Molecular insight into medulloblastoma and central nervous system primitive neuroectodermal tumor biology from hereditary syndromes: a review

Posterior fossa tumors in children: current insights

While in adults most intracranial tumors develop around the cerebral hemispheres, 45 to 60% of pediatric lesions are found in the posterior fossa, although this anatomical region represents only 10% of the intracranial volume. The latest edition of the WHO classification for CNS tumors presented some fundamental paradigm shifts that particularly affected the classification of pediatric tumors, also influencing those that affect posterior fossa. Molecular biomarkers play an important role in the diagnosis, prognosis, and treatment of childhood posterior fossa tumors and can be used to predict patient outcomes and response to treatment and monitor its effectiveness. Although genetic studies have identified several posterior fossa tumor types, differing in terms of their location, cell of origin, genetic mechanisms, and clinical behavior, recent management strategies still depend on uniform approaches, mainly based on the extent of resection. However, significant progress has been made in guiding therapy decisions with biological or molecular stratification criteria and utilizing molecularly targeted treatments that address specific tumor biological characteristics. The primary focus of this review is on the latest advances in the diagnosis and treatment of common subtypes of posterior fossa tumors in children, as well as potential therapeutic approaches in the future.   Conclusion: Molecular biomarkers play a central role, not only in the diagnosis and prognosis of posterior fossa tumors in children but also in customizing treatment plans. They anticipate patient outcomes, measure treatment responses, and assess therapeutic effectiveness. Advances in neuroimaging and treatment have significantly enhanced outcomes for children with these tumors. What is Known: • Central nervous system tumors are the most common solid neoplasms in children and adolescents, with approximately 45 to 60% of them located in the posterior fossa. • Multimodal approaches that include neurosurgery, radiation therapy, and chemotherapy are typically used to manage childhood posterior fossa tumors What is New: • Notable progress has been achieved in the diagnosis, categorization and management of posterior fossa tumors in children, leading to improvement in survival and quality of life.

Effects of different molecular subtypes and tumor biology on the prognosis of medulloblastoma

PURPOSE

Medulloblastoma is one of the most common malignant brain tumors in the pediatric population. Recent studies identified four distinct medulloblastoma subgroups with different molecular alterations and pathways, and natural courses and outcomes. To evaluate the results of surgical and medical treatments of patients with medulloblastoma and compare them among the medulloblastoma subgroups.

METHODS

The clinical and radiological features, medical and surgical management and treatment outcomes and their correlation with molecular subgroups of 58 patients treated for medulloblastoma in the last 20 years were evaluated.

RESULTS

Fifty-eight patients, of whom 35 were male and 23 were female, were evaluated. The median age was 6 years (range, 1-19 years). The most common symptoms were nausea and vomiting (60%). Forty-three percent of the patients had headache and 40% had ataxia. Previous pathology reports revealed that 43 (74%), eight (14%), five (8%), and two (3%) had classic, desmoplastic, desmoplastic/nodular, and anaplastic morphologies, respectively. After the subgroup analyses, five patients (12%) were attributed to the wingless subgroup (WNT) group; 14 (32.5%), to the sonic hedgehog subgroup (SHH) group; and 24 (56%), to the non-WNT non-SHH group. On the basis of immunohistochemical analysis results, 15 patients could not be attributed to any subgroups. The clinical risk groups (average vs high-risk) and age at diagnosis (≥ 3 years vs < 3 years of age) were significant for 5-year event free survival (86% vs 43%, p:0.011 and 59% vs 36%, p:0.039). There was no significant difference in survival or event free survival according to molecular subtypes in this cohort.

CONCLUSION

In corporation of molecular features to the clinicopathologic classification leads to risk-adapted treatment. Although the molecular subgroups did not affect outcome significantly in this study, more studies with larger numbers of patients are needed to understand the tumor pathophysiology of medulloblastoma and design the future medical practice.

Pathology, diagnostics, and classification of medulloblastoma

Medulloblastoma (MB) is the most common CNS embryonal tumor. While the overall cure rate is around 70%, patients with high‐risk disease continue to have poor outcome and experience long‐term morbidity. MB is among the tumors for which diagnosis, risk stratification, and clinical management has shown the most rapid advancement. These advances are largely due to technological improvements in diagnosis and risk stratification which now integrate histomorphologic classification and molecular classification. MB stands as a prototype for other solid tumors in how to effectively integrate morphology and genomic data to stratify clinicopathologic risk and aid design of innovative clinical trials for precision medicine. This review explores the current diagnostic and classification of MB in modern neuropathology laboratories.

Medulloblastoma under Siege: Genetic and Molecular Dissection Concerning Recent Advances in Therapeutic Strategies

Medulloblastoma (MB) is a devastating illness with unmet therapeutic needs, predominantly cytotoxic and nontargeted approaches. Survivors of MB also suffer from severe treatment-related effects of radiation and cytotoxic chemotherapy keeping mortality rate significant. Recently, four distinct molecular subgroups of MB have been identified (WNT [wingless], SHH [sonic hedgehog], Group 3, and Group 4). Novel subgroup-specific therapies are being explored in the daily treatment of patients as a clinical trial and are an important challenge in the near term for the pediatric neurooncology society. Epigenetic modifiers are also recurrently affected in MB suggesting that epigenetic therapy can be considered in a subset of patients. Moreover, a hint on forefront procedure; tracer of cancer's genetic information entitled "liquid biopsy" in MB is described. This review examines the recent scientific progress in MB research, with a focus on the genes, pathways that drive tumorigenesis and the advances in conventional and targeted therapy. The identification of subgroup-specific, actionable therapeutic targets has the potential to revolutionize therapy for patients with MB and results in significantly enriched overall survival.

