Medulloblastoma (MB) is the most common malignant primary pediatric brain tumor and is divided into 4 subtypes based on different genomic alterations and gene expression profiles. This extensive heterogeneity has made it difficult to assess the functional relevance of genes to malignant progression. For example, expression of the transcription factor, Orthodenticle homeobox2 (OTX2) is frequently upregulated in multiple MB variants; however, its role may be subtype-specific. We recently demonstrated that neural precursors derived from transformed human embryonic stem cells (trans-hENs), but not their normal counterparts (hENs), resemble Groups 3 and 4 MBs. These trans-hENs also have >10-fold expression of OTX2. Therefore, we hypothesize that OTX2 has cell context-dependent functions in MB and using both normal and trans-hENs, we can delineate its specific roles in MB progression. Parallel experiments with MB cells revealed that OTX2 exerts inhibitory effects on hEN and sonic hedgehog (SHH) MB cells by regulating growth, self-renewal and migration in vitro and tumor growth in vivo. Overexpression of OTX2 was accompanied by a decrease in expression of pluripotent genes such as SOX2. This was supported by exogenous introduction of SOX2 in OTX2+ SHH MB and hENs that rescued the OTX2 induced cellular deficits including self-renewal and cell migration. In contrast, OTX2 is oncogenic and promotes self-renewal of trans-hENs and Group 3 and 4 MBs by modulating expression of genes related to neurodevelopment and axonal guidance. OTX2 may play a central role in regulating the balance between self-renewal and differentiation in these aggressive MB cells. Our studies underscore the value of hESC derivatives as alternatives to cell lines and heterogeneous patient samples for investigating the contribution of key developmental regulators to MB progression. Using the neural derivatives of hESCs, we have demonstrated a novel role for OTX2 in self-renewal and migration of hENs and MB cells. Moreover, our results reveal a cell context-dependent link between OTX2 and pluripotent genes. The association between OTX2 and axonal guidance genes is important for its oncogenic role and may potentially be exploited for managing drug resistant stem cell and highly motile cellular populations in the most aggressive Group 3 and 4 MB subtypes. / February 2017

Medulloblastoma is the most common brain tumor in children, accounting for 10-20% of primary central nervous system (CNS) neoplasms and approximately 40% of all posterior fossa tumors. It is a highly invasive embryonal neuroepithelial tumor that typically arises in the cerebellar vermis and has a tendency to disseminate throughout the CNS early in its course. The molecular mechanisms of the disease largely remain uncharacterized, as the clinical treatment is still associated with mortality and severe side effects. The development of a clinically relevant in vivo model is important not only to further understand the disease but also to provide a method with which to test novel therapeutics. This study quantified the volumetric growth of a human medulloblastoma (VC312) in the athymic nude mouse cerebellum using Gd- enhanced T1-weighed MRI scans. Additionally, a medulloblastoma flank tumor model was used to explore the in vivo effect of the oral anti-cancer agent that inhibits Akt activation in the phosphoinositide 3-kinase (PI3K) pathway. In the orthotopic intracerebellar tumor model, perifosine significantly increased the survival of treated mice while qualitatively reducing leptomeningeal dissemination. In the flank model, perifosine effectively suppressed the volumetric growth, decreased activation of the AKT pathway and reduced cellular proliferation in treated mice.

