnetic iron oxide nanoparticles (SPIO) and enhanced green fluorescent protein (EGFP). The tropism capacity of MSCs was quantitatively assayed in vitro using the Transwell system. To track the migration of MSCs in vivo, MR imaging was performed both 7 and 14 days after systemic administration of labeled MSCs. After MR imaging, the distribution patterns of MSCs in rats with gliomas were examined using Prussian blue and fluorescence staining.

Results

The in vitro study showed that MSCs possessed significantly greater migratory capacity than fibroblast cells (p < 0.001) and that lysis of F98 glioma cells and cultured F98 cells showed a greater capacity to induce migration of cells than other stimuli (p < 0.05). Seven days after MSC transplantation, the SPIO–EGFP colabeled cells were distributed throughout the tumor, where a well-defined dark hypointense region was represented on gradient echo sequences. After 14 days, most of the colabeled MSCs were found at the border between the tumor and normal parenchyma, which was represented on gradient echo sequences as diluted amorphous dark areas at the edge of the tumors.

Conclusions

This study demonstrated that systemically transplanted MSCs migrate toward gliomas with high specificity in a temporal–spatial pattern, which can be tracked using MR imaging.

Inhibition of angiogenesis and invasion in malignant gliomas

Malignant gliomas confer a dismal prognosis. As the molecular events that underlie tumor angiogenesis are elucidated, angiogenesis inhibition is emerging as a promising therapy for recurrent and newly diagnosed tumors. Data from animal studies suggest that angiogenesis inhibition may promote an invasive phenotype in tumor cells. This may represent an important mechanism of resistance to antiangiogenic therapies. Recent studies have begun to clarify the mechanisms by which glioma cells detach from the tumor mass, remodel the extracellular matrix and infiltrate normal brain. An array of potential therapeutic targets exists. Combination therapy with antiangiogenic and novel anti-invasion agents is a promising approach that may produce a synergistic antitumor effect and a survival benefit for patients with these devastating tumors.

Malignant astrocytic glioma: genetics, biology, and paths to treatment

Malignant astrocytic gliomas such as glioblastoma are the most common and lethal intracranial tumors. These cancers exhibit a relentless malignant progression characterized by widespread invasion throughout the brain, resistance to traditional and newer targeted therapeutic approaches, destruction of normal brain tissue, and certain death. The recent confluence of advances in stem cell biology, cell signaling, genome and computational science and genetic model systems have revolutionized our understanding of the mechanisms underlying the genetics, biology and clinical behavior of glioblastoma. This progress is fueling new opportunities for understanding the fundamental basis for development of this devastating disease and also novel therapies that, for the first time, portend meaningful clinical responses.

Altering DNA base excision repair: use of nuclear and mitochondrial-targeted N-methylpurine DNA glycosylase to sensitize astroglia to chemotherapeutic agents

Primary astrocyte cultures were used to investigate the modulation of DNA repair as a tool for sensitizing astrocytes to genotoxic agents. Base excision repair (BER) is the principal mechanism by which mammalian cells repair alkylation damage to DNA and involves the processing of relatively nontoxic DNA adducts through a series of cytotoxic intermediates during the course of restoring normal DNA integrity. An adenoviral expression system was employed to target high levels of the BER pathway initiator, N-methylpurine glycosylase (MPG), to either the mitochondria or nucleus of primary astrocytes to test the hypothesis that an alteration in BER results in increased alkylation sensitivity. Increasing MPG activity significantly increased BER kinetics in both the mitochondria and nuclei. Although modulating MPG activity in mitochondria appeared to have little effect on alkylation sensitivity, increased nuclear MPG activity resulted in cell death in astrocyte cultures treated with methylnitrosourea (MNU). Caspase-3 cleavage was not detected, thus indicating that these alkylation sensitive astrocytes do not undergo a typical programmed cell death in response to MNU. Astrocytes were found to express relatively high levels of antiapoptotic Bcl-2 and Bcl-XL and very low levels of proapoptotic Bad and Bid suggesting that the mitochondrial pathway of apoptosis may be blocked making astrocytes less vulnerable to proapoptotic stimuli compared with other cell types. Consequently, this unique characteristic of astrocytes may be responsible, in part, for resistance of astrocytomas to chemotherapeutic agents.

Galectins as modulators of tumor progression in head and neck squamous cell carcinomas

Head and neck squamous cell carcinomas (HNSCCs) remain a significant cause of morbidity worldwide. Biological therapies able to induce and/or upregulate antitumor immune responses could represent a complementary approach to conventional treatments for patients with HNSCC because, despite advances in surgery, radiotherapy, and chemotherapy, the overall survival rates for these patients have not changed over recent decades. Galectins are involved in the control of cell proliferation, cell death, and cell migration and in the modulation of various functions of the immune system. In this context, galectin-1 is known to protect HNSCCs from the immune system. The present review details the involvement of galectins in HNSCC biology and suggests a number of approaches to reduce the levels of expression of galectin-1 in HNSCCs, with the aim of improving the efficiency of HNSCC immunotherapy.

