Functional VEGF and VEGF receptors are expressed in human medulloblastomas

High-throughput neural stem cell-based drug screening identifies S6K1 inhibition as a selective vulnerability in sonic hedgehog-medulloblastoma

BACKGROUND

Medulloblastoma (MB) is one of the most common malignant brain tumors in children. Current treatments have increased overall survival but can lead to devastating side effects and late complications in survivors, emphasizing the need for new, improved targeted therapies that specifically eliminate tumor cells while sparing the normally developing brain.

METHODS

Here, we used a sonic hedgehog (SHH)-MB model based on a patient-derived neuroepithelial stem cell system for an unbiased high-throughput screen with a library of 172 compounds with known targets. Compounds were evaluated in both healthy neural stem cells (NSCs) and tumor cells derived from the same patient. Based on the difference of cell viability and drug sensitivity score between normal cells and tumor cells, hit compounds were selected and further validated in vitro and in vivo.

RESULTS

We identified PF4708671 (S6K1 inhibitor) as a potential agent that selectively targets SHH-driven MB tumor cells while sparing NSCs and differentiated neurons. Subsequent validation studies confirmed that PF4708671 inhibited the growth of SHH-MB tumor cells both in vitro and in vivo, and that knockdown of S6K1 resulted in reduced tumor formation.

CONCLUSIONS

Overall, our results suggest that inhibition of S6K1 specifically affects tumor growth, whereas it has less effect on non-tumor cells. Our data also show that the NES cell platform can be used to identify potentially effective new therapies and targets for SHH-MB.

Identification and validation of a metabolism-related gene signature for predicting the prognosis of paediatric medulloblastoma

Medulloblastoma (MB) is a malignant brain tumour that is highly common in children and has a tendency to spread to the brain and spinal cord. MB is thought to be a metabolically driven brain tumour. Understanding tumour cell metabolic patterns and characteristics can provide a promising foundation for understanding MB pathogenesis and developing treatments. Here, by analysing RNA-seq data of MB samples from the Gene Expression Omnibus (GEO) database, 12 differentially expressed metabolic-related genes (DE-MRGs) were chosen for the construction of a predictive risk score model for MB. This model demonstrated outstanding accuracy in predicting the outcomes of MB patients and served as a standalone predictor. An evaluation of functional enrichment revealed that the risk score showed enrichment in pathways related to cancer promotion and the immune response. In addition, a high risk score was an independent poor prognostic factor for MB in patients with different ages, sexes, metastasis stages and subgroups (SHH and Group 4). Consistently, the metabolic enzyme ornithine decarboxylase (ODC1) was upregulated in MB patients with poor survival time. Inhibition of ODC1 in primary and metastatic MB cell lines decreased cell proliferation, migration and invasion but increased immune infiltration. This study could aid in identifying metabolic targets for MB as well as optimizing risk stratification systems and individual treatment plans for MB patients via the use of a metabolism-related gene prognostic risk score signature.

Personalized treatment options of refractory and relapsed medulloblastoma in children: literature review

Medulloblastoma (MB) is the most common malignant tumor of the central nervous system in pediatric patients. Despite the complex anticancer therapy approach, refractory and relapsing forms of the disease remain fatal in most cases and account for approximately 30%. To date, repeated surgery, radiation, and chemotherapy can be used as life-prolonging treatment options; nevertheless, it should be emphasized that there are no standardized approaches based on existing data of molecular variants of MB. It is obvious that only a deep understanding of the biological mechanisms in association with clinical aspects in refractory and relapsing forms of MB would make it possible to personalize second- and subsequent-line therapy in order to achieve maximum efficiency and minimize early and long-term toxicity. The article presents the current understanding of prognostic factors in relapsed/refractory forms of MB, methods of modern diagnostics, as well as existing and perspective treatment options based on the biological and clinical aspects of the disease.

Drugging Hijacked Kinase Pathways in Pediatric Oncology: Opportunities and Current Scenario

Childhood cancer is considered rare, corresponding to ~3% of all malignant neoplasms in the human population. The World Health Organization (WHO) reports a universal occurrence of more than 15 cases per 100,000 inhabitants around the globe, and despite improvements in diagnosis, treatment and supportive care, one child dies of cancer every 3 min. Consequently, more efficient, selective and affordable therapeutics are still needed in order to improve outcomes and avoid long-term sequelae. Alterations in kinases' functionality is a trademark of cancer and the concept of exploiting them as drug targets has burgeoned in academia and in the pharmaceutical industry of the 21st century. Consequently, an increasing plethora of inhibitors has emerged. In the present study, the expression patterns of a selected group of kinases (including tyrosine receptors, members of the PI3K/AKT/mTOR and MAPK pathways, coordinators of cell cycle progression, and chromosome segregation) and their correlation with clinical outcomes in pediatric solid tumors were accessed through the R2: Genomics Analysis and Visualization Platform and by a thorough search of published literature. To further illustrate the importance of kinase dysregulation in the pathophysiology of pediatric cancer, we analyzed the vulnerability of different cancer cell lines against their inhibition through the Cancer Dependency Map portal, and performed a search for kinase-targeted compounds with approval and clinical applicability through the CanSAR knowledgebase. Finally, we provide a detailed literature review of a considerable set of small molecules that mitigate kinase activity under experimental testing and clinical trials for the treatment of pediatric tumors, while discuss critical challenges that must be overcome before translation into clinical options, including the absence of compounds designed specifically for childhood tumors which often show differential mutational burdens, intrinsic and acquired resistance, lack of selectivity and adverse effects on a growing organism.

Medulloblastoma in the Modern Era: Review of Contemporary Trials, Molecular Advances, and Updates in Management

Critical discoveries over the past two decades have transformed our understanding of medulloblastoma from a single entity into a clinically and biologically heterogeneous disease composed of at least four molecularly distinct subgroups with prognostically and therapeutically relevant genomic signatures. Contemporary clinical trials also have provided valuable insight guiding appropriate treatment strategies. Despite therapeutic and biological advances, medulloblastoma patients across the age spectrum experience tumor- and treatment-related morbidity and mortality. Using an updated risk stratification approach integrating both clinical and molecular features, ongoing research seeks to (1) cautiously reduce therapy and mitigate toxicity in low-average risk patients, and (2) thoughtfully intensify treatment with incorporation of novel, biologically guided agents for patients with high-risk disease. Herein, we review important historical and contemporary studies, discuss management updates, and summarize current knowledge of the biological landscape across unique pediatric, infant, young adult, and relapsed medulloblastoma populations.

Medulloblastoma and the DNA Damage Response

Medulloblastoma (MB) is the most common malignant brain tumor in children with standard of care consisting of surgery, radiation, and chemotherapy. Recent molecular profiling led to the identification of four molecularly distinct MB subgroups – Wingless (WNT), Sonic Hedgehog (SHH), Group 3, and Group 4. Despite genomic MB characterization and subsequent tumor stratification, clinical treatment paradigms are still largely driven by histology, degree of surgical resection, and presence or absence of metastasis rather than molecular profile. Patients usually undergo resection of their tumor followed by craniospinal radiation (CSI) and a 6 month to one-year multi-agent chemotherapeutic regimen. While there is clearly a need for development of targeted agents specific to the molecular alterations of each patient, targeting proteins responsible for DNA damage repair could have a broader impact regardless of molecular subgrouping. DNA damage response (DDR) protein inhibitors have recently emerged as targeted agents with potent activity as monotherapy or in combination in different cancers. Here we discuss the molecular underpinnings of genomic instability in MB and potential avenues for exploitation through DNA damage response inhibition.

