DDR2 signaling and mechanosensing orchestrate neuroblastoma cell fate through different transcriptome mechanisms

The extracellular matrix (ECM) regulates carcinogenesis by interacting with cancer cells via cell surface receptors. Discoidin Domain Receptor 2 (DDR2) is a collagen-activated receptor implicated in cell survival, growth, and differentiation. Dysregulated DDR2 expression has been identified in various cancer types, making it as a promising therapeutic target. Additionally, cancer cells exhibit mechanosensing abilities, detecting changes in ECM stiffness, which is particularly important for carcinogenesis given the observed ECM stiffening in numerous cancer types. Despite these, whether collagen-activated DDR2 signaling and ECM stiffness-induced mechanosensing exert similar effects on cancer cell behavior and whether they operate through analogous mechanisms remain elusive. To address these questions, we performed bulk RNA sequencing (RNA-seq) on human SH-SY5Y neuroblastoma cells cultured on collagen-coated substrates. Our results show that DDR2 downregulation induces significant changes in the cell transcriptome, with changes in expression of 15% of the genome, specifically affecting the genes associated with cell division and differentiation. We validated the RNA-seq results by showing that DDR2 knockdown redirects the cell fate from proliferation to senescence. Like DDR2 knockdown, increasing substrate stiffness diminishes cell proliferation. Surprisingly, RNA-seq indicates that substrate stiffness has no detectable effect on the transcriptome. Furthermore, DDR2 knockdown influences cellular responses to substrate stiffness changes, highlighting a crosstalk between these two ECM-induced signaling pathways. Based on our results, we propose that the ECM could activate DDR2 signaling and mechanosensing in cancer cells to orchestrate their cell fate through distinct mechanisms, with or without involving gene expression, thus providing novel mechanistic insights into cancer progression.

Longitudinal evaluation of serum microRNAs as biomarkers for neuroblastoma burden and therapeutic p53 reactivation

Accurate assessment of treatment response and residual disease is indispensable for the evaluation of cancer treatment efficacy. However, performing tissue biopsies for longitudinal follow-up poses a major challenge in the management of solid tumours like neuroblastoma. In the present study, we evaluated whether circulating miRNAs are suitable to monitor neuroblastoma tumour burden and whether treatment-induced changes of miRNA abundance in the tumour are detectable in serum. We performed small RNA sequencing on longitudinally collected serum samples from mice carrying orthotopic neuroblastoma xenografts that were exposed to treatment with idasanutlin or temsirolimus. We identified 57 serum miRNAs to be differentially expressed upon xenograft tumour manifestation, out of which 21 were also found specifically expressed in the serum of human high-risk neuroblastoma patients. The murine serum levels of these 57 miRNAs correlated with tumour tissue expression and tumour volume, suggesting potential utility for monitoring tumour burden. In addition, we describe serum miRNAs that dynamically respond to p53 activation following treatment of engrafted mice with idasanutlin. We identified idasanutlin-induced serum miRNA expression changes upon one day and 11 days of treatment. By limiting to miRNAs with a tumour-related induction, we put forward hsa-miR-34a-5p as a potential pharmacodynamic biomarker of p53 activation in serum.

Abstract B47: Engineering immunomodulatory nanoparticles for "cold"-to-"hot" tumor microenvironment remodeling for treatment of high-risk neuroblastoma

