Systematic review of the receptor tyrosine kinase superfamily in neuroblastoma pathophysiology.

BACKGROUND: Neuroblastoma is a devastating disease accounting for 15% of all childhood cancer deaths. Yet, our understanding of key molecular drivers such as receptor tyrosine kinases (RTKs) in this pathology remains poorly clarified. Here, we provide a systematic analysis of the RTK superfamily in the context of neuroblastoma pathogenesis. METHODS: Statistical correlations for all RTK family members' expression to neuroblastoma patient survival across 10 independent patient cohorts were annotated, synthesized, and ranked using the R2: Genomics Analysis and Visualization Platform. Gene expression of selected members across different cancer cell lines was further analyzed in the Cancer Cell Line Encyclopedia, part of the Cancer Dependency Map portal (depmap portal ( http://depmap.org )). Finally, we provide a detailed literature review for highly ranked candidates. RESULTS: Our analysis defined two subsets of RTKs showing robust associations with either better or worse survival, constituting potential novel players in neuroblastoma pathophysiology, diagnosis, and therapy. We review the available literature regarding the oncogenic functions of these RTKs, their roles in neuroblastoma pathophysiology, and potential utility as therapeutic targets. CONCLUSIONS: Our systematic analysis and review of the RTK superfamily in neuroblastoma pathogenesis provides a new resource to guide the research community towards focused efforts investigating signaling pathways that contribute to neuroblastoma tumor establishment, growth, and/or aggressiveness and targeting these druggable molecules in novel therapeutic strategies.

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

BACKGROUND/OBJECTIVES: Standard supportive care during induction therapy for high-risk neuroblastoma (HR-NBL) includes primary prophylactic granulocyte colony-stimulating factor (G-CSF) aimed at limiting duration of neutropenia, reducing infection risk, and minimizing treatment delays. Preclinical models suggest that G-CSF promotes maintenance of neuroblastoma cancer stem cells and may reduce the efficacy of chemotherapy. This study's objective was to determine the safety and feasibility of administering induction chemotherapy without routine use of prophylactic G-CSF. DESIGN/METHODS: Children with newly diagnosed HR-NBL received six-cycle induction chemotherapy regimen without prophylactic G-CSF in four cycles. G-CSF was administered for stem cell mobilization after cycle 3 and granulocyte-monocyte colony-stimulating factor after cycle 5 prior to surgical resection of primary disease. The primary outcome measure was the incidence of grade 3 or higher infection. We hypothesized that the per patient infection rate would be comparable to our institutional baseline rate of 58% in patients with HR-NBL receiving induction chemotherapy with prophylactic growth factor support. The trial used an A'Hern single-stage design. RESULTS: Twelve patients with HR-NBL received 58 cycles of chemotherapy on study. Three patients completed the entire six-cycle regimen with no infections. Nine patients experienced grade 3 infections (bacteremia four, urinary tract infection two, skin/soft tissue infection three). No patients experienced grade 4 infections or required intensive care treatment for infection. CONCLUSION: A greater than expected number of serious bacterial infections were observed during administration of induction chemotherapy for HR-NBL without primary prophylactic G-CSF. These results support continued prophylactic administration growth factor during induction chemotherapy.

Neuroblastoma pathogenesis: deregulation of embryonic neural crest development.

Neuroblastoma (NB) is an aggressive pediatric cancer that originates from neural crest tissues of the sympathetic nervous system. NB is highly heterogeneous both from a clinical and a molecular perspective. Clinically, this cancer represents a wide range of phenotypes ranging from spontaneous regression of 4S disease to unremitting treatment-refractory progression and death of high-risk metastatic disease. At a cellular level, the heterogeneous behavior of NB likely arises from an arrest and deregulation of normal neural crest development. In the present review, we summarize our current knowledge of neural crest development as it relates to pathways promoting 'stemness' and how deregulation may contribute to the development of tumor-initiating CSCs. There is an emerging consensus that such tumor subpopulations contribute to the evolution of drug resistance, metastasis and relapse in other equally aggressive malignancies. As relapsed, refractory disease remains the primary cause of death for neuroblastoma, the identification and targeting of CSCs or other primary drivers of tumor progression remains a critical, clinically significant goal for neuroblastoma. We will critically review recent and past evidence in the literature supporting the concept of CSCs as drivers of neuroblastoma pathogenesis.

