Polycomb genes expression as a predictor of poor clinical outcome in children with medulloblastoma

Epigenetic-Based Therapy-A Prospective Chance for Medulloblastoma Patients' Recovery

Medulloblastoma (MB) is one of the most frequent and malignant brain tumors in children. The prognosis depends on the advancement of the disease and the patient's age. Current therapies, which include surgery, chemotherapy, and irradiation, despite being quite effective, cause significant side effects that influence the central nervous system's function and cause neurocognitive deficits. Therefore, they substantially lower the quality of life, which is especially severe in a developing organism. Thus, there is a need for new therapies that are less toxic and even more effective. Recently, knowledge about the epigenetic mechanisms that are responsible for medulloblastoma development has increased. Epigenetics is a phenomenon that influences gene expression but can be easily modified by external factors. The best known epigenetic mechanisms are histone modifications, DNA methylation, or noncoding RNAs actions. Epigenetic mechanisms comprehensively explain the complex phenomena of carcinogenesis. At the same time, they seem to be a potential key to treating medulloblastoma with fewer complications than past therapies. This review presents the currently known epigenetic mechanisms that are involved in medulloblastoma pathogenesis and the potential therapies that use epigenetic traits to cure medulloblastoma while maintaining a good quality of life and ensuring a higher median overall survival rate.

HDAC and MAPK/ERK Inhibitors Cooperate To Reduce Viability and Stemness in Medulloblastoma

Medulloblastoma (MB), which originates from embryonic neural stem cells (NSCs) or neural precursors in the developing cerebellum, is the most common malignant brain tumor of childhood. Recurrent and metastatic disease is the principal cause of death and may be related to resistance within cancer stem cells (CSCs). Chromatin state is involved in maintaining signaling pathways related to stemness, and inhibition of histone deacetylase enzymes (HDAC) has emerged as an experimental therapeutic strategy to target this cell population. Here, we observed antitumor actions and changes in stemness induced by HDAC inhibition in MB. Analyses of tumor samples from patients with MB showed that the stemness markers BMI1 and CD133 are expressed in all molecular subgroups of MB. The HDAC inhibitor (HDACi) NaB reduced cell viability and expression of BMI1 and CD133 and increased acetylation in human MB cells. Enrichment analysis of genes associated with CD133 or BMI1 expression showed mitogen-activated protein kinase (MAPK)/ERK signaling as the most enriched processes in MB tumors. MAPK/ERK inhibition reduced expression of the stemness markers, hindered MB neurosphere formation, and its antiproliferative effect was enhanced by combination with NaB. These results suggest that combining HDAC and MAPK/ERK inhibitors may be a novel and more effective approach in reducing MB proliferation when compared to single-drug treatments, through modulation of the stemness phenotype of MB cells.

Co-inhibition of BMI1 and Mel18 enhances chemosensitivity of esophageal squamous cell carcinoma in vitro and in vivo

Esophageal squamous cell carcinoma (ESCC) accounts for almost 90% of esophageal cancer cases and is the sixth most common cause of cancer-associated mortality worldwide. Cisplatin is the standard therapeutic reagent for ESCC; however, chemoresistance frequently occurs after a few weeks, which leads to ESCC recurrence. Aberrant expression of B lymphoma Mo-MLV insertion region 1 homolog (BMI1) has been reported to activate multiple growth-regulatory pathways, induce antiapoptotic abilities in numerous types of cancer cells and promote chemoresistance. However, to the best of our knowledge, the role of BMI1 in cisplatin-resistant ESCC, and the interaction between BMI1 and its homologue melanoma nuclear protein 18 (Mel18) remain unknown. The present study identified that knockdown of BMI1 promoted cytotoxic effects of cisplatin, and co-inhibition of Mel18 and BMI1 enhanced cisplatin-induced apoptosis and cytotoxicity. Inhibition of BMI1 and Mel18 also suppressed the expression of c-Myc. Furthermore, this combined inhibition sensitized esophageal xenograft tumors to cisplatin to a greater extent compared with BMI1 inhibition alone. In summary, the current study demonstrated that inhibition of BMI1 and Mel18 could increase the sensitivity of esophageal cancer cells to cisplatin via inhibition of c-Myc. Therefore, combined targeting of BMI1 and Mel18 may serve as a promising therapeutic strategy for sensitizing ESCC to chemotherapy.

Epigenetic regulation in medulloblastoma

Medulloblastoma is the most common malignant childhood brain tumor. The heterogeneous tumors are classified into four subgroups based on transcription profiles. Recent developments in genome-wide sequencing techniques have rapidly advanced the understanding of these tumors. The high percentages of somatic alterations of genes encoding chromatin regulators in all subgroups suggest that epigenetic deregulation is a major driver of medulloblastoma. In this report, we review the current understanding of epigenetic regulation in medulloblastoma with a focus on the functional studies of chromatin regulators in the initiation and progression of specific subgroups of medulloblastoma. We also discuss the potential usage of epigenetic inhibitors for medulloblastoma treatment.