Potential use of CXCL12/CXCR4 and sonic hedgehog pathways as therapeutic targets in medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor occurring in children, and although high long-term survival rates have been reached with current therapeutic protocols, several neurological injuries are still observed among survivors. It has been shown that the development of MB is highly dependent on the microenvironment surrounding it and that the CXCL12 chemokine and its receptor, CXCR4 and the Sonic Hedgehog (SHH) pathway are crucial for cerebellar development, coordinating proliferation and migration of embryonic cells and malfunctions in these axes can lead to MB development. Indeed, the concomitant overactivation of these axes was suggested to define a new MB molecular subgroup. New molecules are being studied, aiming to inhibit either CXCR4 or the SHH pathways and have been tested in preclinical settings for the treatment of cancers. The use of these molecules could improve MB treatment and save patients from aggressive surgery, chemotherapy and radiotherapy regimens, which are responsible for severe neurological consequences. This review aims to summarize current data about the experimental inhibition of CXCR4 and SHH pathways in MB and its potential implications in treatment of this cancer.

Hedgehog signaling negatively co-regulates BH3-only protein Noxa and TAp73 in TP53-mutated cells

In the present study, we show that pharmacological repression by the Hedgehog (Hh) pathway inhibitor (HPI) GANT61 induces expression of the proapoptotic protein Noxa in TP53-mutated embryonal pediatric tumor cells driven by Hh signaling (i.e. rhabdomyosarcoma (RMS) and medulloblastoma (MB)). Similarly, genetic silencing of Gli1 by siRNA causes increased Noxa mRNA and protein levels, while overexpression of Gli1 results in decreased Noxa expression. Furthermore, TAp73 mRNA and protein levels are increased upon Gli1 knockdown, while Gli1 overexpression reduces TAp73 mRNA and protein levels. However, knockdown of TAp73 fails to block Noxa induction in GANT61-treated cells, suggesting that Noxa is not primarily regulated by TAp73. Interestingly, mRNA levels of the transcription factor EGR1 correlate with those of Noxa and TAp73. Silencing of EGR1 results in decreased Noxa and TAp73 mRNA levels, indicating that EGR1 is involved in regulating transcriptional activity of Noxa and TAp73. These findings suggest that Gli1 represses Noxa and TAp73, possibly via EGR1. These findings could be exploited for the treatment of Hh-driven tumors, e.g. for their sensitization to chemotherapeutic agents.

Case-based review: pediatric medulloblastoma

Medulloblastoma is the most common malignant brain tumor affecting children. These tumors are high grade with propensity to metastasize within the central nervous system and, less frequently, outside the neuraxis. Recent advancements in molecular subgrouping of medulloblastoma refine diagnosis and improve counseling in regards to overall prognosis. Both are predicated on the molecular drivers of each subgroup-WNT-activated, SHH-activated, group 3, and group 4. The traditional therapeutic mainstay for medulloblastoma includes a multimodal approach with surgery, radiation, and multiagent chemotherapy. As we discover more about the molecular basis of medulloblastoma, efforts to adjust treatment approaches based on molecular risk stratification are under active investigation. Certainly, the known neurological, developmental, endocrine, and psychosocial injury related to medulloblastoma and its associated therapies motivate ongoing research towards improving treatment for this life-threatening tumor while at the same time minimizing long-term side effects.

Posterior Fossa Tumors

Pediatric brain tumors are the leading cause of death from solid tumors in childhood. The most common posterior fossa tumors in children are medulloblastoma, atypical teratoid/rhabdoid tumor, cerebellar pilocytic astrocytoma, ependymoma, and brainstem glioma. Location, and imaging findings on computed tomography (CT) and conventional MR (cMR) imaging may provide important clues to the most likely diagnosis. Moreover, information obtained from advanced MR imaging techniques increase diagnostic confidence and help distinguish between different histologic tumor types. Here we discuss the most common posterior fossa tumors in children, including typical imaging findings on CT, cMR imaging, and advanced MR imaging studies.

Molecular Classification of Medulloblastoma

Medulloblastoma (MB) is one of the most frequent malignant brain tumors in children. The current standard treatment regimen consists of surgical resection, craniospinal irradiation, and adjuvant chemotherapy. Although these treatments have the potential to increase the survival of 70–80% of patients with MB, they are also associated with serious treatment-induced morbidity. The current risk stratification of MB is based on clinical factors, including age at presentation, metastatic status, and the presence of residual tumor following resection. In addition, recent genomic studies indicate that MB consists of at least four distinct molecular subgroups: WNT, sonic hedgehog (SHH), Group 3, and Group 4. WNT and SHH MBs are characterized by aberrations in the WNT and SHH signaling pathways, respectively. WNT MB has the best prognosis compared to the other MBs, while SHH MB has an intermediate prognosis. The underlying signaling pathways associated with Group 3 and 4 MBs have not been identified. Group 3 MB is frequently associated with metastasis, resulting in a poor prognosis, while Group 4 is sometimes associated with metastasis and has an intermediate prognosis. Group 4 is the most frequent MB and represents 35% of all MBs. These findings suggest that MB is a heterogeneous disease, and that MB subgroups have distinct molecular, demographic, and clinical characteristics. The molecular classification of MBs is redefining the risk stratification of patients with MB, and has the potential to identify new therapeutic strategies for the treatment of MB.

Clustering of self-organizing map identifies five distinct medulloblastoma subgroups

BACKGROUND

Medulloblastoma is one the most malignant paediatric brain tumours. Molecular subgrouping these medulloblastomas will not only help identify specific cohorts for certain treatment but also improve confidence in prognostic prediction.

OBJECTIVE

Currently, there is a consensus of the existences of four distinct subtypes of medulloblastoma. We proposed a novel bioinformatics method, clustering of self-organizing map, to determine the subgroups and their molecular diversity.

METHODS

Microarray expression profiles of 46 medulloblastoma samples were analysed and five clusters with distinct demographics, clinical outcome and transcriptional profiles were identified.

RESULTS

The previously reported Wnt subgroup was identified as expected. Three other novel subgroups were proposed for later investigation.

CONCLUSIONS

Our findings underscore the value of SOM clustering for discovering the medulloblastoma subgroups. When the suggested subdivision has been confirmed in large cohorts, this method should serve as a part of routine classification of clinical samples.

Brain tumors

The past 2 decades have witnessed a revolution in the management of childhood brain tumors, with the establishment of multidisciplinary teams and national and international consortiums that led to significant improvements in the outcomes of children with brain tumors. Unprecedented cooperation within the pediatric neuro-oncology community and sophisticated rapidly evolving technology have led to advances that are likely to revolutionize treatment strategies and improve outcomes.

