MYCN-amplified Neuroblastoma Cells Research Articles

CDK4/6 inhibitors display a class effect in inducing differentiation of neuroblastoma cells

Background Neuroblastoma is the most common extracranial solid tumour in infants and children, accounting for approximately 15% of paediatric cancer mortality. These tumours are unique in that a subset, namely stage MS, frequently undergo spontaneous regression or differentiation. Differentiation therapy, where cancer cells are re-routed back down their correct developmental pathway, is therefore a promising therapeutic avenue. We have previously shown that the CDK4/6 inhibitor palbociclib induces both decreased proliferation and enhanced neuronal differentiation of neuroblastoma cells in vitro. When combined with retinoic acid, already used clinically for maintenance therapy, this differentiation is enhanced. Methods Here, we investigate two additional CDK4/6 inhibitors, abemaciclib and ribociclib, to induce differentiation of the relapsed, high-risk MYCN-amplified neuroblastoma cell line SK-N-BE(2)C, with and without retinoic acid. We culture SK-N-BE(2)C cells in both adherent and three-dimensional culture and monitor proliferation and differentiation using readouts including live-imaging, immunocytochemistry, qRT-PCR and EdU incorporation. Results We find the CDK4/6 inhibitors palbociclib, abemaciclib and ribociclib all enhance retinoic acid-induced differentiation in both adherent SK-N-BE(2)C cells and 3D spheroids. Conclusions CDK4/6 inhibitors display a class effect in inducing neuronal differentiation together with retinoic acid, both in adherent neuroblastoma cell lines and three-dimensional tumour spheroids. This is an important consideration for potentially developing CDK inhibitor-induced differentiation as a therapy in the clinic.

Golgi-localized Ring Finger Protein 121 is necessary for MYCN-driven neuroblastoma tumorigenesis

MYCN amplification predicts poor prognosis in childhood neuroblastoma. To identify MYCN oncogenic signal dependencies we performed N-ethyl-N-nitrosourea (ENU) mutagenesis on the germline of neuroblastoma-prone TH-MYCN transgenic mice to generate founders which had lost tumorigenesis. Sequencing of the mutant mouse genomes identified the Ring Finger Protein 121 (RNF121WT) gene mutated to RNFM158R associated with heritable loss of tumorigenicity. While the RNF121WT protein localised predominantly to the cis-Golgi Complex, the RNF121M158R mutation in Helix 4 of its transmembrane domain caused reduced RNF121 protein stability and absent Golgi localisation. RNF121WT expression markedly increased during TH-MYCN tumorigenesis, whereas hemizygous RNF121WT gene deletion reduced TH-MYCN tumorigenicity. The RNF121WT-enhanced growth of MYCN-amplified neuroblastoma cells depended on RNF121WT transmembrane Helix 5. RNF121WT directly bound MYCN protein and enhanced its stability. High RNF121 mRNA expression associated with poor prognosis in human neuroblastoma tissues and another MYC-driven malignancy, laryngeal cancer. RNF121 is thus an essential oncogenic cofactor for MYCN and a target for drug development.

L3MBTL2 maintains MYCN-amplified neuroblastoma cell proliferation through silencing NRIP3 and BRME1 genes.

Epigenetic alterations critically affect tumor development. Polycomb-group complexes constitute an evolutionarily conserved epigenetic machinery that regulates stem cell fate and development. They are implicated in tumorigenesis, primarily via histone modification. Polycomb repressive complex 1 (PRC1) complexes 1-6 (PRC1.1-6) mediate the ubiquitination of histone H2A on lysine 119 (H2AK119ub). Here, we studied the functional roles of a PRC1.6 molecule, L3MBTL2, in neuroblastoma (NB) cells. L3MBTL2-knockout and knockdown revealed that L3MBTL2 depletion suppressed NB cell proliferation via cell-cycle arrest and gamma-H2A.X upregulation. L3MBTL2-knockout profoundly suppressed xenograft tumor formation. Transcriptome analysis revealed suppressed cell-cycle-related and activated differentiation-related pathways. Break repair meiotic recombinase recruitment factor 1 (BRME1) and nuclear receptor interacting protein 3 (NRIP3) were notably de-repressed by L3MBTL2-knockout. The deletion of L3MBTL2 reduced enrichment of H2AK119ub and PCGF6 at transcriptional start site proximal regions of the targets. Add-back studies unveiled the importance of L3MBTL2-BRME1 and -NRIP3 axes for NB cell proliferation. We further manifested the association of MYCN with de-repression of NRIP3 in an L3MBTL2-deficient context. Therefore, this study first revealed the significance of L3MBTL2-mediated gene silencing in MYCN-amplified NB cells.