Targeting Angiogenic Factors for the Treatment of Medulloblastoma

OPINION STATEMENT

Medulloblastoma (MB) is the most frequent pediatric brain tumor. Despite conventional therapy, MB patients have high mortality and morbidity rates mainly due to the incomplete understanding of the molecular and cellular processes involved in development of this cancer. Similar to other solid tumors, MB demonstrated high endothelial cell proliferation and angiogenic activity, wherein new blood vessels arise from the pre-existing vasculature, a process named angiogenesis. MB angiogenesis is considered a hallmark for MB development, progression, and metastasis emphasizing its potential target for antitumor therapy. However, angiogenesis is tightly regulated by a set of angiogenic factors making it a complex process to be targeted. Although agents targeting these factors and their receptors are early in development, the potential for their targeting may translate into improvement in the clinical care for MB patients. In this review, we focus on the most potent angiogenic factors and their corresponding receptors, highlighting their basic properties and expression in MB. We describe their contribution to MB tumorigenesis and angiogenesis and the potential therapeutic targeting of these factors.

The Current Landscape of Targeted Clinical Trials in Non-WNT/Non-SHH Medulloblastoma

Simple Summary

Medulloblastoma is a form of malignant brain tumor that arises predominantly in infants and young children and can be divided into different groups based on molecular markers. The group of non-WNT/non-SHH medulloblastoma includes a spectrum of heterogeneous subgroups that differ in their biological characteristics, genetic underpinnings, and clinical course of disease. Non-WNT/non-SHH medulloblastoma is currently treated with surgery, chemotherapy, and radiotherapy; however, new drugs are needed to treat patients who are not yet curable and to reduce treatment-related toxicity and side effects. We here review which new treatment options for non-WNT/non-SHH medulloblastoma are currently clinically tested. Furthermore, we illustrate the challenges that have to be overcome to reach a new therapeutic standard for non-WNT/non-SHH medulloblastoma, for instance the current lack of good preclinical models, and the necessity to conduct trials in a comparably small patient collective.

Abstract

Medulloblastoma is an embryonal pediatric brain tumor and can be divided into at least four molecularly defined groups. The category non-WNT/non-SHH medulloblastoma summarizes medulloblastoma groups 3 and 4 and is characterized by considerable genetic and clinical heterogeneity. New therapeutic strategies are needed to increase survival rates and to reduce treatment-related toxicity. We performed a noncomprehensive targeted review of the current clinical trial landscape and literature to summarize innovative treatment options for non-WNT/non-SHH medulloblastoma. A multitude of new drugs is currently evaluated in trials for which non-WNT/non-SHH patients are eligible, for instance immunotherapy, kinase inhibitors, and drugs targeting the epigenome. However, the majority of these trials is not restricted to medulloblastoma and lacks molecular classification. Whereas many new molecular targets have been identified in the last decade, which are currently tested in clinical trials, several challenges remain on the way to reach a new therapeutic strategy for non-WNT/non-SHH medulloblastoma. These include the severe lack of faithful preclinical models and predictive biomarkers, the question on how to stratify patients for clinical trials, and the relative lack of studies that recruit large, homogeneous patient collectives. Innovative trial designs and international collaboration will be a key to eventually overcome these obstacles.

Temozolomide with irinotecan versus temozolomide, irinotecan plus bevacizumab for recurrent medulloblastoma of childhood: Report of a COG randomized Phase II screening trial

BACKGROUND

Approximately 30% of children with medulloblastoma (MB) experience recurrence, which is usually incurable. This study compared the overall survival (OS) of patients receiving temozolomide (TMZ) and irinotecan with that of patients receiving TMZ, irinotecan, and bevacizumab for recurrent MB/central nervous system (CNS) primitive neuroectodermal tumor (PNET).

METHODS

Patients with relapsed/refractory MB or CNS PNET were randomly assigned to receive TMZ (150 mg/m² /day PO on days 1-5) and irinotecan (50 mg/m² /day IV on days 1-5) with or without bevacizumab (10 mg/kg IV on days 1 and 15).

RESULTS

One hundred five patients were eligible and treated on study. Median OS was 13 months in the standard arm and 19 months with the addition of bevacizumab; median event-free survival (EFS) was 6 months in the standard arm and 9 months with the addition of bevacizumab. The hazard ratio for death from the stratified relative-risk regression model is 0.63. Overall, 23 patients completed 12 courses of planned protocol therapy, 23% (12/52) in the experimental arm with bevacizumab versus 21% (11/53) in the standard arm. Toxicity profiles were comparable in both treatment arms. The estimate of the incidence of feasibility events associated with the bevacizumab arm is three of 52 (5.8%) (95% CI 1.2-16%). Events included myelosuppression, electrolyte abnormalities, diarrhea, and elevated transaminases. One intracranial hemorrhage event was observed in each arm.

CONCLUSION

The addition of bevacizumab to TMZ/irinotecan significantly reduced the risk of death in children with recurrent MB. The combination was relatively well tolerated in this heavily pretreated cohort. The three-drug regimen demonstrated a sufficient risk reduction to warrant further investigation.

Immunosuppression in Medulloblastoma: Insights into Cancer Immunity and Immunotherapy

OPINION STATEMENT

Medulloblastoma (MB) is the most common pediatric brain malignancy, with a 5-year overall survival (OS) rate of around 65%. The conventional MB treatment, comprising surgical resection followed by irradiation and adjuvant chemotherapy, often leads to impairment in normal body functions and poor quality of life, especially with the increased risk of recurrence and subsequent development of secondary malignancies. The development and progression of MB are facilitated by a variety of immune-evading mechanisms such as the secretion of immunosuppressive molecules, activation of immunosuppressive cells, inhibition of immune checkpoint molecules, impairment of adhesive molecules, downregulation of the major histocompatibility complex (MHC) molecules, protection against apoptosis, and activation of immunosuppressive pathways. Understanding the tumor-immune relationship in MB is crucial for effective development of immune-based therapeutic strategies. In this comprehensive review, we discuss the immunological aspect of the brain, focusing on the current knowledge tackling the mechanisms of MB immune suppression and evasion. We also highlight several key immunotherapeutic approaches developed to date for the treatment of MB.

Cytotoxic effects and tolerability of gemcitabine and axitinib in a xenograft model for c-myc amplified medulloblastoma

Medulloblastoma is the most common high-grade brain tumor in childhood. Medulloblastomas with c-myc amplification, classified as group 3, are the most aggressive among the four disease subtypes resulting in a 5-year overall survival of just above 50%. Despite current intensive therapy regimens, patients suffering from group 3 medulloblastoma urgently require new therapeutic options. Using a recently established c-myc amplified human medulloblastoma cell line, we performed an in-vitro-drug screen with single and combinatorial drugs that are either already clinically approved or agents in the advanced stage of clinical development. Candidate drugs were identified in vitro and then evaluated in vivo. Tumor growth was closely monitored by BLI. Vessel development was assessed by 3D light-sheet-fluorescence-microscopy. We identified the combination of gemcitabine and axitinib to be highly cytotoxic, requiring only low picomolar concentrations when used in combination. In the orthotopic model, gemcitabine and axitinib showed efficacy in terms of tumor control and survival. In both models, gemcitabine and axitinib were better tolerated than the standard regimen comprising of cisplatin and etoposide phosphate. 3D light-sheet-fluorescence-microscopy of intact tumors revealed thinning and rarefication of tumor vessels, providing one explanation for reduced tumor growth. Thus, the combination of the two drugs gemcitabine and axitinib has favorable effects on preventing tumor progression in an orthotopic group 3 medulloblastoma xenograft model while exhibiting a favorable toxicity profile. The combination merits further exploration as a new approach to treat high-risk group 3 medulloblastoma.

