Constitutive EGFR signaling confers a motile phenotype to neural stem cells

The Potentials and Pitfalls of Using Adult Stem Cells in Cancer Treatment

Stem cells play a pivotal role in the developmental stages of an organism and in adulthood as well. Therefore, it is not surprising that stem cells constitute a focus of extensive research. Indeed, several decades of stem cell research have tremendously increased our knowledge on the mechanistic understandings of stem cell biology. Interestingly, revealing the fundamental principles of stem cell biology has also fostered its application for therapeutic purposes. Many of the attributes that the stem cells possess, some of which are unique, allow multifaceted exploitation of stem cells in the treatment of various diseases. Cancer, the leading cause of mortality worldwide, is one of the disease groups that has been benefited by the potentials of therapeutic applications of the stem cells. While the modi operandi of how stem cells contribute to cancer treatment are many-sided, two major principles can be conceived. One mode involves harnessing the regenerative power of the stem cells to promote the generation of blood-forming cells in cancer patients after cytotoxic regimens. A totally different kind of utility of stem cells has been exercised in another mode where the stem cells can potentially deliver a plethora of anti-cancer therapeutics in a tumor-specific manner. While both these approaches can improve the treatment of cancer patients, there exist several issues that warrant further research. This review summarizes the basic principles of the utility of the stem cells in cancer treatment along with the current trends and pinpoints the major obstacles to focus on in the future for further improvement.

Gaps and Doubts in Search to Recognize Glioblastoma Cellular Origin and Tumor Initiating Cells

Cellular origin of glioblastoma (GB) is constantly discussed and remains a controversial subject. Unfortunately, neurobiologists are not consistent in defining neural stem cells (NSC) complicating this issue even further. Nevertheless, some suggestions referring to GB origin can be proposed based on comparing GB to central nervous system (CNS) cells. Firstly, GB cells show in vitro differentiation pattern similar to GFAP positive neural cells, rather than classical (GFAP negative) NSC. GB cells in primary cultures become senescent in vitro, similar to GFAP positive neural progenitors, whereas classical NSC proliferate in vitro infinitely. Classical NSC apoptosis triggered by introduction of IDH1R132H undermines hypothesis stating that IDH-mutant (secondary) GB origins from these NSC. Analysis of biological role of typical IDH-wildtype (primary) GB oncogene such as EGFRvIII also favors GFAP positive cells rather than classical NSC as source of GB. Single-cell NGS and single-cell transcriptomics also suggest that GFAP positive cells are GB origin. Considering the above-mentioned and other discussed in articles data, we suggest that GFAP positive cells (astrocytes, radial glia, or GFAP positive neural progenitors) are more likely to be source of GB than classical GFAP negative NSC, and further in vitro assays should be focused on these cells. It is highly possible that several populations of tumor initiating cells (TIC) exist within GB, adjusting their phenotype and even genotype to various environmental conditions including applied therapy and periodically going through different TIC states as well as non-TIC state. This adjustment is driven by changes in number and types of amplicons. The existence of various populations of TIC would enable creating neoplastic foci in different environments and increase tumor aggressiveness.

Pilot Trial of Adoptive Transfer of Chimeric Antigen Receptor-transduced T Cells Targeting EGFRvIII in Patients With Glioblastoma

A deletion variant of epidermal growth factor receptor (EGFRvIII) is a known driver mutation in a subset of primary and secondary glioblastoma multiforme. Adoptive transfer of genetically modified chimeric antigen receptor (CAR) lymphocytes has demonstrated efficacy in hematologic malignancies but is still early in development for solid cancers. The surface expression of the truncated extracellular ligand domain created by EGFRvIII makes it an attractive target for a CAR-based cancer treatment. Patients with recurrent glioblastoma expressing EGFRvIII were enrolled in a dose escalation phase I trial, using a third-generation CAR construct derived from a human antibody. Transduced cells were administered after lymphodepleting chemotherapy and supported posttransfer with intravenous interleukin-2. The dose escalation proceeded at half-log increments from 10 to >10 cells. Primary endpoints were safety and progression-free survival. Eighteen patients were treated with final infusion products ranging from 6.3×10 to 2.6×10 anti-EGFRvIII CAR T cells. Median progression-free survival was 1.3 months (interquartile range: 1.1-1.9), with a single outlier of 12.5 months. Two patients experienced severe hypoxia, including one treatment-related mortality after cell administration at the highest dose level. All patients developed expected transient hematologic toxicities from preparative chemotherapy. Median overall survival was 6.9 months (interquartile range: 2.8-10). Two patients survived over 1 year, and a third patient was alive at 59 months. Persistence of CAR cells correlated with cell dose, but there were no objective responses. Administration of anti-EGFRvIII CAR-transduced T cells did not demonstrate clinically meaningful effect in patients with glioblastoma multiforme in this phase I pilot trial.

Mechanisms of Resistance to EGFR Inhibition Reveal Metabolic Vulnerabilities in Human GBM

Amplification of the epidermal growth factor receptor gene (EGFR) represents one of the most commonly observed genetic lesions in glioblastoma (GBM); however, therapies targeting this signaling pathway have failed clinically. Here, using human tumors, primary patient-derived xenografts (PDX), and a murine model for GBM, we demonstrate that EGFR inhibition leads to increased invasion of tumor cells. Further, EGFR inhibitor-treated GBM demonstrates altered oxidative stress, with increased lipid peroxidation, and generation of toxic lipid peroxidation products. A tumor cell subpopulation with elevated aldehyde dehydrogenase (ALDH) levels was determined to comprise a significant proportion of the invasive cells observed in EGFR inhibitor-treated GBM. Our analysis of the ALDH1A1 protein in newly diagnosed GBM revealed detectable ALDH1A1 expression in 69% (35/51) of the cases, but in relatively low percentages of tumor cells. Analysis of paired human GBM before and after EGFR inhibitor therapy showed an increase in ALDH1A1 expression in EGFR-amplified tumors (P < 0.05, n = 13 tumor pairs), and in murine GBM ALDH1A1-high clones were more resistant to EGFR inhibition than ALDH1A1-low clones. Our data identify ALDH levels as a biomarker of GBM cells with high invasive potential, altered oxidative stress, and resistance to EGFR inhibition, and reveal a therapeutic target whose inhibition should limit GBM invasion.

Challenges and potential of PD-1/PD-L1 checkpoint blockade immunotherapy for glioblastoma

PD-1/PD-L1 checkpoint blockades have achieved significant progress in several kinds of tumours. Pembrolizumab, which targets PD-1, has been approved as a first-line treatment for advanced non-small cell lung cancer (NSCLC) patients with positive PD-L1 expression. However, PD-1/PD-L1 checkpoint blockades have not achieved breakthroughs in treating glioblastoma because glioblastoma has a low immunogenic response and an immunosuppressive microenvironment caused by the precise crosstalk between cytokines and immune cells. A phase III clinical trial, Checkmate 143, reported that nivolumab, which targets PD-1, did not demonstrate survival benefits compared with bavacizumab in recurrent glioblastoma patients. Thus, the combination of a PD-1/PD-L1 checkpoint blockade with RT, TMZ, antibodies targeting other inhibitory or stimulatory molecules, targeted therapy, and vaccines may be an appealing solution aimed at achieving optimal clinical benefit. There are many ongoing clinical trials exploring the efficacy of various approaches based on PD-1/PD-L1 checkpoint blockades in primary or recurrent glioblastoma patients. Many challenges need to be overcome, including the identification of discrepancies between different genomic subtypes in their response to PD-1/PD-L1 checkpoint blockades, the selection of PD-1/PD-L1 checkpoint blockades for primary versus recurrent glioblastoma, and the identification of the optimal combination and sequence of combination therapy. In this review, we describe the immunosuppressive molecular characteristics of the tumour microenvironment (TME), candidate biomarkers of PD-1/PD-L1 checkpoint blockades, ongoing clinical trials and challenges of PD-1/PD-L1 checkpoint blockades in glioblastoma.

