Loss of caspase-8 mRNA expression is common in childhood primitive neuroectodermal brain tumour/medulloblastoma

Targeting anti-apoptotic mechanisms in tumour cells: Strategies for enhancing Cancer therapy

Anti-cancer drug's cytotoxicity is determined by their ability to induce predetermined cell demise, commonly called apoptosis. The cancer-causing cells are able to evade cell death, which has been affiliated with both malignancy as well as resistance to cancer treatments. In order to avoid cell death, cancerous tumour cells often produce an abundance of anti-apoptotic proteins, becoming "dependent" on them. Consequently, protein inhibitors of cell death may prove to be beneficial as pharmacological targets for the future creation of cancer therapies. This article examines the molecular routes of apoptosis, its clinical manifestations, anti-cancer therapy options that target the intrinsic mechanism of apoptosis, proteins that prevent cell death, and members of the B-lymphoma-2 subset. In addition, novel approaches to cell death are highlighted, including how curcumin mitigates chemotherapy-induced apoptosis in healthy tissues and the various ways melatonin modifies apoptosis to improve cancer treatment efficacy, particularly through the TNF superfamily. Cancer treatment-induced increases in anti-apoptotic proteins lead to drug resistance; yet, ligands that trigger cell death by inhibiting these proteins are expected to improve chemotherapy's efficacy. The potential of frequency-modulated dietary phytochemicals as a cancer therapeutic pathway, including autophagy and apoptosis, is also explored. This approach may be more efficient than inhibition alone in overcoming drug resistance. Consequently, this method has the potential to allow for lower medication concentrations, reducing cytotoxicity and unwanted side effects.

Exploring the Molecular Complexity of Medulloblastoma: Implications for Diagnosis and Treatment

Medulloblastoma is the most common malignant brain tumor in children. Over the last few decades, significant progress has been made in revealing the key molecular underpinnings of this disease, leading to the identification of distinct molecular subgroups with different clinical outcomes. In this review, we provide an update on the molecular landscape of medulloblastoma and treatment strategies. We discuss the four main molecular subgroups (WNT-activated, SHH-activated, and non-WNT/non-SHH groups 3 and 4), highlighting the key genetic alterations and signaling pathways associated with each entity. Furthermore, we explore the emerging role of epigenetic regulation in medulloblastoma and the mechanism of resistance to therapy. We also delve into the latest developments in targeted therapies and immunotherapies. Continuing collaborative efforts are needed to further unravel the complex molecular mechanisms and profile optimal treatment for this devastating disease.

Epigenetics and immune cells in medulloblastoma

Medulloblastoma (MB) is a highly malignant childhood tumor of the cerebellum. Transcriptional and epigenetic signatures have classified MB into four molecular subgroups, further stratified into biologically different subtypes with distinct somatic copy-number aberrations, driver genes, epigenetic alterations, activated pathways, and clinical outcomes. The brain tumor microenvironment (BTME) is of importance to regulate a complex network of cells, including immune cells, involved in cancer progression in brain malignancies. MB was considered with a “cold” immunophenotype due to the low influx of immune cells across the blood brain barrier (BBB). Recently, this assumption has been reconsidered because of the identification of infiltrating immune cells showing immunosuppressive phenotypes in the BTME of MB tumors. Here, we are providing a comprehensive overview of the current status of epigenetics alterations occurring during cancer progression with a description of the genomic landscape of MB by focusing on immune cells within the BTME. We further describe how new immunotherapeutic approaches could influence concurring epigenetic mechanisms of the immunosuppressive cells in BTME. In conclusion, the modulation of these molecular genetic complexes in BTME during cancer progression might enhance the therapeutic benefit, thus firing new weapons to fight MB.

Targeting the apoptosis pathway to treat tumours of the paediatric nervous system

New, more effective therapeutics are required for the treatment of paediatric cancers. Current treatment protocols of cytotoxic treatments including chemotherapy trigger cancer-cell death by engaging the apoptosis pathway, and chemotherapy efficacy is frequently impeded by apoptosis dysregulation. Apoptosis dysregulation, through genetic or epigenetic mechanisms, is a feature of many cancer types, and contributes to reduced treatment response, disease progression and ultimately treatment resistance. Novel approaches are required to overcome dysregulated apoptosis signalling, increase the efficacy of cancer treatment and improve patient outcomes. Here, we provide an insight into current knowledge of how the apoptosis pathway is dysregulated in paediatric nervous system tumours, with a focus on TRAIL receptors, the BCL-2 proteins and the IAP family, and highlight preclinical evidence demonstrating that pharmacological manipulation of the apoptosis pathway can restore apoptosis signalling and sensitise cancer cells to treatment. Finally, we discuss the potential clinical implications of these findings.

The Most Competent Plant-Derived Natural Products for Targeting Apoptosis in Cancer Therapy

Cancer is a challenging problem for the global health community, and its increasing burden necessitates seeking novel and alternative therapies. Most cancers share six basic characteristics known as "cancer hallmarks", including uncontrolled proliferation, refractoriness to proliferation blockers, escaping apoptosis, unlimited proliferation, enhanced angiogenesis, and metastatic spread. Apoptosis, as one of the best-known programmed cell death processes, is generally promoted through two signaling pathways, including the intrinsic and extrinsic cascades. These pathways comprise several components that their alterations can render an apoptosis-resistance phenotype to the cell. Therefore, targeting more than one molecule in apoptotic pathways can be a novel and efficient approach for both identifying new anticancer therapeutics and preventing resistance to therapy. The main purpose of this review is to summarize data showing that various plant extracts and plant-derived molecules can activate both intrinsic and extrinsic apoptosis pathways in human cancer cells, making them attractive candidates in cancer treatment.

Apoptosis as anticancer mechanism: function and dysfunction of its modulators and targeted therapeutic strategies

Apoptosis is a form of programmed cell death that results in the orderly and efficient removal of damaged cells, such as those resulting from DNA damage or during development. Apoptosis can be triggered by signals from within the cell, such as genotoxic stress, or by extrinsic signals, such as the binding of ligands to cell surface death receptors. Deregulation in apoptotic cell death machinery is an hallmark of cancer. Apoptosis alteration is responsible not only for tumor development and progression but also for tumor resistance to therapies. Most anticancer drugs currently used in clinical oncology exploit the intact apoptotic signaling pathways to trigger cancer cell death. Thus, defects in the death pathways may result in drug resistance so limiting the efficacy of therapies. Therefore, a better understanding of the apoptotic cell death signaling pathways may improve the efficacy of cancer therapy and bypass resistance. This review will highlight the role of the fundamental regulators of apoptosis and how their deregulation, including activation of anti-apoptotic factors (i.e., Bcl-2, Bcl-xL, etc) or inactivation of pro-apoptotic factors (i.e., p53 pathway) ends up in cancer cell resistance to therapies. In addition, therapeutic strategies aimed at modulating apoptotic activity are briefly discussed.

Synergistic anti-cancer effects of epigenetic drugs on medulloblastoma cells

PURPOSE

Medulloblastomas are aggressive brain malignancies. While considerable progress has been made in the treatment of medulloblastoma patients with respect to overall survival, these patients are still at risk of developing neurologic and cognitive deficits as a result of anti-cancer therapies. It is hypothesized that targeted molecular therapies represent a better treatment option for medulloblastoma patients. Therefore, the aim of the present study was to test a panel of epigenetic drugs for their effect on medulloblastoma cells under mild hypoxic conditions that reflect the physiological concentrations of oxygen in the brain.

