UBE4B interacts with the ITCH E3 ubiquitin ligase to induce Ku70 and c-FLIPL polyubiquitination and enhanced neuroblastoma apoptosis

Expression of the UBE4B ubiquitin ligase is strongly associated with neuroblastoma patient outcomes, but the functional roles of UBE4B in neuroblastoma pathogenesis are not known. We evaluated interactions of UBE4B with the E3 ubiquitin ligase ITCH/AIP4 and the effects of UBE4B expression on Ku70 and c-FLIPL ubiquitination and proteasomal degradation by co-immunoprecipitation and Western blots. We also evaluated the role of UBE4B in apoptosis induced by histone deacetylase (HDAC) inhibition using Western blots. UBE4B binding to ITCH was mediated by WW domains in the ITCH protein. ITCH activation led to ITCH-UBE4B complex formation and recruitment of Ku70 and c-FLIPL via ITCH WW domains, followed by Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination and proteasomal degradation. HDAC inhibition induced Ku70 acetylation, leading to release of c-FLIPL and Bax from Ku70, increased Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination via the ITCH-UBE4B complex, and induction of apoptosis. UBE4B depletion led to reduced polyubiquitination and increased levels of Ku70 and c-FLIPL and to reduced apoptosis induced by HDAC inhibition via stabilization of c-FLIPL and Ku70 and inhibition of caspase 8 activation. Our results have identified novel interactions and novel targets for UBE4B ubiquitin ligase activity and a direct role for the ITCH-UBE4B complex in responses of neuroblastoma cells to HDAC inhibition, suggesting that the ITCH-UBE4B complex plays a critical role in responses of neuroblastoma to therapy and identifying a potential mechanism underlying the association of UBE4B expression with neuroblastoma patient outcomes.

Targeting the RET tyrosine kinase in neuroblastoma: A review and application of a novel selective drug design strategy

The RET (REarranged during Transfection) gene, which encodes for a transmembrane receptor tyrosine kinase, is an established oncogene associated with the etiology and progression of multiple types of cancer. Oncogenic RET mutations and rearrangements resulting in gene fusions have been identified in many adult cancers, including medullary and papillary thyroid cancers, lung adenocarcinomas, colon and breast cancers, and many others. While genetic RET aberrations are much less common in pediatric solid tumors, increased RET expression has been shown to be associated with poor prognosis in children with solid tumors such as neuroblastoma, prompting an interest in RET inhibition as a form of therapy for these children. A number of kinase inhibitors currently in use for patients with cancer have RET inhibitory activity, but these inhibitors also display activity against other kinases, resulting in unwanted side effects and limiting their safety and efficacy. Recent efforts have been focused on developing more specific RET inhibitors, but due to high levels of conservation between kinase binding pockets, specificity remains a drug design challenge. Here, we review the background of RET as a potential therapeutic target in neuroblastoma tumors and the results of recent preclinical studies and clinical trials evaluating the safety and efficacy of RET inhibition in adults and children. We also present a novel approach to drug discovery leveraging the chemical phenomenon of atropisomerism to develop specific RET inhibitors and present preliminary data demonstrating the efficacy of a novel RET inhibitor against neuroblastoma tumor cells.

USP7 Inhibition Suppresses Neuroblastoma Growth via Induction of p53-Mediated Apoptosis and EZH2 and N-Myc Downregulation

Neuroblastoma (NB) is a pediatric malignancy originating from neural crest cells of the sympathetic nervous system that accounts for 15% of all pediatric cancer deaths. Despite advances in treatment, high-risk NB remains difficult to cure, highlighting the need for novel therapeutic approaches. Ubiquitin-specific protease 7 (USP7) is a deubiquitinase that plays a critical role in tumor suppression and DNA repair, and USP7 overexpression has been associated with tumor aggressiveness in a variety of tumors, including NB. Therefore, USP7 is a potential therapeutic target for NB. The tumor suppressor p53 is a known target of USP7, and therefore reactivation of the p53 pathway may be an effective therapeutic strategy for NB treatment. We hypothesized that inhibition of USP7 would be effective against NB tumor growth. Using a novel USP7 inhibitor, Almac4, we have demonstrated significant antitumor activity, with significant decreases in both cell proliferation and cell viability in TP53 wild-type NB cell lines. USP7 inhibition in NB cells activated the p53 pathway via USP7 and MDM2 degradation, leading to reduced p53 ubiquitination and increased p53 expression in all sensitive NB cells. In addition, USP7 inhibition led to decreased N-myc protein levels in both MYCN-amplified and -nonamplified NB cell lines, but no correlation was observed between MYCN amplification and treatment response. USP7 inhibition induced apoptosis in all TP53 wild-type NB cell lines. USP7 inhibition also induced EZH2 ubiquitination and degradation. Lastly, the combination of USP7 and MDM2 inhibition showed enhanced efficacy. Our data suggests that USP7 inhibition may be a promising therapeutic strategy for children with high-risk and relapsed NB.

A phase II trial of nifurtimox combined with topotecan and cyclophosphamide for refractory or relapsed neuroblastoma and medulloblastoma

Children with relapsed/refractory (R/R) neuroblastoma (NB) and medulloblastoma (MB) have poor outcomes. We evaluated the efficacy of nifurtimox (Nfx) in a clinical trial for children with R/R NB and MB. Subjects were divided into three strata: first relapse NB, multiply R/R NB, and R/R MB. All patients received Nfx (30 mg/kg/day divided TID daily), Topotecan (0.75 mg/m² /dose, days 1-5) and Cyclophosphamide (250 mg/m² /dose, days 1-5) every 3 weeks. Response was assessed after every two courses using International Neuroblastoma Response Criteria and Response Evaluation Criteria in Solid Tumors (RECIST) criteria. One hundred and twelve eligible patients were enrolled with 110 evaluable for safety and 76 evaluable for response. In stratum 1, there was a 53.9% response rate (CR + PR), and a 69.3% total benefit rate (CR + PR + SD), with an average time on therapy of 165.2 days. In stratum 2, there was a 16.3% response rate, and a 72.1% total benefit rate, and an average time on study of 158.4 days. In stratum 3, there was a 20% response rate and a 65% total benefit rate, an average time on therapy of 105.0 days. The most common side effects included bone marrow suppression and reversible neurologic complications. The combination of Nfx, topotecan and cyclophosphamide was tolerated, and the objective response rate plus SD of 69.8% in these heavily pretreated populations suggests that this combination is an effective option for patients with R/R NB and MB. Although few objective responses were observed, the high percentage of stabilization of disease and prolonged response rate in patients with multiply relapsed disease shows this combination therapy warrants further testing.

Identification of a novel gene signature for neuroblastoma differentiation using a Boolean implication network

Although induction of differentiation represents an effective strategy for neuroblastoma treatment, the mechanisms underlying neuroblastoma differentiation are poorly understood. We generated a computational model of neuroblastoma differentiation consisting of interconnected gene clusters identified based on symmetric and asymmetric gene expression relationships. We identified a differentiation signature consisting of series of gene clusters comprised of 1251 independent genes that predicted neuroblastoma differentiation in independent datasets and in neuroblastoma cell lines treated with agents known to induce differentiation. This differentiation signature was associated with patient outcomes in multiple independent patient cohorts and validated the role of MYCN expression as a marker of neuroblastoma differentiation. Our results further identified novel genes associated with MYCN via asymmetric Boolean implication relationships that would not have been identified using symmetric computational approaches and that were associated with both neuroblastoma differentiation and patient outcomes. Our differentiation signature included a cluster of genes involved in intracellular signaling and growth factor receptor trafficking pathways that is strongly associated with neuroblastoma differentiation, and we validated the associations of UBE4B, a gene within this cluster, with neuroblastoma cell and tumor differentiation. Our findings demonstrate that Boolean network analyses of symmetric and asymmetric gene expression relationships can identify novel genes and pathways relevant for neuroblastoma tumor differentiation that could represent potential therapeutic targets.

