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E C Holland

Publications and source records attributed to E C Holland.

At least 19 recordsLinked to original sources
PubMed2003

In vivo multiple-mouse imaging at 1.5 T.

A multiple-mouse solenoidal MR coil was developed for in vivo imaging of up to 13 mice simultaneously to screen for tumors on a 1.5 T clinical scanner. For the coil to be effective as a screening tool, it should permit acquisition of MRIs in which orthotopic tumors with diameters >2 mm are detectable in a reasonable period of time (<1 hr magnet time) and their sizes accurately measured. Using a spin echo sequence, we demonstrated that this coil provides sufficient sensitivity for moderately high resolution images (156-176 microm in plane-resolution, 1.5 mm slice thickness). This spatial resolution permitted detection of primary brain tumors in transgenic/knockout mice and orthotopic xenografts. Brain tumor size as measured by MRI was correlated with size measured by histopathology (P < 0.001). Metastatic tumors in the mouse lung were also successfully imaged in a screening setting. The multiple mouse coil is simple in construction and may be implemented without any significant modification to the hardware or software on a clinical scanner.

Animals↗
PubMed2001

Glioma models.

Gliomas are primary central nervous system tumors that arise from astrocytes, oligodendrocytes or their precursors. Gliomas can be classified into several groups according to their histologic characteristics, the most malignant of the gliomas is glioblastoma multiforme. In contrast to the long-standing and well-defined histopathology, the underlying molecular and genetic bases for gliomas are only just emerging. Many genetic alterations have been identified in human gliomas, however, establishing unequivocal correlation between these genetic alterations and gliomagenesis requires accurate animal models for this disease. Here we are reviewing the existing animal models for gliomas with different strategies and our current knowledge on the important issues about this disease, such as activation of signal transduction pathways, disruption of cell cycle arrest pathways, cell-of-origin of gliomas, and therapeutic strategies.

Animals↗
PubMed2001

PDGF autocrine stimulation dedifferentiates cultured astrocytes and induces oligodendrogliomas and oligoastrocytomas from neural progenitors and astrocytes in vivo.

We present evidence that some low-grade oligodendrogliomas may be comprised of proliferating glial progenitor cells that are blocked in their ability to differentiate, whereas malignant gliomas have additionally acquired other mutations such as disruption of cell cycle arrest pathways by loss of Ink4a-Arf. We have modeled these effects in cell culture and in mice by generating autocrine stimulation of glia through the platelet-derived growth factor receptor (PDGFR). In cell culture, PDGF signaling induces proliferation of glial precursors and blocks their differentiation into oligodendrocytes and astrocytes. In addition, coexpression of PDGF and PDGF receptors has been demonstrated in human gliomas, implying that autocrine stimulation may be involved in glioma formation. In this study, using somatic cell type-specific gene transfer we investigated the functions of PDGF autocrine signaling in gliomagenesis by transferring the overexpression of PDGF-B into either nestin-expressing neural progenitors or glial fibrillary acidic protein (GFAP)-expressing astrocytes both in cell culture and in vivo. In cultured astrocytes, overexpression of PDGF-B caused significant increase in proliferation rate of both astrocytes and neural progenitors. Furthermore, PDGF gene transfer converted cultured astrocytes into cells with morphologic and gene expression characteristics of glial precursors. In vivo, gene transfer of PDGF to neural progenitors induced the formation of oligodendrogliomas in about 60% of mice by 12 wk of age; PDGF transfer to astrocytes induced the formation of either oligodendrogliomas or mixed oligoastrocytomas in about 40% of mice in the same time period. Loss of Ink4a-Arf, a mutation frequently found in high-grade human gliomas, resulted in shortened latency and enhanced malignancy of gliomas. The highest percentage of PDGF-induced malignant gliomas arose from of Ink4a-Arf null progenitor cells. These data suggest that chronic autocrine PDGF signaling can promote a proliferating population of glial precursors and is potentially sufficient to induce gliomagenesis. Loss of Ink4a-Arf is not required for PDGF-induced glioma formation but promotes tumor progression toward a more malignant phenotype.

Animals↗
PubMed2001

Animal models of cell cycle dysregulation and the pathogenesis of gliomas.

