Primitive neuroectodermal tumors of the central nervous system

Medulloblastomas, CNS embryonal tumors, and cerebellar mutism syndrome: advances in care and future directions

Central nervous system (CNS) embryonal tumors, commonly found in pediatric patients, represent a heterogeneous mix of lesions with an overall poor (though improving) prognosis. Medulloblastomas are by far the most frequently encountered and most widely studied subtype, though others include atypical teratoid/rhabdoid tumors (AT/RTs), embryonal tumor with multilayered rosettes (ETMRs), and CNS neuroblastomas, FOX-R2 activated. The classification, diagnosis, and treatment of these lesions have evolved drastically over the years as their molecular underpinnings have been elucidated. We describe the most recent 2021 WHO Classification system, discuss current understanding of the genetic basis, and demonstrate current thinking in treatment for these highly complex tumors. Since surgical resection continues to remain a mainstay of treatment, preventing and managing surgical complications, especially cerebellar mutism syndrome (CMS), is paramount. We describe the current theories for the etiology of CMS and two centers' experience in mitigating its risks. As our surgical toolbox continues to evolve along with our understanding of these tumors, we hope future patients can benefit from both improved overall survival and quality of life.

Embryonal Tumors of the Central Nervous System with Multilayered Rosettes and Atypical Teratoid/Rhabdoid Tumors

The 2016 WHO classification of tumors of the central nervous system affected importantly the group of CNS embryonal tumors. Molecular analysis on methylome, genome, and transcriptome levels allowed better classification, identification of specific molecular hallmarks of the different subtypes of CNS embryonal tumors, and their more precise diagnosis. Routine application of appropriate molecular testing and standardized reporting are of pivotal importance for adequate prognosis and treatment, but also for epidemiology studies and search for efficient targeted therapies. As a result of this approach, the term primitive neuroectodermal tumor-PNET was removed and a new clinic-pathological entity was introduced-Embryonal tumor with multilayered rosettes (ETMR). The group of CNS embryonal tumors include also medulloblastoma, medulloepithelioma, CNS neuroblastoma, CNS ganglioneuroblastoma, atypical teratoid/rhabdoid tumor (ATRT) and their subtypes. This chapter will focus mainly on ETMR and ATRT. Embryonal tumors with multilayered rosettes and the atypical teratoid/rhabdoid tumors are undifferentiated or poorly differentiated tumors of the nervous system that originate from primitive brain cells, develop exclusively in childhood or adolescence, and are characterized by a high degree of malignancy, aggressive evolution and a tendency to metastasize to the cerebrospinal fluid. Their clinical presentation is similar to other malignant, intracranial, neoplastic lesions and depends mainly on the localization of the tumor, the rise of the intracranial pressure, and eventually the obstruction of the cerebrospinal fluid pathways. The MRI image characteristics of these tumors are largely overlappingintra-axial, hypercellular, heterogeneous tumors, frequently with intratumoral necrosis and/or hemorrhages. Treatment options for ETMR and ATRT are very restricted. Surgery can seldom achieve radical excision. The rarity of the disease hampers the establishment of a chemotherapy protocol and the usual age of the patients limits severely the application of radiotherapy as a therapeutic option. Consequently, the prognosis of these undifferentiated, malignant, aggressive tumors remains dismal with a 5-year survival between 0 and 30%.

Rare embryonal and sarcomatous central nervous system tumours: State-of-the art and future directions

The introduction of molecular methods into the diagnostics of central nervous system (CNS) tumours and the subsequent deciphering of their molecular heterogeneity has resulted in a significant impact on paediatric neurooncology. Particularly in the field of rare embryonal and sarcomatous CNS tumours, novel tumour types have been delineated and introduced in the recent 5th edition of the WHO classification of CNS tumours. The rarity and novelty of these tumour types result in diagnostic and therapeutic challenges. Apart from distinct histopathological and molecular features, these tumour types exhibit characteristic clinical properties and require different therapeutic approaches for optimal patient management. However, based on the limited availability of clinical data, current therapeutic recommendations have to be based on data from small, predominantly retrospective patient cohorts. Within this article, we provide guidance for diagnostic work-up and clinical management of rare CNS embryonal tumours ('embryonal tumour with multi-layered rosettes', ETMR; 'CNS neuroblastoma, FOXR2-activated', CNS NB-FOXR2; 'CNS tumour with BCOR-ITD, CNS BCOR-ITD) and rare CNS sarcomatous tumours ('primary intracranial sarcoma, DICER1-mutant', CNS DICER1; 'CIC-rearranged sarcoma', CNS CIC). By emphasizing the significant consequences on patient management in paediatric CNS tumours, we want to encourage wide implementation of comprehensive molecular diagnostics and stress the importance for joint international efforts to further collect and study these rare tumour types.

Molecular analysis of pediatric CNS-PNET revealed nosologic heterogeneity and potent diagnostic markers for CNS neuroblastoma with FOXR2-activation

Primitive neuroectodermal tumors of the central nervous system (CNS-PNETs) are highly malignant neoplasms posing diagnostic challenge due to a lack of defining molecular markers. CNS neuroblastoma with forkhead box R2 (FOXR2) activation (CNS_NBL) emerged as a distinct pediatric brain tumor entity from a pool previously diagnosed as primitive neuroectodermal tumors of the central nervous system (CNS-PNETs). Current standard of identifying CNS_NBL relies on molecular analysis. We set out to establish immunohistochemical markers allowing safely distinguishing CNS_NBL from morphological mimics. To this aim we analyzed a series of 84 brain tumors institutionally diagnosed as CNS-PNET. As expected, epigenetic analysis revealed different methylation groups corresponding to the (1) CNS-NBL (24%), (2) glioblastoma IDH wild-type subclass H3.3 G34 (26%), (3) glioblastoma IDH wild-type subclass MYCN (21%) and (4) ependymoma with RELA_C11orf95 fusion (29%) entities. Transcriptome analysis of this series revealed a set of differentially expressed genes distinguishing CNS_NBL from its mimics. Based on RNA-sequencing data we established SOX10 and ANKRD55 expression as genes discriminating CNS_NBL from other tumors exhibiting CNS-PNET. Immunohistochemical detection of combined expression of SOX10 and ANKRD55 clearly identifies CNS_NBL discriminating them to other hemispheric CNS neoplasms harboring “PNET-like” microscopic appearance. Owing the rarity of CNS_NBL, a confirmation of the elaborated diagnostic IHC algorithm will be necessary in prospective patient series.

MRI Features of Histologically Diagnosed Supratentorial Primitive Neuroectodermal Tumors and Pineoblastomas in Correlation with Molecular Diagnoses and Outcomes: A Report from the Children's Oncology Group ACNS0332 Trial

BACKGROUND AND PURPOSE

Supratentorial primitive neuroectodermal tumors and pineoblastomas have traditionally been grouped together for treatment purposes. Molecular profiling of these tumors has revealed a number of distinct entities and has led to the term "CNS-primitive neuroectodermal tumors" being removed from the 2016 World Health Organization classification. The purpose of this study was to describe the MR imaging findings of histologically diagnosed primitive neuroectodermal tumors and pineoblastomas and correlate them with molecular diagnoses and outcomes.

MATERIALS AND METHODS

Histologically diagnosed primitive neuroectodermal tumors and pineoblastomas were enrolled in this Children's Oncology Group Phase III trial, and molecular classification was retrospectively completed using DNA methylation profiling. MR imaging features were systematically studied and correlated with molecular diagnoses and survival.