METHODS

Protein levels of histone deacetylase 1 (HDAC1) and DNA methyltransferase 1 (DNMT1) in medulloblastoma-derived cells (Daoy and D283 Med), as well as in developing and differentiated brain cells, were determined and compared. Class I and II histone deacetylase inhibitors (HDACi) and a DNMT inhibitor, 5-aza-2'-deoxycytidine (5-aza-dC), were applied to Daoy and D283 Med cells, and their effects were studied using viability, apoptosis and cancer sphere assays.

RESULTS

We found that in HDAC1 and DNMT1 overexpressing medulloblastoma-derived cells, cell death was induced under various epigenetic drug conditions tested. At low HDACi concentrations, however, a pro-proliferative effect was observed. Parthenolide, a drug that affects cancer stem cells, was found to be efficient in inducing cell death in both cell lines tested. In contrast, we found that Daoy cells were more resistant to 5-aza-dC than D283 Med cells. When suberoylanilide hydroxamic acid (SAHA) and parthenolide were individually applied to both cell lines in combination with 5-aza-dC, a synergistic effect on cell survival was observed.

CONCLUSIONS

Our current results suggest that the application of HDACi in combination with drugs that target DNMT may represent a promising option for the treatment of medulloblastoma.

Thymoquinone inhibits growth of human medulloblastoma cells by inducing oxidative stress and caspase-dependent apoptosis while suppressing NF-κB signaling and IL-8 expression

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. The transcription factor NF-κB is overexpressed in human MB and is a critical factor for MB tumor growth. NF-κB is known to regulate the expression of interleukin-8 (IL-8), the chemokine that enhances cancer cell growth and resistance to chemotherapy. We have recently shown that thymoquinone (TQ) suppresses growth of hepatocellular carcinoma cells in part by inhibiting NF-κB signaling. Here we sought to extend these studies in MB cells and show that TQ suppresses growth of MB cells in a dose- and time-dependent manner, causes G2M cell cycle arrest, and induces apoptosis. TQ significantly increased generation of reactive oxygen species (ROS), while pretreatment of MB cells with the ROS scavenger N-acetylcysteine (NAC) abrogated TQ-induced cell death and apoptosis, suggesting that TQ-induced cell death and apoptosis are oxidative stress-mediated. TQ inhibitory effects were associated with inhibition of NF-κB and altered expression of its downstream effectors IL-8 and its receptors, the anti-apoptotic Bcl-2, Bcl-xL, X-IAP, and FLIP, as well as the pro-apoptotic TRAIL-R1, caspase-8, caspase-9, Bcl-xS, and cytochrome c. TQ-triggered apoptosis was substantiated by up-regulation of the executioner caspase-3 and caspase-7, as well as cleavage of the death substrate poly(ADP-ribose)polymerase. Interestingly, pretreatment of MB cells with NAC or the pan-caspase inhibitor zVAD-fmk abrogated TQ-induced apoptosis, loss of cyclin B1 and NF-κB activity, suggesting that these TQ-mediated effects are oxidative stress- and caspase-dependent. These findings reveal that TQ induces both extrinsic and intrinsic pathways of apoptosis in MB cells, and suggest its potential usefulness in the treatment of MB.

Caspase Allostery and Conformational Selection

The role of caspase proteases in regulated processes such as apoptosis and inflammation has been studied for more than two decades, and the activation cascades are known in detail. Apoptotic caspases also are utilized in critical developmental processes, although it is not known how cells maintain the exquisite control over caspase activity in order to retain subthreshold levels required for a particular adaptive response while preventing entry into apoptosis. In addition to active site-directed inhibitors, caspase activity is modulated by post-translational modifications or metal binding to allosteric sites on the enzyme, which stabilize inactive states in the conformational ensemble. This review provides a comprehensive global view of the complex conformational landscape of caspases and mechanisms used to select states in the ensemble. The caspase structural database provides considerable detail on the active and inactive conformations in the ensemble, which provide the cell multiple opportunities to fine tune caspase activity. In contrast, the current database on caspase modifications is largely incomplete and thus provides only a low-resolution picture of global allosteric communications and their effects on the conformational landscape. In recent years, allosteric control has been utilized in the design of small drug compounds or other allosteric effectors to modulate caspase activity.

Trailing TRAIL Resistance: Novel Targets for TRAIL Sensitization in Cancer Cells

Resistance to chemotherapeutic drugs is the major hindrance in the successful cancer therapy. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of ligands, which initiates apoptosis in cancer cells through interaction with the death receptors DR4 and DR5. TRAIL is perceived as an attractive chemotherapeutic agent as it specifically targets cancer cells while sparing the normal cells. However, TRAIL therapy has a major limitation as a large number of the cancer develop resistance toward TRAIL and escape from the destruction by the immune system. Therefore, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. Although, various molecular targets leading to TRAIL resistance are well-studied, recent studies have implicated that the contribution of some key cellular processes toward TRAIL resistance need to be fully elucidated. These processes primarily include aberrant protein synthesis, protein misfolding, ubiquitin regulated death receptor expression, metabolic pathways, epigenetic deregulation, and metastasis. Novel synthetic/natural compounds that could inhibit these defective cellular processes may restore the TRAIL sensitivity and combination therapies with such compounds may resensitize TRAIL resistant cancer cells toward TRAIL-induced apoptosis. In this review, we have summarized the key cellular processes associated with TRAIL resistance and their status as therapeutic targets for novel TRAIL-sensitizing agents.

Microenvironmental Influences on Metastasis Suppressor Expression and Function during a Metastatic Cell's Journey