New developments in the treatment of malignant gliomas

Malignant gliomas represent an heterogeneous group of brain tumors both in terms of natural history and response to treatment. The standard therapeutic approach for treating glioblastomas is a combination of radiotherapy and concomitant/adjuvant temozolomide, and methylguanine-DNA methyltransferase promoter methylation is now recognized as an important factor for predicting both prognosis and response to alkylating agents. In the future, the discovery of targeted therapies will increasingly allow personalized medical treatments. Anaplastic oligodendroglial tumors display a better prognosis and are more chemosensitive than glioblastomas; the discovery of molecular factors of prognostic significance, such as 1p/19q codeletion, will lead to different treatment strategies for different subgroups of patients. Gliomatosis cerebri is a rare diffuse glioma, and upfront chemotherapy is increasingly being employed instead of whole-brain radiotherapy to avoid/delay cognitive defects in long surviving patients, despite the lack of data to support this.

A capsid-modified, conditionally replicating oncolytic adenovirus vector expressing TRAIL Leads to enhanced cancer cell killing in human glioblastoma models

Glioblastoma multiforme (GBM) is the most aggressive brain tumor, and patients rarely survive for more than 2 years. Gene therapy may offer new treatment options and improve the prognosis for patients with GBM. Adenovirus-mediated gene therapy strategies for brain tumors have been limited by inefficient gene transfer due to low expression of the adenovirus serotype 5 (Ad5) receptor. We have used an adenovirus vector that specifically replicates in tumor cells and uses an Ad5 capsid and the adenovirus serotype (Ad35) fiber for efficient infection of malignant tumor cells. This vector also expresses adenovirus E1A and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in a tumor-specific manner. Here, we show that this oncolytic vector (Ad5/Ad35.IR-E1A/TRAIL) efficiently infects the GBM tumor cell lines SF767, T98G, and U-87 MG. Tumor cell killing was markedly enhanced with Ad5/Ad35.IR-E1A/TRAIL compared with wild-type Ad5 and Ad35 virus or Ad5/Ad35.IR-E1A- vectors without TRAIL expression in vitro. In vivo experiments using s.c. xenografted U-87 MG cells in NOD/SCID mice showed a significant growth delay of tumors after i.t. injection of Ad5/Ad35.IR-E1A/TRAIL, whereas adenovirus wild-type injections showed only marginal or no effect. Our findings indicate that the use of a capsid-modified adenoviral vector, in combination with TRAIL expression, is a promising novel approach for gene therapy of glioblastoma.

Diffuse glioma growth: a guerilla war

In contrast to almost all other brain tumors, diffuse gliomas infiltrate extensively in the neuropil. This growth pattern is a major factor in therapeutic failure. Diffuse infiltrative glioma cells show some similarities with guerilla warriors. Histopathologically, the tumor cells tend to invade individually or in small groups in between the dense network of neuronal and glial cell processes. Meanwhile, in large areas of diffuse gliomas the tumor cells abuse pre-existent "supply lines" for oxygen and nutrients rather than constructing their own. Radiological visualization of the invasive front of diffuse gliomas is difficult. Although the knowledge about migration of (tumor)cells is rapidly increasing, the exact molecular mechanisms underlying infiltration of glioma cells in the neuropil have not yet been elucidated. As the efficacy of conventional methods to fight diffuse infiltrative glioma cells is limited, a more targeted ("search & destroy") tactic may be needed for these tumors. Hopefully, the study of original human glioma tissue and of genotypically and phenotypically relevant glioma models will soon provide information about the Achilles heel of diffuse infiltrative glioma cells that can be used for more effective therapeutic strategies.

Galectin-1 Knockdown Increases Sensitivity to Temozolomide in a B16F10 Mouse Metastatic Melanoma Model

The rapid increase in the incidence of malignant melanomas has not been associated with improved therapeutic options over the years. Indeed melanomas have proven resistant to apoptosis (type I programmed cell death (PCD)) and consequently to most chemotherapy and immunotherapy. It is believed that this resistance can be partly overcome by proautophagic drugs inducing type II (autophagy) PCD. Change at the genomic, transcriptional, and post-translational level of G-proteins and protein kinases, including Ras, plays an important role in the ability of melanomas to resist apoptosis. Ras transformation itself requires membrane anchorage and the overexpression of galectin-1 increases membrane-associated Ras. In this study, it has been found that decreasing galectin-1 expression in B16F10 mouse melanoma cells in vitro by means of an anti-galectin-1 small interfering RNA approach does not modify their sensitivity to type I and type II PCD. However, it does induce heat shock protein 70-mediated lysosomal membrane permeabilization, a process associated with cathepsin B release into the cytosol, which in turn is believed to sensitize the cells to the proautophagic effects of temozolomide when grafted in vivo. Furthermore, temozolomide when compared to the proapoptotic drug cisplatin, significantly increased the survival times of mice in the B16F10 melanoma model.