RESULTS

Of the 85 patients enrolled, 56 met the inclusion criteria, in whom 28 tumors were in pineal and 28 in nonpineal locations. Methylation profiling revealed a variety of diagnoses, including pineoblastomas (n = 27), high-grade gliomas (n = 17), embryonal tumors (n = 7), atypical teratoid/rhabdoid tumors (n = 3), and ependymomas (n = 2). Thus, 39% overall and 71% of nonpineal tumor diagnoses were discrepant with histopathology. Tumor location, size, margins, and edema were predictors of embryonal-versus-nonembryonal tumors. Larger size and ill-defined margins correlated with poor event-free survival, while metastatic disease by MR imaging did not.

CONCLUSIONS

In nonpineal locations, only a minority of histologically diagnosed primitive neuroectodermal tumors are embryonal tumors; therefore, high-grade glioma or ependymoma should be high on the radiographic differential. An understanding of molecularly defined tumor entities and their relative frequencies and locations will help the radiologist make more accurate predictions of the tumor types.

The incidence of brainstem primitive neuroectodermal tumors of childhood based on SEER data

PURPOSE

Incidence of BS primitive neuroectodermal tumors (BS-PNET) in children is not reported to date. Our main objectives were to estimate the incidence and report the outcome of BS-PNET in children.

METHODS

Data were collected using the Surveillance Epidemiology and End Results cancer registry.

RESULTS

From 1973 to 2013, we identified 83 pediatric patients (aged 0-21 years). Patients were divided into two age groups (0-3 years and 4-21 years). Median overall survival was 53 months. Patients in the older age group had a significant survival advantage (P < 0.001), as did those who received three modalities of therapy (surgery, chemotherapy, and radiation therapy) (P < 0.001) and patients with gross or subtotal tumor resection (P < 0.001).

CONCLUSIONS

This study presents the first estimate of incidence and the largest cohort of pediatric BS-PNETs to date. A high index of suspicion of BS-PNET in similar cases is crucial for diagnosis, treatment, and outcome.

Evaluation of age-dependent treatment strategies for children and young adults with pineoblastoma: analysis of pooled European Society for Paediatric Oncology (SIOP-E) and US Head Start data

Background

Pineoblastoma is a rare pineal region brain tumor. Treatment strategies have reflected those for other malignant embryonal brain tumors.

Patients and Methods

Original prospective treatment and outcome data from international trial groups were pooled. Cox regression models were developed considering treatment elements as time-dependent covariates.

Results

Data on 135 patients with pineoblastoma aged 0.01-20.7 (median 4.9) years were analyzed. Median observation time was 7.3 years. Favorable prognostic factors were age ≥4 years (hazard ratio [HR] for progression-free survival [PFS] 0.270, P < .001) and administration of radiotherapy (HR for PFS 0.282, P < .001). Metastatic disease (HR for PFS 2.015, P = .006), but not postoperative residual tumor, was associated with unfavorable prognosis. In 57 patients <4 years old, 5-year PFS/overall survival (OS) were 11 ± 4%/12 ± 4%. Two patients survived after chemotherapy only, while 3 of 16 treated with craniospinal irradiation (CSI) with boost, and 3 of 5 treated with high-dose chemotherapy (HDCT) and local radiotherapy survived. In 78 patients aged ≥4 years, PFS/OS were 72 ± 7%/73 ± 7% for patients without metastases, and 50 ± 10%/55 ± 10% with metastases. Seventy-three patients received radiotherapy (48 conventionally fractionated CSI, median dose 35.0 [18.0-45.0] Gy, 19 hyperfractionated CSI, 6 local radiotherapy), with (n = 68) or without (n = 6) chemotherapy. The treatment sequence had no impact; application of HDCT had weak impact on survival in older patients.

Conclusion

Survival is poor in young children treated without radiotherapy. In these patients, combination of HDCT and local radiotherapy may warrant further evaluation in the absence of more specific or targeted treatments. CSI combined with chemotherapy is effective for older non-metastatic patients.

Adult medulloblastoma

Medulloblastoma is a highly malignant central nervous system (CNS) tumor that arises from the cerebellum. It is the most common primary malignant intracranial childhood neoplasm. In adults, medulloblastoma are much less common, accounting for < 1% of all adult brain tumors. Herein, author has described a rare case of cerebellar medulloblastoma in adult.

New Brain Tumor Entities Emerge from Molecular Classification of CNS-PNETs

Primitive neuroectodermal tumors of the central nervous system (CNS-PNETs) are highly aggressive, poorly differentiated embryonal tumors occurring predominantly in young children but also affecting adolescents and adults. Herein, we demonstrate that a significant proportion of institutionally diagnosed CNS-PNETs display molecular profiles indistinguishable from those of various other well-defined CNS tumor entities, facilitating diagnosis and appropriate therapy for patients with these tumors. From the remaining fraction of CNS-PNETs, we identify four new CNS tumor entities, each associated with a recurrent genetic alteration and distinct histopathological and clinical features. These new molecular entities, designated "CNS neuroblastoma with FOXR2 activation (CNS NB-FOXR2)," "CNS Ewing sarcoma family tumor with CIC alteration (CNS EFT-CIC)," "CNS high-grade neuroepithelial tumor with MN1 alteration (CNS HGNET-MN1)," and "CNS high-grade neuroepithelial tumor with BCOR alteration (CNS HGNET-BCOR)," will enable meaningful clinical trials and the development of therapeutic strategies for patients affected by poorly differentiated CNS tumors.

Cell-Cycle Gene Expression in Lovastatin-Induced Medulloblastoma Apoptosis

Background:

3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase is a key rate-limiting enzyme in the mevalonate pathway, which generates precursors both for cholesterol biosynthesis and for the production of nonsteroidal mevalonate derivatives that are involved in a number of growth-regulatory processes. We have reported that lovastatin, a competitive inhibitor of HMG-CoA reductase, not only inhibits medulloblastoma proliferation in vitro, but also induces near-complete cell death via apoptosis. The mechanism of this phenomenon is unclear. Possible involvement of changes in expression of certain cell-cycle related genes led us to study some of them in more detail.

Methods:

Medulloblastoma cell lines were exposed in vitro to lovastatin, and the effects of gene expression changes were studied using RT-PCR, antisense oligonucleotide, DNA electrophoresis and Western blotting analysis.

Results:

1) Levels of total Ras gene mRNA and individual Ras gene mRNA are stable in lovastatin treatment in all examined medulloblastoma cell lines. 2) Blocking c-myc gene over-expression does not enhance medulloblastoma cell sensitivity to lovastatin. 3) Following lovastatin treatment, p16 expression exhibits no change, but pronounced increases of p27KIP1 protein are observed in all examined cell lines. Lovastatin induces pronounced increases of p21WAF1 protein only in Daoy and UW228, but not in D283 Med and D341 Med. 4) Following lovastatin treatment, increased p53 protein is detected only in D341 Med, and bax protein is unchanged in all cell lines.

Conclusion:

Lovastatin-induced growth inhibition and apoptosis in medulloblastoma are not dependent on the regulation of Ras and c-myc gene expression, but may be mediated by p27KIP1 gene expression. Lovastatin-induced apoptosis in medulloblastoma is probably p53 independent, but p53 and p21WAF1 gene expression may also mediate anti-proliferative effects of lovastatin on specific medulloblastoma cell lines.

Somatostatin receptor-based PET/CT of intracranial tumors: a potential area of application for 68 Ga-DOTA peptides?

OBJECTIVE

Similar to neuroendocrine tumors (NETs) at other sites, a wide array of intracranial tumors also express somatostatin receptors (SSTRs). This expression can be exploited for both imaging and therapy. The introduction of (68)Ga-labeled tetraazacyclododecanetetraacetic acid (DOTA)-peptide PET/CT has given new dimension to SSTR-based imaging because of its improved sensitivity and excellent spatial resolution.

