Neurosphere culture and human organotypic model to evaluate brain tumor stem cells

Suppression of tumour growth from transplanted astrocytoma cells transfected with luciferase in mice by bioluminescence mediated, systemic, photodynamic therapy

BACKGROUND

Grade 4 astrocytomas are usually incurable due to their diffusely infiltrative nature. Photodynamic therapy (PDT) is a promising therapeutic option, but external light delivery is impractical when cancer cells infiltrate unknown areas of normal brain. Hence the search for endogenous sources to generate light at cancer cells. In vitro, astrocytoma cells, transfected with firefly luciferase, can be killed by bioluminescence-mediated PDT (bPDT). This study asks if bPDT can suppress tumour growth In vivo, when all components of treatment are administered systemically.

METHODS

Transfected astrocytoma cells were injected subcutaneously or intra-cranially in athymic CD1 nu/nu mice. bPDT required ip bolus of mTHPC (photosensitiser) and delivery of the d-luciferin substrate over 7 days via an implanted osmotic pump. Control animals had no treatment, photosensitiser only or d-luciferin only. For subcutaneous tumours, size and BLI (light emitted after d-luciferin bolus) were measured before and every 2 days after PDT. For intracranial tumours, monitoring was weekly BLI.

RESULTS

For subcutaneous tumours, there was significant suppression of the tumour growth rate (P<0.05), and absolute tumour size (P<0.01) after bPDT. Proliferation of subcutaneous and intracranial tumours (monitored by BrdU uptake) was significantly reduced in treated mice. (P<0.001) CONCLUSIONS: This study reports bPDT suppression of tumour growth from luciferase transfected astrocytoma cells with all components of treatment given systemically, as required for effective management of recurrent astrocytomas in unknown sites. However, research on systemic bPDT is needed to establish whether effects on non-transfected tumours can be achieved without any unacceptable effects on normal tissues.

Cell-specific crosstalk proteomics reveals cathepsin B signaling as a driver of glioblastoma malignancy near the subventricular zone

Glioblastoma (GBM) is the most prevalent and aggressive malignant primary brain tumor. GBM proximal to the lateral ventricles (LVs) is more aggressive, potentially due to subventricular zone (SVZ) contact. Despite this, crosstalk between GBM and neural stem/progenitor cells (NSC/NPCs) is not well understood. Using cell-specific proteomics, we show that LV-proximal GBM prevents neuronal maturation of NSCs through induction of senescence. Additionally, GBM brain tumor initiating cells (BTICs) increase expression of CTSB upon interaction with NPCs. Lentiviral knockdown and recombinant protein experiments reveal both cell-intrinsic and soluble CTSB promote malignancy-associated phenotypes in BTICs. Soluble CTSB stalls neuronal maturation in NPCs while promoting senescence, providing a link between LV-tumor proximity and neurogenesis disruption. Finally, we show LV-proximal CTSB upregulation in patients, showing the relevance of this crosstalk in human GBM biology. These results demonstrate the value of proteomic analysis in tumor microenvironment research and provide direction for new therapeutic strategies in GBM.

Highlights

Periventricular GBM is more malignant and disrupts neurogenesis in a rodent model.Cell-specific proteomics elucidates tumor-promoting crosstalk between GBM and NPCs.NPCs induce upregulated CTSB expression in GBM, promoting tumor progression.GBM stalls neurogenesis and promotes NPC senescence via CTSB.

Perivascular invasion of primary human glioblastoma cells in organotypic human brain slices: human cells migrating in human brain

INTRODUCTION

Glioblastoma (GBM) is an aggressive primary brain cancer. Lack of effective therapy is related to its highly invasive nature. GBM invasion has been studied with reductionist systems that do not fully recapitulate the cytoarchitecture of the brain. We describe a human-derived brain organotypic model to study the migratory properties of GBM IDH-wild type ex vivo.

METHODS

Non-tumor brain samples were obtained from patients undergoing surgery (n = 7). Organotypic brain slices were prepared, and green fluorescent protein (GFP)-labeled primary human GBM IDH-wild type cells (GBM276, GBM612, GBM965) were placed on the organotypic slice. Migration was evaluated via microscopy and immunohistochemistry.

RESULTS

After placement, cells migrated towards blood vessels; initially migrating with limited directionality, sending processes in different directions, and increasing their speed upon contact with the vessel. Once merged, migration speed decreased and continued to decrease with time (p < 0.001). After perivascular localization, migration is limited along the blood vessels in both directions. The percentage of cells that contact blood vessels and then continue to migrate along the vessel was 92.5% (- 3.9/ + 2.9)% while the percentage of cells that migrate along the blood vessel and leave was 7.5% (- 2.9/ + 3.9) (95% CI, Clopper-Pearson (exact); n = 256 cells from six organotypic cultures); these percentages are significantly different from the random (50%) null hypothesis (z = 13.6; p < 10-7). Further, cells increase their speed in response to a decrease in oxygen tension from atmospheric normoxia (20% O2) to anoxia (1% O2) (p = 0.033).

CONCLUSION

Human organotypic models can accurately study cell migration ex vivo. GBM IDH-wild type cells migrate toward the perivascular space in blood vessels and their migratory parameters change once they contact vascular structures and under hypoxic conditions. This model allows the evaluation of GBM invasion, considering the human brain microenvironment when cells are removed from their native niche after surgery.