The MYCN 5′ UTR as a therapeutic target in neuroblastoma

Tumor MYCN amplification is seen in high-risk neuroblastoma, yet direct targeting of this oncogenic transcription factor has been challenging. Here, we take advantage of the dependence of MYCN-amplified neuroblastoma cells on increased protein synthesis to inhibit the activity of eukaryotic translation initiation factor 4A1 (eIF4A1) using an amidino-rocaglate, CMLD012824. Consistent with the role of this RNA helicase in resolving structural barriers in 5' untranslated regions (UTRs), CMLD012824 increased eIF4A1 affinity for polypurine-rich 5' UTRs, including that of the MYCN and associated transcripts with critical roles in cell proliferation. CMLD012824-mediated clamping of eIF4A1 spanned the full lengths of mRNAs, while translational inhibition was mediated through 5' UTR binding in a cap-dependent and -independent manner. Finally, CMLD012824 led to growth inhibition in MYCN-amplified neuroblastoma models without generalized toxicity. Our studies highlight the key role of eIF4A1 in MYCN-amplified neuroblastoma and demonstrate the therapeutic potential of disrupting its function.

Abstract 147: Identification of cell sub-populations in Neuroblastoma cell lines with single-cell-sequencing analysis

Abstract Neuroblastoma is the most frequent extracranial tumor in neonatal patients. Engineering SKNBE2 Myc-N amplified Neuroblastoma cell lines we generated individual clones expressing NDM29 non-coding-RNA at different levels. Using these cell models we documented a specific role of NDM29 in tumor cell differentiation leading to the identification of novel genes to be pharmacologically targeted for an efficient control of tumor malignancy (CA9 and MCM2 genes). Further studies taking advantage of the same models suggested the possible co-existence of different cell sub-populations in the apparently homogeneous cell culture with possible different roles in tumor maintenance and growth. Here we test this hypothesis by performing single-cell sequencing analysis and identified different sub-populations on the base of their gene expression patterns. The characterization of their specific profiles of membrane markers allowed an efficient separation of the individual populations by FACS analysis. Our preliminary results show the co-existance of cells with a marked neural phenotype with other two populations one VEGF secreting and the other VEGF recipient/responder. These preliminary findings suggest further detailed investigations of possible paracrine loops that might be at the base of tumor cell nodule growth and maintenance. Citation Format: Michele Tomanelli, Davide Ceresa, Adriana Bajetto, Paola Modesto, Paolo Malatesta, Tullio Florio, Aldo Pagano. Identification of cell sub-populations in Neuroblastoma cell lines with single-cell-sequencing analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 147.

Abstract 5122: Modulating anti-GD2 immunotherapy via dual DFMO and TGF-β inhibition in neuroblastoma

Abstract Neuroblastoma (NB) is an often-lethal childhood solid tumor. Anti-GD2 immunotherapy improves survival but not all responses are durable. Transforming growth factor-beta (TGFβ) has been implicated in solid tumor immunoresistance. High-risk NBs harbor activated MYC or MYCN to coordinately expand intratumoral polyamines (PA), oncometabolites with immunomodulatory roles, to support tumor progression. Difluoromethylornithine (DFMO) is an inhibitor of ornithine decarboxylase, the rate-limiting enzyme in PA synthesis, and has shown activity in preclinical NB models, including TH-MYCN+/+ transgenic mice, and is in clinical trials in children. We sought to augment anti-GD2 therapy using DFMO and the small molecule TGFβ-receptor inhibitor, galunisertib. We randomized TH-MYCN+/+ mice in two experiments (10 therapy arms; n=6-10 mice/arm) to receive combinations of DFMO, galunisertib, and anti-GD2 antibody m14G2a and to assess impact on survival. We measured 770 genes using nCounter Immuno-Oncology 360 (Nanostring), 36 cytokines using xMap bead-arrays (Luminex), and tumor-infiltrating leukocytes using flow cytometry in harvested tumors. Cell line TGFβ signaling was evaluated in tissue culture. In vitro, galunisertib consistently suppressed the upregulated TGFβ-Smad2/3 signaling cascade in MYCN-amplified neuroblastoma cell lines. In vivo, DFMO alone extends mouse survival and increases intra-tumoral neutrophils and natural killer (NK) cells. These NK cells increased surface expression of activation receptors like NKG2D (p<0.05), while tumor cells increased surface expression of NK-ligands. Tumor cells also expressed increased latency-associated peptide (LAP; p<0.05), a TGFβ precursor, suggesting NK cells were poised to kill but restrained by TGFβ. Cytotoxicity assays showed reversal of this inhibition with TGFβR1 inhibitor galunisertib in vitro. In a proof-of-concept trial, DFMO and galunisertib (DFMO/gal) demonstrated a clinical anti-tumor synergistic effect. DFMO/gal treated tumors had upregulated NK cell activity genes and downregulated TGFβ signaling genes. Cytokine analysis confirmed DFMO induced upregulation of TGFβ1 and TGFβ2 (p<0.01) that was modulated by galunisertib. IL6, GCSF, and GMCSF were markedly downregulated in tumors treated with both DFMO and galunisertib (p<0.05). An expanded trial showed DFMO/gal added to m14G2a showed no significant survival benefit over the DFMO and m14G2a combination. Ultimately, DFMO creates a pro-inflammatory cellular and cytokine milieu in TH-MYCN+/+ NBs. DFMO and TGFβR1 inhibition via galunisertib activate NK cells further and decrease the anti-inflammatory cytokine IL6. Ongoing studies are further characterizing the gene expression and cytokine levels of the NB TME under these treatment conditions. Citation Format: Om H. Gandhi, Christina S. Turn, Kangning Liu, Annette T. Vu, Hamid Bassiri, Michael D. Hogarty. Modulating anti-GD2 immunotherapy via dual DFMO and TGF-β inhibition in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5122.

