Neural stem cell biology may be well suited for improving brain tumor therapies

Neuroprotective potential of intranasally delivered L-myc immortalized human neural stem cells in female rats after a controlled cortical impact injury

Efficacious stem cell-based therapies for traumatic brain injury (TBI) depend on successful delivery, migration, and engraftment of stem cells to induce neuroprotection. L-myc expressing human neural stem cells (LMNSC008) demonstrate an inherent tropism to injury sites after intranasal (IN) administration. We hypothesize that IN delivered LMNSC008 cells migrate to primary and secondary injury sites and modulate biomarkers associated with neuroprotection and tissue regeneration. To test this hypothesis, immunocompetent adult female rats received either controlled cortical impact injury or sham surgery. LMNSC008 cells or a vehicle were administered IN on postoperative days 7, 9, 11, 13, 15, and 17. The distribution and migration of eGFP-expressing LMNSC008 cells were quantified over 1 mm-thick optically cleared (CLARITY) coronal brain sections from TBI and SHAM controls. NSC migration was observed along white matter tracts projecting toward the hippocampus and regions of TBI. ELISA and Nanostring assays revealed a shift in tissue gene expression in LMNSC008 treated rats relative to controls. LMNSC008 treatment reduced expression of genes and pathways involved in inflammatory response, microglial function, and various cytokines and receptors. Our proof-of-concept studies, although preliminary, support the rationale of using intranasal delivery of LMNSC008 cells for functional studies in preclinical models of TBI and provide support for potential translatability in TBI patients.

Neuroprotective potential of intranasally delivered L-myc immortalized human neural stem cells in female rats after a controlled cortical impact injury

Efficacious stem cell-based therapies for traumatic brain injury (TBI) depend on successful delivery, migration, and engraftment of stem cells to induce neuroprotection. L-myc expressing human neural stem cells (LMNSC008) demonstrate an inherent tropism to injury sites after intranasal (IN) administration. We hypothesize that IN delivered LMNSC008 cells migrate to primary and secondary injury sites and modulate biomarkers associated with neuroprotection and tissue regeneration. To test this, immunocompetent adult female rats received a controlled cortical impact injury (CCI) or sham surgery. LMNSC008 cells or a vehicle (VEH) were administered IN on postoperative days 7, 9, 11, 13, 15, and 17. The distribution and migration of eGFP-expressing LMNSC008 cells were quantified over 1 mm-thick optically cleared (CLARITY) coronal brain sections from TBI and SHAM controls. NSC migration was observed along white matter tracts projecting toward the hippocampus and regions of TBI. ELISA and Nanostring assays revealed a shift in tissue gene expression in LMNSC008 treated rats relative to controls. LMNSC008 treatment reduced expression of genes and pathways involved in inflammatory response, microglial function, and various cytokines and receptors. The data demonstrate a robust proof-of-concept for LMNSC008 therapy for TBI and provides a strong rationale for IN delivery for translation in TBI patients.

Enhancement of neural regeneration as a therapeutic strategy for Alzheimer's disease (Review)

Alzheimer's disease (AD), the most common cause of dementia worldwide, has gradually become a global health concern for society and individuals with the process of global ageing. Although extensive research has been carried out on AD, the etiology and pathological mechanism of the disease are still unclear, and there is no specific drug to cure or delay AD progression. The exploration of enhancing nerve regeneration in AD has gradually attracted increasing attention. In the current review, the existing therapeutic strategies were summarized to induce nerve regeneration which can increase the number of neurons, and improve the survival of neurons, the plasticity of synapses and synaptic activity. The strategies include increasing neurotrophic expression (such as brain-derived neurotrophic factor and nerve growth factor), inhibiting acetylcholinesterase (such as donepezil, tacrine, rivastigmine and galanthamine), elevating histone deacetylase levels (such as RGFP-966, Tasquinimod, CM-414 and 44B), stimulating the brain by physiotherapy (such as near-infrared light, repetitive transcranial magnetic stimulation, and transcranial direct current stimulation) and transplanting exogenous neural stem cells. However, further evaluations need to be performed to determine the optimal treatment. The present study reviews recent interventions for enhancing adult neurogenesis and attempts to elucidate their mechanisms of action, which may provide a theoretical basis for inducing nerve regeneration to fight against AD.

Stem Cells and Targeted Gene Therapy in Brain and Spinal Cord Tumors

The CNS tumors, in particular those with malignant characteristics, are prominent burdens around the world with high mortality and low cure rate. Given that, researchers were curious about novel treatments with promising effectiveness which resulted in shifting the dogmatism era of neurogenesis to the current concept of postnatal neurogenesis. Considering all existing stem cells, various strategies are available for treating CNS cancers, including hematopoietic stem cells transplantation, mesenchymal stem cells transplantation, neural stem cells (NSCs) transplantation, and using stem cells as genetic carriers called "suicide gene therapy". Despite some complications, this ongoing therapeutic method has succeeded in decreasing tumor volume, inhibiting tumor progression, and enhancing patients' survival. These approaches could lead to acceptable results, relatively better safety, and tolerable side effects compared to conventional chemo and radiotherapy. Accordingly, this treatment will be applicable to a wide range of CNS tumors in the near future. Furthermore, tumor genomic analysis and understanding of the underlying molecular mechanisms will help researchers determine patient selection criteria for targeted gene therapy.