O meduloblastoma (MB) é um tumor embrionário que se origina de alterações genéticas em vias importantes para neurôgenese do cerebelo como Sonic hedgehog (Shh) e Wingless (Wnt). Alterações específicas nessas vias permitem a classificação do MB pelo perfil de expressão e mutacional em quatro subgrupos: SHH, WNT, grupo 3 e grupo 4. A ativação dessas vias pode estar relacionada à hipermetilação de reguladores negativos. A dinâmica da hidroximetilação foi descrita durante o desenvolvimento cerebelar, mas não há relatos na literatura sobre os níveis da hidroximetilação em amostras de MB. Os principais objetivos desse trabalho foram: avaliar os níveis de expressão dos genes TETs e IDHs em MB por qPCR; investigar os níveis de hidroximetilação por meio de imuno-histoquímica e dot-blot; avaliar mutações no éxon 4 de IDH1 e IDH2 por sequenciamento; analisar a metilação e hidroximetilação em genes reguladores negativos das vias SHH, WNT, NOTCH, BMP; modular a atividade dos genes TETs por meio do ácido ascórbico e verificar sua influência funcional e epigenética. Foi observada diminuição na expressão dos genes TETs e IDHs em amostras de MB apenas em comparação com cerebelos fetais, mas não em relação aos cerebelos não-fetais. As linhagens celulares de MB apresentaram expressão diminuída em comparação aos dois grupos controles. A classificação das amostras de MB permitiu verificar uma expressão gênica subgrupo específica. A expressão de TET3 apresentou associação com status da doença; e maiores níveis de IDH2 foram associados à metástase. Não foram encontradas mutações no éxon 4 de IDH1, ou no éxon 4 de IDH2 em MB. Os níveis de hidroximetilação global estão diminuídos em amostras de MB e linhagens celulares em comparação aos cerebelos não-neoplásicos; porém não estão associados com características clínicas dos pacientes. Não foram encontrados níveis detectáveis de hidroximetilação nos genes estudados. Os efeitos do ácido ascórbico foram linhagem-específicos, não ocorreu aumento nos níveis de hidroximetilação, mas alterações na expressão do gene TET3. Em conclusão, níveis de hidroximetilação e expressão dos genes TETs e IDHs são importantes para o MB. No entanto, estudos funcionais direcionados à manipulação desses genes são necessários para elucidar suas funções nesse tumor. / Medulloblastoma (MB) is an embryonic tumor that originates from genetic alterations in pathways that are important to the neurogenesis of cerebellum, such as Sonic hedgehog (Shh) e Wingless (Wnt). These alterations allow us to classify MB based in expression and mutational profile in four subgroups: SHH, WNT, group 3 and group 4. The activation of these pathways could be related to hypermethylation of negative regulators. Hydroxymethylation dynamics was described during cerebellum development, but there are not reports in the literature about hydroxymethylation levels in MB samples. The main aims of this study were: to evaluate TET and IDH genes expression in MB using qPCR; to investigate hydroxymethylation levels using immunohistochemistry and dot-blot; to evaluate mutations in exon 4 of IDH1 and IDH2 genes through sequencing analysis; to analyze methylation and hydroxymethylation levels in genes that regulate SHH, WNT, NOTCH and BMP pathways; to modulate TET genes activity through ascorbic acid and verify its functional and epigenetic influence in MB cell lines. We observed a decrease in TET and IDH genes expression in MB samples compared to fetal cerebellum, but not according to non-fetal cerebellum. MB cell lines presented a decrease when compared to both control groups. The classification of MB samples allowed us to verify a subgroup-specific gene expression. TET3 expression was associated with disease status; and higher levels of IDH2 gene expression were associated with metastasis. We did not find mutations in exon 4 of IDH1 and exon 4 of IDH2 genes in MB samples. Hydroxymethylation levels were decreased in MB samples and cell lines when compared to non-neoplastic cerebellum; however, they were not associated with clinical characteristics of the patients. We did not detect hydroxymethylation levels in the studied genes. Ascorbic acid effects are cell linespecific: we did not observe increase in hydroxymethylation levels, but alterations in TET3 gene expression. In conclusion, hydroxymethylation and expression levels of TET and IDH genes are important for MB. Though, functional assays that target these genes are required to elucidate their function in MB.