Aryl hydrocarbon receptor is a tumor promoter in MYCN-amplified neuroblastoma cells through suppression of differentiation

Neuroblastoma is the most common extracranial solid tumor in children. MYCN amplification is detected in almost half of high-risk cases and is associated with poorly differentiated tumors, poor patient prognosis and poor response to therapy, including retinoids. We identify the aryl hydrocarbon receptor (AhR) as a transcription factor promoting the growth and suppressing the differentiation of MYCN-amplified neuroblastoma. A neuroblastoma specific AhR transcriptional signature reveals an inverse correlation of AhR activity with patients' outcome, suggesting AhR activity is critical for disease progression. AhR modulates chromatin structures, reducing accessibility to regions responsive to retinoic acid. Genetic and pharmacological inhibition of AhR results in induction of differentiation. Importantly, AhR antagonism with clofazimine synergizes with retinoic acid in inducing differentiation both invitro and invivo. Thus, we propose AhR as a target for MYCN-amplified neuroblastoma and that its antagonism, combined with current standard-of-care, may result in a more durable response in patients.

Triple Therapy with Metformin, Ketogenic Diet, and Metronomic Cyclophosphamide Reduced Tumor Growth in MYCN-Amplified Neuroblastoma Xenografts.

Neuroblastoma (NB) is a childhood cancer in which amplification of the MYCN gene is the most acknowledged marker of poor prognosis. MYCN-amplified NB cells rely on both glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) for energy production. Previously, we demonstrated that a ketogenic diet (KD) combined with metronomic cyclophosphamide (CP) delayed tumor growth in MYCN-amplified NB xenografts. The anti-diabetic drug metformin (MET) also targets complex I of the OXPHOS system. Therefore, MET-induced disruptions of mitochondrial respiration may enhance the anti-tumor effect of CP when combined with a KD. In this study, we found that MET decreased cell proliferation and mitochondrial respiration in MYCN-amplified NB cell lines, while the combination of KD, MET, and low-dose CP (triple therapy) also reduced tumor growth and improved survival in vivo in MYCN-amplified NB xenografts. Gene ontology enrichment analysis revealed that this triple therapy had the greatest effect on the transcription of genes involved in fatty acid ß-oxidation, which was supported by the increased protein expression of CPT1A, a key mitochondrial fatty acid transporter. We suspect that alterations to ß-oxidation alongside the inhibition of complex I may hamper mitochondrial energy production, thus explaining these augmented anti-tumor effects, suggesting that the combination of MET and KD is an effective adjuvant therapy to CP in MYCN-amplified NB xenografts.

CCNB1IP1 prevents ubiquitination-mediated destabilization of MYCN and potentiates tumourigenesis of MYCN-amplificated neuroblastoma.