Abstract 3702: UBE4B interacts with the ITCH E3 ubiquitin ligase to induce Ku70 and c-FLIPL K63/K48 branched polyubiquitination and enhanced neuroblastoma HDACi-mediated apoptosis

Expression of the UBE4B ubiquitin ligase is associated with neuroblastoma patient outcomes, but the functional roles of UBE4B in neuroblastoma pathogenesis are not known. We evaluated interactions of UBE4B with the E3 ubiquitin ligase ITCH/AIP4 and the effects of UBE4B expression on Ku70, c-FLIPL, and p53 ubiquitination and proteasomal degradation by co-immunoprecipitation and Western blots. We also evaluated the role of UBE4B in apoptosis induced by HDAC inhibition in our neuroblastoma cell lines model using Western blots. UBE4B was found in a complex with ITCH, with binding mediated by WW domains in the ITCH protein. ITCH activation led to ITCH-UBE4B E3-E4 ubiquitin ligase complex formation and recruitment of Ku70 and c-FLIPL via ITCH WW domains, followed by Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination and proteasomal degradation. Histone deacetylase (HDAC) inhibition induced Ku70 and c-FLIPL acetylation, leading to release of c-FLIPL and Bax from Ku70, increased Ku70 and c-FLIPL Lys48/Lys63 branched polyubiquitination via the ITCH-UBE4B complex, and induction of apoptosis. UBE4B depletion in our neuroblastoma cell lines model led to reduced polyubiquitination and increased levels of Ku70 and c-FLIPL proteins leading to the massive reduction of apoptosis induced by HDAC inhibition via stabilization of Ku70 and c-FLIPL proteins allowing the inhibition of the full caspase 8 activation. Our results have identified novel interactions and novel targets for UBE4B ubiquitin ligase activity and a direct role of the ITCH-UBE4B complex in responses of neuroblastoma cells to HDAC inhibition, suggesting that the ITCH-UBE4B complex plays a critical role in responses of neuroblastoma to therapy and suggesting a potential mechanism underlying the association of UBE4B expression with neuroblastoma patient outcomes.

Citation Format: Christophe Le Clorennec, Divya Subramonian, Yuchen Huo, Peter E. Zage. UBE4B interacts with the ITCH E3 ubiquitin ligase to induce Ku70 and c-FLIPL K63/K48 branched polyubiquitination and enhanced neuroblastoma HDACi-mediated apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3702.

Matched external control analysis of event-free survival (EFS) in patients with high-risk neuroblastoma (HRNB) receiving eflornithine (DFMO) maintenance

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Background: Long term survival in HRNB patients remains a challenge with relapse as the primary cause of mortality. DFMO has been evaluated as a chemopreventative therapy in a single arm study designed to compare EFS outcomes with published rates for the Phase 3 Children’s Oncology Group ch14.18 immunotherapy trial, ANBL0032. In order to address the limitations associated with comparison to a historical control group, we used ANBL0032 patient-level data and propensity-score matching (PSM) to simulate a randomized study comparing EFS of patients treated with DFMO after ch14.18 (treated) to ANBL0032 patients who did not subsequently receive DFMO (control). Methods: A phase 2 trial enrolled a total of 140 HRNB patients in remission at the completion of disease treatment from 2012 to 2016. Patients received 2 years of continuous treatment with DFMO 750 ±250 mg/m2 BID and were followed for up to 7 years. ANBL0032 enrolled a total of 1328 HRNB patients from 2001 to 2015 who were assigned to treatment with ch14.18 immunotherapy and followed for up to 10 years. With FDA input, we defined selection rules to identify like groups of treated and control patients eligible for matching, covariates of potential prognostic importance, and matching algorithm details. PSM was used to balance cohorts on their baseline demographic and characteristics, matching each treated patient with the 3 most closely scored control patients with an exact match on MYCN. The Kaplan-Meier method and Cox regression analyses were used to compare EFS (primary) and overall survival (OS) (key secondary) endpoints. Multiple sensitivity analyses were performed to further investigate the primary comparison. Results: A total of 92 treated patients and 852 control patients met selection criteria, with 91 and 516, respectively, having complete covariate data required for the analysis. Eighty-seven (94.6%) of the treated group had verified participation in ANBL0032 immediately prior to enrollment in the DFMO trial. EFS from end of immunotherapy was significantly improved in the matched DFMO group (n=90) vs. control group (n=270), with a hazard ratio of 0.48 (95% CI: 0.27, 0.85) and a p-value of 0.0114. Four-year EFS was 84.4% (95% CI 75.2, 90.5) in the DFMO group versus 72.8% (95% CI 67.0, 77.7) in the control group. OS rates were also higher for DFMO group in the matched population, with a hazard ratio of 0.36 (95% CI: 0.16, 0.79) and a p-value of 0.0105. EFS sensitivity analyses demonstrated consistent results, including those challenging selection criteria for the control population. Conclusions: Patients in remission after standard upfront therapy treated with DFMO had approximately half the risk of relapse compared to matched control patients. The PSM comparisons represent the most statistically robust findings to date supporting the benefit of DFMO as a maintenance treatment for HRNB. Clinical trial information: NCT02395666, NCT00026312.

Allele-specific expression reveals genes with recurrent cis-regulatory alterations in high-risk neuroblastoma

BACKGROUND

Neuroblastoma is a pediatric malignancy with a high frequency of metastatic disease at initial diagnosis. Neuroblastoma tumors have few recurrent protein-coding mutations but contain extensive somatic copy number alterations (SCNAs) suggesting that mutations that alter gene dosage are important drivers of tumorigenesis. Here, we analyze allele-specific expression in 96 high-risk neuroblastoma tumors to discover genes impacted by cis-acting mutations that alter dosage.

RESULTS

We identify 1043 genes with recurrent, neuroblastoma-specific allele-specific expression. While most of these genes lie within common SCNA regions, many of them exhibit allele-specific expression in copy neutral samples and these samples are enriched for mutations that are predicted to cause nonsense-mediated decay. Thus, both SCNA and non-SCNA mutations frequently alter gene expression in neuroblastoma. We focus on genes with neuroblastoma-specific allele-specific expression in the absence of SCNAs and find 26 such genes that have reduced expression in stage 4 disease. At least two of these genes have evidence for tumor suppressor activity including the transcription factor TFAP2B and the protein tyrosine phosphatase PTPRH.

CONCLUSIONS

In summary, our allele-specific expression analysis discovers genes that are recurrently dysregulated by both large SCNAs and other cis-acting mutations in high-risk neuroblastoma.

Genomic and Transcriptomic Analysis of Relapsed and Refractory Childhood Solid Tumors Reveals a Diverse Molecular Landscape and Mechanisms of Immune Evasion

Children with treatment-refractory or relapsed (R/R) tumors face poor prognoses. As the genomic underpinnings driving R/R disease are not well defined, we describe here the genomic and transcriptomic landscapes of R/R solid tumors from 202 patients enrolled in Beat Childhood Cancer Consortium clinical trials. Tumor mutational burden (TMB) was elevated relative to untreated tumors at diagnosis, with one-third of tumors classified as having a pediatric high TMB. Prior chemotherapy exposure influenced the mutational landscape of these R/R tumors, with more than 40% of tumors demonstrating mutational signatures associated with platinum or temozolomide chemotherapy and two tumors showing treatment-associated hypermutation. Immunogenomic profiling found a heterogenous pattern of neoantigen and MHC class I expression and a general absence of immune infiltration. Transcriptional analysis and functional gene set enrichment analysis identified cross-pathology clusters associated with development, immune signaling, and cellular signaling pathways. While the landscapes of these R/R tumors reflected those of their corresponding untreated tumors at diagnosis, important exceptions were observed suggestive of tumor evolution, treatment resistance mechanisms, and mutagenic etiologies of treatment.

