Preclinical models of pediatric solid tumors (neuroblastoma) and their use in drug discovery

A peptide encoded by the circular form of the SHPRH gene induces apoptosis in neuroblastoma cells

Background

Circular RNAs (circRNAs) and their derived peptides represent largely unchartered areas in cellular biology, with many potential roles yet to be discovered. This study aimed to elucidate the role and molecular interactions of circSHPRH and its peptide derivative SHPRH-146aa in the pathogenesis of neuroblastoma (NB).

Methods

NB samples in the GSE102285 dataset were analyzed to measure circSHPRH expression, followed by in vitro experiments for validation. The role of SHPRH-146aa in NB cell proliferation, migration, and invasion was then examined, and luciferase activity assay was performed after SHPRH-146aa and RUNX1 transfection. Finally, the regulation of NB cell apoptosis by SHPRH-146aa combined with NFKBIA was tested.

Results

The GSE102285 dataset indicated overexpression of circSHPRH in NB samples, further supported by in vitro findings. Overexpression of circ-SHPRH and SHPRH-146aa inhibited proliferation, migration, and invasion of NB cells. A significant increase in apoptosis was observed, with upregulation of Caspase-3 and downregulation of Bcl-2. Furthermore, the peptide derivative SHPRH-146aa, derived from circSHPRH, suppressed NB cell malignancy traits, suggesting its role as a therapeutic target. A direct interaction between SHPRH-146aa and the transcription factor RUNX1 was identified, subsequently leading to increased NFKBIA expression. Notably, NFKBIA knockdown inhibited the pro-apoptotic effect of SHPRH-146aa on NB cells.

Conclusion

The study demonstrates that circ-SHPRH and SHPRH-146aa play significant roles in inhibiting the malignant progression of NB. They induce apoptosis primarily by modulating key apoptotic proteins Caspase-3 and Bcl-2, a process that appears to be regulated by NFKBIA. The SHPRH-146aa-RUNX1 interaction further elucidates a novel pathway in the regulation of apoptosis in NB. These findings indicate that circ-SHPRH and its derived peptide SHPRH-146aa could be potential therapeutic targets for NB treatment.

Anti-CCL2 antibody combined with etoposide prolongs survival in a minimal residual disease mouse model of neuroblastoma

C-C motif chemokine ligand 2 (CCL2) is a monocyte chemoattractant that promotes metastatic disease and portends a poor prognosis in many cancers. To determine the potential of anti-CCL2 inhibition as a therapy for recurrent metastatic disease in neuroblastoma, a mouse model of minimal residual disease was utilized in which residual disease was treated with anti-CCL2 monoclonal antibody with etoposide. The effect of anti-CCL2 antibody on neuroblastoma cells was determined in vitro with cell proliferation, transwell migration, and 2-dimensional chemotaxis migration assays. The in vivo efficacy of anti-CCL2 antibody and etoposide against neuroblastoma was assessed following resection of primary tumors formed by two cell lines or a patient-derived xenograft (PDX) in immunodeficient NOD-scid gamma mice. In vitro, anti-CCL2 antibody did not affect cell proliferation but significantly inhibited neuroblastoma cell and monocyte migration towards an increasing CCL2 concentration gradient. Treatment of mice with anti-CCL2 antibody combined with etoposide significantly increased survival of mice after resection of primary tumors, compared to untreated mice.

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.

Pathological prognosis classification of patients with neuroblastoma using computational pathology analysis

Neuroblastoma is the most common extracranial solid tumor in early childhood. International Neuroblastoma Pathology Classification (INPC) is a commonly used classification system that provides clinicians with a reference for treatment stratification. However, given the complex and subjective assessment of the INPC, there will be inconsistencies in the analysis of the same patient by multiple pathologists. An automated, comprehensive and objective classification method is needed to identify different prognostic groups in patients with neuroblastoma. In this study, we collected 563 hematoxylin and eosin-stained histopathology whole-slide images from 107 patients with neuroblastoma who underwent surgical resection. We proposed a novel processing pipeline for nuclear segmentation, cell-level image feature extraction, and patient-level feature aggregation. Logistic regression model was built to classify patients with favorable histology (FH) and patients with unfavorable histology (UH). On the training/test dataset, patient-level of nucleus morphological/intensity features and age could correctly classify patients with a mean area under the receiver operating characteristic curve (AUC) of 0.946, a mean accuracy of 0.856, and a mean Matthews Correlation Coefficient (MCC) of 0.703,respectively. On the independent validation dataset, the classification model achieved a mean AUC of 0.938, a mean accuracy of 0.865 and a mean MCC of 0.630, showing good generalizability. Our results suggested that automatically derived image features could identify the differences in nuclear morphological and intensity between different prognostic groups, which could provide a reference to pathologists and facilitate the evaluation of the pathological prognosis in patients with neuroblastoma.

MYCN-driven fatty acid uptake is a metabolic vulnerability in neuroblastoma

Neuroblastoma (NB) is a childhood cancer arising from sympatho-adrenal neural crest cells. MYCN amplification is found in half of high-risk NB patients; however, no available therapies directly target MYCN. Using multi-dimensional metabolic profiling in MYCN expression systems and primary patient tumors, we comprehensively characterized the metabolic landscape driven by MYCN in NB. MYCN amplification leads to glycerolipid accumulation by promoting fatty acid (FA) uptake and biosynthesis. We found that cells expressing amplified MYCN depend highly on FA uptake for survival. Mechanistically, MYCN directly upregulates FA transport protein 2 (FATP2), encoded by SLC27A2. Genetic depletion of SLC27A2 impairs NB survival, and pharmacological SLC27A2 inhibition selectively suppresses tumor growth, prolongs animal survival, and exerts synergistic anti-tumor effects when combined with conventional chemotherapies in multiple preclinical NB models. This study identifies FA uptake as a critical metabolic dependency for MYCN-amplified tumors. Inhibiting FA uptake is an effective approach for improving current treatment regimens.

Poloxamer-linked prodrug of a topoisomerase I inhibitor SN22 shows efficacy in models of high-risk neuroblastoma with primary and acquired chemoresistance

High‐risk solid tumors continue to pose a tremendous therapeutic challenge due to multidrug resistance. Biological mechanisms driving chemoresistance in high‐risk primary and recurrent disease are distinct: in newly diagnosed patients, non‐response to therapy is often associated with a higher level of tumor “stemness” paralleled by overexpression of the ABCG2 drug efflux pump, whereas in tumors relapsing after non‐curative therapy, poor drug sensitivity is most commonly linked to the dysfunction of the tumor suppressor protein, p53. In this study, we used preclinical models of aggressive neuroblastoma featuring these characteristic mechanisms of primary and acquired drug resistance to experimentally evaluate a macromolecular prodrug of a structurally enhanced camptothecin analog, SN22, resisting ABCG2‐mediated export, and glucuronidation. Together with extended tumor exposure to therapeutically effective drug levels via reversible conjugation to Pluronic F‐108 (PF108), these features translated into rapid tumor regression and long‐term survival in models of both ABCG2‐overexpressing and p53‐mutant high‐risk neuroblastomas, in contrast to a marginal effect of the clinically used camptothecin derivative, irinotecan. Our results demonstrate that pharmacophore enhancement, increased tumor uptake, and optimally stable carrier‐drug association integrated into the design of the hydrolytically activatable PF108‐[SN22]₂ have the potential to effectively combat multiple mechanisms governing chemoresistance in newly diagnosed (chemo‐naïve) and recurrent forms of aggressive malignancies. As a macromolecular carrier‐based delivery system exhibiting remarkable efficacy against two particularly challenging forms of high‐risk neuroblastoma, PF108‐[SN22]₂ can pave the way to a robust and clinically viable therapeutic strategy urgently needed for patients with multidrug‐resistant disease presently lacking effective treatment options.