Molecular variants and mutations in medulloblastoma

Medulloblastoma is the commonest malignant brain tumor in children. Treatment with surgery, irradiation, and chemotherapy has improved outcomes in recent years, but patients are frequently left with devastating neurocognitive and other sequelae following such therapy. While the prognosis has traditionally been based on conventional histopathology and clinical staging (based on age, extent of resection, and presence or absence of metastasis), it has become apparent in recent years that the inherent biology of the tumor plays a significant part in predicting survival and sometimes supersedes clinical or pathologic risk factors. The advent of deep sequencing gene technology has provided invaluable clues to the molecular makeup of this tumor and allowed neuro-oncologists to understand that medulloblastoma is an amalgamation of several distinct disease entities with unique clinical associations and behavior. This review is a concise summary of the pathology, genetic syndromes, recent advances in molecular subgrouping, and the associated gene mutations and copy number variations in medulloblastoma. The association of molecular alterations with patient prognosis is also discussed, but it should be remembered that further validation is required in prospective clinical trials utilizing uniform treatment approaches.

Familial syndromes associated with intracranial tumours: a review

BACKGROUND

Most cancers of the central nervous system (CNS) occur sporadically in the absence of any known underlying familial disorder or multi-systemic syndrome. Several syndromes are associated with CNS malignancies, however, and their recognition has significant implications for patient management and prognosis. Patients with syndrome-associated CNS malignancies often have multiple tumours (either confined to one region or distributed throughout the body), with similar or different histology.

OBJECTIVE

This review examines syndromes that are strongly associated with CNS cancers: the phakomatosis syndromes, familial syndromes such as Li-Fraumeni and familial polyposis syndromes and dyschondroplasia.

PCAF ubiquitin ligase activity inhibits Hedgehog/Gli1 signaling in p53-dependent response to genotoxic stress

The Hedgehog (Hh) signaling regulates tissue development, and its aberrant activation is a leading cause of malignancies, including medulloblastoma (Mb). Hh-dependent tumorigenesis often occurs in synergy with other mechanisms, such as loss of p53, the master regulator of the DNA damage response. To date, little is known about mechanisms connecting DNA-damaging events to morphogen-dependent processes. Here, we show that genotoxic stress triggers a cascade of signals, culminating with inhibition of the activity of Gli1, the final transcriptional effector of Hh signaling. This inhibition is dependent on the p53-mediated elevation of the acetyltransferase p300/CBP-associated factor (PCAF). Notably, we identify PCAF as a novel E3 ubiquitin ligase of Gli1. Indeed PCAF, but not a mutant with a deletion of its ubiquitination domain, represses Hh signaling in response to DNA damage by promoting Gli1 ubiquitination and its proteasome-dependent degradation. Restoring Gli1 levels rescues the growth arrest and apoptosis effect triggered by genotoxic drugs. Consistently, DNA-damaging agents fail to inhibit Gli1 activity in the absence of either p53 or PCAF. Finally, Mb samples from p53-null mice display low levels of PCAF and upregulation of Gli1 in vivo, suggesting PCAF as potential therapeutic target in Hh-dependent tumors. Together, our data define a mechanism of inactivation of a morphogenic signaling in response to genotoxic stress and unveil a p53/PCAF/Gli1 circuitry centered on PCAF that limits Gli1-enhanced mitogenic and prosurvival response.

Molecular subgroups of medulloblastoma

Recent efforts at stratifying medulloblastomas based on their molecular features have revolutionized our understanding of this morbidity. Collective efforts by multiple independent groups have subdivided medulloblastoma from a single disease into four distinct molecular subgroups characterized by disparate transcriptional signatures, mutational spectra, copy number profiles and, most importantly, clinical features. We present a summary of recent studies that have contributed to our understanding of the core medulloblastoma subgroups, focusing largely on clinically relevant discoveries that have already, and will continue to, shape research.

Medulloblastomics: the end of the beginning

The division of medulloblastoma into different subgroups by microarray expression profiling has dramatically changed our perspective of this malignant childhood brain tumour. Now, the availability of next-generation sequencing and complementary high-density genomic technologies has unmasked novel driver mutations in each medulloblastoma subgroup. The implications of these findings for the management of patients are readily apparent, pinpointing previously unappreciated diagnostic and therapeutic targets. In this Review, we summarize the 'explosion' of data emerging from the application of modern genomics to medulloblastoma, and in particular the recurrent targets of mutation in medulloblastoma subgroups. These data are currently making their way into clinical trials as we seek to integrate conventional and molecularly targeted therapies.

Multiple CDK/CYCLIND genes are amplified in medulloblastoma and supratentorial primitive neuroectodermal brain tumor

Embryonal brain tumors, which include medulloblastoma and the more aggressive supratentorial primitive neuroectodermal tumor (sPNET), comprise one of the largest group of malignant pediatric brain tumors. We observed in high resolution array comparative genomic hybridization and polymerase chain reaction analyses that several different components of the CDK/CYCLIND/pRB regulatory complex, including the CDK4/6 and CCND1/2 loci, are targets of gene amplification in medulloblastoma and sPNET. CDK6 and CCND1 gene amplification were respectively most common and robust, and overall CDK/CYCLIND gene amplification was more commonly observed in sPNET (25%) than medulloblastoma (1-5%). CDK6 overexpression enhanced in vitro and in vivo oncogenicity and endogenous CDK6 or CCND1 knockdown decreased pRB phosphorylation and impaired cell cycle progression in both medulloblastoma and sPNET cell lines. Although animal models implicate the pRB tumor suppressor pathway in medulloblastoma and sPNET, mutations of RB1 or the related INK4 tumor suppressor loci are rare in primary human tumors. Our data suggest that CDK/CYCLIND gene amplification may represent important mechanisms for functional inactivation of pRB in medulloblastoma and sPNET.