Overview and recent advances in the targeting of medulloblastoma cancer stem cells

Introduction: Medulloblastoma, an embryonal small round blue cell tumor primarily arising in the posterior fossa, is the most common malignancy of the central nervous system in children and requires intensive multi-modality therapy for cure. Overall 5-year survival is approximately 75% in children with primary disease, but outcomes for relapsed disease are very poor. Recent advances have identified molecular subgroups with excellent prognosis, with 5-year overall survival rates >90%, and subgroups with very poor prognosis with overall survival rates <50%. Molecular subtyping has allowed for more sophisticated risk stratification of patients, but new treatments for the highest risk patients have not yet improved outcomes. Targeting cancer stem cells may improve outcomes, and several candidate targets and novel drugs are under investigation.Areas covered: We discuss medulloblastoma epidemiology, biology, treatment modalities, risk stratification, and molecular subgroup analysis, links between subgroup and developmental biology, cancer stem cell biology in medulloblastoma including previously described cancer stem cell markers and proposed targeted treatments in the current literature.Expert opinion: The understanding of cancer stem cells in medulloblastoma will advance therapies targeting the most treatment-resistant cells within the tumor and therefore reduce the incidence of treatment refractory and relapsed disease.

Abstract 4871: The roles of E3/E4 ubiquitin ligase UBE4B and its targets p53 and Ku70 in neuroblastoma cell death and differentiation

Children with high-risk neuroblastoma have poor survival rates and need novel treatment strategies. UBE4B is an E3/E4 ubiquitin ligase whose gene is found in the chromosome 1p36 region commonly deleted in high-risk neuroblastoma tumors and whose expression is associated with neuroblastoma patient outcomes. However, the functional roles of UBE4B in neuroblastoma pathogenesis are not known. We hypothesized that UBE4B would interact with mediators of DNA damage and repair pathways, leading to the observed associations between UBE4B and patient outcomes. Using cell lines with stable UBE4B depletion and over-expression, we evaluated the interaction of UBE4B with the E3 ubiquitin ligase ITCH/AIP4 and the effects of UBE4B expression levels on p53 and Ku70 ubiquitination and proteasomal degradation by co-immunoprecipitation and Western blots. We also evaluated the role of UBE4B in neuroblastoma differentiation, cell death, and responses to chemotherapy and HDAC inhibition using continuous live cell imaging and Western blots. We determined that UBE4B directly interacts with ITCH/AIP4 in the last WW domain of ITCH and we also determined that Ku70 directly interacts with ITCH in the three first WW domain of ITCH. We also determined that UBE4B depletion leads to reduced polyubiquitination and degradation of both p53 and Ku70 in neuroblastoma cells. UBE4B depletion also led to reduced apoptosis induced by both HDAC inhibition with vorinostat and chemotherapy treatment with carboplatin and doxorubicin via stabilizaton of the ITCH target protein c-FLIPL leading inhibition of caspase 8 activation. Our results have identified novel interactions and novel targets for UBE4B ubiquitin ligase activity and a direct role of the UBE4B-ITCH complex in HDAC inhibitor and DNA-damage induced cell death, and suggest that the association of UBE4B expression with neuroblastoma patient outcomes may be mediated by effects on responses of patient tumors to chemotherapy.

Citation Format: Christophe Le Clorennec, Jacqueline Lesperance, Yuchen Huo, Peter E. Zage. The roles of E3/E4 ubiquitin ligase UBE4B and its targets p53 and Ku70 in neuroblastoma cell death and differentiation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4871.

Regorafenib is effective against neuroblastoma in vitro and in vivo and inhibits the RAS/MAPK, PI3K/Akt/mTOR and Fos/Jun pathways

BACKGROUND

Regorafenib is an inhibitor of multiple kinases with aberrant expression and activity in neuroblastoma tumours that have potential roles in neuroblastoma pathogenesis.

METHODS

We evaluated neuroblastoma cells treated with regorafenib for cell viability and confluence, and analysed treated cells for apoptosis and cell cycle progression. We evaluated the efficacy of regorafenib in vivo using an orthotopic xenograft model. We evaluated regorafenib-mediated inhibition of kinase targets and performed reverse-phase protein array (RPPA) analysis of neuroblastoma cells treated with regorafenib. Lastly, we evaluated the efficacy and effects of the combination of regorafenib and 13-cis-retinoic acid on intracellular signalling.

RESULTS

Regorafenib treatment resulted in reduced neuroblastoma cell viability and confluence, with both induction of apoptosis and of cell cycle arrest. Regorafenib treatment inhibits known receptor tyrosine kinase targets RET and PDGFRβ and intracellular signalling through the RAS/MAPK, PI3K/Akt/mTOR and Fos/Jun pathways. Regorafenib is effective against neuroblastoma tumours in vivo, and the combination of regorafenib and 13-cis-retinoic acid demonstrates enhanced efficacy compared with regorafenib alone.

CONCLUSIONS

The effects of regorafenib on multiple intracellular signalling pathways and the potential additional efficacy when combined with 13-cis-retinoic acid represent opportunities to develop treatment regimens incorporating regorafenib for children with neuroblastoma.

Characterization of G-CSF receptor expression in medulloblastoma

Background

Identifying mechanisms of medulloblastoma recurrence is a key to improving patient survival, and targeting treatment-resistant subpopulations within tumors could reduce disease recurrence. Expression of the granulocyte colony-stimulating factor receptor (G-CSF-R, CD114) is a potential marker of cancer stem cells, and therefore we hypothesized that a subpopulation of medulloblastoma cells would also express CD114 and would demonstrate chemoresistance and responsiveness to G-CSF.

Methods

Prevalence of CD114-positive (CD114+) cells in medulloblastoma cell lines, patient-derived xenograft (PDX) tumors, and primary patient tumor samples were assessed by flow cytometry. Growth rates, chemoresistance, and responses to G-CSF of CD114+ and CD114-negative (CD114−) cells were characterized in vitro using continuous live cell imaging and flow cytometry. Gene expression profiles were compared between CD114+ and CD114− medulloblastoma cells using quantitative RT-PCR.

Results

CD114+ cells were identifiable in medulloblastoma cell lines, PDX tumors, and primary patient tumors and have slower growth rates than CD114− or mixed populations. G-CSF accelerates the growth of CD114+ cells, and CD114+ cells are more chemoresistant. The CD114+ population is enriched when G-CSF treatment follows chemotherapy. The CD114+ population also has higher expression of the CSF3R, NRP-1, TWIST1, and MYCN genes.

Conclusions

Our data demonstrate that a subpopulation of CD114+ medulloblastoma cells exists in cell lines and tumors, which may evade traditional chemotherapy and respond to exogenous G-CSF. These properties invite further investigation into the role of G-CSF in medulloblastoma therapy and methods to specifically target these cells.

The Potential Functional Roles of NME1 Histidine Kinase Activity in Neuroblastoma Pathogenesis

Neuroblastoma is the most common extracranial solid tumor in childhood. Gain of chromosome 17q material is found in >60% of neuroblastoma tumors and is associated with poor patient prognosis. The NME1 gene is located in the 17q21.3 region, and high NME1 expression is correlated with poor neuroblastoma patient outcomes. However, the functional roles and signaling activity of NME1 in neuroblastoma cells and tumors are unknown. NME1 and NME2 have been shown to possess histidine (His) kinase activity. Using anti-1- and 3-pHis specific monoclonal antibodies and polyclonal anti-pH118 NME1/2 antibodies, we demonstrated the presence of pH118-NME1/2 and multiple additional pHis-containing proteins in all tested neuroblastoma cell lines and in xenograft neuroblastoma tumors, supporting the presence of histidine kinase activity in neuroblastoma cells and demonstrating the potential significance of histidine kinase signaling in neuroblastoma pathogenesis. We have also demonstrated associations between NME1 expression and neuroblastoma cell migration and differentiation. Our demonstration of NME1 histidine phosphorylation in neuroblastoma and of the potential role of NME1 in neuroblastoma cell migration and differentiation suggest a functional role for NME1 in neuroblastoma pathogenesis and open the possibility of identifying new therapeutic targets and developing novel approaches to neuroblastoma therapy.