Targeted drug therapy for meningiomas

✓ Although advances in surgery, radiation therapy, and stereotactic radiosurgery have significantly improved the treatment of meningiomas, there remains an important subset of patients whose tumors are refractory to conventional therapy. Treatment with traditional chemotherapeutic agents has provided minimal benefit. In this review, the role of targeted molecular therapies for recurrent or progressive meningiomas is discussed.

The Amaryllidaceae isocarbostyril narciclasine induces apoptosis by activation of the death receptor and/or mitochondrial pathways in cancer cells but not in normal fibroblasts

Our study has shown that the Amaryllidaceae isocarbostyril narciclasine induces marked apoptosis-mediated cytotoxic effects in human cancer cells but not in normal fibroblasts by triggering the activation of the initiator caspases of the death receptor pathway (caspase-8 and caspase-10) at least in human MCF-7 breast and PC-3 prostate carcinoma cells. The formation of the Fas and death receptor 4 (DR4) death-inducing signaling complex was clearly evidenced in MCF-7 and PC-3 cancer cells. Caspase-8 was found to interact with Fas and DR4 receptors on narciclasine treatment. However, narciclasine-induced downstream apoptotic pathways in MCF-7 cells diverged from those in PC-3 cells, where caspase-8 directly activated effector caspases such as caspase-3 in the absence of any further release of mitochondrial proapoptotic effectors. In contrast, in MCF-7 cells, the apoptotic process was found to require an amplification step that is mitochondria-dependent, with Bid processing, release of cytochrome c, and caspase-9 activation. It is postulated that the high selectivity of narciclasine to cancer cells might be linked, at least in part, to this activation of the death receptor pathway. Normal human fibroblasts appear approximately 250-fold less sensitive to narciclasine, which does not induce apoptosis in these cells probably due to the absence of death receptor pathway activation.

Ca2+-permeable AMPA receptors regulate growth of human glioblastoma via Akt activation

Evidence has been accumulated that glioblastoma cells release and exploit glutamate for proliferation and migration by autocrine or paracrine loops through Ca2+-permeable AMPA-type glutamate receptors. Here, we show that Ca2+ signaling mediated by AMPA receptor regulates the growth and motility of glioblastoma cells via activation of Akt. Ca2+ supplied through Ca2+-permeable AMPA receptor phosphorylated Akt at Ser-473, thereby facilitating proliferation and mobility. A dominant-negative form of Akt inhibited cell proliferation and migration accelerated by overexpression of Ca2+-permeable AMPA receptor. In contrast, introduction of a constitutively active form of Akt rescued tumor cells from apoptosis induced by the conversion of Ca2+-permeable AMPA receptor to Ca2+-impermeable receptors by the delivery of GluR2 cDNA. Therefore, Akt functions as downstream effectors for Ca2+-signaling mediated by AMPA receptor in glioblastoma cells. The activation of the glutamate-AMPA receptor-Akt pathway may contribute to the high degree of anaplasia and invasive growth of human glioblastoma. This novel pathway might give an alternative therapeutic target.

Sodium selenite induces superoxide-mediated mitochondrial damage and subsequent autophagic cell death in malignant glioma cells

Malignant gliomas are resistant to various proapoptotic therapies, such as radiotherapy and conventional chemotherapy. In this study, we show that selenite is preferentially cytotoxic to various human glioma cells over normal astrocytes via autophagic cell death. Overexpression of Akt, survivin, XIAP, Bcl-2, or Bcl-xL failed to block selenite-induced cell death, suggesting that selenite treatment may offer a potential therapeutic strategy against malignant gliomas with apoptotic defects. Before selenite-induced cell death in glioma cells, disruption of the mitochondrial cristae, loss of mitochondrial membrane potential, and subsequent entrapment of disorganized mitochondria within autophagosomes or autophagolysosomes along with degradation of mitochondrial proteins were noted, showing that selenite induces autophagy in which mitochondria serve as the main target. At the early phase of selenite treatment, high levels of superoxide anion were generated and overexpression of copper/zinc superoxide dismutase or manganese superoxide dismutase, but not catalase, significantly blocked selenite-induced mitochondrial damage and subsequent autophagic cell death. Furthermore, treatment with diquat, a superoxide generator, induced autophagic cell death in glioma cells. Taken together, our study clearly shows that superoxide anion generated by selenite triggers mitochondrial damage and subsequent mitophagy, leading to irreversible cell death in glioma cells.