Development of Experimental Three-Dimensional Tumor Models to Study Glioblastoma Cancer Stem Cells and Tumor Microenvironment

Glioblastoma (GBM) is the most common and dismal primary brain tumor. Unfortunately, despite multidisciplinary treatment, most patients will perish approximately 15 months after diagnosis. For this reason, there is an urgent need to improve our understanding of GBM tumor biology and develop novel therapies that can achieve better clinical outcomes. In this setting, three-dimensional tumor models have risen as more appropriate preclinical tools when compared to traditional cell cultures, given that two-dimensional (2D) cultures have failed to accurately recapitulate tumor biology and translate preclinical findings into patient benefits. Three-dimensional cultures using neurospheres, organoids, and organotypic better resemble original tumor genetic and epigenetic profiles, maintaining tumor microenvironment characteristics and mimicking cell-cell and cell-matrix interactions. This chapter summarizes our methods to generate well-characterized glioblastoma neurospheres, organoids, and organotypics.

SARS-CoV2 entry factors are expressed in primary human glioblastoma and recapitulated in cerebral organoid models

PURPOSE

Glioblastoma (GBM) is the most common and malignant primary brain tumor in adults with a median overall survival of only 14.6 months despite aggressive treatment. While immunotherapy has been successful in other cancers, its benefit has been proven elusive in GBM, mainly due to a markedly immunosuppressive tumor microenvironment. SARS-CoV-2 has been associated with the development of a pronounced central nervous system (CNS) inflammatory response when infecting different cells including astrocytes, endothelial cells, and microglia. While SARS-CoV2 entry factors have been described in different tissues, their presence and implication on GBM aggressiveness or microenvironment has not been studied on appropriate preclinical models.

METHODS

We evaluated the presence of crucial SARS-CoV-2 entry factors: ACE2, TMPRSS2, and NRP1 in matched surgically-derived GBM tissue, cells lines, and organoids; as well as in human brain derived specimens using immunohistochemistry, confocal pixel line intensity quantification, and transcriptome analysis.

RESULTS

We show that patient derived-GBM tissue and cell cultures express SARS-CoV2 entry factors, being NRP1 the most crucial facilitator of SARS-CoV-2 infection in GBM. Moreover, we demonstrate that, receptor expression remains present in our GBM organoids, making them an adequate model to study the effect of this virus in GBM for the potential development of viral therapies in the future.

CONCLUSION

Our findings suggest that the SARS-CoV-2 virus entry factors are expressed in primary tissues and organoid models and could be potentially utilized to study the susceptibility of GBM to this virus to target or modulate the tumor microenviroment.

PNJ scaffolds promote microenvironmental regulation of glioblastoma stem-like cell enrichment and radioresistance

Glioblastoma (GBM) brain tumors contain a subpopulation of self-renewing multipotent Glioblastoma stem-like cells (GSCs) that are believed to drive the near inevitable recurrence of GBM. We previously engineered temperature responsive scaffolds based on the polymer poly(N-isopropylacrylamide-co-Jeffamine M-1000 acrylamide) (PNJ) for the purpose of enriching GSCs in vitro from patient-derived samples. Here, we used PNJ scaffolds to study microenvironmental regulation of self-renewal and radiation response in patient-derived GSCs representing classical and proneural subtypes. GSC self-renewal was regulated by the composition of PNJ scaffolds and varied with cell type. PNJ scaffolds protected against radiation-induced cell death, particularly in conditions that also promoted GSC self-renewal. Additionally, cells cultured in PNJ scaffolds exhibited increased expression of the transcription factor HIF2α, which was not observed in neurosphere culture, providing a potential mechanistic basis for differences in radio-resistance. Differences in PNJ regulation of HIF2α in irradiated and untreated conditions also offered evidence of stem plasticity. These data show PNJ scaffolds provide a unique biomaterial for evaluating dynamic microenvironmental regulation of GSC self-renewal, radioresistance, and stem plasticity.

Human Cerebrospinal Fluid Modulates Pathways Promoting Glioblastoma Malignancy

Glioblastoma (GBM) is the most common and devastating primary cancer of the central nervous system in adults. High grade gliomas are able to modify and respond to the brain microenvironment. When GBM tumors infiltrate the Subventricular zone (SVZ) they have a more aggressive clinical presentation than SVZ-distal tumors. We suggest that cerebrospinal fluid (CSF) contact contributes to enhance GBM malignant characteristics in these tumors. We evaluated the impact of human CSF on GBM, performing a transcriptome analysis on human primary GBM cells exposed to CSF to measure changes in gene expression profile and their clinical relevance on disease outcome. In addition we evaluated the proliferation and migration changes of CSF-exposed GBM cells in vitro and in vivo. CSF induced transcriptomic changes in pathways promoting cell malignancy, such as apoptosis, survival, cell motility, angiogenesis, inflammation, and glucose metabolism. A genetic signature extracted from the identified transcriptional changes in response to CSF proved to be predictive of GBM patient survival using the TCGA database. Furthermore, CSF induced an increase in viability, proliferation rate, and self-renewing capacity, as well as the migratory capabilities of GBM cells in vitro. In vivo, GBM cells co-injected with human CSF generated larger and more proliferative tumors compared to controls. Taken together, these results provide direct evidence that CSF is a key player in determining tumor growth and invasion through the activation of complex gene expression patterns characteristic of a malignant phenotype. These findings have diagnostic and therapeutic implications for GBM patients. The changes induced by CSF contact might play a role in the increased malignancy of SVZ-proximal GBM.