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: molecular pathogenesis and therapy.

Neuroblastoma is a developmental tumor of young children arising from the embryonic sympathoadrenal lineage of the neural crest. Neuroblastoma is the primary cause of death from pediatric cancer for children between the ages of one and five years and accounts for ∼13% of all pediatric cancer mortality. Its clinical impact and unique biology have made this aggressive malignancy the focus of a large concerted translational research effort. New insights into tumor biology are driving the development of new classification schemas. Novel targeted therapeutic approaches include small-molecule inhibitors as well as epigenetic, noncoding-RNA, and cell-based immunologic therapies. In this review, recent insights regarding the pathogenesis and biology of neuroblastoma are placed in context with the current understanding of tumor biology and tumor/host interactions. Systematic classification of patients coupled with therapeutic advances point to a future of improved clinical outcomes for this biologically distinct and highly aggressive pediatric malignancy.

A Novel Druggable Dual-Specificity tYrosine-Regulated Kinase3/Calmodulin Kinase-like Vesicle-Associated Signaling Module with Therapeutic Implications in Neuroblastoma.

High-risk neuroblastoma is a very aggressive pediatric cancer, accounting for ~15% of childhood cancer mortality. Therefore, novel therapeutic strategies for the treatment of neuroblastoma are urgently sought. Here, we focused on the potential implications of the Dual-specificity tYrosine-Regulated Kinase (DYRK) family and downstream signaling pathways. We used bioinformatic analysis of public datasets from neuroblastoma cohorts and cell lines to search correlations between patient survival and expression of DYRK kinases. Additionally, we performed biochemical, molecular, and cellular approaches to validate and characterize our observations, as well as an in vivo orthotopic murine model of neuroblastoma. We identified the DYRK3 kinase as a critical mediator of neuroblastoma cell proliferation and in vivo tumor growth. DYRK3 has recently emerged as a key regulator of several biomolecular condensates and has been linked to the hypoxic response of neuroblastoma cells. Our data suggest a role for DYRK3 as a regulator of the neuroblastoma-specific protein CAMKV, which is also required for neuroblastoma cell proliferation. CAMKV is a very understudied member of the Ca2+/calmodulin-dependent protein kinase family, originally described as a pseudokinase. We show that CAMKV is phosphorylated by DYRK3, and that inhibition of DYRK3 kinase activity induces CAMKV aggregation, probably mediated by its highly disordered C-terminal half. Importantly, we provide evidence that the DYRK3/CAMKV signaling module could play an important role for the function of the mitotic spindle during cell division. Our data strongly support the idea that inhibition of DYRK3 and/or CAMKV in neuroblastoma cells could constitute an innovative and highly specific intervention to fight against this dreadful cancer.

Blockade of Discoidin Domain Receptor Signaling with Sitravatinib Reveals DDR2 as a Mediator of Neuroblastoma Pathogenesis and Metastasis.

Oncogene-driven expression and activation of receptor tyrosine kinases (RTK) promotes tumorigenesis and contributes to drug resistance. Increased expression of the kinases DDR2 (Discoid Domain Receptor 2), RET, PDGFRA, KIT, MET, and ALK (Anaplastic Lymphoma Kinase) independently correlate with decreased overall survival (OS) and event free survival (EFS) of pediatric neuroblastoma. The multikinase inhibitor sitravatinib targets DDR2, RET, PDGFRA, KIT and MET with low nanomolar activity and we therefore tested its efficacy against orthotopic and syngeneic tumor models. Sitravatinib markedly reduced cell proliferation and migration in vitro independently of MYCN (N-Myc proto-oncogene), ALK, or MYC (c-Myc proto-oncogene) status, and inhibited proliferation and metastasis of human orthotopic xenografts. Oral administration of sitravatinib to homozygous Th-MYCN transgenic mice (Th-MYCN+/+) after tumor initiation completely arrested further tumor development with no mice dying of disease while maintained on sitravatinib treatment (control cohort 57 days median time to sacrifice). Among these top kinases, DDR2 expression has the strongest correlation with poor survival and high stage at diagnosis, and the highest sensitivity to the drug. We confirmed on-target inhibition of collagen-mediated activation of DDR2. Genetic knockdown of DDR2 partially phenocopies Sitravatinib treatment, limiting tumor development and metastasis across tumor models. Analysis of single cell sequencing data demonstrated that DDR2 is restricted to mesenchymal-type tumor subpopulations and is enriched in Schwann Cell Precursor (SCP) subpopulations found in high-risk disease. These data define an unsuspected role for sitravatinib as a therapeutic agent in neuroblastoma and reveal a novel function for DDR2 as a driver of tumor growth and metastasis.