Metastasis is the process of primary tumor cells breaking away and colonizing distant secondary sites. In order for a tumor cell growing in one microenvironment to travel to, and flourish in, a secondary environment, it must survive a series of events termed the metastatic cascade. Before departing the primary tumor, cells acquire genetic and epigenetic changes that endow them with properties not usually associated with related normal differentiated cells. Those cells also induce a subset of bone marrow-derived stem cells to mobilize and establish pre-metastatic niches [1]. Many tumor cells undergo epithelial-to-mesenchymal transition (EMT), where they transiently acquire morphologic changes, reduced requirements for cell-cell contact and become more invasive [2]. Invasive tumor cells eventually enter the circulatory (hematogenous) or lymphatic systems or travel across body cavities. In transit, tumor cells must resist anoikis, survive sheer forces and evade detection by the immune system. For blood-borne metastases, surviving cells then arrest or adhere to endothelial linings before either proliferating or extravasating. Eventually, tumor cells complete the process by proliferating to form a macroscopic mass [3].Up to 90 % of all cancer related morbidity and mortality can be attributed to metastasis. Surgery manages to ablate most primary tumors, especially when combined with chemotherapy and radiation. But if cells have disseminated, survival rates drop precipitously. While multiple parameters of the primary tumor are predictive of local or distant relapse, biopsies remain an imperfect science. The introduction of molecular and other biomarkers [4, 5] continue to improve the accuracy of prognosis. However, the invasive procedure introduces new complications for the patient. Likewise, the heterogeneity of any tumor population [3, 6, 7] means that sampling error (i.e., since it is impractical to examine the entire tumor) necessitates further improvements.In the case of breast cancer, for example, women diagnosed with stage I diseases (i.e., no evidence of invasion through a basement membrane) still have a ~30 % likelihood of developing distant metastases [8]. Many physicians and patients opt for additional chemotherapy in order to "mop up" cells that have disseminated and have the potential to grow into macroscopic metastases. This means that ~ 70 % of patients receive unnecessary therapy, which has undesirable side effects. Therefore, improving prognostic capability is highly desirable.Recent advances allow profiling of primary tumor DNA sequences and gene expression patterns to define a so-called metastatic signature [9-11], which can be predictive of patient outcome. However, the genetic changes that a tumor cell must undergo to survive the initial events of the metastatic cascade and colonize a second location belie a plasticity that may not be adequately captured in a sampling of heterogeneous tumors. In order to tailor or personalize patient treatments, a more accurate assessment of the genetic profile in the metastases is needed. Biopsy of each individual metastasis is not practical, safe, nor particularly cost-effective. In recent years, there has been a resurrection of the notion to do a 'liquid biopsy,' which essentially involves sampling of circulating tumor cells (CTC) and/or cell free nucleic acids (cfDNA, including microRNA (miRNA)) present in blood and lymph [12-16].The rationale for liquid biopsy is that tumors shed cells and/or genetic fragments into the circulation, theoretically making the blood representative of not only the primary tumor but also distant metastases. Logically, one would predict that the proportion of CTC and/or cfDNA would be proportionate to the likelihood of developing metastases [14]. While a linear relationship does not exist, the information within CTC or cfDNA is beginning to show great promise for enabling a global snapshot of the disease. However, the CTC and cfDNA are present at extremely low levels. Nonetheless, newer technologies capture enough material to enrich and sequence the patient's DNA or quantification of some biomarkers.Among the biomarkers showing great promise are metastasis suppressors which, by definition, block a tumor cell's ability to complete the metastatic process without prohibiting primary tumor growth [17]. Since the discovery of the first metastasis suppressor, Nm23, more than 30 have been functionally characterized. They function at various stages of the metastatic cascade, but their mechanisms of action, for the most part, remain ill-defined. Deciphering the molecular interactions of functional metastasis suppressors may provide insights for targeted therapies when these regulators cease to function and result in metastatic disease.In this brief review, we summarize what is known about the various metastasis suppressors and their functions at individual steps of the metastatic cascade (Table 1). Some of the subdivisions are rather arbitrary in nature, since many metastasis suppressors affect more than one step in the metastatic cascade. Nonetheless what emerges is a realization that metastasis suppressors are intimately associated with the microenvironments in which cancer cells find themselves [18].

The neural adhesion molecule L1CAM confers chemoresistance in human glioblastomas

Glioblastoma multiforme (GBM) represents the most common and malignant brain tumor. GBM tissues exhibit elevated expression of the transforming growth factor-beta1 (TGF-β1) and the adhesion molecule L1CAM. This study investigated the mechanism of L1CAM regulation in GBM cells and its role in the mediation of chemoresistance. L1CAM expression levels varied in GBM cells being highest in A172 cells and low in T98G cells. Inhibition of TGF-β1 signaling in A172 cells reduced L1CAM expression and vice versa stimulation with exogenous TGF-β1 led to upregulation of L1CAM in T98G cells. Additionally, TGF-β1 and L1CAM expression increased during differentiation of glioma stem-like cells. L1CAM expressing GBM cells and differentiated glioma stem-like cells showed a reduced apoptotic response after treatment with the chemotherapeutic drug temozolomide. Accordingly, siRNA-mediated knock-down of L1CAM in A172 cells and differentiated glioma stem-like cells increased chemosensitivity, whereas overexpression of L1CAM in T98G cells and glioma spheroids diminished the apoptotic response. Elevated L1CAM expression caused a diminished expression of caspase-8 in GBM and differentiated glioma stem-like cells. These data show that TGF-β1 dependent upregulation of L1CAM expression in GBM cells leads to the downregulation of caspase-8 and apoptosis resistance pointing to L1CAM as potential target for improved therapy of GBM patients.

Beyond Genetics in Glioma Pathways: The Ever-Increasing Crosstalk between Epigenomic and Genomic Events

Diffuse gliomas are the most frequent brain tumor in adults. This group of brain neoplasms, ranging from histologically benign to aggressive malignant forms, represents a challenge in modern neurooncology because of the diffuse infiltrative growth pattern and the inherent tendency to relapse as a more malignant tumor. Once the disease achieves the stage of glioblastoma multiforme (GBM), the prognosis of patients is dismal and the median survival time is 15 months. Exhaustive genetic analyses have revealed a variety of deregulated genetic pathways involved in DNA repair, apoptosis, cell migration/adhesion, and cell cycle. Recently, investigation of epigenetic alterations in gliomas has contributed to depict the complexity of the molecular lesions leading to these malignancies. Even though, the efficacy of the state-of-the-art form of chemotherapy in malignant gliomas with temozolomide is based on the methylation-associated silencing of the DNA repair gene MGMT. Nevertheless, the whole scenario including global DNA hypomethylation, aberrant promoter hypermethylation, histone modification, chromatin states, and the role of noncoding RNAs in gliomas has only been partially revealed. We discuss the repercussion of epigenetic alterations underlying deregulated molecular pathways in the pathogenesis and evolution of gliomas and their impact on management of patients.

The epigenetics of brain tumors

Glioblastoma, medulloblastoma, and ependymoma represent molecularly and clinically diverse forms of adult and pediatric brain tumors. While each tumor displays genetic, transcriptional, and cytogenetic heterogeneity, the epigenome of these tumors has only recently emerged as a major field of interest. Here, we describe advances in our understanding of the epigenetics of brain tumors, focusing on DNA methylation, histone modifications, and microRNA deregulation which contribute to the pathogenesis of these diseases.

Towards tailored therapy of glioblastoma multiforme

Gliobastoma multiform (GBM) is the most common and aggressive brain tumor, which is characterized by its infiltrative nature. Current standard therapy for GBMs consists of surgery followed by radiotherapy combined with the alkylating agent temozolomide (TMZ). Recent clinical trials have demonstrated that this chemo-irradiation approach results in a significant increase in survival compared to radiotherapy alone. Nevertheless, due to tumor recurrence, the median survival time is still limited to approximately 15 months. Recently, several studies have focused on aberrant signal transduction in GBM, resistance mechanisms of GBM to TMZ and to radiotherapy. Attention has been focused on molecular targets including phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, protein kinase C (pKC) pathway, Ras/mitogen-activated protein kinase pathway (MAPK), Wnt pathway and intrinsic or extrinsic apoptosis pathways. In addition, research has been directed to radiotherapy and radiosensitizing agents, and cancer gene therapy as well. This article will address several resistance mechanisms of GBM to chemotherapy and radiotherapy and the recent preclinical and clinical studies on targeted therapy.

Cambogin is preferentially cytotoxic to cells expressing PDGFR

Platelet-derived growth factor receptors (PDGFRs) have been implicated in a wide array of human malignancies, including medulloblastoma (MB), the most common brain tumor of childhood. Although significant progress in MB biology and therapeutics has been achieved during the past decades, MB remains a horrible challenge to the physicians and researchers. Therefore, novel inhibitors targeting PDGFR signaling pathway may offer great promise for the treatment of MB. In the present study, we investigated the cytotoxicity and mechanisms of cambogin in Daoy MB cells. Our results show that cambogin triggers significant S phase cell cycle arrest and apoptosis via down regulation of cyclin A and E, and activation of caspases. More importantly, further mechanistic studies demonstrated that cambogin inhibits PDGFR signaling in Daoy and genetically defined mouse embryo fibroblast (MEF) cell lines. These results suggest that cambogin is preferentially cytotoxic to cells expressing PDGFR. Our findings may provide a novel approach by targeting PDGFR signaling against MB.