GPC2-CAR T cells tuned for low antigen density mediate potent activity against neuroblastoma without toxicity

Pediatric cancers often mimic fetal tissues and express proteins normally silenced postnatally that could serve as immune targets. We developed T cells expressing chimeric antigen receptors (CARs) targeting glypican-2 (GPC2), a fetal antigen expressed on neuroblastoma (NB) and several other solid tumors. CARs engineered using standard designs control NBs with transgenic GPC2 overexpression, but not those expressing clinically relevant GPC2 site density (∼5,000 molecules/cell, range 1-6 × 10³). Iterative engineering of transmembrane (TM) and co-stimulatory domains plus overexpression of c-Jun lowered the GPC2-CAR antigen density threshold, enabling potent and durable eradication of NBs expressing clinically relevant GPC2 antigen density, without toxicity. These studies highlight the critical interplay between CAR design and antigen density threshold, demonstrate potent efficacy and safety of a lead GPC2-CAR candidate suitable for clinical testing, and credential oncofetal antigens as a promising class of targets for CAR T cell therapy of solid tumors.

CHAF1A Blocks Neuronal Differentiation and Promotes Neuroblastoma Oncogenesis via Metabolic Reprogramming

Neuroblastoma (NB) arises from oncogenic disruption of neural crest (NC) differentiation. Treatment with retinoic acid (RA) to induce differentiation has improved survival in some NB patients, but not all patients respond, and most NBs eventually develop resistance to RA. Loss of the chromatin modifier chromatin assembly factor 1 subunit p150 (CHAF1A) promotes NB cell differentiation; however, the mechanism by which CHAF1A drives NB oncogenesis has remained unexplored. This study shows that CHAF1A gain-of-function supports cell malignancy, blocks neuronal differentiation in three models (zebrafish NC, human NC, and human NB), and promotes NB oncogenesis. Mechanistically, CHAF1A upregulates polyamine metabolism, which blocks neuronal differentiation and promotes cell cycle progression. Targeting polyamine synthesis promotes NB differentiation and enhances the anti-tumor activity of RA. The authors' results provide insight into the mechanisms that drive NB oncogenesis and suggest a rapidly translatable therapeutic approach (DFMO plus RA) to enhance the clinical efficacy of differentiation therapy in NB patients.

Restoration of the molecular clock is tumor suppressive in neuroblastoma

MYCN activation is a hallmark of advanced neuroblastoma (NB) and a known master regulator of metabolic reprogramming, favoring NB adaptation to its microenvironment. We found that the expression of the main regulators of the molecular clock loops is profoundly disrupted in MYCN-amplified NB patients, and this disruption independently predicts poor clinical outcome. MYCN induces the expression of clock repressors and downregulates the one of clock activators by directly binding to their promoters. Ultimately, MYCN attenuates the molecular clock by suppressing BMAL1 expression and oscillation, thereby promoting cell survival. Reestablishment of the activity of the clock activator RORα via its genetic overexpression and its stimulation through the agonist SR1078, restores BMAL1 expression and oscillation, effectively blocks MYCN-mediated tumor growth and de novo lipogenesis, and sensitizes NB tumors to conventional chemotherapy. In conclusion, reactivation of RORα could serve as a therapeutic strategy for MYCN-amplified NBs by blocking the dysregulation of molecular clock and cell metabolism mediated by MYCN.

Environment-Sensitive Polymeric Micelles Encapsulating SN-38 Potently Suppress Growth of Neuroblastoma Cells Exhibiting Intrinsic and Acquired Drug Resistance

Conventional treatment approaches fail to provide durable control over aggressive malignancies due to intrinsic or acquired drug resistance characteristic of high-risk disease. SN-38, a potent camptothecin analog specifically targeting DNA topoisomerase I cleavage complexes, has shown promise in preclinical studies against aggressive solid tumors. However, its clinical utility is limited by inadequate solubility in pharmaceutically acceptable vehicles and by poor chemical and metabolic stability. Micelles formulated from amphiphilic invertible polymers (AIPs) can address these issues by concomitantly enabling solubilization of water-insoluble molecular cargoes and by protecting chemically labile agents from inactivation. Furthermore, the inversion of the AIP and disruption of the carrier-drug complexes triggered by contact with cell membranes makes it possible to deliver the therapeutic payload into the cell interior without compromising its biological activity. In the present study, we characterized a novel AIP-based micellar formulation of SN-38 and evaluated its growth inhibitory effect on neuroblastoma (NB) cells derived either at diagnosis or at relapse after intensive chemoradiotherapy. Colloidally stable, drug-loaded micellar assemblies with a uniform <100 nm size were prepared using an AIP consisting of alternating blocks of poly(ethylene glycol) and polytetrahydrofuran (PEG600-PTHF650). The micellar drug applied in a low nanomolar range (10-50 nM) completely suppressed the growth of chemo-naïve NB cells even after a brief (10 min) exposure. Furthermore, extending the exposure to 24 h resulted in a profound and lasting inhibitory effect of the micellar formulation on the growth of NB cells exhibiting an acquired loss of p53 function. These results suggest that micelle-mediated delivery of SN-38 can potentially offer a new and effective strategy for treating different phases of high-risk disease, including those showing poor response to conventional therapies.

Gut-on-chip: Recreating human intestine in vitro

The human gut is important for food digestion and absorption, as well as a venue for a large number of microorganisms that coexist with the host. Although numerous in vitro models have been proposed to study intestinal pathology or interactions between intestinal microbes and host, they are far from recapitulating the real intestinal microenvironment in vivo. To assist researchers in further understanding gut physiology, the intestinal microbiome, and disease processes, a novel technology primarily based on microfluidics and cell biology, called "gut-on-chip," was developed to simulate the structure, function, and microenvironment of the human gut. In this review, we first introduce various types of gut-on-chip systems, then highlight their applications in drug pharmacokinetics, host-gut microbiota crosstalk, and nutrition metabolism. Finally, we discuss challenges in this field and prospects for better understanding interactions between intestinal flora and human hosts, and then provide guidance for clinical treatment of related diseases.

Anti-CD105 Antibody Eliminates Tumor Microenvironment Cells and Enhances Anti-GD2 Antibody Immunotherapy of Neuroblastoma with Activated Natural Killer Cells

PURPOSE

We determined whether elimination of CD105⁺ cells in the tumor microenvironment (TME) with anti-CD105 antibodies enhanced anti-disialoganglioside (GD2) antibody dinutuximab therapy of neuroblastoma when combined with activated natural killer (aNK) cells.

EXPERIMENTAL DESIGN

The effect of MSCs and monocytes on antibody-dependent cellular cytotoxicity (ADCC) mediated by dinutuximab with aNK cells against neuroblastoma cells was determined in vitro. ADCC with anti-CD105 mAb TRC105 and aNK cells against MSCs, monocytes, and endothelial cells, which express CD105, was evaluated. Anti-neuroblastoma activity in immunodeficient NSG mice of dinutuximab with aNK cells without or with anti-CD105 mAbs was determined using neuroblastoma cell lines and a patient-derived xenograft.