Mutations in gliomas, for the most part, fall into two main categories. The first category of mutations affects genes that produce proteins which activate signal transduction pathways downstream of tyrosine kinase receptors; the second category disrupts the pathways leading to cell cycle arrest. Cell cycle arrest pathways normally maintain cells in the G1 phase of the cell cycle, preventing inappropriate proliferation. The role of disregulation of these pathways in tumor formation is currently the focus of many investigations. Studies carried out with astrocytes and other cell types indicate that these pathways may also function in maintenance of appropriate chromosome number and differentiated phenotype, and in acquisition of senescence. Genetically defined mouse models of gliomagenesis have been helpful in increasing our understanding of how cell cycle arrest pathways cooperate with alterations in signal transduction pathways to provoke tumor formation in many cell types, including glial cells. Various strategies for experimental cell cycle arrest disruption show minimal or no formation of gliomas. In contrast, gliomas are generated with a number of strategies that enhance signal transduction downstream of tyrosine kinase receptors. Experimental disruption of the cell cycle arrest pathways is required for gliomagenesis in some of these models, but not in others. Furthermore in some cases, although not required for gliomagenesis, disruption of the cell cycle arrest pathways appears to enhance glioma formation. The results of these mouse model experiments imply a potentially complex role for cell cycle arrest disruption in human gliomagenesis.

Animals↗
PubMed2001

Modeling gliomagenesis with somatic cell gene transfer using retroviral vectors.

Modeling brain tumor formation in experimental animals with somatic cell gene transfer has a long history. In the early experiments naturally occurring retroviruses were used to induce primary brain tumors in a variety of test animals. The subsequent identification of the v-srconcogene within RSV and other cellular proto-oncogenes encoded by other retroviruses moved the field of oncology into the molecular age. Recombinant retroviruses were originally used to infect cells in vitro followed by transplantation. Since then, retroviral vectors have been used to generate glioma formation in vivo via intracerebral injection of neonatal mice. In the most recent models, primary brain tumors can be induced by injecting avian recombinant retroviruses containing different oncogenes, individually or in combination, into transgenic mice genetically engineered for susceptibility to retroviral gene transfer targeting specific cell types in the brain. Animal modeling experiments have contributed substantially to the understanding of the etiology leading to gliomagenesis. The current models provide tumors, which are genetically and histologically similar to their human counterparts, making them attractive to use in drug discovery for treatment of gliomas.

Animals↗
PubMed2001

Gliomagenesis: genetic alterations and mouse models.

Glioblastoma multiforme is the most malignant of the primary brain tumours and is almost always fatal. The treatment strategies for this disease have not changed appreciably for many years and most are based on a limited understanding of the biology of the disease. However, in the past decade, characteristic genetic alterations have been identified in gliomas that might underlie the initiation or progression of the disease. Recent modelling experiments in mice are helping to delineate the molecular aetiology of this disease and are providing systems to identify and test novel and rational therapeutic strategies.

Animals↗
PubMed2001

Brain tumor animal models: importance and progress.

Recent experiments indicate that some of the genetic abnormalities found in human brain tumors can induce tumors in mice with similar histologic characteristics to their human counterparts. Such studies help unravel the biology of tumorigenesis and indicate that some of the mutations and alterations in gene expression found in human central nervous system tumors may actually contribute to the etiology of these diseases. In addition, these mouse-modeling experiments may identify essential targets for therapy and provide test animals for preclinical trials of mechanistically designed therapeutics.

Animals↗
PubMed2001

Progenitor cells and glioma formation.

The gliomas are a collection of tumors that arise within the central nervous system and have characteristics similar to astrocytes, oligodendrocytes, or their precursors. Whether or not the glial characteristics of these tumors mean that they arise from the differentiated glia that they resemble or their precursors has been debated. Even under normal circumstances the cells within the central nervous system of an adult can trans-differentiate to other cell types. In addition, mutations found in gliomas further destabilize the differentiation status of these cells making a determination of what cell type gives rise to a given tumor histology difficult. Lineage tracing studies in animals can be used to correlate some specific cell characteristics with the histology of gliomas that arise from these cells. From these experiments it appears that undifferentiated cells are more sensitive to the oncogenic effects of certain signaling abnormalities than are differentiated cells, but that with the appropriate genetic abnormalities differentiated astrocytes can act as the cell-of-origin for gliomas. These data imply that small molecules that promote differentiation may be a rational component of glioma therapy in combination with other drugs aimed at specific molecular signaling targets.

Cell Transformation, Neoplastic↗
PubMed2001

Surgical resection of intrinsic insular tumors: complication avoidance.