The multikinase inhibitor RXDX-105 is effective against neuroblastoma in vitro and in vivo

Neuroblastoma is the most common extracranial solid tumor of childhood and accounts for 15% of all pediatric cancer-related deaths. New therapies are needed to improve outcomes for children with high-risk and relapsed tumors. Inhibitors of the RET kinase and the RAS-MAPK pathway have previously been shown to be effective against neuroblastoma, suggesting that combined inhibition may have increased efficacy. RXDX-105 is a small molecule inhibitor of multiple kinases, including the RET and BRAF kinases. We found that treatment of neuroblastoma cells with RXDX-105 resulted in a significant decrease in cell viability and proliferation in vitro and in tumor growth and tumor vascularity in vivo. Treatment with RXDX-105 inhibited RET phosphorylation and phosphorylation of the MEK and ERK kinases in neuroblastoma cells and xenograft tumors, and RXDX-105 treatment induced both apoptosis and cell cycle arrest. RXDX-105 also showed enhanced efficacy in combination with 13-cis-retinoic acid, which is currently a component of maintenance therapy for children with high-risk neuroblastoma. Our results demonstrate that RXDX-105 shows promise as a novel therapeutic agent for children with high-risk and relapsed neuroblastoma.

Abstract 3467: Growth factor receptor trafficking in neuroblastoma differentiation

Background/Objectives: UBE4B is an E3/E4 ubiquitin ligase involved in growth factor receptor (GFR) trafficking. The UBE4B gene is located in the chromosome 1p36 region commonly deleted in high-risk neuroblastoma tumors. We have previously identified associations of UBE4B expression with neuroblastoma patient outcomes. However, the functional roles of UBE4B in neuroblastoma tumor differentiation are not known.

Design/Methods: We analyzed the association of UBE4B gene expression with expression of known markers of neuroblastoma tumor differentiation using publicly available databases and screened cell lines and neuroblastoma tumor samples for UBE4B protein expression using Western blot and quantitative immunohistochemistry. We measured UBE4B expression by Western blot in cell lines before and after induction of differentiation with 13-cis-retinoic acid treatment and determined the effects of UBE4B overexpression and depletion on retinoic acid-induced differentiation using continuous live-cell imaging of neurite morphology, immunohistochemistry, and Western blot for markers of differentiation. Effects on signaling through the Ras/MAPK pathway were measured using Western blots.

Results: UBE4B expression was associated with neuroblastoma differentiation in patient tumors, and UBE4B gene and protein expression were associated with expression levels of known markers of neuroblastoma differentiation. Retinoic acid treatment resulted in increased UBE4B expression in retinoic acid-sensitive, but not -resistant, neuroblastoma cells, and UBE4B depletion was associated with increased ERK phosphorylation, increased proliferation, and inhibition of retinoic acid-induced neuroblastoma differentiation.

Conclusion: We have demonstrated associations between UBE4B expression and tumor differentiation in gene expression databases and in neuroblastoma tumor samples, and our data suggests that UBE4B expression is required for retinoic acid-induced differentiation, potentially through effects on activation of the Ras/MAPK pathway. These associations between UBE4B and neuroblastoma differentiation combined with the established role of UBE4B in GFR trafficking suggest that UBE4B-mediated receptor trafficking may contribute to the responses of neuroblastoma tumors to therapy and to the outcomes of patients with neuroblastoma.

Citation Format: Jacqueline Lesperance, Divya Subramonian, Sarah Woodfield, Rongjun Guo, Andrew Bean, Dolores Lopez-Terrada, Michael Ittmann, Sara Hakim, Peter E. Zage. Growth factor receptor trafficking in neuroblastoma differentiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3467.

Effects of the multikinase inhibitor regorafenib in neuroblastoma

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Background: Neuroblastoma (NB) is the most common extracranial solid pediatric tumor, and children with high-risk NB have poor survival rates and need novel treatment strategies. Regorafenib, a multi-receptor tyrosine kinase (RTK) inhibitor approved for treating adult solid tumors such as advanced metastatic colorectal cancer and gastrointestinal stromal tumors, inhibits many RTKs, including PDGFR-β, VEGFR1-3, RET, c-Kit and FGFR family members. Based on the potential roles for these targets in neuroblastoma pathogenesis, we explored the therapeutic potential of Regorafenib alone and in combination with 13-cis-retinoic acid against neuroblastoma cells. Methods: We treated NB cell lines with increasing concentrations of Regorafenib and measured cell viability using MTT assays. We further measured the occupied percent confluence over time using continuous live cell imaging. We performed Western blots for caspase cleavage to measure apoptosis and flow cytometry to determine cell cycle expression. We performed Reverse Phase Protein Array (RPPA) analysis of neuroblastoma cells before and after treatment with regorafenib combined with 13- cis-retinoic acid. Results: IC50values for the tested cell lines ranged between 2.5mcM and 12.5mcM after 72 hours of exposure to Regorafenib, and decreased viability was due to a combination of apoptosis and cell cycle arrest. RPPA analysis identified alterations in multiple proteins and pathways after Regorafenib with retinoic acid treatment, including the PI3K/Akt/mTOR and Jak/Stat pathways. Phosphorylation of Erk1/2, S6, Akt, and c-Jun were decreased, while protein expression of GATA3 was increased in a dose-dependent manner. Conclusions: Regorafenib treatment results in reduced neuroblastoma cell viability and increased apoptosis via effects on several signaling pathways. Effects on intracellular signaling pathways associated with responses to the combination of regorafenib plus retinoic acid represent opportunities to develop novel combination therapies, representing potential new therapeutic strategies for children with neuroblastoma.

Overview and recent advances in the treatment of neuroblastoma

INTRODUCTION

Children with neuroblastoma have widely divergent outcomes, ranging from cure in >90% of patients with low risk disease to <50% for those with high risk disease. Recent research has shed light on the biology of neuroblastoma, allowing for more accurate risk stratification and treatment reduction in many cases, although newer treatment strategies for children with high-risk and relapsed neuroblastoma are needed to improve outcomes. Areas covered: Neuroblastoma epidemiology, diagnosis, risk stratification, and recent advances in treatment of both newly diagnosed and relapsed neuroblastoma. Expert commentary: The identification of newer tumor targets and of novel cell-mediated immunotherapy agents may lead to novel therapeutic approaches, and clinical trials for regimens designed to target individual genetic aberrations in tumors are underway. A combination of therapeutic modalities will likely be required to improve survival and cure rates for patients with high-risk neuroblastoma.

The novel kinase inhibitor ponatinib is an effective anti-angiogenic agent against neuroblastoma

Background High-risk neuroblastoma has poor outcomes with high rates of relapse despite aggressive treatment, and novel therapies are needed to improve these outcomes. Ponatinib is a multi-tyrosine kinase inhibitor that targets many pathways implicated in neuroblastoma pathogenesis. We hypothesized that ponatinib would be effective against neuroblastoma in preclinical models. Methods We evaluated the effects of ponatinib on survival and migration of human neuroblastoma cells in vitro. Using orthotopic xenograft mouse models of human neuroblastoma, we analyzed tumors treated with ponatinib for growth, gross and histologic appearance, and vascularity. Results Ponatinib treatment of neuroblastoma cells resulted in decreased cell viability and migration in vitro. In mice with orthotopic xenograft neuroblastoma tumors, treatment with ponatinib resulted in decreased growth and vascularity. Conclusions Ponatinib reduces neuroblastoma cell viability in vitro and reduces tumor growth and vascularity in vivo. The antitumor effects of ponatinib suggest its potential as a novel therapeutic agent for neuroblastoma, and further preclinical testing is warranted.