Pharmacologic modulation of nasal epithelium augments neural stem cell targeting of glioblastoma

Glioblastoma (GBM) remains the most lethal and untreatable central nervous system malignancy. The challenges to devise novel and effective anti-tumor therapies include difficulty in locating the precise tumor border for complete surgical resection, and rapid regrowth of residual tumor tissue after standard treatment. Repeatable and non-invasive intranasal application of neural stem cells (NSCs) was recently shown to enable clinically relevant delivery of therapy to tumors. Treatment with chemotactic NSCs demonstrated significant survival benefits when coupled with radiation and oncolytic virotherapy in preclinical models of GBM. In order to further augment the clinical applicability of this novel therapeutic platform, we postulate that the FDA-approved compound, methimazole (MT), can be safely utilized to delay the nasal clearance and improve the ability of NSCs to penetrate the olfactory epithelium for robust in vivo brain tumor targeting and therapeutic actions. METHODS: To examine the role of reversible reduction of the olfactory epithelial barrier in non-invasive intranasal delivery, we explored the unique pharmacologic effect of MT at a single dosage regimen. In our proof-of-concept studies, quantitative magnetic resonance imaging (MRI), immunocytochemistry, and survival analysis were performed on glioma-bearing mice treated with a single dose of MT prior to intranasal anti-GBM therapy using an oncolytic virus (OV)-loaded NSCs. RESULTS: Based on histology and in vivo imaging, we found that disrupting the olfactory epithelium with MT effectively delays clearance and allows NSCs to persist in the nasal cavity for at least 24 h. MT pretreatment amplified the migration of NSCs to the tumor. The therapeutic advantage of this enhancement was quantitatively validated by tissue analysis and MRI tracking of NSCs loaded with superparamagnetic iron oxide nanoparticles (SPIOs) in live animals. Moreover, we observed significant survival benefits in GBM-bearing mice treated with intranasal delivery of oncolytic virus-loaded NSCs following MT injection. Conclusion: Our work identified a novel pharmacologic strategy to accelerate the clinical application of the non-invasive NSCs-based therapeutic platform to tackle aggressive brain tumors.

The Horizon of Materiobiology: A Perspective on Material-Guided Cell Behaviors and Tissue Engineering

Although the biological functions of cell and tissue can be regulated by biochemical factors (e.g., growth factors, hormones), the biophysical effects of materials on the regulation of biological activity are receiving more attention. In this Review, we systematically summarize the recent progress on how biomaterials with controllable properties (e.g., compositional/degradable dynamics, mechanical properties, 2D topography, and 3D geometry) can regulate cell behaviors (e.g., cell adhesion, spreading, proliferation, cell alignment, and the differentiation or self-maintenance of stem cells) and tissue/organ functions. How the biophysical features of materials influence tissue/organ regeneration have been elucidated. Current challenges and a perspective on the development of novel materials that can modulate specific biological functions are discussed. The interdependent relationship between biomaterials and biology leads us to propose the concept of "materiobiology", which is a scientific discipline that studies the biological effects of the properties of biomaterials on biological functions at cell, tissue, organ, and the whole organism levels. This Review highlights that it is more important to develop ECM-mimicking biomaterials having a self-regenerative capacity to stimulate tissue regeneration, instead of attempting to recreate the complexity of living tissues or tissue constructs ex vivo. The principles of materiobiology may benefit the development of novel biomaterials providing combinative bioactive cues to activate the migration of stem cells from endogenous reservoirs (i.e., cell niches), stimulate robust and scalable self-healing mechanisms, and unlock the body's innate powers of regeneration.

Current treatments for advanced melanoma and introduction of a promising novel gene therapy for melanoma (Review)

Metastatic melanoma is a fatal form of skin cancer that has a tendency to proliferate more rapidly than any other solid tumor. Since 2010, treatment options for metastatic melanoma have been developed including chemotherapies, checkpoint inhibition immunotherapies, e.g., anti‑cytotoxic T‑lymphocyte antigen‑4 (CTLA‑4) and anti‑programmed death‑1 (PD‑1), and molecular-targeted therapies, e.g., BRAF and MEK inhibitors. These treatments have shown not only high response rates yet also side‑effects and limitations. Notwithstanding its limitations, stem cell therapy has emerged as a new auspicious therapy for various tumor types. Since stem cells possess the ability to serve as a novel vehicle for delivering therapeutic or suicide genes to primary or metastatic cancer sites, these cells can function as part of gene‑directed enzyme prodrug therapy (GDEPT). This review focuses on introducing engineered neural stem cells (NSCs), which have tumor‑tropic behavior that allows NSCs to selectively approach primary and invasive tumor foci, as a potential gene therapy for melanoma. Therapy using engineered NSCs with cytotoxic agents resulted in markedly reduced tumor volumes and significantly prolonged survival rates in preclinical models of various tumor types. This review elucidates current treatment options for metastatic melanoma and introduces a promising NSC therapy.

MMP14 as a novel downstream target of VEGFR2 in migratory glioma-tropic neural stem cells

Neural stem cell (NSC)-based carriers have been presented as promising therapeutic tools for the treatment of infiltrative brain tumors due to their intrinsic tumor homing property. They have demonstrated the ability to migrate towards distant tumor microsatellites and effectively deliver the therapeutic payload, thus significantly improving survival in experimental animal models for brain tumor. Despite such optimistic results, the efficacy of NSC-based anti-cancer therapy has been limited due to the restricted tumor homing ability of NSCs. To examine this issue, we investigated the mechanisms of tumor-tropic migration of an FDA-approved NSC line, HB1.F3.CD, by performing a gene expression analysis. We identified vascular endothelial growth factor-A (VEGFA) and membrane-bound matrix metalloproteinase (MMP14) as molecules whose expression are significantly elevated in migratory NSCs. We observed increased expression of VEGF receptor 2 (VEGFR2) in the focal adhesion complexes of migratory NSCs, with downstream activation of VEGFR2-dependent kinases such as p-PLCγ, p-FAK, and p-Akt, a signaling cascade reported to be required for cellular migration. In an in vivo orthotopic glioma xenograft model, analysis of the migratory trail showed that NSCs maintained expression of VEGFR2 and preferentially migrated within the perivascular space. Knockdown of VEGFR2 via shRNAs led to significant downregulation of MMP14 expression, which resulted in inhibited tumor-tropic migration. Overall, our results suggest, the involvement of VEGFR2-regulated MMP14 in the tumor-tropic migratory behavior of NSCs. Our data warrant investigation of MMP14 as a target for enhancing the migratory properties of NSC carriers and optimizing the delivery of therapeutic payloads to disseminated tumor burdens.

