Relationship of glioblastoma multiforme to neural stem cell regions predicts invasive and multifocal tumor phenotype

Epigenetic regulation of aging stem cells

The function of adult tissue-specific stem cells declines with age, which may contribute to the physiological decline in tissue homeostasis and the increased risk of neoplasm during aging. Old stem cells can be 'rejuvenated' by environmental stimuli in some cases, raising the possibility that a subset of age-dependent stem cell changes is regulated by reversible mechanisms. Epigenetic regulators are good candidates for such mechanisms, as they provide a versatile checkpoint to mediate plastic changes in gene expression and have recently been found to control organismal longevity. Here, we review the importance of chromatin regulation in adult stem cell compartments. We particularly focus on the roles of chromatin-modifying complexes and transcription factors that directly impact chromatin in aging stem cells. Understanding the regulation of chromatin states in adult stem cells is likely to have important implications for identifying avenues to maintain the homeostatic balance between sustained function and neoplastic transformation of aging stem cells.

Diagnosis and management of multifocal gliomas

Patients who present with multiple cerebral tumors are usually considered as having metastatic disease. If they have a history of a primary cancer in another site, the brain tumors are considered metastases and are usually managed with standard whole-brain radiotherapy. If no primary cancer site is known, a diagnostic work-up is performed, but if no primary site is found, they are still considered as brain metastases from an unknown primary site. Thus, such patients can either have brain biopsy (recommended) for further diagnostic consideration or, occasionally, they can be treated with whole-brain radiotherapy, depending on the age, performance status and wish of the patient. However, in some of these patients the multiple brain tumors represent multifocal glioma rather than metastases, resulting in incorrect treatment. In such cases, various MRI characteristics may be helpful in directing towards the correct diagnosis. Thus, patients who present with multiple brain tumors should not always be considered to have metastatic disease even if they have a previous diagnosis of systemic cancer, and multifocal glioma should be ruled out.

Time-lapse imaging of disease progression in deep brain areas using fluorescence microendoscopy

The combination of intravital microscopy and animal models of disease has propelled studies of disease mechanisms and treatments. However, many disorders afflict tissues inaccessible to light microscopy in live subjects. Here we introduce cellular-level time-lapse imaging deep within the live mammalian brain by one- and two-photon fluorescence microendoscopy over multiple weeks. Bilateral imaging sites allowed longitudinal comparisons within individual subjects, including of normal and diseased tissues. Using this approach, we tracked CA1 hippocampal pyramidal neuron dendrites in adult mice, revealing these dendrites' extreme stability and rare examples of their structural alterations. To illustrate disease studies, we tracked deep lying gliomas by observing tumor growth, visualizing three-dimensional vasculature structure and determining microcirculatory speeds. Average erythrocyte speeds in gliomas declined markedly as the disease advanced, notwithstanding significant increases in capillary diameters. Time-lapse microendoscopy will be applicable to studies of numerous disorders, including neurovascular, neurological, cancerous and trauma-induced conditions.

Longitudinal MRI evidence for decreased survival among periventricular glioblastoma

While the prognosis of patients with glioblastoma (GBM) remains poor despite recent therapeutic advances, variable survival times suggest wide variation in tumor biology and an opportunity for stratified intervention. We used volumetric analysis and morphometrics to measure the spatial relationship between subventricular zone (SVZ) proximity and survival in a cohort of 39 newly diagnosed GBM patients. We collected T2-weighted and gadolinium-enhanced T1-weighted magnetic resonance images (MRI) at pre-operative, post-operative, pre-radiation therapy, and post-radiation therapy time points, measured tumor volumes and distances to the SVZ, and collected clinical data. Univariate and multivariate Cox regression showed that tumors involving the SVZ and tumor growth rate during radiation therapy were independent predictors of shorter progression-free and overall survival. These results suggest that GBMs in close proximity to the ependymal surface of the ventricles convey a worse prognosis-an observation that may be useful for stratifying treatment.