CD114: A New Member of the Neural Crest-Derived Cancer Stem Cell Marker Family

The neural crest is a population of cells in the vertebrate embryo that gives rise to a wide range of tissues and cell types, including components of the peripheral nervous system and the craniofacial skeleton as well as melanocytes and the adrenal medulla. Aberrations in neural crest development can lead to numerous diseases, including cancers such as melanoma and neuroblastoma. Cancer stem cells (CSCs) have been identified in these neural crest-derived tumors, and these CSCs demonstrate resistance to treatment and are likely key contributors to disease relapse. Patients with neural crest-derived tumors often have poor outcomes due to frequent relapses, likely due to the continued presence of residual treatment-resistant CSCs, and therapies directed against these CSCs are likely to improve patient outcomes. CSCs share many of the same genetic and biologic features of primordial neural crest cells, and therefore a better understanding of neural crest development will likely lead to the development of effective therapies directed against these CSCs. Signaling through STAT3 has been shown to be required for neural crest development, and granulocyte colony stimulating factor (GCSF)-mediated activation of STAT3 has been shown to play a role in the pathogenesis of neural crest-derived tumors. Expression of the cell surface marker CD114 (the receptor for GCSF) has been identified as a potential marker for CSCs in neural crest-derived tumors, suggesting that CD114 expression and function may contribute to disease relapse and poor patient outcomes. Here we review the processes of neural crest development and tumorigenesis and we discuss the previously identified markers for CSC subpopulations identified in neural crest tumors and their role in neural crest tumor biology. We also discuss the potential for CD114 and downstream intracellular signaling pathways as potential targets for CSC-directed therapy. J. Cell. Biochem. 118: 221-231, 2017. © 2016 Wiley Periodicals, Inc.

Neuroblastoma patient outcomes, tumor differentiation, and ERK activation are correlated with expression levels of the ubiquitin ligase UBE4B

BACKGROUND

UBE4B is an E3/E4 ubiquitin ligase whose gene is located in chromosome 1p36.22. We analyzed the associations of UBE4B gene and protein expression with neuroblastoma patient outcomes and with tumor prognostic features and histology.

METHODS

We evaluated the association of UBE4B gene expression with neuroblastoma patient outcomes using the R2 Platform. We screened neuroblastoma tumor samples for UBE4B protein expression using immunohistochemistry. FISH for UBE4B and 1p36 deletion was performed on tumor samples. We then evaluated UBE4B expression for associations with prognostic factors and with levels of phosphorylated ERK in neuroblastoma tumors and cell lines.

RESULTS

Low UBE4B gene expression is associated with poor outcomes in patients with neuroblastoma and with worse outcomes in all patient subgroups. UBE4B protein expression was associated with neuroblastoma tumor differentiation, and decreased UBE4B protein levels were associated with high-risk features. UBE4B protein levels were also associated with levels of phosphorylated ERK.

CONCLUSIONS

We have demonstrated associations between UBE4B gene expression and neuroblastoma patient outcomes and prognostic features. Reduced UBE4B protein expression in neuroblastoma tumors was associated with high-risk features, a lack of differentiation, and with ERK activation. These results suggest UBE4B may contribute to the poor prognosis of neuroblastoma tumors with 1p36 deletions and that UBE4B expression may mediate neuroblastoma differentiation.

Binimetinib inhibits MEK and is effective against neuroblastoma tumor cells with low NF1 expression

BACKGROUND

Novel therapies are needed for children with high-risk and relapsed neuroblastoma. We hypothesized that MAPK/ERK kinase (MEK) inhibition with the novel MEK1/2 inhibitor binimetinib would be effective in neuroblastoma preclinical models.

METHODS

Levels of total and phosphorylated MEK and extracellular signal-regulated kinase (ERK) were examined in primary neuroblastoma tumor samples and in neuroblastoma cell lines by Western blot. A panel of established neuroblastoma tumor cell lines was treated with increasing concentrations of binimetinib, and their viability was determined using MTT assays. Western blot analyses were performed to examine changes in total and phosphorylated MEK and ERK and to measure apoptosis in neuroblastoma tumor cells after binimetinib treatment. NF1 protein levels in neuroblastoma cell lines were determined using Western blot assays. Gene expression of NF1 and MEK1 was examined in relationship to neuroblastoma patient outcomes.

RESULTS

Both primary neuroblastoma tumor samples and cell lines showed detectable levels of total and phosphorylated MEK and ERK. IC50 values for cells sensitive to binimetinib ranged from 8 nM to 1.16 μM, while resistant cells did not demonstrate any significant reduction in cell viability with doses exceeding 15 μM. Sensitive cells showed higher endogenous expression of phosphorylated MEK and ERK. Gene expression of NF1, but not MEK1, correlated with patient outcomes in neuroblastoma, and NF1 protein expression also correlated with responses to binimetinib.

CONCLUSIONS

Neuroblastoma tumor cells show a range of sensitivities to the novel MEK inhibitor binimetinib. In response to binimetinib, sensitive cells demonstrated complete loss of phosphorylated ERK, while resistant cells demonstrated either incomplete loss of ERK phosphorylation or minimal effects on MEK phosphorylation, suggesting alternative mechanisms of resistance. NF1 protein expression correlated with responses to binimetinib, supporting the use of NF1 as a biomarker to identify patients that may respond to MEK inhibition. MEK inhibition therefore represents a potential new therapeutic strategy for neuroblastoma.

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.

CD114 Expression Mediates Melanoma Tumor Cell Growth and Treatment Resistance

BACKGROUND/AIM

Melanoma tumor cell sub-populations expressing a variety of specific molecular markers have been identified. We hypothesized that expression of CD114, the cell surface receptor for granulocyte-colony stimulating factor (G-CSF), would be associated with melanoma tumor cell growth and response to treatment.

MATERIALS AND METHODS

We determined the expression of CD114 expression in tumor cell lines by flow cytometry. We separated melanoma tumor cells into CD114-positive and - negative populations by fluorescence-activated cell sorting (FACS) and measured cell growth and responses to temozolomide and etoposide and the anticancer agent nifurtimox.

RESULTS

All tested cell lines demonstrated a sub-population of cells with CD114 surface expression. CD114-positive sub-populations grew faster than CD114-negative ones and demonstrated resistance to temozolomide, etoposide, and nifurtimox.

CONCLUSION

CD114 expression defines a sub-population of melanoma tumor cells with altered growth and resistance to treatment. Further studies on the role of CD114 in melanoma pathogenesis are warranted.

Abstract 3983: The role of UBE4B in neuroblastoma pathogenesis

Background: Neuroblastoma is the most common extracranial solid malignancy in children. Children with aggressive neuroblastoma have an overall survival rate of 30% using current treatment regimens. We recently identified an association between UBE4B gene expression and neuroblastoma patient outcomes. The UBE4B gene is found in the chromosome 1p36 region frequently deleted in neuroblastoma. UBE4B is an E3/E4 ubiquitin ligase involved in the degradation of membrane proteins, including growth factor receptors, and p53. Although the p53 pathway has been shown to be involved in neuroblastoma, the mechanisms underlying the role of UBE4B in neuroblastoma pathogenesis are not known. We previously identified an inverse correlation between EGFR and UBE4B protein expression in neuroblastoma patient tumor samples, suggesting that UBE4B-mediated protein degradation may be critical for neuroblastoma pathogenesis. Additionally, we identified an association between UBE4B gene expression and MYCN amplification, one of the strongest prognostic factors for high-risk neuroblastoma. Previous studies on UBE4B were based on mRNA and Western blotting analysis of frozen tissue specimens, and without addressing potential tumor heterogeneity, a striking feature of neuroblastoma. The purpose of this study was to further explore the role of UBE4B in pathogenesis and its association with other known prognostic factors in neuroblastoma tumors.

Experimental design and Results: Using immunohistochemistry, we evaluated UBE4B and EGFR protein expression in tissue specimens from neuroblastoma patient tumor samples. UBE4B expression was reduced in eighteen cases (51%). This reduction was only seen in poorly differentiated or undifferentiated tumors, or the poorly differentiated component of intermixed tumors. Additionally, tissue microarrays containing primary neuroblastoma tumors were analyzed for EGFR expression. Approximately 80% of the tumor samples contained high EGFR expression. Lastly, using coimmunoprecipitation analysis, we identified a potential interaction between UBE4B and p53.

Conclusions: We found reduced protein UBE4B expression to be a common event in neuroblastoma tumors. This reduced UBE4B expression was associated with a lack of differentiation in neuroblastoma tumors, a hallmark of aggressive malignancies. Furthermore, the potential interaction of UBE4B and p53 represents a novel mechanism to explain the association of UBE4B gene expression with neuroblastoma patient outcomes. Additional studies are underway to further explore these roles of UBE4B in neuroblastoma pathogenesis.