Convergence of normal stem cell and cancer stem cell developmental stage: Implication for differential therapies

Increased evidence shows that normal stem cells may contribute to cancer development and progression by acting as cancer-initiating cells through their interactions with abnormal environmental elements. We postulate that normal stem cells and cancer stem cells (CSC) possess similar mechanisms of self-renewal and differentiation. CSC can be the key to the elaboration of anti-cancer-based therapy. In this article, we focus on a controversial new theme relating to CSC. Tumorigenesis may have a critical stage characterized as a "therapeutic window", which can be identified by association of molecular, biochemical and biological events. Identifying such a stage can allow the production of more effective therapies (e.g. manipulated stem cells) to treat several cancers. More importantly, confirming the existence of a similar therapeutic window during the conversion of normal stem cells to malignant CSC may lead to targeted therapy specifically against CSC. This conversion information may be derived from investigating the biological behaviour of both normal stem cells and cancerous stem cells. Currently, there is little knowledge about the cellular and molecular mechanisms that govern the initiation and maintenance of CSC. Studies on co-evolution and interdependence of cancer with normal tissues may lead to a useful treatment paradigm of cancer. The crosstalk between normal stem cells and cancer formation may converge developmental stages of different types of stem cells (e.g. normal stem cells, CSC and embryonic stem cells). The differential studies of the convergence may result in novel therapies for treating cancers.

NEURO-ONCOLOGIC PHYSICAL THERAPY FOR THE OLDER PERSON

Due to the uncertainty of the course of diagnoses, patients with neuro-oncological malignancies present challenges to the physical therapist. At times, the presentation of impairments and disabilities of these patients with neuro-oncological diagnoses do not necessarily coincide with the involved area of the brain or spinal cord. It is our intention to provide guidance to the physical therapist who will be working with these patients with neuro-oncological diagnoses, in hopes that their encounters will be more productive and meaningful. This article describes a brief overview of common central nervous system malignancies, its medical treatment, as well as possible complications and side effects that would need to be considered in rehabilitating these patients. Special consideration is given to the elderly patients with neuro-oncological diagnoses. Pertinent physical therapy assessments and interventions are discussed.

MMP-2 mediates mesenchymal stem cell tropism towards medulloblastoma tumors

Matrix metalloproteinases (MMPs) are a family of proteinases known to have a role in cell migration. In the present study, we evaluated the role of MMP-2 on tropism of human umbilical cord blood-derived stem cells (hUCBSCs) in a human medulloblastoma tumor model. Consequences of MMP-2 inhibition on stem cell tropism towards medulloblastoma were studied in terms of stem cell migration by using cell culture inserts, transwell chamber assay, western blotting for MMP-2 and migratory molecules, and immunohistochemistry. Conditioned medium from Daoy/D283 cells infected with adenoviral vector encoding MMP-2 small interfering RNA (siRNA) (Ad-MMP-2 si)-reduced stem cell migration as compared with conditioned medium from mock and scrambled vector (Ad-SV) infected cells. In addition, MMP-2 inhibition in the tumor cells decreased the expression of stromal cell-derived factor 1 (SDF1) in the tumor-conditioned medium, which results in impaired SDF1/CXCR4 signaling leading to decreased stem cell tropism towards the tumor cells. We further show that MMP-2 inhibition in the tumor cells repressed stem cell tropism towards medulloblastoma tumors in vivo. In summary, we conclude that hUCBSCs can integrate into human medulloblastoma after local delivery and that MMP-2 expression by the tumor cells mediates this response through the SDF1/CXCR4 axis.

Therapeutic efficacy and safety of TRAIL-producing human adipose tissue-derived mesenchymal stem cells against experimental brainstem glioma

Mesenchymal stem cells (MSCs) have an extensive migratory capacity for gliomas, which is comparable to that of neural stem cells. Among the various types of MSCs, human adipose tissue-derived MSCs (hAT-MSC) emerge as one of the most attractive vehicles for gene therapy because of their high throughput, lack of ethical concerns, and availability and ease of isolation. We evaluated the therapeutic potential and safety of genetically engineered hAT-MSCs encoding the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) against brainstem gliomas. Human AT-MSCs were isolated from human fat tissue, characterized, and transfected with TRAIL using nucleofector. The therapeutic potential of TRAIL-producing hAT-MSCs (hAT-MSC.TRAIL) was confirmed using in vitro and in vivo studies. The final fate of injected hAT-MSCs was traced in long-survival animals. The characterization of hAT-MSCs revealed the expression of MSC-specific cell-type markers and their differentiation potential into mesenchymal lineage. Short-term outcomes included a 56.3% reduction of tumor volume (P < .001) with increased apoptosis (3.03-fold, P < .05) in animals treated with hAT-MSC.TRAIL compared with the control groups. Long-term outcomes included a significant survival benefit in the hAT-MSC.TRAIL-treated group (26 days of median survival in the control group vs 84 days in the hAT-MSC.TRAIL-treated group, P < .0001), without any evidence of mesenchymal differentiation in vivo. Our study demonstrated the therapeutic efficacy and safety of nonvirally engineered hAT-MSCs against brainstem gliomas and showed the possibility of stem-cell-based targeted gene therapy for clinical application.

Concise review: Nanoparticles and cellular carriers-allies in cancer imaging and cellular gene therapy?