TH1 predominance is associated with improved survival in pediatric medulloblastoma patients

Medulloblastoma, a primitive neuro-ectodermal tumor that arises in the posterior fossa, is the most common malignant brain tumor occurring in childhood. Even though 60-70% of children with medulloblastoma will be cured with intensive multimodal therapy, including surgery, radiotherapy, and chemotherapy, a significant proportion of surviving patients may suffer from long-term treatment-related sequelae. Therapeutic success is limited especially in younger children by radiotherapy-induced neurocognitive longterm deficits. In order to avoid or delay craniospinal radiotherapy, high-dose chemotherapy followed by autologous stem cell transplantation (HSCT) has become an established treatment modality. Data on the host immunologic environment in medulloblastoma patients are rare, notably data on cytokine expression and immune reconstitution in patients with medulloblastoma undergoing HSCT are lacking. In this present study, we therefore decided to prospectively assess immune function following 24 consecutive autologous HSCT in 17 children with medulloblastoma treated according to the German-Austrian-Swiss HIT-2000-protocol. TH1 predominance was found to be the most important factor for probability of survival. Already before HSCT, survivors showed higher IFNγ levels in sera as well as higher numbers of IFNγ-positive T-cells. After transplantation, this effect was even more pronounced. Patients with higher numbers of IFNγ- and TNFα-positive T-cells had a more favorable outcome at all analyzed time points. In addition, patients in complete remission (CR) before transplantation, known to have a better prognosis a priori, showed higher expression of IFNγ in T-cells. Taken together, this is the first report to demonstrate that high expression of IFNγ and TNFα in T-cells of medulloblastoma patients in the early post-transplant period correlates with a better prognosis. Our data point toward a potentially important influence of TH1-cytokine expression before and after transplantation on the survival of pediatric medulloblastoma patients.

The enigmatic roles of caspases in tumor development

One function ascribed to apoptosis is the suicidal destruction of potentially harmful cells, such as cancerous cells. Hence, their growth depends on evasion of apoptosis, which is considered as one of the hallmarks of cancer. Apoptosis is ultimately carried out by the sequential activation of initiator and executioner caspases, which constitute a family of intracellular proteases involved in dismantling the cell in an ordered fashion. In cancer, therefore, one would anticipate caspases to be frequently rendered inactive, either by gene silencing or by somatic mutations. From clinical data, however, there is little evidence that caspase genes are impaired in cancer. Executioner caspases have only rarely been found mutated or silenced, and also initiator caspases are only affected in particular types of cancer. There is experimental evidence from transgenic mice that certain initiator caspases, such as caspase-8 and -2, might act as tumor suppressors. Loss of the initiator caspase of the intrinsic apoptotic pathway, caspase-9, however, did not promote cellular transformation. These data seem to question a general tumor-suppressive role of caspases. We discuss several possible ways how tumor cells might evade the need for alterations of caspase genes. First, alternative splicing in tumor cells might generate caspase variants that counteract apoptosis. Second, in tumor cells caspases might be kept in check by cellular caspase inhibitors such as c-FLIP or XIAP. Third, pathways upstream of caspase activation might be disrupted in tumor cells. Finally, caspase-independent cell death mechanisms might abrogate the selection pressure for caspase inactivation during tumor development. These scenarios, however, are hardly compatible with the considerable frequency of spontaneous apoptosis occurring in several cancer types. Therefore, alternative concepts might come into play, such as compensatory proliferation. Herein, apoptosis and/or non-apoptotic functions of caspases may even promote tumor development. Moreover, experimental evidence suggests that caspases might play non-apoptotic roles in processes that are crucial for tumorigenesis, such as cell proliferation, migration, or invasion. We thus propose a model wherein caspases are preserved in tumor cells due to their functional contributions to development and progression of tumors.

Detailed analysis of expression and promoter methylation status of apoptosis-related genes in prostate cancer

Apoptosis is known to be involved in tumorigenesis and a defective ratio between cell proliferation and apoptosis may contribute to the emergence of a malignant phenotype. Transcriptional silencing of apoptosis-related genes associated with aberrant promoter methylation may impair the apoptotic machinery, ultimately leading to cancer development. Aberrant promoter methylation of numerous genes involved in many different pathways is frequent in prostate cancer. Our aim was to quantitatively assess the methylation status of several apoptosis-related genes in prostate adenocarcinoma (PCa) and its precursor lesion, high-grade prostatic intraepithelial neoplasia (HGPIN). First, 120 PCa and 39 HGPIN were screened for altered expression of BCL2, CASP8, CASP3, DAPK DR3, DR4, DR6, FAS, TMS1, TNFR2, using 28 benign prostate hyperplasias and 10 normal prostates as controls. Underexpressed genes were then assessed by quantitative methylation-specific PCR to determine the promoter methylation status. Finally, quantitative mRNA expression of aberrantly methylated genes was performed and methylation data was correlated with standard clinicopathologic parameters. DAPK, DR4 and TNFR2 were significantly overexpressed in HGPIN and PCa, whereas BCL2, TMS1, and FAS were downregulated. Although methylation levels were significantly higher for TMS1 and BCL2 (correlating with advanced stage), an inverse correlation with mRNA expression was found only for BCL2. We concluded that the apoptotic pathways are largely preserved in prostate carcinogenesis, in particular the extrinsic pathway, with the exception of FAS and TMS1, which are epigenetically downregulated. In addition, BCL2 was also found to be frequently silenced in PCa due to aberrant promoter methylation, thus supporting a future role for apoptosis-targeted therapy in prostate cancer.

Analysis of death receptor 5 and caspase-8 expression in primary and metastatic head and neck squamous cell carcinoma and their prognostic impact

Death receptor 5 (DR5) and caspase-8 are major components in the extrinsic apoptotic pathway. The alterations of the expression of these proteins during the metastasis of head and neck squamous cell carcinoma (HNSCC) and their prognostic impact have not been reported. The present study analyzes the expression of DR5 and caspase-8 by immunohistochemistry (IHC) in primary and metastatic HNSCCs and their impact on patient survival. Tumor samples in this study included 100 primary HNSCC with no evidence of metastasis, 100 primary HNSCC with lymph node metastasis (LNM) and 100 matching LNM. IHC analysis revealed a significant loss or downregulation of DR5 expression in primary tumors with metastasis and their matching LNM compared to primary tumors with no evidence of metastasis. A similar trend was observed in caspase-8 expression although it was not statistically significant. Downregulation of caspase-8 and DR5 expression was significantly correlated with poorly differentiated tumors compared to moderately and well differentiated tumors. Univariate analysis indicates that, in HNSCC with no metastasis, higher expression of caspase-8 significantly correlated with better disease-free survival and overall survival. However, in HNSCC with LNM, higher caspase-8 expression significantly correlated with poorer disease-free survival and overall survival. Similar results were also generated when we combined both DR5 and caspase-8. Taken together, we suggest that both DR5 and caspase-8 are involved in regulation of HNSCC metastasis. Our findings warrant further investigation on the dual role of caspase-8 in cancer development.