Overlapping migratory mechanisms between neural progenitor cells and brain tumor stem cells

Neural stem cells present in the subventricular zone (SVZ), the largest neurogenic niche of the mammalian brain, are able to self-renew as well as generate neural progenitor cells (NPCs). NPCs are highly migratory and traverse the rostral migratory stream (RMS) to the olfactory bulb, where they terminally differentiate into mature interneurons. NPCs from the SVZ are some of the few cells in the CNS that migrate long distances during adulthood. The migratory process of NPCs is highly regulated by intracellular pathway activation and signaling from the surrounding microenvironment. It involves modulation of cell volume, cytoskeletal rearrangement, and isolation from compact extracellular matrix. In malignant brain tumors including high-grade gliomas, there are cells called brain tumor stem cells (BTSCs) with similar stem cell characteristics to NPCs but with uncontrolled cell proliferation and contribute to tumor initiation capacity, tumor progression, invasion, and tumor maintenance. These BTSCs are resistant to chemotherapy and radiotherapy, and their presence is believed to lead to tumor recurrence at distal sites from the original tumor location, principally due to their high migratory capacity. BTSCs are able to invade the brain parenchyma by utilizing many of the migratory mechanisms used by NPCs. However, they have an increased ability to infiltrate the tight brain parenchyma and utilize brain structures such as myelin tracts and blood vessels as migratory paths. In this article, we summarize recent findings on the mechanisms of cellular migration that overlap between NPCs and BTSCs. A better understanding of the intersection between NPCs and BTSCs will to provide a better comprehension of the BTSCs' invasive capacity and the molecular mechanisms that govern their migration and eventually lead to the development of new therapies to improve the prognosis of patients with malignant gliomas.

Cancer-selective nanoparticles for combinatorial siRNA delivery to primary human GBM in vitro and in vivo

Novel treatments for glioblastoma (GBM) are urgently needed, particularly those which can simultaneously target GBM cells' ability to grow and migrate. Herein, we describe a synthetic, bioreducible, biodegradable polymer that can package and deliver hundreds of siRNA molecules into a single nanoparticle, facilitating combination therapy against multiple GBM-promoting targets. We demonstrate that siRNA delivery with these polymeric nanoparticles is cancer-selective, thereby avoiding potential side effects in healthy cells. We show that we can deliver siRNAs targeting several anti-GBM genes (Robo1, YAP1, NKCC1, EGFR, and survivin) simultaneously and within the same nanoparticles. Robo1 (roundabout homolog 1) siRNA delivery by biodegradable particles was found to trigger GBM cell death, as did non-viral delivery of NKCC1, EGFR, and survivin siRNA. Most importantly, combining several anti-GBM siRNAs into a nanoparticle formulation leads to high GBM cell death, reduces GBM migration in vitro, and reduces tumor burden over time following intratumoral administration. We show that certain genes, like survivin and EGFR, are important for GBM survival, while NKCC1, is more crucial for cancer cell migration. This represents a powerful platform technology with the potential to serve as a multimodal therapeutic for cancer.

The pro-tumorigenic effects of metabolic alterations in glioblastoma including brain tumor initiating cells

De-regulated cellular energetics is an emerging hallmark of cancer with alterations to glycolysis, oxidative phosphorylation, the pentose phosphate pathway, lipid oxidation and synthesis and amino acid metabolism. Understanding and targeting of metabolic reprogramming in cancers may yield new treatment options, but metabolic heterogeneity and plasticity complicate this strategy. One highly heterogeneous cancer for which current treatments ultimately fail is the deadly brain tumor glioblastoma. Therapeutic resistance, within glioblastoma and other solid tumors, is thought to be linked to subsets of tumor initiating cells, also known as cancer stem cells. Recent profiling of glioblastoma and brain tumor initiating cells reveals changes in metabolism, as compiled here, that may be more broadly applicable. We will summarize the profound role for metabolism in tumor progression and therapeutic resistance and discuss current approaches to target glioma metabolism to improve standard of care.

Engineering principles for guiding spheroid function in the regeneration of bone, cartilage, and skin

There is a critical need for strategies that effectively enhance cell viability and post-implantation performance in order to advance cell-based therapies. Spheroids, which are dense cellular aggregates, overcome many current limitations with transplanting individual cells. Compared to individual cells, the aggregation of cells into spheroids results in increased cell viability, together with enhanced proangiogenic, anti-inflammatory, and tissue-forming potential. Furthermore, the transplantation of cells using engineered materials enables localized delivery to the target site while providing an opportunity to guide cell fate in situ, resulting in improved therapeutic outcomes compared to systemic or localized injection. Despite promising early results achieved by freely injecting spheroids into damaged tissues, growing evidence demonstrates the advantages of entrapping spheroids within a biomaterial prior to implantation. This review will highlight the basic characteristics and qualities of spheroids, describe the underlying principles for how biomaterials influence spheroid behavior, with an emphasis on hydrogels, and provide examples of synergistic approaches using spheroids and biomaterials for tissue engineering applications.