Human glioblastoma-initiating cells invade specifically the subventricular zones and olfactory bulbs of mice after striatal injection

In patients with glioblastoma multiforme, recurrence is the rule despite continuous advances in surgery, radiotherapy and chemotherapy. Within these malignant gliomas, glioblastoma stem cells or initiating cells have been recently described, and they were shown to be specifically involved in experimental tumorigenesis. In this study, we show that some human glioblastoma cells injected into the striatum of immunodeficient nude mice exhibit a tropism for the subventricular zones. There and similarily to neurogenic stem cells, these subventricular glioblastoma cells were then able to migrate toward the olfactory bulbs. Finally, the glioblastoma cells isolated from the adult mouse subventricular zones and olfactory bulbs display high tumorigenicity when secondary injected in a new mouse brain. Together, these data suggest that neurogenic zones could be a reservoir for particular cancer-initiating cells.

Deciphering the signaling pathways of cancer stem cells of glioblastoma multiforme: role of Akt/mTOR and MAPK pathways

These findings emphasize that the mTOR pathway may contribute to maintenance of quiescence of CSCs, and provide a basis for manipulating CSCs in the treatment of GBM. Future research should focus on further defining the PI3K/Akt/mTOR molecular network in the regulation of stem cell quiescence and provide rationale for targeting the cancer-initiating cells of GBM.

Overall survival, prognostic factors, and repeated surgery in a consecutive series of 516 patients with glioblastoma multiforme

OBJECTIVES

To study overall survival (OS), prognostic factors, and repeated surgery in glioblastoma multiforme (GBM).

MATERIAL AND METHODS

Retrospective study of 516 consecutive adult patients who underwent primary surgery for a GBM in year 2003-2008.

RESULTS

Median age at primary surgery was 63.7 years (range 18.0-88.0). Median OS was 9.9 months. Age > 60 years, poor preoperative ECOG score, bilateral tumor, biopsy rather than resection, and no temozolomide chemoradiotherapy were negative risk factors. Repeat surgery was performed in 65 patients (13%). Median time between first and second surgery was 7 months. Indications for second surgery were increasing neurological deficits (35.4%), raised ICP (33.8%), asymptomatic but reoperated because of tumor progression verified on MRI (20.0%), and epileptic seizures (11%). Patients who underwent repeated surgery had longer OS; 18.4 months vs 8.6 months (P < 0.001).

CONCLUSIONS

OS for adult GBM patients was 9.9 months. Negative prognostic factors were increasing age, poor neurological function, bilateral tumor involvement, biopsy instead of resection, and RT alone compared to temozolomide chemoradiotherapy. Our rate of repeated surgery for GBM was 13% and the main indications for second surgery were raised ICP and increasing neurological deficits. In a carefully selected group of patients, repeat surgery significantly prolongs OS.

Maintenance of critical properties of brain tumor stem-like cells after cryopreservation

It would be very useful to be able to classify brain tumor stem cells (BTSCs) by certain criteria to afford the design of specific or individualized treatment. Here, we studied two BTSC lines with differing biological and molecular features and whose respective features were well preserved after cryopreservation as single cells in SFM or 90% serum with 10% DMSO, a method not previously reported. The resuscitated BTSCs shared properties indistinguishable from their respective parental cells, including tumor sphere forming potentials, growth and differentiation properties, and tumorigenesis in vivo. The two cell lines also had differing molecule profiles, which can be well preserved after cryopreservation, similar to that of their respective primary tumors. Therefore, BTSCs from different patients, that have their own properties, were well retained by the present cryopreservation method, which might be a useful and reliable method for preserving BTSCs for long-term studies, such as classification and specific therapy design.

Brain tumor stem cells

Since the end of the ‘no-new-neuron’ theory, emerging evidence from multiple studies has supported the existence of stem cells in neurogenic areas of the adult brain. Along with this discovery, neural stem cells became candidate cells being at the origin of brain tumors. In fact, it has been demonstrated that molecular mechanisms controlling self-renewal and differentiation are shared between brain tumor stem cells and neural stem cells and that corruption of genes implicated in these pathways can direct tumor growth. In this regard, future anticancer approaches could be inspired by uncovering such redundancies and setting up treatments leading to exhaustion of the cancer stem cell pool. However, deleterious effects on (normal) neural stem cells should be minimized. Such therapeutic models underline the importance to study the cellular mechanisms implicated in fate decisions of neural stem cells and the oncogenic derivation of adult brain cells. In this review, we discuss the putative origins of brain tumor stem cells and their possible implications on future therapies.