OBJECT: Surgical resection of tumors located in the insular region is challenging for neurosurgeons, and few have published their surgical results. The authors report their experience with intrinsic tumors of the insula, with an emphasis on an objective determination of the extent of resection and neurological complications and on an analysis of the anatomical characteristics that can lead to suboptimal outcomes. METHODS: Twenty-two patients who underwent surgical resection of intrinsic insular tumors were retrospectively identified. Eight tumors (36%) were purely insular, eight (36%) extended into the temporal pole, and six (27%) extended into the frontal operculum. A transsylvian surgical approach, combined with a frontal opercular resection or temporal lobectomy when necessary, was used in all cases. Five of 13 patients with tumors located in the dominant hemisphere underwent craniotomies while awake. The extent of tumor resection was determined using volumetric analyses. In 10 patients, more than 90% of the tumor was resected; in six patients, 75 to 90% was resected; and in six patients, less than 75% was resected. No patient died within 30 days after surgery. During the immediate postoperative period, the neurological conditions of 14 patients (64%) either improved or were unchanged, and in eight patients (36%) they worsened. Deficits included either motor or speech dysfunction. At the 3-month follow-up examination, only two patients (9%) displayed permanent deficits. Speech and motor dysfunction appeared to result most often from excessive opercular retraction and manipulation of the middle cerebral artery (MCA), interruption of the lateral lenticulostriate arteries (LLAs), interruption of the long perforating vessels of the second segment of the MCA (M2), or violation of the corona radiata at the superior aspect of the tumor. Specific methods used to avoid complications included widely splitting the sylvian fissure and identifying the bases of the periinsular sulci to define the superior and inferior resection planes, identifying early the most lateral LLA to define the medial resection plane, dissecting the MCA before tumor resection, removing the tumor subpially with preservation of all large perforating arteries arising from posterior M2 branches, and performing craniotomy with brain stimulation while the patient was awake. CONCLUSIONS: A good understanding of the surgical anatomy and an awareness of potential pitfalls can help reduce neurological complications and maximize surgical resection of insular tumors.

Adult↗
PubMed2000

Identification of a multipotent astrocytic stem cell in the immature and adult mouse brain.

The mammalian brain contains a population of neural stem cells (NSC) that can both self-renew and generate progeny along the three lineage pathways of the central nervous system (CNS), but the in vivo identification and localization of NSC in the postnatal CNS has proved elusive. Recently, separate studies have implicated ciliated ependymal (CE) cells, and special subependymal zone (SEZ) astrocytes as candidates for NSC in the adult brain. In the present study, we have examined the potential of these two NSC candidates to form multipotent spherical clones-neurospheres-in vitro. We conclude that CE cells are unipotent and give rise only to cells within the glia cell lineage, although they are capable of forming spherical clones when cultured in isolation. In contrast, astrocyte monolayers from the cerebral cortex, cerebellum, spinal cord, and SEZ can form neurospheres that give rise both to neurons and glia. However, the ability to form neurospheres is restricted to astrocyte monolayers derived during the first 2 postnatal wk, except for SEZ astrocytes, which retain this capacity in the mature forebrain. We conclude that environmental factors, simulated by certain in vitro conditions, transiently confer NSC-like attributes on astrocytes during a critical period in CNS development.

Animals↗
PubMed2000

Astrocytes give rise to oligodendrogliomas and astrocytomas after gene transfer of polyoma virus middle T antigen in vivo.

The cells of origin for oligodendrogliomas and astrocytomas are not known but are presumed to be oligodendrocyte and astrocyte precursors, respectively. In this paper we report the generation of mixed gliomas from in vivo transformation of glial fibrillary acidic protein (GFAP)-positive cells (differentiated astrocytes) with polyoma virus middle T antigen (MTA). MTA is a powerful oncogene that activates a number of signal transduction pathways, including those proposed to be involved in gliomagenesis, and has been shown to induce tumors in many cell types. We have achieved transfer of MTA expression specifically to GFAP(+) cells in vivo using somatic cell gene transfer, and find resultant formation of anaplastic gliomas with mixed astrocytoma and oligodendroglioma morphological features. We conclude that GFAP- expressing astrocytes, with appropriate signaling abnormalities, can serve as the cell of origin for oligodendrogliomas, astrocytomas, or mixed gliomas.

Animals↗
PubMed2000

Combined activation of Ras and Akt in neural progenitors induces glioblastoma formation in mice.

Gliomas are the most common primary malignant brain tumours and are classified into four clinical grades, with the most aggressive tumours being grade 4 astrocytomas (also known as glioblastoma multiforme; GBM). Frequent genetic alterations in GBMs (refs 2-5) result in stimulation of common signal transduction pathways involving Ras, Akt and other proteins. It is not known which of these pathways, if any, are sufficient to induce GBM formation. Here we transfer, in a tissue-specific manner, genes encoding activated forms of Ras and Akt to astrocytes and neural progenitors in mice. We found that although neither activated Ras nor Akt alone is sufficient to induce GBM formation, the combination of activated Ras and Akt induces high-grade gliomas with the histological features of human GBMs. These tumours appear to arise after gene transfer to neural progenitors, but not after transfer to differentiated astrocytes. Increased activity of RAS is found in many human GBMs (ref. 11), and we show here that Akt activity is increased in most of these tumours, implying that combined activation of these two pathways accurately models the biology of this disease.