This study seeks to develop a systemic immunomodulatory nanoparticle (immuno-NP) therapy that harnesses proinflammatory innate immune cells to remodel tumor microenvironment (TME) immunity in humanized mouse models of high-risk neuroblastoma (NB). Currently, survival for high-risk metastatic NB remains ~50% at 5 years, even with chemotherapy given at maximal tolerated dosing, which itself imparts debilitating long-term sequelae in >90% of survivors. The success of immunotherapies for leukemias and lymphomas has not translated to pediatric solid tumors, which typically present as immunosuppressed “cold” tumors with microenvironments that limit antigen presentation and sustained activation of cytotoxic CD8+ T cells. To date, immune checkpoint inhibitor and chimeric antigen receptor (CAR) T approaches have primarily focused on augmenting CD8+ T cells that are suppressed by the “cold” TME of high-risk solid tumors. However, it has now been demonstrated that proinflammatory cytokines secreted by innate antigen-presenting cells (APCs), such as dendritic cells (DCs) and macrophages, can restimulate anti-tumor T cell responses by remodeling the TME from “cold” to “hot”. Here, we use a novel engineering approach to design and systemically deliver lipid-based immuno-NPs coencapsulating synergistic innate immune agonists of the stimulator of interferon genes (STNG) and Toll-like receptor 4 (TLR4) pathways to target APCs that are enriched in the TME perivascular region. APCs taking up NPs synergistically produce Type I interferons, priming and recruiting CD8+ T cells for clearance. We hypothesized that treatment of humanized mice bearing human NB xenografts with immuno-NPs will drive APC-mediated “cold”-to-“hot” TME remodeling, leading to sustained recruitment and activation of CD8+ T cells. Humanized NOD scid gamma (NSG) mice bearing orthotopic CMYC-expressing metastatic SH-SY5Y cell xenografts were treated with immuno-NPs and tumor burden assessed via bioluminescent imaging just 3 days afterwards indicated a significant 47% reduction in primary tumor mass and 53% reduction in liver metastasis. Confocal imaging of both the primary tumor and metastatic sites indicated clear immuno-NP deposition surrounding the CD31+ vascular tumor endothelium. Flow cytometry analysis of primary tumors indicated a significant 7.8-fold increase in infiltrating CD8+ T cells in mice that received immuno-NPs compared to control mice that received empty NPs. Subsequent survival experiments demonstrated that immuno-NPs significantly increased survival by driving proinflammatory cytokine production in the TME and also combined effectively with PD1 blockade for enhanced CD8+ T cell activation and function. In conclusion, these findings demonstrated the feasibility of our engineering strategy as a safer, more effective therapy for high-risk NB by confirming that immuno-NPs deposit avidly in NB primary tumors and even sites of metastasis upon systemic delivery, bolster TME APC function and CD8+ T cell-mediated clearance, and drive protective long-term anti-tumor immunity.

Citation Format: Prabhani Atukorale, Jason Shohet, Christina Lusi, Kim Wigglesworth, Griffin Kane, Esteban Rozen. Engineering immunomodulatory nanoparticles for "cold"-to-"hot" tumor microenvironment remodeling for treatment of high-risk neuroblastoma [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr B47.

KDM6B promotes activation of the oncogenic CDK4/6-pRB-E2F pathway by maintaining enhancer activity in MYCN-amplified neuroblastoma

The H3K27me2/me3 histone demethylase KDM6B is essential to neuroblastoma cell survival. However, the mechanism of KDM6B action remains poorly defined. We demonstrate that inhibition of KDM6B activity 1) reduces the chromatin accessibility of E2F target genes and MYCN, 2) selectively leads to an increase of H3K27me3 but a decrease of the enhancer mark H3K4me1 at the CTCF and BORIS binding sites, which may, consequently, disrupt the long-range chromatin interaction of MYCN and E2F target genes, and 3) phenocopies the transcriptome induced by the specific CDK4/6 inhibitor palbociclib. Overexpression of CDK4/6 or Rb1 knockout confers neuroblastoma cell resistance to both palbociclib and the KDM6 inhibitor GSK-J4. These data indicate that KDM6B promotes an oncogenic CDK4/6-pRB-E2F pathway in neuroblastoma cells via H3K27me3-dependent enhancer-promoter interactions, providing a rationale to target KDM6B for high-risk neuroblastoma.

The histone demethylase KDM6B is reported to be essential for neuroblastoma cell survival. Here the authors show that KDM6B regulates CDK4/6-pRB-E2F pathway through H3K27me3-dependent enhancer-promoter interactions in neuroblastoma.

Is high-risk neuroblastoma induction chemotherapy possible without G-CSF? A pilot study of safety and treatment delays in the absence of primary prophylactic hematopoietic growth factors

BACKGROUND/OBJECTIVES

Standard supportive care during induction therapy for high-risk neuroblastoma (HR-NBL) includes primary prophylactic granulocyte colony-stimulating factor (G-CSF) aimed at limiting duration of neutropenia, reducing infection risk, and minimizing treatment delays. Preclinical models suggest that G-CSF promotes maintenance of neuroblastoma cancer stem cells and may reduce the efficacy of chemotherapy. This study's objective was to determine the safety and feasibility of administering induction chemotherapy without routine use of prophylactic G-CSF.

DESIGN/METHODS

Children with newly diagnosed HR-NBL received six-cycle induction chemotherapy regimen without prophylactic G-CSF in four cycles. G-CSF was administered for stem cell mobilization after cycle 3 and granulocyte-monocyte colony-stimulating factor after cycle 5 prior to surgical resection of primary disease. The primary outcome measure was the incidence of grade 3 or higher infection. We hypothesized that the per patient infection rate would be comparable to our institutional baseline rate of 58% in patients with HR-NBL receiving induction chemotherapy with prophylactic growth factor support. The trial used an A'Hern single-stage design.

