Neuroblastoma: developmental biology, cancer genomics and immunotherapy

The CXCR4/CXCR7/CXCL12 Axis Is Involved in a Secondary but Complex Control of Neuroblastoma Metastatic Cell Homing

Neuroblastoma (NB) is one of the most deadly solid tumors of the young child, for which new efficient and targeted therapies are strongly needed. The CXCR4/CXCR7/CXCL12 chemokine axis has been involved in the progression and organ-specific dissemination of various cancers. In NB, CXCR4 expression was shown to be associated to highly aggressive undifferentiated tumors, while CXCR7 expression was detected in more differentiated and mature neuroblastic tumors. As investigated in vivo, using an orthotopic model of tumor cell implantation of chemokine receptor-overexpressing NB cells (IGR-NB8), the CXCR4/CXCR7/CXCL12 axis was shown to regulate NB primary and secondary growth, although without any apparent influence on organ selective metastasis. In the present study, we addressed the selective role of CXCR4 and CXCR7 receptors in the homing phase of metastatic dissemination using an intravenous model of tumor cell implantation. Tail vein injection into NOD-scid-gamma mice of transduced IGR-NB8 cells overexpressing CXCR4, CXCR7, or both receptors revealed that all transduced cell variants preferentially invaded the adrenal gland and typical NB metastatic target organs, such as the liver and the bone marrow. However, CXCR4 expression favored NB cell dissemination to the liver and the lungs, while CXCR7 was able to strongly promote NB cell homing to the adrenal gland and the liver. Finally, coexpression of CXCR4 and CXCR7 receptors significantly and selectively increased NB dissemination toward the bone marrow. In conclusion, CXCR4 and CXCR7 receptors may be involved in a complex and organ-dependent control of NB growth and selective homing, making these receptors and their inhibitors potential new therapeutic targets.

JARID1B Expression Plays a Critical Role in Chemoresistance and Stem Cell-Like Phenotype of Neuroblastoma Cells

Neuroblastoma (NB) is a common neural crest-derived extracranial solid cancer in children. Among all childhood cancers, NB causes devastating loss of young lives as it accounts for 15% of childhood cancer mortality. Neuroblastoma, especially high-risk stage 4 NB with MYCN amplification has limited treatment options and associated with poor prognosis. This necessitates the need for novel effective therapeutic strategy. JARID1B, also known as KDM5B, is a histone lysine demethylase, identified as an oncogene in many cancer types. Clinical data obtained from freely-accessible databases show a negative correlation between JARID1B expression and survival rates. Here, we demonstrated for the first time the role of JARID1B in the enhancement of stem cell-like activities and drug resistance in NB cells. We showed that JARID1B may be overexpressed in either MYCN amplification (SK-N-BE(2)) or MYCN-non-amplified (SK-N-SH and SK-N-FI) cell lines. JARID1B expression was found enriched in tumor spheres of SK-N-BE(2) and SK-N-DZ. Moreover, SK-N-BE(2) spheroids were more resistant to chemotherapeutics as compared to parental cells. In addition, we demonstrated that JARID1B-silenced cells acquired a decreased propensity for tumor invasion and tumorsphere formation, but increased sensitivity to cisplatin treatment. Mechanistically, reduced JARID1B expression led to the downregulation of Notch/Jagged signaling. Collectively, we provided evidence that JARID1B via modulation of stemness-related signaling is a putative novel therapeutic target for treating malignant NB.

Temporal proteomics of NGF-TrkA signaling identifies an inhibitory role for the E3 ligase Cbl-b in neuroblastoma cell differentiation

SH-SY5Y neuroblastoma cells respond to nerve growth factor (NGF)-mediated activation of the tropomyosin-related kinase A (TrkA) with neurite outgrowth, thereby providing a model to study neuronal differentiation. We performed a time-resolved analysis of NGF-TrkA signaling in neuroblastoma cells using mass spectrometry-based quantitative proteomics. The combination of interactome, phosphoproteome, and proteome data provided temporal insights into the molecular events downstream of NGF binding to TrkA. We showed that upon NGF stimulation, TrkA recruits the E3 ubiquitin ligase Cbl-b, which then becomes phosphorylated and ubiquitylated and decreases in abundance. We also found that recruitment of Cbl-b promotes TrkA ubiquitylation and degradation. Furthermore, the amount of phosphorylation of the kinase ERK and neurite outgrowth increased upon Cbl-b depletion in several neuroblastoma cell lines. Our findings suggest that Cbl-b limits NGF-TrkA signaling to control the length of neurites.

Wild-type ALK and activating ALK-R1275Q and ALK-F1174L mutations upregulate Myc and initiate tumor formation in murine neural crest progenitor cells

The anaplastic lymphoma kinase (ALK) gene is overexpressed, mutated or amplified in most neuroblastoma (NB), a pediatric neural crest-derived embryonal tumor. The two most frequent mutations, ALK-F1174L and ALK-R1275Q, contribute to NB tumorigenesis in mouse models, and cooperate with MYCN in the oncogenic process. However, the precise role of activating ALK mutations or ALK-wt overexpression in NB tumor initiation needs further clarification.

Human ALK-wt, ALK-F1174L, or ALK-R1275Q were stably expressed in murine neural crest progenitor cells (NCPC), MONC-1 or JoMa1, immortalized with v-Myc or Tamoxifen-inducible Myc-ER^T, respectively. While orthotopic implantations of MONC-1 parental cells in nude mice generated various tumor types, such as NB, osteo/chondrosarcoma, and undifferentiated tumors, due to v-Myc oncogenic activity, MONC-1-ALK-F1174L cells only produced undifferentiated tumors. Furthermore, our data represent the first demonstration of ALK-wt transforming capacity, as ALK-wt expression in JoMa1 cells, likewise ALK-F1174L, or ALK-R1275Q, in absence of exogenous Myc-ER^T activity, was sufficient to induce the formation of aggressive and undifferentiated neural crest cell-derived tumors, but not to drive NB development. Interestingly, JoMa1-ALK tumors and their derived cell lines upregulated Myc endogenous expression, resulting from ALK activation, and both ALK and Myc activities were necessary to confer tumorigenic properties on tumor-derived JoMa1 cells in vitro.

NCYM promotes calpain-mediated Myc-nick production in human MYCN-amplified neuroblastoma cells

NCYM is a cis-antisense gene of MYCN and is amplified in human neuroblastomas. High NCYM expression is associated with poor prognoses, and the NCYM protein stabilizes MYCN to promote proliferation of neuroblastoma cells. However, the molecular mechanisms of NCYM in the regulation of cell survival have remained poorly characterized. Here we show that NCYM promotes cleavage of MYCN to produce the anti-apoptotic protein, Myc-nick, both in vitro and in vivo. NCYM and Myc-nick were induced at G2/M phase, and NCYM knockdown induced apoptotic cell death accompanied by Myc-nick downregulation. These results reveal a novel function of NCYM as a regulator of Myc-nick production in human neuroblastomas.

Development and characterization of a human orthotopic neuroblastoma xenograft

Neuroblastoma is a pediatric cancer of the developing sympathoadrenal lineage. The tumors are known to develop from the adrenal gland or paraspinal ganglia and have molecular and cellular features of sympathetic neurons such as dense core vesicles and catecholamine production. Here we present the detailed molecular, cellular, genetic and epigenetic characterization of an orthotopic xenograft derived from a high-risk stage 4 neuroblastoma patient. Overall, the xenografted tumor retained the high risk features of the primary tumor and showed aggressive growth and metastasis in the mouse. Also, the genome was preserved with no additional copy number variations, structural variations or aneuploidy. There were 13 missense mutations identified in the xenograft that were not present in the patient's primary tumor and there were no new nonsense mutations. None of the missense mutations acquired in the xenograft were in known cancer genes. We also demonstrate the feasibility of using the orthotopic neuroblastoma xenograft to test standard of care chemotherapy and molecular targeted therapeutics. Finally, we optimized a new approach to produce primary cultures of the neuroblastoma xenografts for high-throughput drug screening which can be used to test new combinations of therapeutic agents for neuroblastoma.