A proposed classification system that projects outcomes based on preoperative variables for adult patients with glioblastoma multiforme

OBJECT

Glioblastoma multiforme (GBM) is the most common and aggressive type of primary brain tumor in adults. Although the average survival is approximately 12 months, individual survival is heterogeneous. The ability to predict short- and long-term survivors is limited. Therefore, the aims of this study were to ascertain preoperative risk factors associated with survival, develop a preoperative prognostic grading system, and evaluate the utility of this grading system in predicting survival for patients undergoing resection of a primary intracranial GBM.

METHODS

Cases involving adult patients who underwent surgery for an intracranial primary (de novo) GBM between 1997 and 2007 at The Johns Hopkins Hospital, an academic tertiary-care institution, were retrospectively reviewed. Multivariate proportional hazards regression analysis was used to identify preoperative factors associated with survival, after controlling for extent of resection and adjuvant therapies. The identified associations with survival were then used to develop a grading system based on preoperative variables. Survival as a function of time was plotted using the Kaplan-Meier method, and survival rates were compared using Log-rank analysis. Associations with p < 0.05 were considered statistically significant.

RESULTS

Of the 393 patients in this study, 310 (79%) had died as of most recent follow-up (median time from surgery to death 11.9 months). The preoperative factors, independent of extent of resection and adjuvant therapies (carmustine wafers, temozolomide, and radiation), found to be negatively associated with survival were: age > 60 years (p < 0.0001), Karnofsky performance status score < or = 80 (p < 0.0001), motor deficit (p = 0.02), language deficit (p = 0.001), and periventricular tumor location (p = 0.04). Patients possessing 0-1, 2, 3, and 4-5 of these variables were assigned a preoperative grade of 1, 2, 3, and 4, respectively. Patients with a preoperative grade of 1, 2, 3, and 4 had a median survival of 16.6, 10.2, 6.8, and 6.1 months, respectively.

CONCLUSIONS

The present study found that older age, poor performance status, motor deficit, language deficit, and periventricular tumor location independently predicted poorer survival in patients undergoing GBM resection. A grading system based on these factors was able to identify 4 distinct groups of patients with different survival rates. This grading system, based only on preoperative variables, may provide patients and physicians with prognostic information that may guide medical and surgical therapy before any intervention is pursued.

The Oncogenic Potential of Mesenchymal Stem Cells in the Treatment of Cancer: Directions for Future Research

Mesenchymal stem cells (MSCs) represent a promising new approach to the treatment of several diseases that are associated with dismal outcomes. These include myocardial damage, graft versus host disease, and possibly cancer. Although the potential therapeutic aspects of MSCs continue to be well-researched, the possible hazards of MSCs, and in particular their oncogenic capacity are poorly understood. This review addresses the oncogenic and tumor-supporting potential of MSCs within the context of cancer treatment. The risk for malignant transformation is discussed for each stage of the clinical lifecycle of MSCs. This includes malignant transformation in vitro during production phases, during insertion of potentially therapeutic transgenes, and finally in vivo via interactions with tumor stroma. The immunosuppressive qualities of MSCs, which may facilitate evasion of the immune system by a tumor, are also addressed. Limitations of the methods employed in clinical trials to date are reviewed, including the absence of long term follow-up and lack of adequate screening methods to detect formation of new tumors. Through discussions of the possible oncogenic and tumor-supporting mechanisms of MSCs, directions for future research are identified which may eventually facilitate the future clinical translation of MSCs for the treatment of cancer and other diseases.

Antiangiogenic therapy and mechanisms of tumor resistance in malignant glioma

Despite advances in surgery, radiation therapy, and chemotherapeutics, patients with malignant glioma have a dismal prognosis. The formations of aberrant tumour vasculature and glioma cell invasion are major obstacles for effective treatment. Angiogenesis is a key event in the progression of malignant gliomas, a process involving endothelial cell proliferation, migration, reorganization of extracellular matrix and tube formation. Such processes are regulated by the homeostatic balance between proangiogenic and antiangiogenic factors, most notably vascular endothelial growth factors (VEGFs) produced by glioma cells. Current strategies targeting VEGF-VEGF receptor signal transduction pathways, though effective in normalizing abnormal tumor vasculature, eventually result in tumor resistance whereby a highly infiltrative and invasive phenotype may be adopted. Here we review recent anti-angiogenic therapy for malignant glioma and highlight implantable devices and nano/microparticles as next-generation methods for chemotherapeutic delivery. Intrinsic and adaptive modes of glioma resistance to anti-angiogenic therapy will be discussed with particular focus on the glioma stem cell paradigm.