MYCN amplification as a common genetic alteration that correlates with a poor prognosis for neuroblastoma (NB) patients. However, given the challenge of directly targeting MYCN, indirect strategies to modulate MYCN by interfering with its cofactors are attractive in NB treatment. Although cyclin B1 interacting protein 1 (CCNB1IP1) has been found to be upregulated in MYCN-driven mouse NB tissues, its regulation with MYCN and collaboration in driving the biological behaviour of NB remains unknown. To evaluate the expression and clinical significance of CCNB1IP1 in NB patients, public datasets, clinical NB samples and cell lines were explored. MTT, EdU incorporation, colony and tumour sphere formation assays, and a mouse xenograft tumour model were utilized to examine the biological function of CCNB1IP1. The reciprocal manipulation of CCNB1IP1 and MYCN and the underlying mechanisms involved were investigated by gain- and loss-of-function approaches, dual-luciferase assay, chromatin immunoprecipitation (CHIP) and co-immunoprecipitation (Co-IP) experiments. CCNB1IP1 was upregulated in MYCN-amplified (MYCN-AM) NB cell lines and patients-derived tumour tissues, which was associated with poor prognosis. Phenotypic studies revealed that CCNB1IP1 facilitated the proliferation and tumourigenicity of NB cells in cooperation with MYCN in vitro and in vivo. Mechanistically, MYCN directly mediates the transcription of CCNB1IP1, which in turn attenuated the ubiquitination and degradation of MYCN protein, thus enhancing CCNB1IP1-MYCN cooperativity. Moreover, CCNB1IP1 competed with F box/WD-40 domain protein 7 (FBXW7) for MYCN binding and enabled MYCN-mediated tumourigenesis in a C-terminal domain-dependent manner. Our study revealed a previously uncharacterized mechanism of CCNB1IP1-mediated MYCN protein stability and will provide new prospects for precise treatment of MYCN-AM NB based on MYCN-CCNB1IP1 interaction.

DNA Ligase 4 Contributes to Cell Proliferation against DNA-PK Inhibition in MYCN-Amplified Neuroblastoma IMR32 Cells.

Identifying the vulnerability of altered DNA repair machinery that displays synthetic lethality with MYCN amplification is a therapeutic rationale in unfavourable neuroblastoma. However, none of the inhibitors for DNA repair proteins are established as standard therapy in neuroblastoma. Here, we investigated whether DNA-PK inhibitor (DNA-PKi) could inhibit the proliferation of spheroids derived from neuroblastomas of MYCN transgenic mice and MYCN-amplified neuroblastoma cell lines. DNA-PKi exhibited an inhibitory effect on the proliferation of MYCN-driven neuroblastoma spheroids, whereas variable sensitivity was observed in those cell lines. Among them, the accelerated proliferation of IMR32 cells was dependent on DNA ligase 4 (LIG4), which comprises the canonical non-homologous end-joining pathway of DNA repair. Notably, LIG4 was identified as one of the worst prognostic factors in patients with MYCN-amplified neuroblastomas. It may play complementary roles in DNA-PK deficiency, suggesting the therapeutic potential of LIG4 inhibition in combination with DNA-PKi for MYCN-amplified neuroblastomas to overcome resistance to multimodal therapy.

RNA N6-methyladenosine reader IGF2BP3 interacts with MYCN and facilitates neuroblastoma cell proliferation

Neuroblastoma (NB) is a kind of typical life-threatening extracranial tumor in children. N6-methyladenosine (m6A) modification is closely related to multiple cancer pathological processes. Insulin-like growth factor 2 mRNA binding protein 3 (IGF2BP3) is a top-ranked prognostic risk gene in NB; however, its function is uncertain. The expression of m6A-associated enzymes in patients with NB was analyzed using the Gene Expression Omnibus (GEO) and Therapeutically Applicable Research to Generate Effective Treatments (TARGET) database. The IGF2BP3 level in NB cell lines and primary samples was tested using quantitative real-time polymerase chain reaction (qRT-PCR), western blot method, and immunohistochemical analysis. The IGF2BP3 function in cell proliferation was clarified based on many functional in vitro and in vivo experiments. The interaction between IGF2BP3 and N-myc was researched via RNA immunoprecipitation (RIP), m6A RNA immunoprecipitation (MeRIP), and chromatin immunoprecipitation (ChIP) assays. The 16 m6A-regulated enzymes in NB were researched, and the result indicated that IGF2BP3 overexpression was related to cancer progression, COG risk, and survival based on the GEO and TARGET databases. Besides, the IGF2BP3 and MYCN levels were positively correlated. IGF2BP3 expression levels increased in MYCN-amplified NB clinical samples and cells. Knockdown of IGF2BP3 inhibited N-myc expression and NB cell proliferation in vitro and in vivo. IGF2BP3 regulates MYCN RNA stability by modifying m6A. In addition, we demonstrated that N-myc is a transcription factor that directly promotes IGF2BP3 expression in NB cells. IGF2BP3 regulates the proliferation of NB cells via m6A modification of MYCN. N-myc also acts as a transcription factor that regulates IGF2BP3 expression. A positive feedback loop between IGF2BP3 and N-myc facilitates NB cell proliferation.