The neuro-steroid, 3beta androstene 17alpha diol exhibits potent cytotoxic effects on human malignant glioma and lymphoma cells through different programmed cell death pathways

The neuro-steroids 3β-androstene-17α-diol (17α-AED), 3β-androstene-17β-diol (17β-AED), 3β-androstene-7α,-17β-triol (7α-AET) and 3β-androstene-7β,-17β-triol (7β-AET) are metabolites of dehydroepiandrosterone and are produced in neuro-ectodermal tissue. Both epimers of androstenediols (17α-AED and 17β-AED) and androstenetriols (7α-AET and 7β-AET) have markedly different biological functions of their chemical analogue. We investigated the cytotoxic activity of these neuro-steroids on human T98G and U251MG glioblastoma and U937 lymphoma cells. Proliferation studies showed that 17α-AED is the most potent inhibitor, with an IC₅₀ ∼15 μM. For T98G glioma, 90% inhibition was achieved with 25 μM of 17α-AED. Other neuro-steroids tested only marginally suppressed cell proliferation. Reduced cell adherence and viability could be detected after 18 h of 17α-AED exposure. Treatment with 17α-AED induced a significant level of apoptosis in U937 lymphoma cells, but not in the glioma cells. Cytopathology of 17α-AED-treated T98G cells revealed the presence of multiple cytoplasmic vacuoles. Acridine orange staining demonstrated the formation of acidic vesicular organelles in 17α-AED-treated T98G and U251MG, which was inhibited by bafilomycin A1. These findings indicate that 17α-AED bears the most potent cytotoxic activity of the neuro-steroids tested, and the effectiveness may depend on the number of hydroxyls and their position on the androstene molecule. These cytotoxic effects may utilize a non-apoptotic pathway in malignant glioma cells.

Cardiotonic steroids on the road to anti-cancer therapy

The sodium pump, Na(+)/K(+)-ATPase, could be an important target for the development of anti-cancer drugs as it serves as a versatile signal transducer, it is a key player in cell adhesion and its aberrant expression and activity are implicated in the development and progression of different cancers. Cardiotonic steroids, known ligands of the sodium pump have been widely used for the treatment of heart failure. However, early epidemiological evaluations and subsequent demonstration of anti-cancer activity in vitro and in vivo have indicated the possibility of developing this class of compound as chemotherapeutic agents in oncology. Their development to date as anti-cancer agents has however been impaired by a narrow therapeutic margin resulting from their potential to induce cardiovascular side-effects. The review will thus discuss (i) sodium pump structure, function, expression in diverse cancers and its chemical targeting and that of its sub-units, (ii) reported in vitro and in vivo anti-cancer activity of cardiotonic steroids, (iii) managing the toxicity of these compounds and the limitations of existing preclinical models to adequately predict the cardiotoxic potential of new molecules in man and (iv) the potential of chemical modification to reduce the cardiovascular side-effects and improve the anti-cancer activity of new molecules.

New chemotherapy options for the treatment of malignant gliomas

This review focuses on the recent advances in chemotherapy of malignant gliomas, with special emphasis on the most common primary brain tumor in adults, glioblastoma. The demonstration of the superiority of concomitant and adjuvant temozolomide with standard radiotherapy over radiotherapy alone in patients with newly diagnosed glioblastomas by means of phase III international trial has been the major advance in the care of these patients so far. Moreover, patients whose tumors display the hypermethylation of the promoter of the gene for the repairing enzyme O-methylguanine-DMA methyltransferase are most likely to benefit from the combination regimen. The advantage of a postsurgical local administration of carmustine by slow-release polymers ('gliadel wafers') is more modest, and the efficacy and safety of a sequence of carmustine wafers followed by temozolomide combined with radiotherapy remain to be defined. Different DNA repair modulation strategies are being investigated to further improve the results: dose-dense regimens of temozolomide, combination of temozolomide with specific inhibitors of O-methylguanine-DMA methyltransferase and combination of temozolomide with specific inhibitors of base excision repair [poly(ADP-ribose) polymerase inhibitors]. Other developments include the combination of cytotoxic, cytostatic and targeted therapies. Multitargeted compounds that simultaneously affect multiple signaling pathways, such as those involving epidermal growth factor receptor, platelet-derived growth factor receptor and vascular endothelial growth factor receptor, are increasingly employed. In the future, innovative trial designs (factorial and adaptative designs), pretreatment molecular profiling of individual tumors and the adoption of biological end-points (changes in serum tumor markers, measures of target inhibition), in addition to the traditional clinical and radiographic end-points, will be needed to achieve further advances.

4-IBP, a sigma1 receptor agonist, decreases the migration of human cancer cells, including glioblastoma cells, in vitro and sensitizes them in vitro and in vivo to cytotoxic insults of proapoptotic and proautophagic drugs

Although the molecular function of sigma receptors has not been fully defined and the natural ligand(s) is still not known, there is increasing evidence that these receptors and their ligands might play a significant role in cancer biology. 4-(N-benzylpiperidin-4-yl)-4-iodobenzamide (4-IBP), a selective sigma1 agonist, has been used to investigate whether this compound is able to modify: 1) in vitro the migration and proliferation of human cancer cells; 2) in vitro the sensitivity of human glioblastoma cells to cytotoxic drugs; and 3) in vivo in orthotopic glioblastoma and non-small cell lung carcinoma (NSCLC) models the survival of mice co-administered cytotoxic agents. 4-IBP has revealed weak antiproliferative effects on human U373-MG glioblastoma and C32 melanoma cells but induced marked concentration-dependent decreases in the growth of human A549 NSCLC and PC3 prostate cancer cells. The compound was also significantly antimigratory in all four cancer cell lines. This may result, at least in U373-MG cells, from modifications to the actin cytoskeleton. 4-IBP modified the sensitivity of U373-MG cells in vitro to proapoptotic lomustin and proautophagic temozolomide, and markedly decreased the expression of two proteins involved in drug resistance: glucosylceramide synthase and Rho guanine nucleotide dissociation inhibitor. In vivo, 4-IBP increased the antitumor effects of temozolomide and irinotecan in immunodeficient mice that were orthotopically grafted with invasive cancer cells.