Alteration of Electrostatic Surface Potential Enhances Affinity and Tumor Killing Properties of Anti-ganglioside GD2 Monoclonal Antibody hu3F8

Ganglioside GD2 is highly expressed on neuroectodermal tumors and an attractive therapeutic target for antibodies that have already shown some clinical efficacy. To further improve the current antibodies, which have modest affinity, we sought to improve affinity by using a combined method of random mutagenesis and in silico assisted design to affinity-mature the anti-GD2 monoclonal antibody hu3F8. Using yeast display, mutants in the Fv with enhanced binding over the parental clone were FACS-sorted and cloned. In silico modeling identified the minimal key interacting residues involved in the important charged interactions with the sialic acid groups of GD2. Two mutations, D32H (L-CDR1) and E1K (L-FR1) altered the electrostatic surface potential of the antigen binding site, allowing for an increase in positive charge to enhance the interaction with the negatively charged GD2-pentasaccharide headgroup. Purified scFv and IgG mutant forms were then tested for antigen specificity by ELISA, for tissue specificity by immunohistochemistry, for affinity by BIACORE, for antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-mediated cytotoxicity in vitro, and for anti-tumor efficacy in xenografted humanized mice. The nearly 7-fold improvement in affinity of hu3F8 with a single D32H (L-CDR1) mutation translated into a ∼12-fold improvement in NK92MI-transfected CD16-mediated ADCC, a 6-fold improvement in CD32-mediated ADCC, and a 2.5-fold improvement in complement-mediated cytotoxicity while maintaining restricted normal tissue cross-reactivity and achieving substantial improvement in tumor ablation in vivo. Despite increasing GD2 affinity, the double mutation D32H (L-CDR1) and E1K (L-FR1) did not further improve anti-tumor efficacy.

Tumor-infiltrating T lymphocytes improve clinical outcome of therapy-resistant neuroblastoma

Neuroblastoma grows within an intricate network of different cell types including epithelial, stromal and immune cells. The presence of tumor-infiltrating T cells is considered an important prognostic indicator in many cancers, but the role of these cells in neuroblastoma remains to be elucidated. Herein, we examined the relationship between the type, density and organization of infiltrating T cells and clinical outcome within a large collection of neuroblastoma samples by quantitative analysis of immunohistochemical staining. We found that infiltrating T cells have a prognostic value greater than, and independent of, the criteria currently used to stage neuroblastoma. A variable in situ structural organization and different concurrent infiltration of T-cell subsets were detected in tumors with various outcomes. Low-risk neuroblastomas were characterized by a higher number of proliferating T cells and a more structured T-cell organization, which was gradually lost in tumors with poor prognosis. We defined an immunoscore based on the presence of CD3⁺, CD4⁺ and CD8⁺ infiltrating T cells that associates with favorable clinical outcome in MYCN-amplified tumors, improving patient survival when combined with the v-myc avian myelocytomatosis viral oncogene neuroblastoma derived homolog (MYCN) status. These findings support the hypothesis that infiltrating T cells influence the behavior of neuroblastoma and might be of clinical importance for the treatment of patients.

Assessment of the chemosensitizing activity of TAT-RasGAP317-326 in childhood cancers

Although current anti-cancer protocols are reasonably effective, treatment-associated long-term side effects, induced by lack of specificity of the anti-cancer procedures, remain a challenging problem in pediatric oncology. TAT-RasGAP317-326 is a RasGAP-derived cell-permeable peptide that acts as a sensitizer to various anti-cancer treatments in adult tumor cells. In the present study, we assessed the effect of TAT-RasGAP317-326 in several childhood cancer cell lines. The RasGAP-derived peptide-induced cell death was analyzed in several neuroblastoma, Ewing sarcoma and leukemia cell lines (as well as in normal lymphocytes). Cell death was evaluated using flow cytometry methods in the absence or in the presence of the peptide in combination with various genotoxins used in the clinics (4-hydroperoxycyclophosphamide, etoposide, vincristine and doxorubicin). All tested pediatric tumors, in response to at least one genotoxin, were sensitized by TAT-RasGAP317-326. The RasGAP-derived peptide did not increase cell death of normal lymphocytes, alone or in combination with the majority of the tested chemotherapies. Consequently, TAT-RasGAP317-326 may benefit children with tumors by increasing the efficacy of anti-cancer therapies notably by allowing reductions in anti-cancer drug dosage and the associated drug-induced side effects.

Upregulation of MAPK Negative Feedback Regulators and RET in Mutant ALK Neuroblastoma: Implications for Targeted Treatment

PURPOSE

Activating ALK mutations are present in almost 10% of primary neuroblastomas and mark patients for treatment with small-molecule ALK inhibitors in clinical trials. However, recent studies have shown that multiple mechanisms drive resistance to these molecular therapies. We anticipated that detailed mapping of the oncogenic ALK-driven signaling in neuroblastoma can aid to identify potential fragile nodes as additional targets for combination therapies.

EXPERIMENTAL DESIGN

To achieve this goal, transcriptome profiling was performed in neuroblastoma cell lines with the ALK(F1174L) or ALK(R1275Q) hotspot mutations, ALK amplification, or wild-type ALK following pharmacologic inhibition of ALK using four different compounds. Next, we performed cross-species genomic analyses to identify commonly transcriptionally perturbed genes in MYCN/ALK(F1174L) double transgenic versus MYCN transgenic mouse tumors as compared with the mutant ALK-driven transcriptome in human neuroblastomas.

RESULTS

A 77-gene ALK signature was established and successfully validated in primary neuroblastoma samples, in a neuroblastoma cell line with ALK(F1174L) and ALK(R1275Q) regulable overexpression constructs and in other ALKomas. In addition to the previously established PI3K/AKT/mTOR, MAPK/ERK, and MYC/MYCN signaling branches, we identified that mutant ALK drives a strong upregulation of MAPK negative feedback regulators and upregulates RET and RET-driven sympathetic neuronal markers of the cholinergic lineage.

CONCLUSIONS

We provide important novel insights into the transcriptional consequences and the complexity of mutant ALK signaling in this aggressive pediatric tumor. The negative feedback loop of MAPK pathway inhibitors may affect novel ALK inhibition therapies, whereas mutant ALK induced RET signaling can offer novel opportunities for testing ALK-RET oriented molecular combination therapies.

Cordycepin induces apoptosis and autophagy in human neuroblastoma SK-N-SH and BE(2)-M17 cells

Cordycepin, also termed 3'-deoxyadenosine, is a derivative of the nucleoside adenosine that represents a potential novel class of anticancer drugs targeting the 3' untranslated region of RNAs. Cordycepin has been reported to induce apoptosis in certain cancer cell lines, but the effects of cordycepin on human neuroblastoma cells have not been studied. In the present study, an MTT assay revealed that cordycepin inhibits the viability of neuroblastoma SK-N-SH and BE(2)-M17 cells in a dose-dependent manner. In addition, cordycepin increases the early-apoptotic cell population of SK-N-SH cells, as determined by fluorescence-activated cell sorting analysis. The induction of apoptosis in neuroblastoma cells by cordycepin was further confirmed by western blotting, which revealed cleavage of caspase-3 and poly(adenosine diphosphate-ribose) polymerase 1 in the SK-N-SH and BE(2)-M17 cells. Cordycepin also induced the formation of a punctate pattern of light-chain 3 (LC3)-associated green fluorescence in the SK-N-SH cells transfected with a pEGFP-LC3 vector. Furthermore, western blotting revealed cleavage of LC3 A/B in cordycepin-treated neuroblastoma SK-N-SH cells. Taken together, the results indicate that cordycepin significantly increases apoptosis and autophagy in neuroblastoma cells, and may therefore be a drug candidate for neuroblastoma therapy, but requires additional evaluation.

IGF2BP1 harbors prognostic significance by gene gain and diverse expression in neuroblastoma

PURPOSE

Chromosomal 17q21-ter gain in neuroblastoma is both a common and prognostically significant event. The insulin-like growth factor-2 mRNA-binding protein 1 (IGF2BP1) gene is located near the proximal edge of this region. Here, its prognostic value is evaluated in neuroblastoma.

METHODS

The mRNA expression of IGF2BP family members was first evaluated by microarray data sets. In addition, in a separate cohort of 69 tumors, IGF2BP1 gene copy number, mRNA, and protein abundance were determined and compared with clinical parameters.