Recent advances and future of immunotherapy for glioblastoma

INTRODUCTION

Outcome for glioma (GBM) remains dismal despite advances in therapeutic interventions including chemotherapy, radiotherapy and surgical resection. The overall survival benefit observed with immunotherapies in cancers such as melanoma and prostate cancer has fuelled research into evaluating immunotherapies for GBM.

AREAS COVERED

Preclinical studies have brought a wealth of information for improving the prognosis of GBM and multiple clinical studies are evaluating a wide array of immunotherapies for GBM patients. This review highlights advances in the development of immunotherapeutic approaches. We discuss the strategies and outcomes of active and passive immunotherapies for GBM including vaccination strategies, gene therapy, check point blockade and adoptive T cell therapies. We also focus on immunoediting and tumor neoantigens that can impact the efficacy of immunotherapies.

EXPERT OPINION

Encouraging results have been observed with immunotherapeutic strategies; some clinical trials are reaching phase III. Significant progress has been made in unraveling the molecular and genetic heterogeneity of GBM and its implications to disease prognosis. There is now consensus related to the critical need to incorporate tumor heterogeneity into the design of therapeutic approaches. Recent data also indicates that an efficacious treatment strategy will need to be combinatorial and personalized to the tumor genetic signature.

Epidemiological trends of histopathologically WHO classified CNS tumors in developing countries: systematic review

BACKGROUND

Many developing countries are lagging behind in reporting epidemiological data for individual central nervous system (CNS) tumors. This paper aimed to elicit patterns for the epidemiology of individual World Health Organization (WHO) classified CNS tumors in countries registered by WHO as "developing".

MATERIALS AND METHODS

Cyber search was carried out through 66 cancer networks/registries and 181 PubMed published papers that reported counts of CNS tumors for the period of 2009-2012. The relationship between the natural log of incidence Age Standardized Rate (ASR) reported by Globocan and Latitude/ Longitude was investigated.

RESULTS

Registries for 21 countries displayed information related to CNS tumors. In contrast tends for classified CNS tumor cases were identified for 38 countries via 181 PubMed publications. Extracted data showed a majority of unclassified reported cases [PubMed (38 countries, 45.7%), registries (21 countries, 96.1%)]. For classified tumors, astrocytic tumors were the most frequently reported type [PubMed (38 countries, 1,245 cases, 15.7%), registries (21 countries, 627 cases, 1.99%]. A significant linear regression relationship emerged between latitudes and reported cases of CNS tumors.

CONCLUSIONS

Previously unreported trends of frequencies for individually classified CNS tumors were elucidated and a possible link of CNS tumors occurrence with geographical location emerged.

Linkage between Twist1 and Bmi1: molecular mechanism of cancer metastasis/stemness and clinical implications

Cancer metastasis is the major cause of cancer-related death despite significant improvements in multimodal cancer therapy. Epithelial-mesenchymal transition (EMT), a major mechanism of cancer metastasis, is a process that generates cells with stem cell-like properties (cancer stemness). Cancer stemness is a concept that describes a minor population of cells (cancer stem cells) residing within a tumour that are able to self-renew and are resistant to conventional therapy. The mechanisms delineating the generation of cancer stemness and its connection to cancer metastasis remain largely unknown. Twist1 is an EMT regulator and increased Twist1 expression, which has prognostic significance in various human cancers, has been widely reported. Bmi1 is a critical component of polycomb repressive complex (PRC) 1, which maintains self-renewal and stemness. Bmi1 is frequently overexpressed in different types of human cancers and can induce drug resistance (Table 2). Recent studies have shown that Twist1 directly activates Bmi1 expression and that these two molecules function together to mediate cancer stemness and EMT. These results present a unique mechanism of EMT-induced cancer metastasis and stemness. Further investigation of the mechanisms of EMT-mediated cancer metastasis and stemness will contribute to the management and treatment of metastatic cancers.

Epigenetic changes in pediatric solid tumors: promising new targets

Cancer is being reinterpreted in the light of recent discoveries related to the histone code and the dynamic nature of epigenetic regulation and control of gene programs during development, as well as insights gained from whole cancer genome sequencing. Somatic mutations in or deregulated expression of genes that encode chromatin-modifying enzymes are being identified with high frequency. Nowhere is this more relevant than in pediatric embryonal solid tumors. A picture is emerging that shows that classic genetic alterations associated with these tumors ultimately converge on the epigenome to dysregulate developmental programs. In this review, we relate how alterations in components of the transcriptional machinery and chromatin modifier genes contribute to the initiation and progression of pediatric solid tumors. We also discuss how dramatic progress in our understanding of the fundamental mechanisms that contribute to epigenetic deregulation in cancer is providing novel avenues for targeted cancer therapy.