CONCLUSION

However, in contrast to gastropancreatic and bronchopulmonary NETs, limited literature is available regarding the use of (68)Ga-DOTA-peptide PET/CT in intracranial tumors. Here, we briefly review the available literature and highlight the potential role that (68)Ga-DOTA-peptide PET/CT can play in the management of intracranial tumors.

Contrast-enhanced MR imaging in neuroimaging

MR imaging without and with gadolinium-based contrast agents (GBCAs) is an important imaging tool for defining normal anatomy and characteristics of lesions. GBCAs have been used in contrast-enhanced MR imaging in defining and characterizing lesions of the central nervous system for more than 20 years. The combination of unenhanced and GBCA-enhanced MR imaging is the clinical gold standard for the noninvasive detection and delineation of most intracranial and spinal lesions. MR imaging has a high predictive value that rules out neoplasm and most inflammatory and demyelinating processes of the central nervous system.

Cytologic and immunohistochemical characterization of a primitive neuroectodermal tumor in the brain of a dog

A 6-year-old intact female Pointer dog was presented for evaluation of acute onset of ataxia, circling, and head tilt. Neurologic assessment revealed overall decreased postural reaction, left-sided hemiparesis with incoordination, rigidity of fore- and hindlimbs, strabismus of the right eye, and bilateral horizontal nystagmus. Using magnetic resonance imaging, a mass lesion was identified in the cerebrum adjacent to the left side of the cerebellum compressing the brain stem ventrally. The mass was incompletely resected, and during surgery fine-needle aspiration and biopsy of the mass were performed. Cytologically, smears were highly cellular and contained predominantly small to medium-sized discrete round cells with high nuclear to cytoplasmic ratios and round nuclei with rare deep clefts or indentation, smooth chromatin, and indistinct nucleoli. Numerous cytoplasmic fragments were noted in the background. The primary diagnosis was lymphoma; other differential diagnoses included neuroendocrine tumor and poorly differentiated tumor of neural origin. The histologic diagnosis was lymphoma, and the lesion was presumed to be metastatic. On immunohistochemical analysis, the cells expressed neither CD3 nor CD79a. Re-examination of the histologic section revealed disorganized sheets of cells with multifocal palisading and perivascular arrangements of rosette-like structures. An expanded panel of antibodies to vimentin, cytokeratin, glial fibrillary acid protein (GFAP), neuron-specific enolase (NSE), synaptophysin (SYN), S-100, and CD45 was applied to histologic sections. Neoplastic cells were immunoreactive for vimentin, NSE, and S-100. Based on the histologic appearance and immunophenotype of the tumor, a diagnosis of primitive neuroectodermal tumor (PNET) was made. PNET, although rare in dogs, should be considered as a differential diagnosis for round cell tumors in the brain.

Pathogenesis of medulloblastoma and current treatment outlook

Medulloblastoma is the most common malignant tumor of the cerebellum in children, with a tendency to metastasize via CSF pathway. Survival rate varies depending on several factors, but is rather favorable, with radiotherapy as the treatment of choice. Irradiation of the craniospinal axis results, however, in severe neuropsychological and psychosocial impairments pertaining to memory, attention, motor functioning, language, and visuospatial abilities. Precise mechanisms underlying the formation of medulloblastoma are still unclear, but implication of at least three signaling molecules is postulated: insulin-like growth factor-I, WNT, and Sonic hedgehog. Thanks to increasing knowledge on the cellular mechanisms contributing to tumor formation, it is possible to propose new therapies that could replace radiotherapy or allow decreasing irradiation doses. The current review presents recent developments in medulloblastoma pathophysiology research and proposed inhibitors that could constitute good candidates for further pharmacological research.

Surgical management of pediatric brain tumors

Brain tumors are the most common cause of cancer-related death and the second most common form of cancer in pediatric patients. Many of these tumors are treated primarily with surgery, either alone or in combination with radiation or chemotherapy. Recent advances have lead to greater survival and decreased morbidities in childhood brain tumor patients. A full understanding of the biology and primary treatment modalities for the particular tumor are essential for any professional treating these patients, including the neurosurgeon. Each tumor type has features in common with, and unique from, other tumors that need to be understood prior to undertaking a rational treatment plan. This article summarizes some of these features.

Supratentorial primitive neuroectodermal tumors: a Canadian pediatric brain tumor consortium report

INTRODUCTION

Supratentorial primitive neuroectodermal tumors (SPNET) are rare tumors accounting for only 2.5% of childhood brain tumors. The purpose of this study was to describe the range of treatment regimens used to treat pediatric SPNET in Canada and to identify prognostic factors for overall survival in this population.

METHODS

This study was a retrospective clinical analysis of SPNET patients treated over the last 10 years in Canada. A questionnaire was developed and distributed to all institutions in Canada who treat pediatric patients. Data were collected for patients <19 years of age who were diagnosed and treated for SPNET between 1995 and 2005.

RESULTS

Data were obtained for 48 eligible patients. The stages of patients for whom complete data were provided were 80, 3, and 16% for metastatic stage M0, M1, and M2/3, respectively. The best responses to therapy included complete response in 44%, partial response in 8%, still on therapy in 2%, progressive disease in 31%, toxic death in 2%, and no therapy given in 12%. The 4-year survival was 37.7 +/- 7.6%. The factors associated with an increase in survival were the use of radiation therapy and chemotherapy, and age >2 years. Overall survival was not affected by metastatic disease at diagnosis, tumor site, or degree of initial resection.

CONCLUSIONS

Survival is poor in SPNET patients but highest in those who received chemotherapy and radiation therapy. Further studies are needed to improve the survival of these patients.

Medulloblastoma: therapy and biologic considerations

Tremendous strides have been made in both the treatment and the biologic understanding of medulloblastoma. Present optimal treatment can cure most medulloblastoma patients. A substantial minority of patients, however, will have recurrent or progressive disease. Recent studies have demonstrated that the success of treatment is not simply a matter of chance, but rather can be predicted based on specific biologic markers. These markers predict outcome independent of clinical staging and make clear that medulloblastomas are a biologically diverse group of tumors with variable clinical behavior. Molecular biologic investigation, including replication of tumorigenesis in transgenic mice, has further elucidated the complex biology of medulloblastoma. Current standard and investigational treatments, however, do not yet make use of biologic markers that predict risk of recurrence. Practical limitations have slowed the pace at which treatment paradigms can be revised to incorporate biologic insights. Mouse medulloblastoma models may provide an important bridge between biologic investigation and the development of new therapeutic approaches.

Paediatric PNET: pre-surgical MRI features

AIM

To describe the preoperative magnetic resonance imaging (MRI) characteristics of primitive neuroectodermal tumours (PNETs), in particular the diffusion-weighted imaging (DWI), MR spectroscopy (MRS) features and cerebrospinal fluid (CSF) tumour dissemination.

MATERIAL AND METHODS

Twelve patients with PNETs were reviewed: nine with medulloblastoma and three with supratentorial PNETs (SPNETs). The MRI examination included contrast-enhanced intracranial and spinal MRI, and in some patients, gradient recalled echo, fluid-attenuated inversion recovery (FLAIR), DWI, and MRS.

RESULTS

All PNETs were either hypointense or isointense on T1-weighted images. Ten of the 12 tumours were either isointense or hypointense on T2-weighted images, and 11 were isointense on FLAIR images. Patients with SPNETs had large, vascular and haemorrhagic tumours. On DWI, all PNETs were hyperintense and had restricted apparent diffusion coefficient. MRS (two patients with medulloblastoma and one with a SPNET), showed elevated choline, decreased N-acetyl aspartate, and a small taurine peak in all three patients. Intraspinal tumour dissemination, visible as uniform or nodular enhancement coating the conus medullaris, was detected in six of 12 patients, two of whom also had intracranial dissemination.