Drosophila melanogaster as a Model System for Human Glioblastomas

Glioblastoma multiforme (GBM) is the most common primary malignant adult brain tumor. Genomic amplifications, activating mutations, and overexpression of receptor tyrosine kinases (RTKs) such as EGFR, and genes in core RTK signaling transduction pathways such as PI3K are common in GBM. However, efforts to target these pathways have been largely unsuccessful in the clinic, and the median survival of GBM patients remains poor at 14-15 months. Therefore, to improve patient outcomes, there must be a concerted effort to elucidate the underlying biology involved in GBM tumorigenesis. Drosophila melanogaster has been a highly effective model for furthering our understanding of GBM tumorigenesis due to a number of experimental advantages it has over traditional mouse models. For example, there exists extensive cellular and genetic homology between humans and Drosophila, and 75% of genes associated with human disease have functional fly orthologs. To take advantage of these traits, we developed a Drosophila GBM model with constitutively active variants of EGFR and PI3K that effectively recapitulated key aspects of GBM disease. Researchers have utilized this model in forward genetic screens and have expanded on its functionality to make a number of important discoveries regarding requirements for key components in GBM tumorigenesis, including genes and pathways involved in extracellular matrix signaling, glycolytic metabolism, invasion/migration, stem cell fate and differentiation, and asymmetric cell division. Drosophila will continue to reveal novel biological pathways and mechanisms involved in gliomagenesis, and this knowledge may contribute to the development of effective treatment strategies to improve patient outcomes.

Vascular endothelial growth factor activates neural stem cells through epidermal growth factor receptor signal after spinal cord injury

AIMS

Neural stem cells (NSCs) in the adult mammalian spinal cord are activated in response to spinal cord injury (SCI); however, mechanisms modulating this process are not clear. Here, we noticed SCI elevated expression of vascular endothelial growth factor (VEGF) and we aimed to validate the roles of VEGF in NSCs activation after SCI and investigated the related signals during the process.

METHODS

In vitro we detected whether VEGF promoted spinal cord NSCs proliferation and investigated the involved signals; In vivo, we injected VEGF into rat spinal cord to check the NSCs activation.

RESULTS

In vitro, VEGF triggered spinal cord NSCs proliferation and maintained self-renewal. Further investigations demonstrated VEGF transactivated epidermal growth factor receptor (EGFR) through VEGF receptor 2 (VEGFR2) to promote spinal cord NSCs proliferation. In vivo, we injected VEGF into spinal cord by laminectomy to confirm the roles of VEGF-VEGFR2-EGFR signals in NSCs activation. VEGF significantly elevated the number of activated NSCs and increased EGFR phosphorylation. In contrast, intraspinal injection of specific inhibitors targeting EGFR and VEGFR2 decreased NSCs activation after SCI. Our results demonstrate that VEGF-VEGFR2-EGFR axis is important for NSCs activation after SCI, providing new insights into the mechanisms of spinal cord NSCs activation postinjury.

A Rationally Designed Fully Human EGFRvIII:CD3-Targeted Bispecific Antibody Redirects Human T Cells to Treat Patient-derived Intracerebral Malignant Glioma

Purpose: Conventional therapy for malignant glioma fails to specifically target tumor cells. In contrast, substantial evidence indicates that if appropriately redirected, T cells can precisely eradicate tumors. Here we report the rational development of a fully human bispecific antibody (hEGFRvIII-CD3 bi-scFv) that redirects human T cells to lyse malignant glioma expressing a tumor-specific mutation of the EGFR (EGFRvIII).Experimental Design: We generated a panel of bispecific single-chain variable fragments and optimized design through successive rounds of screening and refinement. We tested the ability of our lead construct to redirect naïve T cells and induce target cell-specific lysis. To test for efficacy, we evaluated tumor growth and survival in xenogeneic and syngeneic models of glioma. Tumor penetrance following intravenous drug administration was assessed in highly invasive, orthotopic glioma models.Results: A highly expressed bispecific antibody with specificity to CD3 and EGFRvIII was generated (hEGFRvIII-CD3 bi-scFv). Antibody-induced T-cell activation, secretion of proinflammatory cytokines, and proliferation was robust and occurred exclusively in the presence of target antigen. hEGFRvIII-CD3 bi-scFv was potent and target-specific, mediating significant lysis of multiple malignant glioma cell lines and patient-derived malignant glioma samples that heterogeneously express EGFRvIII. In both subcutaneous and orthotopic models, well-engrafted, patient-derived malignant glioma was effectively treated despite heterogeneity of EGFRvIII expression; intravenous hEGFRvIII-CD3 bi-scFv administration caused significant regression of tumor burden (P < 0.0001) and significantly extended survival (P < 0.0001). Similar efficacy was obtained in highly infiltrative, syngeneic glioma models, and intravenously administered hEGFRvIII-CD3 bi-scFv localized to these orthotopic tumors.Conclusions: We have developed a clinically translatable bispecific antibody that redirects human T cells to safely and effectively treat malignant glioma. On the basis of these results, we have developed a clinical study of hEGFRvIII-CD3 bi-scFv for patients with EGFRvIII-positive malignant glioma. Clin Cancer Res; 24(15); 3611-31. ©2018 AACR.

A transcriptome comparison of time-matched developing human, mouse and rat neural progenitor cells reveals human uniqueness

It is widely accepted that human brain development has unique features that cannot be represented by rodents. Obvious reasons are the evolutionary distance and divergent physiology. This might lead to false predictions when rodents are used for safety or pharmacological efficacy studies. For a better translation of animal-based research to the human situation, human in vitro systems might be useful. In this study, we characterize developing neural progenitor cells from prenatal human and time-matched rat and mouse brains by analyzing the changes in their transcriptome profile during neural differentiation. Moreover, we identify hub molecules that regulate neurodevelopmental processes like migration and differentiation. Consequences of modulation of three of those hubs on these processes were studied in a species-specific context. We found that although the gene expression profiles of the three species largely differ qualitatively and quantitatively, they cluster in similar GO terms like cell migration, gliogenesis, neurogenesis or development of multicellular organism. Pharmacological modulation of the identified hub molecules triggered species-specific cellular responses. This study underlines the importance of understanding species differences on the molecular level and advocates the use of human based in vitro models for pharmacological and toxicological research.