O meduloblastoma é o tumor maligno do sistema nervoso central mais frequente na infância e adolescência. A expressão de genes tipicamente expressos em células-tronco está correlacionada com pior prognóstico em pacientes com meduloblastoma e a expressão de POU5F1 se mostrou capaz de distinguir pacientes com desfecho clínico desfavorável e pior sobrevida. Apesar do seu valor prognóstico, não há evidências diretas da contribuição de OCT4 para a aquisição de fenótipos mais agressivos em meduloblastoma. Nesse contexto, o presente trabalho investigou o papel da isoforma OCT4A em características pró-tumorigênicas de meduloblastoma in vitro e in vivo, e também avaliou as alterações moleculares que podem ser responsáveis pela aquisição de fenótipo mais agressivo em células de meduloblastoma humano. Para tanto, foi realizada a superexpressão de OCT4A mediada por retrovírus em três linhagens celulares de meduloblastoma (Daoy, D283Med e USP-13-Med). As células de meduloblastoma com superexpressão de OCT4A exibiram maior proliferação e alterações no ciclo celular. Foram observados também aumentos na atividade clonogênica, geração de esferas tumorais e desenvolvimento tumoral em modelo subcutâneo, sendo esses efeitos dependentes dos níveis de OCT4A. A avaliação da mobilidade celular in vitro demonstrou diminuição na adesão celular e aumento da invasão celular de esferoide 3D. Em modelo ortotópico de meduloblastoma, as células com superexpressão de OCT4A geraram tumores mais desenvolvidos, com fenótipos mais agressivos, infiltrativos e metastáticos. A superexpressão de OCT4A foi associada a maior instabilidade genômica, entretanto, as aberrações em números de cópias variaram em frequência e tipo de alteração dependendo da linhagem celular, e sendo pouco associada com os genes diferencialmente expressos. De forma interessante, uma relevante expressão diferencial de RNAs não-codificadores de proteínas foi observada em células de meduloblastoma com superexpressão de OCT4A, incluindo os recém descobertos e pouco caracterizados RNAs não codificadores longos, além de múltiplos RNAs pequenos nucleolares. Assim, os resultados aqui apresentados fundamentam a relevância de fatores envolvidos em pluripotência para o agravamento de traços associados com desfecho clínico desfavorável em meduloblastoma e destacam o valor prognóstico e terapêutico de OCT4A neste tumor pediátrico do sistema nervoso central / Medulloblastoma is the most common malignant brain tumor in infants. The expression of typical pluripotency genes is correlated with poor prognosis in medulloblastoma and POU5F1 expression was shown capable of discriminating patients with poor survival outcome. Despite this prognostic value, direct evidences of OCT4 contribution to more aggressive traits in medulloblastoma are missing. In this context, we investigated the role of OCT4A isoform on pro-tumorigenic features of medulloblastoma in vitro and in vivo and evaluated molecular alterations that could be responsible for acquisition of a more aggressive phenotype in medulloblastoma cells. Retroviral-mediated overexpression of OCT4A were performed in three medulloblastoma cell lines (Daoy, D283Med and USP-13-Med). Medulloblastoma cells overexpressing OCT4A displayed enhanced cell proliferation and cell cycle alterations. Increased clonogenic activity, tumorsphere generation capability and subcutaneous tumor development were also observed, and these effects were OCT4A expression level-dependent. Evaluation of cell mobility in vitro showed loss of cell adhesion and greater 3D-spheroid invasion. In an orthotopic model of medulloblastoma, OCT4A overexpressing cells generated more developed, aggressive, infiltrative and metastatic tumors. OCT4A overexpression was associated with chromosomal instability but copy number aberrations varied in frequency and type according to the cell line, with little association with differently expressed genes. Interestingly, marked differential expression of non-coding RNAs, including newly discovered, still poorly characterized, long non-coding RNAs and multiple small nucleolar RNAs were observed in medulloblastoma cells with OCT4A overexpression. Altogether, our findings support the relevance of pluripotency-related factors in the aggravation of medulloblastoma traits classically associated with poor clinical outcome, and underscore the prognostic and therapeutic value of OCT4A in this challenging type of pediatric brain cancer