Citation Format: Sandra M. Indiviglio, Sarah E. Woodfield, Linna Zhang, Rongjun Guo, Dolores Lopez-Terrada, Andrew J. Bean, Peter E. Zage. The role of UBE4B in neuroblastoma pathogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3983. doi:10.1158/1538-7445.AM2014-3983

Etoposide-loaded immunoliposomes as active targeting agents for GD2-positive malignancies

Systemic chemotherapeutics remain the standard of care for most malignancies even though they frequently suffer from narrow therapeutic index, poor serum solubility, and off-target effects. In this study, we have encapsulated etoposide, a topoisomerase inhibitor effective against a wide range of cancers, in surface-modified liposomes decorated with anti-GD2 antibodies. We characterized the properties of the liposomes using a variety of methods including dynamic light scattering, electron microscopy, and Fourier transformed infrared spectroscopy. We examined whether these immunoliposomes were able to target cell lines expressing varying levels of surface GD2 and affect cellular proliferation. Anti-GD2 liposomes were generally targeted in a manner that correlated with GD2 expression and inhibited proliferation in cell lines to which they were efficiently targeted. The mechanism by which the immunoliposomes entered targeted cells appeared to be via clathrin-dependent uptake as demonstrated using flow cytometry and confocal microscopy. These studies suggest that anti-GD2-targeted, etoposide-loaded liposomes represent a potential strategy for more effective delivery of anti-cancer drugs that could be used for GD2 positive tumors.

Validation of a prognostic multi-gene signature in high-risk neuroblastoma using the high throughput digital NanoString nCounter™ system

Microarray-based molecular signatures have not been widely integrated into neuroblastoma diagnostic classification systems due to the complexities of the assay and requirement for high-quality RNA. New digital technologies that accurately quantify gene expression using RNA isolated from formalin-fixed paraffin embedded (FFPE) tissues are now available. In this study, we describe the first use of a high-throughput digital system to assay the expression of genes in an "ultra-high risk" microarray classifier in FFPE high-risk neuroblastoma tumors. Customized probes corresponding to the 42 genes in a published multi-gene neuroblastoma signature were hybridized to RNA isolated from 107 FFPE high-risk neuroblastoma samples using the NanoString nCounter™ Analysis System. For classification of each patient, the Pearson's correlation coefficient was calculated between the standardized nCounter™ data and the molecular signature from the microarray data. We demonstrate that the nCounter™ 42-gene panel sub-stratified the high-risk cohort into two subsets with statistically significantly different overall survival (p = 0.0027) and event-free survival (p = 0.028). In contrast, none of the established prognostic risk markers (age, stage, tumor histology, MYCN status, and ploidy) were significantly associated with survival. We conclude that the nCounter™ System can reproducibly quantify expression levels of signature genes in FFPE tumor samples. Validation of this microarray signature in our high-risk patient cohort using a completely different technology emphasizes the prognostic relevance of this classifier. Prospective studies testing the prognostic value of molecular signatures in high-risk neuroblastoma patients using FFPE tumor samples and the nCounter™ System are warranted.

UBE4B protein couples ubiquitination and sorting machineries to enable epidermal growth factor receptor (EGFR) degradation

The signaling of plasma membrane proteins is tuned by internalization and sorting in the endocytic pathway prior to recycling or degradation in lysosomes. Ubiquitin modification allows recognition and association of cargo with endosomally associated protein complexes, enabling sorting of proteins to be degraded from those to be recycled. The mechanism that provides coordination between the cellular machineries that mediate ubiquitination and endosomal sorting is unknown. We report that the ubiquitin ligase UBE4B is recruited to endosomes in response to epidermal growth factor receptor (EGFR) activation by binding to Hrs, a key component of endosomal sorting complex required for transport (ESCRT) 0. We identify the EGFR as a substrate for UBE4B, establish UBE4B as a regulator of EGFR degradation, and describe a mechanism by which UBE4B regulates endosomal sorting, affecting cellular levels of the EGFR and its downstream signaling. We propose a model in which the coordinated action of UBE4B, ESCRT-0, and the deubiquitinating enzyme USP8 enable the endosomal sorting and lysosomal degradation of the EGFR.

UBE4B levels are correlated with clinical outcomes in neuroblastoma patients and with altered neuroblastoma cell proliferation and sensitivity to epidermal growth factor receptor inhibitors

BACKGROUND

The UBE4B gene, which is located on chromosome 1p36, encodes a ubiquitin ligase that interacts with hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), a protein involved in epidermal growth factor receptor (EGFR) trafficking, suggesting a link between EGFR trafficking and neuroblastoma pathogenesis. The authors analyzed the roles of UBE4B in the outcomes of patients with neuroblastoma and in neuroblastoma tumor cell proliferation, EGFR trafficking, and response to EGFR inhibition.

METHODS

The association between UBE4B expression and the survival of patients with neuroblastoma was examined using available microarray data sets. UBE4B and EGFR protein levels were measured in patient tumor samples, EGFR degradation rates were measured in neuroblastoma cell lines, and the effects of UBE4B on neuroblastoma tumor cell growth were analyzed. The effects of the EGFR inhibitor cetuximab were examined in neuroblastoma cells that expressed wild-type and mutant UBE4B.

RESULTS

Low UBE4B gene expression is associated with poor outcomes in patients with neuroblastoma. UBE4B overexpression reduced neuroblastoma tumor cell proliferation, and UBE4B expression was inversely related to EGFR expression in tumor samples. EGFR degradation rates correlated with cellular UBE4B levels. Enhanced expression of catalytically active UBE4B resulted in reduced sensitivity to EGFR inhibition.

CONCLUSIONS

The current study demonstrates associations between UBE4B expression and the outcomes of patients with neuroblastoma and between UBE4B and EGFR expression in neuroblastoma tumor samples. Moreover, levels of UBE4B influence neuroblastoma tumor cell proliferation, EGFR degradation, and response to EGFR inhibition. These results suggest UBE4B-mediated growth factor receptor trafficking may contribute to the poor prognosis of patients who have neuroblastoma tumors with 1p36 deletions and that UBE4B expression may be a marker that can predict responses of neuroblastoma tumors to treatment.

New aspects of neuroblastoma treatment: ASPHO 2011 symposium review

Neuroblastoma is the most common extracranial solid tumor of childhood, and the outcomes for children with high-risk and relapsed disease remain poor. However, new international strategies for risk stratification and for treatment based on novel tumor targets and including immunotherapy are being employed in attempts to improve the outcomes of children with neuroblastoma. A new international neuroblastoma risk classification system has been developed which is being incorporated into cooperative group clinical trials in North America, Japan, and Europe, resulting in standardized approaches for the initial evaluation and treatment stratification of neuroblastoma patients. Furthermore, novel treatment regimens are being developed based on improved understanding of neuroblastoma biology and on the recruitment of the immune system to specifically target neuroblastoma tumors. These approaches will lead to new therapeutic strategies that likely will improve the outcomes for children with neuroblastoma worldwide.

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

9534

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

Notch pathway activation induces neuroblastoma tumor cell growth arrest

BACKGROUND

Notch pathway signaling has critical roles in differentiation, proliferation, and survival, and has oncogenic or tumor suppressor effects in a variety of malignancies. The goal of this study was to evaluate the effects of Notch activation on human neuroblastoma cells.

PROCEDURE

Quantitative RT-PCR, immunoblots, and immunohistochemistry were used to determine the expression of Notch receptors (Notch1-4), cleaved Notch1 (ICN1), and downstream targets (HES1-5) in human neuroblastoma cell lines and patient tumor samples. Notch pathway signaling was induced using intracellular Notch (ICN1-3) and HES gene constructs or direct culture on Notch ligands. Quantitative methylation-specific PCR was used to quantify methylation of the HES gene promoters, and the effects of treatment with decitabine were measured.

