Up-regulation of neuropoiesis generating glial progenitors that infiltrate rat intracranial glioma

The subventricular zone structure, function and implications for neurological disease

The subventricular zone (SVZ) is a region surrounding the lateral ventricles that contains neural stem cells and neural progenitor cells, which can proliferate and differentiate into various neural and glial cells. SVZ cells play important roles in neurological diseases like neurodegeneration, neural injury, and glioblastoma multiforme. Investigating the anatomy, structure, composition, physiology, disease associations, and related mechanisms of SVZ is significant for neural stem cell therapy and treatment/prevention of neurological disorders. However, challenges remain regarding the mechanisms regulating SVZ cell proliferation, differentiation, and migration, delivering cells to damaged areas, and immune responses. In-depth studies of SVZ functions and related therapeutic developments may provide new insights and approaches for treating brain injuries and degenerative diseases, as well as a scientific basis for neural stem cell therapy. This review summarizes research findings on SVZ and neurological diseases to provide references for relevant therapies.

Glioblastoma Proximity to the Lateral Ventricle Alters Neurogenic Cell Populations of the Subventricular Zone

Despite current strategies combining surgery, radiation, and chemotherapy, glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor in adults. Tumor location plays a key role in the prognosis of patients, with GBM tumors located in close proximity to the lateral ventricles (LVs) resulting in worse survival expectancy and higher incidence of distal recurrence. Though the reason for worse prognosis in these patients remains unknown, it may be due to proximity to the subventricular zone (SVZ) neurogenic niche contained within the lateral wall of the LVs. We present a novel rodent model to analyze the bidirectional signaling between GBM tumors and cells contained within the SVZ. Patient-derived GBM cells expressing GFP and luciferase were engrafted at locations proximal, intermediate, and distal to the LVs in immunosuppressed mice. Mice were either sacrificed after 4 weeks for immunohistochemical analysis of the tumor and SVZ or maintained for survival analysis. Analysis of the GFP+ tumor bulk revealed that GBM tumors proximal to the LV show increased levels of proliferation and tumor growth than LV-distal counterparts and is accompanied by decreased median survival. Conversely, numbers of innate proliferative cells, neural stem cells (NSCs), migratory cells and progenitors contained within the SVZ are decreased as a result of GBM proximity to the LV. These results indicate that our rodent model is able to accurately recapitulate several of the clinical aspects of LV-associated GBM, including increased tumor growth and decreased median survival. Additionally, we have found the neurogenic and cell division process of the SVZ in these adult mice is negatively influenced according to the presence and proximity of the tumor mass. This model will be invaluable for further investigation into the bidirectional signaling between GBM and the neurogenic cell populations of the SVZ.

Targeting Subventricular Zone Progenitor Cells with Intraventricular Liposomal Encapsulated Cytarabine in Patients with Secondary Glioblastoma : A Report of Two Cases

Background

Current treatments for glioblastoma (GB), the most common and malignant primary brain tumor are inadequate and as such, the median survival for most patients with GB is on the order of months, even after cytoreductive surgery, radiation and chemotherapy.

Case Description

Current study reports two cases of glioblastoma (GB) with subventricular zone (SVZ) involvement. SVZ biopsies demonstrated the presence of hypercellularity, nestin immunoreactivity, and a Ki-67 labeling index (LI) of 1-2%. Interestingly, tumor morphology and proliferative indices are different in the SVZ specimens than the hemispheric recurrences, which displayed similar nestin immunoreactivity, but a greater LI of 10%. Biopsy specimens demonstrated both intense nestin immunoreactivity and GFAP immunoreactivity in and around the GB recurrence. Nestin positive cells were more abundant closer to the SVZ nearest to the dorsolateral horn of the left lateral ventricle, while GFAP immunoreactivity was more intense closer to the center of the tumor recurrence. Additionally, co-labeling of cells with Ki67 and several different progenitor markers (CD133, CD140, TUJ-1, and nestin) demonstrated that these cells found in and around the GB recurrence were actively dividing. Having failed standard therapy with evidence of bi-hemispheric spread and progression to GB, we report a novel approach of using intraventricular liposomal encapsulated cytarabine (DepoCyt) for the treatment for GB by suppressing glial progenitor cells that surround the ventricular system in patients with GB.