Introdução: O Meduloblastoma (MB) é o tumor sólido maligno mais comum do sistema nervoso central em crianças. Corresponde a aproximadamente 20% de todos os tumores intracranianos pediátricos, surge no cerebelo e sua origem é embrionária, sendo altamente invasivo. Como tratamento padrão usa-se a ressecção cirúrgica do tumor, quimioterapia e radioterapia crânio-espinhal; porém, a taxa de sobrevida livre de eventos (SLE) em cinco anos para os pacientes de baixo risco é de aproximadamente 70% e a maioria dos pacientes que sobrevivem sofre de efeitos secundários a longo prazo. Portanto, crescem as buscas por novos tratamentos que apresentem menores efeitos colaterais ou que diminuam/eliminem a necessidade de radiação. Vários fatores contribuem para o desenvolvimento e progressão da doença, entre eles, a regulação da expressão gênica por microRNAs (miRNAs). Essas moléculas regulam diversos processos biológicos, exercendo regulação gênica negativa a nível pós-transcricional; no entanto, seu papel em MB ainda é pouco explorado. Objetivo: Avaliar o perfil de expressão de miRNAs diferencialmente expressos em amostras de pacientes portadores de MB e correlacionar seus níveis de expressão com características clínicas dos pacientes, assim como identificar possíveis marcadores de prognóstico. Metodologia: Foram selecionados 15 miRNAs a partir de dados prévios obtidos pela técnica de microarranjo. Foi realizada a expressão desses miRNAs por PCR quantitativa em tempo real (RT-qPCR) e feita a comparação com as características clínicas, utilizando amostras de pacientes portadores de MB adultos e pediátricos (N=51) e amostras de cerebelos não neoplásicos fetais (N=10) e não fetais (N=7). A comparação entre os grupos foi feita por teste de Mann-Whitney e a análise de sobrevida livre de eventos (SLE) e sobrevida global (SG) por curvas de Kaplan-Meier e teste log-rank. A análise multivariada por modelo de regressão de Cox foi utilizada para avaliação dos fatores prognósticos. Resultados: Os miRNAs miR-329, -383, -433, -485-3p, -485-5p, -491-5p, -512-3p, -539-5p estão hipoexpressos nos tumores em relação aos cerebelos fetais e não fetais; o miR-31-5p está hipoexpresso e o miR-199a-5p está hiperexpresso nos tumores em relação ao cerebelos não fetais; o miR-202-3p e o miR-650 estão hipoexpressos nos tumores em relação aos cerebelos fetais. Além disso, os miRNAsmiR-199a-5p e -329 estãoshipoexpressos em pacientes menores que 3 anos, com relação aos maiores de 3 anos; os miRNAs miR-202-3p, -329, -491-4p e -512-3p estão hipoexpressos em pacientes que tiveram grau de ressecção completo do tumor, em comparação aos que tiveram grau incompleto; e os miRNAs miR-202-3p e -512-3p estão hipoexpressos em pacientes classificados como baixo risco em comparação aos classificados como alto risco. Adicionalmente, o miR-211-5p está hipoexpresso nos pacientes com menor sobrevida global e livre de eventos; e o miR-512-3p está hiperexpresso nos pacientes com menor sobrevida global e livre de eventos. Expressão do miR-211-5p foi fator prognóstico independente para SLE quando analisada com as variáveis expressão do miR-512-3p e grupo de risco por modelo de regressão de Cox. Conclusão: É possível observar um padrão diferencial de expressão desses miRNAs no MB, podendo ser biomarcadores importantes para esta doença. Estudos futuros serão realizados para investigar o papel desses miRNAs na progressão desse tumor. / Introduction: Medulloblastoma (MB) is the most common malignant solid tumor of the central nervous system in children,and it arises in the cerebellum with an embrionary origin. MB corresponds to approximately 20% of all pediatric intracranial tumors, and it is highly invasive. The standard treatment relies on tumor surgical resection, chemotherapy and craniospinal radiotherapy; however, the five years event-free survival for low-risk patients is approximately 70%, and most survival patients suffer from long-term side effects. Thus, the search for new treatments with fewer side effects or aiming to reduce/eliminate radiation is of great interest. Several factors contribute to the development and progression of this disease, among them the regulation of gene expression by microRNAs (miRNAs). These molecules regulate diverse biological processes, exerting negative regulation in gene expression at posttranscriptional