RESULTS

ADCC mediated by dinutuximab with aNK cells against neuroblastoma cells in vitro was suppressed by addition of MSCs and monocytes, and dinutuximab with aNK cells was less effective against neuroblastomas formed with coinjected MSCs and monocytes in NSG mice than against those formed by tumor cells alone. Anti-CD105 antibody TRC105 with aNK cells mediated ADCC against MSCs, monocytes, and endothelial cells. Neuroblastomas formed in NSG mice by two neuroblastoma cell lines or a patient-derived xenograft coinjected with MSCs and monocytes were most effectively treated with dinutuximab and aNK cells when anti-human (TRC105) and anti-mouse (M1043) CD105 antibodies were added, which depleted human MSCs and murine endothelial cells and macrophages from the TME.

CONCLUSIONS

Immunotherapy of neuroblastoma with anti-GD2 antibody dinutuximab and aNK cells is suppressed by CD105⁺ cells in the TME, but suppression is overcome by adding anti-CD105 antibodies to eliminate CD105⁺ cells.

In vitro vascularized liver and tumor tissue microenvironments on a chip for dynamic determination of nanoparticle transport and toxicity

This paper presents the development of a vascularized breast tumor and healthy or tumorigenic liver microenvironments-on-a-chip connected in series. This is the first description of a vascularized multi tissue-on-a-chip microenvironment for modeling cancerous breast and cancerous/healthy liver microenvironments, to allow for the study of dynamic and spatial transport of particles. This device enables the dynamic determination of vessel permeability, the measurement of drug and nanoparticle transport, and the assessment of the associated efficacy and toxicity to the liver. The platform is utilized to determine the effect of particle size on the spatiotemporal diffusion of particles through each microenvironment, both independently and in response to the circulation of particles in varying sequences of microenvironments. The results show that when breast cancer cells were cultured in the microenvironments they had a 2.62-fold higher vessel porosity relative to vessels within healthy liver microenvironments. Hence, the permeability of the tumor microenvironment increased by 2.35- and 2.77-fold compared with a healthy liver for small and large particles, respectively. The extracellular matrix accumulation rate of larger particles was 2.57-fold lower than smaller particles in a healthy liver. However, the accumulation rate was 5.57-fold greater in the breast tumor microenvironment. These results are in agreement with comparable in vivo studies. Ultimately, the platform could be utilized to determine the impact of the tissue or tumor microenvironment, or drug and nanoparticle properties, on transport, efficacy, selectivity, and toxicity in a dynamic, and high-throughput manner for use in treatment optimization.

Preclinical evaluation of the first intravenous small molecule MDM2 antagonist alone and in combination with temozolomide in neuroblastoma

High‐risk neuroblastoma, a predominantly TP53 wild‐type (wt) tumour, is incurable in >50% patients supporting the use of MDM2 antagonists as novel therapeutics. Idasanutlin (RG7388) shows in vitro synergy with chemotherapies used to treat neuroblastoma. This is the first study to evaluate the in vivo efficacy of the intravenous idasanutlin prodrug, RO6839921 (RG7775), both alone and in combination with temozolomide in TP53 wt orthotopic neuroblastoma models. Detection of active idasanutlin using liquid chromatography‐mass spectrometry and p53 pathway activation by ELISA assays and Western analysis showed peak plasma levels 1 h post‐treatment with maximal p53 pathway activation 3–6 h post‐treatment. RO6839921 and temozolomide, alone or in combination in mice implanted with TP53 wt SHSY5Y‐Luc and NB1691‐Luc cells showed that combined RO6839921 and temozolomide led to greater tumour growth inhibition and increase in survival compared to vehicle control. Overall, RO6839921 had a favourable pharmacokinetic profile consistent with intermittent dosing and was well tolerated alone and in combination. These preclinical studies support the further development of idasanutlin in combination with temozolomide in neuroblastoma in early phase clinical trials.

What's new?

Long‐term survival of high‐risk neuroblastoma patients currently averages than 50%. New therapies that both improve survival and reduce treatment toxicity are urgently needed. MDM2 antagonists are a novel class of anti‐cancer agents that stabilize the p53 pathway and lead to tumour suppression. In this preclinical study, the authors tested a prodrug of the MDM2 inhibitor idasanutlin in mice. They found that this compound inhibited tumour growth and increased survival, especially in combination with temozolomide. These results support the further development of idasanutlin plus temozolomide in clinical trials for neuroblastoma.

Colony stimulating factor 1 receptor blockade improves the efficacy of chemotherapy against human neuroblastoma in the absence of T lymphocytes

Tumor-associated macrophages can promote growth of cancers. In neuroblastoma, tumor-associated macrophages have greater frequency in metastatic versus loco-regional tumors, and higher expression of genes associated with macrophages helps to predict poor prognosis in the 60% of high-risk patients who have MYCN-non-amplified disease. The contribution of cytotoxic T-lymphocytes to anti-neuroblastoma immune responses may be limited by low MHC class I expression and low exonic mutation frequency. Therefore, we modelled human neuroblastoma in T-cell deficient mice to examine whether depletion of monocytes/macrophages from the neuroblastoma microenvironment by blockade of CSF-1R can improve the response to chemotherapy. In vitro, CSF-1 was released by neuroblastoma cells, and topotecan increased this release. In vivo, neuroblastomas formed by subcutaneous co-injection of human neuroblastoma cells and human monocytes into immunodeficient NOD/SCID mice had fewer human CD14⁺ and CD163⁺ cells and mouse F4/80⁺ cells after CSF-1R blockade. In subcutaneous or intra-renal models in immunodeficient NSG or NOD/SCID mice, CSF-1R blockade alone did not affect tumor growth or mouse survival. However, when combined with cyclophosphamide plus topotecan, the CSF-1R inhibitor BLZ945, either without or with anti-human and anti-mouse CSF-1 mAbs, inhibited neuroblastoma growth and synergistically improved mouse survival. These findings indicate that depletion of tumor-associated macrophages from neuroblastomas can be associated with increased chemotherapeutic efficacy without requiring a contribution from T-lymphocytes, suggesting the possibility that combination of CSF-1R blockade with chemotherapy might be effective in patients who have limited anti-tumor T-cell responses.

Novel multi-targeted ErbB family inhibitor afatinib blocks EGF-induced signaling and induces apoptosis in neuroblastoma

Neuroblastoma is the most common extracranial solid tumor in children. The ErbB family of proteins is a group of receptor tyrosine kinases that promote the progression of various malignant cancers including neuroblastoma. Thus, targeting them with small molecule inhibitors is a promising strategy for neuroblastoma therapy. In this study, we investigated the anti-tumor effect of afatinib, an irreversible inhibitor of members of the ErbB family, on neuroblastoma. We found that afatinib suppressed the proliferation and colony formation ability of neuroblastoma cell lines in a dose-dependent manner. Afatinib also induced apoptosis and blocked EGF-induced activation of PI3K/AKT/mTOR signaling in all neuroblastoma cell lines tested. In addition, afatinib enhanced doxorubicin-induced cytotoxicity in neuroblastoma cells, including the chemoresistant LA-N-6 cell line. Finally, afatinib exhibited antitumor efficacy in vivo by inducing apoptosis in an orthotopic xenograft neuroblastoma mouse model. Taken together, these results show that afatinib inhibits neuroblastoma growth both in vitro and in vivo by suppressing EGFR-mediated PI3K/AKT/mTOR signaling. Our study supports the idea that EGFR is a potential therapeutic target in neuroblastoma. And targeting ErbB family protein kinases with small molecule inhibitors like afatinib alone or in combination with doxorubicin is a viable option for treating neuroblastoma.