RESULTS

Twelve patients with HR-NBL received 58 cycles of chemotherapy on study. Three patients completed the entire six-cycle regimen with no infections. Nine patients experienced grade 3 infections (bacteremia four, urinary tract infection two, skin/soft tissue infection three). No patients experienced grade 4 infections or required intensive care treatment for infection.

CONCLUSION

A greater than expected number of serious bacterial infections were observed during administration of induction chemotherapy for HR-NBL without primary prophylactic G-CSF. These results support continued prophylactic administration growth factor during induction chemotherapy.

Circulating microRNA biomarkers for metastatic disease in neuroblastoma patients

In this study, the circulating miRNome from diagnostic neuroblastoma serum was assessed for identification of noninvasive biomarkers with potential in monitoring metastatic disease. After determining the circulating neuroblastoma miRNome, 743 miRNAs were screened in 2 independent cohorts of 131 and 54 patients. Evaluation of serum miRNA variance in a model testing for tumor stage, MYCN status, age at diagnosis, and overall survival revealed tumor stage as the most significant factor impacting miRNA abundance in neuroblastoma serum. Differential abundance analysis between patients with metastatic and localized disease revealed 9 miRNAs strongly associated with metastatic stage 4 disease in both patient cohorts. Increasing levels of these miRNAs were also observed in serum from xenografted mice bearing human neuroblastoma tumors. Moreover, murine serum miRNA levels were strongly associated with tumor volume. These findings were validated in longitudinal serum samples from metastatic neuroblastoma patients, where the 9 miRNAs were associated with disease burden and treatment response.

Abstract B21: Epigenetic modifiers MLL1 and JMJD3 regulate neuroblastoma tumorigenicity by maintaining a cancer stem cell-like population

High-risk neuroblastoma (NB) represents a major clinical challenge in pediatric oncology. Despite significant dose escalation of intense therapies, long-term survival for NB patients remains poor (<45%), and the disease accounts for almost 15% of all pediatric cancer deaths. Relapse of metastatic, drug-resistant disease and treatment-related toxicities mandates the development of new therapeutic strategies. Recently, we discovered a highly tumorigenic, chemoresistant, and self-renewing subpopulation in NB with features similar to cancer stem cells (CSCs). This G-CSF receptor (CD114)-expressing subpopulation can escape initial therapy and cause aggressively invasive relapsed disease. Therefore, developing direct targeting strategies and understanding for the molecular mechanisms maintaining this NB CSC-like subpopulation is essential to delineate effective therapeutics for NB patients. By using siRNA screening approach and low-density pathway arrays, we found that the epigenetic regulators mixed-lineage leukemia-1 (MLL1; KMT2A; a H3K4me3 methyltransferase) and Jumonji D3 (JMJD3; KDM6B; a H3K27me3 demethylase) are important epigenetic regulators for NB proliferation and growth. Interestingly, we found that epigenetic regulators MLL1 and JMJD3 are aberrantly expressed in CD114+ subpopulation and regulate the expression of the G-CSF receptor gene (CSF3R) itself, by maintaining active histone modifications at the promoter locus. Inhibition of MLL1 and JMJD3 with specific small-molecule inhibitors reverses the histone patterns at CSF3R promoter and blocks gene expression, induces apoptosis selectively in CD114+ cells, and inhibits overall NB proliferation in vitro. Furthermore, inhibiting MLL1 and JMJD3 leads to dramatic tumor regression (p<0.001) and reduction in incidences of metastasis (p<0.001) in vivo. Most interestingly, both of these inhibitors increase the overall survival of the treated mice in vivo. As expected, reduction in tumor size was significantly correlated with the reduction in tumor CD114+ cells. Taken together, these data highlight that: a) neuroblastoma is maintained by the complex interplay of epigenetic modifiers, and b) direct targeting of these epigenetic modifiers and combining this approach with current therapy is a novel therapeutic approach to high-risk NB.

Citation Format: Saurabh Agarwal, Julie Tomolonis, Sanjeev Vasudevan, Jason Shohet. Epigenetic modifiers MLL1 and JMJD3 regulate neuroblastoma tumorigenicity by maintaining a cancer stem cell-like population [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B21.