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

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

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

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

PRMT5 activates AKT via methylation to promote tumor metastasis.

Protein arginine methyltransferase 5 (PRMT5) is the primary methyltransferase generating symmetric-dimethyl-arginine marks on histone and non-histone proteins. PRMT5 dysregulation is implicated in multiple oncogenic processes. Here, we report that PRMT5-mediated methylation of protein kinase B (AKT) is required for its subsequent phosphorylation at Thr308 and Ser473. Moreover, pharmacologic or genetic inhibition of PRMT5 abolishes AKT1 arginine 15 methylation, thereby preventing AKT1 translocation to the plasma membrane and subsequent recruitment of its upstream activating kinases PDK1 and mTOR2. We show that PRMT5/AKT signaling controls the expression of the epithelial-mesenchymal-transition transcription factors ZEB1, SNAIL, and TWIST1. PRMT5 inhibition significantly attenuates primary tumor growth and broadly blocks metastasis in multiple organs in xenograft tumor models of high-risk neuroblastoma. Collectively, our results suggest that PRMT5 inhibition augments anti-AKT or other downstream targeted therapeutics in high-risk metastatic cancers.

Effect of MDM2 and vascular endothelial growth factor inhibition on tumor angiogenesis and metastasis in neuroblastoma.

Neuroblastoma is the most common pediatric abdominal tumor and principally a p53 wild-type, highly vascular, aggressive tumor, with limited response to anti-VEGF therapies alone. MDM2 is a key inhibitor of p53 and a positive activator of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) activity with an important role in neuroblastoma pathogenesis. We hypothesized that concurrent inhibition of both MDM2 and VEGF signaling would have cooperative anti-tumor effects, potentiating anti-angiogenic strategies for neuroblastoma and other p53 wild-type tumors. We orthotopically implanted SH-SY5Y neuroblastoma cells into nude mice (n = 40) and treated as follows: control, bevacizumab, Nutlin-3a, combination of bevacizumab plus Nutlin-3a. Expression of HIF-1α and VEGF were measured by qPCR, Western blot, and ELISA. Tumor apoptosis was measured by immunohistochemistry and caspase assay. Angiogenesis was evaluated by immunohistochemistry for vascular markers (CD-31, type-IV collagen, αSMA). Both angiogenesis and metastatic burden were digitally quantified. In vitro, Nutlin-3a suppresses HIF-1α expression with subsequent downregulation of VEGF. Bevacizumab plus Nutlin-3a leads to significant suppression of tumor growth compared to control (P < 0.01) or either agent alone. Combination treated xenograft tumors display a marked decrease in endothelial cells (P < 0.0001), perivascular basement membrane (P < 0.04), and vascular mural cells (P < 0.004). Nutlin-3a alone and in combination with bevacizumab leads to significant tumor apoptosis (P < 0.0001 for both) and significant decrease in incidence of metastasis (P < 0.05) and metastatic burden (P < 0.03). Bevacizumab plus Nutlin-3a cooperatively inhibits tumor growth and angiogenesis in neuroblastoma in vivo with dramatic effects on tumor vascularity. Concomitantly targeting VEGF and p53 pathways potently suppresses tumor growth, and these results support further clinical development of this approach.

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

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

MYCN-directed centrosome amplification requires MDM2-mediated suppression of p53 activity in neuroblastoma cells.