Drug penetration in pediatric brain tumors: Challenges and opportunities

Larger clinical trial enrollments and a greater understanding of biological heterogeneity have led to improved survival rates for children diagnosed with brain tumors in the last 50 years. However, reducing long-term morbidities and improving survival rates of high-risk tumors remain major challenges. Chemotherapy can reduce tumor burden, but effective drug penetration at the tumor site is limited by barriers in the route of drug administration and within the tumor microenvironment. Bioavailability of drugs is impeded by the blood-brain barrier, plasma protein binding, and structural components by the tumor including the matrix and vasculature contributing to increased interstitial fluid pressure, hypoxia, and acidity. Designing drug delivery systems to circumvent these barriers could lead to improved drug penetration at the tumor site and reduce adverse systemic side effects. In this review, we expand on how systemic and local barriers limit drug penetration and present potential methods to enhance drug penetration in pediatric brain tumors.

REST promotes ETS1-dependent vascular growth in medulloblastoma

Expression of the RE1‐silencing transcription factor (REST), a master regulator of neurogenesis, is elevated in medulloblastoma (MB) tumors. A cell‐intrinsic function for REST in MB tumorigenesis is known. However, a role for REST in the regulation of MB tumor microenvironment has not been investigated. Here, we implicate REST in remodeling of the MB vasculature and describe underlying mechanisms. Using REST^TG mice, we demonstrate that elevated REST expression in cerebellar granule cell progenitors, the cells of origin of sonic hedgehog (SHH) MBs, increased vascular growth. This was recapitulated in MB xenograft models and validated by transcriptomic analyses of human MB samples. REST upregulation was associated with enhanced secretion of proangiogenic factors. Surprisingly, a REST‐dependent increase in the expression of the proangiogenic transcription factor E26 oncogene homolog 1, and its target gene encoding the vascular endothelial growth factor receptor‐1, was observed in MB cells, which coincided with their localization at the tumor vasculature. These observations were confirmed by RNA‐Seq and microarray analyses of MB cells and SHH‐MB tumors. Thus, our data suggest that REST elevation promotes vascular growth by autocrine and paracrine mechanisms.

Brain Cancer-Activated Microglia: A Potential Role for Sphingolipids

Almost no neurological disease exists without microglial activation. Microglia has exert a pivotal role in the maintenance of the central nervous system and its response to external and internal insults. Microglia have traditionally been classified as, in the healthy central nervous system, "resting", with branched morphology system and, as a response to disease, "activated", with amoeboid morphology; as a response to diseases but this distinction is now outmoded. The most devastating disease that hits the brain is cancer, in particular glioblastoma. Glioblastoma multiforme is the most aggressive glioma with high invasiveness and little chance of being surgically removed. During tumor onset, many brain alterations are present and microglia have a major role because the tumor itself changes microglia from the pro-inflammatory state to the anti-inflammatory and protects the tumor from an immune intervention. What are the determinants of these changes in the behavior of the microglia? In this review, we survey and discuss the role of sphingolipids in microglia activation in the progression of brain tumors, with a particular focus on glioblastoma.

Medulloblastoma, macrocephaly, and a pathogenic germline PTEN variant: Cause or coincidence?

Background

Medulloblastomas (MBs) are a heterogeneous group of childhood brain tumors with four consensus subgroups, namely MB_SHH, MB_WNT, MB_{Group 3}, and MB_{Group 4}, representing the second most common type of pediatric brain cancer after high‐grade gliomas. They suffer from a high prevalence of genetic predisposition with up to 20% of MB_SHH caused by germline mutations in only six genes. However, the spectrum of germline mutations in MB_SHH remains incomplete.

Methods

Comprehensive Next‐Generation Sequencing panels of both tumor and patient blood samples were performed as molecular genetic characterization. The panels cover genes that are known to predispose to cancer.

Results

Here, we report on a patient with a pathogenic germline PTEN variant resulting in an early stop codon p.(Glu7Argfs*4) (ClinVar ID: 480383). The patient developed macrocephaly and MB_SHH, but reached remission with current treatment protocols.

Conclusions

We propose that pathogenic PTEN variants may predispose to medulloblastoma, and show that remission was reached with current treatment protocols. The PTEN gene should be included in the genetic testing provided to patients who develop medulloblastoma at an early age. We recommend brain magnetic resonance imaging upon an unexpected acceleration of growth of head circumference for pediatric patients harboring pathogenic germline PTEN variants.

A microfluidic competitive immuno-aggregation assay for high sensitivity cell secretome detection

We report a high-sensitivity cell secretome detection method using competitive immuno-aggregation and a micro-Coulter counter. A target cell secretome protein competes with anti-biotin-coated microparticles (MPs) to bind with a biotinylated antibody (Ab), causing decreased aggregation of the functionalized MPs and formation of a mixture of MPs and aggregates. In comparison, without the target cell secretome protein, more microparticles are functionalized, and more aggregates are formed. Thus, a decrease in the average volume of functionalized microparticles/aggregates indicates an increase in cell secretome concentration. This volume change is measured by the micro-Coulter counter, which is used to quantitatively estimate the cell secretome concentration. Vascular endothelial growth factor (VEGF), one of the key cell secretome proteins that regulate angiogenesis and vascular permeabilization, was used as the target protein to demonstrate the sensing principle. A standard calibration curve was generated by testing samples with various VEGF concentrations. A detection range from 0.01 ng/mL to 100.00 ng/mL was achieved. We further demonstrated the quantification of VEGF concentration in exogenous samples collected from the secretome of human mesenchymal stem cells (hMSCs) at different incubation times. The results from the assay agree well with the results of a parallel enzyme-linked immunoabsorbent assay (ELISA) test, indicating the specificity and reliability of the competitive immuno-aggregation assay. With its simple structure and easy sample preparation, this assay not only enables high sensitivity detection of VEGF but also can be readily extended to other types of cell secretome analysis as long as the specific Ab is known.

The FDA approved PI3K inhibitor GDC-0941 enhances in vitro the anti-neoplastic efficacy of Axitinib against c-myc-amplified high-risk medulloblastoma

Aberrant receptor kinase signalling and tumour neovascularization are hallmarks of medulloblastoma development and are both considered valuable therapeutic targets. In addition to VEGFR1/2, expression of PDGFR α/β in particular has been documented as characteristic of metastatic disease correlating with poor prognosis. Therefore, we have been suggested that the clinically approved multi‐kinase angiogenesis inhibitor Axitinib, which specifically targets these kinases, might constitute a promising option for medulloblastoma treatment. Indeed, our results delineate anti‐neoplastic activity of Axitinib in medulloblastoma cell lines modelling the most aggressive c‐myc‐amplified Non‐WNT/Non‐SHH and SHH‐TP53‐mutated tumours. Exposure of medulloblastoma cell lines to Axitinib results in marked inhibition of proliferation and profound induction of cell death. The differential efficacy of Axitinib is in line with target expression of medulloblastoma cells identifying VEGFR 1/2, PDGFR α/β and c‐kit as potential markers for drug application. The high specificity of Axitinib and the consequential low impact on the haematopoietic and immune system render this drug ideal multi‐modal treatment approaches. In this context, we demonstrate that the clinically available PI3K inhibitor GDC‐0941 enhances the anti‐neoplastic efficacy of Axitinib against c‐myc‐amplified medulloblastoma. Our findings provide a rational to further evaluate Axitinib alone and in combination with other therapeutic agents for the treatment of most aggressive medulloblastoma subtypes.