A physiologically relevant 3D collagen-based scaffold-neuroblastoma cell system exhibits chemosensitivity similar to orthotopic xenograft models

3D scaffold-based in vitro cell culturing is a recent technological advancement in cancer research bridging the gap between conventional 2D culture and in vivo tumours. The main challenge in treating neuroblastoma, a paediatric cancer of the sympathetic nervous system, is to combat tumour metastasis and resistance to multiple chemotherapeutic drugs. The aim of this study was to establish a physiologically relevant 3D neuroblastoma tissue-engineered system and explore its therapeutic relevance. Two neuroblastoma cell lines, chemotherapeutic sensitive Kelly and chemotherapeutic resistant KellyCis83 were cultured in a 3D in vitro model on two collagen-based scaffolds containing either glycosaminoglycan (Coll-GAG) or nanohydroxyapatite (Coll-nHA) and compared to 2D cell culture and an orthotopic murine model. Both neuroblastoma cell lines actively infiltrated the scaffolds and proliferated displaying >100-fold increased resistance to cisplatin treatment when compared to 2D cultures, exhibiting chemosensitivity similar to orthotopic xenograft in vivo models. This model demonstrated its applicability to validate miRNA-based gene delivery. The efficacy of liposomes bearing miRNA mimics uptake and gene knockdown was similar in both 2D and 3D in vitro culturing models highlighting the proof-of-principle for the applicability of 3D collagen-based scaffolds cell system for validation of miRNA function. Collectively, this data shows the successful development and characterisation of a physiologically relevant, scaffold-based 3D tissue-engineered neuroblastoma cell model, strongly supporting its value in the evaluation of chemotherapeutics, targeted therapies and investigation of neuroblastoma pathogenesis. While neuroblastoma is the specific disease being focused upon, the platform may have multi-functionality beyond this tumour type.

STATEMENT OF SIGNIFICANCE

Traditional 2D cell cultures do not completely capture the 3D architecture of cells and extracellular matrix contributing to a gap in our understanding of mammalian biology at the tissue level and may explain some of the discrepancies between in vitro and in vivo results. Here, we demonstrated the successful development and characterisation of a physiologically relevant, scaffold-based 3D tissue-engineered neuroblastoma cell model, strongly supporting its value in the evaluation of chemotherapeutics, targeted therapies and investigation of neuroblastoma pathogenesis. The ability to test drugs in this reproducible and controllable tissue-engineered model system will help reduce the attrition rate of the drug development process and lead to more effective and tailored therapies. Importantly, such 3D cell models help to reduce and replace animals for pre-clinical research addressing the principles of the 3Rs.

Dual targeting of MDM2 and BCL2 as a therapeutic strategy in neuroblastoma

Wild-type p53 tumor suppressor activity in neuroblastoma tumors is hampered by increased MDM2 activity, making selective MDM2 antagonists an attractive therapeutic strategy for this childhood malignancy. Since monotherapy in cancer is generally not providing long-lasting clinical responses, we here aimed to identify small molecule drugs that synergize with idasanutlin (RG7388). To this purpose we evaluated 15 targeted drugs in combination with idasanutlin in three p53 wild type neuroblastoma cell lines and identified the BCL2 inhibitor venetoclax (ABT-199) as a promising interaction partner. The venetoclax/idasanutlin combination was consistently found to be highly synergistic in a diverse panel of neuroblastoma cell lines, including cells with high MCL1 expression levels. A more pronounced induction of apoptosis was found to underlie the synergistic interaction, as evidenced by caspase-3/7 and cleaved PARP measurements. Mice carrying orthotopic xenografts of neuroblastoma cells treated with both idasanutlin and venetoclax had drastically lower tumor weights than mice treated with either treatment alone. In conclusion, these data strongly support the further evaluation of dual BCL2/MDM2 targeting as a therapeutic strategy in neuroblastoma.

Heterogeneous Uptake of Nanoparticles in Mouse Models of Pediatric High-Risk Neuroblastoma