RESULTS

Neuroblastoma cells express varying levels of Notch receptors and low levels of HES genes at baseline. However, no endogenous activation of the Notch pathway was detected in neuroblastoma cell lines or patient tumor samples. Expression of activated Notch intracellular domains and HES gene products led to growth arrest. The HES2 and HES5 gene promoters were found to be heavily methylated in most neuroblastoma lines, and HES gene expression could be induced through treatment with decitabine.

CONCLUSIONS

We report that neuroblastoma cell lines express multiple Notch receptors, which are inactive at baseline. Activation of the Notch pathway via ligand binding consistently resulted in growth arrest. HES gene expression appears to be regulated epigenetically and could be induced with decitabine. These findings support a tumor suppressor role for Notch signaling in neuroblastoma.

Treatment of recurrent diffuse intrinsic pontine glioma: the MD Anderson Cancer Center experience

Recurrent diffuse intrinsic pontine gliomas (DIPG) are traditionally treated with palliative care since no effective treatments have been described for these tumors. Recently, clinical studies have been emerging, and individualized treatment is attempted more frequently. However, an informative way to compare the treatment outcomes has not been established, and historical control data are missing for recurrent disease. We conducted a retrospective chart review of patients with recurrent DIPG treated between 1998 and 2010. Response progression-free survival and possible influencing factors were evaluated. Thirty-one patients were identified who were treated in 61 treatment attempts using 26 treatment elements in 31 different regimens. The most frequently used drugs were etoposide (14), bevacizumab (13), irinotecan (13), nimotuzumab (13), and valproic acid (13). Seven patients had repeat radiation therapy to the primary tumor. Response was recorded after 58 treatment attempts and was comprised of 0 treatment attempts with complete responses, 7 with partial responses, 20 with stable diseases, and 31 with progressive diseases The median progression-free survival after treatment start was 0.16 years (2 months) and was found to be correlated to the prior time to progression but not to the number of previous treatment attempts. Repeat radiation resulted in the highest response rates (4/7), and the longest progression-free survival. These data provide a basis to plan future clinical trials for recurrent DIPG. Repeat radiation therapy should be tested in a prospective clinical study.

Chromatin remodelling at the topoisomerase II-beta promoter is associated with enhanced sensitivity to etoposide in human neuroblastoma cell lines

Etoposide, an inhibitor of topoisomerase II, promotes DNA damage and apoptosis of cancer cells and is a component of standard therapy for neuroblastoma. Resistance to etoposide has been observed in neural tumour cells expressing lower levels of topoisomerase II. In the present study, we have examined the contribution of epigenetic modulation of gene expression in the potentiation of etoposide-mediated cytotoxicity in neuroblastoma cells. Specifically, we studied the effects of histone deacetylase inhibition with valproic acid on topoisomerase II gene expression and apoptosis in response to etoposide. Using human neuroblastoma cell lines SK-N-AS and SK-N-SH, we show that although the combination of valproic acid and etoposide promoted a reduction in growth compared to either drug alone in both cells, the effect was substantially enhanced in SK-N-AS compared to SK-N-SH cells. An increase in histone H3 acetylation and p21 expression was observed in both cell lines, however, upregulation of topoisomerase II-beta gene expression and an increase in PARP cleavage was observed in SK-N-AS cells only. Furthermore, chromatin immunoprecipitation assays revealed an increase in acetylation of histone H3 at the cognate topoisomerase II-beta gene after treatment with valproic acid in SK-N-AS cells. These results suggest a potential epigenetic mechanism of regulation of the topoisomerase II-beta gene and a possible role for its increased expression in the sensitivity of SK-N-AS neuroblastoma cells to etoposide.

The combination of the novel glycolysis inhibitor 3-BrOP and rapamycin is effective against neuroblastoma

Children with high-risk and recurrent neuroblastoma have poor survival rates, and novel therapies are needed. Many cancer cells have been found to preferentially employ the glycolytic pathway for energy generation, even in the presence of oxygen. 3-BrOP is a novel inhibitor of glycolysis, and has demonstrated efficacy against a wide range of tumor types. To determine whether human neuroblastoma cells are susceptible to glycolysis inhibition, we evaluated the role of 3-BrOP in neuroblastoma model systems. Neuroblastoma tumor cell lines demonstrated high rates of lactate accumulation and low rates of oxygen consumption, suggesting a potential susceptibility to inhibitors of glycolysis. In all ten human tested neuroblastoma tumor cell lines, 3-BrOP induced cell death via apoptosis in a dose and time dependent manner. Furthermore, 3-BrOP-induced depletion of ATP levels correlated with decreased neuroblastoma cell viability. In a mouse neuroblastoma xenograft model, glycolysis inhibition with 3-BrOP demonstrated significantly reduced final tumor weight. In neuroblastoma tumor cells, treatment with 3-BrOP induced mTOR activation, and the combination of 3-BrOP and mTOR inhibition with rapamycin demonstrated synergistic efficacy. Based on these results, neuroblastoma tumor cells are sensitive to treatment with inhibitors of glycolysis, and the demonstrated synergy with rapamycin suggests that the combination of glycolysis and mTOR inhibitors represents a novel therapeutic approach for neuroblastoma that warrants further investigation.

Signaling of ERBB receptor tyrosine kinases promotes neuroblastoma growth in vitro and in vivo

BACKGROUND

ERBB receptor tyrosine kinases can mediate proliferation, migration, adhesion, differentiation, and survival in many types of cells and play critical roles in many malignancies. Recent reports suggest a role for EGFR signaling in proliferation and survival of neuroblastoma, a common form of pediatric cancer that often has an extremely poor outcome.

METHODS

The authors examined ERBB family expression in neuroblastoma cell lines and patient samples by flow cytometry, western blot, and quantitative real time polymerase chain reaction (Q-PCR). Response to ERBB inhibition was assessed in vitro by cell-cycle analysis and western blot and in vivo by serial tumor-size measurements.

RESULTS

A panel of neuroblastoma cell lines and primary patient tumors expressed EGFR, HER-3, and HER-4, with HER-2 in some tumors. HER-4 mRNA was expressed predominantly in cleavable isoforms. Whereas EGFR inhibition with erlotinib and pan-ERBB inhibition with CI-1033 inhibited EGF-induced phosphorylation of EGFR, AKT, and ERK1/2, only CI-1033 induced growth inhibition and dose-dependent apoptosis in vitro. Both CI-1033 and erlotinib treatment of neuroblastoma xenograft tumors resulted in decreased tumor growth in vivo, although CI-1033 was more effective. In vivo expression of EGFR was observed predominantly in vascular endothelial cells.

CONCLUSIONS

Pan-ERBB inhibition is required for ERBB-related neuroblastoma apoptosis in vitro, although EGFR contributes indirectly to tumor growth in vivo. Inhibition of EGFR in endothelial cells may be an important aspect of erlotinib's impact on neuroblastoma growth in vivo. Our results suggest that non-EGFR ERBB family members contribute directly to neuroblastoma growth and survival, and pan-ERBB inhibition represents a potential therapeutic target for treating neuroblastoma.

A novel therapeutic combination for neuroblastoma: the vascular endothelial growth factor receptor/epidermal growth factor receptor/rearranged during transfection inhibitor vandetanib with 13-cis-retinoic acid

BACKGROUND

High-risk cases of neuroblastoma have poor survival rates, and novel therapies are needed. Vandetanib (ZD6474, Zactima) is an inhibitor of the vascular endothelial growth factor receptor, epidermal growth factor receptor, and rearranged during transfection (RET) tyrosine kinases, which have each been implicated in neuroblastoma pathogenesis. The authors hypothesized that vandetanib combined with 13-cis-retinoic acid (CRA), a differentiating agent used in most current neuroblastoma treatment regimens, would be effective against neuroblastoma tumor models.

METHODS

The authors evaluated the effects of vandetanib with and without CRA on RET phosphorylation and on the proliferation and survival of human neuroblastoma cell lines in vitro. Using a subcutaneous mouse xenograft model of human neuroblastoma, they analyzed tumors treated with CRA, vandetanib, and the combination of vandetanib plus CRA for growth, gross and histologic appearance, vascularity, and apoptosis.