Ineffective treatment and poor patient management continue to plague the arena of clinical oncology. The crucial issues include inadequate treatment efficacy due to ineffective targeting of cancer deposits, systemic toxicities, suboptimal cancer detection and disease monitoring. This has led to the quest for clinically relevant, innovative multifaceted solutions such as development of targeted and traceable therapies. Mesenchymal stem cells (MSCs) have the intrinsic ability to "home" to growing tumors and are hypoimmunogenic. Therefore, these can be used as (a) "Trojan Horses" to deliver gene therapy directly into the tumors and (b) carriers of nanoparticles to allow cell tracking and simultaneous cancer detection. The camouflage of MSC carriers can potentially tackle the issues of safety, vector, and/or transgene immunogenicity as well as nanoparticle clearance and toxicity. The versatility of the nanotechnology platform could allow cellular tracking using single or multimodal imaging modalities. Toward that end, noninvasive magnetic resonance imaging (MRI) is fast becoming a clinical favorite, though there is scope for improvement in its accuracy and sensitivity. In that, use of superparamagnetic iron-oxide nanoparticles (SPION) as MRI contrast enhancers may be the best option for tracking therapeutic MSC. The prospects and consequences of synergistic approaches using MSC carriers, gene therapy, and SPION in developing cancer diagnostics and therapeutics are discussed.

Stem cell transplantation in brain tumors: a new field for molecular imaging?

Neural stem cells have been proposed as a new and promising treatment modality in various pathologies of the central nervous system, including malignant brain tumors. However, the underlying mechanism by which neural stem cells target tumor areas remains elusive. Monitoring of these cells is currently done by use of various modes of molecular imaging, such as optical imaging, magnetic resonance imaging and positron emission tomography, which is a novel technology for visualizing metabolism and signal transduction to gene expression. In this new context, the microenvironment of (malignant) brain tumors and the blood-brain barrier gains increased interest. The authors of this review give a unique overview of the current molecular-imaging techniques used in different therapeutic experimental brain tumor models in relation to neural stem cells. Such methods for molecular imaging of gene-engineered neural stem/progenitor cells are currently used to trace the location and temporal level of expression of therapeutic and endogenous genes in malignant brain tumors, closing the gap between in vitro and in vivo integrative biology of disease in neural stem cell transplantation.

Iron labeling and pre-clinical MRI visualization of therapeutic human neural stem cells in a murine glioma model

BACKGROUND

Treatment strategies for the highly invasive brain tumor, glioblastoma multiforme, require that cells which have invaded into the surrounding brain be specifically targeted. The inherent tumor-tropism of neural stem cells (NSCs) to primary and invasive tumor foci can be exploited to deliver therapeutics to invasive brain tumor cells in humans. Use of the strategy of converting prodrug to drug via therapeutic transgenes delivered by immortalized therapeutic NSC lines have shown efficacy in animal models. Thus therapeutic NSCs are being proposed for use in human brain tumor clinical trials. In the context of NSC-based therapies, MRI can be used both to non-invasively follow dynamic spatio-temporal patterns of the NSC tumor targeting allowing for the optimization of treatment strategies and to assess efficacy of the therapy. Iron-labeling of cells allows their presence to be visualized and tracked by MRI. Thus we aimed to iron-label therapeutic NSCs without affecting their cellular physiology using a method likely to gain United States Federal Drug Administration (FDA) approval.

METHODOLOGY

For human use, the characteristics of therapeutic Neural Stem Cells must be clearly defined with any pertubation to the cell including iron labeling requiring reanalysis of cellular physiology. Here, we studied the effect of iron-loading of the therapeutic NSCs, with ferumoxide-protamine sulfate complex (FE-Pro) on viability, proliferation, migratory properties and transgene expression, when compared to non-labeled cells. FE-Pro labeled NSCs were imaged by MRI at tumor sites, after intracranial administration into the hemisphere contralateral to the tumor, in an orthotopic human glioma xenograft mouse model.

CONCLUSION

FE-Pro labeled NSCs retain their proliferative status, tumor tropism, and maintain stem cell character, while allowing in vivo cellular MRI tracking at 7 Tesla, to monitor their real-time migration and distribution at brain tumor sites. Of significance, this work directly supports the use of FE-Pro-labeled NSCs for real-time tracking in the clinical trial under development: "A Pilot Feasibility Study of Oral 5-Fluorocytosine and Genetically modified Neural Stem Cells Expressing Escherichia coli Cytosine Deaminase for Treatment of Recurrent High-Grade Gliomas".

Applications of neural and mesenchymal stem cells in the treatment of gliomas

In addition to stem cells providing a better understanding about the biology and origins of gliomas, new therapeutic approaches have been developed based on the use of stem cells as delivery vehicles. The unique ability of stem cells to track down tumor cells makes them a very appealing therapeutic modality. This review introduces neural and mesenchymal stem cells, discusses the advances that have been made in the utilization of these stem cells as therapies and in diagnostic imaging (to track the advancement of the stem cells towards the tumor cells), and concludes by addressing various challenges and concerns regarding these therapies.

The role of CXC chemokine ligand (CXCL)12-CXC chemokine receptor (CXCR)4 signalling in the migration of neural stem cells towards a brain tumour

AIMS

It has been shown that neural stem cells (NSCs) migrate towards areas of brain injury or brain tumours and that NSCs have the capacity to track infiltrating tumour cells. The possible mechanism behind the migratory behaviour of NSCs is not yet completely understood. As chemokines are involved in the migration of immune cells in the injured brain, they may also be involved in chemoattraction of NSCs towards a brain tumour.

METHODS

The expression profile of various chemokine receptors in NSCs, harvested from the subventricular zone of adult mice, was investigated by reverse transcriptase- polymerase chain reaction analysis. Furthermore, the functionality of the chemokine receptors was assessed in in vitro chemotaxis assays and calcium signalling experiments. To test the in vivo migration of NSCs, a syngeneic mouse model was developed, whereby a B16F10 melanoma cell line was grafted into one hemisphere and later NSCs were grafted in the contralateral hemisphere. Furthermore, the expression of chemokines in this melanoma cell line was investigated.

RESULTS AND CONCLUSIONS

Adult mouse NSCs functionally express various chemokine receptors of which CXC chemokine receptor (CXCR)4 shows the highest mRNA levels and most pronounced functional responses in vitro. CXC chemokine ligand (CXCL)12, the ligand for CXCR4, is expressed by the melanoma cell line. In this mouse model for metastatic brain tumours, it is shown that NSCs express CXCR4 at their cell membranes while they migrate towards the tumour, which produces CXCL12. It is therefore suggested that the CXCR4/CXCL12 pathway plays a role in the mechanism underlying tumour-mediated attraction of NSCs.