Mathematical model of the Drosophila circadian clock: loop regulation and transcriptional integration

Eukaryotic circadian clocks include interconnected positive and negative feedback loops. The clock-cycle dimer (CLK-CYC) and its homolog, CLK-BMAL1, are key transcriptional activators of central components of the Drosophila and mammalian circadian networks, respectively. In Drosophila, negative loops include period-timeless and vrille; positive loops include par domain protein 1. Clockwork orange (CWO) is a recently discovered negative transcription factor with unusual effects on period, timeless, vrille, and par domain protein 1. To understand the actions of this protein, we introduced a new system of ordinary differential equations to model regulatory networks. The model is faithful in the sense that it replicates biological observations. CWO loop actions elevate CLK-CYC; the transcription of direct targets responds by integrating opposing signals from CWO and CLK-CYC. Loop regulation and integration of opposite transcriptional signals appear to be central mechanisms as they also explain paradoxical effects of period gain-of-function and null mutations.

A new caspase-8 isoform caspase-8s increased sensitivity to apoptosis in Jurkat cells

Caspase-8 is a key initiator of death receptor-induced apoptosis. Here we report a novel short isoform of caspase-8 (caspase-8s), which encodes the first (Death Effector Domain) DED and part of the second DED, missing the C-terminal caspase domain. In vivo binding assays showed that transfected caspase-8s bound to (Fas-associated death domain protein) FADD, the adaptor protein in (death-induced signal complex) DISC. To investigate the potential effects of caspase-8s on cell apoptosis, Jurkat cells were stably transfected with caspase-8s. Overexpression of caspase-8s increased sensitivity to the apoptotic stimuli, Fas-agonistic antibody CH11. These results suggest that caspase-8s may act as a promoter of apoptosis through binding to FADD and is involved in the regulation of apoptosis. In addition, the results also indicate that the first DED was an important structure mediating combination between caspase-8 and FADD.

Reactivation of death receptor 4 (DR4) expression sensitizes medulloblastoma cell lines to TRAIL

OBJECT

Apoptosis, a key cellular response to therapeutic agents is often inactivated in tumor cells. In this study, we evaluated the expression of the tumor necrosis family of death receptors, DR4 and DR5, in medulloblastoma tumor samples and cell lines to determine if epigenetic modulation of gene expression could sensitize tumor cell lines to TRAIL-mediated apoptosis.

METHODS

Human medulloblastoma samples and cell lines were analyzed for DR4 and DR5 expression by quantitative PCR and immunofluorescence assays. Cell lines with downregulated expression of one or both genes were treated with the histone deacetylase inhibitor, MS-275, and the expression of DR4 and DR5 measured by quantitative PCR, Western blotting, flow cytometry and chromatin immunoprecipitation assays. Induction of apoptosis in the presence of MS-275 was evaluated by TUNEL assay and its ability to augment TRAIL-mediated cytotoxicity was determined by MTT assays, Western blotting and flow cytometry.

RESULTS

Compared to normal cerebellum, DR4, but not DR5 expression was consistently downregulated in medulloblastoma tumor samples and in Daoy and D283 cell lines. Interestingly, MS-275 decreased cell growth and induced apoptosis in Daoy and D283 cells. In Daoy cells, this coincided with increased histone H3 and H4 acetylation at the DR4 promoter and enhanced DR4 gene and protein expression as well as elevated Caspase-8 activity. The involvement of DR4 in the cellular response to MS-275 was further confirmed by the observation that knockdown of DR4 and FADD abrogated apoptosis. Further, addition of TRAIL to MS-275 treated cells resulted in an enhancement of apoptosis, suggesting that the upregulated death receptors were functional.

CONCLUSION

Our study provides an understanding of the role of DR4 in apoptosis of medulloblastoma cell lines and suggests a potential contribution of aberrant histone deacetylation to the resistance of medulloblastoma cells to therapeutic death.

Hepatocyte growth factor enhances death receptor-induced apoptosis by up-regulating DR5

BACKGROUND

Hepatocyte growth factor (HGF) and its receptor c-MET are commonly expressed in malignant gliomas and embryonic neuroectodermal tumors including medulloblastoma and appear to play an important role in the growth and dissemination of these malignancies. Dependent on cell context and the involvement of specific downstream effectors, both pro- and anti-apoptotic effects of HGF have been reported.

METHODS

Human medulloblastoma cells were treated with HGF for 24-72 hours followed by death receptor ligand TRAIL (Tumor necrosis factor-related apoptosis-inducing ligand) for 24 hours. Cell death was measured by MTT and Annexin-V/PI flow cytometric analysis. Changes in expression levels of targets of interest were measured by Northern blot analysis, quantitative reverse transcription-PCR, Western blot analysis as well as immunoprecipitation.

RESULTS

In this study, we show that HGF promotes medulloblastoma cell death induced by TRAIL. TRAIL alone triggered apoptosis in DAOY cells and death was enhanced by pre-treating the cells with HGF for 24-72 h prior to the addition of TRAIL. HGF (100 ng/ml) enhanced TRAIL (10 ng/ml) induced cell death by 36% (P<0.001). No cell death was associated with HGF alone. Treating cells with PHA-665752, a specific c-Met receptor tyrosine kinase inhibitor, significantly abrogated the enhancement of TRAIL-induced cell death by HGF, indicating that its death promoting effect requires activation of its canonical receptor tyrosine kinase. Cell death induced by TRAIL+HGF was predominately apoptotic involving both extrinsic and intrinsic pathways as evidenced by the increased activation of caspase-3, 8, 9. Promotion of apoptosis by HGF occurred via the increased expression of the death receptor DR5 and enhanced formation of death-inducing signal complexes (DISC).

CONCLUSION

Taken together, these and previous findings indicate that HGF:c-Met pathway either promotes or inhibits medulloblastoma cell death via pathway and context specific mechanisms.

TRAIL recombinant adenovirus triggers robust apoptosis in multidrug-resistant HL-60/Vinc cells preferentially through death receptor DR5

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic because of its highly selective apoptosis-inducing action on neoplastic versus normal cells. However, some cancer cells express resistance to recombinant soluble TRAIL. To overcome this problem, we used a TRAIL adenovirus (Ad5/35-TRAIL) to induce apoptosis in a drug-sensitive and multidrug-resistant variant of HL-60 leukemia cells and determined the molecular mechanisms of Ad5/35-TRAIL-induced apoptosis. Ad5/35-TRAIL did not induce apoptosis in normal human lymphocytes, but caused massive apoptosis in acute myelocytic leukemia cells. It triggered more efficient apoptosis in drug-resistant HL-60/Vinc cells than in HL-60 cells. Treating the cells with anti-DR4 and anti-DR5 neutralizing antibodies (particularly anti-DR5) reduced, whereas anti-DcR1 antibody enhanced, the apoptosis triggered by Ad5/35-TRAIL. Whereas Ad5/35-TRAIL induced apoptosis in both cell lines through activation of caspase-3 and caspase-10, known to link the cell death receptor pathway to the mitochondrial pathway, it triggered increased mitochondrial membrane potential change (m) only in HL-60/Vinc cells. Ad5/35-TRAIL also increased the production of reactive oxygen species, which play an important role in apoptosis. Therefore, using Ad5/35-TRAIL may be an effective therapeutic strategy for eliminating TRAIL-resistant malignant cells and these studies may provide clues to treat and eradicate acute myelocytic leukemias.

Dysregulation of apoptotic signaling in cancer: molecular mechanisms and therapeutic opportunities

Apoptosis is a tightly regulated cell suicide program that plays an essential role in the maintenance of tissue homeostasis by eliminating unnecessary or harmful cells. Defects in this native defense mechanism promote malignant transformation and frequently confer chemoresistance to transformed cells. Indeed, the evasion of apoptosis has been recognized as a hallmark of cancer. Given that multiple mechanisms function at many levels to orchestrate the regulation of apoptosis, a multitude of opportunities for apoptotic dysregulation are present within the intricate signaling network of cell. Several of the molecular mechanisms by which cancer cells are protected from apoptosis have been elucidated. These advances have facilitated the development of novel apoptosis-inducing agents that have demonstrated single-agent activity against various types of cancers cells and/or sensitized resistant cancer cells to conventional cytotoxic therapies. Herein, we will highlight several of the central modes of apoptotic dysregulation found in cancer. We will also discuss several therapeutic strategies that aim to reestablish the apoptotic response, and thereby eradicate cancer cells, including those that demonstrate resistance to traditional therapies.