MYCN Amplification Is Associated with Reduced Expression of Genes Encoding γ-Secretase Complex and NOTCH Signaling Components in Neuroblastoma.

Amplification of the MYCN oncogene is found in ~20% of neuroblastoma (NB) cases and correlates with high-risk disease and poor prognosis. Despite the plethora of studies describing the role of MYCN in NB, the exact molecular mechanisms underlying MYCN's contribution to high-risk disease are not completely understood. Herein, we implemented an integrative approach combining publicly available RNA-Seq and MYCN ChIP-Seq datasets derived from human NB cell lines to define biological processes directly regulated by MYCN in NB. Our approach revealed that MYCN-amplified NB cell lines, when compared to non-MYCN-amplified cell lines, are characterized by reduced expression of genes involved in NOTCH receptor processing, axoneme assembly, and membrane protein proteolysis. More specifically, we found genes encoding members of the γ-secretase complex, which is known for its ability to liberate several intracellular signaling molecules from membrane-bound proteins such as NOTCH receptors, to be down-regulated in MYCN-amplified NB cell lines. Analysis of MYCN ChIP-Seq data revealed an enrichment of MYCN binding at the transcription start sites of genes encoding γ-secretase complex subunits. Notably, using publicly available gene expression data from NB primary tumors, we revealed that the expression of γ-secretase subunits encoding genes and other components of the NOTCH signaling pathway was also reduced in MYCN-amplified tumors and correlated with worse overall survival in NB patients. Genetic or pharmacological depletion of MYCN in NB cell lines induced the expression of γ-secretase genes and NOTCH-target genes. Chemical inhibition of γ-secretase activity dampened the expression of NOTCH-target genes upon MYCN depletion in NB cells. In conclusion, this study defines a set of MYCN-regulated pathways that are specific to MYCN-amplified NB tumors, and it suggests a novel role for MYCN in the suppression of genes of the γ-secretase complex, with an impact on the NOTCH-target gene expression in MYCN-amplified NB.

Abstract 481: Investigating molecular glues as a new therapeutic approach to high-risk neuroblastoma

Abstract High-risk neuroblastoma (NB) is the most common extracranial solid tumor of childhood. Despite extensive study, treatments remain highly toxic and are often insufficient to cure. Thus, there is an urgent need to develop more effective and less toxic treatments for children with NB. NB commonly displays reliance on a relatively small cohort of transcription factors (TFs) and epigenetic proteins to drive cell growth, however, many of these targets are inaccessible with conventional small molecules. In recent years, new modalities such as targeted protein degradation (TPD) have emerged. TPD may permit small molecule degradation of traditionally “undruggable” targets, such as TFs. This makes TPD a particularly attractive modality for defining new therapeutic strategies for high-risk NB. One category of TPD agents are molecular glues (MGs). MGs are monovalent small molecules capable of simultaneously binding to an E3 ligase receptor such as CRBN (cereblon), and a target protein of interest. Importantly, in comparison to conventional protein inhibitors, MGs do not require a conventional binding pocket on the protein of interest to bind to it, and can be utilized in sub-stoichiometric concentrations. Thus, this may result in the recruitment, polyubiquitination, and subsequent proteasomal degradation of proteins previously thought to be “undruggable.” Here, we demonstrate that high-risk NB cells are critically sensitive to a cluster of previously unknown MGs. We performed high-throughput screening of a proprietary library (>4000 unique compounds) of MGs in two MYCN-amplified NB cell lines, Kelly and MHHNB11. These two cell lines demonstrate a strikingly close correlation in Cell-Titer Glo-based growth response to MGs, as compared with an outgroup of other MG-responsive cancer cell lines. We identified a unique subcluster of 112 common MGs that display >70% growth inhibition in both cell lines. To identify the mechanism of cell growth inhibition, we established Kelly cells with stable knockout of CRBN, and coupled these with screening to confirm that the majority of these MGs (84%; 94/112) require CRBN expression. To rule out common off-target effects of MGs, candidate compounds were then tested in cells transgenically expressing either wild-type or degradation-resistant GSPT1 (G575N) constructs, revealing a subset of MGs retaining cytotoxicity without effecting GSPT1 protein levels. Current studies are focused on determining the targets of these high confidence MGs, as a foundation for preclinical in vivo studies. These studies will identify new compounds with defined mechanisms of action, with an ultimate goal of developing new treatments that are more effective and less toxic for children with NB. Citation Format: Ian Delahunty, Gisele Nishiguchi, Yang Zhang, Abigail Fish, Anand Mayasundari, Jun Qi, Brian Abraham, Anang Shelat, Zoran Rankovic, Adam Durbin. Investigating molecular glues as a new therapeutic approach to high-risk neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 481.