Necrosis induction in glioblastoma cells reveals a new "bioswitch" function for the MT1-MMP/G6PT signaling axis in proMMP-2 activation versus cell death decision

Cytoskeleton disorganization is an early step in the activation process of matrix metalloproteinase 2 (MMP-2) by membrane type 1 MMP (MT1-MMP) but is also associated with endoplasmic reticulum (ER) dysfunction and subsequent cell death. Given evidence that the ER-embedded glucose-6-phosphate transporter (G6PT) regulates glioblastoma cell survival and that MT1-MMP is a key enzyme in the cancer cell invasive phenotype, we explored the molecular link between G6PT and MT1-MMP. Cytoskeleton-disrupting agents such as concanavalin A (ConA) and cytochalasin D triggered proMMP-2 activation and cell death in U87 glioma cells. ConA decreased G6PT gene expression, an event that was also observed in cells overexpressing the full-length recombinant MT1-MMP protein. Overexpression of a membrane-bound catalytically active but cytoplasmic domain-deleted MT1-MMP was unable to downregulate G6PT gene expression or to trigger necrosis. Gene silencing of MT1-MMP with small interfering RNA prevented proMMP-2 activation and induced G6PT gene expression. ConA inhibited Akt phosphorylation, whereas overexpression of recombinant G6PT rescued the cells from ConA-induced proMMP-2 activation and increased Akt phosphorylation. Altogether, new functions of MT1-MMP in cell death signaling may be linked to those of G6PT. Our study indicates a molecular signaling axis regulating the invasive phenotype of brain tumor cells and highlights a new "bioswitch" function for G6PT in cell survival.

Aberrant constitutive activation of nuclear factor kappaB in glioblastoma multiforme drives invasive phenotype

Several recent studies have shown that aberrant constitutive activation of nuclear factor kappaB (NF-kappaB) is present in a variety of cancers including gliomas. NF-kappaB is known to play important roles in the physiological regulation of diverse cellular processes such as inflammation, growth and immunity. In contrast, aberrant activation of this latent transcription factor promotes cancer cell migration, invasion and resistance to chemotherapy. Here we show by electro-mobility shift assay (EMSA) and immuno-staining that constitutive NF-kappaB activation is present in various malignant glioma cell lines as well as in primary cultures derived from tumor tissue. This activation was not serum dependent and it led to high IL-8 gene transcription and protein production. Over-expression of an I-kappaB super-repressor (I-kappaB SR) transgene completely blocked constitutive NF-kappaB activation, nuclear localization and transcription of some but not all NF-kappaB regulated genes indicating that NF-kappaB signaling in glioma cells is I-kappaB dependent. Surprisingly, over-expression of IkappaBSR did not have any effect on the transcription levels of anti-apoptotic genes in these glioma cultures and cell lines. Down-regulation of NF-kappaB activation reduced invasion of glioma cells through matrigel. Collectively these data suggest that aberrant constitutive activation of NF-kappaB in glioblastoma cells promotes their invasive phenotype. Interruption of this aberrant NF-kappaB activity may help reduce the spread of this infiltrative tumor.

Modified expression of Mts1/S100A4 protein in C6 glioma cells or surrounding astrocytes affects migration of tumor cells in vitro and in vivo

The calcium-binding Mts1/S100A4 protein plays an important role in motility and metastatic activity of tumor cells. Recently we showed that Mts1/S100A4 is expressed in white matter astrocytes and influences their migration in vitro and in vivo. Here, we have investigated the role of Mts1/S100A4 expression in C6 glioma cells or surrounding astrocytes for migration of C6 cells on astrocytes, using short interference (si) RNA to silence Mts1/S100A4 expression. We find that in vitro, the migration of Mts1/S100A4 expressing and silenced C6 cells on astrocytes is predominantly dependent on the expression of Mts1/S100A4 in astrocytes, i.e. C6 cells preferably migrate on Mts1/S100A4-silenced astrocytes. In vivo, Mts1/S100A4-positive C6 cells preferably migrate in white matter. In contrast Mts1/S100A4-silenced C6 cells avoid white matter and migrate in gray matter and meninges. Thus, the migration pattern of C6 cells is affected by their intrinsic Mts1/S100A4 expression as well as Mts1/S100A4 expression in astrocytes. To investigate if Mts1/S100A4 has a significant role on brain tumor progression, we made quantitative RT-PCR analysis for the expression of S100A4/Mts1 in various grades of astrocytic tumors. Our data showed that high-grade glioblastomas express higher amount of S100A4/Mts1 than low-grade astrocytic tumors.