Novel Src/Abl tyrosine kinase inhibitor bosutinib suppresses neuroblastoma growth via inhibiting Src/Abl signaling

Neuroblastoma (NB) is the most common extracranial solid tumor in children. Aberrant activation of the non-receptor tyrosine kinases Src and c-Abl contributes to the progression of NB. Thus, targeting these kinases could be a promising strategy for NB therapy. In this paper, we report that the potent dual Src/Abl inhibitor bosutinib exerts anti-tumor effects on NB. Bosutinib inhibited NB cell proliferation in a dose-dependent manner and suppressed colony formation ability of NB cells. Mechanistically, bosutinib effectively decreased the activity of Src/Abl and PI3K/AKT/mTOR, MAPK/ERK, and JAK/STAT3 signaling pathways. In addition, bosutinib enhanced doxorubicin (Dox)- and etoposide (VP-16)-induced cytotoxicity in NB cells. Furthermore, bosutinib demonstrated anti-tumor efficacy in an orthotopic xenograft NB mouse model in a similar mechanism as of that in vitro. In summary, our results reveal that Src and c-Abl are potential therapeutic targets in NB and that the novel Src/Abl inhibitor bosutinib alone or in combination with other chemotherapeutic agents may be a valuable therapeutic option for NB patients.

Novel multiple tyrosine kinase inhibitor ponatinib inhibits bFGF-activated signaling in neuroblastoma cells and suppresses neuroblastoma growth in vivo

Neuroblastoma (NB) is one of the most common pediatric malignancies in children. Abnormal activation of receptor tyrosine kinases contributes to the pathological development of NB. Therefore, targeting tyrosine kinase receptors to cure NB is a promising strategy. Here, we report that a multi-targeted tyrosine kinase inhibitor ponatinib inhibited NB cell proliferation and induced NB cell apoptosis in a dose-dependent manner. In addition, ponatinib suppressed the colony formation ability of NB cells. Mechanistically, ponatinib effectively inhibited the FGFR1-activated signaling pathway. Ponatinib also enhanced the cytotoxic effects of doxorubicin on NB cells. Furthermore, ponatinib demonstrated anti-tumor efficacy in vivo by inhibiting tumor growth in an orthotopic xenograft NB mouse model. In summary, our results showed that ponatinib inhibited NB growth both in vitro and in vivo.

Small molecule inhibitor regorafenib inhibits RET signaling in neuroblastoma cells and effectively suppresses tumor growth in vivo

Neuroblastoma (NB), the most common extracranial pediatric solid tumor, continues to cause significant cancer-related morbidity and mortality in children. Dysregulation of oncogenic receptor tyrosine kinases (RTKs) has been shown to contribute to tumorigenesis in various human cancers and targeting these RTKs has had therapeutic benefit. RET is an RTK which is commonly expressed in NB, and high expression of RET correlates with poor outcomes in patients with NB. Herein we report that RET is required for NB cell proliferation and that the small molecule inhibitor regorafenib (BAY 73-4506) blocks glial cell derived neurotrophic factor (GDNF)-induced RET signaling in NB cells and inhibits NB growth both in vitro and in vivo. We found that regorafenib significantly inhibited cell proliferation and colony formation ability of NB cells. Moreover, regorafenib suppressed tumor growth in both an orthotopic xenograft NB mouse model and a TH-MYCN transgenic NB mouse model. Finally, regorafenib markedly improved the overall survival of TH-MYCN transgenic tumor-bearing mice. In summary, our study suggests that RET is a potential therapeutic target in NB, and that using a novel RET inhibitor, like regorafenib, should be investigated as a therapeutic treatment option for children with NB.

EWS-FLI1 and RNA helicase A interaction inhibitor YK-4-279 inhibits growth of neuroblastoma

Treatment failure in high risk neuroblastoma (NB) is largely due to the development of chemotherapy resistance. We analyzed the gene expression changes associated with exposure to chemotherapy in six high risk NB tumors with the aid of the Connectivity Map bioinformatics platform. Ten therapeutic agents were predicted to have a high probability of reversing the transcriptome changes associated with neoadjuvant chemotherapy treatment. Among these agents, initial screening showed the EWS-FLI1 and RNA helicase A interaction inhibitor YK-4-279, had obvious cytotoxic effects on NB cell lines. Using a panel of NB cell lines, including MYCN nonamplified (SK-N-AS, SH-SY5Y, and CHLA-255), and MYCN amplified (NB-19, NGP, and IMR-32) cell lines, we found that YK-4-279 had cytotoxic effects on all lines tested. In addition, YK-4-279 also inhibited cell proliferation and anchorage-independent growth and induced cell apoptosis of these cells. YK-4-279 enhanced the cytotoxic effect of doxorubicin (Dox). Moreover, YK-4-279 was able to overcome the established chemoresistance of LA-N-6 NB cells. In an orthotopic xenograft NB mouse model, YK-4-279 inhibited NB tumor growth and induced apoptosis in tumor cells through PARP and Caspase 3 cleavage in vivo. While EWS-FLI1 fusion protein is not frequently found in NB, using the R2 public database of neuroblastoma outcome and gene expression, we found that high expression of EWSR1 was associated with poor patient outcome. Knockdown of EWSR1 inhibited the oncogenic potential of neuroblastoma cell lines. Taken together, our results indicate that YK-4-279 might be a promising agent for treatment of NB that merits further exploration.

p53 Nongenotoxic Activation and mTORC1 Inhibition Lead to Effective Combination for Neuroblastoma Therapy

Purpose: mTORC1 inhibitors are promising agents for neuroblastoma therapy; however, they have shown limited clinical activity as monotherapy, thus rational drug combinations need to be explored to improve efficacy. Importantly, neuroblastoma maintains both an active p53 and an aberrant mTOR signaling.Experimental Design: Using an orthotopic xenograft model and modulating p53 levels, we investigated the antitumor effects of the mTORC1 inhibitor temsirolimus in neuroblastoma expressing normal, decreased, or mutant p53, both as single agent and in combination with first- and second-generation MDM2 inhibitors to reactivate p53.Results: Nongenotoxic p53 activation suppresses mTOR activity. Moreover, p53 reactivation via RG7388, a second-generation MDM2 inhibitor, strongly enhances the in vivo antitumor activity of temsirolimus. Single-agent temsirolimus does not elicit apoptosis, and tumors rapidly regrow after treatment suspension. In contrast, our combination therapy triggers a potent apoptotic response in wild-type p53 xenografts and efficiently blocks tumor regrowth after treatment completion. We also found that this combination uniquely led to p53-dependent suppression of survivin whose ectopic expression is sufficient to rescue the apoptosis induced by our combination.Conclusions: Our study supports a novel highly effective strategy that combines RG7388 and temsirolimus in wild-type p53 neuroblastoma, which warrants testing in early-phase clinical trials. Clin Cancer Res; 23(21); 6629-39. ©2017 AACR.