GBM heterogeneity as a function of variable epidermal growth factor receptor variant III activity

Abnormal activation of the epidermal growth factor receptor (EGFR) due to a deletion of exons 2-7 of EGFR (EGFRvIII) is a common alteration in glioblastoma (GBM). While this alteration can drive gliomagenesis, tumors harboring EGFRvIII are heterogeneous. To investigate the role for EGFRvIII activation in tumor phenotype we used a neural progenitor cell-based murine model of GBM driven by EGFR signaling and generated tumor progenitor cells with high and low EGFRvIII activation, pEGFR^Hi and pEGFR^Lo. In vivo, ex vivo, and in vitro studies suggested a direct association between EGFRvIII activity and increased tumor cell proliferation, decreased tumor cell adhesion to the extracellular matrix, and altered progenitor cell phenotype. Time-lapse confocal imaging of tumor cells in brain slice cultures demonstrated blood vessel co-option by tumor cells and highlighted differences in invasive pattern. Inhibition of EGFR signaling in pEGFR^Hi promoted cell differentiation and increased cell-matrix adhesion. Conversely, increased EGFRvIII activation in pEGFR^Lo reduced cell-matrix adhesion. Our study using a murine model for GBM driven by a single genetic driver, suggests differences in EGFR activation contribute to tumor heterogeneity and aggressiveness.

In vitro antineoplastic effects of brivaracetam and lacosamide on human glioma cells

Background

Epilepsy is a frequent symptom in patients with glioma. Although treatment with antiepileptic drugs is generally effective in controlling seizures, drug-resistant patients are not uncommon. Multidrug resistance proteins (MRPs) and P-gp are over-represented in brain tissue of patients with drug-resistant epilepsy, suggesting their involvement in the clearance of antiepileptic medications. In addition to their anticonvulsant action, some drugs have been documented for cytotoxic effects. Aim of this study was to evaluate possible in vitro cytotoxic effects of two new-generation antiepileptic drugs on a human glioma cell line U87MG.

Methods

Cytotoxicity of brivaracetam and lacosamide was tested on U87MG, SW1783 and T98G by MTS assay. Expression of chemoresistance molecules was evaluated using flow cytometry in U87MG and human umbilical vein endothelial cells (HUVECs). To investigate the putative anti-proliferative effect, apoptosis assay, microRNA expression profile and study of cell cycle were performed.

Results

Brivaracetam and lacosamide showed a dose-dependent cytotoxic and anti-migratory effects. Cytotoxicity was not related to apoptosis. The exposure of glioma cells to brivaracetam and lacosamide resulted in the modulation of several microRNAs; particularly, the effect of miR-195-5p modulation seemed to affect cell cycle, while miR-107 seemed to be implicated in the inhibition of cells migration. Moreover, brivaracetam and lacosamide treatment did not modulate the expression of chemoresistance-related molecules MRPs1-3-5, GSTπ, P-gp on U87MG and HUVECs.

Conclusion

Based on antineoplastic effect of brivaracetam and lacosamide on glioma cells, we assume that patients with glioma could benefit by the treatment with these two molecules, in addition to standard therapeutic options.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0546-9) contains supplementary material, which is available to authorized users.

Emerging immunotherapies for glioblastoma

INTRODUCTION

Immunotherapy for brain cancer has evolved dramatically over the past decade, owed in part to our improved understanding of how the immune system interacts with tumors residing within the central nervous system (CNS). Glioblastoma (GBM), the most common primary malignant brain tumor in adults, carries a poor prognosis (<15 months) and only few advances have been made since the FDA's approval of temozolomide (TMZ) in 2005. Importantly, several immunotherapies have now entered patient trials based on promising preclinical data, and recent studies have shed light on how GBM employs a slew of immunosuppressive mechanisms that may be targeted for therapeutic gain. Altogether, accumulating evidence suggests immunotherapy may soon earn its keep as a mainstay of clinical management for GBM.

AREAS COVERED

Here, we review cancer vaccines, checkpoint inhibitors, adoptive T-cell immunotherapy, and oncolytic virotherapy.

EXPERT OPINION

Checkpoint blockade induces antitumor activity by preventing negative regulation of T-cell activation. This platform, however, depends on an existing frequency of tumor-reactive T cells. GBM tumors are exceptionally equipped to prevent this, occupying low levels of antigen expression and elaborate mechanisms of immunosuppression. Therefore, checkpoint blockade may be most effective when used in combination with a DC vaccine or adoptively transferred tumor-specific T cells generated ex vivo. Both approaches have been shown to induce endogenous immune responses against tumor antigens, providing a rationale for use with checkpoint blockade where both primary and secondary responses may be potentiated.

In Vivo Detection of EGFRvIII in Glioblastoma via Perfusion Magnetic Resonance Imaging Signature Consistent with Deep Peritumoral Infiltration: The φ-Index

Purpose: The epidermal growth factor receptor variant III (EGFRvIII) mutation has been considered a driver mutation and therapeutic target in glioblastoma, the most common and aggressive brain cancer. Currently, detecting EGFRvIII requires postoperative tissue analyses, which are ex vivo and unable to capture the tumor's spatial heterogeneity. Considering the increasing evidence of in vivo imaging signatures capturing molecular characteristics of cancer, this study aims to detect EGFRvIII in primary glioblastoma noninvasively, using routine clinically acquired imaging.Experimental Design: We found peritumoral infiltration and vascularization patterns being related to EGFRvIII status. We therefore constructed a quantitative within-patient peritumoral heterogeneity index (PHI/φ-index), by contrasting perfusion patterns of immediate and distant peritumoral edema. Application of φ-index in preoperative perfusion scans of independent discovery (n = 64) and validation (n = 78) cohorts, revealed the generalizability of this EGFRvIII imaging signature.Results: Analysis in both cohorts demonstrated that the obtained signature is highly accurate (89.92%), specific (92.35%), and sensitive (83.77%), with significantly distinctive ability (P = 4.0033 × 10^-10, AUC = 0.8869). Findings indicated a highly infiltrative-migratory phenotype for EGFRvIII⁺ tumors, which displayed similar perfusion patterns throughout peritumoral edema. Contrarily, EGFRvIII^- tumors displayed perfusion dynamics consistent with peritumorally confined vascularization, suggesting potential benefit from extensive peritumoral resection/radiation.Conclusions: This EGFRvIII signature is potentially suitable for clinical translation, since obtained from analysis of clinically acquired images. Use of within-patient heterogeneity measures, rather than population-based associations, renders φ-index potentially resistant to inter-scanner variations. Overall, our findings enable noninvasive evaluation of EGFRvIII for patient selection for targeted therapy, stratification into clinical trials, personalized treatment planning, and potentially treatment-response evaluation. Clin Cancer Res; 23(16); 4724-34. ©2017 AACR.

EGFR as a Target for Glioblastoma Treatment: An Unfulfilled Promise

The receptor for epidermal growth factor (EGFR) is a prime target for cancer therapy across a broad variety of tumor types. As it is a tyrosine kinase, small molecule tyrosine kinase inhibitors (TKIs) targeting signal transduction, as well as monoclonal antibodies against the EGFR, have been investigated as anti-tumor agents. However, despite the long-known enigmatic EGFR gene amplification and protein overexpression in glioblastoma, the most aggressive intrinsic human brain tumor, the potential of EGFR as a target for this tumor type has been unfulfilled. This review analyses the attempts to use TKIs and monoclonal antibodies against glioblastoma, with special consideration given to immunological approaches, the use of EGFR as a docking molecule for conjugates with toxins, T-cells, oncolytic viruses, exosomes and nanoparticles. Drug delivery issues associated with therapies for intracerebral diseases, with specific emphasis on convection enhanced delivery, are also discussed.