Expression of cellular adhesion molecule 'OPCML' is down-regulated in gliomas and other brain tumours

The four GPI-anchored cell adhesion molecules that exemplify the IgLON family are most highly expressed in the nervous system and associate to form up to six different heterodimeric 'Diglons' that can modify cell adhesion and inhibit axon migration. Recently, two members, OPCML and LSAMP, were identified as putative tumour suppressor genes in ovarian and renal carcinomas respectively. In this study, we investigated OPCML expression in nonneoplastic brain tissue and 35 brain tumours (18 glioblastoma multiformes, five anaplastic gliomas, five meningiomas, six metastases and one medulloblastoma) and four glioma cell lines using quantitative reverse transcriptase polymerase chain reaction (RT-PCR). OPCML was highly expressed in cerebellum, less so in cerebral cortex, frontal lobe and meninges and was significantly reduced or absent in 83% of brain tumours and all cell lines compared with nonneoplastic whole brain. Two OPCML splice variants have been identified in humans, termed alpha1 and alpha2, but the latter has not been demonstrated in human neural tissues. Using PCR with specific primers, nonneoplastic brain and 3/6 of tested brain tumours expressed both splice variants, whereas the remaining brain tumours only expressed the alpha2 variant. Hypermethylation of the alpha1 OPCML promoter, associated with down-regulation of expression in ovarian tumours, did not correlate with expression levels in the subset of brain tumours tested, implying transcription of OPCML from an alternative promoter or a different mechanism of down-regulation. This study demonstrates that OPCML down-regulation occurs in the majority of brain tumours tested, warranting further investigation of OPCML and other IgLONs in the development and progression of brain tumours.

Can anti-migratory drugs be screened in vitro? A review of 2D and 3D assays for the quantitative analysis of cell migration

The aim of the present review is to detail and analyze the pros and cons of in vitro tests available to quantify the anti-migratory effects of anti-cancer drugs for their eventual use in combating the dispersal of tumor cells, a clinical need which currently remains unsatisfied. We therefore briefly sum up why anti-migratory drugs constitute a promising approach in oncology while at the same time emphasizing that migrating cancer cells are resistant to apoptosis. To analyze the pros and cons of the various in vitro tests under review we also briefly sum up the molecular and cellular stages of cancer cell migration, an approach that enables us to argue both that no single in vitro test is sufficient to characterize the anti-migratory potential of a drug and that standardization is needed for the efficient quantitative analysis of cell locomotion in a 3D environment. Before concluding our review we devote the final two parts (i) to the description of new prototypes which, in the near future, could enter the screening process with a view to identifying novel anti-migratory compounds, and (ii) to the anti-migratory compounds currently developed against cancer, with particular emphasis on how these compounds were selected before entering the clinical trial phase.

The in vitro influences of neurotensin on the motility characteristics of human U373 glioblastoma cells

Astrocytic tumours are associated with dismal prognoses due to their pronounced ability to diffusely invade the brain parenchyma. Various neuropeptides, including gastrin, are able to modulate tumour astrocyte migration. While neurotensin has been shown to influence the proliferation of glioma cells and the migratory ability of a large set of other cell types, its role in glioma cell migration has never been investigated. Neurotensin-induced modifications to the motility features of human U373 glioblastoma cells therefore constitute the topic of the present study. We evidenced that three subtypes of neurotensin receptors (NTR1, NTR2 and NTR3) are expressed in U373 glioblastoma cells, at least as far as their mRNAs are concerned. Treating U373 tumour cells with 10 nM neurotensin markedly modified the morphological patterns of these cells and also profoundly altered the organization of their actin cytoskeletons. Pull-down assays revealed that neurotensin induced the activation in U373 cells of both Rac1 and Cdc42 but not RhoA. Scratch wound assays evidenced that neurotensin (0.1 and 10 nM) very significantly inhibited wound colonization by U373 cells cultured in the absence of serum. In addition, quantitative phase-contrast videomicroscopy analyses showed that neurotensin decreases the motility levels of U373 glioblastoma cells when these cells are cultured on plastic. In sharp contrast, neurotensin stimulates the motility of U373 cells when they are cultured on laminin, which is a pro-adhesive extracellular matrix component ubiquitously secreted by glioma cells. Our data thus strongly suggest that, in addition to gastrin, neurotensin is a neuropeptide capable of modulating tumour astrocyte migration into the brain parenchyma.