Maintaining and engineering neural stem cells for delivery of genetically encoded therapy to brain tumors

Despite advances for the treatment of cancer, the prognosis for patients suffering from malignant brain tumors remains dismal. High-grade neoplasms, such as gliomas, are highly invasive and spawn widely disseminated microsatellites that have limited the efficacy of surgical and adjunctive therapies. The cancer stem cell hypothesis suggests that conventional chemotherapeutic treatments kill differentiated and differentiating cells which often form the bulk of the tumor. One major concern is that the cells which give rise to the tumor, the cancer stem cells, remain untouched and may be responsible for a relapse of the disease. Therefore, an adjunctive therapy to current cancer treatment is critical for the survivability of patients suffering from brain tumors. We have successfully engineered tumor-tropic neural stem cells to deliver antineoplastic gene products directly to the tumor-producing cells. This potential therapeutic strategy may safely eradicate tumor-producing cells in the brain while minimizing damage to normal, healthy cells.

Neural stem cell delivery to the spinal cord in an ovine model of fetal surgery for spina bifida

BACKGROUND

We introduce the notion of prenatal neural stem cell (NSC) delivery to the spinal cord as an adjuvant to fetal repair of spina bifida.

METHODS

Fetal lambs with experimental myelomeningocele (MMC; n = 25) were divided in 3 groups: group I, no repair; group II, standard surgical MMC coverage; and group III, MMC coverage plus delivery of a murine NSCs clone into the spinal cord defect. Donor cells constitutively expressed lacZ encoding for Escherichia coli beta-galactosidase, yet they were further labeled by exposure to either BrdU and/or to the fluorescent membrane dye PKH-26. Blinded initial clinical evaluations and multiple spinal cord analyses were undertaken soon after birth.

RESULTS

Both survival and the incidence of major paraparesis were significantly worse in group I compared with groups II and III. In group III, NSC density was highest within the most damaged areas of the spinal cord, with selective engraftment within those regions. Donor NSCs retained an undifferentiated state in vivo, producing neurotrophic factors within the defect. No animals in group III had a worsened condition following this intervention.

CONCLUSIONS

Neural stem cells retain an undifferentiated state and produce neurotrophic factors in the short term after delivery to the fetal spinal cord, in the setting of experimental MMC. Further scrutiny of NSC delivery to the spinal cord as a therapeutic strategy against spina bifida is warranted.

Neural stem cells in the mammalian brain

New fundamental results on stem cell biology have been obtained in the past 15 years. These results allow us to reinterpret the functioning of the cerebral tissue in health and disease. Proliferating stem cells have been found in the adult brain, which can be involved in postinjury repair and can replace dead cells under specific conditions. Numerous genomic mechanisms controlling stem cell proliferation and differentiation have been identified. The involvement of stem cells in the genesis of malignant tumors has been demonstrated. Neural stem cell tropism toward tumors has been shown. These findings suggest new lines of research on brain functioning and development. Stem cells can be used to develop radically new treatments of neurodegenerative and cancer diseases of the brain.

Potential of neural stem cells for the treatment of brain tumors

Neural stem cells (NSCs) are self-renewing multipotent cells that generate the main phenotypes of the nervous system, neurons, astrocytes and oligodendrocytes. As such they hold the promise to treat a broad range of neurological diseases and injuries. Neural progenitor and stem cells have been isolated and characterized in vitro, from adult, fetal and post-mortem tissues, providing sources of material for cellular therapy. However, NSCs are still elusive cells and remain to be unequivocally identified and characterized, limiting their potential use for therapy. Neural progenitor and stem cells, isolated and cultured in vitro, can be genetically modified and when transplanted migrate to tumor sites in the brain. These intrinsic properties of neural progenitor and stem cells provide tremendous potential to bolster the translation of NSC research to therapy. It is proposed to combine gene therapy and cellular therapy to treat brain cancers. Hence, neural progenitor and stem cells provide new opportunities for the treatment of brain cancers.

Embryonic stem cell biology

ES cell research represents an exploding field of exploration. Initially predicted to provide rapid cures for numerous human diseases, the clinical usefulness of ES cell-derived cells remains untested in humans. However, ES cells have rapidly expanded our knowledge of human development and the molecular details of differentiation. Our ability to generate relatively pure populations of specifically differentiated cells for transplantation has markedly improved. It is hoped that soon researchers will overcome the biologic impediments to successful treatment of human disease with ES cell-derived cells.

Gliomagenesis and neural stem cells: Key role of hypoxia and concept of tumor “neo-niche”

Gliomas represent the most common primary brain tumors and the most devastating pathology of the central nervous system. Despite progress in conventional treatments, the prognosis remains dismal. Recent studies have suggested that a glioma brain tumor may arise from a "cancer stem cell". To understand this theory we summarize studies of the concepts of neural stem cell, and its specialized microenvironment, namely the niche which can regulate balanced self-renewal, differentiation and stem cell quiescence. We summarize the molecular mechanism known or postulated to be involved in the disregulation of normal stem cells features allowing them to undergo neoplasic transformation. We seek data pointing out the key role of hypoxia in normal homeostasis of stem cells and in the initiation, development and aggressiveness of gliomas. We develop the concept of tumor special microenvironment and we propose the new concept of neo-niche, surrounding the glioma, in which hypoxia could be a key factor to recruit and deregulate different stem cells for gliogenesis process. Substantial advances in treatment would come from obtaining better knowledge of molecular impairs of this disease.