RESULTS

In two independent microarray data sets, 77% to 100% of tumors had substantial IGF2BP1 mRNA levels measured. High IGF2BP1 transcript abundance was significantly associated with stage 4 tumors (P < .001) and decreased patient survival (P < .001). IGF2BP1 was also associated with MYCN gene amplification and MYCN mRNA abundance. In the 69 neuroblastoma samples, IGF2BP1 DNA copy number (increased in 84% of tumors), mRNA, and protein abundance were significantly higher in stage 4 compared with stage 1 tumors. Importantly, IGF2BP1 protein levels were associated with lower overall patient survival (P = .012) and positively correlated with MYCN mRNA, even when excluding MYCN-amplified tumors. Moreover, IGF2BP1 clearly affected MYCN expression and neuroblastoma cell survival in vitro.

CONCLUSION

In neuroblastoma, IGF2BP1 was expressed in the majority of neuroblastoma specimens analyzed and was associated with lower overall patient survival and MYCN abundance. These data demonstrate that IGF2BP1 is a potential oncogene and an independent negative prognostic factor in neuroblastoma.

High-throughput screening for chemical modulators of post-transcriptionally regulated genes

Both transcriptional and post-transcriptional regulation have a profound impact on genes expression. However, commonly adopted cell-based screening assays focus on transcriptional regulation, being essentially aimed at the identification of promoter-targeting molecules. As a result, post-transcriptional mechanisms are largely uncovered by gene expression targeted drug development. Here we describe a cell-based assay aimed at investigating the role of the 3' untranslated region (3' UTR) in the modulation of the fate of its mRNA, and at identifying compounds able to modify it. The assay is based on the use of a luciferase reporter construct containing the 3' UTR of a gene of interest stably integrated into a disease-relevant cell line. The protocol is divided into two parts, with the initial focus on the primary screening aimed at the identification of molecules affecting luciferase activity after 24 hr of treatment. The second part of the protocol describes the counter-screening necessary to discriminate compounds modulating luciferase activity specifically through the 3' UTR. In addition to the detailed protocol and representative results, we provide important considerations about the assay development and the validation of the hit(s) on the endogenous target. The described cell-based reporter gene assay will allow scientists to identify molecules modulating protein levels via post-transcriptional mechanisms dependent on a 3' UTR.

Interaction between bone marrow stromal cells and neuroblastoma cells leads to a VEGFA-mediated osteoblastogenesis

The potential role of osteoblasts in bone and bone marrow (BM) metastases in neuroblastoma (NBL) remains unclear. In this study, we examined the effect of NBL cells on the osteoblastic differentiation of BM-derived mesenchymal stromal cells (BMMSC). We show that the presence of NBL cells enhanced the osteoblastic differentiation of BMMSC driven by bone morphogenetic protein (BMP)-4, in the absence of any effect on NBL cell proliferation. Expression profiles of BMMSC driven toward osteoblastic differentiation revealed an increase in vascular endothelial growth factor A (Vegfa) expression in the presence of NBL cells. We demonstrated that NBL cells increased BMMSC-derived VEGFA mRNA and protein and that this was enhanced by BMP-4. However, in similar conditions, neither the addition of an mVEGFA blocking antibody nor exogenous recombinant (r) mVEGFA affected osteoblastic differentiation. In contrast, siRNA- mediated knock-down of VEGFA in BMMSC prevented osteoblastic differentiation in BMP-4-treated cocultures, an effect that was not reversed in the presence of rmVEGFA. An analysis of murine bones injected with hNBL cells revealed an increase of mVEGFA producing cells near tumor cells concomitantly with an increase in Vegfa and Runx2 mRNA. This coincided with an increase in osteoclasts, in Rankl/Opg mRNA ratio and with the formation of osteolytic lesions. Thus NBL cells promote osteoblastogenesis in the BM by increasing VEGFA expression in BMMSC. Our study provides a new insight into the role of VEGFA in NBL metastases by pointing to the role of stroma-derived intracrine VEGFA in osteoblastogenesis.

Individual patient risk stratification of high-risk neuroblastomas using a two-gene score suited for clinical use

Several gene expression-based prognostic signatures have been described in neuroblastoma, but none have successfully been applied in the clinic. Here we have developed a clinically applicable prognostic gene signature, both with regards to number of genes and analysis platform. Importantly, it does not require comparison between patients and is applicable amongst high-risk patients. The signature is based on a two-gene score (R-score) with prognostic power in high-stage tumours (stage 4 and/or MYCN-amplified diagnosed after 18 months of age). QPCR-based and array-based analyses of matched cDNAs confirmed cross platform (array-qPCR) transferability. We also defined a fixed cut-off value identifying prognostically differing subsets of high-risk patients on an individual patient basis. This gene expression signature independently contributes to the current neuroblastoma classification system, and if prospectively validated could provide further stratification of high-risk patients, and potential upfront identification of a group of patients that are in need of new/additional treatment regimens.

Hyperactivation of Alk induces neonatal lethality in knock-in AlkF1178L mice

The ALK (Anaplastic Lymphoma Kinase) gene encodes a tyrosine kinase receptor preferentially expressed in the central and peripheral nervous systems. A syndromic presentation associating congenital neuroblastoma with severe encephalopathy and an abnormal shape of the brainstem has been described in patients harbouring de novo germline F1174V and F1245V ALK mutations. Here, we investigated the phenotype of knock-in (KI) mice bearing the Alk^F1178L mutation (F1174L in human). Although heterozygous KI mice did not reproduce the severe breathing and feeding difficulties observed in human patients, behavioral tests documented a reduced activity during dark phases and an increased anxiety of mutated mice. Matings of heterozygotes yielded the expected proportions of wild-type, heterozygotes and homozygotes at birth but a high neonatal lethality was noticed for homozygotes. We documented Alk expression in several motor nuclei of the brainstem involved in the control of sucking and swallowing. Evaluation of basic physiological functions 12 hours after birth revealed slightly more apneas but a dramatic reduced milk intake for homozygotes compared to control littermates. Overall, our data demonstrate that Alk activation above a critical threshold is not compatible with survival in mice, in agreement with the extremely severe phenotype of patients carrying aggressive de novo ALK germline mutations.

A cell-based high-throughput screen addressing 3'UTR-dependent regulation of the MYCN gene

Neuroblastoma is the most common extracranial solid tumor of infancy. Amplification of MYCN oncogene is found in approximately 20 % of all neuroblastoma patients and correlates with advanced disease stages, rapid tumor progression, and poor prognosis, making this gene an obvious therapeutic target. However, being a transcriptional factor MYCN is difficult for pharmacological targeting, and there are currently no clinical trials aiming MYCN protein directly. Here we describe an alternative approach to address deregulated MYCN expression. In particular, we focus on the role of a 3′ untranslated region (3′UTR) of the MYCN gene in the modulation of its mRNA fate and identification of compounds able to affect it. The luciferase reporter construct with the full length MYCN 3′UTR was generated and subsequently integrated in the CHP134 neuroblastoma cell line. After validation, the assay was used to screen a 2000 compound library. Molecules affecting luciferase activity were checked for reproducibility and counter-screened for promoter effects and cytotoxic activity resulting in selection of four hits. We propose this cell-based reporter gene assay as a valuable tool to screen chemical libraries for compounds modulating post-transcriptional control mechanisms. Identification of such compounds could potentially result in development of clinically relevant therapeutics for various diseases including neuroblastoma.

Pediatric solid tumor genomics and developmental pliancy

Pediatric solid tumors are remarkably diverse in their cellular origins, developmental timing and clinical features. Over the last 5 years, there have been significant advances in our understanding of the genetic lesions that contribute to the initiation and progression of pediatric solid tumors. To date, over 1000 pediatric solid tumors have been analyzed by Next-Generation Sequencing. These genomic data provide the foundation to launch new research efforts to address one of the fundamental questions in cancer biology—why are some cells more susceptible to malignant transformation by particular genetic lesions at discrete developmental stages than others? Because of their developmental, molecular, cellular and genetic diversity, pediatric solid tumors provide an ideal platform to begin to answer this question. In this review, we highlight the diversity of pediatric solid tumors and provide a new framework for studying the cellular and developmental origins of pediatric cancer. We also introduce a new unifying concept called cellular pliancy as a possible explanation for susceptibility to cancer and the developmental origins of pediatric solid tumors.