The clinical implications of medulloblastoma subgroups

Medulloblastoma, the most common malignant paediatric brain tumour, is currently diagnosed and stratified using a combination of clinical and demographic variables. Recent transcriptomic approaches have demonstrated that the histological entity known as medulloblastoma is comprised of multiple clinically and molecularly distinct subgroups. The current consensus is that four defined subgroups of medulloblastoma exist: WNT, SHH, Group 3, and Group 4. Each subgroup probably contains at least one additional level of hierarchy, with some evidence for multiple subtypes within each subgroup. The demographic and clinical differences between the subgroups present immediate and pressing questions to be addressed in the next round of clinical trials for patients with medulloblastoma. Many of the genetically defined targets for rational medulloblastoma therapies are unique to a given subgroup, suggesting the need for subgroup-specific trials of novel therapies. The development of practical, robust and widely accepted subgroup biomarkers that are amenable to the conditions of a prospective clinical trial is, therefore, an urgent need for the paediatric neuro-oncology community. In this Review, we discuss the clinical implications of molecular subgrouping in medulloblastoma, highlighting how these subgroups are transitioning from a research topic in the laboratory to a clinically relevant topic with important implications for patient care.

Molecular subgroups of medulloblastoma: the current consensus

Medulloblastoma, a small blue cell malignancy of the cerebellum, is a major cause of morbidity and mortality in pediatric oncology. Current mechanisms for clinical prognostication and stratification include clinical factors (age, presence of metastases, and extent of resection) as well as histological subgrouping (classic, desmoplastic, and large cell/anaplastic histology). Transcriptional profiling studies of medulloblastoma cohorts from several research groups around the globe have suggested the existence of multiple distinct molecular subgroups that differ in their demographics, transcriptomes, somatic genetic events, and clinical outcomes. Variations in the number, composition, and nature of the subgroups between studies brought about a consensus conference in Boston in the fall of 2010. Discussants at the conference came to a consensus that the evidence supported the existence of four main subgroups of medulloblastoma (Wnt, Shh, Group 3, and Group 4). Participants outlined the demographic, transcriptional, genetic, and clinical differences between the four subgroups. While it is anticipated that the molecular classification of medulloblastoma will continue to evolve and diversify in the future as larger cohorts are studied at greater depth, herein we outline the current consensus nomenclature, and the differences between the medulloblastoma subgroups.

Genome sequencing of pediatric medulloblastoma links catastrophic DNA rearrangements with TP53 mutations

Genomic rearrangements are thought to occur progressively during tumor development. Recent findings, however, suggest an alternative mechanism, involving massive chromosome rearrangements in a one-step catastrophic event termed chromothripsis. We report the whole-genome sequencing-based analysis of a Sonic-Hedgehog medulloblastoma (SHH-MB) brain tumor from a patient with a germline TP53 mutation (Li-Fraumeni syndrome), uncovering massive, complex chromosome rearrangements. Integrating TP53 status with microarray and deep sequencing-based DNA rearrangement data in additional patients reveals a striking association between TP53 mutation and chromothripsis in SHH-MBs. Analysis of additional tumor entities substantiates a link between TP53 mutation and chromothripsis, and indicates a context-specific role for p53 in catastrophic DNA rearrangements. Among these, we observed a strong association between somatic TP53 mutations and chromothripsis in acute myeloid leukemia. These findings connect p53 status and chromothripsis in specific tumor types, providing a genetic basis for understanding particularly aggressive subtypes of cancer.

FISH and chips: the recipe for improved prognostication and outcomes for children with medulloblastoma

Rapidly evolving genomic technologies have permitted progressively detailed studies of medulloblastoma biology in recent years. These data have increased our understanding of the molecular pathogenesis of medulloblastoma, identified prognostic markers, and suggested future avenues for targeted therapy. Although current randomized trials are still stratified based largely on clinical variables, the use of molecular markers is approaching routine use in the clinic. In particular, integrated genomics has uncovered that medulloblastoma comprises four distinct molecular and clinical variants: WNT, sonic hedgehog (SHH), group 3, and group 4. Children with WNT medulloblastoma have improved survival, whereas those with group 3 medulloblastoma have a dismal prognosis. Additionally, integrated genomics has shown that adult medulloblastoma is molecularly and clinically distinct from the childhood variants. Prognostic and predictive markers identified by genomics should drive changes in stratification of treatment protocols for medulloblastoma patients on clinical trials once they can be demonstrated to be reliable, reproducible, and practical. Cases with excellent prognoses (WNT cases) should be considered for therapy de-escalation, whereas those with bleak prognoses (group 3 cases) should be prioritized for experimental therapy. In this review, we will summarize the genomic data published over the past decade and attempt to interpret its prognostic significance, relevance to the clinic, and use in upcoming clinical trials.

Epigenetic mechanisms regulating neural development and pediatric brain tumor formation

Pediatric brain tumors are the leading cause of cancer-related death in children, and among them, embryonal tumors represent the largest group with an associated poor prognosis and long-term morbidity for survivors. The field of cancer epigenetics has emerged recently as an important area of investigation and causation of a variety of neoplasms, and is defined as alterations in gene expression without changes in DNA sequence. The best studied epigenetic modifications are DNA methylation, histone modifications, and RNA-based mechanisms. These modifications play an important role in normal development and differentiation but their dysregulation can lead to altered gene function and cancer. In this review the authors describe the mechanisms of normal epigenetic regulation, how they interplay in neuroembryogenesis, and how these can cause brain tumors in children when dysregulated. The potential use of epigenetic markers to design more effective treatment strategies for children with malignant brain tumors is also discussed.

PCDH10 is a candidate tumour suppressor gene in medulloblastoma

PURPOSE

The aim of this study was to investigate the genetic and epigenetic mechanisms contributing to PCDH10 down-regulation in medulloblastoma. We examined the role of PCDH10 as a mediator of medulloblastoma cell proliferation, cell cycle progression, and cell migration.

METHODS

We identified a focal homozygous deletion of PCDH10 in medulloblastoma by surveying a cohort of 212 tumours by Affymetrix SNP array analysis. PCDH10 expression was assessed by quantitative reverse transcriptase PCR in a series of 26 tumours. The promoter methylation status of PCDH10 was determined using methylation specific PCR and Sequenom MassCLEAVE analysis. Functional studies examining the role of PCDH10 in medulloblastoma development were performed by re-expression of PCDH10 in the DAOY medulloblastoma cell line, and then, cell proliferation, cell cycle distribution, and cell migration assays were performed.