Glioblastoma multiforme regional genetic and cellular expression patterns: influence on anatomic and physiologic MR imaging

PURPOSE

To determine whether magnetic resonance (MR) imaging is influenced by genetic and cellular features of glioblastoma multiforme (GBM) aggressiveness.

MATERIALS AND METHODS

In this HIPAA-compliant institutional review board-approved study, multiple enhancing and peritumoral nonenhancing stereotactic neurosurgical biopsy samples from treatment-naïve GBMs were collected prospectively, with guidance from cerebral blood volume (CBV) MR imaging measurements. By using monoclonal antibodies, tissue specimens were examined for microvascular expression, hypoxia, tumor and overall cellular density, and histopathologic features of GBM aggressiveness. Genetic expression patterns were investigated with RNA microarrays. Imaging and histopathologic variables were compared with the Welch t test and Pearson correlations. Microarray analysis was performed by using false discovery rate (FDR) statistics.

RESULTS

Tumor biopsy of 13 adult patients yielded 16 enhancing and 14 peritumoral nonenhancing specimens. Enhancing regions had elevated relative CBV and reduced relative apparent diffusion coefficient (ADC) measurements compared with peritumoral nonenhancing biopsy regions (P < .01). A positive correlation was found between relative CBV and all histopathologic features of aggressiveness (P < .04). An inverse correlation was found between relative ADC and all histopathologic features of aggressiveness (P < .05). RNA expression patterns between tumor regions were found to be significantly different (FDR < 0.05), with hierarchical clustering by biopsy region only.

CONCLUSION

These findings suggest MR imaging is significantly influenced by GBM genetic and cellular biologic features of aggressiveness and imply physiologic MR imaging may be useful in pinpointing regions of highest malignancy within heterogeneous tissues, thus facilitating histologic grading of primary glial brain tumors.

Chromosome 7 and 19 trisomy in cultured human neural progenitor cells

Background

Stem cell expansion and differentiation is the foundation of emerging cell therapy technologies. The potential applications of human neural progenitor cells (hNPCs) are wide ranging, but a normal cytogenetic profile is important to avoid the risk of tumor formation in clinical trials. FDA approved clinical trials are being planned and conducted for hNPC transplantation into the brain or spinal cord for various neurodegenerative disorders. Although human embryonic stem cells (hESCs) are known to show recurrent chromosomal abnormalities involving 12 and 17, no studies have revealed chromosomal abnormalities in cultured hNPCs. Therefore, we investigated frequently occurring chromosomal abnormalities in 21 independent fetal-derived hNPC lines and the possible mechanisms triggering such aberrations.

Methods and Findings

While most hNPC lines were karyotypically normal, G-band karyotyping and fluorescent in situ hybridization (FISH) analyses revealed the emergence of trisomy 7 (hNPC⁺⁷) and trisomy 19 (hNPC⁺¹⁹), in 24% and 5% of the lines, respectively. Once detected, subsequent passaging revealed emerging dominance of trisomy hNPCs. DNA microarray and immunoblotting analyses demonstrate epidermal growth factor receptor (EGFR) overexpression in hNPC⁺⁷ and hNPC⁺¹⁹ cells. We observed greater levels of telomerase (hTERT), increased proliferation (Ki67), survival (TUNEL), and neurogenesis (β_III-tubulin) in hNPC⁺⁷ and hNPC⁺¹⁹, using respective immunocytochemical markers. However, the trisomy lines underwent replicative senescence after 50–60 population doublings and never showed neoplastic changes. Although hNPC⁺⁷ and hNPC⁺¹⁹ survived better after xenotransplantation into the rat striatum, they did not form malignant tumors. Finally, EGF deprivation triggered a selection of trisomy 7 cells in a diploid hNPC line.