Neuroblastoma: paradigm for precision medicine

Neuroblastoma (NB) is the third most common pediatric cancer. Although NB accounts for 7% of pediatric malignancies, it is responsible for more than 10% of childhood cancer-related mortality. Prognosis and treatment are determined by clinical and biological risk factors. Estimated 5-year survival rates for patients with non-high-risk and high-risk NB are more than 90% and less than 50%, respectively. Recent clinical trials have continued to reduce therapy for patients with non-high-risk NB, including the most favorable subsets who are often followed with observation approaches. In contrast, high-risk patients are treated aggressively with chemotherapy, radiation, surgery, and myeloablative and immunotherapies.

Epigenetic therapy of cancer stem and progenitor cells by targeting DNA methylation machineries

Recent advances in stem cell biology have shed light on how normal stem and progenitor cells can evolve to acquire malignant characteristics during tumorigenesis. The cancer counterparts of normal stem and progenitor cells might be occurred through alterations of stem cell fates including an increase in self-renewal capability and a decrease in differentiation and/or apoptosis. This oncogenic evolution of cancer stem and progenitor cells, which often associates with aggressive phenotypes of the tumorigenic cells, is controlled in part by dysregulated epigenetic mechanisms including aberrant DNA methylation leading to abnormal epigenetic memory. Epigenetic therapy by targeting DNA methyltransferases (DNMT) 1, DNMT3A and DNMT3B via 5-Azacytidine (Aza) and 5-Aza-2’-deoxycytidine (Aza-dC) has proved to be successful toward treatment of hematologic neoplasms especially for patients with myelodysplastic syndrome. In this review, I summarize the current knowledge of mechanisms underlying the inhibition of DNA methylation by Aza and Aza-dC, and of their apoptotic- and differentiation-inducing effects on cancer stem and progenitor cells in leukemia, medulloblastoma, glioblastoma, neuroblastoma, prostate cancer, pancreatic cancer and testicular germ cell tumors. Since cancer stem and progenitor cells are implicated in cancer aggressiveness such as tumor formation, progression, metastasis and recurrence, I propose that effective therapeutic strategies might be achieved through eradication of cancer stem and progenitor cells by targeting the DNA methylation machineries to interfere their “malignant memory”.

The P2X7 receptor is a key modulator of the PI3K/GSK3β/VEGF signaling network: evidence in experimental neuroblastoma

Neuroblastoma (NB) is an aggressive pediatric tumor, responsible for 15% of cancer-related deaths in childhood, lacking an effective treatment in its advanced stages. The P2X7 receptor for extracellular ATP was associated to NB cell proliferation and recently emerged as a promoter of tumor engraftment, growth and vascularization. In an effort to identify new therapeutic options for neuroblastoma, we studied the role of P2X7 receptor in NB biology. We first analyzed the effect of P2X7 activation or down-modulation of the main biochemical ways involved in NB progression: the PI3K/Akt/GSK3β/MYCN and the HIF1α/VEGF pathways. In ACN human NB cells, P2X7 stimulation enhanced PI3K/Akt, while decreasing GSK3β activity. In the same model, P2X7 silencing or antagonist administration reduced the activity of PI3K/Akt and increased that of GSK3β, leading to a decrease in cellular glycogen stores. Similarly, P2X7 downmodulation caused a reduction in HIF1α levels and vascular endothelial growth factor (VEGF) secretion. Systemic administration of two different P2X7 antagonists (AZ10606120 or A740003) in nude/nude mice reduced ACN-derived tumor growth. An even stronger effect of P2X7 blockade was obtained in a syngeneic immune-competent neuroblastoma model: Neuro2A cells injected in AlbinoJ mice. Together with tumor regression, treatment with P2X7 antagonists caused downmodulation of the Akt/HIF1α axis, leading to reduced VEGF content and decreased vessel formation. Interestingly, in both experimental models, P2X7 antagonists strongly reduced the expression of the probably best-accepted oncogene in NB: MYCN. Finally, we associated P2X7 overexpression with poor prognosis in advanced-stage NB patients. Taken together, our data suggest that P2X7 receptor is an upstream regulator of the main signaling pathways involved in NB growth, metabolic activity and angiogenesis, and a promising therapeutic target for neuroblastoma treatment.

Phosphatidylinositol 3-kinase, class 2 beta (PI3KC2β) isoform contributes to neuroblastoma tumorigenesis

Phosphatidylinositol 3-kinases (PI3Ks) play important roles in human tumorigenesis. Activation of the PI3K target AKT is frequent in neuroblastoma (NB) and correlates with poor prognosis. PI3K pan-inhibitors reduce NB tumor formation but present severe toxicity, which limits their therapeutic potential. Therefore, defining the importance of specific PI3K isoforms may aid in developing more effective therapeutic strategies. We previously demonstrated that PI3K Class IIβ (PI3KC2β) and its regulator intersectin 1 (ITSN1) are highly expressed in primary NB tumors and cell lines. Silencing ITSN1 dramatically reduced the tumorigenic potential of NB cells. Interestingly, overexpression of PI3KC2β rescued the anchorage-independent growth of ITSN1-silenced cells suggesting that PI3KC2β mediates ITSN1's function in NB cells. To address the importance of PI3KC2β in NBs, we generated PI3KC2β-silenced lines and examined their biologic activity. Herein, we demonstrate that PI3KC2β-silencing inhibits early stages of NB tumorigenic growth. We also show that loss of endogenous PI3KC2β or ITSN1 reduces AKT activation but does not impact ERK-MAPK activation. These data reveal a novel role for PI3KC2β in human NB tumorigenesis.

Disialoganglioside GD2 as a therapeutic target for human diseases

INTRODUCTION

Ganglioside GD2 is found in vertebrates and invertebrates, overexpressed among pediatric and adult solid tumors, including neuroblastoma, glioma, retinoblastoma, Ewing's family of tumors, rhabdomyosarcoma, osteosarcoma, leiomyosarcoma, liposarcoma, fibrosarcoma, small cell lung cancer and melanoma. It is also found on stem cells, neurons, some nerve fibers and basal layer of the skin.

AREAS COVERED

GD2 provides a promising clinical target for radiolabeled antibodies, bispecific antibodies, chimeric antigen receptor (CAR)-modified T cells, drug conjugates, nanoparticles and vaccines. Here, we review its biochemistry, normal physiology, role in tumorigenesis, important characteristics as a target, as well as anti-GD2-targeted strategies.

EXPERT OPINION

Bridging the knowledge gaps in understanding the interactions of GD2 with signaling molecules within the glycosynapses, and the regulation of its cellular expression should improve therapeutic strategies targeting this ganglioside. In addition to anti-GD2 IgG mAbs, their drug conjugates, radiolabeled forms especially when genetically engineered to improve therapeutic index and novel bispecific forms or CARs to retarget T-cells are promising candidates for treating metastatic cancers.

Translational downregulation of HSP90 expression by iron chelators in neuroblastoma cells

Iron is an essential cellular nutrient, being a critical cofactor of several proteins involved in cell growth and replication. Compared with normal cells, neoplastic cells have been shown to require a greater amount of iron, thus laying the basis for the promising anticancer activity of iron chelators. In this work, we evaluated the effects of molecules with iron chelation activity on neuroblastoma (NB) cell lines. Of the 17 iron chelators tested, six reduced cell viability of two NB cell lines with an inhibition of growth of 50% below 10 µM; four of the six molecules-ciclopirox olamine (CPX), piroctone, 8-hydroxyquinoline, and deferasirox-were also shown to efficiently chelate intracellular iron within minutes after addition. Effects on cell viability of one of the compounds, CPX, were indeed dependent on chelation of intracellular iron and mediated by both G0/G1 cell cycle block and induction of apoptosis. By combined transcriptome and translatome profiling we identified early translational downregulation of several members of the heat shock protein group as a specific effect of CPX treatment. We functionally confirmed iron-dependent depletion of HSP90 and its client proteins at pharmacologically achievable concentrations of CPX, and we extended this effect to piroctone, 8-hydroxyquinoline, and deferasirox. Given the documented sensitivity of NB cells to HSP90 inhibition, we propose CPX and other iron chelators as investigational antitumor agents in NB therapy.