Actin cytoskeleton regulator Arp2/3 complex is required for DLL1 activating Notch1 signaling to maintain the stem cell phenotype of glioma initiating cells

Glioblastoma (GBM) is the most common and lethal primary intracranial tumor. Actin cytoskeleton regulator Arp2/3 complex stimulates glioma cell motility and migration, and thus triggers tumor invasion. However, little is known regarding the role of actin cytoskeleton in maintaining the stem cell phenotype. Here, we showed that Arp2/3 complex improved stem cell phenotype maintenance through sustaining the activated Notch signaling. ShRNA targeting Notch ligand Delta-like 1 (DLL1) decreased CD133 and Nestin expression, and impaired the self-renewal ability of CD133+ U87-MG and U251-MG glioma cells, indicating DLL1/Notch1 signaling promoted stem cell phenotype maintenance. Interestingly, inhibiting Arp2/3 complex also induced the similar effect of shDLL1. Silencing DLL1 in the Arp2/3 inhibited CD133+ cells did not further abrogate the stem cell phenotype, suggesting DLL1 function requires Arp2/3 complex in glioma initiating cells (GICs). However, exogenous soluble DLL1 (sDLL1) instead of endogenous DLL1 rescued the Arp2/3 inhibition-induced stem cell phenotype suppression. The underlying mechanism was that Arp2/3 inhibition impeded DLL1 vesicular transport from cytoplasm to cell membrane, which resulted in DLL1 unable to activate Notch pathway. Furthermore, we illustrated that Arp2/3 inhibition abolished the tumorigenicity of CD133+ U87-MG neurosphere cells in the intracranial model. These findings suggested that cytoskeleton maintained the stem cell phenotype in GBM, which provide novel therapeutic strategy that anti-invasive targeted therapies may help eliminate GICs.

Three-Dimensional Models of the Human Brain Development and Diseases

Deciphering the human brain pathophysiology remains one of the greatest challenges of the 21st century. Neurological disorders represent a significant proportion of diseases burden; however, the complexity of the brain physiology makes it challenging to model its diseases. Simple in vitro models have been very useful for precise measurements in controled conditions. However, existing models are limited in their ability to replicate complex interactions between various cells in the brain. Studying human brain requires sophisticated models to reconstitute the tangled architecture and functions of brain cells. Recently, advances in the development of three-dimensional (3D) brain cell culture models have begun to recapitulate various aspects of the human brain physiology in vitro and replicate basic disease processes of Alzheimer's disease, amyotrophic lateral sclerosis, and microcephaly. In this review, we discuss the progress, advantages, limitations, and future directions of 3D cell culture systems for modeling the human brain development and diseases.

Brief Report: Robo1 Regulates the Migration of Human Subventricular Zone Neural Progenitor Cells During Development

Human neural progenitor cell (NPC) migration within the subventricular zone (SVZ) of the lateral ganglionic eminence is an active process throughout early brain development. The migration of human NPCs from the SVZ to the olfactory bulb during fetal stages resembles what occurs in adult rodents. As the human brain develops during infancy, this migratory stream is drastically reduced in cell number and becomes barely evident in adults. The mechanisms regulating human NPC migration are unknown. The Slit-Robo signaling pathway has been defined as a chemorepulsive cue involved in axon guidance and neuroblast migration in rodents. Slit and Robo proteins expressed in the rodent brain help guide neuroblast migration from the SVZ through the rostral migratory stream to the olfactory bulb. Here, we present the first study on the role that Slit and Robo proteins play in human-derived fetal neural progenitor cell migration (hfNPC). We describe that Robo1 and Robo2 isoforms are expressed in the human fetal SVZ. Furthermore, we demonstrate that Slit2 is able to induce a chemorepellent effect on the migration of hfNPCs derived from the human fetal SVZ. In addition, when Robo1 expression is inhibited, hfNPCs are unable to migrate to the olfactory bulb of mice when injected in the anterior SVZ. Our findings indicate that the migration of human NPCs from the SVZ is partially regulated by the Slit-Robo axis. This pathway could be regulated to direct the migration of NPCs in human endogenous neural cell therapy. Stem Cells 2017;35:1860-1865.

Electrophoresis of cell membrane heparan sulfate regulates galvanotaxis in glial cells

Endogenous electric fields modulate many physiological processes by promoting directional migration, a process known as galvanotaxis. Despite the importance of galvanotaxis in development and disease, the mechanism by which cells sense and migrate directionally in an electric field remains unknown. Here, we show that electrophoresis of cell surface heparan sulfate (HS) critically regulates this process. HS was found to be localized at the anode-facing side in fetal neural progenitor cells (fNPCs), fNPC-derived astrocytes and brain tumor-initiating cells (BTICs), regardless of their direction of galvanotaxis. Enzymatic removal of HS and other sulfated glycosaminoglycans significantly abolished or reversed the cathodic response seen in fNPCs and BTICs. Furthermore, Slit2, a chemorepulsive ligand, was identified to be colocalized with HS in forming a ligand gradient across cellular membranes. Using both imaging and genetic modification, we propose a novel mechanism for galvanotaxis in which electrophoretic localization of HS establishes cell polarity by functioning as a co-receptor and provides repulsive guidance through Slit-Robo signaling.

Somatic retrotransposition is infrequent in glioblastomas

Background

Gliomas are the most common primary brain tumors in adults. We sought to understand the roles of endogenous transposable elements in these malignancies by identifying evidence of somatic retrotransposition in glioblastomas (GBM). We performed transposon insertion profiling of the active subfamily of Long INterspersed Element-1 (LINE-1) elements by deep sequencing (TIPseq) on genomic DNA of low passage oncosphere cell lines derived from 7 primary GBM biopsies, 3 secondary GBM tissue samples, and matched normal intravenous blood samples from the same individuals.