MYCN Amplification, along with Wild-Type RB1 Expression, Enhances CDK4/6 Inhibitors' Efficacy in Neuroblastoma Cells.

Neuroblastoma (NB) is one of the primary causes of death for pediatric malignancies. Given the high heterogeneity in NB's mutation landscape, optimizing individualized therapies is still challenging. In the context of genomic alterations, MYCN amplification is the most correlated event with poor outcomes. MYCN is involved in the regulation of several cellular mechanisms, including cell cycle. Thus, studying the influence of MYCN overexpression in the G1/S transition checkpoint of the cell cycle may unveil novel druggable targets for the development of personalized therapeutical approaches. Here, we show that high expression of E2F3 and MYCN correlate with poor prognosis in NB despite the RB1 mRNA levels. Moreover, we demonstrate through luciferase reporter assays that MYCN bypasses RB function by incrementing E2F3-responsive promoter activity. We showed that MYCN overexpression leads to RB inactivation by inducing RB hyperphosphorylation during the G1 phase through cell cycle synchronization experiments. Moreover, we generated two MYCN-amplified NB cell lines conditionally knockdown (cKD) for the RB1 gene through a CRISPRi approach. Indeed, RB KD did not affect cell proliferation, whereas cell proliferation was strongly influenced when a non-phosphorylatable RB mutant was expressed. This finding revealed the dispensable role of RB in regulating MYCN-amplified NB's cell cycle. The described genetic interaction between MYCN and RB1 provides the rationale for using cyclin/CDK complexes inhibitors in NBs carrying MYCN amplification and relatively high levels of RB1 expression.

P300 Interacted With N-Myc and Regulated Its Protein Stability via Altering Its Post-Translational Modifications in Neuroblastoma

MYCN amplification is an independent risk factor for poor prognosis in neuroblastoma (NB), but its protein product cannot be directly targeted because of protein structure. Thus, this study aimed to explore novel ways to indirectly target N-Myc by regulating its post-translational modifications (PTMs) and therefore protein stability. N-Myc coimmunoprecipitation combined with HPLC–MS/MS identified 16 PTM residues and 114 potential N-Myc-interacting proteins. Notably, both acetylation and ubiquitination were identified on lysine 199 of N-Myc. We then discovered that p300, which can interact with N-Myc, modulated the protein stability of N-Myc in MYCN-amplified NB cell lines and simultaneously regulated the acetylation level and ubiquitination level on lysine-199 of N-Myc protein in vitro. Furthermore, p300 correlated with poor prognosis in NB patients. Taken together, p300 can be considered as a potential therapeutic target to treat MYCN-amplified NB patients, and other identified PTMs and interacting proteins also provide potential targets for further study.

ONC201 Suppresses Neuroblastoma Growth by Interrupting Mitochondrial Function and Reactivating Nuclear ATRX Expression While Decreasing MYCN.

Neuroblastoma (NB) is characterized by several malignant phenotypes that are difficult to treat effectively without combination therapy. The therapeutic implication of mitochondrial ClpXP protease ClpP and ClpX has been verified in several malignancies, but is unknown in NB. Firstly, we observed a significant increase in ClpP and ClpX expression in immature and mature ganglion cells as compared to more malignant neuroblasts and less malignant Schwannian-stroma-dominant cell types in human neuroblastoma tissues. We used ONC201 targeting ClpXP to treat NB cells, and found a significant suppression of mitochondrial protease, i.e., ClpP and ClpX, expression and downregulation of mitochondrial respiratory chain subunits SDHB and NDUFS1. The latter was associated with a state of energy depletion, increased reactive oxygen species, and decreased mitochondrial membrane potential, consequently promoting apoptosis and suppressing cell growth of NB. Treatment of NB cells with ONC201 as well as the genetic attenuation of ClpP and ClpX through specific short interfering RNA (siRNA) resulted in the significant upregulation of the tumor suppressor alpha thalassemia/mental retardation X-linked (ATRX) and promotion of neurite outgrowth, implicating mitochondrial ClpXP proteases in MYCN-amplified NB cell differentiation. Furthermore, ONC201 treatment significantly decreased MYCN protein expression and suppressed tumor formation with the reactivation of ATRX expression in MYCN-amplified NB-cell-derived xenograft tumors. Taken together, ONC201 could be the potential agent to provide diversified therapeutic application in NB, particularly in NB with MYCN amplification.