Bone marrow minimal residual disease was an early response marker and a consistent independent predictor of survival after anti-GD2 immunotherapy

PURPOSE

Immunotherapy is a standard of care for children with high-risk neuroblastoma, where bone marrow (BM) is the predominant metastatic site. Early response markers of minimal residual disease (MRD) in the BM that are also predictive of survival could help individualize patient therapies.

PATIENTS AND METHODS

After achieving first remission (n = 163), primary refractory disease (n = 102), or second remission (n = 95), children with stage 4 neuroblastoma received anti-GD2 3F8 antibody immunotherapy. BM MRD before 3F8 treatment and after cycle 2 (postMRD) was measured using a four-marker panel (B4GALNT1, PHOX2B, CCND1, and ISL1) by quantitative reverse transcription polymerase chain reaction. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method. Prognostic variables were tested in both univariable and multivariable analyses, and MRD markers were further assessed individually and in combination as binary composite (postMRD: 0 and 1) and as equal sum (postMRDSum: 0 to 4) using the Cox regression models, and their predictive accuracy was determined by the concordance index.

RESULTS

When BM was evaluated after cycle 2, individual markers were highly predictive of PFS and OS. The prediction accuracy improved when they were combined in postMRDSum. A multivariable model taking into account all the variables significant in the univariable analyses identified postMRDSum to be independently predictive of PFS and OS. When the model for OS also included missing killer immunoglobulin-like receptor ligand, human antimouse antibody response, and the enrollment disease status, the concordance index was 0.704.

CONCLUSION

BM MRD after two cycles of immunotherapy was confirmed as an early response marker and a consistent independent predictor of survival.

Energy metabolism in neuroblastoma and Wilms tumor

To support high proliferation, the majority of cancer cells undergo fundamental metabolic changes such as increasing their glucose uptake and shifting to glycolysis for ATP production at the expense of far more efficient mitochondrial energy production by oxidative phosphorylation (OXPHOS), which at first glance is a paradox. This phenomenon is known as the Warburg effect. However, enhanced glycolysis is necessary to provide building blocks for anabolic growth. Apart from the generation of ATP, intermediates of glycolysis serve as precursors for a variety of biosynthetic pathways essential for cell proliferation. In the last 10-15 years the field of tumor metabolism has experienced an enormous boom in interest. It is now well established that tumor suppressor genes and oncogenes often play a central role in the regulation of cellular metabolism. Therefore, they significantly contribute to the manifestation of the Warburg effect. While much attention has focused on adult solid tumors, so far there has been comparatively little effort directed at elucidation of the mechanism responsible for the Warburg effect in childhood cancers. In this review we focus on metabolic pathways in neuroblastoma (NB) and Wilms tumor (WT), the two most frequent solid tumors in children. Both tumor types show alterations of the OXPHOS system and glycolytic features. Chromosomal alterations and activation of oncogenes like MYC or inactivation of tumor suppressor genes like TP53 can in part explain the changes of energy metabolism in these cancers. The strict dependence of cancer cells on glucose metabolism is a fairly common feature among otherwise biologically diverse types of cancer. Therefore, inhibition of glycolysis or starvation of cancer cells through glucose deprivation via a high-fat low-carbohydrate diet may be a promising avenue for future adjuvant therapeutic strategies.

Novel Platinum(II) compounds modulate insulin-degrading enzyme activity and induce cell death in neuroblastoma cells

The properties of three novel Platinum(II) compounds toward the insulin-degrading enzyme (IDE) enzymatic activity have been investigated under physiological conditions. The rationale of this study resides on previous observations that these compounds, specifically designed and synthesized by some of us, induce apoptosis in various cancer cell lines, whereas IDE has been proposed as a putative oncogene involved in neuroblastoma onset and progression. Two of these compounds, namely [PtCl(O,O'-acac)(DMSO)] and [Pt(O,O'-acac)(γ-acac)(DMS)], display a modulatory behavior, wherefore activation or inhibition of IDE activity occurs over different concentration ranges (suggesting the existence of two binding sites on the enzyme). On the other hand, [Pt(O,O'-acac)(γ-acac)(DMSO)] shows a typical competitive inhibitory pattern, characterized by a meaningful affinity constant (K i  = 0.95 ± 0.21 μM). Although all three compounds induce cell death in neuroblastoma SHSY5Y cells at concentrations exceeding 2 μM, the two modulators facilitate cells' proliferation at concentrations ≤ 1.5 μM, whereas the competitive inhibitor [Pt(O,O'-acac)(γ-acac)(DMSO)] only shows a pro-apoptotic activity at all investigated concentrations. These features render the [Pt(O,O'-acac)(γ-acac)(DMSO)] a promising "lead compound" for the synthesis of IDE-specific inhibitors (not characterized yet) with therapeutic potentiality.

HMGB1-induced autophagy in Schwann cells promotes neuroblastoma proliferation

Neuroblastoma inflicts mostly on children, and the pathogenesis remains elusive. Clinical diagnosis and therapeutic approaches are still on the incipient stage, so further understanding of the molecular and cellular mechanisms of the disease is necessary. Inflammation has been commonly regarded as a hallmark in tumorigenesis and development, and we identified a new inflammatory factor, HMGB1, is considerably increased in neuroblastoma. Our study shows that HMGB1 induces autophagy in Schwann cells through activation of TLR4, and knockdown of TLR4 obviates the HMGB1-induced autophagy. The HMGB1-induced autophagy is through classical pathway, as deficiency of Beclin 1 deprived autophagy in Schwann cells. Coculture of neuroblastoma with Schwann cells pretreated with HMGB1 promoted the proliferation of neuroblastoma cells, and if Beclin 1 is knocked down in Schwann cells, no promotion effects is observed. Taken together, our study demonstrates that HMGB1-induced autophagy in Schwann cells contributes to neuroblastoma cell proliferation, thus providing a potential therapeutic approach on neuroblastoma development.

Retargeting T cells to GD2 pentasaccharide on human tumors using Bispecific humanized antibody

Anti-disialoganglioside GD2 IgG antibodies have shown clinical efficacy in solid tumors that lack human leukocyte antigens (e.g., neuroblastoma) by relying on Fc-dependent cytotoxicity. However, there are pain side effects secondary to complement activation. T-cell retargeting bispecific antibodies (BsAb) also have clinical potential, but it is thus far only effective against liquid tumors. In this study, a fully humanized hu3F8-BsAb was developed, in which the anti-CD3 huOKT3 single-chain Fv fragment (ScFv) was linked to the carboxyl end of the anti-GD2 hu3F8 IgG1 light chain, and was aglycosylated at N297 of Fc to prevent complement activation and cytokine storm. In vitro, hu3F8-BsAb activated T cells through classic immunologic synapses, inducing GD2-specific tumor cytotoxicity at femtomolar EC50 with >10⁵-fold selectivity over normal tissues, releasing Th1 cytokines (TNFα, IFNγ, and IL2) when GD2⁺ tumors were present. In separate murine neuroblastoma and melanoma xenograft models, intravenous hu3F8-BsAb activated T cells in situ and recruited intravenous T cells for tumor ablation, significantly prolonging survival from local recurrence or from metastatic disease. Hu3F8-BsAb, but not control BsAb, drove T cells and monocytes to infiltrate tumor stroma. These monocytes were necessary for sustained T-cell proliferation and/or survival and contributed significantly to the antitumor effect. The in vitro and in vivo antitumor properties of hu3F8-BsAb and its safety profile support its further clinical development as a cancer therapeutic, and provide the rationale for exploring aglycosylated IgG-scFv as a structural platform for retargeting human T cells.

Involvement of aldehyde dehydrogenase 1A2 in the regulation of cancer stem cell properties in neuroblastoma

Despite the introduction of 13-cis-retinoic acid (13-cis-RA) into the current chemotherapy, more than half of high-risk neuroblastoma patients have experienced tumor relapses driven by chemoresistant cancer stem cells (CSCs) that can be isolated by their ability to grow as spheres. Although aldehyde dehydrogenase (ALDH) has been used to characterize CSCs in certain cancers, ALDH remains elusive in neuroblastoma. In the present study, we determined ALDH activity and expression of its 19 isoforms in spheres and parental cells of neuroblastoma. ALDH activity and several ALDH isoforms were consistently induced in spheres of different neuroblastoma cells. While ALDH1A2, ALDH1L1 and ALDH3B2 expression was consistently induced in spheres and associated with the sphere and colony formation, only ALDH1A2 expression was significantly correlated with the poor prognosis of neuroblastoma patients. ALDH1A2 expression was further associated with the growth and undifferentiation of neuroblastoma xenografts and the resistance of neuroblastoma cells to 13-cis-RA. These results suggest that ALDH1A2 is involved in the regulation of CSC properties in neuroblastoma.