Comparative effect of immature neuronal or glial cell transplantation on motor functional recovery following experimental traumatic brain injury in rats

The present study evaluated the comparative effect of stereotaxically transplanted immature neuronal or glial cells in brain on motor functional recovery and cytokine expression after cold-induced traumatic brain injury (TBI) in adult rats. A total of 60 rats were divided into four groups (n=15/group): Sham group; TBI only group; TBI plus neuronal cells-transplanted group (NC-G); and TBI plus glial cells-transplanted group (GC-G). Cortical lesions were induced by a touching metal stamp, frozen with liquid nitrogen, to the dura mater over the motor cortex of adult rats. Neuronal and glial cells were isolated from rat embryonic and newborn cortices, respectively, and cultured in culture flasks. Rats received neurons or glia grafts (~1×10⁶ cells) 5 days after TBI was induced. Motor functional evaluation was performed with the rotarod test prior to and following glial and neural cell grafts. Five rats from each group were sacrificed at 2, 4 and 6 weeks post-cell transplantation. Immunofluorescence staining was performed on brain section to identify the transplanted neuronal or glial cells using neural and astrocytic markers. The expression levels of cytokines, including transforming growth factor-β, glial cell-derived neurotrophic factor and vascular endothelial growth factor, which have key roles in the proliferation, differentiation and survival of neural cells, were analyzed by immunohistochemistry and western blotting. A localized cortical lesion was evoked in all injured rats, resulting in significant motor deficits. Transplanted cells successfully migrated and survived in the injured brain lesion, and the expression of neuronal and astrocyte markers were detected in the NC-G and GC-G groups, respectively. Rats in the NC-G and GC-G cell-transplanted groups exhibited significant motor functional recovery and reduced histopathologic lesions, as compared with the TBI-G rats that did not receive neural cells (P<0.05, respectively). Furthermore, GC-G treatment induced significantly improved motor functional recovery, as compared with the NC-G group (P<0.05). Increased cytokine expression levels were detected in the NC-G and GC-G groups, as compared with the TBI-G; however, no differences were found between the two groups. These data suggested that transplanted immature neural cells may promote the survival of neural cells in cortical lesion and motor functional recovery. Furthermore, transplanted glial cells may be used as an effective therapeutic tool for TBI patients with abnormalities in motor functional recovery and cytokine expression.

EGFRvIII mutations can emerge as late and heterogenous events in glioblastoma development and promote angiogenesis through Src activation

BACKGROUND

Amplification of the epidermal growth factor receptor (EGFR) and its mutant EGFRvIII are among the most common genetic alterations in glioblastoma (GBM), the most frequent and most aggressive primary brain tumor.

METHODS

In the present work, we analyzed the clonal evolution of these major EGFR aberrations in a small cohort of GBM patients using a unique surgical multisampling technique. Furthermore, we overexpressed both receptors separately and together in 2 patient-derived GBM stem cell lines (GSCs) to analyze their functions in vivo in orthotopic xenograft models.

RESULTS

In human GBM biopsies, we identified EGFR amplification as an early event because EGFRvIII mutations emerge from intratumoral heterogeneity later in tumor development. To investigate the biological relevance of this distinct developmental pattern, we established experimental model systems. In these models, EGFR⁺ tumor cells showed activation of classical downstream signaling pathways upon EGF stimulation and displayed enhanced invasive growth without evidence of angiogenesis in vivo. In contrast, EGFRvIII⁺ tumors were driven by activation of the prototypical Src family kinase c-Src that promoted VEGF secretion leading to angiogenic tumor growth.

CONCLUSIONS

The presented work shows that sequential EGFR amplification and EGFRvIII mutations might represent concerted evolutionary events that drive the aggressive nature of GBM by promoting invasion and angiogenesis via distinct signaling pathways. In particular, c-SRC may be an attractive therapeutic target for tumors harboring EGFRvIII as we identified this protein specifically mediating angiogenic tumor growth downstream of EGFRvIII.

Mifepristone-inducible transgene expression in neural progenitor cells in vitro and in vivo

Numerous gene and cell therapy strategies are being developed for the treatment of neurodegenerative disorders. Many of these strategies use constitutive expression of therapeutic transgenic proteins, and although functional in animal models of disease, this method is less likely to provide adequate flexibility for delivering therapy to humans. Ligand-inducible gene expression systems may be more appropriate for these conditions, especially within the central nervous system (CNS). Mifepristone's ability to cross the blood-brain barrier makes it an especially attractive ligand for this purpose. We describe the production of a mifepristone-inducible vector system for regulated expression of transgenes within the CNS. Our inducible system used a lentivirus-based vector platform for the ex vivo production of mifepristone-inducible murine neural progenitor cells that express our transgenes of interest. These cells were processed through a series of selection steps to ensure that the cells exhibited appropriate transgene expression in a dose-dependent and temporally controlled manner with minimal background activity. Inducible cells were then transplanted into the brains of rodents, where they exhibited appropriate mifepristone-inducible expression. These studies detail a strategy for regulated expression in the CNS for use in the development of safe and efficient gene therapy for neurological disorders.

Sulfated polysaccharide isolated from the sea cucumber Stichopus japonicas promotes the SDF-1α/CXCR4 axis-induced NSC migration via the PI3K/Akt/FOXO3a, ERK/MAPK, and NF-κB signaling pathways

The present study describes a positive regulatory loop between SJP and the SDF-1α/CXCR4 axis in NSC migration. The treatment of NSCs with SJP and SDF-1α increases the cell migration capacity and promotes cell migration from the neurospheres. These effects are accompanied by the up-regulation of Nestin, N-cadherin, TLR4, TNF-α, Cyclin D1, EGFR, Alpha 6 integrin, MMP-2, MMP-9, and iNOS, including SDF-1α and CXCR4 themselves. However, these effects are blocked by AMD3100, LY294002, U0126, and PDTC. SJP enhances the SDF-1α/CXCR4 axis-induced MMP-2 and MMP-9 secretion and NO release. Results demonstrate that interaction of SJP with the SDF-1α/CXCR4 axis regulates NSC migration via the PI3K/Akt/FOXO3a, ERK-MAPK, and NF-κB signaling pathways.

Immunotherapy for malignant glioma

Malignant gliomas (MG) are the most common type of primary malignant brain tumor. Most patients diagnosed with glioblastoma (GBM), the most common and malignant glial tumor, die within 12-15 months. Moreover, conventional treatment, which includes surgery followed by radiation and chemotherapy, can be highly toxic by causing nonspecific damage to healthy brain and other tissues. The shortcomings of standard-of-care have thus created a stimulus for the development of novel therapies that can target central nervous system (CNS)-based tumors specifically and efficiently, while minimizing off-target collateral damage to normal brain. Immunotherapy represents an investigational avenue with the promise of meeting this need, already having demonstrated its potential against B-cell malignancy and solid tumors in clinical trials. T-cell engineering with tumor-specific chimeric antigen receptors (CARs) is one proven approach that aims to redirect autologous patient T-cells to sites of tumor. This platform has evolved dramatically over the past two decades to include an improved construct design, and these modern CARs have only recently been translated into the clinic for brain tumors. We review here emerging immunotherapeutic platforms for the treatment of MG, focusing on the development and application of a CAR-based strategy against GBM.