Biological background of pediatric medulloblastoma and ependymoma: a review from a translational research perspective

Survival rates of pediatric brain tumor patients have significantly improved over the years due to developments in diagnostic techniques, neurosurgery, chemotherapy, radiotherapy, and supportive care. However, brain tumors are still an important cause of cancer-related deaths in children. Prognosis is still highly dependent on clinical characteristics, such as the age of the patient, tumor type, stage, and localization, but increased knowledge about the genetic and biological features of these tumors is being obtained and might be useful to further improve outcome for these patients. It has become clear that the deregulation of signaling pathways essential in brain development, for example, sonic hedgehog (SHH), Wnt, and Notch pathways, plays an important role in pathogenesis and biological behavior, especially for medulloblastomas. More recently, data have become available about the cells of origin of brain tumors and the possible existence of brain tumor stem cells. Newly developed array-based techniques for studying gene expression, protein expression, copy number aberrations, and epigenetic events have led to the identification of other potentially important biological abnormalities in pediatric medulloblastomas and ependymomas.

Prognostic value of bax, cytochrome C, and caspase-8 protein expression in primary osteosarcoma

The prognostic significance of bax, cytochrome c, and caspase-8 in patients with primary osteosarcoma is unknown. We examined the immunohistochemical expression of these genes in 35 surgically treated patients with primary osteosarcoma. Clinicopathological and survival data were correlated with the staining result. Eighteen tissue specimens from non-malignant osseous lesions were used as controls. Bax, cytochrome c, and caspase-8 positive staining was observed in 29 (82.9%), 16 (45.7%), and 0 (0%) patients, respectively, but did not stain any of the 18 benign osseous lesions used as controls. None of the genes studied predicted overall or disease-free survival. Patients, however, bearing bax(+)/cytochrome c(+) or bax(+)/cytochrome c(+ +) tumors had a decreased 4-year disease-free survival rate compared to the rest of the group (p = 0.0489 and p = 0.0208, respectively), identifying two groups of patients where more intensive adjuvant treatment could possibly be applied to prevent high postoperative recurrence rates.

Retinoic acid induces caspase-8 transcription via phospho-CREB and increases apoptotic responses to death stimuli in neuroblastoma cells

Caspase-8 is frequently deleted or silenced in neuroblastoma and other solid tumor such as medulloblastoma and small cell lung carcinoma. Caspase-8 expression can be re-established in neuroblastoma cell lines by treatment with demethylating agents or with IFN-gamma. Here we show that four different retinoic acid (RA) derivatives also increase caspase-8 protein expression in neuroblastoma, medulloblastoma and small cell lung carcinoma cell lines. This increase in protein expression is mirrored by an increase in RNA expression in NB cells. However, the promoter region of the caspase-8 gene was not responsible for the induction of caspase-8 expression. Rather, we identified another intronic region containing a CREB binding site that was required for maximal induction of caspase-8 via RA. DNA-protein interaction assays revealed increased phospho-CREB binding to this response element in RA-treated NB cells. Furthermore, mutations of the CREB binding site completely blocked caspase-8 induction in the luciferase reporter system assay and transfection of dominant-negative form of CREB repressed the up-regulation of caspase-8 by RA. Importantly, RA-released cells maintained caspase-8 expression for at least 2-5 days and were more sensitive to doxorubicin and TNFalpha. Thus, RA treatment in conjunction with TNFalpha and/or subsets of cytotoxic agents may have therapeutic benefits.

Phase III Randomized, Intergroup Trial Assessing Imatinib Mesylate At Two Dose Levels in Patients With Unresectable or Metastatic Gastrointestinal Stromal Tumors Expressing the Kit Receptor Tyrosine Kinase: S0033

Purpose

To assess potential differences in progression-free or overall survival when imatinib mesylate is administered to patients with incurable gastrointestinal stromal tumors (GIST) at a standard dose (400 mg daily) versus a high dose (400 mg twice daily).

Patients and Methods

Patients with metastatic or surgically unresectable GIST were eligible for this phase III open-label clinical trial. At registration, patients were randomly assigned to either standard or high-dose imatinib, with close interval follow-up. If objective progression occurred by Response Evaluation Criteria in Solid Tumors, patients on the standard-dose arm could reregister to the trial and receive the high-dose imatinib regimen.

Results

Seven hundred forty-six patients with advanced GIST from 148 centers across the United States and Canada were enrolled onto this trial in 9 months. With a median follow-up of 4.5 years, median progression-free survival was 18 months for patients on the standard-dose arm, and 20 months for those receiving high-dose imatinib. Median overall survival was 55 and 51 months, respectively. There were no statistically significant differences in objective response rates, progression-free survival, or overall survival. After progression on standard-dose imatinib, 33% of patients who crossed over to the high-dose imatinib regimen achieved either an objective response or stable disease. There were more grade 3, 4, and 5 toxicities noted on the high-dose imatinib arm.

Conclusion

This trial confirms the effectiveness of imatinib as primary systemic therapy for patients with incurable GIST but did not show any advantage to higher dose treatment. It appears reasonable to initiate therapy with 400 mg daily and to consider dose escalation on progression of disease.

TLR2 and caspase-8 are essential for group B Streptococcus-induced apoptosis in microglia

Microglia, the resident innate immune cells of the CNS, detect invading pathogens via various receptors, including the TLR. Microglia are involved in a number of neurodegenerative diseases in which their activation may be detrimental to neurons. It is largely unknown how this potentially deleterious action can be countered on a cellular level. We previously found that the interaction of TLR2 with group B Streptococcus (GBS), the most important pathogen in neonatal bacterial meningitis, activates microglia that in turn generate neurotoxic NO. We report in this study that GBS not only activates microglia, but also induces apoptosis in these cells via TLR2 and the TLR-adaptor molecule MyD88. Soluble toxic mediators, such as NO, are not responsible for this form of cell death. Instead, interaction of GBS with TLR2 results in formation and activation of caspase-8, a process that involves the transcription factor family Ets. Whereas caspase-8 plays an essential role in GBS-induced microglial apoptosis, caspase-3 is dispensable in this context. We suggest that TLR2- and caspase-8-mediated microglial apoptosis constitutes an autoregulatory mechanism that limits GBS-induced overactivation of the innate immune system in the CNS.

Interferon-gamma mediated up-regulation of caspase-8 sensitizes medulloblastoma cells to radio- and chemotherapy

Loss of caspase-8 expression - which has been demonstrated in a subset of Medulloblastoma (MB) - might block important apoptotic signalling pathways and therefore contribute to treatment resistance. In this study, IFN-gamma mediated up-regulation of caspase-8 in human MB cells was found to result in chemosensitization to cisplatin, doxorubicin and etoposide, and sensitisation to radiation. These effects were more prominent in D425 and D341 MB cells (low basal caspase-8 expression) when compared to DAOY MB cells (high basal caspase-8 expression). IFN-gamma mediated chemosensitization and radiosensitization effects were reduced by treatment with the caspase-8 specific inhibitor z-IETD-fmk. Treatment of IFN-gamma resulted in activation of STAT1 in DAOY MB cells and to a lesser extent in D425, but not in D341, indicating that IFN-gamma acts in MB cells through STAT1-dependent and -independent signalling pathways. Taken together, our results demonstrate that IFN-gamma mediated restoration of caspase-8 in MB cells might enhance apoptotic pathways relevant to the response to chemo- and radiotherapy.