Stem cells engineering for cell-based therapy

Stem cells carry the promise to cure a broad range of diseases and injuries, from diabetes, heart and muscular diseases, to neurological diseases, disorders and injuries. Significant progresses have been made in stem cell research over the past decade; the derivation of embryonic stem cells (ESCs) from human tissues, the development of cloning technology by somatic cell nuclear transfer (SCNT) and the confirmation that neurogenesis occurs in the adult mammalian brain and that neural stem cells (NSCs) reside in the adult central nervous system (CNS), including that of humans. Despite these advances, there may be decades before stem cell research will translate into therapy. Stem cell research is also subject to ethical and political debates, controversies and legislation, which slow its progress. Cell engineering has proven successful in bringing genetic research to therapy. In this review, I will review, in two examples, how investigators are applying cell engineering to stem cell biology to circumvent stem cells' ethical and political constraints and bolster stem cell research and therapy.

Intravascular administration of tumor tropic neural progenitor cells permits targeted delivery of interferon-beta and restricts tumor growth in a murine model of disseminated neuroblastoma

BACKGROUND

Interferon-beta (IFN-beta) has potent antitumor activity; however, systemic toxicity has limited its clinical use. We investigated the potential of targeted delivery using tumor-tropic neural progenitor cells (NPCs) transduced to express human IFN-beta (hIFN-beta).

METHODS

Disseminated neuroblastoma was established in SCID mice by tail vein injection of tumor cells. Fourteen days after tumor cell inoculation, systemic disease was confirmed with bioluminescence imaging (BLI). Mice were then treated by intravenous injection of human F3.C1 NPCs that had been transduced with a replication deficient adenovirus to overexpress hIFN-beta (F3-IFN-beta). Two injections were given: the first at 14 days and the second at 28 days following tumor cell injection. Control mice received NPCs transduced with empty vector adenovirus at the same time points. Progression of disease was monitored using BLI. At sacrifice, organ weights and histology further evaluated tumor burden.

RESULTS

After initiation of therapy, BLI demonstrated a significant decrease in the rate of disease progression in mice receiving F3-IFN-beta. At necropsy, control mice had bulky tumor replacing the liver and kidneys, as well as extensive retroperitoneal and mediastinal adenopathy. Impressively, these sites within mice receiving F3-IFN-beta therapy appeared grossly normal with the exception of small nodules within the kidneys of some of the F3-IFN-beta-treated mice. The accumulation of F3.C1 cells within sites of tumor growth was confirmed by fluorescence imaging. Importantly, systemic levels of hIFN-beta in the treated mice remained below detectable levels.

CONCLUSIONS

These data indicate that in this model of disseminated neuroblastoma, the tumor-tropic property of F3.C1 NPCs was exploited to target delivery of IFN-beta to disseminated tissue foci, resulting in significant tumor growth delay. The described novel approach for effective IFN-beta therapy may circumvent limitations associated with the systemic toxicity of IFN-beta.

Structure-specific patterns of neural stem cell engraftment after transplantation in the adult mouse brain

Transplantation of neural stem cells (NSCs) may be useful for delivering exogenous gene products to the diseased CNS. When NSCs are transplanted into the developing mouse brain, they can migrate extensively and differentiate into cells appropriate to the sites of engraftment, in response to the normal signals directing endogenous cells to their appropriate fates. Much of the prior work on NSC migration in the adult brain has examined directed migration within or toward focal areas of injury such as ischemia, brain tumors, or 6-hydroxydopamine (6-OHDA) lesions. However, treatment of many genetic disorders that affect the CNS will require widespread dissemination of the donor cells in the postnatal brain, because the lesions are typically distributed globally. We therefore tested the ability of NSCs to migrate in the unlesioned adult mouse brain after stereotaxic transplantation into several structures including the cortex and hippocampus. NSC engraftment was monitored in live animals by magnetic resonance imaging (MRI) after superparamagnetic iron oxide (SPIO) labeling of cells. Histological studies demonstrated that the cells engrafted in significantly different patterns within different regions of the brain. In the cerebral cortex, donor cells migrated in all directions from the injection site. The cells maintained an immature phenotype and cortical migration was enhanced by trypsin treatment of the cells, indicating a role for cell surface proteins. In the hippocampus, overall cell survival and migration were lower but there was evidence of neuronal differentiation. In the thalamus, the transplanted cells remained in a consolidated mass at the site of injection. These variations in pattern of engraftment should be taken into account when designing treatment approaches in nonlesion models of neurologic disease.

Gene therapy for malignant glioma: current clinical status

Glioblastoma is an aggressive brain tumor with a dismal prognosis. Gene therapy may offer a new option for the treatment of these patients. Several gene therapy approaches have shown anti-tumor efficiency in experimental studies, and the first clinical trials for the treatment of malignant glioma were conducted in the 1990s. HSV-tk gene therapy has been the pioneering and most commonly used approach, but oncolytic conditionally replicating adenoviruses and herpes simplex virus mutant vectors, p53, interleukins, interferons, and antisense oligonucleotides have also been used. During the past few years, adenoviruses have become the most popular gene transfer vectors, and some recent randomized, controlled trials have shown significant anti-tumor efficacy in clinical use. However, efficient gene delivery into the brain still presents a major problem, and there is a lack of definitive phase III trials, which would avoid potential problems associated with a small number of patients, inadvertent patient selection, and overinterpretation of results based on a few long-time survivors. For clinical efficacy, median survival is one of the most rigorous endpoints. It is used here to evaluate the usefulness of various treatment approaches and current clinical status of gene therapy for malignant glioma.

Neural stem cells as novel cancer therapeutic vehicles

The startling resemblance of many of the behaviours of brain tumours to the intrinsic properties of the neural stem/progenitor cell has triggered a recent dual interest in arming stem cells to track and help eradicate tumours and in viewing stem cell biology as somehow integral to the emergence and/or propagation of the neoplasm itself. These aspects are reviewed and discussed here.