RESULTS

We report a very focal homozygous deletion on chromosome 4q28.3 harbouring the PCDH10 gene. We demonstrate that PCDH10 transcription is down-regulated in 19/26 (73%) of medulloblastomas suggesting that other mechanisms also could be involved in gene repression. We found that DNA hypermethylation contributed to the deregulation of PCDH10 in 11/44 (25%) of medulloblastoma cell lines and primary tumours. Using a stable cell line (DAOY) re-expressing PCDH10, we observed that cell migration was impaired upon restoration of PCDH10 expression.

CONCLUSIONS

Our findings suggest that genetic and epigenetic deregulation of PCDH10 occurs in a significant portion of medulloblastoma patients. Failure to express PCDH10 may result in loss of inhibition of cell migration, thereby contributing to medulloblastoma progression.

GLI2 is a potential therapeutic target in pediatric medulloblastoma

To determine whether the zinc finger transcription factors GLI1 to GLI3 and suppressor of fused (SUFU) components of the Sonic hedgehog signaling pathway may be prognostic markers and potential therapeutic targets in pediatric medulloblastoma (MB), we investigated the relationship of the expression of these proteins to prognosis in the MB of 124 patients who had undergone surgery at the Hospital for Sick Children (Toronto, Ontario, Canada). The expressions of GLI1 (p = 0.011) and GLI2 (p = 0.003), but not of GLI3 (p = 0.774) or SUFU (p = 0.137), in the MB were associated with a worse overall survival by Kaplan-Meier analysis. Overall survival of patients positive for GLI1 and GLI2 was 6.01 ± 0.85 years and 5.27 ± 1.44 years, respectively, versus 10.11 ± 1.52 years and 10.18 ± 0.22 years for patients negative for GLI1 and GLI2, respectively. Knockdown of GLI2 in 3 MB cell lines resulted in decreased cell number and viability, as determined by the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay; knockdown of GLI1 had no effect. The decrease in cell number with GLI2 knockdown was caused by G0 cell cycle arrest; there was no induction of apoptosis. These results suggest that targeting the Sonic hedgehog pathway in positive patients may be a useful adjuvant therapeutic strategy for MB.

Molecular diagnostics of CNS embryonal tumors

Tremendous progress has recently been made in both molecular subgrouping, and the establishment of prognostic biomarkers for embryonal brain tumors, particularly medulloblastoma. Several prognostic biomarkers that were initially identified in retrospective cohorts of medulloblastoma, including MYC and MYCN amplification, nuclear β-catenin accumulation, and chromosome 17 aberrations have now been validated in clinical trials. Moreover, molecular subgroups based on distinct transcriptome profiles have been consistently reported from various groups on different platforms demonstrating that the concept of distinct medulloblastoma subgroups is very robust. Well-described subgroups of medulloblastomas include tumors showing wingless signaling pathway (Wnt) activation, and another characterized by sonic hedgehog pathway activity. Two or more additional subgroups were consistently reported to contain the vast majority of high-risk tumors, including most tumors with metastatic disease at diagnosis and/or large cell/anaplastic histology. Several years ago, atypical teratoid rhabdoid tumor (AT/RT) was recognized as a separate entity based on its distinct biology and particularly aggressive clinical behavior. These tumors may occur supra or infratentorially and are usually found to have genetic alterations of SMARCB1 (INI1/hSNF5), a tumor suppressor gene located on chromosome 22q. Subsequent loss of SMARCB1 protein expression comprises a relatively specific and sensitive diagnostic marker for AT/RT. For CNS primitive neuroectodermal tumors (CNS PNETs), a consistent finding has been that they are molecularly distinct from medulloblastoma. Furthermore, a distinct fraction of CNS PNETs with particularly poor prognosis only occurring in young children was delineated, which was previously labeled ependymoblastoma or embryonal tumor with abundant neuropil and true rosettes (ETANTR) and which is morphologically characterized by the presence of multilayered "ependymoblastic" rosettes. This group of tumors shows a unique cytogenetic abnormality not seen in other brain tumors: focal amplification of a micro-RNA cluster at chromosome 19q13.42, which has never been found to be amplified in other CNS PNETs, medulloblastoma or AT/RT. In summary, these consistent findings have significantly contributed to our ability to sub-classify embryonal brain tumors into clinically and biologically meaningful strata and, for some of the subgroups, have led to the identification of specific targets for future development of molecularly targeted therapies.

Childhood medulloblastoma: novel approaches to the classification of a heterogeneous disease

Increasing recognition of pediatric medulloblastoma as a heterogeneous disease, with histopathological and molecular variants that have distinct biological behaviors, will impact how the disease is classified and treated. A combination of clinicopathological evaluation and assays based on molecular subgroups of disease will allow stratification of patients into risk groups and a more tailored approach to therapy. Patients with low-risk disease could be treated with de-escalated adjuvant therapy to maximize cure while reducing long-term adverse effects, and novel therapies could be sought for patients with high-risk disease. My review encompasses a brief overview of the clinical landscape, the current World Health Organization (WHO) classification of medulloblastoma, the status of molecular subgroups, and how potential stratification schemes might impact pathologists and their practice.

Genetics of medulloblastoma: clues for novel therapies

Medulloblastoma is the most common malignant brain tumor in children. Current medulloblastoma therapy entails surgery, radiation and chemotherapy. The 5-year survival rate for patients ranges from 40 to 70%, with most survivors suffering from serious long-term treatment-related sequelae. Additional research on the molecular biology and genetics of medulloblastoma is needed to identify robust prognostic markers for disease-risk stratification, to improve current treatment regimes and to discover novel and more effective molecular-targeted therapies. Recent advances in molecular biology have led to the development of powerful tools for the study of medulloblastoma tumorigenesis, which have revealed new insights into the molecular underpinnings of this disease. Here we discuss the signaling pathway alterations implicated in medulloblastoma pathogenesis, the techniques used in molecular profiling of these tumors and recent molecular subclassification schemes. Particular emphasis is given to the identification of novel molecular targets for less toxic, patient-tailored therapeutic approaches.