The anti-neoplastic activity of Vandetanib against high-risk medulloblastoma variants is profoundly enhanced by additional PI3K inhibition

Medulloblastoma is comprised of at least four molecular subgroups with distinct clinical outcome (WHO classification 2016). SHH-TP53-mutated as well as MYC-amplified Non-WNT/Non-SHH medulloblastoma show the worst prognosis.Here we present evidence that single application of the multi-kinase inhibitor Vandetanib displays anti-neoplastic efficacy against cell lines derived from high-risk SHH-TP53-mutated and MYC-amplified Non-WNT/Non-SHH medulloblastoma. The narrow target spectrum of Vandetanib along with a favourable toxicity profile renders this drug ideal for multimodal treatment approaches. In this context our investigation documents that Vandetanib in combination with the clinically available PI3K inhibitor GDC-0941 leads to enhanced cytotoxicity against MYC-amplified and SHH-TP53-mutated medulloblastoma. In line with these findings we show for MYC-amplified medulloblastoma a profound reduction in activity of the oncogenes STAT3 and AKT. Furthermore, we document that Vandetanib and the standard chemotherapeutic Etoposide display additive anti-neoplastic efficacy in the investigated medulloblastoma cell lines that could be further enhanced by PI3K inhibition. Of note, the combination of Vandetanib, GDC-0941 and Etoposide results in MYC-amplified and SHH-TP53-mutated cell lines in complete loss of cell viability. Our findings therefore provide a rational to further evaluate Vandetanib in combination with PI3K inhibitors as well as standard chemotherapeutics in vivo for the treatment of most aggressive medulloblastoma variants.

Addition of Anti-Angiogenetic Therapy with Bevacizumab to Chemo- and Radiotherapy for Leptomeningeal Metastases in Primary Brain Tumors

Leptomeningeal dissemination of a primary brain tumor is a condition which is challenging to treat, as it often occurs in rather late disease stages in highly pretreated patients. Its prognosis is dismal and there is still no accepted standard of care. We report here a good clinical effect with a partial response in three out of nine patients and a stable disease with improvement on symptoms in two more patients following systemic anti-angiogenic treatment with bevacizumab (BEV) alone or in combination with chemo- and/or radiotherapy in a series of patients with leptomeningeal dissemination from primary brain tumors (diffuse astrocytoma WHO°II, anaplastic astrocytoma WHO°III, anaplastic oligodendroglioma WHO°III, primitive neuroectodermal tumor and glioblastoma, both WHO°IV). This translated into effective symptom control in five out of nine patients, but only moderate progression-free and overall survival times were reached. Partial responses as assessed by RANO criteria were observed in three patients (each one with anaplastic oligodendroglioma, primitive neuroectodermal tumor and glioblastoma). In these patients progression-free survival (PFS) intervals of 17, 10 and 20 weeks were achieved. In three patients (each one with diffuse astrocytoma, anaplastic astrocytoma and primitive neuroectodermal tumor) stable disease was observed with PFS of 13, 30 and 8 weeks. Another three patients (all with glioblastoma) were primary non-responders and deteriorated rapidly with PFS of 3 to 4 weeks. No severe adverse events were seen. These experiences suggest that the combination of BEV with more conventional therapy schemes with chemo- and/or radiotherapy may be a palliative treatment option for patients with leptomeningeal dissemination of brain tumors.

An epigenetic gateway to brain tumor cell identity

Precise targeting of genetic lesions alone has been insufficient to extend brain tumor patient survival. Brain cancer cells are diverse in their genetic, metabolic and microenvironmental compositions, accounting for their phenotypic heterogeneity and disparate responses to therapy. These factors converge at the level of the epigenome, representing a unified node that can be disrupted by pharmacologic inhibition. Aberrant epigenomes define many childhood and adult brain cancers, as demonstrated by widespread changes to DNA methylation patterns, redistribution of histone marks and disruption of chromatin structure. In this Review, we describe the convergence of genetic, metabolic and microenvironmental factors on mechanisms of epigenetic deregulation in brain cancer. We discuss how aberrant epigenetic pathways identified in brain tumors affect cell identity, cell state and neoplastic transformation, as well as addressing the potential to exploit these alterations as new therapeutic strategies for the treatment of brain cancer.

Expression levels of vascular endothelial cell growth factor and microRNA-210 are increased in medulloblastoma and metastatic medulloblastoma

The present study aimed to investigate the roles of the vascular endothelial cell growth factor (VEGF) and micro (mi)RNA-210 in the metastasis of primary medulloblastoma (MB) tumors. A total of 86 adult patients diagnosed with cerebellar MB were enrolled in the present study, of which 11 patients had metastatic MB in the subarachnoid space. The following samples were collected: MB primary tumor tissue, MB secondary tumor tissue, tumor adjacent tissues and cerebrospinal fluid (CSF). Immunohistochemical analyses of the tissue samples were conducted in order to detect patterns of VEGF expression. In addition, the expression levels of VEGF mRNA and miRNA-210 were analyzed using reverse transcription-quantititative polymerase chain reaction, and western blot analyses were used to investigate VEGF protein expression levels. The positive expression rate of VEGF was significantly higher in MB tumor tissue, as compared with adjacent tissues (P<0.01). In addition, VEGF mRNA and protein expression levels in MB primary and secondary tumor tissues, and in the CSF of patients with metastatic MB, were significantly upregulated, as compared with tumor adjacent tissues and the CSF of patients with non-metastatic MB, respectively (P<0.01). miRNA-210 expression levels were significantly upregulated in MB tumor tissues, the CSF of patients with metastatic MB and in tumor tissues of metastatic MB (P<0.01). In the present study, the expression levels of VEGF and miRNA-210 were upregulated in patients with MB and metastatic MB; thus suggesting that miRNA-210 may promote the metastasis of MB primary tumors by regulating the expression of VEGF.

Pancreatic endoplasmic reticulum kinase activation promotes medulloblastoma cell migration and invasion through induction of vascular endothelial growth factor A

Evidence is accumulating that activation of the pancreatic endoplasmic reticulum kinase (PERK) in response to endoplasmic reticulum (ER) stress adapts tumor cells to the tumor microenvironment and enhances tumor angiogenesis by inducing vascular endothelial growth factor A (VEGF-A). Recent studies suggest that VEGF-A can act directly on certain tumor cell types in an autocrine manner, via binding to VEGF receptor 2 (VEGFR2), to promote tumor cell migration and invasion. Although several reports show that PERK activation increases VEGF-A expression in medulloblastoma, the most common solid malignancy of childhood, the role that either PERK or VEGF-A plays in medulloblastoma remains elusive. In this study, we mimicked the moderate enhancement of PERK activity observed in tumor patients using a genetic approach and a pharmacologic approach, and found that moderate activation of PERK signaling facilitated medulloblastoma cell migration and invasion and increased the production of VEGF-A. Moreover, using the VEGFR2 inhibitor SU5416 and the VEGF-A neutralizing antibody to block VEGF-A/VEGFR2 signaling, our results suggested that tumor cell-derived VEGF-A promoted medulloblastoma cell migration and invasion through VEGFR2 signaling, and that both VEGF-A and VEGFR2 were required for the promoting effects of PERK activation on medulloblastoma cell migration and invasion. Thus, these findings suggest that moderate PERK activation promotes medulloblastoma cell migration and invasion through enhancement of VEGF-A/VEGFR2 signaling.