New approaches to primary brain tumor treatment

Primary brain tumors represent over 100 different tumor types with widely divergent biologies and clinical outcomes, but these neoplasms frequently pose similar challenges to neuro-oncologists. Malignant gliomas are the most common type of primary intrinsic brain tumor in adults and remain extremely lethal. Current standard-of-care therapies for these cancers include surgery, radiation and palliative cytotoxics, which have significant side-effects and limited efficacy. Advances in our understanding of the molecular underpinnings of cancer have led to targeted molecular therapies that may permit improvement in therapeutic efficacy and reduced toxicity; these therapies, however, still face many challenges. Signal transduction pathways that are inappropriately regulated in brain cancers include growth factors and their receptors (e.g. epidermal growth factor receptor, vascular endothelial growth factor receptor and platelet-derived growth factor receptor), which regulate cellular interactions with the microenvironment and intracellular oncogenic pathways. Low-molecular-weight inhibitors have been developed to target many kinases and may have advantages in terms of delivery. Monoclonal antibodies may have greater specificity, but face delivery restrictions. Preferential tumor delivery of chemotherapies, conjugated toxins and radioisotopes has been achieved through convection-enhanced delivery, intratumoral implants and intra-arterial infusion. Despite these advances, few molecularly targeted therapies have demonstrated significant antineoplastic activity for a broad range of patients, possibly due to tumor and patient heterogeneity. Improved functional neuropathology and imaging may permit identification of patient subgroups for which clinical responses may be enriched. It is probable, however, that targeted therapies will be most effective in combination either with one another or with cytotoxic therapies. In this study, we review the current state of new therapies for malignant gliomas.

Activated Ras induces cytoplasmic vacuolation and non-apoptotic death in glioblastoma cells via novel effector pathways

Expression of activated H-Ras induces a unique form of non-apoptotic cell death in human glioblastoma cells and other specific tumor cell lines. The major cytopathological features of this form of death are the accumulation of large phase-lucent, LAMP1-positive, cytoplasmic vacuoles. In this study we sought to determine if induction of cytoplasmic vacuolation a) depends on Ras farnesylation, b) is specific to H-Ras, and c) is mediated by signaling through the major known Ras effector pathways. We find that the unusual effects of activated H-Ras depend on farnesylation and membrane association of the GTPase. Both H-Ras(G12V) and K-Ras4B(G12V) stimulate vacuolation, but activated forms of Cdc42 and RhoA do not. Amino acid substitutions in the Ras effector domain, which are known to selectively impair its interactions with Raf kinase, class-I phosphatidylinositide 3-kinase (PI3K), or Ral nucleotide exchange factors, initially pointed to Raf as a possible mediator of cell vacuolation. However, the MEK inhibitor, PD98059, did not block the induction of vacuoles, and constitutively active Raf-Caax did not mimic the effects of Ras(G12V). Introduction of normal PTEN together with H-Ras(G12V) into U251 glioblastoma cells reduced the PI3K-dependent activation of Akt, but had no effect on vacuolation. Finally, co-expression of H-Ras(G12V) with a dominant-negative form of RalA did not suppress vacuolation. Taken together, the observations indicate that Ras activates non-conventional and perhaps unique effector pathways to induce cytoplasmic vacuolation in glioblastoma cells. Identification of the relevant signaling pathways may uncover specific molecular targets that can be manipulated to activate non-apoptotic cell death in this type of cancer.

PLXDC1 (TEM7) is identified in a genome-wide expression screen of glioblastoma endothelium

Glioblastomas are a highly aggressive brain tumor, with one of the highest rates of new blood vessel formation. In this study we used a combined experimental and bioinformatics strategy to determine which genes were highly expressed and specific for glioblastoma endothelial cells (GBM-ECs), compared to gene expression in normal tissue and endothelium. Starting from fresh glioblastomas, several rounds of negative and positive selection were used to isolate GBM-ECs and extract total RNA. Using Serial Analysis of Gene Expression (SAGE), 116,259 transcript tags (35,833 unique tags) were sequenced. From this expression analysis, we found 87 tags that were not expressed in normal brain. Further subtraction of normal endothelium, bone marrow, white blood cell and other normal tissue transcripts resulted in just three gene transcripts, ANAPC10, PLXDC1(TEM7), and CYP27B1, that are highly specific to GBM-ECs. Immunohistochemistry with an antibody for PLXDC1 showed protein expression in GBM microvasculature, but not in the normal brain endothelium tested. Our results suggest that this study succeeded in identifying GBM-EC specific genes. The entire gene expression profile for the GBM-ECs and other tissues used in this study are available at SAGE Genie (http://cgap.nci.nih.gov/SAGE). Functionally, the protein products of the three tags most specific to GBM-ECs have been implicated in processes critical to endothelial cell proliferation and differentiation, and are potential targets for anti-angiogenesis based therapy.

Molecular biology of human gliomas

Human gliomas are the most common primary central nervous system neoplasm, and they are a complex, heterogeneous, and difficult disease to treat. In the past two decades, advances in molecular biology have revolutionized our understanding of the mechanism by which these neoplasms are initiated and progress. While surgery, radiation therapy, and chemotherapy have roles to play in the treatment of patients with gliomas; these therapies are self-limited because of the intrinsic resistance of glioma cells to therapy, and the diffusely infiltrating nature of the lesions. It is now known that malignant gliomas arise from a number of well-characterized genetic alterations and activations of oncogenes and inactivation of tumor suppressor genes. These genetic alterations disrupt critical cell cycle, growth factor activation, apoptotic, cell motility, and invasion pathways that lead to phenotypic changes and neoplastic transformation. Research in each of these fields has uncovered potential therapeutic targets that look promising for disease control. Gliomas can now be modeled with fidelity and reproducibility using several transgenic and knockout strategies. Transgenic mouse models are facilitating the testing of various therapeutic strategies in vivo. Finally, the recognition of the putative brain tumor stem cell, the tumor initiating cell in brain cancer, provides an enticing target through which we could eliminate the source of the brain tumor with increased efficacy and less toxicity to normal tissues. In this review, we provide an up-to-date discussion of the many of key technologies and tools that are being used in molecular biology to advance our understanding of the biological behavior of human malignant gliomas.