Tumors of the neural crest: Common themes in development and cancer

The neural crest (NC) is a remarkable transient structure in the vertebrate embryo that gives rise to a highly versatile population of pluripotent cells that contribute to the formation of multiple tissues and organs throughout the body. In order to achieve their task, NC-derived cells have developed specialized mechanisms to promote (1) their transition from an epithelial to a mesenchymal phenotype, (2) their capacity for extensive migration and cell proliferation, and (3) their ability to produce diverse cell types largely depending on the microenvironment encountered during and after their migratory path. Following embryogenesis, these same features of cellular motility, invasion, and proliferation can become a liability by contributing to tumorigenesis and metastasis. Ample evidence has shown that cancer cells have cleverly co-opted many of the genetic and molecular features used by developing NC cells. This review focuses on tumors that arise from NC-derived tissues and examines mechanistic themes shared during their oncogenic and metastatic development with embryonic NC cell ontogeny.

Genome-wide microarray expression and genomic alterations by array-CGH analysis in neuroblastoma stem-like cells

Neuroblastoma has a very diverse clinical behaviour: from spontaneous regression to a very aggressive malignant progression and resistance to chemotherapy. This heterogeneous clinical behaviour might be due to the existence of Cancer Stem Cells (CSC), a subpopulation within the tumor with stem-like cell properties: a significant proliferation capacity, a unique self-renewal capacity, and therefore, a higher ability to form new tumors. We enriched the CSC-like cell population content of two commercial neuroblastoma cell lines by the use of conditioned cell culture media for neurospheres, and compared genomic gains and losses and genome expression by array-CGH and microarray analysis, respectively (in CSC-like versus standard tumor cells culture). Despite the array-CGH did not show significant differences between standard and CSC-like in both analyzed cell lines, the microarray expression analysis highlighted some of the most relevant biological processes and molecular functions that might be responsible for the CSC-like phenotype. Some signalling pathways detected seem to be involved in self-renewal of normal tissues (Wnt, Notch, Hh and TGF-β) and contribute to CSC phenotype. We focused on the aberrant activation of TGF-β and Hh signalling pathways, confirming the inhibition of repressors of TGF-β pathway, as SMAD6 and SMAD7 by RT-qPCR. The analysis of the Sonic Hedgehog pathway showed overexpression of PTCH1, GLI1 and SMO. We found overexpression of CD133 and CD15 in SIMA neurospheres, confirming that this cell line was particularly enriched in stem-like cells. This work shows a cross-talk among different pathways in neuroblastoma and its importance in CSC-like cells.

ALK mutations confer differential oncogenic activation and sensitivity to ALK inhibition therapy in neuroblastoma

Genetic studies have established anaplastic lymphoma kinase (ALK), a cell surface receptor tyrosine kinase, as a tractable molecular target in neuroblastoma. We describe comprehensive genomic, biochemical, and computational analyses of ALK mutations across 1,596 diagnostic neuroblastoma samples. ALK tyrosine kinase domain mutations occurred in 8% of samples--at three hot spots and 13 minor sites--and correlated significantly with poorer survival in high- and intermediate-risk neuroblastoma. Biochemical and computational studies distinguished oncogenic (constitutively activating) from nononcogenic mutations and allowed robust computational prediction of their effects. The mutated variants also showed differential in vitro crizotinib sensitivities. Our studies identify ALK genomic status as a clinically important therapeutic stratification tool in neuroblastoma and will allow tailoring of ALK-targeted therapy to specific mutations.

A novel murine T-cell receptor targeting NY-ESO-1

Cancer testis antigens, such as NY-ESO-1, are expressed in a variety of prevalent tumors and represent potential targets for T-cell receptor (TCR) gene therapy. DNA encoding a murine anti-NY-ESO-1 TCR gene (mTCR) was isolated from immunized HLA-A*0201 transgenic mice and inserted into a γ-retroviral vector. Two mTCR vectors were produced and used to transduce human PBL. Transduced cells were cocultured with tumor target cell lines and T2 cells pulsed with the NY-ESO-1 peptide, and assayed for cytokine release and cell lysis activity. The most active TCR construct was selected for production of a master cell bank for clinical use. mTCR-transduced PBL maintained TCR expression in short-term and long-term culture, ranging from 50% to 90% efficiency 7-11 days after stimulation and 46%-82% 10-20 days after restimulation. High levels of interferon-γ secretion were observed (1000-12000 pg/mL), in tumor coculture assays and recognition of peptide-pulsed cells was observed at 0.1 ng/mL, suggesting that the new mTCR had high avidity for antigen recognition. mTCR-transduced T cells also specifically lysed human tumor targets. In all assays, the mTCR was equivalent or better than the comparable human TCR. As the functional activity of TCR-transduced cells may be affected by the formation of mixed dimers, mTCRs, which are less likely to form mixed dimers with endogenous hTCRs, may be more effective in vivo. This new mTCR targeted to NY-ESO-1 represents a novel potential therapeutic option for adoptive cell-transfer therapy for a variety of malignancies.

Essential role of GATA3 in regulation of differentiation and cell proliferation in SK-N-SH neuroblastoma cells

Neuroblastoma is a common solid malignant tumor of the sympathetic nervous system, which contributes to 15% of cancer‑related mortality in children. The differentiation status of neuroblastoma is correlated with clinical outcome, and the induction of differentiation thus constitutes a therapeutic approach in this disease. However, the molecular mechanisms that control the differentiation of neuroblastoma remain poorly understood. The present study aimed to define whether GATA3 is involved in the differentiation of neuroblastoma cells. The results demonstrated that GATA3 is a prognostic marker for survival in patients with neuroblastoma, and that high‑level GATA3 expression is associated with increased self‑renewal and proliferation of neuroblastoma cells. Retinoic acid treatment led to GATA3 downregulation together with neuronal differentiation, suppression of cell proliferation and inhibition of tumorigenecity in neuroblastoma cells. These findings suggest that GATA3 is a key regulator of neuroblastoma differentiation, and provide a novel potential therapeutic strategy for the induction of neuroblastoma differentiation.

Triptolide inhibits cell proliferation and tumorigenicity of human neuroblastoma cells

Triptolide is a diterpene triepoxide, extracted from the Chinese herb Tripterygium wilfordii Hook F, which has been shown to have antitumor activity in a number of cancers. Neuroblastoma is an aggressive extracranial pediatric solid tumor, with significant chemotherapeutic resistance. In this study, triptolide was hypothesized to be a potential therapeutic agent for neuroblastoma. The effects of triptolide on neuroblastoma cell growth and tumor development were investigated. Cell growth and proliferation were evaluated using a cell counting kit-8 assay and a 5-bromo-2-deoxyuridine staining assay. Cell cycle and apoptosis were detected by flow cytometry. Reverse transcription-quantitative polymerase chain reaction was conducted to detect the expression levels of the apoptosis-associated proteins, caspase-3 and caspase-9. The tumorigenicity of neuroblastoma cells was assessed by a soft agar clonogenic assay and an in vivo tumorigenic assay. The results demonstrated that exposure of BE(2)-C human neuroblastoma cells to triptolide resulted in a reduction in cell growth and proliferation, and the induction of cell death and apoptosis, together with cell cycle arrest in the S phase. A soft agar assay indicated that triptolide inhibited the colony-forming ability of BE(2)-C neuroblastoma cells. The xenograft experiment showed that triptolide significantly reduced tumor growth and development in vivo. The data suggested that this Chinese herb may be a potential novel chemotherapeutic agent for neuroblastoma.