Prognostic relevance of c-Myc and BMI1 expression in patients with glioblastoma

Although the c-Myc oncogene is frequently deregulated in human cancer, its involvement in the pathogenesis of glioblastoma is not clear. We conducted immunohistochemical analysis of the expression of c-Myc, polycomb ring finger oncogene (BMI1), and acetylation of the lysine 9 (H3K9Ac) of histone 3 in 48 patients with glioblastoma who underwent surgery followed by radiotherapy and temozolomide treatment. The expression of c-Myc, BMI1, and H3K9ac was correlated with clinical characteristics and outcome. We found that overexpression of c-Myc was significantly associated with that of BMI1 (P = .009), and that patients who harbored glioblastomas overexpressing c-Myc and BMI1 showed significantly longer overall survival (P < .0001 and P = .0009, respectively). Our results provide the first evidence of the prognostic value of c-Myc and associated genes in patients with glioblastoma. The favorable effect of c-Myc and BMI1 expression on survival is likely mediated by the sensitization of cancer cells to radiotherapy and temozolomide through the activation of apoptotic pathways.

Medulloblastoma stem cells: modeling tumor heterogeneity

Brain tumors represent the leading cause of childhood cancer mortality, with medulloblastoma (MB) being the most frequent malignant tumor. In this review we discuss the morphological and molecular heterogeneity of this malignant childhood brain tumor and how this key feature has implicated the presence of a MB stem cell. We focus on evidence from cerebellar development, histopathological and molecular subtypes of MB, the recent identification of brain tumor-initiating cells (BTICs, also referred to as MB stem cells), and the current limitations in studying the interplay between MB stem cells and tumor heterogeneity.

Medulloblastoma stem cells: where development and cancer cross pathways

Brain tumors are the leading cause of childhood cancer mortality, with medulloblastoma (MB) representing the most frequent malignant tumor. The recent molecular classification of MB has reconceptualized the heterogeneity that exists within pathological subtypes by giving context to the role of key developmental signaling pathways in MB pathogenesis. The identification of cancer stem cell (CSC) populations, termed brain tumor-initiating cells (BTICs), in MB has provided novel cellular targets for the study of these aberrantly activated signaling pathways, namely, Sonic hedgehog (Shh) and Wingless (Wnt), along with the identification of novel BTIC self-renewal pathways. In this review, we discuss recent evidence for the presence of a MB stem cell that drives tumorigenesis in this malignant childhood tumor. We focus on evidence from cerebellar development, the recent identification of BTICs, the presence of activated developmental signaling pathways in MB, the role of epigenetic stem cell regulatory mechanisms, and how these developmental and epigenetic pathways may be targeted for novel therapeutic options.

Sonic hedgehog regulates Bmi1 in human medulloblastoma brain tumor-initiating cells

Bmi1 is a key stem cell regulatory gene implicated in the pathogenesis of many aggressive cancers, including medulloblastoma. Overexpression of Bmi1 promotes cell proliferation and is required for hedgehog (Hh) pathway-driven tumorigenesis. This study aimed to determine if Sonic hedgehog (Shh) modulates the key stem cell regulatory gene Bmi1 in childhood medulloblastoma brain tumor-initiating cells (BTICs). Although current literature suggests that there is a correlation between Shh pathway genes and Bmi1 expression, it is unclear whether there is indeed a direct regulatory mechanism. To address whether Shh induces expression of Bmi1, stem cell-enriched populations from medulloblastoma cell lines and primary samples were treated with Shh ligand and KAAD-cyclopamine (Shh antagonist). Our data indicate that Bmi1 expression positively correlates with increasing Shh ligand concentrations. Chromatin immunoprecipitation reveals that Gli1 preferentially binds to the Bmi1 promoter, and Bmi1 transcript levels are increased and decreased by Gli1 overexpression and downregulation, respectively. Knockdown experiments of Bmi1 in vitro and in vivo demonstrate that Hh signaling not only drives Bmi1 expression, but a feedback mechanism exists wherein downstream effectors of Bmi1 may, in turn, activate Hh pathway genes. These findings implicate Bmi1 and Hh as mutually indispensable pathways in medulloblastoma BTIC maintenance. Recent molecular characterization of medulloblastoma also reveals that Bmi1 is overexpressed across all subgroups of medulloblastoma, particularly in the most aggressive subtypes. Lastly, despite recent identification of BTIC markers, the molecular characterization of these cell populations remains unclear. In this work, we propose that the BTIC marker CD133 may segregate a cell population with a Hh-receptor phenotype, thus demonstrating a cell-cell interaction between the CD133+ Hh receptor cells and the CD133- Hh-secreting cells.