Conclusions

We report that hNPCs are susceptible to accumulation of chromosome 7 and 19 trisomy in long-term cell culture. These results suggest that micro-environmental cues are powerful factors in the selection of specific hNPC aneuploidies, with trisomy of chromosome 7 being the most common. Given that a number of stem cell based clinical trials are being conducted or planned in USA and a recent report in PLoS Medicine showing the dangers of grafting an inordinate number of cells, these data substantiate the need for careful cytogenetic evaluation of hNPCs (fetal or hESC-derived) before their use in clinical or basic science applications.

A dosimetric comparison of four treatment planning methods for high grade glioma

Background

High grade gliomas (HGG) are typically treated with a combination of surgery, radiotherapy and chemotherapy. Three dimensional (3D) conformal radiotherapy treatment planning is still the main stay of treatment for these patients. New treatment planning methods suggest better dose distributions and organ sparing but their clinical benefit is unclear. The purpose of the current study was to compare normal tissue sparing and tumor coverage using four different radiotherapy planning methods in patients with high grade glioma.

Methods

Three dimensional conformal (3D), sequential boost IMRT, integrated boost (IB) IMRT and Tomotherapy (TOMO) treatment plans were generated for 20 high grade glioma patients. T1 and T2 MRI abnormalities were used to define GTV and CTV with 2 and 2.5 cm margins to define PTV1 and PTV2 respectively.

Results

The mean dose to PTV2 but not to PTV1 was less then 95% of the prescribed dose with IB and IMRT plans. The mean doses to the optic chiasm and the ipsilateral globe were highest with 3D plans and least with IB plans. The mean dose to the contralateral globe was highest with TOMO plans. The mean of the integral dose (ID) to the brain was least with the IB plan and was lower with IMRT compared to 3D plans. The TOMO plans had the least mean D10 to the normal brain but higher mean D50 and D90 compared to IB and IMRT plans. The mean D10 and D50 but not D90 were significantly lower with the IMRT plans compared to the 3D plans.

Conclusion

No single treatment planning method was found to be superior to all others and a personalized approach is advised for planning and treating high-grade glioma patients with radiotherapy. Integral dose did not reflect accurately the dose volume histogram (DVH) of the normal brain and may not be a good indicator of delayed radiation toxicity.

An analysis of image texture, tumor location, and MGMT promoter methylation in glioblastoma using magnetic resonance imaging

In glioblastoma (GBM), promoter methylation of the DNA repair gene O(6)-methylguanine-DNA methyltransferase (MGMT) is associated with benefit from chemotherapy. Correlations between MGMT promoter methylation and visually assessed imaging features on magnetic resonance (MR) have been reported suggesting that noninvasive detection of MGMT methylation status might be possible. Our study assessed whether MGMT methylation status in GBM could be predicted using MR imaging. We conducted a retrospective analysis of MR images in patients with newly diagnosed GBM. Tumor texture was assessed by two methods. First, we analyzed texture by expert consensus describing the tumor borders, presence or absence of cysts, pattern of enhancement, and appearance of tumor signal in T2-weighted images. Then, we applied space-frequency texture analysis based on the S-transform. Tumor location within the brain was determined using automatized image registration and segmentation techniques. Their association with MGMT methylation was analyzed. We confirmed that ring enhancement assessed visually is significantly associated with unmethylated MGMT promoter status (P=0.006). Texture features on T2-weighted images assessed by the space-frequency analysis were significantly different between methylated and unmethylated cases (P<0.05). However, blinded classification of MGMT promoter methylation status reached an accuracy of only 71%. There were no significant differences in the locations of methylated and unmethylated GBM tumors. Our results provide further evidence that individual MR features are associated with MGMT methylation but better algorithms for predicting methylation status are needed. The relevance of this study lies on the application of novel techniques for the analysis of anatomical MR images of patients with GBM allowing the evaluation of subtleties not seen by an observer and facilitating the standardization of the methods, decreasing the potential for interobserver bias.