Liposomal chemotherapeutics are exemplified by DOXIL® are commonly used in adult cancers. While these agents exhibit improved safety profile compared to their free drug counterparts, their treatment response rates have been ~ 20%, often attributed to the heterogeneous intratumoral uptake and distribution of liposomal nanoparticles. Non-invasive and quantitative monitoring of the uptake and distribution of liposomal nanoparticles in solid tumors could allow for patient stratification and personalized cancer nanomedicine. In this study, the variability of liposomal nanoparticle intratumoral distribution and uptake in orthotopic models of pediatric neuroblastoma was investigated using a liposomal nanoprobe visualized by high-resolution computed tomography (CT). Two human neuroblastoma cell lines (NGP: a MYCN-amplified line, and SH-SY5Y a MYCN non-amplified line) were implanted in the renal capsule of nude mice to establish the model. Intratumoral nanoparticle uptake was measured at tumor ages 1, 2, 3 and 4 weeks post implantation. The locations of uptake within the tumor were mapped in the 3-dimensional reconstructed images. Total uptake was measured by integration of the x-ray absorption signal over the intratumoral uptake locations. Both tumor models showed significant variation in nanoparticle uptake as the tumors aged. Observation of the uptake patterns suggested that the nanoparticle uptake was dominated by vascular leak at the surface/periphery of the tumor, and localized, heterogeneous vascular leak in the interior of the tumor. Slow growing SH-SY5Y tumors demonstrated uptake that correlated directly with the tumor volume. Faster growing NGP tumor uptake did not correlate with any tumor geometric parameters, including tumor volume, tumor surface area, and R30 and R50, measures of uptake localized to the interior of the tumor. However, uptake for both SH-SY5Y and NGP tumors correlated almost perfectly with the leak volume, as measured by CT. These results suggest that the uptake of nanoparticles is heterogeneous and not governed by tumor geometry. An imaging nanoprobe remains the best measure of nanoparticle uptake in these tumor models.

Abstract B31: Combined siRNA and small molecule screening identifies Aurora B kinase as an effective target in MYCN-driven neuroblastoma

Despite advances in multimodal treatment, neuroblastoma (NB) is often fatal for children with high-risk disease and many survivors need to cope with long-term side effects from high-dose chemotherapy and radiation. To identify new therapeutic targets, we performed a siRNA screen of the druggable genome combined with a small molecule screen of 465 compounds targeting 39 different mechanisms of actions in four NB cell lines. We identified 58 genes as targets, including AURKB, in at least one cell line. In the drug screen, aurora kinase inhibitors (nine molecules) and in particular the AURKB-selective compound, barasertib, were the most discriminatory with regard to sensitivity for MYCN-amplified cell lines. In an expanded panel of NB cell lines, those with MYCN amplification and wild-type TP53 were the most sensitive to low nanomolar concentrations of barasertib. Inhibition of the AURKB kinase activity resulted in decreased phosphorylation of its known target histone H3, and upregulation of p53 pathway in MYCN-amplified NB cells with wild-type TP53. Both wild-type and p53-mutant MYCN-amplified cell lines arrested in G2/M phase upon AURKB inhibition. Additionally, barasertib induced endoreduplication and apoptosis. Treatment of MYCN-amplified/TP53 wild-type neuroblastoma xenografts resulted in profound growth inhibition and tumor regression. Therefore, aurora B kinase inhibition is highly effective in aggressive neuroblastoma and warrants further investigation in clinical trials.

Citation Format: Dominik Bogen, Jun S. Wei, David O. Azorsa, Pinar Ormanoglu, Eugen Buehler, Rajarshi Guha, Jonathan M. Keller, Lesley A. Mathews Griner, Marc Ferrer, Young K. Song, Hongling Liao, Arnulfo Mendoza, Berkley E. Gryder, Sivasish Sindri, Jianbin He, Xinyu Wen, Xinyu Wen, Shile Zhang, John F. Shern, Marielle E. Yohe, Sabine Taschner-Mandl, Jason Shohet, Craig J. Thomas, Scott E. Martin, Peter F. Ambros, Javed Khan. Combined siRNA and small molecule screening identifies Aurora B kinase as an effective target in MYCN-driven neuroblastoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr B31.

MYCN controls an alternative RNA splicing program in high-risk metastatic neuroblastoma

The molecular mechanisms underlying the aggressive behavior of MYCN driven neuroblastoma (NBL) is under intense investigation; however, little is known about the impact of this family of transcription factors on the splicing program. Here we used high-throughput RNA sequencing to systematically study the expression of RNA isoforms in stage 4 MYCN-amplified NBL, an aggressive subtype of metastatic NBL. We show that MYCN-amplified NBL tumors display a distinct gene splicing pattern affecting multiple cancer hallmark functions. Six splicing factors displayed unique differential expression patterns in MYCN-amplified tumors and cell lines, and the binding motifs for some of these splicing factors are significantly enriched in differentially-spliced genes. Direct binding of MYCN to promoter regions of the splicing factors PTBP1 and HNRNPA1 detected by ChIP-seq demonstrates that MYCN controls the splicing pattern by direct regulation of the expression of these key splicing factors. Furthermore, high expression of PTBP1 and HNRNPA1 was significantly associated with poor overall survival of stage4 NBL patients (p ≤ 0.05). Knocking down PTBP1, HNRNPA1 and their downstream target PKM2, an isoform of pro-tumor-growth, result in repressed growth of NBL cells. Therefore, our study reveals a novel role of MYCN in controlling global splicing program through regulation of splicing factors in addition to its well-known role in the transcription program. These findings suggest a therapeutically potential to target the key splicing factors or gene isoforms in high-risk NBL with MYCN-amplification.