Combined epigenetic and differentiation-based treatment inhibits neuroblastoma tumor growth and links HIF2α to tumor suppression

Neuroblastoma is a pediatric cancer characterized by variable outcomes ranging from spontaneous regression to life-threatening progression. High-risk neuroblastoma patients receive myeloablative chemotherapy with hematopoietic stem-cell transplant followed by adjuvant retinoid differentiation treatment. However, the overall survival remains low; hence, there is an urgent need for alternative therapeutic approaches. One feature of high-risk neuroblastoma is the high level of DNA methylation of putative tumor suppressors. Combining the reversibility of DNA methylation with the differentiation-promoting activity of retinoic acid (RA) could provide an alternative strategy to treat high-risk neuroblastoma. Here we show that treatment with the DNA-demethylating drug 5-Aza-deoxycytidine (AZA) restores high-risk neuroblastoma sensitivity to RA. Combined systemic distribution of AZA and RA impedes tumor growth and prolongs survival. Genome-wide analysis of treated tumors reveals that this combined treatment rapidly induces a HIF2α-associated hypoxia-like transcriptional response followed by an increase in neuronal gene expression and a decrease in cell-cycle gene expression. A small-molecule inhibitor of HIF2α activity diminishes the tumor response to AZA+RA treatment, indicating that the increase in HIF2α levels is a key component in tumor response to AZA+RA. The link between increased HIF2α levels and inhibited tumor growth is reflected in large neuroblastoma patient datasets. Therein, high levels of HIF2α, but not HIF1α, significantly correlate with expression of neuronal differentiation genes and better prognosis but negatively correlate with key features of high-risk tumors, such as MYCN amplification. Thus, contrary to previous studies, our findings indicate an unanticipated tumor-suppressive role for HIF2α in neuroblastoma.

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.

Wip1 inhibitor GSK2830371 inhibits neuroblastoma growth by inducing Chk2/p53-mediated apoptosis

Neuroblastoma (NB) is the most common extracranial tumor in children. Unlike in most adult tumors, tumor suppressor protein 53 (p53) mutations occur with a relatively low frequency in NB and the downstream function of p53 is intact in NB cell lines. Wip1 is a negative regulator of p53 and hindrance of Wip1 activity by novel inhibitor GSK2830371 is a potential strategy to activate p53’s tumor suppressing function in NB. Yet, the in vivo efficacy and the possible mechanisms of GSK2830371 in NB have not yet been elucidated. Here we report that novel Wip1 inhibitor GSK2830371 induced Chk2/p53-mediated apoptosis in NB cells in a p53-dependent manner. In addition, GSK2830371 suppressed the colony-formation potential of p53 wild-type NB cell lines. Furthermore, GSK2830371 enhanced doxorubicin- (Dox) and etoposide- (VP-16) induced cytotoxicity in a subset of NB cell lines, including the chemoresistant LA-N-6 cell line. More importantly, GSK2830371 significantly inhibited tumor growth in an orthotopic xenograft NB mouse model by inducing Chk2/p53-mediated apoptosis in vivo. Taken together, this study suggests that GSK2830371 induces Chk2/p53-mediated apoptosis both in vitro and in vivo in a p53 dependent manner.

Depletion of tRNA-halves enables effective small RNA sequencing of low-input murine serum samples

The ongoing ascent of sequencing technologies has enabled researchers to gain unprecedented insights into the RNA content of biological samples. MiRNAs, a class of small non-coding RNAs, play a pivotal role in regulating gene expression. The discovery that miRNAs are stably present in circulation has spiked interest in their potential use as minimally-invasive biomarkers. However, sequencing of blood-derived samples (serum, plasma) is challenging due to the often low RNA concentration, poor RNA quality and the presence of highly abundant RNAs that dominate sequencing libraries. In murine serum for example, the high abundance of tRNA-derived small RNAs called 5' tRNA halves hampers the detection of other small RNAs, like miRNAs. We therefore evaluated two complementary approaches for targeted depletion of 5' tRNA halves in murine serum samples. Using a protocol based on biotinylated DNA probes and streptavidin coated magnetic beads we were able to selectively deplete 95% of the targeted 5' tRNA half molecules. This allowed an unbiased enrichment of the miRNA fraction resulting in a 6-fold increase of mapped miRNA reads and 60% more unique miRNAs detected. Moreover, when comparing miRNA levels in tumor-carrying versus tumor-free mice, we observed a three-fold increase in differentially expressed miRNAs.

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.

The zebrafish as a model for studying neuroblastoma

Neuroblastoma is a tumor arising in the peripheral sympathetic nervous system and is the most common cancer in childhood. Since most of the cellular and molecular mechanisms underlying neuroblastoma onset and progression remain unknown, the generation of new in vivo models might be appropriate to better dissect the peripheral sympathetic nervous system development in both physiological and disease states. This review is focused on the use of zebrafish as a suitable and innovative model to study neuroblastoma development. Here, we briefly summarize the current knowledge about zebrafish peripheral sympathetic nervous system formation, focusing on key genes and cellular pathways that play a crucial role in the differentiation of sympathetic neurons during embryonic development. In addition, we include examples of how genetic changes known to be associated with aggressive neuroblastoma can mimic this malignancy in zebrafish. Thus, we note the value of the zebrafish model in the field of neuroblastoma research, showing how it can improve our current knowledge about genes and biological pathways that contribute to malignant transformation and progression during embryonic life.

TGFβR1 Blockade with Galunisertib (LY2157299) Enhances Anti-Neuroblastoma Activity of the Anti-GD2 Antibody Dinutuximab (ch14.18) with Natural Killer Cells

PURPOSE

Immunotherapy of high-risk neuroblastoma using the anti-GD2 antibody dinutuximab induces antibody-dependent cell-mediated cytotoxicity (ADCC). Galunisertib, an inhibitor of TGFβR1, was examined for its ability to enhance the efficacy of dinutuximab in combination with human ex vivo activated NK (aNK) cells against neuroblastoma.

EXPERIMENTAL DESIGN

TGFB1 and TGFBR1 mRNA expression was determined for 249 primary neuroblastoma tumors by microarray analysis. The ability of galunisertib to inhibit SMAD activity induced by neuroblastoma patient blood and bone marrow plasmas in neuroblastoma cells was tested. The impact of galunisertib on TGFβ1-induced inhibition of aNK cytotoxicity and ADCC in vitro and on anti-neuroblastoma activity in NOD-scid gamma (NSG) mice was determined.

RESULTS

Neuroblastomas express TGFB1 and TGFBR1 mRNA. Galunisertib suppressed SMAD activation in neuroblastoma cells induced by exogenous TGFβ1 or by patient blood and bone marrow plasma, and suppressed SMAD2 phosphorylation in human neuroblastoma cells growing in NSG mice. In NK cells treated in vitro with exogenous TGFβ1, galunisertib suppressed SMAD2 phosphorylation and restored the expression of DNAM-1, NKp30, and NKG2D cytotoxicity receptors and the TRAIL death ligand, the release of perforin and granzyme A, and the direct cytotoxicity and ADCC of aNK cells against neuroblastoma cells. Addition of galunisertib to adoptive cell therapy with aNK cells plus dinutuximab reduced tumor growth and increased survival of mice injected with two neuroblastoma cell lines or a patient-derived xenograft.

CONCLUSIONS

Galunisertib suppresses activation of SMAD2 in neuroblastomas and aNK cells, restores NK cytotoxic mechanisms, and increases the efficacy of dinutuximab with aNK cells against neuroblastoma tumors. Clin Cancer Res; 23(3); 804-13. ©2016 AACRSee related commentary by Zenarruzabeitia et al., p. 615.