Stem cell associated gene expression in glioblastoma multiforme: relationship to survival and the subventricular zone

Current therapies for glioblastoma (GBM) target bulk tumor through measures such as resection and radiotherapy. However, recent evidence suggests that targeting a subset of tumor cells, so-called cancer stem cells, may be critical for inhibiting tumor growth and relapse. The subventricular zone (SVZ), which lines the ventricles of the brain, is thought to be the origin for the majority of neural stem cells and potentially cancer stem cells. Therefore, we assessed the relationship between tumor contact with the SVZ as determined by MRI, cancer stem cell gene expression and survival in 47 patients with GBM. Using DNA microarrays, we found that genes associated with cancer stem cells were not over-expressed in tumors contacting the SVZ. Contact with the SVZ trended with shorter survival (median 358 versus 644, P = 0.066). Over-expression of CD133 (prominin-1) and maternal embryonic leucine zipper kinase (MELK) was associated with shorter survival, whereas mitogen activated protein kinase 8 (MAPK8) was associated with longer survival (P values 0.008, 0.005 and 0.002 respectively). Thus we found no evidence of a stem-cell derived genetic signature specific for GBM in contact with the SVZ, but there was a relationship between stem cell gene expression and survival. More research is required to clarify the relationship between the SVZ, cancer stem cells and survival.

Expression of mutant p53 proteins implicates a lineage relationship between neural stem cells and malignant astrocytic glioma in a murine model

Recent studies have identified genes and core pathways that are altered in human glioblastoma. However, the mechanisms by which alterations of these glioblastoma genes singly and cooperatively transform brain cells remain poorly understood. Further, the cell of origin of glioblastoma is largely elusive. By targeting a p53 in-frame deletion mutation to the brain, we show that p53 deficiency provides no significant growth advantage to adult brain cells, but appears to induce pleiotropic accumulation of cooperative oncogenic alterations driving gliomagenesis. Our data show that accumulation of a detectable level of mutant p53 proteins occurs first in neural stem cells in the subventricular zone (SVZ) and that subsequent expansion of mutant p53-expressing Olig2(+) transit-amplifying progenitor-like cells in the SVZ-associated areas initiates glioma formation.

Origins and clinical implications of the brain tumor stem cell hypothesis

With the advent of the cancer stem cell hypothesis, the field of cancer research has experienced a revolution in how we think of and approach cancer. The discovery of "brain tumor stem cells" has offered an explanation for several long-standing conundrums on why brain tumors behave the way they do to treatment. Despite the great amount of research that has been done in order to understand the molecular aspects of malignant gliomas, the prognosis of brain tumors remains dismal. The slow progress in extending the survival of patients with malignant CNS neoplasms is very likely due to poor understanding of the cell of origin in these tumors. This review article discusses the progress in our understanding of brain tumor stem cells as the cell of origin in brain cancers. We review the different proposed mechanisms of how brain tumor stem cells may originate, the intracellular pathways disrupted in the pathogenesis of BTSCs, the molecular markers used to identify BTSCs, the molecular mechanisms of cancer initiation and progression, and finally the clinical implications of this research.

GFAP-Cre-mediated activation of oncogenic K-ras results in expansion of the subventricular zone and infiltrating glioma

A subset of neoplastic cells within human high-grade gliomas has features associated with stem cells. These cells may sustain glioma growth, and their stem-like properties may confer resistance to standard glioma treatments. Whether glioma stem cells derive from indigenous neural stem cells (NSC), or from tumor cells that have reacquired stem cell-like properties, is unknown. However, signaling pathways that are tightly regulated and central to NSC biology, including the Ras/Raf/Erk pathway, are hyperactive and pathogenic in gliomagenesis. Furthermore, data in animal models suggests that, in some cases, tumors are initiated in the subventricular zone (SVZ), a stem/progenitor cell niche in the mature brain. We activated oncogenic K-ras in mouse glioneuronal precursor cells and adult SVZ cells using GFAP-Cre. GFAP-Cre+/K-ras(G12D) mice showed a marked expansion of glial fibriallary acidic protein (GFAP)- and TUJ1-expressing cell populations in the SVZ. In addition, mice developed intermediate grade, infiltrating glioma with 100% penetrance. Tumors were consistently located in the amygdalohippocampal region and nearby cortex, often in association with the lateral ventricle and expanded SVZ. Tumor cells expressed markers associated with neural progenitor cells, including Olig2, Bmi-1, and PDGFR-alpha. These data suggest that infiltrating tumor cells may arise from NSC transformed by activation of oncogenic K-ras in vivo.

Prognostic significance of c-Met expression in glioblastomas

BACKGROUND

The authors investigated whether expression of c-Met protein in glioblastomas is associated with overall survival and biologic features representing tumor invasiveness in patients with glioblastomas.