Abstract A025: Assessing the role of bivalency in MYCN-amplified neuroblastoma

Abstract Introduction: Neuroblastoma is an embryonic pediatric cancer with a broad spectrum of clinical behavior. In aggressive neuroblastoma tumors, we previously demonstrated enrichment of 5-hydroxymethylcytosine (5-hmC), a marker of transcriptional activation, on genes targeted by the repressive Polycomb Repressive Complex 2 (PRC2). PRC2 has been shown to be a dependency of MYCN-amplified neuroblastoma. In embryonic stem cells, 5-hmC is disproportionately enriched at the transcription start sites (TSS) of bivalent genes that are characterized by the presence of both repressive and activating histone modifications (H3K27me3 and H3K4me3). Bivalent genes are postulated to be poised for rapid activation during embryogenesis. We hypothesized that bivalent genes enriched for 5-hmC at the TSS play a key role in regulating the undifferentiated phenotype of MYCN-amplified neuroblastoma. Methods: Tumor derived 5-hmC profiles were obtained previously. Nano-hmC-seal was used to generate genome-wide 5-hmC profiles in the MYCN-amplified or overexpressed SK-N-BE2, LA1-55n, LA1-5s, NBLW-N, NBLW-S, NBL-S, and MYCN-non-amplified SH-SY5Y, and SHEP cell lines. H3K27me3, H3K4me3, and H3K27ac profiles were generated in these cell lines using ChIP-Seq. KAS-Seq, a chemical pulldown of ssDNA that marks active enhancers and transcribed genes, and RNA-Seq profiling were performed. MACS2 and deepTools were used to analyze ChIP-Seq, 5-hmC, and KAS-Seq data. Results: A comparison of 5-hmC profiles derived from diagnostic tumor biopsy samples with and without MYCN-amplification demonstrated increased 5-hmC deposition on SUZ12 and EZH2 (PRC2 subunits) target genes. MYCN-amplified and MYC overexpressing cell lines but not MYCN-non-amplified lines bore a TSS specific association between 5-hmC deposition and H3K27me3 enrichment. Using the SK-N-BE2 and NBLW-N cell lines, we identified 313 genes with both H3K4me3 and H3K27me3 deposition, which we defined as bivalent, and 806 genes with only H3K27me3 deposition. Both H3K27me3-only and bivalent genes had TSS specific 5-hmC deposition, were enriched in development and differentiation pathways, and had significantly lower expression in cell lines with high MYCN expression. However, unlike H3K27me3-only genes, bivalent genes were also enriched for transcription factor biding sites of AP-2 and E2F which co-regulate MYCN. Using a publicly available dataset of 498 tumors, we found that bivalent genes were transcriptionally repressed in MYCN-amplified tumor samples. Within the cohort of 175 high-risk patients, those with lower expression of bivalent genes (N=55) had worse overall survival (OS) from diagnosis than those (N=120) with high expression (5-year OS: 27.2% vs. 52.0%; 95% CI: 17.1%-43.3% vs 42.9%-63.1%, p=0.001 by log-rank test). Conclusion: The low-level expression of bivalent genes enriched for 5-hmC at the TSS in MYCN-amplified neuroblastoma cells may represent a novel mechanism by which dedifferentiated states and aggressive phenotype is maintained in MYCN-amplified neuroblastoma. Citation Format: Mohansrinivas Chennakesavalu, Gepoliano Chaves, Kelley Moore, Tong Wu, Ruitu Lyu, Rachel TerHaar, Alexandre Chlenski, Chuan He, Susan Cohn, Andrea Piunti, Mark Applebaum. Assessing the role of bivalency in MYCN-amplified neuroblastoma. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr A025.