Novel proteasome inhibitor ixazomib sensitizes neuroblastoma cells to doxorubicin treatment

Neuroblastoma (NB) is the most common extracranial malignant solid tumor seen in children and continues to lead to the death of many pediatric cancer patients. The poor outcome in high risk NB is largely attributed to the development of chemoresistant tumor cells. Doxorubicin (dox) has been widely employed as a potent anti-cancer agent in chemotherapeutic regimens; however, it also leads to chemoresistance in many cancer types including NB. Thus, developing novel small molecules that can overcome dox-induced chemoresistance is a promising strategy in cancer therapy. Here we show that the second generation proteasome inhibitor ixazomib (MLN9708) not only inhibits NB cell proliferation and induces apoptosis in vitro but also enhances dox-induced cytotoxicity in NB cells. Ixazomib inhibits dox-induced NF-κB activity and sensitizes NB cells to dox-induced apoptosis. More importantly, ixazomib demonstrated potent anti-tumor efficacy in vivo by enhancing dox-induced apoptosis in an orthotopic xenograft NB mouse model. Collectively, our study illustrates the anti-tumor efficacy of ixazomib in NB both alone and in combination with dox, suggesting that combination therapy including ixazomib with traditional therapeutic agents such as dox is a viable strategy that may achieve better outcomes for NB patients.

Multiple CDK inhibitor dinaciclib suppresses neuroblastoma growth via inhibiting CDK2 and CDK9 activity

Neuroblastoma (NB), the most common extracranial solid tumor of childhood, is responsible for approximately 15% of cancer-related mortality in children. Aberrant activation of cyclin-dependent kinases (CDKs) has been shown to contribute to tumor cell progression in many cancers including NB. Therefore, small molecule inhibitors of CDKs comprise a strategic option in cancer therapy. Here we show that a novel multiple-CDK inhibitor, dinaciclib (SCH727965, MK-7965), exhibits potent anti-proliferative effects on a panel of NB cell lines by blocking the activity of CDK2 and CDK9. Dinaciclib also significantly sensitized NB cell lines to the treatment of chemotherapeutic agents such as doxorubicin (Dox) and etoposide (VP-16). Furthermore, dinaciclib revealed in vivo antitumor efficacy in an orthotopic xenograft mouse model of two NB cell lines and blocked tumor development in the TH-MYCN transgenic NB mouse model. Taken together, this study suggests that CDK2 and CDK9 are potential therapeutic targets in NB and that abrogating CDK2 and CDK9 activity by small molecules like dinaciclib is a promising strategy and a treatment option for NB patients.

Farewell to Animal Testing: Innovations on Human Intestinal Microphysiological Systems

The human intestine is a dynamic organ where the complex host-microbe interactions that orchestrate intestinal homeostasis occur. Major contributing factors associated with intestinal health and diseases include metabolically-active gut microbiota, intestinal epithelium, immune components, and rhythmical bowel movement known as peristalsis. Human intestinal disease models have been developed; however, a considerable number of existing models often fail to reproducibly predict human intestinal pathophysiology in response to biological and chemical perturbations or clinical interventions. Intestinal organoid models have provided promising cytodifferentiation and regeneration, but the lack of luminal flow and physical bowel movements seriously hamper mimicking complex host-microbe crosstalk. Here, we discuss recent advances of human intestinal microphysiological systems, such as the biomimetic human "Gut-on-a-Chip" that can employ key intestinal components, such as villus epithelium, gut microbiota, and immune components under peristalsis-like motions and flow, to reconstitute the transmural 3D lumen-capillary tissue interface. By encompassing cutting-edge tools in microfluidics, tissue engineering, and clinical microbiology, gut-on-a-chip has been leveraged not only to recapitulate organ-level intestinal functions, but also emulate the pathophysiology of intestinal disorders, such as chronic inflammation. Finally, we provide potential perspectives of the next generation microphysiological systems as a personalized platform to validate the efficacy, safety, metabolism, and therapeutic responses of new drug compounds in the preclinical stage.

The MDM2 small-molecule inhibitor RG7388 leads to potent tumor inhibition in p53 wild-type neuroblastoma

Neuroblastoma is an aggressive pediatric malignancy which is >98% p53 wild-type at diagnosis. As a primary repressor of p53 activity and part of a p53-activated negative feedback loop, targeting of mouse double minute 2 homolog (MDM2) is an attractive therapeutic approach to reactivation of p53. Since development of the first selective MDM2 inhibitor, Nutlin-3a, newer compounds have been developed for increased potency and improved bioavailability. Herein, we sought to determine the efficacy and specificity of a second-generation MDM2 inhibitor, RG7388, in neuroblastoma cell lines and xenografts and examine its effect on the p53-independent pathway of hypoxia-inducible factor-1 alpha (HIF-1α)/vascular endothelial growth factor (VEGF). Cell viability and apoptosis studies were performed on the neuroblastoma cell lines, NGP, SH-SY5Y, LAN-5, LAN-5 si-p53 (p53 silenced), and SK-N-AS (p53 null). RG7388 potently decreased cell proliferation and activated p53-dependent apoptosis. Tumor-bearing mice treated with RG7388 demonstrated significant tumor inhibition by 59% in NGP (P=0.003), 67% in SH-SY5Y (P=0.006), and 75% in LAN-5 (P=0.0019) p53 wild-type xenograft tumors, but no inhibitory effect on LAN-5 si-p53 or SK-N-AS p53-silenced/null xenograft tumors. Moreover, RG7388 was found to inhibit the p53-independent pathway of HIF-1α/VEGF with decreased gene expression and alteration of angiogenesis. Our study supports the further evaluation of RG7388 as a novel treatment option in p53 wild-type neuroblastoma at diagnosis and relapse.

mTOR ATP-competitive inhibitor INK128 inhibits neuroblastoma growth via blocking mTORC signaling

High-risk neuroblastoma often develops resistance to high-dose chemotherapy. The mTOR signaling cascade is frequently deregulated in human cancers and targeting mTOR signaling sensitizes many cancer types to chemotherapy. Here, using a panel of neuroblastoma cell lines, we found that the mTOR inhibitor INK128 showed inhibitory effects on both anchorage-dependent and independent growth of neuroblastoma cells and significantly enhanced the cytotoxic effects of doxorubicin (Dox) on these cell lines. Treatment of neuroblastoma cells with INK128 blocked the activation of downstream mTOR signaling and enhanced Dox-induced apoptosis. Moreover, INK128 was able to overcome the established chemoresistance in the LA-N-6 cell line. Using an orthotopic neuroblastoma mouse model, we found that INK128 significantly inhibited tumor growth in vivo. In conclusion, we have shown that INK128-mediated mTOR inhibition possessed substantial antitumor activity and could significantly increase the sensitivity of neuroblastoma cells to Dox therapy. Taken together, our results indicate that using INK128 can provide additional efficacy to current chemotherapeutic regimens and represent a new paradigm in restoring drug sensitivity in neuroblastoma.

NSC-87877 inhibits DUSP26 function in neuroblastoma resulting in p53-mediated apoptosis

Dual specificity protein phosphatase 26 (DUSP26) is overexpressed in high-risk neuroblastoma (NB) and contributes to chemoresistance by inhibiting p53 function. In vitro, DUSP26 has also been shown to effectively inhibit p38 MAP kinase. We hypothesize that inhibiting DUSP26 will result in decreased NB cell growth in a p53 and/or p38-mediated manner. NSC-87877 (8-hydroxy-7-[(6-sulfo-2-naphthyl)azo]-5-quinolinesulfonic acid), a novel DUSP26 small molecule inhibitor, shows effective growth inhibition and induction of apoptosis in NB cell lines. NB cell lines treated with small hairpin RNA (shRNA) targeting DUSP26 also exhibit a proliferation defect both in vitro and in vivo. Treatment of NB cell lines with NSC-87877 results in increased p53 phosphorylation (Ser37 and Ser46) and activation, increased activation of downstream p38 effector proteins (heat shock protein 27 (HSP27) and MAP kinase-activated protein kinase 2 (MAPKAPK2)) and poly ADP ribose polymerase/caspase-3 cleavage. The cytotoxicity resulting from DUSP26 inhibition is partially reversed by knocking down p53 expression with shRNA and also by inhibiting p38 activity with SB203580 (4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl]pyridine). In an intrarenal mouse model of NB, NSC-87877 treatment results in decreased tumor growth and increased p53 and p38 activity. Together, these results suggest that DUSP26 inhibition with NSC-87877 is an effective strategy to induce NB cell cytotoxicity in vitro and in vivo through activation of the p53 and p38 mitogen-activated protein kinase (MAPK) tumor-suppressor pathways.