METHODS

Paraffin-embedded specimens of glioblastomas from 62 patients treated in a single institution were assessed by immunohistochemical (IHC) analysis of c-Met expression. On the basis of the clinical data for these patients, the association between c-Met expression and clinicobiologic features representing tumor invasiveness was analyzed.

RESULTS

c-Met overexpression was detected in 29.0% (18 of 62) of glioblastomas. In patients with c-Met overexpression, the median survival was 11.7 months (95% confidence interval [95% CI], 9.9 months-13.5 months), compared with a median survival of 14.3 months (95% CI, 7.6 months-21.0 months) for patients whose tumors had no or little expression of c-Met (P=.031). On the radiographic analysis, 9 of 18 patients (50%) with tumors overexpressing c-Met demonstrated invasive and multifocal lesions on the initial magnetic resonance images, whereas only 9 of 44 patients (20.5%) with tumors that expressed no or little c-Met demonstrated these features (P=.030). Using immunohistochemistry, we also found a significant association between c-Met expression and matrix metalloproteinase-2,-9 (P=.020 and P=.013). Furthermore, Myc overexpression was found to be closely correlated with c-Met overexpression on IHC analysis (P=.004).

CONCLUSIONS

The authors suggest that c-Met overexpression is associated with shorter survival time and poor treatment response in glioblastomas, the mechanism for which is elevated tumor invasiveness on the molecular and clinical phenotypes. This implies that more effective therapeutic strategies targeting c-Met receptors may have important clinical implication.

Radial glia cells in the developing human brain

Human radial glia (RG) share many of the features described in rodents, but also have a number of characteristics unique to the human brain. Results obtained from different mammalian species including human and non-human primates reveal differences in the involvement of RG in neurogenesis and oligodendrogenesis and in the timing of the initial expression of typical RG immunomarkers. A common problem in studying the human brain is that experimental procedures using modern molecular and genetic methods, such as in vivo transduction with retroviruses or creation of knockout or transgenic mutants, are not possible. Nevertheless, abundant and valuable information about the development of the human brain has been revealed using postmortem human material. Additionally, a combination and spectrum of in vitro techniques are used to gain knowledge about normal developmental processes in the human brain, including better understanding of RG as progenitor cells. Molecular and functional characterization of multipotent progenitors, such as RG, is important for future cell replacement therapies in neurological and psychiatric disorders, which are often resistant to conventional treatments. The protracted time of development and larger size of the human brain could provide insight into processes that may go unnoticed in the much smaller rodent cortex, which develops over a much shorter period. With that in mind, we summarize results on the role of RG in the human fetal brain.

Glioma stem cells: a midterm exam

Several years ago, the discovery of a highly tumorigenic subpopulation of stem-like cells embedded within fresh surgical isolates of malignant gliomas lent support to a new paradigm in cancer biology--the cancer stem cell hypothesis. At the same time, these "glioma stem cells" seemed to resolve a long-standing conundrum on the cell of origin for primary cancers of the brain. However, central tenets of the cancer stem cell hypothesis have recently been challenged, and the cellular origins of stem-like cells within malignant glioma are still contended. Here, we summarize the issues that are still in play with respect to the cancer stem cell hypothesis, and we revisit the developmental origins of malignant glioma. Do glioma stem cells arise from developmentally stalled neural progenitors or from dedifferentiated astrocytes? Five separate predictions of a neural progenitor cell of origin are put to the test.

The new challenge of stem cell: brain tumour therapy

The surprising similarity of much brain tumour behavior to the intrinsic properties of the neural stem/progenitor cell has triggered a recent interest in both arming stem cells to track and help eradicate tumours and in viewing stem cell biology as somehow integral to the emergence and/or production of the neoplasm itself. Moreover, based on the unique capacity of neural stem cells (NSCs) to migrate throughout the brain and to target invading tumour cells, the transplantation of NSCs offers a new potential therapeutic approach as a cell-based delivery system for gene therapy in brain tumours. On the one hand, both stem cells and cancer cells are thought to be capable of unlimited proliferation. While on the other, many tumours and cancer cell lines express stem cell markers, suggesting either that cancer cells resemble stem cells or that cancers contain stem-like cells. In this review we highlight the close relationship between normal neural stem cells and brain tumour stem cells and also suggest the possible clinical implications that these similarities could offer.