Results

We found and PCR validated one somatically acquired tumor-specific insertion in a case of secondary GBM. No LINE-1 insertions present in primary GBM oncosphere cultures were missing from corresponding blood samples. However, several copies of the element (11) were found in genomic DNA from blood and not in the oncosphere cultures. SNP 6.0 microarray analysis revealed deletions or loss of heterozygosity in the tumor genomes over the intervals corresponding to these LINE-1 insertions.

Conclusions

These findings indicate that LINE-1 retrotransposon can act as an infrequent insertional mutagen in secondary GBM, but that retrotransposition is uncommon in these central nervous system tumors as compared to other neoplasias.

Electronic supplementary material

The online version of this article (doi:10.1186/s13100-016-0077-5) contains supplementary material, which is available to authorized users.

Collective cancer cell invasion induced by coordinated contractile stresses

The physical underpinnings of fibrosarcoma cell dissemination from a tumor in a surrounding collagen-rich matrix are poorly understood. Here we show that a tumor spheroid embedded in a 3D collagen matrix exerts large contractile forces on the matrix before invasion. Cell invasion is accompanied by complex spatially and temporally dependent patterns of cell migration within and at the surface of the spheroids that are fundamentally different from migratory patterns of individual fibrosarcoma cells homogeneously distributed in the same type of matrix. Cells display a continuous transition from a round morphology at the spheroid core, to highly aligned elongated morphology at the spheroid periphery, which depends on both β₁-integrin-based cell-matrix adhesion and myosin II/ROCK-based cell contractility. This isotropic-to-anisotropic transition corresponds to a shift in migration, from a slow and unpolarized movement at the core, to a fast, polarized and persistent one at the periphery. Our results also show that the ensuing collective invasion of fibrosarcoma cells is induced by anisotropic contractile stresses exerted on the surrounding matrix.

Quantification of cellular and nuclear uptake rates of polymeric gene delivery nanoparticles and DNA plasmids via flow cytometry

Non-viral, biomaterial-mediated gene delivery has the potential to treat many diseases, but is limited by low efficacy. Elucidating the bottlenecks of plasmid mass transfer can enable an improved understanding of biomaterial structure-function relationships, leading to next-generation rationally designed non-viral gene delivery vectors. As proof of principle, we transfected human primary glioblastoma cells using a poly(beta-amino ester) complexed with eGFP plasmid DNA. The polyplexes transfected 70.6±0.6% of the cells with 101±3% viability. The amount of DNA within the cytoplasm, nuclear envelope, and nuclei was assessed at multiple time points using fluorescent dye conjugated plasmid up to 24h post-transfection using a quantitative multi-well plate-based flow cytometry assay. Conversion to plasmid counts and degradation kinetics were accounted for via quantitative PCR (plasmid degradation rate constants were determined to be 0.62h(-1) and 0.084h(-1) for fast and slow phases respectively). Quantitative cellular uptake, nuclear association, and nuclear uptake rate constants were determined by using a four-compartment first order mass-action model. The rate limiting step for these poly(beta-amino ester)/DNA polyplex nanoparticles was determined to be cellular uptake (7.5×10(-4)h(-1)) and only 0.1% of the added dose was taken up by the human brain cancer cells, whereas 12% of internalized DNA successfully entered the nucleus (the rate of nuclear internalization of nuclear associated plasmid was 1.1h(-1)). We describe an efficient new method for assessing cellular and nuclear uptake rates of non-viral gene delivery nanoparticles using flow cytometry to improve understanding and design of polymeric gene delivery nanoparticles.

STATEMENT OF SIGNIFICANCE

In this work, a quantitative high throughput flow cytometry-based assay and computational modeling approach was developed for assessing cellular and nuclear uptake rates of non-viral gene delivery nanoparticles. This method is significant as it can be used to elucidate structure-function relationships of gene delivery nanoparticles and improve their efficiency. This method was applied to a particular type of biodegradable polymer, a poly(beta-amino ester), that transfected human brain cancer cells with high efficacy and without cytotoxicity. A four-compartment first order mass-action kinetics model was found to model the experimental transport data well without requiring external fitting parameters. Quantitative rate constants were identified for the intracellular transport, including DNA degradation rate from polyplexes, cellular uptake rate, and nuclear uptake rate, with cellular uptake identified as the rate-limiting step.

Implications of irradiating the subventricular zone stem cell niche

Radiation therapy is a standard treatment for brain tumor patients. However, it comes with side effects, such as neurological deficits. While likely multi-factorial, the effect may in part be associated with the impact of radiation on the neurogenic niches. In the adult mammalian brain, the neurogenic niches are localized in the subventricular zone (SVZ) of the lateral ventricles and the dentate gyrus of the hippocampus, where the neural stem cells (NSCs) reside. Several reports showed that radiation produces a drastic decrease in the proliferative capacity of these regions, which is related to functional decline. In particular, radiation to the SVZ led to a reduced long-term olfactory memory and a reduced capacity to respond to brain damage in animal models, as well as compromised tumor outcomes in patients. By contrast, other studies in humans suggested that increased radiation dose to the SVZ may be associated with longer progression-free survival in patients with high-grade glioma. In this review, we summarize the cellular and functional effects of irradiating the SVZ niche. In particular, we review the pros and cons of using radiation during brain tumor treatment, discussing the complex relationship between radiation dose to the SVZ and both tumor control and toxicity.