Abstract B44: The epigenetic modifier CHAF1A opposes neuroblastoma differentiation via metabolic reprogramming

Background: Neuroblastoma arises from embryonal neural crest secondary to a block in differentiation and long-term survival inversely correlates with the degree of neuronal differentiation. Inhibition of epigenetically controlled developmental programs is critical for neuronal de-differentiation and neuroblastoma pathogenesis. Treatment with differentiation agents has modestly improved survival.

Methods: Loss-of-function studies in neuroblastoma cell lines with inducible and stable CHAF1A knockdown were performed in vitro and in vivo. Gene expression profiling of knockdown and control cell lines was performed on the Affymetrix U133+2.0 arrays. GSEA (Gene Set Enrichment Analysis) defined the transcriptional response to CHAF1A silencing. Quantitative-PCR assays were used to correlate CHAF1A expression with outcome and to validate the most significant enriched gene sets.

Results: Here we demonstrate a novel function for the histone chaperone and epigenetic regulator CHAF1A in maintaining the highly de-differentiated state of neuroblastoma. CHAF1A is a subunit of the Chromatin Assembly Factor-1 (CAF1) which regulates H3K9-trimethylation and DNA methylation. High CHAF1A expression strongly correlates with poor prognosis in a large clinical cohort of 348 neuroblastoma patients (Progression-Free and Overall Survival p<0.001). Loss-of-function effectively controls tumor growth and drives neuronal differentiation both in vitro and in vivo. GSEA reveals that genes regulated by CHAF1A are associated with major metabolism and oncogenic pathways. CHAF1A silencing significantly (nominal p-value <0.05 and FDR q-value <0.25) enriches for cell metabolism pathways (valine, leucine, and isoleucine degradation, glutamate metabolism and insulin pathways) and suppresses pathways with known oncogenic function in neuroblastoma (KRAS, ALK, Akt and BMI1). Quantitative-PCR confirms that the most affected genes belong to the glucose and insulin pathway.

Conclusions: Our findings support the hypothesis that CHAF1A expression restricts neural crest differentiation and contributes to the pathogenesis of high-risk neuroblastoma by epigenetic regulation of glucose metabolism. In particular, we believe that the oncogenic functions of CHAF1A in neuroblastoma in part direct the metabolic reprogramming, thus conferring cell survival advantages and blocking cell differentiation. Further understanding of the metabolic changes epigenetically induced by CHAF1A will identify vulnerable points to impair neuroblastoma cell growth and guide the development of novel therapies.

Citation Format: Eveline Barbieri, Zaowen Chen, Anna Lakoma, Eugene Kim, Jason Shohet. The epigenetic modifier CHAF1A opposes neuroblastoma differentiation via metabolic reprogramming. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B44.

Abstract A26: MYCN modifies p53 transcriptional responses to oppose apoptosis and activate cell cycle progression

Introduction: The MYCN transcription factor plays a central role in neuroblastoma pathogenesis. This aggressive pediatric malignancy is p53 wild type and repression of p53 functions is required for tumorigenesis. MYC family transcription factors activate and repress a larger number of genes involved in cell proliferation, metastasis and tumorigenesis through direct and indirect mechanisms. We hypothesized that MYCN promotes NB tumorigenesis through repression of p53 transcriptional function.

Design: To define MYCN mediated alterations in p53 activity, we performed RNA sequencing on NB cells treated with the MDM2 inhibitor, Nutlin 3a, in the presence or absence of MYCN expression (conditional Tet-on system). MYCN3 cells were either uninduced or induced with doxycycline for 16 h followed by treatment for 8 hours with either Nutlin 3a or control. Total RNA was isolated and used for RNA-seq on the HiSeqTM platform (Illumina).