The future of glioblastoma therapy: synergism of standard of care and immunotherapy

The current standard of care for glioblastoma (GBM) is maximal surgical resection with adjuvant radiotherapy and temozolomide (TMZ). As the 5-year survival with GBM remains at a dismal <10%, novel therapies are needed. Immunotherapies such as the dendritic cell (DC) vaccine, heat shock protein vaccines, and epidermal growth factor receptor (EGFRvIII) vaccines have shown encouraging results in clinical trials, and have demonstrated synergistic effects with conventional therapeutics resulting in ongoing phase III trials. Chemoradiation has been shown to have synergistic effects when used in combination with immunotherapy. Cytotoxic ionizing radiation is known to trigger pro-inflammatory signaling cascades and immune activation secondary to cell death, which can then be exploited by immunotherapies. The future of GBM therapeutics will involve finding the place for immunotherapy in the current treatment regimen with a focus on developing strategies. Here, we review current GBM therapy and the evidence for combination of immune checkpoint inhibitors, DC and peptide vaccines with the current standard of care.

Exploiting the curative potential of adoptive T-cell therapy for cancer

Adoptive T-cell therapy (ACT) is a potent and flexible cancer treatment modality that can induce complete, durable regression of certain human malignancies. Long-term follow-up of patients receiving tumor-infiltrating lymphocytes (TILs) for metastatic melanoma reveals a substantial subset that experienced complete, lasting tumor regression - and may be cured. Increasing evidence points to mutated gene products as the primary immunological targets of TILs from melanomas. Recent technological advances permit rapid identification of the neoepitopes resulting from these somatic gene mutations and of T cells with reactivity against these targets. Isolation and adoptive transfer of these T cells may improve TIL therapy for melanoma and permit its broader application to non-melanoma tumors. Extension of ACT to other malignancies may also be possible through antigen receptor gene engineering. Tumor regression has been observed following transfer of T cells engineered to express chimeric antigen receptors against CD19 in B-cell malignancies or a T-cell receptor against NY-ESO-1 in synovial cell sarcoma and melanoma. Herein, we review recent clinical trials of TILs and antigen receptor gene therapy for advanced cancers. We discuss lessons from this experience and consider how they might be applied to realize the full curative potential of ACT.

Inhibition of epidermal growth factor signaling by the cardiac glycoside ouabain in medulloblastoma

Epidermal growth factor (EGF) signaling regulates cell growth, proliferation, and differentiation. Upon receptor binding, EGF triggers cascades of downstream signaling, including the MAPK and phosphoinositide-3-kinase (PI3K)/Akt signaling pathways. Aberrant expression/activation of EGFR is found in multiple human cancers, including medulloblastoma, the most prevalent pediatric brain cancer, and often has been associated with metastasis, poor prognosis, and resistance to chemotherapy. Na,K-ATPase is an ion pump well known for its role in intracellular ion homeostasis. Recent studies showed that Na,K-ATPase also functions as a signaling platform and revealed a role in EGFR, MAPK, and PI3K signaling. While both EGFR and Na,K-ATPase seem to modulate similar signaling pathways, cardiac glycosides that are steroid-like inhibitors of Na,K-ATPase, exhibit antiproliferative and proapoptotic properties in cancer cells. Thus, we sought to better understand the relationship between EGF and cardiac glycoside signaling. Here, we show that in medulloblastoma cells, both EGF and ouabain activate Erk1/2 and PI3K/Akt signaling. Nevertheless, in medulloblastoma cells ouabain did not transactivate EGFR as has been reported in various other cell lines. Indeed, ouabain inhibited EGF-induced Erk1/2 and Akt activation and, moreover, prevented EGF-induced formation of actin stress fibers and cell motility, probably by activating a stress signaling response. Na,K-ATPase has been proposed to act as a signaling scaffold and our studies suggest that in medulloblastoma cells Na,K-ATPase might act as a check point to integrate EGF-associated signaling pathways. Thus, Na,K-ATPase might serve as a valid target to develop novel therapeutic approaches in tumors with aberrant activation of the EGFR signaling cascades.

Antibody-based immunotherapy for malignant glioma

Conventional therapy for malignant glioma (MG) fails to specifically eliminate tumor cells, resulting in toxicity that limits therapeutic efficacy. In contrast, antibody-based immunotherapy uses the immune system to eliminate tumor cells with exquisite specificity. Increased understanding of the pathobiology of MG and the profound immunosuppression present among patients with MG has revealed several biologic targets amenable to antibody-based immunotherapy. Novel antibody engineering techniques allow for the production of fully human antibodies or antibody fragments with vastly reduced antigen-binding dissociation constants, increasing safety when used clinically as therapeutics. In this report, we summarize the use of antibody-based immunotherapy for MG. Approaches currently under investigation include the use of antibodies or antibody fragments to: (1) redirect immune effector cells to target tumor mutations, (2) inhibit immunosuppressive signals and thereby stimulate an immunological response against tumor cells, and (3) provide costimulatory signals to evoke immunologic targeting of tumor cells. These approaches demonstrate highly compelling safety and efficacy for the treatment of MG, providing a viable adjunct to current standard-of-care therapy for MG.

Differential transcriptome profile of peripheral white cells to identify biomarkers involved in oxaliplatin induced neuropathy

Anticancer chemotherapy (CT) produces non-desirable effects on normal healthy cells and tissues. Oxaliplatin is widely used in the treatment of colorectal cancer and responsible for the development of sensory neuropathy in varying degrees, from complete tolerance to chronic neuropathic symptoms. We studied the differential gene expression of peripheral leukocytes in patients receiving oxaliplatin-based chemotherapy to find genes and pathways involved in oxaliplatin-induced peripheral neuropathy. Circulating white cells were obtained prior and after three cycles of FOLFOX or CAPOX chemotherapy from two groups of patients: with or without neuropathy. RNA was purified, and transcriptomes were analyzed. Differential transcriptomics revealed a total of 502 genes, which were significantly up- or down-regulated as a result of chemotherapy treatment. Nine of those genes were expressed in only one of two situations: CSHL1, GH1, KCMF1, IL36G and EFCAB8 turned off after CT, and CSRP2, IQGAP1, GNRH2, SMIM1 and C5orf17 turned on after CT. These genes are likely to be associated with the onset of oxaliplatin-induced peripheral neuropathy. The quantification of their expression in peripheral white cells may help to predict non-desirable side effects and, consequently, allow a better, more personalized chemotherapy.

An EGFRvIII-targeted bispecific T-cell engager overcomes limitations of the standard of care for glioblastoma

While advanced surgical techniques, radiation therapy and chemotherapeutic regimens provide a tangible benefit for patients with glioblastoma (GBM), the average survival from the time of diagnosis remains less than 15 months. Current therapy for GBM is limited by the nonspecific nature of treatment, prohibiting therapy that is aggressive and prolonged enough to eliminate all malignant cells. As an alternative, bispecific antibodies can redirect the immune system to eliminate malignant cells with exquisite potency and specificity. We have recently developed an EGF receptor variant III (EGFRvIII)-targeted bispecific antibody that redirects T cells to eliminate EGFRvIII-expressing GBM. The absolute tumor specificity of EGFRvIII and the lack of immunologic crossreactivity with healthy cells allow this therapeutic to overcome limitations associated with the nonspecific nature of the current standard of care for GBM. Evidence indicates that the molecule can exert therapeutically significant effects in the CNS following systemic administration. Additional advantages in terms of ease-of-production and off-the-shelf availability further the clinical utility of this class of therapeutics.