In comparative analysis of multi-kinase inhibitors for targeted medulloblastoma therapy pazopanib exhibits promising in vitro and in vivo efficacy

Regardless of the recent advances in cytotoxic therapies, 30% of children diagnosed with medulloblastoma. succumb to the disease. Therefore, novel therapeutic approaches are warranted. Here we demonstrate that Pazopanib a clinically approved multi-kinase angiogenesis inhibitor (MKI) inhibits proliferation and apoptosis in medulloblastoma cell lines. Moreover, Pazopanib profoundly attenuates medulloblastoma cell migration, a prerequisite for tumor invasion and metastasis. In keeping with the observed anti-neoplastic activity of Pazopanib, we also delineate reduced phosphorylation of the STAT3 protein, a key regulator of medulloblastoma proliferation and cell survival. Finally, we document profound in vivo activity of Pazopanib in an orthotopic mouse model of the most aggressive c-myc amplified human medulloblastoma variant. Pazopanib reduced the growth rate of intracranial growing medulloblastoma and significantly prolonged the survival. Furthermore, to put these results into a broader perspective we analysed Pazopanib side by side with the MKI Sorafenib. Both compounds share a similar target profile but display different pharmacodynamics and pharmacokinetics with distinct cytotoxic activity in different tumor entities. Thus, we identified Pazopanib as a new promising candidate for a rational clinical assessment for targeted paediatric medulloblastoma therapy.

Differences in vascular endothelial growth factor receptor expression and correlation with the degree of enhancement in medulloblastoma

OBJECT

Vascular endothelial growth factor (VEGF) is the major proangiogenic factor in many solid tumors. Vascular endothelial growth factor receptor (VEGFR) is expressed in abundance in pediatric patients with medulloblastoma and is associated with tumor metastasis, poor prognosis, and proliferation. Gadolinium enhancement on MRI has been suggested to have prognostic significance for some tumors. The association of VEGF/VEGFR and Gd enhancement in medulloblastoma has never been closely examined. The authors therefore sought to evaluate whether Gd-enhancing medulloblastomas have higher levels of VEGFR and CD31. Outcomes and survival in patients with enhancing and nonenhancing tumors were also compared.

METHODS

A retrospective analysis of patients with enhancing, nonenhancing, and partially enhancing medulloblastomas was performed. Primary end points included risk stratification, extent of resection, and perioperative complications. A cohort of 3 enhancing and 3 nonenhancing tumors was selected for VEGFR and CD31 analysis as well as microvessel density measurements.

RESULTS

Fifty-eight patients were analyzed, and 20.7% of the medulloblastomas in these patients were nonenhancing. Enhancing medulloblastomas exhibited strong VEGFR1/2 and CD31 expression relative to nonenhancing tumors. There was no significant difference in perioperative complications or patient survival between the 2 groups.

CONCLUSIONS

These results suggest that in patients with medulloblastoma the presence of enhancement on MRI may correlate with increased vascularity and angiogenesis, but does not correlate with worse patient prognosis in the short or long term.

Secreted meningeal chemokines, but not VEGFA, modulate the migratory properties of medulloblastoma cells

Leptomeningeal metastasis is a cause of morbidity and mortality in medulloblastoma, but the understanding of molecular mechanisms driving this process is nascent. In this study, we examined the secretory chemokine profile of medulloblastoma cells (DAOY) and a meningothelial cell line (BMEN1). Conditioned media (CM) of meningothelial cells increased adhesion, spreading and migration of medulloblastoma. VEGFA was identified at elevated levels in the CM from BMEN1 cells (as compared to DAOY CM); however, recombinant VEGFA alone was insufficient to enhance medulloblastoma cell migration. In addition, bevacizumab, the VEGFA scavenging monoclonal antibody, did not block the migratory phenotype induced by the CM. These results reveal that paracrine factors secreted by meningothelial cells can influence migration and adherence of medulloblastoma tumor cells, but VEGFA may not be a specific target for therapeutic intervention in this context.

The rationale for targeted therapies in medulloblastoma

Medulloblastoma (MB) is the most frequent malignant brain tumor in children. Patients with MB who are classified as having high-risk disease or those with recurrent disease respond poorly to current therapies and have an increased risk of MB-related mortality. Preclinical studies and molecular profiling of MB tumors have revealed upregulation or activation of several key signaling pathways such as the sonic hedgehog and WNT pathways. Although the exact mechanisms underlying MB tumorigenesis remain poorly understood, inhibiting these key pathways with molecularly targeted therapies represents an important approach to improving MB outcomes. Several molecularly targeted therapies are already under clinical investigation in MB patients. We discuss current preclinical and clinical data, as well as data from clinical trials of targeted therapies that are either ongoing or in development for MB.

Angiogenesis and angiogenic tyrosine kinase receptor expression in pediatric brain tumors

Tumor angiogenesis and receptor tyrosine kinases (RTK) are major novel targets in anticancer molecular therapy. Accordingly, we characterized the vascular network and the expression pattern of angiogenic RTK in the most frequent pediatric brain tumors. In a retrospective collection of 44 cases (14 astrocytoma, 16 ependymoma and 14 medulloblastoma), immunohistochemistry for VEGFR1, VEGFR2, PDGFRα, PDGFRβ, and c-Kit as well as microvessel labeling with CD34 and SMA were conducted on surgical specimens. We found a significantly higher vascular density in ependymoma. Glomeruloid formations were abundant in medulloblastoma but rare or almost absent in astrocytoma and ependymoma, respectively. C-Kit and VEGFR2 labeled blood vessels were more abundant in ependymoma than in the other two types of tumors. In contrast, medulloblastoma contained higher number of PDGFRα expressing vessels. In tumor cells, we found no VEGFR2 but VEGFR1 expression in all three tumor types. PDGFRα was strongly expressed on the tumor cells in all three malignancies, while PDGFRβ tumor cell expression was present in the majority of medulloblastoma cases. Interestingly, small populations of c-Kit expressing cancer cells were found in a number of medulloblastoma and ependymoma cases. Our study suggests that different angiogenic mechanisms are present in ependymoma and medulloblastoma. Furthermore ependymoma patients may benefit from anti-angiogenic therapies based on the high vascularization as well as the endothelial expression of c-kit and VEGFR2. The expression pattern of the receptors on tumor cells also suggests the targeting of specific angiogenic tyrosine kinase receptors may have direct antitumor activity. Further preclinical and biomarker driven clinical investigations are needed to establish the application of tyrosine kinase inhibitors in the treatment of pediatric brain tumors.

Microscopic Delineation of Medulloblastoma Margins in a Transgenic Mouse Model Using a Topically Applied VEGFR-1 Probe

The unambiguous demarcation of tumor margins is critical at the final stages in the surgical treatment of brain tumors because patient outcomes have been shown to correlate with the extent of resection. Real-time high-resolution imaging with the aid of a tumor-targeting fluorescent contrast agent has the potential to enable intraoperative differentiation of tumor versus normal tissues with accuracy approaching the current gold standard of histopathology. In this study, a monoclonal antibody targeting the vascular endothelial growth factor receptor 1 (VEGFR-1) was conjugated to fluorophores and evaluated as a tumor contrast agent in a transgenic mouse model of medulloblastoma. The probe was administered topically, and its efficacy as an imaging agent was evaluated in vitro using flow cytometry, as well as ex vivo on fixed and fresh tissues through immunohistochemistry and dual-axis confocal microscopy, respectively. Results show a preferential binding to tumor versus normal tissue, suggesting that a topically applied VEGFR-1 probe can potentially be used with real-time intraoperative optical sectioning microscopy to guide brain tumor resections.