Results: Between 6.2 × 107 to 7.6 × 107 sequence tags were obtained for each condition which uniquely mapped onto the human genome reference sequence (HG19) using the PASH algorithm. We normalized the data sets using a genomic distribution (FDR < 0.001). Next, determined fold changes in gene expression in response to p53 activation with high or low MYCN levels using stringent cutoffs of FKM ≥ 1 and log fold change ≥ 1.3. We found total 103 genes whose transcription was increased in response to Nutlin treatment and 161 genes whose transcription was repressed (p value of < 0.05). Comparison of p53 target gene transcript levels under these four conditions (low MYCN / low p53, low MYCN / high p53, high MYCN / low p53 and high MCYN / high p53) revealed that MYCN levels altered the transcriptional response to p53 activation with Nutlin. MYCN inhibited expression of 25 genes activated by p53 and promoted expression of 30 genes repressed by p53 (log fold change cutoff of ≤ 0.5 with a p value of < 0.01). Bioinformatic analysis using DAVID and GSEA further demonstrated that p53 response genes, altered by MYCN, are primarily involved in apoptotic pathways, cell cycle, and mitotic regulation. Next, we used MYCN ChIP-seq and p53 ChIP-seq datasets to evaluate gene promoters for presence of MYCN binding and p53 binding. Remarkably, we found that the promoters of p53 activated genes which were repressed by the presence of MYCN consistently bound both transcription factors, while the p53 repressed genes bound only MYCN and didn't display p53 binding. We have confirmed these ChIP-seq results with ChIP-qPCR for a subset of genes with central roles in tumor suppression and tumorigenicity (e.g. CDKN1A, CHEK1, AEN, MDM2, Notch1). In addition, a subset of these MYCN modulated p53 transcriptional targets is over expressed in tumors from patients with high-risk disease.

Conclusions: Over all these data provide the first unbiased, genome-wide evaluation of how MYCN can modify p53 transcriptional function. Our data suggest a mechanism of direct interactions between MYCN and p53 on the promoters of p53 transcriptional targets, acting to inhibit p53 pro-apoptotic pathways. These data identify key components of the p53 transcriptional response altered by MYCN (i.e. apoptosis, mitotic checkpoints and cell cycle) and we propose that reactivation of elements provides a novel therapeutic strategy.

Citation Format: Saurabh Agarwal, Kimal Rajapakshe, Cristian Coarfa, Jason Shohet. MYCN modifies p53 transcriptional responses to oppose apoptosis and activate cell cycle progression. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr A26.

Genome-based outcome prediction in MYCN nonamplified high-risk neuroblastoma

9534

Background: Less than 40% of children with high-risk neuroblastoma achieve long-term survival, and at diagnosis, it is not possible to identify patients who will be cured. Microarray studies have proposed expression signatures associated with outcome within high-risk cohorts. However, integrating this technology as a clinical test has been difficult, in part due to the lack of available frozen tissue and high quality RNA. The nCounter overcomes this obstacle, using formalin-fixed paraffin embedded tissue (FFPE). Our objective is to test the correlation of a previously published “ultra high-risk” microarray gene signature developed in the MYCN nonamplified high-risk population (Asgharzadeh et al, J Natl Cancer Inst, 2006) with the gene expression signature obtained with the nCounter (NanoString Technologies) using RNA isolated from FFPE MYCN nonamplified high-risk neuroblastoma samples. Methods: FFPE tumor samples linked to clinical outcome data were obtained from 6 collaborative institutions. Tumor content of each sample was assessed morphologically. RNA was isolated using the RNeasy FFPE-kit. Customized probes corresponding to the candidate genes were designed by NanoString. Hybridization reactions were performed in duplicate using 100 ng of RNA. Positive and negative control probes and housekeeping probes were included in every reaction and were used to normalize data for differences in purification, hybridization, and capture efficiencies Results: Forty-two MYCN nonamplified high-risk neuroblastoma samples were analyzed by the nCounter. The cohort 5-year event-free survival and overall survival were 44.6 +/- 8.0% and 53.8 +/- 8.4% respectively. Highly degraded RNA (RIN ~ 1.5-2.8) was obtained. Unsupervised clustering and principle components analysis on normalized expression data showed differential expression of most of the genes with clustering of cases depending upon outcome (FDR = 0.05). Conclusions: Our results demonstrate that the nCounter can yield gene expression profiles that are similar to microarray gene signatures. Further investigation of the clinical utility the nCounter technology to prognosticate outcome in patients with high-risk neuroblastoma is warranted.