Multifaceted targeting in cancer: the recent cell death players meet the usual oncogene suspects

Recent complicated advances towards the blueprinting of the altered molecular networks that lie behind cancer development have paved the way for targeted therapy in cancer. This directed a significant part of the research community to the development of specialized targeted agents, many of which are already available or in clinical trials. The prospect of patient-tailored therapeutic strategies, although very close to becoming a reality also raises the level of complexity of the therapeutic approach. This review summarizes the functions, in vivo expression patterns and aberrations of factors presently targeted or representing potential targets by therapeutic agents, focusing on those implicated in death receptor-induced apoptosis. The authors overview the regulation of these factors and death receptor-induced apoptosis by classical oncogenes (e.g., RAS, MYC, HER2) and their effectors/regulators, most of which are also being targeted. In addition, the importance of orthologic systemic approaches in future patient-tailored therapies are discussed.

Antisense treatment of IGF-IR induces apoptosis and enhances chemosensitivity in central nervous system atypical teratoid/rhabdoid tumours cells

Central nervous system (CNS) atypical teratoid/rhabdoid tumours (AT/RT) are among the paediatric malignant tumours with the worst prognosis and fatal outcome. Insulin-like growth factor I receptor (IGF-IR) protects cancer cells from apoptosis induced by a variety of anticancer drugs and radiation. In the present study, IGF-IR was expressed in 8/8 primary AT/RT as detected by immunohistochemistry. Moreover, we found IGF-I and IGF-II mRNA in BT-16 CNS AT/RT cells and IGF-II mRNA in BT-12 CNS AT/RT cells, and autophosphorylated IGF-IR in both cell lines, indicating the potential presence of an autocrine/paracrine IGF-I/II/IGF-IR loop in CNS AT/RT. IGF-IR antisense oligonucleotide treatment of human CNS AT/RT cells resulted in significant down-regulation of IGF-IR mRNA and protein expression, induction of apoptosis, and chemosensitisation to doxorubicin and cisplatin. These studies provide evidence for the influence of IGF-IR on cellular responses to chemotherapy and raise the possibility that curability of selected CNS AT/RT may be improved by pharmaceutical strategies directed towards the IGF-IR.

Array-based profiling of reference-independent methylation status (aPRIMES) identifies frequent promoter methylation and consecutive downregulation of ZIC2 in pediatric medulloblastoma

Existing microarray-based approaches for screening of DNA methylation are hampered by a number of shortcomings, such as the introduction of bias by DNA copy-number imbalances in the test genome and negligence of tissue-specific methylation patterns. We developed a method designated array-based profiling of reference-independent methylation status (aPRIMES) that allows the detection of direct methylation status rather than relative methylation. Array-PRIMES is based on the differential restriction and competitive hybridization of methylated and unmethylated DNA by methylation-specific and methylation-sensitive restriction enzymes, respectively. We demonstrate the accuracy of aPRIMES in detecting the methylation status of CpG islands for different states of methylation. Application of aPRIMES to the DNA from desmoplastic medulloblastomas of monozygotic twins showed strikingly similar methylation profiles. Additional analysis of 18 sporadic medulloblastomas revealed an overall correlation between highly methylated tumors and poor clinical outcome and identified ZIC2 as a frequently methylated gene in pediatric medulloblastoma.

CpG island promoter hypermethylation of the pro-apoptotic gene caspase-8 is a common hallmark of relapsed glioblastoma multiforme

Glioblastoma multiforme (GBM) is an incurable malignancy with inherent tendency to recur. In this study, we have comparatively analyzed the epigenetic profile of 32 paired tumor samples of relapsed GBM and their corresponding primary neoplasms with special attention to genes involved in the mitochondria-independent apoptotic pathway. The CpG island promoter hypermethylation status was assessed by methylation-specific polymerase chain reaction and selected samples were double checked by bisulfite genomic sequencing. Thirteen genes were analyzed for DNA methylation: the pro-apoptotic CASP8, CASP3, CASP9, DcR1, DR4, DR5 and TMS1; the cell adherence CDH1 and CDH13; the candidate tumor suppressor RASSF1A and BLU; the cell cycle regulator CHFR and the DNA repair MGMT. The CpG island promoter hypermethylation profile of relapsed GBM in comparison with their corresponding primary tumors was identical in 37.5% of the cases, whereas in 62.5% of patients, differences in the DNA methylation patterns of the 13 genes were observed. The most prominent distinction was the presence of previously undetected CASP8 hypermethylation in the GBM relapses (P = 0.031). This finding was also linked to the observation that an unmethylated CASP8 CpG island together with methylated BLU promoter in the primary GBM was associated with prolonged time to tumor progression (P = 0.0035). Our data strongly suggest that hypermethylation of the pro-apoptotic CASP8 is a differential feature of GBM relapses. These remarkable findings may foster the development of therapeutic approaches using DNA demethylating drugs and activators of the extrinsic apoptotic pathway to improve the dismal prognosis of GBM.

Anti-proliferative activity of the quassinoid NBT-272 in childhood medulloblastoma cells

BACKGROUND

With current treatment strategies, nearly half of all medulloblastoma (MB) patients die from progressive tumors. Accordingly, the identification of novel therapeutic strategies remains a major goal. Deregulation of c-MYC is evident in numerous human cancers. In MB, over-expression of c-MYC has been shown to correlate with anaplasia and unfavorable prognosis. In neuroblastoma--an embryonal tumor with biological similarities to MB--the quassinoid NBT-272 has been demonstrated to inhibit cellular proliferation and to down-regulate c-MYC protein expression.

METHODS

To study MB cell responses to NBT-272 and their dependence on the level of c-MYC expression, DAOY (wild-type, empty vector transfected or c-MYC transfected), D341 (c-MYC amplification) and D425 (c-MYC amplification) human MB cells were used. The cells were treated with different concentrations of NBT-272 and the impact on cell proliferation, apoptosis and c-MYC expression was analyzed.

RESULTS

NBT-272 treatment resulted in a dose-dependent inhibition of cellular proliferation (IC50 in the range of 1.7-9.6 ng/ml) and in a dose-dependent increase in apoptotic cell death in all human MB cell lines tested. Treatment with NBT-272 resulted in up to 90% down-regulation of c-MYC protein, as demonstrated by Western blot analysis, and in a significant inhibition of c-MYC binding activity. Anti-proliferative effects were slightly more prominent in D341 and D425 human MB cells with c-MYC amplification and slightly more pronounced in c-MYC over-expressing DAOY cells compared to DAOY wild-type cells. Moreover, treatment of synchronized cells by NBT-272 induced a marked cell arrest at the G1/S boundary.

CONCLUSION

In human MB cells, NBT-272 treatment inhibits cellular proliferation at nanomolar concentrations, blocks cell cycle progression, induces apoptosis, and down-regulates the expression of the oncogene c-MYC. Thus, NBT-272 may represent a novel drug candidate to inhibit proliferation of human MB cells in vivo.