Chemokines regulate the migration of neural progenitors to sites of neuroinflammation

Many studies have shown that transplanted or endogenous neural progenitor cells will migrate toward damaged areas of the brain. However, the mechanism underlying this effect is not clear. Here we report that, using hippocampal slice cultures, grafted neural progenitor cells (NPs) migrate toward areas of neuroinflammation and that chemokines are a major regulator of this process. Migration of NPs was observed after injecting an inflammatory stimulus into the area of the fimbria and transplanting enhanced green fluorescent protein (EGFP)-labeled NPs into the dentate gyrus of cultured hippocampal slices. Three to 7 d after transplantation, EGFP-NPs in control slices showed little tendency to migrate and had differentiated into neurons and glia. In contrast, in slices injected with inflammatory stimuli, EGFP-NPs migrated toward the site of the injection. NPs in these slices also survived less well. The inflammatory stimuli used were a combination of the cytokines tumor necrosis factor-alpha and interferon-gamma, the bacterial toxin lipopolysaccharide, the human immunodeficiency virus-1 coat protein glycoprotein 120, or a beta-amyloid-expressing adenovirus. We showed that these inflammatory stimuli increased the synthesis of numerous chemokines and cytokines by hippocampal slices. When EGFP-NPs from CC chemokine receptor CCR2 knock-out mice were transplanted into slices, they exhibited little migration toward sites of inflammation. Similarly, wild-type EGFP-NPs exhibited little migration toward inflammatory sites when transplanted into slices prepared from monocyte chemoattractant protein-1 (MCP-1) knock-out mice. These data indicate that factors secreted by sites of neuroinflammation are attractive to neural progenitors and suggest that chemokines such as MCP-1 play an important role in this process.

Mammalian stem cells

Stem cells are quickly coming into focus of much biomedical research eventually aiming at the therapeutic applications for various disorders and trauma. It is important, however, to keep in mind the difference between the embryonic stem cells, somatic stem cells and somatic precursor cells when considering potential clinical applications. Here we provide the review of the current status of stem cell field and discuss the potential of therapeutic applications for blood and Immune system disorders, multiple sclerosis, hypoxic-ischemic brain injury and brain tumors. For the complimentary information about various stem cells and their properties we recommend consulting the National Institutes of Health stem cell resources (http://stemcells.nih.gov/info/basics).

Targeting of melanoma brain metastases using engineered neural stem/progenitor cells

Brain metastases are an increasingly frequent and serious clinical problem for cancer patients, especially those with advanced melanoma. Given the extensive tropism of neural stem/progenitor cells (NSPCs) for pathological areas in the central nervous system, we expanded investigations to determine whether NSPCs could also target multiple sites of brain metastases in a syngeneic experimental melanoma model. Using cytosine deaminase-expressing NSPCs (CD-NSPCs) and systemic 5-fluorocytosine (5-FC) pro-drug administration, we explored their potential as a cell-based targeted drug delivery system to disseminated brain metastases. Our results indicate a strong tropism of NSPCs for intracerebral melanoma metastases. Furthermore, in our therapeutic paradigm, animals with established melanoma brain metastasis received intracranial implantation of CD-NSPCs followed by systemic 5-FC treatment, resulting in a significant (71%) reduction in tumor burden. These data provide proof of principle for the use of NSPCs for targeted delivery of therapeutic gene products to melanoma brain metastases.

Selective migration of neuralized embryonic stem cells to stem cell factor and media conditioned by glioma cell lines

BACKGROUND

Pluripotent mouse embryonic stem (ES) cells can be induced in vitro to become neural progenitors. Upon transplantation, neural progenitors migrate toward areas of damage and inflammation in the CNS. We tested whether undifferentiated and neuralized mouse ES cells migrate toward media conditioned by glioma cell lines (C6, U87 & N1321) or Stem Cell Factor (SCF).

RESULTS

Cell migration assays revealed selective migration by neuralized ES cells to conditioned media as well as to synthetic SCF. Migration of undifferentiated ES cells was extensive, but not significantly different from that of controls (Unconditioned Medium). RT-PCR analysis revealed that all the three tumor cell lines tested synthesized SCF and that both undifferentiated and neuralized ES cells expressed c-kit, the receptor for SCF.

CONCLUSION

Our results demonstrate that undifferentiated ES cells are highly mobile and that neural progenitors derived from ES cells are selectively attracted toward factors produced by gliomas. Given that the glioma cell lines synthesize SCF, SCF may be one of several factors that contribute to the selective migration observed.

Genetic strategies for brain tumor therapy

Gene therapy is a potentially useful approach in the treatment of human brain tumors, which are notoriously refractory to conventional approaches. Most human clinical trials to date have been unsuccessful in terms of improving patient outcome. Recent improvements in viral vectors, the development of stem cell technology, and increased understanding of the mechanism of action of therapeutic transgenes provide hope that the next generation of gene therapeutics may show increased efficacy in treatment of this devastating disease.

PEX-Producing Human Neural Stem Cells Inhibit Tumor Growth in a Mouse Glioma Model

A unique characteristic of neural stem cells is their capacity to track glioma cells that have migrated away from the main tumor mass into the normal brain parenchyma. PEX, a naturally occurring fragment of human metalloproteinase-2, acts as an inhibitor of glioma and endothelial cell proliferation, migration, and angiogenesis. In the present study, we evaluated the antitumor activity of PEX-producing human neural stem cells against malignant glioma. The HB1.F3 cell line (immortalized human neural stem cell) was transfected by a pTracer vector with PEX. The retention of the antiproliferative activity and migratory ability of PEX-producing HB1.F3 cells (HB1.F3-PEX) was confirmed in vitro. For the in vivo studies, DiI-labeled HB1.F3-PEX cells were stereotactically injected into established glioma tumor in nude mice. Tumor size was subsequently measured by magnetic resonance imaging and at the termination of the studies by histologic analysis including tumor volume, microvessel density, proliferation, and apoptosis rate. Histologic analysis showed that DiI-labeled HB1.F3-PEX cells migrate at the tumor boundary and cause a 90% reduction of tumor volume (P < 0.03). This reduction in tumor volume in animals treated with HB1.F3-PEX was associated with a significant decrease in angiogenesis (44.8%, P < 0.03) and proliferation (23.6%, P < 0.03). These results support the use of neural stem cells as delivery vehicle for targeting therapeutic genes against human glioma.