Cellular microenvironment modulates the galvanotaxis of brain tumor initiating cells

Galvanotaxis is a complex process that represents the collective outcome of various contributing mechanisms, including asymmetric ion influxes, preferential activation of voltage-gated channels, and electrophoretic redistribution of membrane components. While a large number of studies have focused on various up- and downstream signaling pathways, little is known about how the surrounding microenvironment may interact and contribute to the directional response. Using a customized galvanotaxis chip capable of carrying out experiments in both two- and three-dimensional microenvironments, we show that cell-extracellular matrix (ECM) interactions modulate the galvanotaxis of brain tumor initiating cells (BTICs). Five different BTICs across three different glioblastoma subtypes were examined and shown to all migrate toward the anode in the presence of a direct-current electric field (dcEF) when cultured on a poly-L-ornithine/laminin coated surface, while the fetal-derived neural progenitor cells (fNPCs) migrated toward the cathode. Interestingly, when embedded in a 3D ECM composed of hyaluronic acid and collagen, BTICs exhibited opposite directional response and migrated toward the cathode. Pharmacological inhibition against a panel of key molecules involved in galvanotaxis further revealed the mechanistic differences between 2- and 3D galvanotaxis in BTICs. Both myosin II and phosphoinositide 3-kinase (PI3K) were found to hold strikingly different roles in different microenvironments.

Bioreducible Poly(Beta-Amino Ester)s for Intracellular Delivery of SiRNA

RNA interference (RNAi) is a powerful tool to target and knockdown gene expression in a sequence-specific manner. RNAi can be achieved by the intracellular introduction of SiRNA; however, intracellular SiRNA delivery remains a challenging obstacle. Herein we describe the use of bioreducible nanoparticles formed using poly(beta-amino ester)s (PBAEs) for safe and efficient SiRNA delivery. Methods for polymer synthesis, nanoparticle formation, and SiRNA delivery using these particles are described. A template protocol for nanoparticle screening is presented and can be used to quickly optimize SiRNA delivery for novel applications.

Human cerebrospinal fluid regulates proliferation and migration of stem cells through insulin-like growth factor-1

Mesenchymal stem cells (MSCs) and neural progenitor cells (NPCs) have been regarded for their clinical therapeutic potential for central nervous system (CNS) pathologies. Their potential utility is a result of their intrinsic ability to repair damaged tissues, deliver therapeutic proteins, and migrate to sites of pathology within the brain. However, it remains unclear whether the CNS promotes any changes in these potential therapeutic cells, which would be critical to understand before clinical application. A major component of the CNS is cerebrospinal fluid (CSF). Therefore, the aim of this study was to evaluate the influence that human CSF has on the function of human adipose-derived MSCs (hAMSCs) and human fetal-derived NPCs (hfNPCs) in regard to cell proliferation, survival, and migration. This study demonstrated that human noncancerous CSF promoted proliferation and inhibited apoptosis of hAMSCs and hfNPCs. Preculturing these stem cells in human CSF also increased their migratory speed and distance traveled. Furthermore, insulin-like growth factor-1 (IGF-1) in human CSF enhanced the migration capacity and increased the expression of C-X-C chemokine receptor type 4 (CXCR4) in both stem cell types. These current findings highlight a simple and natural way in which human CSF can enhance the proliferation, migration, and viability of human exogenous primary hAMSCs and hfNPCs. This study may provide insight into improving the clinical efficacy of stem cells for the treatment of CNS pathologies.

Mesenchymal stem cells from human fat engineered to secrete BMP4 are nononcogenic, suppress brain cancer, and prolong survival

PURPOSE

Glioblastoma is the most common adult primary malignant intracranial cancer. It is associated with poor outcomes because of its invasiveness and resistance to multimodal therapies. Human adipose-derived mesenchymal stem cells (hAMSC) are a potential treatment because of their tumor tropism, ease of isolation, and ability to be engineered. In addition, bone morphogenetic protein 4 (BMP4) has tumor-suppressive effects on glioblastoma and glioblastoma brain tumor-initiating cells (BTIC), but is difficult to deliver to brain tumors. We sought to engineer BMP4-secreting hAMSCs (hAMSCs-BMP4) and evaluate their therapeutic potential on glioblastoma.

EXPERIMENTAL DESIGN

The reciprocal effects of hAMSCs on primary human BTIC proliferation, differentiation, and migration were evaluated in vitro. The safety of hAMSC use was evaluated in vivo by intracranial coinjections of hAMSCs and BTICs in nude mice. The therapeutic effects of hAMSCs and hAMSCs-BMP4 on the proliferation and migration of glioblastoma cells as well as the differentiation of BTICs, and survival of glioblastoma-bearing mice were evaluated by intracardiac injection of these cells into an in vivo intracranial glioblastoma murine model.

RESULTS

hAMSCs-BMP4 targeted both the glioblastoma tumor bulk and migratory glioblastoma cells, as well as induced differentiation of BTICs, decreased proliferation, and reduced the migratory capacity of glioblastomas in vitro and in vivo. In addition, hAMSCs-BMP4 significantly prolonged survival in a murine model of glioblastoma. We also demonstrate that the use of hAMSCs in vivo is safe.

CONCLUSIONS

Both unmodified and engineered hAMSCs are nononcogenic and effective against glioblastoma, and hAMSCs-BMP4 are a promising cell-based treatment option for glioblastoma.