Cell-SELEX aptamer for highly specific radionuclide molecular imaging of glioblastoma in vivo

Glioblastoma (GBM) is the most frequent and aggressive primary adult brain tumor with poor prognosis. Epidermal growth factor receptor variant III (EGFRvIII) is the most common and highly oncogenic EGFR mutant in GBM. With the aim to generate specific molecular probes able to target EGFRvIII with high affinity, we selected four DNA aptamers (U2, U8, U19 and U31) specifically bound to U87-EGFRvIII cells that over expressed EGFRvIII with Kd values in the nanomole range by a cell-based systematic evolution of ligands by exponential enrichment (cell-SELEX) process. U87MG cells were introduced as control cells for counter selection. We further affirmed U2 and U8 identified EGFRvIII on the surface of target cells specifically. Then we radiolabeled U2 with 188Re to serve as a molecular imaging probe and observed 188Re -labeled U2 significantly targeted EGFRvIII over-expressing glioblastoma exnografts in mice. In conclusion, aptamers obtained from whole cell-SELEX strategy have great potential as molecular imaging probes that are probably beneficial to GBM diagnoses.

Rindopepimut: a promising immunotherapeutic for the treatment of glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive glial cell-derived primary tumor. Current standard of care for patients with GBM includes maximal tumor resection plus adjuvant radiotherapy and temozolomide chemotherapy, increasing median overall survival to a mere 15 months from diagnosis. Because these therapies are inherently nonspecific, there is an increased likelihood of off-target and incomplete effects; therefore, targeted modalities are required for enhanced safety and efficacy. Rindopepimut is emerging as a safe and potentially effective drug for the treatment of GBM. Rindopepimut consists of a 14-mer peptide that spans the length of EGF receptor variant III, a mutant variant of EGF receptor found on approximately 30% of primary GBM, conjugated to the carrier protein keyhole limpet hemocyanin. Vaccination with rindopepimut has been shown to specifically eliminate cells expressing EGF receptor variant III. Phase II clinical trials have suggested that vaccination of newly diagnosed GBM patients with rindopepimut plus adjuvant granulocyte-macrophage colony-stimulating factor results in prolonged progression-free and overall survival with minimal toxicity. This review will outline the development of rindopepimut, as well as the current status of this vaccine.

EGFRvIII mCAR-modified T-cell therapy cures mice with established intracerebral glioma and generates host immunity against tumor-antigen loss

PURPOSE

Chimeric antigen receptor (CAR) transduced T cells represent a promising immune therapy that has been shown to successfully treat cancers in mice and humans. However, CARs targeting antigens expressed in both tumors and normal tissues have led to significant toxicity. Preclinical studies have been limited by the use of xenograft models that do not adequately recapitulate the immune system of a clinically relevant host. A constitutively activated mutant of the naturally occurring epidermal growth factor receptor (EGFRvIII) is antigenically identical in both human and mouse glioma, but is also completely absent from any normal tissues.

EXPERIMENTAL DESIGN

We developed a third-generation, EGFRvIII-specific murine CAR (mCAR), and performed tests to determine its efficacy in a fully immunocompetent mouse model of malignant glioma.

RESULTS

At elevated doses, infusion with EGFRvIII mCAR T cells led to cures in all mice with brain tumors. In addition, antitumor efficacy was found to be dependent on lymphodepletive host conditioning. Selective blockade with EGFRvIII soluble peptide significantly abrogated the activity of EGFRvIII mCAR T cells in vitro and in vivo, and may offer a novel strategy to enhance the safety profile for CAR-based therapy. Finally, mCAR-treated, cured mice were resistant to rechallenge with EGFRvIII(NEG) tumors, suggesting generation of host immunity against additional tumor antigens.

CONCLUSION

All together, these data support that third-generation, EGFRvIII-specific mCARs are effective against gliomas in the brain and highlight the importance of syngeneic, immunocompetent models in the preclinical evaluation of tumor immunotherapies.

Differentiation of glioblastoma multiforme stem-like cells leads to downregulation of EGFR and EGFRvIII and decreased tumorigenic and stem-like cell potential

Glioblastoma multiforme (GBM) is the most common and devastating primary brain tumor among adults. Despite recent treatment progress, most patients succumb to their disease within 2 years of diagnosis. Current research has highlighted the importance of a subpopulation of cells, assigned brain cancer stem-like cells (bCSC), to play a pivotal role in GBM malignancy. bCSC are identified by their resemblance to normal neural stem cells (NSC), and it is speculated that the bCSC have to be targeted in order to improve treatment outcome for GBM patients. One hallmark of GBM is aberrant expression and activation of the epidermal growth factor receptor (EGFR) and expression of a deletion variant EGFRvIII. In the normal brain, EGFR is expressed in neurogenic areas where also NSC are located and it has been shown that EGFR is involved in regulation of NSC proliferation, migration, and differentiation. This led us to speculate if EGFR and EGFRvIII are involved in the regulation of bCSC. In this study we use GBM neurosphere cultures, known to preserve bCSC features. We demonstrate that EGFR and EGFRvIII are downregulated upon differentiation and moreover that when EGFR signaling is abrogated, differentiation is induced. Furthermore, we show that differentiation leads to decreased tumorigenic and stem cell-like potential of the neurosphere cultures and that by specifically inhibiting EGFR signaling it is possible to target the bCSC population. Our results suggest that differentiation therapy, possibly along with anti-EGFR treatment would be a feasible treatment option for patients with GBM, by targeting the bCSC population.

Receptor tyrosine kinase (RTK) signalling in the control of neural stem and progenitor cell (NSPC) development

Important developmental responses are elicited in neural stem and progenitor cells (NSPC) by activation of the receptor tyrosine kinases (RTK), including the fibroblast growth factor receptors, epidermal growth factor receptor, platelet-derived growth factor receptors and insulin-like growth factor receptor (IGF1R). Signalling through these RTK is necessary and sufficient for driving a number of developmental processes in the central nervous system. Within each of the four RTK families discussed here, receptors are activated by sets of ligands that do not cross-activate receptors of the other three families, and therefore, their activation can be independently regulated by ligand availability. These RTK pathways converge on a conserved core of signalling molecules, but differences between the receptors in utilisation of signalling molecules and molecular adaptors for intracellular signal propagation become increasingly apparent. Intracellular inhibitors of RTK signalling are widely involved in the regulation of developmental signalling in NSPC and often determine developmental outcomes of RTK activation. In addition, cellular responses of NSPC to the activation of a given RTK may be significantly modulated by signal strength. Cellular propensity to respond also plays a role in developmental outcomes of RTK signalling. In combination, these mechanisms regulate the balance between NSPC maintenance and differentiation during development and in adulthood. Attribution of particular developmental responses of NSPC to specific pathways of RTK signalling becomes increasingly elucidated. Co-activation of several RTK in developing NSPC is common, and analysis of co-operation between their signalling pathways may advance knowledge of RTK role in NSPC development.

Cells with intense EGFR staining and a high nuclear to cytoplasmic ratio are specific for infiltrative glioma: a useful marker in neuropathological practice

BACKGROUND

The differential diagnosis between infiltrative glioma (IG) and benign or curable glial lesions, such as gliosis, pilocytic astrocytoma, dysembryoplastic neuroepithelial tumor, ganglioglioma, or demyelinating disease, may be challenging for the pathologist because specific markers are lacking. Recently, we described a strong EGFR immunolabelling pattern in cells with a high nuclear to cytoplasmic ratio that enables the discrimination of low-grade IG from gliosis. The aim of this study was to extend our observation to high-grade glioma to assess whether EGFR expression pattern is of value in the discrimination of all IG from noninfiltrative glial lesions (NIG), including gliosis, benign tumors, and demyelinating disease.