CONCLUSION

PNETs have a characteristic imaging appearance on FLAIR, DWI and MRS, which may help in differentiating these highly cellular neoplasms from other tumours. There is CSF tumour dissemination in a high proportion of patients, and spinal imaging is important for disease staging and to formulate treatment protocols.

Quantitative mRNA expression analysis of neurotrophin-receptor TrkC and oncogene c-MYC from formalin-fixed, paraffin-embedded primitive neuroectodermal tumor samples

Most recent studies analyzing candidate biological prognostic factors (including neurotrophin receptor TrkC and proto-oncogene c-MYC) in childhood primitive neuroectodermal brain tumors (PNET) are limited by small patient numbers due to dependence on fresh-frozen tumor material. In contrast, large archives of formalin-fixed, paraffin-embedded PNET samples exist from homogeneously treated patients. The ability of real-time RT-PCR to assay very small mRNA fragments makes this assay amenable to studies where the RNA is moderately or even highly degraded. We have optimized RNA isolation from archive PNET samples and found that TrkC and c-MYC mRNA measurements significantly correlated with those obtained from matching fresh-frozen tissues. Exploitation of already existing archives of formalin-fixed paraffin-embedded PNET samples may accelerate the building of better stratification systems for PNET patients.

Intracranial hypertension as an initial manifestation of spinal neuroectodermal tumor

A 19-year-old girl had headaches, blurred vision and vomiting for 2 weeks. Neurological examination revealed only bilateral papilloedema and left abducens palsy. Neuroimaging of the brain was normal. Cerebrospinal fluid study showed intracranial hypertension (IH), hypoglycorrhachia, hyperproteinorrhachia, and a negative cytology study. Eight months after the onset, paraparesis occurred. Spinal magnetic resonance imaging showed intramedullary masses at the cervical and thoracic cords with extensive seeding. Biopsy of the mass showed primitive neuroectodermal tumor (PNET). IH rarely occurs in patients with spinal cord neoplasms. Its incidence is low and the condition is always associated with signs of myelopathy. We report a patient whose initial manifestation of spinal PNET was IH only. Spinal tumor should be considered in IH patients whose intracranial examinations are negative.

Somatostatin receptor subtype 2 is expressed by supratentorial primitive neuroectodermal tumors of childhood and can be targeted for somatostatin receptor imaging

PURPOSE

Although gliomas predominate among central nervous system (CNS) neoplasms in adulthood, embryonal tumors are the most common malignant brain tumors in children. Despite novel treatment approaches, including improved radiotherapy and high-dose chemotherapy, survival rates remain unsatisfactory. The timely diagnosis of residual or recurrent embryonal CNS tumors and thus the earliest possible time point for intervention is often hampered by inaccuracies of conventional imaging techniques. Novel and refined imaging methodologies are urgently needed.

EXPERIMENTAL DESIGN

We have previously demonstrated the use of somatostatin receptor imaging (SRI) in the diagnosis of recurrent and residual medulloblastomas. Here, we evaluated somatostatin receptor type 2 (sst(2)) expression using an antibody in an array of CNS tumors of childhood. Eight high-grade gliomas, 4 atypical teratoid/rhabdoid tumors, 7 supratentorial primitive neuroectodermal tumors (stPNET), 1 medulloepithelioma (ME), and 8 ependymomas were screened. Tumors positive in vitro were additionally analyzed in vivo using SRI.

RESULTS

Abundant expression of somatostatin receptor type 2 in stPNET, a ME, and ependymomas warranted in vivo imaging of 7 stPNET, 1 rhabdomyosarcoma, 3 ependymomas, 1 ME, and 1 glioblastoma. Although SRI was positive in 6/7 stPNET, 1 rhabdomyosarcoma, and 1 ME, none of the ependymomas nor the glioblastoma could be imaged using SRI. In selected cases SRI was more sensitive in the detection of relapse than conventional imaging by magnetic resonance imaging and computed tomography.

CONCLUSIONS

SRI should be considered in the evaluation of residual or recurrent embryonal CNS tumors, especially stPNET. The strengths of SRI lie in the differentiation of reactive tissue changes versus residual or recurrent tumor, the detection of small lesions, and possibly in the distinction of stPNET from gliomas.

Double immunolabeling of central nervous system atypical teratoid/rhabdoid tumors

The central nervous system atypical teratoid/rhabdoid tumor (ATRT) is a highly malignant tumor with a heterogeneous immunohistochemical profile and with some morphologic similarity to central nervous system primitive neuroectodermal tumors (PNET). Although several studies have investigated double immunolabeling in PNET, we are aware of no studies of double labeling of ATRT. A total of 10 ATRT from surgical and consultation materials at the Children's Hospital of Philadelphia were selected and stained for a variety of antigens using indirect immunofluorescence to detect single and double labeling. Most tumor cells showed only single labeling; rare cells showed double labeling as follows: 70% of tumors coexpressed (VIM) and glial fibrillary acidic protein (GFAP), 30% smooth muscle actin and GFAP, 20% epithelial membrane antigen (EMA) and VIM, 20% EMA/GFAP, and 20% EMA/SMA. These results are discussed in view of current debates over the histogenesis of CNS PNET and ATRT, and in reference to the classification of rhabdoid tumors as an entity or phenotype.

Cancerous stem cells can arise from pediatric brain tumors

Pediatric brain tumors are significant causes of morbidity and mortality. It has been hypothesized that they derive from self-renewing multipotent neural stem cells. Here, we tested whether different pediatric brain tumors, including medulloblastomas and gliomas, contain cells with properties similar to neural stem cells. We find that tumor-derived progenitors form neurospheres that can be passaged at clonal density and are able to self-renew. Under conditions promoting differentiation, individual cells are multipotent, giving rise to both neurons and glia, in proportions that reflect the tumor of origin. Unlike normal neural stem cells, however, tumor-derived progenitors have an unusual capacity to proliferate and sometimes differentiate into abnormal cells with multiple differentiation markers. Gene expression analysis reveals that both whole tumors and tumor-derived neurospheres express many genes characteristic of neural and other stem cells, including CD133, Sox2, musashi-1, bmi-1, maternal embryonic leucine zipper kinase, and phosphoserine phosphatase, with variation from tumor to tumor. After grafting to neonatal rat brains, tumor-derived neurosphere cells migrate, produce neurons and glia, and continue to proliferate for more than 4 weeks. The results show that pediatric brain tumors contain neural stem-like cells with altered characteristics that may contribute to tumorigenesis. This finding may have important implications for treatment by means of specific targeting of stem-like cells within brain tumors.

I. Perinatal brain tumors: a review of 250 cases

Central nervous system tumors occur considerably less often in the fetus and neonate than in the older child. These tumors are not entirely the same as those found later in life. Their location, biologic behavior, response to therapy, and histologic types are different. Reports of 250 fetal and neonatal brain tumors were collected from the literature and studied for this review. The overall survival rate was 28%. The entire cranial cavity may be filled with tumor, and stillbirth is not uncommon. Macrocephaly was the most frequent presentation regardless of histology. Outcome is related to the size and location of the tumor, the histologic type, surgical resectability, and the condition of the infant at the time of diagnosis. Neonates with choroid plexus papillomas, gangliogliomas, and low-grade astrocytomas have the best prognosis, whereas those with teratomas and primitive neuroectodermal tumors have the worst prognosis.

Incidence and trends in pediatric malignancies medulloblastoma/primitive neuroectodermal tumor: a SEER update. Surveillance Epidemiology and End Results

BACKGROUND

It has been suggested that cerebellar medulloblastoma (M) and primitive neuroectodermal tumors (PNET) arising elsewhere in the nervous system, represent a single entity (M/PNET), although this concept is controversial. Cancer registries permit population-based description of cases reported as medulloblastoma, those reported as PNET and description of the aggregate, M/PNET.