Learning from Jekyll to control Hyde: Hedgehog signaling in development and cancer

The Hedgehog (Hh) cascade controls cell proliferation, differentiation and patterning of tissues during embryogenesis but is largely suppressed in the adult. The Hh pathway can become reactivated in cancer. Here, we assimilate data from recent studies to understand how and when the Hh pathway is turned on to aid the neoplastic process. Hh signaling is now known to have a role in established tumors, enabling categorization of tumors based on the role Hh signaling plays in their growth. This categorization has relevance for prognosis and targeted therapeutics. In the first category, abnormal Hh signaling initiates the tumor. In the second category, Hh signaling helps maintain the tumor. In the third category, Hh signaling is implicated but its role is not yet defined.

Genomics of medulloblastoma: from Giemsa-banding to next-generation sequencing in 20 years

Advances in the field of genomics have recently enabled the unprecedented characterization of the cancer genome, providing novel insight into the molecular mechanisms underlying malignancies in humans. The application of high-resolution microarray platforms to the study of medulloblastoma has revealed new oncogenes and tumor suppressors and has implicated changes in DNA copy number, gene expression, and methylation state in its etiology. Additionally, the integration of medulloblastoma genomics with patient clinical data has confirmed molecular markers of prognostic significance and highlighted the potential utility of molecular disease stratification. The advent of next-generation sequencing technologies promises to greatly transform our understanding of medulloblastoma pathogenesis in the next few years, permitting comprehensive analyses of all aspects of the genome and increasing the likelihood that genomic medicine will become part of the routine diagnosis and treatment of medulloblastoma.

Neurooncology of familial cancer syndromes

The majority of tumors of the nervous system are sporadic. However, a subset of patients with tumors and their families are predisposed to developing cancers of the central nervous system and other organs because of a germline mutation. In the last decade, many of the genes responsible for these typically autosomal dominant familial tumor syndromes have been identified. Additionally, our understanding of the mechanisms of carcinogenesis in these syndromes has increased, allowing for more targeted therapies for these patients as well as those with sporadic cancers. Because these patients present a unique set of issues regarding diagnosis and neurooncological management, the most common familial cancer syndromes involving the nervous system are reviewed: neurofibromatosis type 1 and 2; tuberous sclerosis complex; von Hippel Lindau, Li-Fraumeni, Gorlin, and Turcot syndrome.

Medulloblastoma: what is the role of molecular genetics?

Among pediatric malignancies, medulloblastoma (MB) is one of the most common malignant tumors of the CNS. In the past few years, thanks to a multidisciplinary approach including surgery, chemo- and radiation therapy, survival has significantly improved. Despite that, a third of patients still have a low chance of being cured and long-term survivors experience severe treatment-related sequelae. MBs are usually classified according to a clinical risk stratification, based on histological features, age at diagnosis, extent of tumor resection and presence or absence of metastases. However, these clinical variables have recently been reported to be poor for defining risk-related disease. Retrospective studies have identified histological or biological factors that have distinct roles in prognosis. As several pathways have been discovered to be involved in MB pathogenesis, they should be taken into account to more accurately stratify patients and their treatment and to develop innovative therapies.

Family cancer history and risk of brain tumors in children: results of the SEARCH international brain tumor study

OBJECTIVE

To examine whether childhood brain tumors (CBTs) are associated with a family history of brain tumors or other cancers in an international case-control study.

METHODS

Cancers in children's first- and second-degree relatives were ascertained by interview with parents of 620 children with astroglial tumors, 255 with primitive neuroectodermal tumors, 324 with other CBTs, and 2,218 controls from Australia, Canada, France, Israel, Italy, Spain, and the US. These were used with histories of neurofibromatosis or tuberous sclerosis to exclude in subanalyses children with Li-Fraumeni or other hereditary syndromes predisposing to brain tumors.

RESULTS

A first- or second-degree relative of 4% of children with astroglial tumors, 6% with PNET, 5% with other CBTs, and 5% of controls had had a brain tumor. Any potential differences were statistically non-significant, including when focusing on relatives diagnosed in childhood. In the US, where anatomical sites of relatives' other cancers were known, CBT occurrence was not associated with any other specific site. Results were not markedly altered by exclusion of children with hereditary syndromes.

CONCLUSION

Consistent with most prior studies using these methods, we observed no strong relationship between CBT occurrence and cancers in family members.

Functional and molecular interactions between the HGF/c-Met pathway and c-Myc in large-cell medulloblastoma

The growth factor hepatocyte growth factor (HGF), also known as scatter factor, and its tyrosine kinase receptor c-Met play important roles in medulloblastoma malignancy. The transcription factor c-Myc is another contributor to the malignancy of these most common pediatric brain tumors. In the present study, we observed strong morphological similarities between medulloblastoma xenografts overexpressing HGF and medulloblastoma xenografts overexpressing c-Myc. We therefore hypothesized a biologically significant link between HGF/c-Met and c-Myc in medulloblastoma malignancy and studied the molecular and functional interactions between them. We found that HGF induces c-Myc mRNA and protein in established and primary medulloblastoma cells. HGF regulated c-Myc levels via transcriptional and post-transcriptional mechanisms as evidenced by HGF induction of c-Myc promoter activity and induction of c-Myc protein levels in the setting of inhibited transcription and translation. We also found that HGF induces cell cycle progression, cell proliferation, apoptosis and increase in cell size in a c-Myc-dependent manner. Activation of MAPK and PI3K, inhibition of GSK-3beta and translocation of beta-catenin to the nucleus as well as Tcf/Lef transcriptional activity were involved in mediating c-Myc induction by HGF. Induction of Cdk2 kinase activity was involved in mediating the cell cycle progression effects, and downregulation of Bcl-XL was involved in mediating the proapoptotic effects of HGF downstream of c-Myc. All molecules that mediated the effects of HGF on c-Myc expression, cell proliferation and apoptosis were expressed in human large-cell medulloblastoma tissues. We therefore established for the first time a functional cooperation between HGF/c-Met and c-Myc in human medulloblastoma and elucidated the molecular mechanisms of this cooperation. The findings provide a potential explanation for the high frequency of c-Myc overexpression in medulloblastoma and suggest a cooperative role for c-Met and c-Myc in large-cell anaplastic medulloblastoma formation.