G-CSF Promotes Neuroblastoma Tumorigenicity and Metastasis via STAT3-Dependent Cancer Stem Cell Activation

Increasing evidence suggests that inflammatory cytokines play a critical role in tumor initiation and progression. A cancer stem cell (CSC)-like subpopulation in neuroblastoma is known to be marked by expression of the G-CSF receptor (G-CSFR). Here, we report on the mechanistic contributions of the G-CSFR in neuroblastoma CSCs. Specifically, we demonstrate that the receptor ligand G-CSF selectively activates STAT3 within neuroblastoma CSC subpopulations, promoting their expansion in vitro and in vivo. Exogenous G-CSF enhances tumor growth and metastasis in human xenograft and murine neuroblastoma tumor models. In response to G-CSF, STAT3 acts in a feed-forward loop to transcriptionally activate the G-CSFR and sustain neuroblastoma CSCs. Blockade of this G-CSF-STAT3 signaling loop with either anti-G-CSF antibody or STAT3 inhibitor depleted the CSC subpopulation within tumors, driving correlated tumor growth inhibition, decreased metastasis, and increased chemosensitivity. Taken together, our results define G-CSF as a CSC-activating factor in neuroblastoma, suggest a comprehensive reevaluation of the clinical use of G-CSF in these patients to support white blood cell counts, and suggest that direct targeting of the G-CSF-STAT3 signaling represents a novel therapeutic approach for neuroblastoma.

Heparanase promotes tumor infiltration and antitumor activity of CAR-redirected T lymphocytes

Adoptive transfer of chimeric antigen receptor (CAR)-redirected T lymphocytes (CAR-T cells) has had less striking effects in solid tumors^1–3 than in lymphoid malignancies^{4, 5}. Although active tumor-mediated immunosuppression may play a role in limiting efficacy⁶, functional changes in T lymphocytes following their ex vivo manipulation may also account for cultured CAR-T cells’ reduced ability to penetrate stroma-rich solid tumors. We therefore studied the capacity of human in vitro-cultured CAR-T cells to degrade components of the extracellular matrix (ECM). In contrast to freshly isolated T lymphocytes, we found that in vitro-cultured T lymphocytes lack expression of the enzyme heparanase (HPSE) that degrades heparan sulphate proteoglycans, which are main components of ECM. We found that HPSE mRNA is down regulated in in vitro-expanded T cells, which may be a consequence of p53 binding to the HPSE gene promoter. We therefore engineered CAR-T cells to express HPSE and showed improved capacity to degrade ECM, which promoted tumor T-cell infiltration and antitumor activity. Employing this strategy may enhance the activity of CAR-T cells in individuals with stroma-rich solid tumors.

Retinoic acid signaling and neuronal differentiation

The identification of neurological symptoms caused by vitamin A deficiency pointed to a critical, early developmental role of vitamin A and its metabolite, retinoic acid (RA). The ability of RA to induce post-mitotic, neural phenotypes in various stem cells, in vitro, served as early evidence that RA is involved in the switch between proliferation and differentiation. In vivo studies have expanded this "opposing signal" model, and the number of primary neurons an embryo develops is now known to depend critically on the levels and spatial distribution of RA. The proneural and neurogenic transcription factors that control the exit of neural progenitors from the cell cycle and allow primary neurons to develop are partly elucidated, but the downstream effectors of RA receptor (RAR) signaling (many of which are putative cell cycle regulators) remain largely unidentified. The molecular mechanisms underlying RA-induced primary neurogenesis in anamniote embryos are starting to be revealed; however, these data have been not been extended to amniote embryos. There is growing evidence that bona fide RARs are found in some mollusks and other invertebrates, but little is known about their necessity or functions in neurogenesis. One normal function of RA is to regulate the cell cycle to halt proliferation, and loss of RA signaling is associated with dedifferentiation and the development of cancer. Identifying the genes and pathways that mediate cell cycle exit downstream of RA will be critical for our understanding of how to target tumor differentiation. Overall, elucidating the molecular details of RAR-regulated neurogenesis will be decisive for developing and understanding neural proliferation-differentiation switches throughout development.

Nanoparticle-mediated delivery of a rapidly activatable prodrug of SN-38 for neuroblastoma therapy

Nanomedicine-based strategies have the potential to improve therapeutic performance of a wide range of anticancer agents. However, the successful implementation of nanoparticulate delivery systems requires the development of adequately sized nanocarriers delivering their therapeutic cargo to the target in a protected, pharmacologically active form. The present studies focused on a novel nanocarrier-based formulation strategy for SN-38, a topoisomerase I inhibitor with proven anticancer potential, whose clinical application is compromised by toxicity, poor stability and incompatibility with conventional delivery vehicles. SN-38 encapsulated in biodegradable sub-100 nm sized nanoparticles (NP) in the form of its rapidly activatable prodrug derivative with tocopherol succinate potently inhibited the growth of neuroblastoma cells in a dose- and exposure time-dependent manner, exhibiting a delayed response pattern distinct from that of free SN-38. In a xenograft model of neuroblastoma, prodrug-loaded NP caused rapid regression of established large tumors, significantly delayed tumor regrowth after treatment cessation and markedly extended animal survival. The NP formulation strategy enabled by a reversible chemical modification of the drug molecule offers a viable means for SN-38 delivery achieving sustained intratumoral drug levels and contributing to the potency and extended duration of antitumor activity, both prerequisites for effective treatment of neuroblastoma and other cancers.

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 novel kinase inhibitor EMD1214063 is effective against neuroblastoma

BACKGROUND

Children with high-risk neuroblastoma have poor survival rates, and novel therapies are needed. Previous studies have identified a role for the HGF/c-Met pathway in neuroblastoma pathogenesis. We hypothesized that EMD1214063 would be effective against neuroblastoma tumor cells and tumors in preclinical models via inhibition of HGF/c-Met signaling. Methods We determined the expression of c-Met protein by Western blots in a panel of neuroblastoma tumor cell lines and neuroblastoma cell viability after treatment with EMD1214063 using MTT assays. TUNEL assays and assays for DNA ladder formation, were performed to measure the induction of apoptosis after EMD1214063 treatment. Inhibition of intracellular signaling was measured by Western blot analysis of treated and untreated cells. To investigate the efficacy of EMD1214063 against neuroblastoma tumors in vivo, neuroblastoma cells were injected orthotopically into immunocompromised mice, and mice were treated with oral EMD1214063. Tumors were evaluated for growth, histologic appearance, and induction of apoptosis by immunohistochemistry. Results All neuroblastoma cell lines were sensitive to EMD1214063, and IC50 values ranged from 2.4 to 8.5 μM. EMD1214063 treatment inhibited HGF-mediated c-Met phosphorylation and MEK phosphorylation in neuroblastoma cells. EMD1214063 induced apoptosis in all tested cell lines. In mice with neuroblastoma xenograft tumors, EMD1214063 treatment reduced tumor growth. Conclusions Treatment of neuroblastoma tumor cells with EMD1214063 inhibits HGF-induced c-Met phosphorylation and results in cell death. EMD1214063 treatment is also effective in reducing tumor growth in vivo. EMD1214063 therefore represents a novel therapeutic agent for neuroblastoma, and further preclinical studies of EMD1214063 are warranted.