Medulloblastoma-biology and microenvironment: a review

Medulloblastoma (MB) is a cancer of the cerebellum and the most common primary pediatric malignancy of the central nervous system. Classified as a primitive neural ectoderm tumor; it is thought to arise from granule cell precursors in the cerebellum. The standard of care consists of surgery, chemotherapy and age-dependent radiation therapy. Despite aggressive multimodality therapy; approximately 30% of MB patients remain incurable. Moreover, for long-term survivors, the treatment related sequelae are often debilitating. Side effects include cerebellar mutism, sterility, neurocognitive deficits, and a substantial risk of developing secondary cancers. In a quest for more effective and targeted therapies, scientists have begun to investigate the biological events that not only initiate but also sustain the malignant phenotype in MB. Of particular interest is, the role of the tumor microenvironment in tumor pathogenesis. This review seeks to highlight several key processes observed in cancer biology, particularly the involvement of the tumor microenvironment, with relevant examples from MB.

Croix B. Selective blockade of tumor angiogenesis

Blocking tumor angiogenesis is an important goal of cancer therapy, but clinically approved anti-angiogenic agents suffer from limited efficacy and adverse side effects, fueling the need to identify alternative angiogenesis regulators. Tumor endothelial marker 8 (TEM8) is a highly conserved cell surface receptor overexpressed on human tumor vasculature. Genetic disruption of Tem8 in mice revealed that TEM8 is important for promoting tumor angiogenesis and tumor growth but dispensable for normal development and wound healing. The induction of TEM8 in cultured endothelial cells by nutrient or growth factor deprivation suggests that TEM8 may be part of a survival response pathway that is activated by tumor microenvironmental stress. In preclinical studies, antibodies targeted against the extracellular domain of TEM8 inhibited tumor angiogenesis and blocked the growth of multiple human tumor xenografts. Anti-TEM8 antibodies augmented the activity of other anti-angiogenic agents, vascular targeting agents and conventional chemotherapeutic agents and displayed no detectable toxicity. Thus, anti-TEM8 antibodies provide a promising new tool for selective blockade of neovascularization associated with cancer and possibly other angiogenesis-dependent diseases.

The NF-κB pathway mediates lysophosphatidic acid (LPA)-induced VEGF signaling and cell invasion in epithelial ovarian cancer (EOC)

OBJECTIVES

Our previous report has implicated the involvement of VEGF-VEGFR-2 h signaling in LPA-induced EOC invasion. However, the mechanism by which LPA regulates VEGF and VEGFR-2 expression remains to be elucidated. In the present study, we systematically examined the signal transduction pathways activated by LPA and further evaluated whether LPA's effect on VEGF-VEGFR-2 signaling and EOC invasion was mediated by the activation of NF-κB pathway.

METHODS

Using a signal transduction PathwayFinder PCR array, we examined the expression change of 86 key genes representing 18 signal transduction pathways in DOV13 and SKOV3 cells upon LPA (20 μM) treatment. We also used quantitative PCR, Western blotting and ELISA to evaluate the effect of NF-κB pathway inhibition on VEGF(121), VEGF(165) and VEGFR-2 mRNA and protein expression/secretion with or without the presence of LPA (20 μM) in SKOV3. Cell invasion under various treatment conditions was assessed by Matrigel invasion assay and MMP-2 secretion was detected by gelatin zymography.

RESULTS

Our results showed that in both DOV13 and SKOV3, several of the NF-κB pathway components, such as TNF, are consistently activated by LPA stimulation. In addition, treatment with an NF-κB pathway activation inhibitor, at 10 μM, significantly decreased LPA-induced VEGF(121), VEGF(165) and VEGFR-2 mRNA expression and VEGF secretion, as well as LPA-induced SKOV3 invasion (p<0.05). When combined with an EGFR inhibitor, NF-κB pathway inhibition exhibited a significantly stronger effect than used alone (p<0.05) on reducing LPA-induced VEGF secretion and cell invasion. Additionally, NF-κB inhibition also decreased LPA-induced MMP-2 secretion and MMP-1 expression (p<0.05).

CONCLUSIONS

These results suggest that the NF-κB pathway plays an important role in LPA-induced VEGF signaling and EOC invasion and targeting this pathway may reveal potential therapeutic options for metastatic EOC.

Complex oncogenic signaling networks regulate brain tumor-initiating cells and their progenies: pivotal roles of wild-type EGFR, EGFRvIII mutant and hedgehog cascades and novel multitargeted therapies

Complex signaling cross-talks between different growth factor cascades orchestrate the primary brain cancer development. Among the frequent deregulated oncogenic pathways, the ligand-activated wild-type epidermal growth factor receptor (EGFR), constitutively activated EGFRvIII mutant and sonic hedgehog pathways have attracted much attention because of their pivotal roles in pediatric medulloblastomas and adult glioblastoma multiformes (GBM) brain tumors. The enhanced expression levels and activation of EGFR, EGFRvIII mutant and hedgehog signaling elements can provide key roles for the sustained growth, migration and local invasion of brain tumor-initiating cells (BTICs) and their progenies, resistance to current therapies and disease relapse. These tumorigenic cascades also can cooperate with Wnt/β-catenin, Notch, platelet-derived growth factor (PDGF)/PDGF receptors (PDGFRs), hepatocyte growth factor (HGF)/c-Met receptor and vascular endothelial growth factor (VEGF)/VEGF receptors (VEGFRs) for the acquisition of a more malignant behavior and survival advantages by brain tumor cells during disease progression. Therefore, the simultaneous targeting of these oncogenic signaling components including wild-type EGFR, EGFRvIII mutant and hedgehog pathways may constitute a potential therapeutic approach of great clinical interest to eradicate BTICs and improve the efficacy of current clinical treatments by radiation and/or chemotherapy against aggressive and recurrent medulloblastomas and GBMs.

Dual Inhibitor AEE788 Reduces Tumor Growth in Preclinical Models of Medulloblastoma

Medulloblastoma is the most frequent malignant pediatric brain tumor with a dismal prognosis in 30% of cases. We examined the activity of AEE788, a dual inhibitor of human epidermal receptor (HER) 1/2 and vascular endothelial growth factor receptor (VEGFR) 1/2, in medulloblastoma preclinical models. Established lines (Daoy and D283), chemoresistant (Daoy(Pt)), and ectopically HER2-overexpressing (Daoy(HER2)) cells expressed diverse levels of total and activated AEE788 target receptors. In vitro, AEE788 inhibited cell proliferation (IC(50) from 1.7 to 3.8 µM) and prevented epidermal growth factor- and neuregulin-induced HER1, HER2, and HER3 activation. Inhibition of Akt paralleled that of HER receptors. In vivo, AEE788 growth inhibited Daoy, Daoy(Pt), and Daoy(HER2) xenografts by 51%, 45%, and 72%, respectively. Immunohistochemical analysis of mock- and HER2-transfected xenografts revealed that the latter showed, along with high HER2 expression, high VEGFR2 staining in tumor and endothelial cells and increased expression of the endothelial marker CD31. AEE788 reduced the activation of target receptors and angiogenesis. In 21 primary medulloblastoma, HER2 expression significantly correlated (P < .01) with VEGFR2 (r = 0.56) and VEGF (r = 0.61). In conclusion, AEE788 shows similar growth-suppressive activities in chemosensitive and chemoresistant medulloblastoma cells in vitro and in vivo. Ectopic HER2 overexpression sensitizes cells to AEE788 in vivo, but not in vitro, possibly through host-mediated processes. Together with the experimental data, the finding that HER2 positively correlates with VEGFR2 and VEGF in human medulloblastoma specimens indicates HER2-overexpressing medulloblastoma as the subset that most likely might benefit from AEE788 treatment.