Abstract 674: Cooperative induction of apoptosis through p53 signaling and mTOR inhibition in neuroblastoma

The use of MDM2 inhibitors (e.g. Nutlin 3a) to stabilize p53 and induce apoptosis is an attractive therapeutic approach for neuroblastoma which is predominantly p53 wild-type at diagnosis and relapse. We sought to identify additional pathways to potentiate the p53 response. Mammalian target of rapamycin (mTOR) signaling pathway is active in neuroblastoma and mTOR inhibition has antiproliferative effects in vivo in neuroblastoma. It was recently demonstrated that two p53 target genes, Sestrin1 and Sestrin2, inhibit mTOR activity, linking genotoxic stress, p53 and the mTOR signaling pathway. We investigated the role of Sestrin1 and Sestrin2 in p53-mediated apoptosis in neuroblastoma and the interaction of mTOR and p53 pathways after their simultaneous blockade using the mTOR inhibitor, Temsirolimus and the MDM2 inhibitor, Nutlin 3a.

We show here that stabilization and activation of wt-p53 through MDM2 inhibition result in significant and rapid p53-dependent apoptosis. Using microarray analysis in primary tumor line and RT-PCR in several neuroblastoma lines, we demonstrate that the global transcriptional response is p53-dependent and that Sestrin1 and Sestrin2 are significantly up-regulated in response to Nutlin. With MTT and Tunnel assays we demonstrate a p53-dependent synergistic effect of combined Nutlin 3a and Temsirolimus treatment on cell growth and apoptosis. Flow cytometric analysis of the phospho-S6 ribosomal protein demonstrates a profound dephosphorylation of S6 in vitro when low dose Nutlin 3a is combined with Temsirolimus. Additional in vivo studies suggest that mTOR inhibition reduces tumor burden and proliferation of neuroblastoma xenografts in nude mice. We conclude that MDM2 inhibition and p53 driven Sestrin1 and Sestrin2 activation enhance the apoptotic response to mTOR inhibition. Thus the therapeutic strategy of combined MDM2 and mTOR inhibition may represent a clinically potent approach to de novo and relapsed neuroblastoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 674.

The MYCN oncogene is a direct target of miR-34a

Loss of 1p36 heterozygosity commonly occurs with MYCN amplification in neuroblastoma tumors, and both are associated with an aggressive phenotype. Database searches identified five microRNAs that map to the commonly deleted region of 1p36 and we hypothesized that the loss of one or more of these microRNAs contributes to the malignant phenotype of MYCN-amplified tumors. By bioinformatic analysis, we identified that three out of the five microRNAs target MYCN and of these miR-34a caused the most significant suppression of cell growth through increased apoptosis and decreased DNA synthesis in neuroblastoma cell lines with MYCN amplification. Quantitative RT-PCR showed that neuroblastoma tumors with 1p36 loss expressed lower level of miR-34a than those with normal copies of 1p36. Furthermore, we demonstrated that MYCN is a direct target of miR-34a. Finally, using a series of mRNA expression profiling experiments, we identified other potential direct targets of miR-34a, and pathway analysis demonstrated that miR-34a suppresses cell-cycle genes and induces several neural-related genes. This study demonstrates one important regulatory role of miR-34a in cell growth and MYCN suppression in neuroblastoma.

Neurotologic follow-up after radiation of posterior fossa tumors

OBJECTIVE

Stereotactic radiation treatment, also known as gamma knife surgery or radiosurgery, has come into acceptance as a treatment alternative to surgical removal for posterior fossa tumors. The purpose of this article is to describe the role of the neurotologist in the optimal management of neurotologic complications after stereotactic radiation, as illustrated by five patients.

STUDY DESIGN

Retrospective chart review.

PATIENTS

Five patients who underwent stereotactic radiation of posterior fossa tumors.

MAIN OUTCOME MEASURES

Presence or absence of neurotologic complications (tumor growth, hearing loss, imbalance/ataxia, vertigo, and facial paralysis) or neurosurgical complaints (facial numbness, motor weakness, headache, hydrocephalus, and subarachnoid cysts).

RESULTS

Postradiation neurotologic complaints included vertigo, imbalance/ataxia, and progressive hearing loss in four of the five patients. Continued tumor growth occurred in two patients; two patients had no growth; in one patient the tumor became smaller. The complications of facial nerve paralysis, facial numbness, motor weakness, headache, hydrocephalus, cerebellar edema, and posterior fossa arachnoid cyst formation occurred less frequently.

CONCLUSIONS

Stereotactic radiation of posterior fossa tumors can produce significant neurotologic problems. It is imperative that neurotologists remain involved in the follow-up care of patients with posterior fossa tumors to offer optimal treatment alternatives for the neurotologic disorders.