METHODS

One hundred one IG and 58 NIG were compared for immunohistochemical expression of EGFR with use of an antibody that recognizes an epitope in the extracellular domain of both EGFRwt and EGFRvIII. Highly EGFR-positive cells with a high nuclear to cytoplasmic ratio were isolated and further characterized.

RESULTS

Cells with intense EGFR staining and a high nuclear to cytoplasmic ratio were significantly associated with the diagnosis of IG (P < .0001). The sensitivity and specificity of this staining pattern for the diagnosis of IG were 95% and 100%, respectively. EGFR expression was independent of IDH1 mutations and EGFR amplification. Finally, we showed that these particular cells displayed the phenotype and properties of glial progenitors and coexpressed CXCR4, a marker of invasiveness.

CONCLUSIONS

We demonstrate that cells with intense EGFR staining and a high nuclear to cytoplasmic ratio are specific criteria for the diagnosis of IG, irrespective of grade, histological subtype, and progression pathway, and their identification represents a tool to discriminate IG from benign or curable glial lesions.

Rindopepimut: anti-EGFRvIII peptide vaccine, oncolytic

Glioblastoma, the most common primary malignant brain tumor, is among the most difficult cancers to treat. Despite the aggressive standard of care, including surgical removal followed by radiotherapy with concomitant and adjuvant chemotherapy, the often sudden onset, diffuse infiltrating nature and highly malignant features of the lesion result in a median overall survival of < 15 months. Currently employed standard- of-care therapy for glioblastoma is nonspecific, leading to premature withdrawal of treatment due to off-target toxicity. Rindopepimut is a peptide-based vaccine that elicits a potent humoral and cellular immune response specifically against cells expressing EGFRvIII, a rearranged, cell-surface tyrosine kinase receptor present exclusively in glioblastoma and other common neoplasms. Several phase I and phase II clinical trials have demonstrated that vaccination with rindopepimut is safe, well tolerated and produces a highly potent immune response that effectively eradicates EGFRvIII-expressing tumor cells, leading to a 73% increase in survival among patients with newly diagnosed glioblastoma. Furthermore, temozolomide-induced lymphopenia enhances the rindopepimut-induced immune response against EGFRvIII, allowing for enhanced vaccination responses in the context of standard-of-care chemotherapy. Rindopepimut is currently undergoing evaluation in a phase III international trial for newly diagnosed glioblastoma and is under clinical investigation for recurrent glioblastoma and pediatric brain stem gliomas.

Recognition of glioma stem cells by genetically modified T cells targeting EGFRvIII and development of adoptive cell therapy for glioma

No curative treatment exists for glioblastoma, with median survival times of less than 2 years from diagnosis. As an approach to develop immune-based therapies for glioblastoma, we sought to target antigens expressed in glioma stem cells (GSCs). GSCs have multiple properties that make them significantly more representative of glioma tumors than established glioma cell lines. Epidermal growth factor receptor variant III (EGFRvIII) is the result of a novel tumor-specific gene rearrangement that produces a unique protein expressed in approximately 30% of gliomas, and is an ideal target for immunotherapy. Using PCR primers spanning the EGFRvIII-specific deletion, we found that this tumor-specific gene is expressed in three of three GCS lines. Based on the sequence information of seven EGFRvIII-specific monoclonal antibodies (mAbs), we assembled chimeric antigen receptors (CARs) and evaluated the ability of CAR-engineered T cells to recognize EGFRvIII. Three of these anti-EGFRvIII CAR-engineered T cells produced the effector cytokine, interferon-γ, and lysed antigen-expressing target cells. We concentrated development on a CAR produced from human mAb 139, which specifically recognized GSC lines and glioma cell lines expressing mutant EGFRvIII, but not wild-type EGFR and did not recognize any normal human cell tested. Using the 139-based CAR, T cells from glioblastoma patients could be genetically engineered to recognize EGFRvIII-expressing tumors and could be expanded ex vivo to large numbers, and maintained their antitumor activity. Based on these observations, a γ-retroviral vector expressing this EGFRvIII CAR was produced for clinical application.

Rindopepimut: an evidence-based review of its therapeutic potential in the treatment of EGFRvIII-positive glioblastoma

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and is universally fatal. Despite surgical resection, radiotherapy, and systemic chemotherapy, the median overall survival is less than 15 months. As current therapies are not tumor-specific, treatment commonly results in toxicity. The epidermal growth factor receptor variant III (EGFRvIII) is a naturally occurring mutant of EGFR and is expressed on approximately 20% to 30% of GBMs. As it is not expressed on normal cells, it is an ideal therapeutic target. Rindopepimut is a peptide vaccine which elicits EGFRvIII-specific humoral and cellular immune responses. Phase I and II clinical trials have demonstrated significantly higher progression-free and overall survival times in vaccinated patients with EGFRvIII-expressing GBM tumors. Side effects are minimal and mainly consist of hypersensitivity reactions. Due to the efficacy and safety of rindopepimut, it is a promising therapy for patients with GBM. Currently, rindopepimut is undergoing clinical testing in an international Phase III trial for newly diagnosed GBM and a Phase II trial for relapsed GBM.

Regulation of brain tumor dispersal by NKCC1 through a novel role in focal adhesion regulation

Glioblastoma (GB) is a highly invasive and lethal brain tumor due to its universal recurrence. Although it has been suggested that the electroneutral Na(+)-K(+)-Cl(-) cotransporter 1 (NKCC1) can play a role in glioma cell migration, the precise mechanism by which this ion transporter contributes to GB aggressiveness remains poorly understood. Here, we focused on the role of NKCC1 in the invasion of human primary glioma cells in vitro and in vivo. NKCC1 expression levels were significantly higher in GB and anaplastic astrocytoma tissues than in grade II glioma and normal cortex. Pharmacological inhibition and shRNA-mediated knockdown of NKCC1 expression led to decreased cell migration and invasion in vitro and in vivo. Surprisingly, knockdown of NKCC1 in glioma cells resulted in the formation of significantly larger focal adhesions and cell traction forces that were approximately 40% lower than control cells. Epidermal growth factor (EGF), which promotes migration of glioma cells, increased the phosphorylation of NKCC1 through a PI3K-dependant mechanism. This finding is potentially related to WNK kinases. Taken together, our findings suggest that NKCC1 modulates migration of glioma cells by two distinct mechanisms: (1) through the regulation of focal adhesion dynamics and cell contractility and (2) through regulation of cell volume through ion transport. Due to the ubiquitous expression of NKCC1 in mammalian tissues, its regulation by WNK kinases may serve as new therapeutic targets for GB aggressiveness and can be exploited by other highly invasive neoplasms.