Update on the management of familial central nervous system tumor syndromes

Hereditary central nervous tumor syndromes are a varied group of conditions that include neurofibromatosis type 1 and 2, tuberous sclerosis, Von Hippel-Lindau disease, and Cowden, Turcot, and Gorlin syndromes. The responsible genes have been identified in most of these disorders. These genes typically act as tumor suppressor genes, maintain normal cellular function and homeostasis, and regulate cell growth and differentiation. Familial central nervous system tumors are mostly inherited as autosomal dominant traits and involve germline mutations. Neoplastic development occurs when a somatic mutation inactivates the second allele. These patients also present unique challenges for their management. This review highlights the clinical manifestations, molecular genetics, pathophysiology, and current treatment options of these disorders with a focus on neuro-oncologic manifestations of the diseases.

Medulloblastoma: tumorigenesis, current clinical paradigm, and efforts to improve risk stratification

Medulloblastoma is the most common brain malignancy in children and tremendous advances have recently been made in understanding the pathogenesis of this tumor. The Hedgehog and Wingless signaling pathways are implicated in medulloblastoma development, and both pathways were discovered as a result of analyses of genetic syndromes associated with the tumor. Over the past 80 years, considerable progress has been made in the treatment of what was once a fatal disease. The first survival reports followed the introduction of craniospinal irradiation, and yet the success of this modality, which continues to be a central component of treatment regimens for patients older than 3 years, comes at a significant cost. The present challenge in medulloblastoma treatment is to improve upon existing survival rates and to minimize the side effects of treatment. The current tools of clinical risk assessment fail to adequately identify patients older than 3 years who require less radiation and those who require more radiation. Significant effort has been made to improve clinical risk stratification and titration of treatment by analyzing properties of the tumor cells themselves for prognostic significance. These efforts include identifying histopathologic, cytogenetic, and molecular features that may correlate with prognosis.

Current concepts in the molecular genetics of pediatric brain tumors: implications for emerging therapies

BACKGROUND

The revolution in molecular biology that has taken place over the past 2 decades has provided researchers with new and powerful tools for detailed study of the molecular mechanisms giving rise to the spectrum of pediatric brain tumors. Application of these tools has greatly advanced our understanding of the molecular pathogenesis of these lesions.

REVIEW

After familiarizing readers with some promising new techniques in the field of oncogenomics, this review will present the current state of knowledge as it pertains to the molecular biology of pediatric brain neoplasms. Along the way, we hope to highlight specific instances where the detailed mechanistic knowledge acquired thus far may be exploited for therapeutic advantage.

c-myc overexpression causes anaplasia in medulloblastoma

Both anaplasia and increased c-myc gene expression have been shown to be negative prognostic indicators for survival in medulloblastoma patients. myc gene amplification has been identified in many large cell/anaplastic medulloblastoma, but no causative link between c-myc and anaplastic changes has been established. To address this, we stably overexpressed c-myc in two medulloblastoma cell lines, DAOY and UW228, and examined the changes in growth characteristics. When analyzed in vitro, cell lines with increased levels of c-myc had higher rates of growth and apoptosis as well as significantly improved ability to form colonies in soft agar compared with control. When injected s.c. into nu/nu mice, flank xenograft tumors with high levels of c-myc in DAOY cell line background were 75% larger than those derived from control. Overexpression of c-myc was required for tumor formation by UW228 cells. Most remarkably, the histopathology of the Myc tumors was severely anaplastic, with large areas of necrosis/apoptosis, increased nuclear size, and macronucleoli. Indices of proliferation and apoptosis were also significantly higher in Myc xenografts. Thus, c-myc seems to play a causal role in inducing anaplasia in medulloblastoma. Because anaplastic changes are often observed in recurrent medulloblastoma, we propose that c-myc dysregulation is involved in the progression of these malignant embryonal neoplasms.

The scatter factor/hepatocyte growth factor: c-met pathway in human embryonal central nervous system tumor malignancy

Embryonal central nervous system (CNS) tumors, which comprise medulloblastoma, are the most common malignant brain tumors in children. The role of the growth factor scatter factor/hepatocyte growth factor (SF/HGF) and its tyrosine kinase receptor c-Met in these tumors has been until now completely unknown. In the present study, we show that human embryonal CNS tumor cell lines and surgical tumor specimens express SF/HGF and c-Met. Furthermore, c-Met mRNA expression levels statistically significantly correlate with poor clinical outcome. Treatment of medulloblastoma cells with SF/HGF activates c-Met and downstream signal transduction as evidenced by c-Met, mitogen-activated protein kinase, and Akt phosphorylation. SF/HGF induces tumor cell proliferation, anchorage-independent growth, and cell cycle progression beyond the G1-S checkpoint. Using dominant-negative Cdk2 and a degradation stable p27 mutant, we show that cell cycle progression induced by SF/HGF requires Cdk2 function and p27 inhibition. SF/HGF also protects medulloblastoma cells against apoptosis induced by chemotherapy. This cytoprotective effect is associated with reduction of proapoptotic cleaved poly(ADP-ribose) polymerase and cleaved caspase-3 proteins and requires phosphoinositide 3-kinase activity. SF/HGF gene transfer to medulloblastoma cells strongly enhances the in vivo growth of s.c. and intracranial tumor xenografts. SF/HGF-overexpressing medulloblastoma xenografts exhibit increased invasion and morphologic changes that resemble human large cell anaplastic medulloblastoma. This first characterization establishes SF/HGF:c-Met as a new pathway of malignancy with multifunctional effects in human embryonal CNS tumors.

Medulloblastoma: mouse models and novel targeted therapies based on the Sonic hedgehog pathway

Understanding molecular pathways, signaling cascades, and genetic alterations activated during tumorigenesis is essential for the development of targeted cancer treatments. In children, tumors of the central nervous system are thought to arise from progenitor cells that show considerable temporal and spatial heterogeneity in a developmental environment that is different from that of the adult. Investigating the molecular basis of pediatric tumors is critical because it is likely to generate novel treatments. Animal models have brought many important advances in this field. In this review the authors discuss the mouse models based on the Sonic hedgehog pathway, which have provided a better knowledge of the genetic and molecular alterations of medulloblastoma.