Conclusions

MRI and immunohistochemistry demonstrated that the SVZ is the incubator for future recurrences of GB and propose targeting SVZ progenitor cells with intraventricular liposomal encapsulated Ara-C. Two patients treated using this novel regimen have demonstrated partial radiographic responses warranting further studies looking at targeting the subventricular zone.

Radiation therapy for glioma stem cells

Radiation therapy is the most effective adjuvant treatment modality for virtually all patients with high-grade glioma. Its ability to improve patient survival has been recognized for decades. Cancer stem cells provide new insights into how tumor biology is affected by radiation and the role that this cell population can play in disease recurrence. Glioma stem cells possess a variety of intracellular mechanisms to resist and even flourish in spite of radiation, and their proliferation and maintenance appear tied to supportive stimuli from the tumor microenvironment. This chapter reviews the basis for our current use of radiation to treat high-grade gliomas, and addresses this model in the context of therapeutically resistant stem cells. We discuss the available evidence highlighting current clinical efforts to improve radiosensitivity, and newer targets worthy of further development.

Cancer stem cells from a rare form of glioblastoma multiforme involving the neurogenic ventricular wall

BACKGROUND

The cancer stem cell (CSC) hypothesis posits that deregulated neural stem cells (NSCs) form the basis of brain tumors such as glioblastoma multiforme (GBM). GBM, however, usually forms in the cerebral white matter while normal NSCs reside in subventricular and hippocampal regions. We attempted to characterize CSCs from a rare form of glioblastoma multiforme involving the neurogenic ventricular wall.

METHODS

We described isolating CSCs from a GBM involving the lateral ventricles and characterized these cells with in vitro molecular biomarker profiling, cellular behavior, ex vivo and in vivo techniques.

RESULTS

The patient's MRI revealed a heterogeneous mass with associated edema, involving the left subventricular zone. Histological examination of the tumor established it as being a high-grade glial neoplasm, characterized by polygonal and fusiform cells with marked nuclear atypia, amphophilic cytoplasm, prominent nucleoli, frequent mitotic figures, irregular zones of necrosis and vascular hyperplasia. Recurrence of the tumor occurred shortly after the surgical resection. CD133-positive cells, isolated from the tumor, expressed stem cell markers including nestin, CD133, Ki67, Sox2, EFNB1, EFNB2, EFNB3, Cav-1, Musashi, Nucleostemin, Notch 2, Notch 4, and Pax6. Biomarkers expressed in differentiated cells included Cathepsin L, Cathepsin B, Mucin18, Mucin24, c-Myc, NSE, and TIMP1. Expression of unique cancer-related transcripts in these CD133-positive cells, such as caveolin-1 and -2, do not appear to have been previously reported in the literature. Ex vivo organotypic brain slice co-culture showed that the CD133+ cells behaved like tumor cells. The CD133-positive cells also induced tumor formation when they were stereotactically transplanted into the brains of the immune-deficient NOD/SCID mice.

CONCLUSIONS

This brain tumor involving the neurogenic lateral ventricular wall was comprised of tumor-forming, CD133-positive cancer stem cells, which are likely the driving force for the rapid recurrence of the tumor in the patient.

Low Concentration Microenvironments Enhance the Migration of Neonatal Cells of Glial Lineage

Glial tumors have demonstrated abilities to sustain growth via recruitment of glial progenitor cells (GPCs), which is believed to be driven by chemotactic cues. Previous studies have illustrated that mouse GPCs of different genetic backgrounds are able to replicate the dispersion pattern seen in the human disease. How GPCs with genetic backgrounds transformed by tumor paracrine signaling respond to extracellular cues via migration is largely unexplored, and remains a limiting factor in utilizing GPCs as therapeutic targets. In this study, we utilized a microfluidic device to examine the chemotaxis of three genetically-altered mouse GPC populations towards tumor conditioned media, as well as towards three growth factors known to initiate the chemotaxis of cells excised from glial tumors: Hepatocyte Growth Factor (HGF), Platelet-Derived Growth Factor-BB (PDGF-BB), and Transforming Growth Factor-α (TGF-α). Our results illustrate that GPC types studied exhibited chemoattraction and chemorepulsion by different concentrations of the same ligand, as well as enhanced migration in the presence of ultra-low ligand concentrations within environments of high concentration gradient. These findings contribute towards our understanding of the causative and supportive roles that GPCs play in tumor growth and reoccurrence, and also point to GPCs as potential therapeutic targets for glioma treatment.