Laboratory models for central nervous system tumor stem cell research

Central nervous system (CNS) tumors are complex organ systems comprising of a neoplastic component with associated vasculature, inflammatory cells, and reactive cellular and extracellular components. Research has identified a subset of cells in CNS tumors that portray defining properties of neural stem cells, namely, that of self-renewal and multi-potency. Growing evidence suggests that these tumor stem cells (TSC) play an important role in the maintenance and growth of the tumor. Furthermore, these cells have also been shown to be refractory to conventional therapy and may be crucial for tumor recurrence and metastasis. Current investigations are focusing on isolating these TSC from CNS tumors to investigate their unique biological processes. This understanding will help identify and develop more effective and comprehensive treatment strategies. This chapter provides an overview of some of the most commonly used laboratory models for CNSTSC research.

Isolation and characterization of stem cells from human central nervous system malignancies

Central Nervous System (CNS) tumors include some of the most invasive and lethal tumors in humans. The poor prognosis in patients with CNS tumors is ascribed to their invasive nature. After the description of a stem cell-like cohort in hematopoietic cancers, tumor stem cells (TSCs) have been isolated from a variety of solid tumors, including brain tumors. Further research has uncovered the crucial role these cells play in the initiation and propagation of brain tumors. More importantly, TSCs have also been shown to be relatively resistant to conventional cytotoxic therapeutics, which may also account for the alarmingly high rate of CNS tumor recurrence. In order to elucidate prospective therapeutic targets it is imperative to study these cells in detail and to accomplish this, we need to be able to reliably isolate and characterize these cells. This chapter will therefore, provide an overview of the methods used to isolate and characterize stem cells from human CNS malignancies.

Glucose-6-phosphatase is a key metabolic regulator of glioblastoma invasion

Glioblastoma (GBM) remains the most aggressive primary brain cancer in adults. Similar to other cancers, GBM cells undergo metabolic reprogramming to promote proliferation and survival. Glycolytic inhibition is widely used to target such reprogramming. However, the stability of glycolytic inhibition in GBM remains unclear especially in a hypoxic tumor microenvironment. In this study, it was determined that glucose-6-phosphatase (G6PC/G6Pase) expression is elevated in GBM when compared with normal brain. Human-derived brain tumor-initiating cells (BTIC) use this enzyme to counteract glycolytic inhibition induced by 2-deoxy-d-glucose (2DG) and sustain malignant progression. Downregulation of G6PC renders the majority of these cells unable to survive glycolytic inhibition, and promotes glycogen accumulation through the activation of glycogen synthase (GYS1) and inhibition of glycogen phosphorylase (PYGL). Moreover, BTICs that survive G6PC knockdown are less aggressive (reduced migration, invasion, proliferation, and increased astrocytic differentiation). Collectively, these findings establish G6PC as a key enzyme with promalignant functional consequences that has not been previously reported in GBM and identify it as a potential therapeutic target.

IMPLICATIONS

This study is the first to demonstrate a functional relationship between the critical gluconeogenic and glycogenolytic enzyme G6PC with the metabolic adaptations during GBM invasion.

Biodegradable polymeric nanoparticles show high efficacy and specificity at DNA delivery to human glioblastoma in vitro and in vivo

Current glioblastoma therapies are insufficient to prevent tumor recurrence and eventual death. Here, we describe a method to treat malignant glioma by nonviral DNA delivery using biodegradable poly(β-amino ester)s (PBAEs), with a focus on the brain tumor initiating cells (BTICs), the tumor cell population believed to be responsible for the formation of new tumors and resistance to many conventional therapies. We show transfection efficacy of >60% and low biomaterial-mediated cytotoxicity in primary human BTICs in vitro even when the BTICs are grown as 3-D oncospheres. Intriguingly, we find that these polymeric nanoparticles show intrinsic specificity for nonviral transfection of primary human BTICs over primary healthy human neural progenitor cells and that this specificity is not due to differences in cellular growth rate or total cellular uptake of nanoparticles. Moreover, we demonstrate that biodegradable PBAE/DNA nanoparticles can be fabricated, lyophilized, and then stored for at least 2 years without losing efficacy, increasing the translational relevance of this technology. Using lyophilized nanoparticles, we show transgene expression by tumor cells after intratumoral injection into an orthotopic murine model of human glioblastoma. PBAE/DNA nanoparticles were more effective than naked DNA at exogenous gene expression in vivo, and tumor cells were transfected more effectively than noninvaded brain parenchyma in vivo. This work shows the potential of nonviral gene delivery tools to target human brain tumors.

The relationship between brain tumor cell invasion of engineered neural tissues and in vivo features of glioblastoma

Glioblastoma is an aggressive brain tumor characterized by its high propensity for local invasion, formation of secondary foci within the brain, as well as areas of necrosis. This study aims to (i) provide a technical approach to reproduce features of the disease in vitro and (ii) characterize the tumor/host brain tissue interaction at the molecular level. Human engineered neural tissue (ENT) obtained from pluripotent stem cells was generated and co-cultured with human glioblastoma-initiating cells. Within two weeks, glioblastoma cells invaded the nervous tissue. This invasion displayed features of the disease in vivo: a primary tumor mass, diffuse migration of invading single cells into the nervous tissue, secondary foci, as well as peritumoral cell death. Through comparative molecular analyses, this model allowed the identification of more than 100 genes that are specifically induced and up-regulated by the nervous tissue/tumor interaction. Notably the type I interferon response, extracellular matrix-related genes were most highly represented and showed a significant correlation with patient survival. In conclusion, glioblastoma development within a nervous tissue can be engineered in vitro, providing a relevant model to study the disease and allows the identification of clinically-relevant genes induced by the tumor/host tissue interaction.