Molecular genetics of supratentorial primitive neuroectodermal tumors and pineoblastoma

The supratentorial primitive neuroectodermal tumors (PNETs) are a group of highly malignant lesions primarily affecting young children. Although these tumors are histologically indistinguishable from infratentorial medulloblastoma, they often respond poorly to medulloblastoma-specific therapy. Indeed, existing molecular genetic studies indicate that supratentorial PNETs have transcriptional and cytogenetic profiles that are different from those of medullo-blastomas, thus pointing to unique biological derivation for the supratentorial PNET. Due to the rarity of these tumors and disagreement about their histopathological diagnoses, very little is known about the molecular characteristics of the supratentorial PNET. Clearly, future concerted efforts to characterize the molecular features of these rare tumors will be necessary for development of more effective supratentorial PNET treatment protocols and appropriate disease models. In this article the authors review existing molecular genetic data derived from human and mouse studies, with the aim of providing some insight into the putative histogenesis of these rare tumors and the underlying transforming pathways that drive their development. Studies of the related but distinct pineoblastoma PNET are also reviewed.

Two Sides of the Same Coin: Wnt Signaling in Neurodegeneration and Neuro-Oncology

Wnts function through the activation of at least three intracellular signal transduction pathways, of which the canonical β-catenin mediated pathway is the best understood. Aberrant canonical Wnt signaling has been involved in both neurodegeneration and cancer. An impairment of Wnt signals appears to be associated with aspects of neurodegenerative pathologies while overactivation of Wnt signaling is a common theme in several types of human tumors. Therefore, although therapeutic approaches aimed at modulating Wnt signaling in neurodegenerative and hyperproliferative diseases might impinge on the same molecular mechanisms, different pharmacological outcomes are required. Here we review recent developments on the understanding of the role of Wnt signaling in Alzheimer's disease and CNS tumors, and identify possible avenues for therapeutic intervention within a complex and multi-faceted signaling pathway.

Molecular diagnostics in central nervous system tumors

Central nervous system (CNS) neoplasms can be diagnostically challenging, due to remarkably wide ranges in histologic appearance, biologic behavior, and therapeutic approach. Nevertheless, accurate diagnosis is the critical first step in providing optimal patient care. As with other oncology-based specialties, there is a rapidly expanding interest and enthusiasm for identifying and utilizing new biomarkers to enhance the day-to-day practice of surgical neuropathology. In this regard, the field is primed by recent advances in basic research, elucidating the molecular mechanisms of tumorigenesis and progression in the most common adult and pediatric brain tumors. Thus far, few have made the transition into routine clinical practice, the most notable example being 1p and 19q testing in oligodendroglial tumors. However, the field is rapidly evolving and many other biomarkers are likely to emerge as useful ancillary diagnostic, prognostic, or therapeutic aids. The goal of this article is to highlight the most common genetic alterations currently implicated in CNS tumors, focusing most on those that are either already in common use in ancillary molecular diagnostics testing or are likely to become so in the near future.

Recent advances in embryonal tumours of the central nervous system

INTRODUCTION

Embryonal tumours of the central nervous system (CNS) are the commonest malignant paediatric brain tumours. This group includes medulloblastomas, supratentorial primitive neuroectodermal tumours, atypical teratoid/rhabdoid tumours, ependymoblastomas, and medulloepitheliomas. Earlier, all these tumours were grouped under a broad category of primitive neuroectodermal tumours (PNETs). However, the current WHO classification (2000) separates them into individual types based on significant progress in the understanding of their distinctive clinical, pathological, molecular genetic, histogenetic, and behavioural characteristics. Furthermore, advances in histopathology and molecular genetics have shown great promise for refining risk assessment in these tumours, especially medulloblastomas, thus providing a more accurate basis for tailoring therapies to individual patients. Correlation of histological changes with genetic events has also led to a new model of medulloblastoma tumorigenesis.

REVIEW

This review presents an updated comparative profile of these tumours, highlighting the clinical and biological relevance of the recent advances.

The search for the retinoblastoma cell of origin

The cellular effects of the genetic defects associated with tumorigenesis are context dependent. To better understand the reasons that different cell types require distinct combinations of mutations to form tumours, it is essential to identify and characterize a tumour's 'cell of origin'. Retinoblastoma, a rare childhood cancer of the retina that is caused by RB inactivation, is a good model in which to search for a tumour cell of origin, because retinal development is well understood and the initiating genetic lesion is well characterized. Identifying the cell of origin for this tumour would advance our understanding of how cellular context affects the requirement of specific mutations for cancer initiation and progression.

Identification of differentially expressed and developmentally regulated genes in medulloblastoma using suppression subtraction hybridization

To increase our understanding of the molecular pathogenesis of medulloblastoma (MB), we utilized the technique of suppression subtractive hybridization (SSH) to identify genes that are dysregulated in MB when compared to cerebellum. SSH-enriched cDNA libraries from both human and Ptch+/- heterozygous murine MBs were generated by subtracting common cDNAs from corresponding non-neoplastic cerebellum. For the human classic MB library, total human cerebellar RNA was used as control tissue; for the Ptch+/- heterozygous MB, non-neoplastic cerebellum from an unaffected Ptch+/- littermate was used as the control. Through differential screening of these libraries, over 100 upregulated tumor cDNA fragments were isolated, sequenced and identified with the NCBI BLAST program. From these, we selected genes involved in cellular proliferation, antiapoptosis, and cerebellar differentiation for further analysis. Upregulated genes identified in the human MB library included Unc33-like protein (ULIP), SOX4, Neuronatin (NNAT), the mammalian homologue of Drosophila BarH-like 1(BARHL1), the nuclear matix protein NRP/B (ENC1), and the homeobox OTX2 gene. Genes found to be upregulated in the murine MB library included cyclin D2 (Ccnd2), thymopoietin (Tmpo), Musashi-1 (Msh1), protein phosphatase 2A inhibitor-2 (I-2pp2a), and Unc5h4(D). Using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR), the mRNA expression levels for these genes were markedly higher in human MBs than in cerebellum. Western blot analysis was used to further confirm the overexpression of a subset of these genes at the protein level. Notch pathway overactivity was demonstrated in the TE671 MB cell line expressing high levels of MSH1 through HES1-Luciferase transfections. This study has revealed a panel of developmentally regulated genes that may be involved in the pathogenesis of MB.