Galectin-1: a small protein with major functions

Galectins are a family of carbohydrate-binding proteins with an affinity for beta-galactosides. Galectin-1 (Gal-1) is differentially expressed by various normal and pathological tissues and appears to be functionally polyvalent, with a wide range of biological activity. The intracellular and extracellular activity of Gal-1 has been described. Evidence points to Gal-1 and its ligands as one of the master regulators of such immune responses as T-cell homeostasis and survival, T-cell immune disorders, inflammation and allergies as well as host-pathogen interactions. Gal-1 expression or overexpression in tumors and/or the tissue surrounding them must be considered as a sign of the malignant tumor progression that is often related to the long-range dissemination of tumoral cells (metastasis), to their dissemination into the surrounding normal tissue, and to tumor immune-escape. Gal-1 in its oxidized form plays a number of important roles in the regeneration of the central nervous system after injury. The targeted overexpression (or delivery) of Gal-1 should be considered as a method of choice for the treatment of some kinds of inflammation-related diseases, neurodegenerative pathologies and muscular dystrophies. In contrast, the targeted inhibition of Gal-1 expression is what should be developed for therapeutic applications against cancer progression. Gal-1 is thus a promising molecular target for the development of new and original therapeutic tools.

Related to testes-specific, vespid, and pathogenesis protein-1 (RTVP-1) is overexpressed in gliomas and regulates the growth, survival, and invasion of glioma cells

In this study, we examined the expression and functions of related to testes-specific, vespid, and pathogenesis protein 1 (RTVP-1) in glioma cells. RTVP-1 was expressed in high levels in glioblastomas, whereas its expression in low-grade astrocytomas and normal brains was very low. Transfection of glioma cells with small interfering RNAs targeting RTVP-1 decreased cell proliferation in all the cell lines examined and induced cell apoptosis in some of them. Overexpression of RTVP-1 increased astrocyte and glioma cell proliferation and the anchorage-independent growth of the cells. In addition, overexpression of RTVP-1 rendered glioma cells more resistant to the apoptotic effect of tumor necrosis factor-related apoptosis-inducing ligand and serum deprivation. To delineate the molecular mechanisms involved in the survival effects of RTVP-1, we examined the expression and phosphorylation of various apoptosis-related proteins. We found that overexpression of RTVP-1 decreased the phosphorylation of c-Jun-NH2-kinase and increased the expression of Bcl2 and that the protective effect of RTVP-1 was partially mediated by Bcl2. Finally, we found that RTVP-1 regulated the invasion of glioma cells as was evident by their enhanced migration through Matrigel and by their increased invasion in a spheroid confrontation assay. The increased invasive potential of the RTVP-1 overexpressors was also shown by the increased activity of matrix metalloproteinase 2 in these cells. Our results suggest that the expression of RTVP-1 is correlated with the degree of malignancy of astrocytic tumors and that RTVP-1 is involved in the regulation of the growth, survival, and invasion of glioma cells. Collectively, these findings suggest that RTVP-1 is a potential therapeutic target in gliomas.

Gene therapy and targeted toxins for glioma

The most common primary brain tumor in adults is glioblastoma. These tumors are highly invasive and aggressive with a mean survival time of nine to twelve months from diagnosis to death. Current treatment modalities are unable to significantly prolong survival in patients diagnosed with glioblastoma. As such, glioma is an attractive target for developing novel therapeutic approaches utilizing gene therapy. This review will examine the available preclinical models for glioma including xenographs, syngeneic and genetic models. Several promising therapeutic targets are currently being pursued in pre-clinical investigations. These targets will be reviewed by mechanism of action, i.e., conditional cytotoxic, targeted toxins, oncolytic viruses, tumor suppressors/oncogenes, and immune stimulatory approaches. Preclinical gene therapy paradigms aim to determine which strategies will provide rapid tumor regression and long-term protection from recurrence. While a wide range of potential targets are being investigated preclinically, only the most efficacious are further transitioned into clinical trial paradigms. Clinical trials reported to date are summarized including results from conditionally cytotoxic, targeted toxins, oncolytic viruses and oncogene targeting approaches. Clinical trial results have not been as robust as preclinical models predicted, this could be due to the limitations of the GBM models employed. Once this is addressed, and we develop effective gene therapies in models that better replicate the clinical scenario, gene therapy will provide a powerful approach to treat and manage brain tumors.