Mesenchymal stem cells derived from adipose tissue vs bone marrow: in vitro comparison of their tropism towards gliomas

INTRODUCTION

Glioblastoma is the most common primary malignant brain tumor, and is refractory to surgical resection, radiation, and chemotherapy. Human mesenchymal stem cells (hMSC) may be harvested from bone marrow (BMSC) and adipose (AMSC) tissue. These cells are a promising avenue of investigation for the delivery of adjuvant therapies. Despite extensive research into putative mechanisms for the tumor tropism of MSCs, there remains no direct comparison of the efficacy and specificity of AMSC and BMSC tropism towards glioma.

METHODS

Under an IRB-approved protocol, intraoperative human Adipose MSCs (hAMSCs) were established and characterized for cell surface markers of mesenchymal stem cell origin in conjunction with the potential for tri-lineage differentiation (adipogenic, chondrogenic, and osteogenic). Validated experimental hAMSCs were compared to commercially derived hBMSCs (Lonza) and hAMSCs (Invitrogen) for growth responsiveness and glioma tropism in response to glioma conditioned media obtained from primary glioma neurosphere cultures.

RESULTS

Commercial and primary culture AMSCs and commercial BMSCs demonstrated no statistically significant difference in their migration towards glioma conditioned media in vitro. There was statistically significant difference in the proliferation rate of both commercial AMSCs and BMSCs as compared to primary culture AMSCs, suggesting primary cultures have a slower growth rate than commercially available cell lines.

CONCLUSIONS

Adipose- and bone marrow-derived mesenchymal stem cells have similar in vitro glioma tropism. Given the well-documented ability to harvest larger numbers of AMSCs under local anesthesia, adipose tissue may provide a more efficient source of MSCs for research and clinical applications, while minimizing patient morbidity during cell harvesting.

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.

Expression of epidermal growth factor variant III (EGFRvIII) in pediatric diffuse intrinsic pontine gliomas

Despite numerous clinical trials over the past 2 decades, the overall survival for children diagnosed with diffuse intrinsic pontine glioma (DIPG) remains 9-10 months. Radiation therapy is the only treatment with proven effect and novel therapies are needed. Epidermal growth factor receptor variant III (EGFRvIII) is the most common variant of the epidermal growth factor receptor and is expressed in many tumor types but is rarely found in normal tissue. A peptide vaccine targeting EGFRvIII is currently undergoing investigation in phase 3 clinical trials for the treatment of newly diagnosed glioblastoma (GBM), the tumor in which this variant receptor was first discovered. In this study, we evaluated EGFRvIII expression in pediatric DIPG samples using immunohistochemistry with a double affinity purified antibody raised against the EGFRvIII peptide. Staining of pediatric DIPG histological samples revealed expression in 4 of 9 cases and the pattern of staining was consistent with what has been seen in EGFRvIII transfected cells as well as GBMs from adult trials. In addition, analysis of tumor samples collected immediately post mortem and of DIPG cells in culture by RT-PCR, western blot analysis, and flow cytometry confirmed EGFRvIII expression. We were therefore able to detect EGFRvIII expression in 6 of 11 DIPG cases. These data suggest that EGFRvIII warrants investigation as a target for these deadly pediatric tumors.

IL-13Rα2-Targeted Therapy Escapees: Biologic and Therapeutic Implications

Glioblastoma multiforme (GBM) overexpresses interleukin 13 receptor α2 (IL-13Rα2), a tumor-restricted receptor that is not present in normal brain. We and others have created targeted therapies that specifically eradicate tumors expressing this promising tumor-restricted biomarker. As these therapies head toward clinical implementation, it is critical to explore mechanisms of potential resistance. We therefore used a potent IL-13Rα2-targeted bacterial cytotoxin to select for naturally occurring "escapee" cells from three different IL-13Rα2-expressing GBM cell lines. We found that these side populations of escapee cells had significantly decreased IL-13Rα2 expression. We examined clinically relevant biologic characteristics of escapee cell lines compared to their parental cell lines and found that they had similar proliferation rates and equal sensitivity to temozolomide and radiation, the standard therapies given to GBM patients. In contrast, our escapee cell lines were less likely to form colonies in culture and migrated more slowly in wound healing assays. Furthermore, we found that escapee cells formed significantly less neurospheres in vitro, suggesting that IL-13Rα2-targeted therapy preferentially targeted the "stem-like" cell population and possibly indicating decreased tumorigenicity in vivo. We therefore tested escapee cells for in vivo tumorigenicity and found that they were significantly less tumorigenic in both subcutaneous and intracranial mouse models compared to matching parental cells. These data, for the first time, establish and characterize the clinically relevant biologic properties of IL-13Rα2-targeted therapy escapees and suggest that these cells may have less malignant characteristics than parental tumors.

Non-viral gene delivery nanoparticles based on poly(β-amino esters) for treatment of glioblastoma

Glioblastoma (GB) is currently characterized by low survival rates and therapies with insufficient efficacy. Here, we describe biodegradable polymers that can deliver genes to primary GB cells as well as GB tumor stem cells in vitro with low non-specific toxicity and transfection efficiencies of up to 60.6 ± 5% in normal (10%) serum conditions. We developed polymer-DNA nanoparticles that remained more stable in normal serum and could also be stored for at least 3 months in ready-to-use form with no measurable decrease in efficacy, expanding their potential in a practical or clinical setting. A subset of polymers was identified that shows a high degree of specificity to tumor cells compared with healthy astrocytes and human neural stem cells when cultured (separately or in co-culture), yielding higher transfection in GB cells while having little to no apparent effect on healthy cells.