Pericyte deficiencies lead to aberrant tumor vascularizaton in the brain of the NG2 null mouse

Tightly regulated crosstalk between endothelial cells and pericytes is required for formation and maintenance of functional blood vessels. When the NG2 proteoglycan is absent from pericyte surfaces, vascularization of syngeneic tumors growing in the C57Bl/6 mouse brain is aberrant in several respects, resulting in retardation of tumor progression. In the NG2 null mouse brain, pericyte investment of the tumor vascular endothelium is reduced, causing deficiencies in both pericyte and endothelial cell maturation, as well as reduced basal lamina assembly. While part of this deficit may be due to the previously-identified role of NG2 in beta1 integrin-dependent periyte/endothelial cell crosstalk, the ablation of NG2 also appears responsible for loss of collagen VI anchorage, in turn leading to reduced collagen IV deposition. Poor functionality of tumor vessels in NG2 null brain is reflected by reduced vessel patency and increased vessel leakiness, resulting in large increases in tumor hypoxia. These findings demonstrate the importance of NG2-dependent pericyte/endothelial cell interaction in the development and maturation of tumor blood vessels, identifying NG2 as a potential target for anti-angiogenic cancer therapy.

Understanding the origins of gliomas and developing novel therapies: cerebrospinal fluid and subventricular zone interplay

Glioblastoma multiforme (GBM), the most common malignant primary brain tumor in adults, carries a poor prognosis, with median survival generally less than 1 year. Although initial therapy often eradicates the bulk of the tumor, disease recurrence, usually within 2 cm of the original tumor, is almost inevitable. This may be due to a failure of current therapies to eradicate viable chemotherapy- and radiotherapy-resistant neoplastic progenitor cells, which may then repopulate tumors. An increasing body of preclinical data suggests that these cells may correspond to stem cells derived from the subventricular zone (SVZ), which migrate to tumor sites and contribute to glioma growth and recurrence. Therapeutic targeting of SVZ stem cell populations via cerebrospinal fluid (CSF)-directed therapy may provide a means for limiting tumor recurrence. This approach has proved successful in the treatment of medulloblastoma, another brain tumor thought to be derived from stem cells. We discuss the rationale and design considerations for a clinical trial to evaluate the efficacy of CSF-directed therapy for preventing GBM recurrence.

Chemokine CXC receptor 4--mediated glioma tumor tracking by bone marrow--derived neural progenitor/stem cells

Malignant gliomas manifest frequent tumor recurrence after surgical resection and/or other treatment because of their nature of invasiveness and dissemination. The recognized brain tumor-tracking property of neural progenitor/stem cells opened the possibility of targeting malignant brain tumors using neural progenitor/stem cells. We and others have previously shown that fetal neural progenitor/stem cells can be used to deliver therapeutic molecules to brain tumors. Our recent work has further shown that gene delivery by bone marrow-derived neural progenitor/stem cells achieves therapeutic effects in a glioma model. In this study, we isolate and characterize bone marrow-derived neural progenitor/stem cells, which also express the chemokine receptor chemokine CXC receptor 4 (CXCR4). We show that CXCR4 is required for their chemotaxis and extracellular matrix invasion against a gradient of glioma soluble factors. Furthermore, beta-galactosidase-labeled bone marrow-derived neural progenitor/stem cells implanted in the contralateral side of the brain were shown to track gliomas as early as day 1 and increased through days 3 and 7. Intracranial glioma tracking by bone marrow-derived neural progenitor/stem cells is significantly inhibited by preincubation of bone marrow-derived neural progenitor/stem cells with a blocking anti-CXCR4 antibody, suggesting a CXCR4-dependent tracking mechanism. Glioma tracking bone marrow-derived neural progenitor/stem cells were found to express progenitor/stem cell markers, as well as CXCR4. Although bromodeoxyuridine incorporation assays and proliferating antigen staining indicated that tumor tracking bone marrow-derived neural progenitor/stem cells were mostly nonproliferating, these cells survive in the local tumor environment with little apoptosis. Elucidating the molecular mechanism of brain tumor tracking by adult source stem cells may provide basis for the development of future targeted therapy for malignant brain tumors.