The kinase ALK stimulates the kinase ERK5 to promote the expression of the oncogene MYCN in neuroblastoma

Anaplastic lymphoma kinase (ALK) is an important molecular target in neuroblastoma. Although tyrosine kinase inhibitors abrogating ALK activity are currently in clinical use for the treatment of ALK-positive (ALK(+)) disease, monotherapy with ALK tyrosine kinase inhibitors may not be an adequate solution for ALK(+) neuroblastoma patients. Increased expression of the gene encoding the transcription factor MYCN is common in neuroblastomas and correlates with poor prognosis. We found that the kinase ERK5 [also known as big mitogen-activated protein kinase (MAPK) 1 (BMK1)] is activated by ALK through a pathway mediated by phosphoinositide 3-kinase (PI3K), AKT, MAPK kinase kinase 3 (MEKK3), and MAPK kinase 5 (MEK5). ALK-induced transcription of MYCN and stimulation of cell proliferation required ERK5. Pharmacological or RNA interference-mediated inhibition of ERK5 suppressed the proliferation of neuroblastoma cells in culture and enhanced the antitumor efficacy of the ALK inhibitor crizotinib in both cells and xenograft models. Together, our results indicate that ERK5 mediates ALK-induced transcription of MYCN and proliferation of neuroblastoma, suggesting that targeting both ERK5 and ALK may be beneficial in neuroblastoma patients.

Deoxyhypusine synthase (DHPS) inhibitor GC7 induces p21/Rb-mediated inhibition of tumor cell growth and DHPS expression correlates with poor prognosis in neuroblastoma patients

PURPOSE

Neuroblastoma (NB) is an aggressive pediatric malignancy that typically occurs in infants and children under the age of 5 years. High-stage tumors relapse frequently even after aggressive multimodal treatment, resulting in therapy resistance and eventually in patient death. Clearly, new biologically-targeted drugs are needed that more efficiently suppress tumor growth and prevent relapse. We and others previously showed that polyamines such as spermidine play an essential role in NB tumorigenesis and that DFMO, an inhibitor of the central polyamine synthesis gene ODC, is effective in vitro and in vivo, prompting its evaluation in NB clinical trials. However, the specific molecular actions of polyamines remain poorly defined. Spermidine and deoxyhypusine synthase (DHPS) are essential components in the hypusination-driven post-translational activation of eukaryotic initiation factor 5A (eIF5A).

METHODS

We assessed the role of DHPS in NB and the impact of its inhibition by N(1)-guanyl-1,7-diaminoheptane (GC7) on tumor cell growth using cell proliferation assays, Western blot, immunofluorescence microscopy, and Affymetrix micro-array mRNA expression analyses in NB tumor samples.

RESULTS

We found that GC7 inhibits NB cell proliferation in a dose-dependent manner, through induction of the cell cycle inhibitor p21 and reduction of total and phosphorylated Rb proteins. Strikingly, high DHPS mRNA expression correlated significantly with unfavorable clinical parameters, including poor patient survival, in a cohort of 88 NB tumors (all P < 0.04).

CONCLUSIONS

These results suggest that spermidine and DHPS are key contributing factors in NB tumor proliferation through regulation of the p21/Rb signaling axis.

Common genetic variants in NEFL influence gene expression and neuroblastoma risk

The genetic etiology of sporadic neuroblastoma is still largely obscure. In a genome-wide association study, we identified single-nucleotide polymorphisms (SNP) associated with neuroblastoma at the CASC15, BARD1, LMO1, DUSP12, HSD17B12, HACE1, and LIN28B gene loci, but these explain only a small fraction of neuroblastoma heritability. Other neuroblastoma susceptibility genes are likely hidden among signals discarded by the multiple testing corrections. In this study, we evaluated eight additional genes selected as candidates for further study based on proven involvement in neuroblastoma differentiation. SNPs at these candidate genes were tested for association with disease susceptibility in 2,101 cases and 4,202 controls, with the associations found replicated in an independent cohort of 459 cases and 809 controls. Replicated associations were further studied for cis-effect using gene expression, transient overexpression, silencing, and cellular differentiation assays. The neurofilament gene NEFL harbored three SNPs associated with neuroblastoma (rs11994014: Pcombined = 0.0050; OR, 0.88; rs2979704: Pcombined = 0.0072; OR, 0.87; rs1059111: Pcombined = 0.0049; OR, 0.86). The protective allele of rs1059111 correlated with increased NEFL expression. Biologic investigations showed that ectopic overexpression of NEFL inhibited cell growth specifically in neuroblastoma cells carrying the protective allele. NEFL overexpression also enhanced differentiation and impaired the proliferation and anchorage-independent growth of cells with protective allele and basal NEFL expression, while impairing invasiveness and proliferation of cells homozygous for the risk genotype. Clinically, high levels of NEFL expression in primary neuroblastoma specimens were associated with better overall survival (P = 0.03; HR, 0.68). Our results show that common variants of NEFL influence neuroblastoma susceptibility and they establish that NEFL expression influences disease initiation and progression.

Neuroblastoma patient-derived orthotopic xenografts retain metastatic patterns and geno- and phenotypes of patient tumours

Neuroblastoma is a childhood tumour with heterogeneous characteristics and children with metastatic disease often have a poor outcome. Here we describe the establishment of neuroblastoma patient-derived xenografts (PDXs) by orthotopic implantation of viably cryopreserved or fresh tumour explants of patients with high risk neuroblastoma into immunodeficient mice. In vivo tumour growth was monitored by magnetic resonance imaging and fluorodeoxyglucose–positron emission tomography. Neuroblastoma PDXs retained the undifferentiated histology and proliferative capacity of their corresponding patient tumours. The PDXs expressed neuroblastoma markers neural cell adhesion molecule, chromogranin A, synaptophysin and tyrosine hydroxylase. Whole genome genotyping array analyses demonstrated that PDXs retained patient-specific chromosomal aberrations such as MYCN amplification, deletion of 1p and gain of chromosome 17q. Thus, neuroblastoma PDXs recapitulate the hallmarks of high-risk neuroblastoma in patients. PDX-derived cells were cultured in serum-free medium where they formed free-floating neurospheres, expressed neuroblastoma gene markers MYCN, CHGA, TH, SYP and NPY, and retained tumour-initiating and metastatic capacity in vivo. PDXs showed much higher degree of infiltrative growth and distant metastasis as compared to neuroblastoma SK-N-BE(2)c cell line-derived orthotopic tumours. Importantly, the PDXs presented with bone marrow involvement, a clinical feature of aggressive neuroblastoma. Thus, neuroblastoma PDXs serve as clinically relevant models for studying and targeting high-risk metastatic neuroblastoma.

The neural crest: a versatile organ system

The neural crest is the name given to the strip of cells at the junction between neural and epidermal ectoderm in neurula-stage vertebrate embryos, which is later brought to the dorsal neural tube as the neural folds elevate. The neural crest is a heterogeneous and multipotent progenitor cell population whose cells undergo EMT then extensively and accurately migrate throughout the embryo. Neural crest cells contribute to nearly every organ system in the body, with derivatives of neuronal, glial, neuroendocrine, pigment, and also mesodermal lineages. This breadth of developmental capacity has led to the neural crest being termed the fourth germ layer. The neural crest has occupied a prominent place in developmental biology, due to its exaggerated migratory morphogenesis and its remarkably wide developmental potential. As such, neural crest cells have become an attractive model for developmental biologists for studying these processes. Problems in neural crest development cause a number of human syndromes and birth defects known collectively as neurocristopathies; these include Treacher Collins syndrome, Hirschsprung disease, and 22q11.2 deletion syndromes. Tumors in the neural crest lineage are also of clinical importance, including the aggressive melanoma and neuroblastoma types. These clinical aspects have drawn attention to the selection or creation of neural crest progenitor cells, particularly of human origin, for studying pathologies of the neural crest at the cellular level, and also for possible cell therapeutics. The versatility of the neural crest lends itself to interlinked research, spanning basic developmental biology, birth defect research, oncology, and stem/progenitor cell biology and therapy.