[The role of chemotherapy in pediatric medulloblastoma]

Medulloblastoma is one of the most frequent brain tumors in childhood. The mortality of medulloblastoma decreased significantly during the last few decades, which was the result of the better surgical and radiotherapeutic methods and of the development of chemotherapy. The aim of this publication is the critical review of the present chemotherapeutic treatment. The new therapeutic trials based on the molecular genetic mechanism of these tumors are also mentioned.

Feasibility and tolerability of bevacizumab in children with primary CNS tumors

BACKGROUND

Bevacizumab, an antibody to the vascular endothelial growth factor, has demonstrated anti-cancer activity in a number of solid tumors. Fear of intratumoral hemorrhage, however, has slowed its introduction into the treatment of central nervous system (CNS) tumors. Currently, only a small number of children with gliomas received bevacizumab.

METHODS

We retrospectively analyzed 30 patients who received bevacizumab between January 2007 and August 2009. The median age at start of bevacizumab treatment was 9.9 years (range: 1.5-18). Most patients had recurrent/progressive disease, 25 high-grade and 5 low-grade tumors. The median dose of bevacizumab was 9.5 mg/kg (range 5-15 mg/kg) every 2-3 weeks. In total, 478 courses were administered (median/patient 15.9, range: 2-52). The median duration of bevacizumab treatment was 10.0 months (range: 1.6-30.4). Twenty-nine of 30 patients received additional therapy concomitant to bevacizumab.

RESULTS

No bevacizumab related intratumoral hemorrhage occurred in any of our 30 patients. Grade III hypertension was seen in two patients. One patient developed nephrotic syndrome requiring cessation of treatment. Grade III and I proteinuria were observed in one and five patients, respectively. New onset lymphopenia occurred in 12/30 and new onset hypothyroidism in 7/30 patients. Impaired wound healing was manageable. No immediate bevacizumab-related cardiotoxicity was observed as evidenced by echocardiography.

CONCLUSIONS

Bevacizumab appears to be safe for children with primary CNS tumors. Adverse effects did occur but were manageable. No treatment-related death occurred. Long-term monitoring is advisable to detect lymphopenia and hypothyroidism. Hypertension occurred less frequently than in adult patients. Further prospective studies including more patients are warranted.

Childhood medulloblastoma: current status of biology and treatment

Medulloblastoma, a primitive neuro-ectodermal tumour that arises in the posterior fossa, is the most common malignant brain tumour occurring in childhood. Over the past half century, the long-term survival for children with medulloblastoma has improved remarkably from a certain fatal diagnosis to a cancer that is often curable. Although overall survival for children with non-disseminated and non-anaplastic medulloblastoma can approach 80%, the current multidisciplinary therapeutic approach is not without long-term sequelae. Chemotherapy has improved the long-term survival and allowed for reductions in the amount of radiation given, thereby reducing some of the long-term toxicities. In this review, we describe the current understanding of the basic biology of medulloblastoma and report on the current active chemotherapeutic agents utilized in medulloblastoma therapy. Ultimately, our understanding of the basic biology of medulloblastoma may lead to further advances in therapy by providing targets that are more specific and potentially less toxic.

Sunitinib induces apoptosis and growth arrest of medulloblastoma tumor cells by inhibiting STAT3 and AKT signaling pathways

Medulloblastomas are the most frequent malignant brain tumors in children. Sunitinib is an oral multitargeted tyrosine kinase inhibitor used in clinical trials as an antiangiogenic agent for cancer therapy. In this report, we show that sunitinib induced apoptosis and inhibited cell proliferation of both a short-term primary culture (VC312) and an established cell line (Daoy) of human medulloblastomas. Sunitinib treatment resulted in the activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase and upregulation of proapoptotic genes, Bak and Bim, and inhibited the expression of survivin, an antiapoptotic protein. Sunitinib treatment also downregulated cyclin E, cyclin D2, and cyclin D3 and upregulated p21Cip1, all of which are involved in regulating cell cycle. In addition, it inhibited phosphorylation of signal transducer and activator of transcription 3 (STAT3) and AKT (protein kinase B) in the tumor cells. Dephosphorylation of STAT3 (Tyr(705)) induced by sunitinib was helped by a reduction in activities of Janus-activated kinase 2 and Src. Additionally, sodium vanadate, an inhibitor of protein tyrosine phosphatases, partially blocked the inhibition of phosphorylated STAT3 by sunitinib. Loss of phosphorylated AKT after sunitinib treatment was accompanied by decreased phosphorylation of downstream proteins glycogen synthase kinase-3beta and mammalian target of rapamycin. Expression of a constitutively activated STAT3 mutant or myristoylated AKT partially blocked the effects of sunitinib in these tumor cells. Sunitinib also inhibited the migration of medulloblastoma tumor cells in vitro. These findings suggest the potential use of sunitinib for the treatment of pediatric medulloblastomas.

Antiangiogenic therapy in the treatment of recurrent medulloblastoma in the adult: case report and review of the literature

Medulloblastoma is a rare tumor in central nervous system, with an even rarer occurrence in adulthood. The management of a recurrent disease is a medical challenge; chemotherapy has been used as the treatment of choice, while reirradiation has been employed in selected cases. We report the case of a 51-year-old man with recurrent medulloblastoma. He was treated with local reirradiation, chemotherapy, and antiangiogenic drug, with the latter giving the longer progression-free interval. The aim of this report is to show that recurrent medulloblastoma in adults can be approached with a multimodality treatment and that antiangiogenic therapy should have a role in the management of this disease.

Amplification and overexpression of KIT, PDGFRA, and VEGFR2 in medulloblastomas and primitive neuroectodermal tumors

Medulloblastomas (MB) and primitive neuroectodermal tumors (PNET) are the most common malignant brain tumors in children. These two tumor types are histologically similar, but have different genetic backgrounds and clinical outcomes. Other brain tumors, such as gliomas, frequently have coamplification and overexpression of receptor tyrosine kinases KIT, platelet-derived growth factor receptor alpha (PDGFRA), and vascular endothelial growth factor receptor 2 (VEGFR2). We investigated protein expression and gene copy numbers of KIT, PDGFRA, and VEGFR2 in 41 MB and 11 PNET samples by immunohistochemistry (IHC) and chromogenic in situ hybridization (CISH). KIT and PDGFRA expression was detected in both MBs and PNETs, whereas VEGFR2 expression was weak in these tumors. KIT, PDGFRA, and VEGFR2 amplifications were all present in 4% of MBs/PNETs, and KIT amplification was associated with concurrent PDGFRA and VEGFR2 amplifications (P <or= 0.001). Most strikingly, increased gene copy number of PDGFRA was associated with poor overall survival (P = 0.027). We suggest that coamplification of PDGFRA or VEGFR2 with KIT may be clinically useful novel molecular markers in MBs and PNETs.

VEGFR-2 silencing by small interference RNA (siRNA) suppresses LPA-induced epithelial ovarian cancer (EOC) invasion

BACKGROUND

The VEGF-VEGF receptor (VEGFR) signaling axis has emerged as a promising target for cancer therapy, attributing to its vital role in tumor angiogenesis and growth. We have previously reported the regulation of epithelial ovarian cancer (EOC) invasion and migration by VEGF and the implication of VEGF-VEGFR-2 axis in lysophosphatidic acid (LPA)-induced EOC invasion. However, the expression profile of VEGF and VEGFRs in EOC, their association with tumor aggressiveness, and their regulation by LPA remain unclear.