Identification of proteins involved in neural progenitor cell targeting of gliomas

BACKGROUND

Glioblastoma are highly aggressive tumors with an average survival time of 12 months with currently available treatment. We have previously shown that specific embryonic neural progenitor cells (NPC) have the potential to target glioma growth in the CNS of rats. The neural progenitor cell treatment can cure approximately 40% of the animals with malignant gliomas with no trace of a tumor burden 6 months after finishing the experiment. Furthermore, the NPCs have been shown to respond to signals from the tumor environment resulting in specific migration towards the tumor. Based on these results we wanted to investigate what factors could influence the growth and progression of gliomas in our rodent model.

METHODS

Using microarrays we screened for candidate genes involved in the functional mechanism of tumor inhibition by comparing glioma cell lines to neural progenitor cells with or without anti-tumor activity. The expression of candidate genes was confirmed at RNA level by quantitative RT-PCR and at the protein level by Western blots and immunocytochemistry. Moreover, we have developed in vitro assays to mimic the antitumor effect seen in vivo.

RESULTS

We identified several targets involved in glioma growth and migration, specifically CXCL1, CD81, TPT1, Gas6 and AXL proteins. We further showed that follistatin secretion from the NPC has the potential to decrease tumor proliferation. In vitro co-cultures of NPC and tumor cells resulted in the inhibition of tumor growth. The addition of antibodies against proteins selected by gene and protein expression analysis either increased or decreased the proliferation rate of the glioma cell lines in vitro.

CONCLUSION

These results suggest that these identified factors might be useful starting points for performing future experiments directed towards a potential therapy against malignant gliomas.

Relationship of gliomas to the ventricular walls

The role of neural stem cells in gliomagenesis remains controversial. The aim of this study was to determine the anatomic relationship of human gliomas to the lining of the ventricular walls, known as the subventricular zone, an area replete with neural stem cells. We performed a retrospective radiographic analysis of 100 consecutive patients with gliomas and sought to determine the relationship of the lesions to the ventricular walls as seen on their MRI scans. Our results indicated that in 93% of cases the lesions contacted at least one region of the lateral ventricular wall. Contact with the ventricular wall was independent of the glioma size or mass effect. These findings were correlated to cytoarchitectural studies of the human subventricular zone. Our findings lend further support that there is an intimate association between gliomas and the subventricular zone.

Mechanisms of Disease: the role of stem cells in the biology and treatment of gliomas

The study of neural stem cell and progenitor cell biology has improved our understanding of the biology of brain tumors in a developmental context. Recent work has demonstrated that brain tumors may harbor small subpopulations of cells that share characteristics of neural stem cells. There is still an ongoing debate about the specific role of these stem-like cells in cancer initiation, development and progression. Nonetheless, the concept of cancer stem cells has offered a new paradigm to understand tumor biology and resistance to current treatment modalities. Molecular aberrations in these cancer stem cells might be crucial targets for therapeutic intervention, with the hope of achieving more durable clinical responses. Recent studies have demonstrated that endogenous and transplanted neural stem cells and progenitor cells show a marked tropism to brain tumors. Although the mechanisms that govern these processes are poorly understood, the use of neural stem cells and progenitor cells as delivery vehicles for molecules toxic to tumors offers a promising experimental treatment strategy. This Review summarizes recent advances in the basic understanding of neural stem cell and cancer stem cell biology and the progress towards translating these novel concepts into the clinic.

Distribution of nestin and other stem cell-related molecules in developing and diseased human spinal cord

In mammalian spinal cords, no neurogenesis has been observed after initial development. However developed mammalian spinal cords seemingly contain neural stem cells (NSC), which can give rise to neurons and glial cells when they are placed in appropriate environments. The purpose of the present paper was to investigate the developing, developed, and diseased human spinal cord to see which cell types have an immunophenotype similar to NSC. In 12 specimens from preterm neonates and term infants up to 14 months old, nestin was expressed in cells that extended fibrous processes and were located around the midline in the ependymal layer. In all the preterm neonates, Musashi-1 and glial fibrillary acidic protein (GFAP) were also expressed in this subpopulation, whereas Lewis X was detected in a less restricted subpopulation. Nestin expression by these cells was not detected in most adult spinal cords, but was observed in three spinal cords from 13 amyotrophic lateral sclerosis patients and eight of 14 spinal cords involved by the tumor. The present observations suggest that during gestation a subpopulation of cells in the ependymal layer remains undifferentiated as potential NSC/neural progenitor cells, and becomes unidentifiable in early infancy. These cells, however, appear in response to disease conditions, especially tumor involvement.