N-Myc differentially regulates expression of MXI1 isoforms in neuroblastoma

Amplification of the MYCN proto-oncogene is associated with a poor prognosis in patients with metastatic neuroblastoma (NB). MYCN encodes the N-Myc protein, a transcriptional regulator that dimerizes with the Max transcription factor, binds to E-box DNA sequences, and regulates genes involved in cell growth and apoptosis. Overexpression of N-Myc leads to transcriptional activation and an increase in NB cell proliferation. Mxi1, a member of the Myc family of transcriptional regulators, also binds to Max. However, Mxi1 is a transcriptional repressor and inhibits proliferation of NB cells, suggesting that Mxi1 functions as an N-Myc antagonist. Our laboratory previously identified Mxi1-0, an alternatively transcribed Mxi1 isoform. Mxi1-0 has properties distinct from those of Mxi1; in contrast to Mxi1, Mxi1-0 is unable to suppress c-Myc-dependent transcription. We now show that Mxi1-0 expression increases in response to MYCN overexpression in NB cells, with a positive correlation between MYCN and MXI1-0 RNA levels. We also show that N-Myc expression differentially regulates the MXI1 and MXI1-0 promoters: Increased MYCN expression suppresses MXI1 promoter activity while enhancing transcription through the MXI1-0 promoter. Finally, induction of Mxi1-0 leads to increased proliferation, whereas expression of Mxi1 inhibits cell growth, indicating differential roles for these two proteins. These data suggest that N-Myc differentially regulates the expression of MXI1 and MXI1-0 and can alter the balance between the two transcription factors. Furthermore, MXI1-0 appears to be a downstream target of MYCN-dependent signaling pathways and may contribute to N-Myc-dependent cell growth and proliferation.

Sialic acid metabolic engineering: a potential strategy for the neuroblastoma therapy

Background

Sialic acids (Sia) represent negative-charged terminal sugars on most glycoproteins and glycolipids on the cell surface of vertebrates. Aberrant expression of tumor associated sialylated carbohydrate epitopes significantly increases during onset of cancer. Since Sia contribute towards cell migration ( =  metastasis) and to chemo- and radiation resistance. Modulation of cellular Sia concentration and composition poses a challenge especially for neuroblastoma therapy, due to the high heterogeneity and therapeutic resistance of these cells. Here we propose that Metabolic Sia Engineering (MSE) is an effective strategy to reduce neuroblastoma progression and metastasis.

Methods

Human neuroblastoma SH-SY5Y cells were treated with synthetic Sia precursors N-propanoyl mannosamine (ManNProp) or N-pentanoyl mannosamine (ManNPent). Total and Polysialic acids (PolySia) were investigated by high performance liquid chromatography. Cell surface polySia were examined by flow-cytometry. Sia precursors treated cells were examined for the migration, invasion and sensitivity towards anticancer drugs and radiation treatment.

Results

Treatment of SH-SY5Y cells with ManNProp or ManNPent (referred as MSE) reduced their cell surface sialylation significantly. We found complete absence of polysialylation after treatment of SH-SY5Y cells with ManNPent. Loss of polysialylation results in a reduction of migration and invasion ability of these cells. Furthermore, radiation of Sia-engineered cells completely abolished their migration. In addition, MSE increases the cytotoxicity of anti-cancer drugs, such as 5-fluorouracil or cisplatin.

Conclusions

Metabolic Sia Engineering (MSE) of neuroblastoma cells using modified Sia precursors reduces their sialylation, metastatic potential and increases their sensitivity towards radiation or chemotherapeutics. Therefore, MSE may serve as an effective method to treat neuroblastoma.

An unexpected role for caspase-2 in neuroblastoma

Caspase-2 has been implicated in various cellular functions, including cell death by apoptosis, oxidative stress response, maintenance of genomic stability and tumor suppression. The loss of the caspase-2 gene (Casp2) enhances oncogene-mediated tumorigenesis induced by E1A/Ras in athymic nude mice, and also in the Eμ-Myc lymphoma and MMTV/c-neu mammary tumor mouse models. To further investigate the function of caspase-2 in oncogene-mediated tumorigenesis, we extended our studies in the TH-MYCN transgenic mouse model of neuroblastoma. Surprisingly, we found that loss of caspase-2 delayed tumorigenesis in the TH-MYCN neuroblastoma model. In addition, tumors from TH-MYCN/Casp2^−/− mice were predominantly thoracic paraspinal tumors and were less vascularized compared with tumors from their TH-MYCN/Casp2^+/+ counterparts. We did not detect any differences in the expression of neuroblastoma-associated genes in TH-MYCN/Casp2^−/− tumors, or in the activation of Ras/MAPK signaling pathway that is involved in neuroblastoma progression. Analysis of expression array data from human neuroblastoma samples showed a correlation between low caspase-2 levels and increased survival. However, caspase-2 levels correlated with clinical outcome only in the subset of MYCN-non-amplified human neuroblastoma. These observations indicate that caspase-2 is not a suppressor in MYCN-induced neuroblastoma and suggest a tissue and context-specific role for caspase-2 in tumorigenesis.

A role for TRAIL/TRAIL-R2 in radiation-induced apoptosis and radiation-induced bystander response of human neural stem cells

Adult neurons, which are terminally differentiated cells, demonstrate substantial radioresistance. In contrast, human neural stem cells (NSC), which have a significant proliferative capacity, are highly sensitive to ionizing radiation. Cranial irradiation that is widely used for treatment of brain tumors may induce death of NSC and further cause substantial cognitive deficits such as impairing learning and memory. The main goal of our study was to determine a mechanism of NSC radiosensitivity. We observed a constitutive high-level expression of TRAIL-R2 in human NSC. On the other hand, ionizing radiation through generation of reactive oxygen species targeted cell signaling pathways and dramatically changed the pattern of gene expression, including upregulation of TRAIL. A significant increase of endogenous expression and secretion of TRAIL could induce autocrine/paracrine stimulation of the TRAIL-R2-mediated signaling cascade with activation of caspase-3-driven apoptosis. Furthermore, paracrine stimulation could initiate bystander response of non-targeted NSC that is driven by death ligands produced by directly irradiated NSC. Experiments with media transfer from directly irradiated NSC to non-targeted (bystander) NSC confirmed a role of secreted TRAIL for induction of a death signaling cascade in non-targeted NSC. Subsequently, TRAIL production through elimination of bystander TRAIL-R-positive NSC might substantially restrict a final yield of differentiating young neurons. Radiation-induced TRAIL-mediated apoptosis could be partially suppressed by anti-TRAIL antibody added to the cell media. Interestingly, direct gamma-irradiation of SK-N-SH human neuroblastoma cells using clinical doses (2-5 Gy) resulted in low levels of apoptosis in cancer cells that was accompanied however by induction of a strong bystander response in non-targeted NSC. Numerous protective mechanisms were involved in the maintenance of radioresistance of neuroblastoma cells, including constitutive PI3K-AKT over-activation and endogenous synthesis of TGFβ1. Specific blockage of these survival pathways was accompanied by a dramatic increase in radiosensitivity of neuroblastoma cells. Intercellular communication between cancer cells and NSC could potentially be involved in amplification of cancer pathology in the brain.

The impact of S6K1 kinase on neuroblastoma cell proliferation is independent of GLI1 signaling

Background

The crosstalk between Hedgehog (HH) signaling and other signal transduction cascades has been extensively studied in different cancers. In neuroblastoma, mTOR/S6K1 signaling is known to have a role in the development of this disease and recent evidence also implicates the HH pathway. Moreover, S6K1 kinase has been shown to phosphorylate GLI1, the effector of HH signaling, promoting GLI1 transcriptional activity and oncogenic function in esophageal adenocarcinoma. In this study, we examined the possible interplay of S6K1 and GLI1 signaling in neuroblastoma.

Methods

siRNA knockdowns were used to suppress S6K1 and GLI1 expression, and the siRNA effects were validated by real-time PCR and Western blotting. Cell proliferation analysis was performed with the EdU incorporation assay. Cytotoxic analysis with increasing concentrations of PI3K/mTOR and GLI inhibitors, individually and in combination, was used to determine drug response.

Results

Although knockdown of either S6K1 or GLI1 reduces the cellular proliferation of neuroblastoma cells, there is little effect of S6K1 on the expression of GLI1 mRNA and protein and on the capacity of GLI1 to activate target genes. No detectable phosphorylation of GLI1 is observed prior or following S6K1 knockdown. GLI1 overexpression can not rescue the reduced proliferation elicited by S6K1 knockdown. Moreover, inhibitors of PI3K/mTOR and GLI signaling reduced neuroblastoma cell growth, but no additional growth inhibitory effects were detected when the two classes of drugs were combined.

Conclusion

Our results demonstrate that the impact of S6K1 kinase on neuroblastoma cells is not mediated through modulation of GLI1 expression/activity.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-600) contains supplementary material, which is available to authorized users.