level, however its role in MB is still poorly explored. Objective: Evaluate the profile of differentially expressed miRNAs in MB samples, correlate their expression levels with patients clinical features, and identify potential prognostic markers. Material and methods: 15 miRNAs were selected based on previous data obtained from a large-scale gene expression analysis using the microarray assay. It was performed their expression and compared with the clinical features of the patients by RT-qPCR. For this, it was used pediatric and adult patients samples (n=51) diagnosed with MB and non-neoplastic fetal (n=10) and non fetal (n=7) cerebellum samples. The comparison between groups was performed by Mann-Whitney test and event-free survival (EFS) analysis and overall survival (OS) by Kaplan-Meier and log-rank test. Multivariate analysis by Cox regression model was used to evaluate the prognostic factors. Results: The miRNAs miR-329, -383, -433, -485-3p, -485- 5p, -491-5p, -512-3p, -539-5p are downregulated in tumors when compared to fetal and nonfetal cerebellum; miR-31-5p is downregulated and miR-199a-5p is upregulated only in tumors compared to non-fetal cerebellum; miR-202-3p and miR-650 are downregulated in tumors only when compared to fetal cerebellum. In addition, miR-199a-5p and miR-329 are downregulated in patients under 3 years old compared to those who are higher than 3 year; miR-202-3p,miR-329, miR-491-5p and miR-512-3p are downregulated in patients who had complete tumor resection compared to those who had incomplete tumor resection; and miR- 202-3p and miR-512-3p are downregulated in low risk patients compared to high risk patients. In addition, miR-211-5p is downregulated and miR-512-3p is upregulated in patients with a poorer event-free survival and overall survival. The expression of miR-211-5p was an independent prognostic factor for EFS when analyzed with the variables miR-512-3p expression and risk group by Cox regression model Conclusion: It is possible to observe a differential pattern of expression of these miRNAs in MB and they may be important biomarkers for this disease. Further studies will be conducted to investigate the role of these miRNAs in the progression of this tumor.

Introdução: O Meduloblastoma (MB) é o tumor sólido maligno mais comum do sistema nervoso central em crianças. Corresponde a aproximadamente 20% de todos os tumores intracranianos pediátricos, surge no cerebelo e sua origem é embrionária, sendo altamente invasivo. Como tratamento padrão usa-se a ressecção cirúrgica do tumor, quimioterapia e radioterapia crânio-espinhal; porém, a taxa de sobrevida livre de eventos (SLE) em cinco anos para os pacientes de baixo risco é de aproximadamente 70% e a maioria dos pacientes que sobrevivem sofre de efeitos secundários a longo prazo. Portanto, crescem as buscas por novos tratamentos que apresentem menores efeitos colaterais ou que diminuam/eliminem a necessidade de radiação. Vários fatores contribuem para o desenvolvimento e progressão da doença, entre eles, a regulação da expressão gênica por microRNAs (miRNAs). Essas moléculas regulam diversos processos biológicos, exercendo regulação gênica negativa a nível pós-transcricional; no entanto, seu papel em MB ainda é pouco explorado. Objetivo: Avaliar o perfil de expressão de miRNAs diferencialmente expressos em amostras de pacientes portadores de MB e correlacionar seus níveis de expressão com características clínicas dos pacientes, assim como identificar possíveis marcadores de prognóstico. Metodologia: Foram selecionados 15 miRNAs a partir de dados prévios obtidos pela técnica de microarranjo. Foi realizada a expressão desses miRNAs por PCR quantitativa em tempo real (RT-qPCR) e feita a comparação com as características clínicas, utilizando amostras de pacientes portadores de MB adultos e pediátricos (N=51) e amostras de cerebelos não neoplásicos fetais (N=10) e não fetais (N=7). A comparação entre os grupos foi feita por teste de Mann-Whitney e a análise de sobrevida livre de eventos (SLE) e sobrevida global (SG) por curvas de Kaplan-Meier e teste log-rank. A análise multivariada por modelo de regressão de Cox foi utilizada para avaliação dos fatores prognósticos. Resultados: Os miRNAs miR-329, -383, -433, -485-3p, -485-5p, -491-5p, -512-3p, -539-5p estão hipoexpressos nos tumores em relação aos cerebelos fetais e não fetais; o miR-31-5p está