Characterization of the subventricular zone neurogenic response to rat malignant brain tumors

The subventricular zone (SVZ) is one of the neurogenic regions of the adult brain. We characterized the neurogenic response of the SVZ to the growth of brain tumors in the rat striatum. Abundant nestin positive cells, most likely representing reactive astrocytes, were found surrounding the tumor. However, we observed no substantial migration of nestin positive cells from the SVZ toward the tumor. Tumor growth resulted in decreased numbers of bromodeoxyuridine positive and Ki-67 positive proliferating cells and a concomitant increase in doublecortin and polysialylated neural cell adhesion molecule immunoreactivity within the SVZ. Neuroblasts were observed in high numbers in the area between the SVZ and the tumor, most likely pointing to the SVZ as the principal source of these cells. Neuroblasts located between the SVZ and the tumor expressed the transcription factor Pbx, a marker for immature striatal neurons. However, no evidence of neuroblast differentiation into fully mature neurons was found. This study thus demonstrates increased neuroblast immunoreactivity within the SVZ ipsilateral to a brain tumor in the striatum. SVZ-derived neuroblasts attracted by the tumor adopt an immature striatal phenotype indicating a region specific reparative mechanism in response to a malignant tumor.

Instructive cross-talk between neural progenitor cells and gliomas

Gliomas are the most common primary brain tumors and offer a poor prognosis in patients because of their infiltrative and treatment-resistant nature. The median survival time after diagnosis is approximately 11-12 months. There is a strong need for novel treatment modalities in targeting gliomas, and recent advances use neural progenitor cells as delivery systems for different therapeutic strategies. In this study, we show that rat embryonic neural progenitor cell (NPC) lines, transplanted at a distant site from a 3-day-preestablished glioma in the striatum, were able to migrate toward and colocalize with tumor isles without general spread into the brain parenchyma. Upon encounter with tumor, neural progenitor cells changed phenotype and became vimentin positive. These results demonstrate that transplanted neural progenitor cells respond to queues from a tumor and home to and exert an antitumor effect on the preestablished glioma, significantly decreasing the tumor volume with approximately 67% compared with control tumors after 1-2 weeks. Moreover, these early effects could be translated into increased survival times of animals treated with neural progenitor cell grafts 3 days after intrastriatal tumor inoculation. In contrast, there was no activation or migration of endogenous subventricular zone (SVZ) neuroblasts in response to an intrastriatal syngeneic tumor. In conclusion, NPC possess the ability to influence tumor growth as well as respond to queues from the tumor or tumor microenvironment, demonstrating a cross-talk between the cells.

Glial progenitors in adult white matter are driven to form malignant gliomas by platelet-derived growth factor-expressing retroviruses

To test the gliomagenic potential of adult glial progenitors, we infected adult rat white matter with a retrovirus that expresses high levels of PDGF and green fluorescent protein (GFP). Tumors that closely resembled human glioblastomas formed in 100% of the animals by 14 d postinfection. Surprisingly, the tumors were composed of a heterogeneous population of cells, <20% of which expressed the retroviral reporter gene (GFP). The vast majority of both GFP+ and GFP- tumor cells expressed markers of glial progenitors. Thus, the tumors arose from the massive expansion of both infected and uninfected glial progenitors, suggesting that PDGF was driving tumor formation via autocrine and paracrine stimulation of glial progenitor cells. To explore this possibility further, we coinjected a retrovirus expressing PDGF-IRES-DsRed with a control retrovirus expressing only GFP. The resulting tumors contained a mixture of red cells (PDGF-expressing/tumor-initiating cells) and green cells (recruited progenitors). Both populations were highly proliferative and infiltrative. In contrast, when the control GFP retrovirus was injected alone, the animals never formed tumors and the majority of infected cells differentiated along the oligodendrocyte lineage. Together, these results reveal that adult white matter progenitors not only have the capacity to give rise to gliomas, but resident progenitors are recruited to proliferate within the mitogenic environment of the tumor and in this way contribute significantly to the heterogeneous mass of cells that compose a malignant glioma.