PROCEDURE

We reviewed the 768 cases of M/PNET (633 diagnosed medulloblastoma and 135 diagnosed PNET) among persons under 20 years of age in the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) database.

RESULTS

The incidence of M/PNET rose 23%, from 4 per 10(6) person-years in 1973-77 to 4.9 per 10(6) person-years in 1993-98. Cases reported as PNET were more likely than those reported as medulloblastoma to be supratentorial (30.4% vs. 1.9%, P < 0.001) and to be female (42.2% vs. 35.4%, P = 0.13). The difference in 5-year survival between the 600 children with infratentorial medulloblastoma vs. the 49 children with infratentorial PNET was not statistically significant (55% vs. 43%). Regardless of reporting diagnosis, survival was poorer among children age 0-3 years and those with supratentorial tumors. Children diagnosed in the more recent period from 1985-1998 had a longer median survival than children diagnosed in 1973-84 (4.9 years vs. 10 years, P < 0.05). Rates were 42% higher among Whites compared to Blacks (4.5/10(6) person-years vs. 3.1/10(6) person-years, P < 0.01).

CONCLUSIONS

We found M/PNET is increasing in incidence and more frequent among Whites. Given that medulloblastoma and PNET are histologically identical and have similar epidemiologic profiles, future studies should provide analyses that combine these entities.

Are childhood and adult medulloblastomas different? A comparative study of clinicopathological features, proliferation index and apoptotic index

Childhood medulloblastomas have been suspected to be biologically different from adult tumors, though comparative studies are sparse in the literature. The present study aims to establish any differences or nexus in the biological characteristics between childhood and adult medulloblastomas. A total of 181 medulloblastomas were studied with respect to clinical and histological characteristics, MIB-1 labeling index (MIB-1 LI), apoptotic index (AI), ratio of apoptotic to LI, p53 and Bcl-2 protein expressions. Two-thirds (112) of the 181 medulloblastomas occurred in children (< or = 15 years) and 69 in adults (> 15 years). Childhood tumors were more commonly of classical histology and midline location while the desmoplastic variant and lateral location occurred more frequently in adults. Adult medulloblastomas were biologically less aggressive, having lower growth rate parameters (mean MIB-1 LI 19.1 +/- 15.7; AI 3.73 +/- 2.71 and AI:LI 0.207 +/- 0.162) as compared to childhood tumors (mean MIB-1 LI 28.3 +/- 20.4; AI 2.86 +/- 2.14 and AI:LI 0.108 +/- 0.111). p53 and Bcl-2 protein expressions were infrequent in all groups of tumors. No difference was noted in any of the parameters when classical and desmoplastic medulloblastomas were compared as a whole. But when compared between the age groups, an interesting observation (hitherto unreported in English literature) was that both classical and desmoplastic variants of childhood medulloblastomas had higher LI, lower AI and lower AI:LI ratio than their counterparts in adults, indicating that differences in growth rates cannot be attributed to differences in the frequency of occurrence of the histological variants in the two age groups. Thus, this study conclusively shows that there is a biological difference between childhood and adult medulloblastomas which is independent of standard histology and appeared to be associated more with age-related factors. This also warrants less-aggressive therapy for adult medulloblastoma.

Pleomorphic primitive neuroectodermal tumor with glial and neuronal differentiation: clinical, pathological, cultural, and chromosomal analysis of a case

This paper examines a case of pleomorphic primitive neuroectodermal tumor (PNET) with glial and neuronal differentiation in a 7-year-old girl who was clinicopathologically reported with immunohistochemical and chromosomal analysis. Clinically, a highly aggressive behavior leading to early recurrence with cerebrospinal fluid seedings was characteristic despite total removal and chemoradiation therapy. Pathologically, severe pleomorphism was noted and large ganglioid cells were predominant. Immunohistochemically, the expression of low-molecular neurofilament was recognized in the surgical specimens and increased in the recurrence. Coexpression of vimentin and neurofilament/GFAP was recognized in the culture. Chromosomal analysis showed near-diploidy, but different karyotype from that PNETs previously reported. These findings suggested that PNETs with pleomorphism and differentiation into both glial and neuronal lineages may show aggressiveness and require more aggressive therapy.

The WHO classification of tumors of the nervous system

The new World Health Organization (WHO) classification of nervous system tumors, published in 2000, emerged from a 1999 international consensus conference of neuropathologists. New entities include chordoid glioma of the third ventricle, cerebellar liponeurocytoma, atypical teratoid/rhabdoid tumor, and perineurioma. Several histological variants were added, including tanycytic ependymoma, large cell medulloblastoma, and rhabdoid meningioma. The WHO grading scheme was updated and, for meningiomas, extensively revised. In recognition of the emerging role of molecular diagnostic approaches to tumor classification, genetic profiles have been emphasized, as in the distinct subtypes of glioblastoma and the already clinically useful 1p and 19q markers for oligodendroglioma and 22q/INI1 for atypical teratoid/rhabdoid tumors. In accord with the new WHO Blue Book series, the actual classification is accompanied by extensive descriptions and illustrations of clinicopathological characteristics of each tumor type, including molecular genetic features, predictive factors, and separate chapters on inherited tumor syndromes. The 2000 WHO classification of nervous system tumors aims at being used and implemented by the neuro-oncology and biomedical research communities worldwide.

Supratentorial embryonal tumors in children under 5 years of age: an SFOP study of treatment with postoperative chemotherapy alone

BACKGROUND

To determine the effectiveness of multiagent chemotherapy as sole post-operative treatment of supratentorial central nervous system (CNS) embryonal tumors in young children.

PROCEDURE

The data of 25 children under 5 years of age diagnosed with supratentorial embryonal tumors (17 primitive neuroectodermal tumors, four pinealoblastomas, and four medulloepitheliomas) treated exclusively by postoperative chemotherapy (CT) between 1990 and 1997 were reviewed.

RESULTS

Fifteen tumors were hemispheric and 10 were deeply seated. Four children presented with disseminated leptomeningeal disease. Total resection was performed in nine patients, subtotal in 9, partial in 3, and a diagnostic biopsy only in 2. Two children did not undergo surgery. Twenty-four children relapsed with a median time of 5.5 months. The median overall survival was 12 months, and the 2-, and 5- year survivals were 30 and 14%, respectively. The 2- year disease-free survival was 4%. There was a significantly worse prognosis in patients undergoing incomplete resection and in the group with deeply situated tumors. Four relapses were treated by second surgery followed by high-dose chemotherapy and radiotherapy. Two of them remain in CR2, and all these children are free of late sequelae.

CONCLUSIONS

CT alone failed to maintain disease-free survival in most of the children, although, disease progression was delayed to some extent. Children under 5 years with supratentorial embryonal tumors should undergo total surgical resection if possible.

Aberrant promoter methylation of previously unidentified target genes is a common abnormality in medulloblastomas--implications for tumor biology and potential clinical utility

Medulloblastomas exhibit an array of diverse cytogenetic abnormalities. To evaluate the significance of epigenetic rather than genetic lesions in medulloblastomas and other primitive neuroectodermal tumors (PNETs) of the childhood CNS we performed a systematic analysis of gene specific and global methylation. Methylation-specific PCR detected no methylation for p15(INK4B), von Hippel Lindau and TP53 and only limited methylation for E-Cadherin and p16(INK4A) in tumors. The cell lines Daoy and MHH-PNET-5 in which the p16(INK4A) promoter was methylated did not express the gene, but demonstrated abnormalities by SSCP. Immunohistochemistry for p16 was negative in all examined normal cerebella and medulloblastomas. Using the technique of Restriction Landmark Genomic Scanning we detected methylation affecting up to 1% of all CpG islands in primary MB/PNETs and 6% in MB cell lines. Methylation patterns differed between medulloblastomas and PNETs. Examination of several methylated sequences revealed homologies to known genes and expressed sequences. Analysis of survival data identified seven of 30 hypermethylated sequences significantly correlating with poor prognosis. We suggest that DNA hypermethylation has an outstanding potential for the identification of novel tumor suppressors as well as diagnostic and therapeutic targets in MBs and other PNETs of the CNS.