hipoexpresso e o miR-199a-5p está hiperexpresso nos tumores em relação ao cerebelos não fetais; o miR-202-3p e o miR-650 estão hipoexpressos nos tumores em relação aos cerebelos fetais. Além disso, os miRNAsmiR-199a-5p e -329 estãoshipoexpressos em pacientes menores que 3 anos, com relação aos maiores de 3 anos; os miRNAs miR-202-3p, -329, -491-4p e -512-3p estão hipoexpressos em pacientes que tiveram grau de ressecção completo do tumor, em comparação aos que tiveram grau incompleto; e os miRNAs miR-202-3p e -512-3p estão hipoexpressos em pacientes classificados como baixo risco em comparação aos classificados como alto risco. Adicionalmente, o miR-211-5p está hipoexpresso nos pacientes com menor sobrevida global e livre de eventos; e o miR-512-3p está hiperexpresso nos pacientes com menor sobrevida global e livre de eventos. Expressão do miR-211-5p foi fator prognóstico independente para SLE quando analisada com as variáveis expressão do miR-512-3p e grupo de risco por modelo de regressão de Cox. Conclusão: É possível observar um padrão diferencial de expressão desses miRNAs no MB, podendo ser biomarcadores importantes para esta doença. Estudos futuros serão realizados para investigar o papel desses miRNAs na progressão desse tumor. / Introduction: Medulloblastoma (MB) is the most common malignant solid tumor of the central nervous system in children,and it arises in the cerebellum with an embrionary origin. MB corresponds to approximately 20% of all pediatric intracranial tumors, and it is highly invasive. The standard treatment relies on tumor surgical resection, chemotherapy and craniospinal radiotherapy; however, the five years event-free survival for low-risk patients is approximately 70%, and most survival patients suffer from long-term side effects. Thus, the search for new treatments with fewer side effects or aiming to reduce/eliminate radiation is of great interest. Several factors contribute to the development and progression of this disease, among them the regulation of gene expression by microRNAs (miRNAs). These molecules regulate diverse biological processes, exerting negative regulation in gene expression at posttranscriptional level, however its role in MB is still poorly explored. Objective: Evaluate the profile of differentially expressed miRNAs in MB samples, correlate their expression levels with patients clinical features, and identify potential prognostic markers. Material and methods: 15 miRNAs were selected based on previous data obtained from a large-scale gene expression analysis using the microarray assay. It was performed their expression and compared with the clinical features of the patients by RT-qPCR. For this, it was used pediatric and adult patients samples (n=51) diagnosed with MB and non-neoplastic fetal (n=10) and non fetal (n=7) cerebellum samples. The comparison between groups was performed by Mann-Whitney test and event-free survival (EFS) analysis and overall survival (OS) by Kaplan-Meier and log-rank test. Multivariate analysis by Cox regression model was used to evaluate the prognostic factors. Results: The miRNAs miR-329, -383, -433, -485-3p, -485- 5p, -491-5p, -512-3p, -539-5p are downregulated in tumors when compared to fetal and nonfetal cerebellum; miR-31-5p is downregulated and miR-199a-5p is upregulated only in tumors compared to non-fetal cerebellum; miR-202-3p and miR-650 are downregulated in tumors only when compared to fetal cerebellum. In addition, miR-199a-5p and miR-329 are downregulated in patients under 3 years old compared to those who are higher than 3 year; miR-202-3p,miR-329, miR-491-5p and miR-512-3p are downregulated in patients who had complete tumor resection compared to those who had incomplete tumor resection; and miR- 202-3p and miR-512-3p are downregulated in low risk patients compared to high risk patients. In addition, miR-211-5p is downregulated and miR-512-3p is upregulated in patients with a poorer event-free survival and overall survival. The expression of miR-211-5p was an independent prognostic factor for EFS when analyzed with the variables miR-512-3p expression and risk group by Cox regression model Conclusion: It is possible to observe a differential pattern of expression of these miRNAs in MB and they may be important biomarkers for this disease. Further studies will be conducted to investigate the role of these miRNAs in the progression of this tumor.