Animals↗
PubMed2000

Toward a molecular classification of the gliomas: histopathology, molecular genetics, and gene expression profiling.

As many as 100,000 new cases of brain tumor are diagnosed each year in the United States. About half of these are primary gliomas and the remaining half are metastatic tumors and non-glial primary tumors. Currently, gliomas are classified based on phenotypic characteristics. Recent progress in the elucidation of genetic alterations found in gliomas have raised the exciting possibility of using genetic and molecular analyses to resolve some of the problematic issues currently associated with the histological approach to glioma classification. Recently, immunohistochemical studies using novel proliferation markers have significantly advanced the assessment of tumor growth potential and the grading criteria of some tumor subtypes. Preliminary studies using cDNA array technologies suggest that the profiling of gene expression patterns may provide a novel and meaningful approach to glioma classification and subclassification. Furthermore, cDNA array technologies may also be used to identify candidate genes involved in glioma tumor development, invasion, and progression. This review summarizes current glioma classification schemes that are based on histopathological characteristics and discusses the potential for using cDNA array technology in the molecular classification of gliomas.

Brain Neoplasms↗
PubMed1998

Modeling mutations in the G1 arrest pathway in human gliomas: overexpression of CDK4 but not loss of INK4a-ARF induces hyperploidy in cultured mouse astrocytes.

Nearly all human gliomas exhibit alterations in one of three genetic loci governing G1 arrest: INK4a-ARF, CDK4, or RB. To discern the roles of CDK4 amplification and INK4a-ARF loss in gliomagenesis, we compared the behavior of astrocytes lacking a functional INK4a-ARF locus with astrocytes overexpressing CDK4. Either a deficiency of p16(INK4a) and p19(ARF) or an increase in Cdk4 allows cultured astrocytes to grow without senescence. Astrocytes overexpressing CDK4 grow more slowly than INK4a-ARF-deficient astrocytes and convert to a tetraploid state at high efficiency; in contrast, INK4a-ARF-deficient cells remain pseudodiploid, consistent with properties observed in human gliomas with corresponding lesions in these genes.

Animals↗
PubMed1998

A constitutively active epidermal growth factor receptor cooperates with disruption of G1 cell-cycle arrest pathways to induce glioma-like lesions in mice.

The epidermal growth factor receptor (EGFR) gene is amplified or mutated in 30%-50% of human gliobastoma multiforme (GBM). These mutations are associated usually with deletions of the INK4a-ARF locus, which encodes two gene products (p16(INK4a) and p19(ARF)) involved in cell-cycle arrest and apoptosis. We have investigated the role of EGFR mutation in gliomagenesis, using avian retroviral vectors to transfer a mutant EGFR gene to glial precursors and astrocytes in transgenic mice expressing tv-a, a gene encoding the retrovirus receptor. TVA, under control of brain cell type-specific promoters. We demonstrate that expression of a constitutively active, mutant form of EGFR in cells in the glial lineage can induce lesions with many similarities to human gliomas. These lesions occur more frequently with gene transfer to mice expressing tv-a from the progenitor-specific nestin promoter than to mice expressing tv-a from the astrocyte-specific glial fibrillary acidic protein (GFAP) promoter, suggesting that tumors arise more efficiently from immature cells in the glial lineage. Furthermore, EGFR-induced gliomagenesis appears to require additional mutations in genes encoding proteins involved in cell-cycle arrest pathways. We have produced these combinations by simultaneously infecting tv-a transgenic mice with vectors carrying cdk4 and EGFR or by infecting tv-a transgenic mice bearing a disrupted INK4a-ARF locus with the EGFR-carrying vector alone. Moreover, EGFR-induced gliomagenesis does not occur in conjunction with p53 deficiency, unless the mice are also infected with a vector carrying cdk4. The gliomagenic combinations of genetic lesions required in mice are similar to those found in human gliomas.

Animals↗
PubMed1998

Basic fibroblast growth factor induces cell migration and proliferation after glia-specific gene transfer in mice.

Basic fibroblast growth factor (bFGF) is overexpressed in most high-grade human gliomas, implying that it is involved in the pathogenesis of these tumors. To assess the biological effect of inappropriate production of bFGF in normal astrocytes, we developed a system for glia-specific gene transfer in transgenic mice. A transgene encoding the receptor for subgroup A avian leukosis virus and controlled by the astrocyte-specific glial fibrillary acidic protein promoter permits efficient glia-specific transfer of genes carried by subgroup A avian leukosis virus vectors. With this system, we have demonstrated that bFGF induces proliferation and migration of glial cells in vivo, without the induction of tumors.

Alkaline Phosphatase↗