Gastrointestinal stromal tumors treated with imatinib: monitoring response with contrast-enhanced sonography

OBJECTIVE

The purpose of this study was to evaluate contrast-enhanced Doppler sonography with perfusion software as a predictor of early tumor response to imatinib (Glivec) in c-kit-positive gastrointestinal stromal tumors (GISTs).

SUBJECTS AND METHODS

Thirty patients (59 tumors) with metastases or a recurrence from a GIST were prospectively included in a single-center imaging trial. Contrast-enhanced Doppler sonography was performed with an Aplio scanner the day before (day-1) starting oral treatment (400 mg) and at days 1, 7, 14, 60, 90, and 6 months, 9 months, and 1 year. The percentage of contrast uptake (Levovist or Sonovue) before treatment and at the different stages of follow-up was evaluated by two radiologists. Digitized quantification was performed using Photoshop software. To define the benchmark standard, all patients were rated as responders or nonresponders at 2 and 6 months by a board consisting of oncologists and radiologists who had all clinical and imaging data at their disposal. Changes in the percentage of contrast uptake at each sonographic examination were compared statistically.

RESULTS

A total of 185 examinations were performed. Forty-four lesions in 24 patients were completely evaluated at 2 months, and 29 lesions in 15 patients were completely evaluated at 6 months. Initial contrast uptake at day 1 was predictive of the future response. A strong correlation was found between the decline in tumor contrast uptake at days 7 and 14 and tumor response (p < 10(-4)).

CONCLUSION

Contrast-enhanced Doppler sonography is a noninvasive imaging technique that allows the early prediction of tumor response in c-kit-positive GIST treated with Glivec.

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.

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

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

Evaluation of IFN-γ effects on apoptosis and gene expression in neuroblastoma—Preclinical studies

Loss of caspase-8 expression and resistance to cytotoxic agents occurs frequently in late stage neuroblastoma (NB). Interferon-gamma (IFN-gamma) induces caspase-8 in NB cells, sensitizing them to death receptor mediated apoptosis. This study characterizes the kinetics of this phenomenon and examines the effects of IFN-gamma on global gene expression to determine whether IFN-gamma responses are achievable at physiologically relevant doses and to define the biological effects of this cytokine. Here we examine the IFN-gamma responses of 16 NB cell lines. A single <5-min exposure to IFN-gamma (0.5 ng/ml) induced caspase-8 expression in all non-expressing cell lines and in 3/6 cell lines which already expressed high caspase-8. This increase in caspase-8 proteins was observed within 16 h and persisted for up to 9 days. Furthermore, IFN-gamma pretreatment of NB cells increased doxorubicin-induced apoptosis nearly 3-fold. Microarray analysis was used to identify additional genes involved in proliferation, signaling and apoptosis whose expression was modulated via IFN-gamma. Altered expression of these genes should further enhance the responsiveness of NB cells to chemotherapeutics. Thus, the use of IFN-gamma to sensitize NB cells to cytotoxic agents represents an attractive therapeutic strategy and warrants further investigation.

Inhibition of DNA methylation sensitizes glioblastoma for tumor necrosis factor-related apoptosis-inducing ligand-mediated destruction

Life expectancy of patients affected by glioblastoma multiforme is extremely low. The therapeutic use of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been proposed to treat this disease based on its ability to kill glioma cell lines in vitro and in vivo. Here, we show that, differently from glioma cell lines, glioblastoma multiforme tumors were resistant to TRAIL stimulation because they expressed low levels of caspase-8 and high levels of the death receptor inhibitor PED/PEA-15. Inhibition of methyltransferases by decitabine resulted in considerable up-regulation of TRAIL receptor-1 and caspase-8, down-regulation of PED/PEA-15, inhibition of cell growth, and sensitization of primary glioblastoma cells to TRAIL-induced apoptosis. Exogenous caspase-8 expression was the main event able to restore TRAIL sensitivity in primary glioblastoma cells. The antitumor activity of decitabine and TRAIL was confirmed in vivo in a mouse model of glioblastoma multiforme. Evaluation of tumor size, apoptosis, and caspase activation in nude mouse glioblastoma multiforme xenografts showed dramatic synergy of decitabine and TRAIL in the treatment of glioblastoma, whereas the single agents were scarcely effective in terms of reduction of tumor mass, apoptosis induction, and caspase activation. Thus, the combination of TRAIL and demethylating agents may provide a key tool to overcome glioblastoma resistance to therapeutic treatments.

Molecular neuro-oncology and the development of targeted therapeutic strategies for brain tumors. Part 5: apoptosis and cell cycle

Brain tumors are a diverse group of malignancies that remain refractory to conventional treatment approaches. Molecular neuro-oncology has now begun to clarify the transformed phenotype of brain tumors and identify oncogenic pathways that might be amenable to targeted therapy. Abnormalities of the apoptotic and cell cycle signaling pathways are key molecular features of many brain tumors and are currently under evaluation for potential therapeutic intervention. The apoptosis pathway has numerous targets for molecular therapeutic development, including p53, Bax, Bcl-2, cFLIP, effector caspases, growth factor receptors, phosphatidylinositol-3-kinase, Akt and apoptosis inhibitors. Current molecular treatment approaches include antisense techniques, gene therapy and small-molecule modulators and inhibitors. Potential targets of the cell cycle pathway include the cyclins, cyclin-dependent kinases, p53, retinoblastoma, E2F and the cyclin-dependent kinase inhibitors. Developmental molecular therapeutics for this pathway include adenoviral and gene therapy, small-peptide cyclin-dependent kinase modulators, proteasomal inhibitors and small-molecule cyclin-dependent kinase inhibitors. Several of these recently identified agents have begun evaluation in clinical trials. Further development of targeted therapies designed to modulate apoptosis and the cell cycle, and evaluation of these new agents in clinical trials, will be needed to improve survival and quality of life for patients with brain tumors.

Epigenetic inactivation of MCJ (DNAJD1) in malignant paediatric brain tumours

MCJ (DNAJD1) is a recently discovered member of the DNAJ protein family whose expression is controlled epigenetically by methylation of a CpG island located within the 5' transcribed region of its gene. Methylation-dependent transcriptional silencing of MCJ has been observed in ovarian cancers and associated with increased resistance to chemotherapeutic agents; however, its role in other cancer types has not been widely investigated. We examined the status of MCJ in intracranial primitive neuroectodermal tumours [PNETs, comprising cerebellar PNETs (medulloblastomas) and supratentorial PNETs (stPNETs)] and ependymomas, together representing the most common malignant brain tumours of childhood. Evidence of MCJ hypermethylation was found in all 3 tumour types [medulloblastomas, 3/9 (33%) cell lines, 2/28 (7%) primary tumours; stPNETs, 2/2 (100%) cell lines, 3/10 (30%) primary tumours; and ependymomas, 2/20 (10%) primary tumours] but not in nonneoplastic brain tissues (n = 11), indicating that MCJ methylation is a tumour-specific event. In methylated cases, the distribution of methylated CpG sites across the CpG island could be broadly divided into 2 patterns: (i) extensive methylation of the majority of CpG sites across the island or (ii) limited methylation of individual CpG sites concentrated towards the 5' end of the island. Extensive methylation patterns were associated with the methylation-dependent transcriptional silencing of MCJ in medulloblastoma and stPNET cell lines. Further investigations of the mechanism of MCJ inactivation revealed that its loss could occur either through biallelic epigenetic methylation or by methylation in association with genetic loss of its second allele. These data indicate that epigenetic inactivation of MCJ may play a role in the development of a range of paediatric brain tumour types, and its role in disease pathogenesis and chemotherapeutic resistance should now be investigated further.