The role of myosin II in glioma invasion of the brain

The ability of gliomas to invade the brain limits the efficacy of standard therapies. In this study, we have examined glioma migration in living brain tissue by using two novel in vivo model systems. Within the brain, glioma cells migrate like nontransformed, neural progenitor cells-extending a prominent leading cytoplasmic process followed by a burst of forward movement by the cell body that requires myosin II. In contrast, on a two-dimensional surface, glioma cells migrate more like fibroblasts, and they do not require myosin II to move. To explain this phenomenon, we studied glioma migration through a series of synthetic membranes with defined pore sizes. Our results demonstrate that the A and B isoforms of myosin II are specifically required when a glioma cell has to squeeze through pores smaller than its nuclear diameter. They support a model in which the neural progenitor-like mode of glioma invasion and the requirement for myosin II represent an adaptation needed to move within the brain, which has a submicrometer effective pore size. Furthermore, the absolute requirement for myosin II in brain invasion underscores the importance of this molecular motor as a potential target for new anti-invasive therapies to treat malignant brain tumors.

Relationship of glioblastoma multiforme to the lateral ventricles predicts survival following tumor resection

OBJECTIVE

There has been an increased focus on the region adjacent to the lateral ventricles (LV) as a potential source of malignant tumors and/or more aggressive disease. We set out to determine if glioblastoma multiforme (GBM) bordering the LV was associated with decreased survival as compared to non-LV GBM.

METHODS

We reviewed the clinical records of 69 consecutive patients undergoing craniotomy for GBM at a single academic institution. Twenty-six patients were identified with contrast-enhancing lesions (CEL) bordering the LV (LV CEL). These 26 patients were matched with 26 patients with CEL not bordering the LV (non-LV CEL). These cohorts were matched for factors consistently shown to be associated with survival, which were age, tumor size, Karnofsky performance score, extent of resection, Gliadel implantation, and Temodar chemotherapy. Overall survival was compared between the cohorts via Log-rank analysis.

RESULTS

Despite similarities in pre-operative clinical status, tumor size, peri-operative outcome, and treatment regimens, the median survival for patients with LV CEL was significantly decreased as compared to patients with non-LV CEL (8 months vs. 11 months), P = 0.02. Additionally, survival analysis in patients stratified by primary and secondary resection also demonstrated a strong trend towards decreased survival after resection of LV CEL. After primary and secondary resection, patients with LV CEL versus non-LV CEL had a median survival of 11 months vs. 14 months (P = 0.10) and 7 months vs. 10 months (P = 0.11), respectively.

CONCLUSION

While the causal factors underlying this observation are not provided with this observational study, GBM bordering the LV may carry a prognostic significance.

Characterization of adult neural stem cells and their relation to brain tumors

The adult mammalian brain contains neural stem cells that are capable of generating new neurons and glia over the course of a lifetime. Neural stem cells reside in 2 germinal niches, the subventricular zone (SVZ) and the dentate gyrus subgranular zone. These primary progenitors have been identified in their niche in vivo; these cells have characteristics of astrocytes. Recent studies have shown that adult SVZ stem cells are derived from radial glia, the stem cells in the developing brain, which in turn are derived from the neuroepithelum, the earliest brain progenitors. Thus, SVZ stem cells are a continuum from neuroepithelium to radial glia to astrocytes, and are contained within what has been considered the lineage for astrocytes. However, it seems that only a small subset of the astrocytes present in the adult brain have stem cell properties. Recent findings have shown that SVZ stem cell astrocytes express a receptor for platelet-derived growth factor (PDGF), suggesting that the ability to respond to specific growth factor stimuli, such as PDGF, epidermal growth factor and others, may be unique to these stem cell astrocytes. Intriguingly, activation of these same signaling pathways is widely implicated in brain tumor formation. Since the adult brain has very few proliferating cells capable of accumulating the numerous mutations required for transformation, the adult neural stem and/or progenitor cells may be likely candidates for the brain tumor cell of origin. Indeed, activation of the PDGF or epidermal growth factor pathways in adult neural stem or progenitor cells confers tumor-like properties on these cells, lending support to this hypothesis.