Semaphorin 3A-vascular endothelial growth factor-165 balance mediates migration and apoptosis of neural progenitor cells by the recruitment of shared receptor

The dynamic and coordinated interaction between cells and their microenvironment controls cell migration, proliferation, and apoptosis, mediated by different cell surface molecules. We have studied the response of a neuroectodermal progenitor cell line, Dev, to a guidance molecule, semaphorin 3A (Sema3A), described previously as a repellent-collapsing signal for axons, and we have shown that Sema3A acts as a repellent guidance cue for migrating progenitor cells and, on prolonged application, induces apoptosis. Both repulsion and induction of cell death are mediated by neuropilin-1, the ligand-binding component of the Sema3A receptor. The vascular endothelial growth factor, VEGF165, antagonizes Sema3A-induced apoptosis and promotes cell survival, migration, and proliferation. Surprisingly, repulsion by Sema3A also depends on expression of VEGFR1, a VEGF165 receptor, expressed in Dev cells. Moreover, we found that these repulsive effects of Sema3A require tyrosine kinase activity, which can be attributed to VEGFR1. These results indicate that the balance between guidance molecules and angiogenic factors can modulate the migration, apoptosis (or survival), and proliferation of neural progenitor cells through shared receptors.

Semaphorin 3A-vascular endothelial growth factor-165 balance mediates migration and apoptosis of neural progenitor cells by the recruitment of shared receptor

The dynamic and coordinated interaction between cells and their microenvironment controls cell migration, proliferation, and apoptosis, mediated by different cell surface molecules. We have studied the response of a neuroectodermal progenitor cell line, Dev, to a guidance molecule, semaphorin 3A (Sema3A), described previously as a repellent-collapsing signal for axons, and we have shown that Sema3A acts as a repellent guidance cue for migrating progenitor cells and, on prolonged application, induces apoptosis. Both repulsion and induction of cell death are mediated by neuropilin-1, the ligand-binding component of the Sema3A receptor. The vascular endothelial growth factor, VEGF165, antagonizes Sema3A-induced apoptosis and promotes cell survival, migration, and proliferation. Surprisingly, repulsion by Sema3A also depends on expression of VEGFR1, a VEGF165 receptor, expressed in Dev cells. Moreover, we found that these repulsive effects of Sema3A require tyrosine kinase activity, which can be attributed to VEGFR1. These results indicate that the balance between guidance molecules and angiogenic factors can modulate the migration, apoptosis (or survival), and proliferation of neural progenitor cells through shared receptors.

Cytogenetic and histopathologic studies of congenital supratentorial primitive neuroectodermal tumors: a case report

Primitive neuroectodermal tumors (PNET) represent about 25% of primary central nervous system tumors in childhood, but congenital PNETs are rare. Cytogenetic studies and studies on molecular pathology have identified several genetic alterations in medulloblastoma, but molecular investigations on supratentorial PNETs are infrequent. We present a male newborn with a large congenital PNET of the right cerebral hemisphere and the molecular analysis of the tumor. Tumor tissue was investigated by routine histology and immunohistochemistry. Fluorescence in-situ hybridization was carried out on native tumor tissue to investigate deletions on chromosome 17p and to analyze c-Myc or N-Myc amplifications. Histologic examination revealed a primitive neuroectodermal tumor with massive extension covering almost the entire right hemisphere. Genetic analysis of the native tumor tissue of our patient excluded a deletion of chromosome 17p. An amplification of the c-Myc or N-Myc oncogene was absent using fluorescence in-situ hybridization. Despite unremarkable genetic analysis in our case prognosis was poor, suggesting that there are additional, yet unknown constitutional genetic aberrations in the pathogenesis of congenital supratentorial PNET.

Differential expression of somatostatin receptors in medulloblastoma

OBJECT

Somatostatin receptors have been found on a variety of tumours like neuroendocrine breast or brain tumours. Their detection opens new diagnostic and therapeutic paths. The aim of this work was to investigate their expression in medulloblastomas.

METHODS

Using both techniques, reverse transcriptase-polymerase chain reaction and immunohistochemistry, we analysed mRNA of different subtypes of somatostatin receptors in 15 medulloblastomas and the localisation of the subtype SSTR2 receptor at the cellular level in 13 medulloblastomas. All five subtypes mRNA were variably expressed in each medulloblastoma. The signal obtained after Southern blotting for SSTR2 receptor amplification was the highest as compared to the signal obtained for the other receptor subtypes. Immunostaining for SSTR2A receptor was present in every tumour specimen and was specifically located to the cellular membrane of neoplastic cells. No staining was identified at the level of peritumoral veins.

CONCLUSION

The evidence of predominant expression of SSTR2 receptors in medulloblastomas opens interesting prospects for their diagnosis and therapy.

Primitive neuroectodermal tumors of the brainstem: investigation of seven cases

OBJECTIVE

We discuss the clinical aspects, pathology, and molecular genetics of 7 patients with primitive neuroectodermal tumors (PNETs) arising in the brainstem that were treated at our institution from 1986 through 1995. Most neuro-oncologists avoid performing biopsies in children with pontine tumors. This article raises the question as to whether biopsies should be performed, because treatment recommendations might differ if a PNET was diagnosed rather than a pontine glioma.

PATIENTS AND METHODS

We reviewed the clinical neuro-oncology database and the files of the Division of Neuropathology at New York University Medical Center from 1986 through 1995 and identified 7 histologically confirmed PNETs arising in the brainstem among 146 pediatric brainstem tumors. The clinical, neuroradiological, and neuropathological data were reviewed. Postmortem examinations were performed in 2 cases. Formalin-fixed, paraffin-embedded tumor tissues were also available in 6 of 7 patients that were tested for p53 gene mutations using single-strand conformation polymorphism analysis. We also tested 9 cerebellar PNETs, 9 brainstem gliomas, and 3 normal brains for p53 gene mutations as controls.

RESULTS

All 7 patients presented with focal cranial nerve deficits, and 2 were also hemiparetic. The median age at diagnosis was 2.7 (1-8 years). Magnetic resonance imaging (MRI) characteristics included a focal intrinsic exophytic nonenhancing brainstem lesion that had low T1-weighted and high T2-weighted signals. Hydrocephalus was present in 5 patients at diagnosis, 3 of whom had leptomeningeal dissemination. Meningeal dissemination occurred later in the course of the disease in 3 other patients. Five children required shunts at diagnosis and another 2 at recurrence. Despite therapy, all 7 PNET patients died within 17 months of diagnosis with a mean survival of 8 (4-17) months. No mutation in the p53 gene was detected.

CONCLUSIONS

Brainstem PNETs tend to arise at a younger age than brainstem gliomas and medulloblastomas. The MRI pattern suggests a localized rather than a diffuse intrinsic nonenhancing brainstem tumor. Like other PNETs, brainstem PNETs have a high predilection to disseminate within the central nervous system. The absence of p53 mutations is similar to other PNETs. Despite their origin close to the cerebellum, brainstem PNETs exhibit a more aggressive behavior and result in worse clinical outcomes than do cerebellar PNETs.