EGFR kinase promotes acquisition of stem cell-like properties: a potential therapeutic target in head and neck squamous cell carcinoma stem cells

Members of the EGFR/ErbB family of tyrosine kinases are found to be highly expressed and deregulated in many cancers, including head and neck squamous cell carcinoma (HNSCC). The ErbB family, including EGFR, has been demonstrated to play key roles in metastasis, tumorigenesis, cell proliferation, and drug resistance. Recently, these characteristics have been linked to a small subpopulation of cells classified as cancer stem cells (CSCs) which are believed to be responsible for tumor initiation and maintenance. In this study, we investigated the possible role of EGFR as a regulator of "stemness" in HNSCC cells. Activation of EGFR by the addition of EGF ligand or ectopic expression of EGFR in two established HNSCC cell lines (UMSCC-22B and HN-1) resulted in the induction of CD44, BMI-1, Oct-4, NANOG, CXCR4, and SDF-1. Activation of EGFR also resulted in increased tumorsphere formation, a characteristic ability of cancer stem cells. Conversely, treatment with the EGFR kinase inhibitor, Gefinitib (Iressa), resulted in decreased expression of the aforementioned genes, and loss of tumorsphere-forming ability. Similar trends were observed in a 99.9% CD44 positive stem cell culture derived from a fresh HNSCC tumor, confirming our findings for the cell lines. Additionally, we found that these putative cancer stem cells, when treated with Gefitinib, possessed a lower capacity to invade and became more sensitive to cisplatin-induced death in vitro. These results suggest that EGFR plays critical roles in the survival, maintenance, and function of cancer stem cells. Drugs that target EGFR, perhaps administered in combination with conventional chemotherapy, might be an effective treatment for HNSCC.

Drosophila melanogaster as a model system for human brain cancers

Glioblastomas (GBM), the most common primary brain tumors, infiltrate the brain, grow rapidly, and are refractory to current therapies. Signature genetic lesions in glioblastomas include mutation of the epidermal growth factor receptor tyrosine kinase (EGFR) receptor tyrosine kinase and activating mutations in components of the PI-3 kinase (PI3K) pathway. Despite years of study, how these pathways specifically regulate glial pathogenesis is unclear. To address the genetic and cellular origins of this disease, a novel Drosophila GBM model has been developed in which glial progenitor cells give rise to proliferative and invasive neoplastic cells that create transplantable tumors in response to constitutive co-activation of the EGFR-Ras and PI3K pathways. Standing with a rich literature demonstrating the direct relevance of Drosophila to studies on human cancer, neurological disease, and neurodevelopment, this model represents a robust cell-type specific Drosophila neurological disease model in which malignant cells are created by mutations in genetic pathways thought to be driving forces in a homologous human disease. Using lineage analysis and cell-type specific markers, neoplastic glial cells were found to originate from committed glial progenitor cells, rather than from multipotent neuroblasts. Genetic analyses demonstrated that EGFR-Ras and PI3K induce fly glial neoplasia through activation of a combinatorial genetic network composed, in part, of other genetic pathways also commonly mutated in human glioblastomas. In the future, large-scale forward genetic screens with this model may reveal new insights into the origins and treatments of human glioblastoma.

Pro-neural miR-128 is a glioma tumor suppressor that targets mitogenic kinases

MicroRNAs (miRNAs) carry out post-transcriptional control of a multitude of cellular processes. Aberrant expression of miRNA can lead to diseases, including cancer. Gliomas are aggressive brain tumors that are thought to arise from transformed glioma-initiating neural stem cells (giNSCs). With the use of giNSCs and human glioblastoma cells, we investigated the function of miRNAs in gliomas. We identified pro-neuronal miR-128 as a candidate glioma tumor suppressor miRNA. Decreased expression of miR-128 correlates with aggressive human glioma subtypes. With a combination of molecular, cellular and in vivo approaches, we characterize miR-128's tumor suppressive role. miR-128 represses giNSC growth by enhancing neuronal differentiation. miR-128 represses growth and mediates differentiation by targeting oncogenic receptor tyrosine kinases (RTKs) epithelial growth factor receptor and platelet-derived growth factor receptor-α. Using an autochthonous glioma mouse model, we demonstrated that miR-128 repressed gliomagenesis. We identified miR-128 as a glioma tumor suppressor that targets RTK signaling to repress giNSC self-renewal and enhance differentiation.

Maintenance of EGFR and EGFRvIII expressions in an in vivo and in vitro model of human glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common, and most aggressive primary brain tumor among adults. A vast majority of the tumors express high levels of the epidermal growth factor receptor (EGFR) as a consequence of gene amplification. Furthermore, gene amplification is often associated with mutation of EGFR, and the constitutive activated deletion variant EGFRvIII is the most common EGFR mutation found in GBM. Activated EGFR signaling, through overexpression and/or mutation, is involved in increased tumorigenic potential. As such, EGFR is an attractive target for GBM therapy. However, clinical studies with EGFR inhibitors have shown inconsistent results, and as such, further knowledge regarding the role of EGFR and EGFRvIII in GBM is needed. For this, an appropriate in vivo/in vitro tumor model is required. Here, we report the establishment of an experimental GBM model in which the expressions of EGFR and EGFRvIII are maintained both in xenograft tumors growing subcutaneously on mice and in cell cultures established in stem cell conditions. With this model it will be possible to further study the role of EGFR and EGFRvIII, and response to targeted therapy, in GBM.

Epidermal growth factor receptor in glioma: signal transduction, neuropathology, imaging, and radioresistance

Aberrant epidermal growth factor receptor (EGFR) signaling is common in cancer. Increased expression of wild type and mutant EGFR is a widespread feature of diverse types of cancer. EGFR signaling in cancer has been the focus of intense investigation for decades primarily for two reasons. First, aberrant EGFR signaling is likely to play an important role in the pathogenesis of cancer, and therefore, the mechanisms of EGFR-mediated oncogenic signaling are of interest. Second, the EGFR signaling system is an attractive target for therapeutic intervention. EGFR gene amplification and overexpression are a particularly striking feature of glioblastoma (GBM), observed in approximately 40% of tumors. GBM is the most common primary malignant tumor of the central nervous system in adults. In approximately 50% of tumors with EGFR amplification, a specific EGFR mutant (EGFRvIII, also known as EGFR type III, de2-7, Delta EGFR) can be detected. This mutant is highly oncogenic and is generated from a deletion of exons 2 to 7 of the EGFR gene, which results in an in-frame deletion of 267 amino acids from the extracellular domain of the receptor. EGFRvIII is unable to bind ligand, and it signals constitutively. Although EGFRvIII has the same signaling domain as the wild type receptor, it seems to generate a distinct set of downstream signals that may contribute to an increased tumorigenicity. In this review, we discuss recent progress in key aspects of EGFR signaling in GBM, focusing on neuropathology, signal transduction, imaging of the EGFR, and the role of the EGFR in mediating resistance to radiation therapy in GBM.

The WNKs: atypical protein kinases with pleiotropic actions

WNKs are serine/threonine kinases that comprise a unique branch of the kinome. They are so-named owing to the unusual placement of an essential catalytic lysine. WNKs have now been identified in diverse organisms. In humans and other mammals, four genes encode WNKs. WNKs are widely expressed at the message level, although data on protein expression is more limited. Soon after the WNKs were identified, mutations in genes encoding WNK1 and -4 were determined to cause the human disease familial hyperkalemic hypertension (also known as pseudohypoaldosteronism II, or Gordon's Syndrome). For this reason, a major focus of investigation has been to dissect the role of WNK kinases in renal regulation of ion transport. More recently, a different mutation in WNK1 was identified as the cause of hereditary sensory and autonomic neuropathy type II, an early-onset autosomal disease of peripheral sensory nerves. Thus the WNKs represent an important family of potential targets for the treatment of human disease, and further elucidation of their physiological actions outside of the kidney and brain is necessary. In this review, we describe the gene structure and mechanisms regulating expression and activity of the WNKs. Subsequently, we outline substrates and targets of WNKs as well as effects of WNKs on cellular physiology, both in the kidney and elsewhere. Next, consequences of these effects on integrated physiological function are outlined. Finally, we discuss the known and putative pathophysiological relevance of the WNKs.