OBJECTIVES AND METHODS

In this study, we examined the expression of VEGFR-1, VEGFR-2, neuropilin-1 (NRP-1), NRP-2, VEGF(121), and VEGF(165) in established EOC cell lines and assessed their correlation with cell invasiveness. Moreover, using an ovarian cancer tissue qPCR array, we analyzed VEGFR-2 expression across a panel of 48 tissues with different disease stages and histological grades. We also tested the effect of LPA on VEGF and VEGFR-2 expression and examined whether blocking VEGFR-2 by RNA interference (RNAi) affects LPA-induced EOC invasion.

RESULTS

We show that VEGF and VEGFR-2 expression correlates with cell invasiveness and VEGFR-2 expression in ovarian cancer tissues correlate with tumor grade. In addition, LPA, at 20 muM, significantly induced the expression of VEGF(121), VEGF(165), and VEGFR-2 in SKOV3 and DOV13 cells (P<0.05). VEGFR-2 small interference RNA (siRNA) transfection remarkably decreased LPA's invasion-promoting effect (P<0.001) in SKOV3 cells without significantly decreasing SKOV3 cells' basal invasiveness. In DOV13 cells, VEGFR-2 silencing significantly decreases both the basal level cell invasion and LPA's invasion promoting effect (P<0.001).

CONCLUSION

These results suggest that decreasing VEGFR-2 expression by RNAi may prove to be an effective method to reduce the metastatic potential of EOC cells exposed to elevated levels of LPA.

The blood oxygen level-dependent functional MR imaging signal can be used to identify brain tumors and distinguish them from normal tissue

BACKGROUND AND PURPOSE

In neuro-oncology, a major problem is clear identification of tumor from the surrounding normal tissue. We hypothesized that we could use the blood oxygen level-dependent functional MR imaging (BOLD fMRI) signals from tumors and normal brain to identify the tumors and distinguish them from the surrounding brain.

MATERIALS AND METHODS

Fourteen patients with meningiomas, gliomas, and metastatic tumors were scanned before surgery. All subjects performed a motor task; 2 subjects were also scanned while in a resting state. The BOLD signals were taken from selected points within the tumor and from the surrounding normal brain and were analyzed by using correlation analysis to determine how closely they were related.

RESULTS

The BOLD signals from all of the tumors were significantly different from those in the surrounding normal tissue. In meningiomas and gliomas, selection of a voxel in the tumor for signal-intensity analysis highlighted the entire tumor mass while excluding the normal tissue. The BOLD signal intensity was the same whether the subjects were motionless or finger tapping.

CONCLUSIONS

Analysis of the BOLD signal intensity provides a relatively simple and straightforward method for identifying brain tumors and distinguishing them from normal tissue. This approach may be of use in neurosurgery.

Sorafenib inhibits signal transducer and activator of transcription 3 signaling associated with growth arrest and apoptosis of medulloblastomas

Medulloblastomas are the most frequent malignant brain tumors in children. Sorafenib (Nexavar, BAY43-9006), a multikinase inhibitor, blocks cell proliferation and induces apoptosis in a variety of tumor cells. Sorafenib inhibited proliferation and induced apoptosis in two established cell lines (Daoy and D283) and a primary culture (VC312) of human medulloblastomas. In addition, sorafenib inhibited phosphorylation of signal transducer and activator of transcription 3 (STAT3) in both cell lines and primary tumor cells. The inhibition of phosphorylated STAT3 (Tyr(705)) occurs in a dose- and time-dependent manner. In contrast, AKT (protein kinase B) was only decreased in D283 and VC312 medulloblastoma cells and mitogen-activated protein kinases (extracellular signal-regulated kinase 1/2) were not inhibited by sorafenib in these cells. Both D-type cyclins (D1, D2, and D3) and E-type cyclin were down-regulated by sorafenib. Also, expression of the antiapoptotic protein Mcl-1, a member of the Bcl-2 family, was decreased and correlated with apoptosis induced by sorafenib. Finally, sorafenib suppressed the growth of human medulloblastoma cells in a mouse xenograft model. Together, our data show that sorafenib blocks STAT3 signaling as well as expression of cell cycle and apoptosis regulatory proteins, associated with inhibition of cell proliferation and induction of apoptosis in medulloblastomas. These findings provide a rationale for treatment of pediatric medulloblastomas with sorafenib.

Sorafenib inhibits signal transducer and activator of transcription 3 signaling associated with growth arrest and apoptosis of medulloblastomas

Medulloblastomas are the most frequent malignant brain tumors in children. Sorafenib (Nexavar, BAY43-9006), a multikinase inhibitor, blocks cell proliferation and induces apoptosis in a variety of tumor cells. Sorafenib inhibited proliferation and induced apoptosis in two established cell lines (Daoy and D283) and a primary culture (VC312) of human medulloblastomas. In addition, sorafenib inhibited phosphorylation of signal transducer and activator of transcription 3 (STAT3) in both cell lines and primary tumor cells. The inhibition of phosphorylated STAT3 (Tyr(705)) occurs in a dose- and time-dependent manner. In contrast, AKT (protein kinase B) was only decreased in D283 and VC312 medulloblastoma cells and mitogen-activated protein kinases (extracellular signal-regulated kinase 1/2) were not inhibited by sorafenib in these cells. Both D-type cyclins (D1, D2, and D3) and E-type cyclin were down-regulated by sorafenib. Also, expression of the antiapoptotic protein Mcl-1, a member of the Bcl-2 family, was decreased and correlated with apoptosis induced by sorafenib. Finally, sorafenib suppressed the growth of human medulloblastoma cells in a mouse xenograft model. Together, our data show that sorafenib blocks STAT3 signaling as well as expression of cell cycle and apoptosis regulatory proteins, associated with inhibition of cell proliferation and induction of apoptosis in medulloblastomas. These findings provide a rationale for treatment of pediatric medulloblastomas with sorafenib.

Signaling pathways in medulloblastoma

Medulloblastoma is the most common brain tumor of childhood. Multiple signaling pathways have been associated with medulloblastoma formation and growth. These include the developmental pathways Hedgehog, (Hh) Notch, and Wnt as well as the receptor tyrosine kinases (RTK) c-Met, erbB2, IGF-R and TrkC, and the oncoprotein Myc. Here we review the involvement of these pathways in medulloblastoma malignancy with a focus on their mode of deregulation, prognostic value, functional effects, cellular and molecular mechanisms of action, and implications for therapy.

Exploiting the tumor microenvironment in the development of targeted cancer gene therapy

The future success of cancer gene therapy is critically dependent upon the development of safe, practical and effective targeting strategies. In this study, we describe a novel and broadly applicable targeting approach in which the induction of apoptotic tumor cell death is linked to the differential expression within the tumor microenvironment of elevated levels of the pro-angiogenic cytokine vascular endothelial growth factor (VEGF). As VEGF is generally absent or produced at only low levels in most normal tissues, undesirable toxicity will not result even if the therapeutic gene in question is inadvertently expressed in non-targeted tissue sites. The basic approach makes use of a chimeric cell-surface protein in which the membrane-spanning and cytoplasmic 'death domain' of the pro-apoptotic protein Fas are fused in frame to the extracellular ligand-binding domain of the VEGF receptor Flk-1/KDR/VEGFR2 (Flk-1/Fas). The resultant chimeric Flk-1/Fas receptor was found to be stable and capable of inducing a rapid apoptotic response when expressed in tumor cells that produce endogenous VEGF. Importantly, in the absence of VEGF, transduced tumor cells remain viable although they can be triggered to die by the addition of recombinant VEGF. Given the key role played by VEGF in tumor development and progression, it is proposed that the Flk-1/Fas chimera may have great potential in the context of tumor cell-targeted cancer gene therapy.