O meduloblastoma (MB) é um câncer do sistema nervoso central, de origem embrionária, que surge no cerebelo. É o tumor maligno cerebral mais frequente na infância e corresponde a aproximadamente 20% de todos os tumores intracranianos pediátricos. Atualmente, o tratamento é realizado com cirurgia, quimioterapia e radioterapia e está relacionado com diversos efeitos colaterais em médio e longo prazo. Diversos fatores contribuem para o seu desenvolvimento e progressão, entre estes, alterações nas vias de sinalização, como a Sonic Hedgehog (SHH) e Wingless. As modificações nos padrões epigenéticos, como a metilação do DNA, tem também um papel central na biologia deste tumor. Tais alterações comprometem funções básicas da célula como o controle da proliferação, sobrevivência celular e apoptose. Drogas epigenéticas como os inibidores de DNA metiltransferases (DNMTs) têm demonstrado efeitos antineoplásicos e resultados promissores para terapia do câncer. A Zebularina é um inibidor de DNMTs, que consequentemente reduz a metilação do DNA, e tem se mostrado uma importante droga antitumoral, com baixa toxicidade e atividade adjuvante à quimioterapia em tumores quimio-resistentes. Diversos estudos têm descrito seus efeitos em diferentes tipos de neoplasias, entretanto, não há relatos da sua ação em MB. Sendo assim, o presente trabalho teve como objetivo analisar os potenciais efeitos antineoplásicos da Zebularina em quatro linhagens de MB pediátrico (DAOY, ONS-76, UW402 e UW473). Foi observado que o tratamento com a Zebularina promoveu inibição da proliferação celular e da capacidade clonogênica, aumentou o número de células apoptóticas e células na fase S do ciclo celular (p<0,05). Adicionalmente, o tratamento induziu um aumento na expressão proteica de p53, p21 e Bax e uma diminuição da ciclina A, Bcl-2 e Survivina. Além disso, quando combinada com o quimioterápico vincristina agiu de modo sinérgico; e de modo antagônico quando combinada com a cisplatina. Através de análises de expressão gênica em larga escala (plataforma Agilent de microarray), foi encontrada diferentes vias moduladas pela droga, incluindo a dos Receptores Toll-Like e o aumento dos genes SUFU e BATF2. Aqui, foi encontrado que a Zebularina pode modular a ativação da via SHH, reduzindo os níveis de SMO, de GLI1 e de um de seus alvos, o PTCH1; contudo sem alterar os níveis de SUFU. Confirmou-se que o gene BATF2 é induzido pela Zebularina e possui regiões ricamente metiladas. Além disso, a baixa expressão do gene BATF2 está associada à um pior prognóstico em MB. Todos esses dados sugerem que a Zebularina pode ser uma droga em potencial para o tratamento adjuvante do MB / Medulloblastoma (MB) is an embryonal cerebellum tumor. It is the most common brain malignancy in children and accounts for approximately 20% of all pediatric intracranial tumors. Currently, treatment consists of surgery, chemotherapy and radiation and is associated to medium- and long-term side effects. Several factors contribute to the development and progression of MB, for instance, alterations in signaling pathways, such as Sonic Hedgehog (SHH) and Wingless. Epigenetic changes in DNA methylation patterns also play a central role in the biology of this tumor. Such changes are able to alter basic cell functions, controlling cell proliferation, survival and apoptosis. Epigenetic drugs as DNA methyltransferases (DNMTs) inhibitors have shown anticancer effects and promising results for cancer therapy. Zebularine is a low toxicity DNMTs inhibitor that induces DNA demethylation and has been reported as an important antitumor drug with adjuvant activity to chemotherapy in chemoresistant tumors. Studies have described its effects on different types of cancer, however, there are not data concerning its action in MB. Therefore, this study aimed to analyze the potential anticancer effects of Zebularine in four pediatric MB lines (UW402, UW473, ONS- 76 and DAOY). It was observed that treatment with Zebularine promoted inhibition of cell proliferation and clonogenic capacity, increased the number of apoptosis rate and cells in S phase of the cycle (p <0.05). In addition, the treatment induced an increasing in the protein expression of p53, p21 and Bax and a decreasing in cyclin A, Survivin and Bcl-2. Also, when combined with the chemotherapeutic agent vincristine acted synergistically but resulted in antagonism when combined with cisplatin. Through large-scale gene expression analysis (Agilent microarray platform), it was found different pathways modulated by Zebularine, including the Toll-Like Receptors pathway and the overexpression of SUFU and BATF2 genes. Zebularine was able to modulate SHH pathway activation, by reducing levels of SMO, GLI1 and one of its targets, PTCH1, whereas there were no changes in SUFU levels. It was confirmed that the gene BATF2 is induced by Zebularine and contains regions richly methylated. In addition, BATF2 low expression is associated with a worse prognosis in MB. All these data suggest that Zebularine may be a potential drug for the adjuvant treatment of MB