In vivo functions of the patched protein: requirement of the C terminus for target gene inactivation but not Hedgehog sequestration

The membrane protein Patched (Ptc) is a key regulator of Hedgehog (Hh) signaling in development and is mutated in human tumors. Ptc opposes Hh-induced gene transcription and sequesters Hh protein. To dissect these functions, we tested partially deleted forms of Ptc in Drosophila. Deletion of either half of Ptc abolishes all function while coexpression of the halves restores nearly full activity. Deletion of the final 156 residues of Ptc permits Hh sequestration but abolishes inhibition of Hh targets. This deletion has dominant-negative activity, promoting target gene activation in a ligand-independent manner. We observe little or no association of full-length or partially deleted Ptc with the membrane protein Smoothened in Drosophila cultured cells.

Voltage- and gamma-aminobutyric acid-activated membrane currents in the human medulloblastoma cell line MHH-MED-3

The whole-cell patch clamp technique was used to characterize voltage- and neurotransmitter-activated currents in the medulloblastoma cell line MHH-MED-3 and cells from tissue slices and primary cultures of two medulloblastoma biopsies. These preparations revealed similar electrophysiological properties. All tested cells displayed 4-aminopyridine-sensitive delayed rectifying K(+) currents, gamma-aminobutyric acid(A) receptor-mediated Cl(-) currents and most of them inward rectifier K(+) currents. Transient inward currents were mainly carried by low-voltage activated T-type Ca(2+) channels in MHH-MED-3 cells, and tetrodotoxin-sensitive Na(+) channels in cells from the primary culture. From these characteristics we conclude that medulloblastoma cells share physiological features with developing cerebellar granule cells at an immature stage.

TrkC expression predicts good clinical outcome in primitive neuroectodermal brain tumors

PURPOSE

To identify biologic prognostic factors in childhood primitive neuroectodermal tumors (PNET), including medulloblastoma, that accurately define patient groups with sufficiently good prognosis to permit a reduction in treatment intensity.

PATIENTS AND METHODS

We determined expression levels of the neurotrophin receptor TrkC mRNA in formalin-fixed tumor samples from 87 well characterized PNET patients using in situ hybridization. Comparison of TrkC mRNA expression levels with clinical and other laboratory variables was performed using univariate and multivariate Cox regression analysis.

RESULTS

High TrkC mRNA expression was found to be associated more with higher 5-year cumulative survival rate than was low TrkC mRNA expression (89% v 46%, respectively). When compared with established clinical prognostic factors and laboratory variables of potential prognostic significance, TrkC mRNA expression, by univariate analysis, was found to be the single most powerful predictor of outcome (hazards ratio, 4.81; P <.00005), exceeding all clinical prognostic factors. In multivariate analysis, the hazards ratio remained significant (P <.00005).

CONCLUSION

High TrkC mRNA expression in PNET is a powerful independent predictor of favorable clinical outcome. Assessment of TrkC mRNA levels may aid in treatment planning for patients with PNETs and should be incorporated prospectively into PNET clinical trials.

Expression of the neurotrophin receptor p75NTR in medulloblastomas is correlated with distinct histological and clinical features: evidence for a medulloblastoma subtype derived from the external granule cell layer

Medulloblastomas (MBs) are primitive neuroectodermal tumors (PNET) of the cerebellum. They represent the most frequent malignant pediatric brain tumors, but their origin still remains unresolved and controversial. MB cells correspond to different stages of neural development and differentiation as illustrated by their expression of neuronal and glial markers. In the present study, we examined the expression pattern of the common low-affinity neurotrophin receptor p75NTR in a series of 167 MBs by immunohistochemistry. While p75NTR was present in only 17% of classic MBs (CMB), we found expression of p75NTR in all desmoplastic (nodular) MBs (DMB) examined, and in 71% of those MBs with a significant desmoplastic component. Furthermore, both desmoplastic histology and p75NTR expression were present preferentially in those tumors of adolescents and adults that are frequently located laterally in the cerebellar hemispheres. In DMBs, p75NTR was expressed predominantly in the proliferative, reticulin-rich areas, which may show coexpression of GFAP. In the pale islands of DMB, p75NTR was expressed only weakly or was absent. The expression pattern showed an inverse relation to that of the synaptic vesicle protein synaptophysin that was predominant in p75NTR negative classic MBs. Since the neurotrophin receptor p75NTR is expressed in cells of the external granule cell layer (EGL) of the fetal cerebellum, our findings suggest that progenitor cells of the EGL are the cellular origin of a distinct subset of MB, namely the desmoplastic variant and MBs with a significant desmoplastic component.

Membranous expression of glucose transporter-1 protein (GLUT-1) in embryonal neoplasms of the central nervous system

The human erythrocyte GLUT-1 is a transmembrane protein which facilitates transport of glucose in the cell in an energy-independent fashion. Neuroectodermal stem cells show strong membrane immunoreactivitry with this marker at early developmental stages in rodents. Membranous expression by undifferentiated neuroectodermal cells gradually decreases while GLUT-1 becomes confined to the endothelial cells, when these acquire blood-brain barrier function. We thus sought to determine whether GLUT-1 expression was limited to embryonal neoplasms of the central nervous system (CNS) which are presumably derived from developmentally arrested neuroectodermal stem cells. Archival material of 40 primary CNS neoplasms were examined for immunoreactivity with anti-GLUT-1. This included both non-embryonal neoplasms (18 astrocytic tumours, one ependymoma and three oligodendroglioma) and embryonal neoplasms (12 cerebellar medulloblastomas, four supratentorial PNETs and two atypical teratoid/rhabdoid tumours (AT/RhT)). In addition, cell lines and nude mice xenografts derived from both undifferentiated and differentiated tumours were assessed for GLUT-1 immunoreactivity by both immunohistochemistry and Western blotting. All embryonal tumours, MBs and PNET xenografts consistently showed GLUT-1 membrane staining. Non-embryonal neoplasms were negative except for vascular staining. Membrane protein fraction of embryonal tumours cell lines immunoreacted by immunoblot with GLUT-1, whereas the glioblastoma cell line was negative. Expression of GLUT-1 supports the stem cell nature of the cells of origin of MBs, supratentorial PNET and AT/RhTs. As a result, GLUT-1 is a useful marker to define the embryonal nature of CNS neoplasms.

A novel apoptotic pathway induced by nerve growth factor-mediated TrkA activation in medulloblastoma

Nerve growth factor (NGF) induces apoptosis in a human medulloblastoma cell line (MED283) engineered to express TrkA (MED283-TrkA) (Muragaki, Y., Chou, T. T., Kaplan, D. R., Trojanowski, J. Q., and Lee, V. M. (1997) J. Neurosci. 17, 530-542). To dissect the molecular signaling pathway that mediates this novel effect, specific receptor mutations in Trk have been employed. We showed that phosphorylation of tyrosine 490 is required for activation of phosphoinositide 3-OH kinase, whereas phosphorylation of tyrosine 785 is required for activation of phospholipase C-gamma. TrkA-mediated apoptosis was abolished when either the ATP-binding site or both tyrosines 490 and 785 were mutated. Because tyrosines 490 and 785 mediate redundant signaling through the Ras-extracellular signal-regulated kinase (Ras-ERK) pathway, we examined the role of Ras-ERK signaling in NGF-induced apoptosis. We found that MED283-TrkA cells expressing a dominant negative Ras inhibitor (N17Ras) failed to undergo ERK activation and apoptosis following NGF treatment, whereas the ERK kinase (mitogen-activated protein kinase kinase) inhibitors PD98059 and U0126 eliminated ERK activation but had no effect on apoptosis. We infer from these data that NGF-induced apoptosis is mediated by a novel Ras and/or Raf signaling pathway.

Mevalonate prevents lovastatin-induced apoptosis in medulloblastoma cell lines

BACKGROUND

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) is a key rate-limiting enzyme in the mevalonate pathway, which generates precursors for cholesterol biosynthesis and the production of non-steroidal mevalonate derivatives that are involved in a number of growth-regulatory processes. We have reported that lovastatin, a competitive inhibitor of HMG-CoA reductase, not only inhibits medulloblastoma proliferation in vitro, but also induces near-complete cell death via apoptosis. The present study explores some of the pathways which may be involved in lovastatin-induced apoptosis.