Stem cells and brain cancer

One of the most devastating CNS pathologies is brain cancer. The undifferentiated character of brain tumor cells and recent reports of cancer stem cells prompt questions regarding the involvement of normal stem/progenitor cells in brain tumor biology, their potential contribution to the tumor itself, and whether they are the cause or the consequence of tumor initiation and progression. The cancer stem cell model proposes a clonally derived brain tumor arising from a cancer stem cell. This tumor cell-of-origin originates from a stem/progenitor or more differentiated cell via acquisition of oncogenic mutations that dysregulate or allow reacquisition of self-renewal mechanisms. The tumor cells differentiate unidirectionally from the cancer stem cell in a way parallel to normal development. However, several properties of brain tumors add complexity to this model. For example, the apparent lineage and differentiation status of tumor cells are significantly affected by signaling abnormalities that are causally related to formation of the tumor. In addition, these tumors recruit normal CNS stem and progenitor cells to the tumor mass leading to the possibility of a heterogeneous and polyclonal cell population. It is likely that a complete description of the role of stem cells in brain tumors will be more complex than our current models.

At the interface of the immune system and the nervous system: how neuroinflammation modulates the fate of neural progenitors in vivo

Neural stem and progenitor cells express a variety of receptors that enable them to sense and react to signals emanating from physiological and pathophysiological conditions in the brain as well as elsewhere in the body. Many of these receptors and were first described in investigations of the immune system, particularly with respect to hematopoietic stem cells. This emerging view of neurobiology has two major implications. First, many phenomena known from the hematopoietic system may actually be generalizable to stem cells from many organ systems, reflecting the cells' progenitor-mediated regenerative potential. Second, regenerative interfaces may exist between diverse organ systems; populations of cells of neuroectodermal and hematopoietic origin may interact to play a crucial role in normal brain physiology, pathology, and repair. An understanding of the origins of signals and the neural progenitors' responses might lead to the development of effective therapeutic strategies to counterbalance acute and chronic neurodegenerative processes. Such strategies may include modifying and modulating cells with regenerative potential in subtle ways. For example, stem cells might be able to detect pathology-associated signals and be used as "interpreters" to mediate drug and other therapeutic interventions. This review has focused on the role of inflammation in brain repair. We propose that resident astroglia and blood-born cells both contribute to an inflammatory signature that is unique to each kind of neuronal degeneration or injury. These cells play a key role in coordinating the neural progenitor cell response to brain injury by exerting direct and indirect environmentally mediated influence on neural progenitor cells. We suggest that investigations of the neural progenitor-immunologic interface will provide valuable data related to the mechanisms by which endogenous and exogenous neural progenitor cells react to brain pathology, ultimately aiding in the design of more effective therapeutic applications of stem cell biology. Such improvements will include: (1) ascertaining the proper timing for implanting exogenous neural progenitor cells in relation to the administration of anti-inflammatory agents; (2) identifying what types of molecules might be administered during injury to enhance the mobilization and differentiation of endogenous and exogenous neural progenitor cells while also inhibiting the detrimental aspects of the inflammatory reaction; (3) divining clues as to which molecules may be required to change the lesioned environment in order to invite the homing of reparative neural progenitor cells.

Neuronally expressed stem cell factor induces neural stem cell migration to areas of brain injury

Neural stem/progenitor cell (NSPC) migration toward sites of damaged central nervous system (CNS) tissue may represent an adaptive response for the purpose of limiting and/or repairing damage. Little is known of the mechanisms responsible for this migratory response. We constructed a cDNA library of injured mouse forebrain using subtractive suppression hybridization (SSH) to identify genes that were selectively upregulated in the injured hemisphere. We demonstrate that stem cell factor (SCF) mRNA and protein are highly induced in neurons within the zone of injured brain. Additionally, the SCF receptor c-kit is expressed on NSPCs in vitro and in vivo. Finally, we demonstrate that recombinant SCF induces potent NSPC migration in vitro and in vivo through the activation of c-kit on NSPCs. These data suggest that the SCF/c-kit pathway is involved in the migration of NSPCs to sites of brain injury and that SCF may prove useful for inducing progenitor cell recruitment to specific areas of the CNS for cell-based therapeutic strategies.

Human amnion mesenchyme cells express phenotypes of neuroglial progenitor cells

Previous studies from our laboratory showed that human amnion epithelial cells (AECs) have multiple functions, such as synthesis and release of catecholamines, acetylcholine, neurotrophic factors, activin, and noggin. In this study, we investigated the identity of neural progenitor cells in human amnion mesenchyme cells (AMCs), which lie immediately adjacent to the AECs. Cryostat sections revealed that vimentin expression was detected in the AMCs and CK19 in AECs. Vimentin-positive cells made up 97.5% of total cells tested in cultured AMCs. Interestingly, 3.6% of total AMCs expressed the phenotype CK19+/vimentin+, indicating coexpression of epithelial and mesenchyme cell markers. In culturing with bromodeoxyuridine (BrdU) for 24 hr, 66-82% of cells were found to be BrdU positive, suggesting that they have proliferating potency. By using RT-PCR, AMCs express mRNA of nestin and Musashi1. With a neural cell differentiating protocol, cell bodies extended long bipolar or complex multipolar processes. Nestin (87.7% of total cells tested) and Musashi1 (93.1%) were expressed in undifferentiated cells, and their positively stained cells increased in number slightly after induction. Undifferentiated cells were stained by anti-Tuj1 and NF-M, and their positively stained cells increased significantly in number after induction, to 72.8% and 46.0%, respectively. Meanwhile, glial fibrillary acidic protein-positive cells increased from 25.4% to 43.2% after induction. These studies demonstrate that AMCs have phenotypes of neuroglial progenitor cells and can be differentiated into neuroglial phenotypes by optimal differentiation protocol. Eventually, AMC-derived stem cells may be a favorable cell vehicle in regenerative medicine.