Medulloblastoma cells do not contain detectable amounts of the bZIP protein Zhangfei. However, previous work has shown that expression of this protein in cells of the ONS-76 line, derived from a human medulloblastoma, causes the cells to stop growing and develop processes that resemble neuritis (a characteristic of differentiated neurons). Zhangfei-expressing cells eventually die. My objective was to determine the molecular mechanisms by which Zhangfei influences ONS-76 cells. My strategy was to infect ONS-76 cells with adenovirus vectors expressing either Zhangfei or the control E. coli protein â-galactosidase (LacZ) and then to compare the following parameters in Zhangfei and LacZ-expressing cells: a) markers of apoptosis, autophagy and macropinocytosis (the three main pathways of cell death); b) transcripts for genes involved in neurogenesis and apoptosis; c) phosphorylation of peptide targets of selected cellular protein kinases; and d) active transcription factors. Zhangfei-expressing cells appeared to succumb to apoptosis as determined by the expression of phosphatidylserine on the cell surface and intensity of nuclear staining with the DNA dye Hoechst. Increased staining for autophagic vesicles and upregulated expression of autophagy response genes in these cells indicated that they were undergoing autophagy, possibly associated with apoptosis. My analysis of steady-state transcripts for genes involved in apoptosis and neurogenesis and functional protein kinases in Zhangfei-expressing cells indicated that the mitogen-activated protein kinase (MAPK) pathway was active in these cells. In addition, I found that the transcription factor Brn3a as well as factors implicated in differentiation were also active. These observations led me to hypothesize that Zhangfei enhances the expression of Brn3a, a known inducer of TrkA, the high-affinity receptor for nerve growth factor (NGF). TrkA then binds in an autocrine manner to NGF, triggering the MAPK pathway and leading to differentiation of ONS-76 cells into neuron and glia-like cells, eventually bringing about cell death by apoptosis and autophagy. I tested this hypothesis by showing that Zhangfei could enhance transcription from the isolated Brn3a promoter, that ONS-76 cells produce NGF as detected in a bioassay, and that antibodies against NGF and inhibitors of TrkA and selected components of the MAPK pathway could partially restore the growth of Zhangfei-expressing ONS-76 cells. My work supports previous work highlighting the importance of NGF-TrkA signaling in the outcome of medulloblastomas and shows how Zhangfei is able to trigger this pathway.

Medulloblastoma is the most common malignant paediatric brain tumour. Similar to other tumours, medulloblastoma pathogenesis involves abnormal regulation of several developmental growth pathways. As my thesis project, I studied the effects of aberrant HGF/MET signalling on medulloblastoma formation in two ways. In my first objective, I investigated the role that mutations play in activated HGF/MET signalling in medulloblastoma by searching for mutations in HGF/MET pathway genes, SPINT1, SPINT2, and MET, within primary medulloblastoma specimens. This screen identified several single nucleotide polymorphisms (SNPs) and two novel variations, one in each SPINT1 and SPINT2 genes. In my second objective, I generated a transgenic mouse model with cerebellar-specific aberrant MET signalling. These mice developed extensive cerebellar abnormalities but formed no tumours. These results indicate that mutations in the HGF/MET pathway components alone are not sufficient to initiate medulloblastoma formation and must coincide with additional genetic insults to promote tumour formation, maintenance, and progression.

Medulloblastoma (MB) is the most common pediatric malignant brain tumor. Little is known about aggressive forms of this disease. In order to identify pathways mediating aggressiveness in MB, we performed microarray experiments. Primary human MBs were compared to their patient matched recurrent or metastatic counterparts. Murine tumors from two MB mouse models that present with differing clinical severities were also evaluated. We identified the Transforming Growth Factor-beta (TGF-β) as a potential contributor to MB pathogenesis in both species. Smad3, a major downstream component of the TGF-β pathway, was shown to correlate with MB metastasis and survival in human tissue. Similarly, Smad3 expression during development identified a subset of cerebellar neuronal precursors as putative cells of origin for the Smad3 positive MBs. To our knowledge, this is the first study that links TGF-β to MB pathogenesis. Our research suggests that canonical activation of this pathway leads to better prognosis for patients.