TAK1 inhibitor 5Z-7-oxozeaenol sensitizes neuroblastoma to chemotherapy

Treatment failure in high risk neuroblastoma is largely due to development of chemoresistance. NF-κB activation is one of the resistance mechanisms for cancer cells to escape from chemotherapy-induced cell-death. TAK1 is an essential component in genotoxic stresses-induced NF-κB activation; however, the role of TAK1 in the development of chemoresistance in neuroblastoma remains unknown. Using a panel of neuroblastoma cell lines, we found that TAK1 inhibitor 5Z-7-oxozeaenol significantly augmented the cytotoxic effects of doxorubicin (Dox) and etoposide (VP-16) on neuroblastoma cell lines. TAK1 inhibition also enhanced the inhibitory effect of Dox and VP-16 on anchorage-independent growth. Treatment of neuroblastoma cells with 5Z-7-oxozeaenol blocked Dox- and VP16-induced NF-κB activation and enhanced Dox- and VP16-induced apoptosis. Moreover, 5Z-7-oxozeaenol was able to overcome the established chemoresistance in LA-N-6 neuroblastoma cells. Using an orthotopic neuroblastoma mouse model, we found that 5Z-7-oxozeaenol significantly enhanced chemotherapeutic efficacy in vivo. Together, our results provide a proof-of-concept that TAK1 inhibition significantly increases the sensitivity of neuroblastoma cells to chemotherapy-induced cell-death and can serve as an effective adjunct to current chemotherapeutic regimens for high risk diseases.

A small-molecule inhibitor of UBE2N induces neuroblastoma cell death via activation of p53 and JNK pathways

Neuroblastoma (NB) is the most common extracranial neoplasm in children. In NB, loss of p53 function is largely due to cytoplasmic sequestration rather than mutation. Ubiquitin-conjugating enzyme E2 N (UBE2N), also known as Ubc13, is an E2 ubiquitin-conjugating enzyme that promotes formation of monomeric p53 that results in its cytoplasmic translocation and subsequent loss of function. Therefore, inhibition of UBE2N may reactivate p53 by promoting its nuclear accumulation. Here, we show that NSC697923, a novel UBE2N inhibitor, exhibits potent cytotoxicity in a panel of NB cell lines evidenced by its ability to induce apoptosis. In p53 wild-type NB cells, NSC697923 induced nuclear accumulation of p53, which led to its increased transcriptional activity and tumor suppressor function. Interestingly, in p53 mutant NB cells, NSC697923 induced cell death by activating JNK pathway. This effect was reversible by blocking JNK activity with its selective inhibitor, SP600125. More importantly, NSC697923 impeded cell growth of chemoresistant LA-N-6 NB cell line in a manner greater than conventional chemotherapy drugs doxorubicin and etoposide. NSC697923 also revealed in vivo antitumor efficacy in NB orthotopic xenografts. Taken together, our results suggest that UBE2N is a potential therapeutic target in NB and provide a basis for the rational use of UBE2N inhibitors like NSC697923 as a novel treatment option for NB patients.

In vivo Lineage-tracing Studies in a Cancer Stem Cell Population in Neuroblastoma

Tumors are comprised of heterogeneous subpopulations that may exhibit differing capacity for differentiation, self-renewal, and tumorigenicity. In vivo lineage-tracing studies are a powerful tool for defining the role of tumor subpopulations in tumor growth and as targets for therapeutic agents. This protocol describes using a neuroblastoma cancer cell line transduced with two different fluorescent proteins (GFP and td Tomato) to track the specific contributions of cells expressing the GCSF receptor (CD114⁺) or not (CD114^-) on tumor growth in vivo.

USP7 inhibitor P22077 inhibits neuroblastoma growth via inducing p53-mediated apoptosis

Neuroblastoma (NB) is a common pediatric cancer and contributes to more than 15% of all pediatric cancer-related deaths. Unlike adult tumors, recurrent somatic mutations in NB, such as tumor protein 53 (p53) mutations, occur with relative paucity. In addition, p53 downstream function is intact in NB cells with wild-type p53, suggesting that reactivation of p53 may be a viable therapeutic strategy for NB treatment. Herein, we report that the ubiquitin-specific protease 7 (USP7) inhibitor, P22077, potently induces apoptosis in NB cells with an intact USP7-HDM2-p53 axis but not in NB cells with mutant p53 or without human homolog of MDM2 (HDM2) expression. In this study, we found that P22077 stabilized p53 by inducing HDM2 protein degradation in NB cells. P22077 also significantly augmented the cytotoxic effects of doxorubicin (Dox) and etoposide (VP-16) in NB cells with an intact USP7-HDM2-p53 axis. Moreover, P22077 was found to be able to sensitize chemoresistant LA-N-6 NB cells to chemotherapy. In an in vivo orthotopic NB mouse model, P22077 significantly inhibited the xenograft growth of three NB cell lines. Database analysis of NB patients shows that high expression of USP7 significantly predicts poor outcomes. Together, our data strongly suggest that targeting USP7 is a novel concept in the treatment of NB. USP7-specific inhibitors like P22077 may serve not only as a stand-alone therapy but also as an effective adjunct to current chemotherapeutic regimens for treating NB with an intact USP7-HDM2-p53 axis.

G-CSF receptor positive neuroblastoma subpopulations are enriched in chemotherapy-resistant or relapsed tumors and are highly tumorigenic

Neuroblastoma is a neural crest-derived embryonal malignancy, which accounts for 13% of all pediatric cancer mortality, primarily due to tumor recurrence. Therapy-resistant cancer stem cells are implicated in tumor relapse, but definitive phenotypic evidence of the existence of these cells has been lacking. In this study, we define a highly tumorigenic subpopulation in neuroblastoma with stem cell characteristics, based on the expression of CSF3R, which encodes the receptor for granulocyte colony-stimulating factor (G-CSF). G-CSF receptor positive (aka G-CSFr(+) or CD114(+)) cells isolated from a primary tumor and the NGP cell line by flow cytometry were highly tumorigenic and capable of both self-renewal and differentiation to progeny cells. CD114(+) cells closely resembled embryonic and induced pluripotent stem cells with respect to their profiles of cell cycle, miRNA, and gene expression. In addition, they reflect a primitive undifferentiated neuroectodermal/neural crest phenotype revealing a developmental hierarchy within neuroblastoma tumors. We detected this dedifferentiated neural crest subpopulation in all established neuroblastoma cell lines, xenograft tumors, and primary tumor specimens analyzed. Ligand activation of CD114 by the addition of exogenous G-CSF to CD114(+) cells confirmed intact STAT3 upregulation, characteristic of G-CSF receptor signaling. Together, our data describe a novel distinct subpopulation within neuroblastoma with enhanced tumorigenicity and a stem cell-like phenotype, further elucidating the complex heterogeneity of solid tumors such as neuroblastoma. We propose that this subpopulation may represent an additional target for novel therapeutic approaches to this aggressive pediatric malignancy.