Combination bromo- and extraterminal domain and poly (ADP-ribose) polymerase inhibition synergistically enhances DNA damage and inhibits neuroblastoma tumorigenesis

PurposeJQ1 is a bromo- and extraterminal (BET) domain inhibitor that downregulates MYC expression and impairs the DNA damage response. Poly (ADP-ribose) polymerase (PARP) inhibitors prevent DNA damage sensing and repair. We hypothesized that JQ1 would promote a DNA repair-deficient phenotype that sensitizes neuroblastoma cells to PARP inhibition.MethodsFour human neuroblastoma cell lines were examined: two MYCN-amplified (BE(2)-C and IMR-32), and two non-MYCN-amplified (SK-N-SH and SH-SY5Y). Cells were treated with JQ1 (BET inhibitor), Olaparib (PARP inhibitor), or in combination to assess for therapeutic synergy of JQ1 and Olaparib. Treated cells were harvested and analyzed. Quantitative assessment of combination treatment synergy was performed using the median effect principle of Chou and Talalay.ResultsCombination treatment with Olaparib decreased the IC50 of JQ1 by 19.9-fold, 2.0-fold, 12.1-fold, and 2.0-fold in the BE(2)-C, IMR-32, SK-N-SH, and SH-SY5Y cell lines, respectively. In the MYCN-amplified cell lines, BE(2)-C and IMR-32, combination treatment decreased gene expression of MYCN relative to single-drug treatment alone or control. Combination treatment decreased protein expression of DNA repair proteins Ku80 and RAD51, led to accumulation of DNA damage marker phospho-histone H2A.X, and increased caspase activity. In the non-MYCN-amplified cell lines, SK-N-SH and SH-SY5Y, combination treatment induced G0/G1 cell cycle arrest.ConclusionsCombination BET and PARP inhibition synergistically inhibited neuroblastoma tumorigenesis in vitro. In MYCN-amplified neuroblastoma cells, this effect may be induced by downregulation of MYCN transcription, defects in DNA repair, accumulation of DNA damage, and apoptosis. In non-MYCN-amplified cell lines, combination treatment induced cell cycle arrest.

Polycomb EZH1 regulates cell cycle/5-fluorouracil sensitivity of neuroblastoma cells in concert with MYCN.

In the present study, we found that EZH1 depletion in MYCN-amplified neuroblastoma cells resulted in significant cell death as well as xenograft inhibition. EZH1 depletion decreased the level of H3K27me1; the interaction and protein stabilization of MYCN and EZH1 appear to play roles in epigenetic transcriptional regulation. Transcriptome analysis of EZH1-depleted cells resulted in downregulation of the cell cycle progression-related pathway. In particular, Gene Set Enrichment Analysis revealed downregulation of reactome E2F-mediated regulation of DNA replication along with key genes of this process, TYMS, POLA2, and CCNA1. TYMS and POLA2 were transcriptionally activated by MYCN and EZH1-related epigenetic modification. Treatment with the EZH1/2 inhibitor UNC1999 also induced cell death, decreased H3K27 methylation, and reduced the levels of TYMS in neuroblastoma cells. Previous reports indicated neuroblastoma cells are resistant to 5-fluorouracil (5-FU) and TYMS (encoding thymidylate synthetase) has been considered the primary site of action for folate analogues. Intriguingly, UNC1999 treatment significantly sensitized MYCN-amplified neuroblastoma cells to 5-FU treatment, suggesting that EZH inhibition could be an effective strategy for development of a new epigenetic treatment for neuroblastoma.

LncRNA SNHG1 regulates neuroblastoma cell fate via interactions with HDAC1/2

The small nucleolar RNA host gene 1 (SNHG1) is a novel oncogenic long non-coding RNA (lncRNA) aberrantly expressed in different tumor types. We previously found highly expressed SNHG1 was associated with poor prognosis and MYCN status in neuroblastoma (NB). However, the molecular mechanisms of SNHG1 in NB are still unclear. Here, we disrupted endogenous SNHG1 in the MYCN-amplified NB cell line SK-N-BE(2)C using the CRISPR/Cas9 system and demonstrated the proliferation and colony formation ability of SNHG1-knowndown cells were suppressed. The transcriptome analysis and functional assays of SNHG1-knockdown cells revealed SNHG1 was involved in various biological processes including cell growth, migration, apoptosis, cell cycle, and reactive oxygen species (ROS). Interestingly, the expression of core regulatory circuitry (CRC) transcription factors in MYCN-amplified NB, including PHOX2B, HAND2, GATA3, ISL1, TBX1, and MYCN, were decreased in SNHG1-knockdown cells. The chromatin-immunoprecipitation sequencing (ChIP-seq) and transposase-accessible chromatin using sequencing (ATAC-seq) analyses showed that chromatin status of these CRC members was altered, which might stem from interactions between SNHG1 and HDAC1/2. These findings demonstrate that SNHG1 plays a crucial role in maintaining NB identity via chromatin regulation and reveal the function of the lncRNA SNHG1 in NB.