RESULTS

Vandetanib treatment inhibited RET phosphorylation and resulted in induction of apoptosis in the majority of neuroblastoma cell lines in vitro, whereas CRA treatment induced morphologic differentiation and cell-cycle arrest. Treatment with vandetanib plus CRA resulted in more significant reduction in neuroblastoma cell viability than either alone. In a mouse xenograft model, the combination of vandetanib with CRA demonstrated significantly more growth inhibition than either alone, via both reduction in tumor vascularity and induction of apoptosis.

CONCLUSIONS

Vandetanib induces neuroblastoma tumor cell death in vitro and reduces tumor growth and vascularity in vivo. The combination of vandetanib with CRA was more effective in reducing tumor growth than either treatment alone. The antitumor effects of vandetanib plus CRA suggest a novel combination for use in neuroblastoma patients.

Identification and preclinical characterization of AZ-23, a novel, selective, and orally bioavailable inhibitor of the Trk kinase pathway

Tropomyosin-related kinases (TrkA, TrkB, and TrkC) are receptor tyrosine kinases that, along with their ligands, the neurotrophins, are involved in neuronal cell growth, development, and survival. The Trk-neurotrophin pathway may also play a role in tumorigenesis through oncogenic fusions, mutations, and autocrine signaling, prompting the development of novel Trk inhibitors as agents for cancer therapy. This report describes the identification of AZ-23, a novel, potent, and selective Trk kinase inhibitor. In vitro studies with AZ-23 showed improved selectivity over previous compounds and inhibition of Trk kinase activity in cells at low nanomolar concentrations. AZ-23 showed in vivo TrkA kinase inhibition and efficacy in mice following oral administration in a TrkA-driven allograft model and significant tumor growth inhibition in a Trk-expressing xenograft model of neuroblastoma. AZ-23 represents a potent and selective Trk kinase inhibitor from a novel series with the potential for use as a treatment for cancer.

Outcomes of the POG 9340/9341/9342 trials for children with high-risk neuroblastoma: a report from the Children's Oncology Group

BACKGROUND

From 1993 to 1995, the Pediatric Oncology Group (POG) enrolled patients with high-risk neuroblastoma on three sequential, conjoined studies: a phase II induction window (9340), followed by intensive multiagent induction chemotherapy (9341), and subsequent myeloablative therapy with autologous stem cell rescue (9342). We report here the outcomes of patients treated on these studies.

PATIENTS AND METHODS

Patients were between 1 and 21 years old with high-risk neuroblastoma. Phase II window therapy consisted of two courses of either paclitaxel, topotecan, or cyclophosphamide with topotecan. Induction therapy consisted of at least five cycles of intensive chemotherapy, followed by myeloablative therapy with purged autologous stem cell reinfusion. Patient responses, treatment toxicities, and overall and event-free survival rates were calculated.

RESULTS

Eighty-four percent of patients responded to induction chemotherapy, with 39% achieving complete response. Toxicities were primarily hematologic. The 7-year EFS and OS rates for all eligible patients on POG 9341 were 23 +/- 4% and 28 +/- 4%, respectively. The 7-year EFS and OS rates for patients treated on POG 9342 were 27 +/- 6% and 29 +/- 6%, respectively.

CONCLUSIONS

These studies were the first attempt by POG to use autologous stem cell transplantation for neuroblastoma treatment in a cooperative group setting. Toxicities and outcomes were comparable to contemporary cooperative group studies. The phase II induction window had no detectable effect on outcomes. New strategies are needed to improve survival for this devastating disease.

Outcomes of a two-drug chemotherapy regimen for intraocular retinoblastoma

BACKGROUND

Retinoblastoma is the most common intraocular tumor of childhood. Vision salvage rates in advanced cases are less than ideal, and the optimal treatment for intraocular retinoblastoma has not been established. We report the results of an institutional retinoblastoma treatment trial to determine the vision salvage rates and toxicity of a regimen combining carboplatin and etoposide with focal retinal therapy.

PROCEDURE

Twenty-nine patients diagnosed with retinoblastoma in 48 eyes were treated between 1992 and 2004 with at least six cycles of carboplatin and etoposide combined with focal retinal therapy.

RESULTS

The response rate of eyes after six cycles of chemotherapy was 85.4%. Twenty-two eyes were enucleated, but only seven eyes received EBRT. The vision salvage rate without EBRT was 82.6% for eyes with Reese-Ellsworth (R-E) groups I-IV tumors and 20% for eyes with R-E group V tumors. The vision salvage rate without EBRT for eyes with Murphree groups A and B tumors was 77.3% but was only 26.9% for eyes with groups C and D tumors. Acute side effects were minimal.

CONCLUSIONS

The combination of carboplatin and etoposide with focal therapy is a well-tolerated regimen that has acceptable vision salvage rates for R-E groups I-IV and Murphree groups A and B retinoblastoma. This combination avoids the use of EBRT and the toxicity of additional chemotherapy agents. However, patients with R-E group V and Murphree groups C and D retinoblastoma have poorer outcomes and require more intensive therapy.

Predicting tumor cell repopulation after response: mathematical modeling of cancer cell growth

The kinetics of regrowth of tumor cells after treatment may offer a new end-point for clinical trials. Based on our testing, it is best described in this manner: y(t) = a*exp(-b*t) + c*exp(d*t). Human malignant glioma cells U87 MG were treated with etoposide and allowed to regrow after treatment. The cell number versus time data were fitted mathematically to the two-term exponential model. Parameters b and d were independent of the drug concentration, while a increased c decreased as the drug dose increased. The concentration independence of b and d indicated that both cell proliferation and cell death kinetics were independent of the drug treatment, which suggests constant times for cell cycle and apoptosis. The concentration dependence of c suggests that the time until the cells started regrowing depended on the treatment, repair mechanisms taking longer after heavy damage. The two-term exponential model predicted tumor repopulation in this in vitro system. These results indicated that the velocities of the logarithm of cell growth and cell death were independent of drug treatment, while the recovery time of the tumor repopulation was dependent on the drug dose. The two-term exponential model can be used to predict tumor repopulation in an in vitro system and this model will be further tested using clinical data.

Integrins interact with focal adhesions through multiple distinct pathways

Integrin signaling involves oligomerization and a transmembrane conformational change induced by receptor occupancy. Previous work has shown that subsets of focal adhesion-associated proteins are recruited to integrins as a result of clustering, ligand binding, or both. However, it is unclear whether these discrete subsets reflect the differential binding of cytoplasmic proteins to the integrin or whether a single protein or set of proteins binds the integrin and is differentially activated by receptor occupancy or clustering. To address this question, we made mutations of the beta1 integrin cytoplasmic domain in the context of a single subunit chimera and studied their activation of various known integrin-mediated signaling pathways. We show here that the indirect association of the integrin with actin is distinct from its interactions with both preformed focal adhesions and FAK. Therefore, multiple independent signaling pathways exist from the integrin to the focal adhesion, which may reflect the association of independent factors with the integrin beta1 cytoplasmic domain.

The membrane proximal region of the integrin beta cytoplasmic domain can mediate oligomerization

Integrin-ligand binding generates many intracellular signals, including signals to initiate focal contact formation and to regulate cellular decisions concerning growth and differentiation. Oligomerization of the beta subunit cytoplasmic domain appears to be required for many of these events. In order to study these processes, we have generated a novel chimeric protein, consisting of the chicken integrin beta 1 cytoplasmic domain connected to the central rod domain of a neuronal intermediate filament, alpha-internexin. This chimeric protein, when expressed transiently in 293T cells, oligomerizes in a beta cytoplasmic domain-dependent manner. This oligomerization requires the membrane proximal amino acids LLMII of the beta 1 cytoplasmic domain, as demonstrated by deletion analysis. Therefore, the integrin beta cytoplasmic domain in this system contains an oligomerization function, which may provide some insight as to the function of intact integrins in vivo.