METHODS

Medulloblastoma cell lines were exposed in vitro to lovastatin with or without mevalonate, and document the effects using morphology, flow cytometry. DNA electrophoresis and Northern analysis.

RESULTS

1) Mevalonate prevents apoptosis when co-incubated with lovastatin, or when administered to lovastatin-pretreated cells. 2) Mevalonate restores the lovastatin-arrested cell cycle, allowing S phase entry. 3) Mevalonate does not prevent lovastatin-induced apoptosis after a critical duration of lovastatin pretreatment. For cell lines Daoy and UW228 this was 24 hours, and for D283 Med and D341 Med it was 48 hours. 4) Increases in HMG-CoA reductase mRNA levels induced by lovastatin are abrogated by co-incubation with lovastatin and mevalonate.

CONCLUSIONS

These results confirm that lovastatin inhibition of this enzyme results in blockage of the mevalonate pathway, and that such a block is a critical step in the mechanism of lovastatin-induced apoptosis.

Extracerebellar primitive neuroectodermal tumors: A clinicopathologic study with bcl-2 and CD99 immunohistochemistry

Supratentorial primitive neuroectodermal tumors (S-PNETs) are uncommon lesions that occur predominantly in children and are histologically identical to cerebellar medulloblastomas. Like their cerebellar counterparts, S-PNETs often show divergent differentiation along neuronal, glial, and mesenchymal lines. The relationship of S-PNETs to medulloblastoma and other embryonal neoplasms remains controversial, largely because the cell of origin and histogenesis of these lesions are incompletely understood. To clarify these issues, we examined eight S-PNETs with antibodies to bcl-2 (an antiapoptosis protooncogene that has been postulated to be a marker of neuronal differentiation) and CD99 (a glycoprotein present in most peripheral embryonal tumors). S-PNETs in eight patients (seven males and one female; age range, 2 months to 40 years) were studied. All lesions were composed predominantly of small round cells with deeply basophilic nuclei and minimal surrounding cytoplasm. Tumors in two patients demonstrated no evidence of differentiation, two tumors neuronal differentiation only, and four tumors both neuronal and glial differentiation. No tumors stained with CD99. Three tumors showed focal, strong cytoplasmic staining with bcl-2. The positive lesions included one tumor showing neuronal differentiation only and two tumors with both neuronal and astrocytic differentiation. Patients were treated with various combinations of radiation and chemotherapy; five patients died from their tumor a mean of 1.7 years after diagnosis, two patients were alive with residual disease at 3 months and 3 years, and one patient was alive without disease at 17 months. Our findings suggest that bcl-2 positivity may identify a subgroup of patients having inhibition of apoptosis as a pathogenetic mechanism; we were unable to show any definite relationship between bcl-2 staining and neuronal differentiation. Despite their morphologic similarity, supratentorial and peripheral embryonal tumors appear to be distinct pathogenetic lesions, as evidenced by their different staining patterns with CD99.

Retroviral vectors for the expression of two genes in human multipotent neural precursors and their differentiated neuronal and glial progeny

Retroviral vectors allow stable integration of exogenous DNA into genomic DNA and therefore gene transmission to progeny. Multipotent neural precursors and immortal cell lines prepared from them have been demonstrated to integrate into either adult or developing brain in a nontumorigenic, functional manner, without interfering with normal neurobiological processes. These cells thus appear to provide a Trojan horse ideally adapted to directing the expression of transgenes appropriately in a host brain. Here we investigated and optimized the transduction capacity of MuLV-based retroviral vectors in which internal ribosomal entry segments (IRESs) drive coexpression of two heterologous gene products from a single bicistronic mRNA in a human multipotent neural precursor cell line, "Dev," which was prepared from a medulloblastoma. For this, two vectors containing two different combinations of three viral IRESs were used and the capacity of different pseudotyped vectors to permit an efficient and stable transduction of Dev cells was compared. Our data show that (1) the best recombinant vectors for Dev cell transduction are those pseudotyped with the 10A1 MuLV envelope (40% of transduction) and (2) the initial coexpression of neo and plap, observed in transduced undifferentiated Dev cells, is maintained in differentiated Dev cells with a neuronal or glial phenotype. Therefore, these double-IRES vectors may provide an efficient means of transducing the coexpression of two proteins in undifferentiated human neural precursors that is maintained in their differentiated progeny. These data suggest that the double-IRES strategy is well adapted to potential therapeutic situations when coexpression of two different transgenes may be required in the same cell.

High expression of somatostatin receptor subtype 2 (sst2) in medulloblastoma: implications for diagnosis and therapy

Medulloblastoma is a pediatric malignancy, which arises in cerebellum. The neuropeptide somatostatin (SS-14) is a neuromodulator and growth regulator in the developing cerebellum. SS-14 has previously been demonstrated in medulloblastomas with immunohistochemical techniques, but somatostatin receptor (sst) expression is less well understood. We analyzed somatostatin and sst subtype expression (sst1-5) in central primitive neuroectodermal tumors (cPNET), including 23 medulloblastomas, 6 supratentorial PNET, and 10 cPNET cell lines. The expression of SS-14 and sst genes in cPNET was compared with expression of these genes in 17 tumors of the Ewing's sarcoma family of tumors using reverse transcriptase-PCR, Southern hybridization, quantitative in vitro receptor autoradiography, and competitive membrane binding assays. The sst1 subtype was expressed in similar frequency in cPNET (83%) and Ewing's sarcoma family of tumors (71%). Nine of the 10 cell lines and 76% of the cPNET expressed mRNA for sst2 compared with 35% of the Ewing's sarcoma family of tumors. High-affinity binding of SS-14 was demonstrated in cPNET by quantitative autoradiography as well as by competitive binding assays. The cPNET cell line D283 Med bound SS-14 and octreotide with high affinity; SS-14 inhibited proliferation of D283 Med cells as measured by a decrease in [3H]thymidine uptake. We conclude that both sst1 and sst2 are highly expressed in cPNET and suggest that somatostatin may regulate proliferation and differentiation in these developmental tumors.

Bone morphogenetic proteins-2 and -4 attenuate apoptosis in a cerebellar primitive neuroectodermal tumor cell line

Similarities between primitive neuroectodermal tumors and central nervous system (CNS) progenitor cells have evoked interest in the response of these tumors to endogenous growth factors. The bone morphogenetic proteins (BMPs) have recently been found to regulate survival and differentiation of CNS progenitor cell populations. In this study, we investigated the effects of BMP-2, BMP-4, and BMP-6 on the undifferentiated cerebellar primitive neuroectodermal tumor or medulloblastoma cell line DAOY. Analysis by reverse transcriptase-polymerase chain reaction showed that mRNAs for type IA and type II BMP receptors were present in control cultures. In cultures treated with BMP-2, mRNAs for BMP receptor type IB and the activin R-I receptor became evident. Cultures were analyzed for total cell counts, proliferating cell nuclear antigen (PCNA), and apoptotic DNA fragmentation. There was a significant increase in total cell number in the BMP-2 and BMP-4 treatment groups, without any change in PCNA reactivity, and a dramatic decrease in the proportion of apoptotic nuclei at concentrations of BMP-2 and BMP-4 above 5 ng/ml (P<0.001). These effects were not observed with BMP-6, TGF-beta1 or GDNF. These results suggest that the increase in total cell number is due to the attenuation of apoptosis by BMP-2 and BMP-4. The anti-apoptotic effect of BMP-2 and BMP-4 on this neuroectodermal cell line has potential clinical implications for neuroectodermal tumors.