The MYC family oncogenes cause transformation and tumor progression by corrupting multiple cellular pathways, altering cell cycle progression, apoptosis, and genomic instability. Several recent studies show that MYCC (c-Myc) expression alters DNA repair mechanisms, cell cycle checkpoints, and karyotypic stability, and this is likely partially due to alterations in centrosome replication control. In neuroblastoma cell lines, MYCN (N-Myc) expression induces centrosome amplification in response to ionizing radiation. Centrosomes are cytoplasmic domains that critically regulate cytokinesis, and aberrations in their number or structure are linked to mitotic defects and karyotypic instability. Whereas centrosome replication is linked to p53 and Rb/E2F-mediated cell cycle progression, the mechanisms downstream of MYCN that generate centrosome amplification are incompletely characterized. We hypothesized that MDM2, a direct transcriptional target of MYCN with central inhibitory effects on p53, plays a role in MYC-mediated genomic instability by altering p53 responses to DNA damage, facilitating centrosome amplification. Herein we show that MYCN mediates centrosome amplification in a p53-dependent manner. Accordingly, inhibition of the p53-MDM2 interaction with Nutlin 3A (which activates p53) completely ablates the MYCN-dependent contribution to centrosome amplification after ionizing radiation. We further show that modulating MDM2 expression levels by overexpression or RNA interference-mediated posttranscriptional inhibition dramatically affects centrosome amplification in MYCN-induced cells, indicating that MDM2 is a necessary and sufficient mediator of MYCN-mediated centrosome amplification. Finally, we show a significant correlation between centrosome amplification and MYCN amplification in primary neuroblastoma tumors. These data support the hypothesis that elevated MDM2 levels contribute to MYCN-induced genomic instability through altered regulation of centrosome replication in neuroblastoma.

Correction: MYCN acts as a direct co-regulator of p53 in MYCN amplified neuroblastoma.

[This corrects the article DOI: 10.18632/oncotarget.24859.].

MYCN acts as a direct co-regulator of p53 in MYCN amplified neuroblastoma.

The MYC oncogenes and p53 have opposing yet interrelated roles in normal development and tumorigenesis. How MYCN expression alters the biology and clinical responsiveness of pediatric neuroblastoma remains poorly defined. Neuroblastoma is p53 wild type at diagnosis and repression of p53 signaling is required for tumorigenesis. Here, we tested the hypothesis that MYCN amplification alters p53 transcriptional activity in neuroblastoma. Interestingly, we found that MYCN directly binds to the tetrameric form of p53 at its C-terminal domain, and this interaction is independent of MYCN/MAX heterodimer formation. Chromatin analysis of MYCN and p53 targets reveals dramatic changes in binding, as well as co-localization of the MYCN-p53 complex at p53-REs and E-boxes of genes critical to DNA damage responses and cell cycle progression. RNA sequencing studies show that MYCN-p53 co-localization significantly modulated the expression of p53 target genes. Furthermore, MYCN-p53 interaction leads to regulation of alternative p53 targets not regulated in the presence of low MYCN levels. These novel targets include a number of genes involved in lipid metabolism, DNA repair, and apoptosis. Taken together, our findings demonstrate a novel oncogenic role of MYCN as a transcriptional co-regulator of p53 in high-risk MYCN amplified neuroblastoma. Targeting this novel oncogenic function of MYCN may enhance p53-mediated responses and sensitize MYCN amplified tumors to chemotherapy.

Circulating microRNA biomarkers for metastatic disease in neuroblastoma patients.

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

MDM2 inhibition sensitizes neuroblastoma to chemotherapy-induced apoptotic cell death.

Novel therapeutic approaches are urgently needed for high-stage neuroblastoma, a major therapeutic challenge in pediatric oncology. The majority of neuroblastoma tumors are p53 wild type with intact downstream p53 signaling pathways. We hypothesize that stabilization of p53 would sensitize this aggressive tumor to genotoxic chemotherapy via inhibition of MDM2, the primary negative upstream regulator of p53. We used pharmacologic inhibition of the MDM2-p53 interaction with the small-molecule inhibitor Nutlin and studied the subsequent response to chemotherapy in neuroblastoma cell lines. We did 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and terminal deoxynucleotidyl transferase assays to measure proliferation and apoptosis in several cell lines (IMR32, MYCN3, and JF) treated with combinations of cisplatin, etoposide, and Nutlin. We found consistent and robust decreases in proliferation and increases in apoptosis with the addition of Nutlin 3a to etoposide or cisplatin in all cell lines tested and no response to the inactive Nutlin 3b enantiomer. We also show a rapid and robust accumulation of p53 protein by Western blot in these cells within 1 to 2 hours of treatment. We conclude that MDM2 inhibition dramatically enhances the activity of genotoxic drugs in neuroblastoma and should be considered as an adjuvant to chemotherapy for this aggressive pediatric cancer and for possibly other p53 wild-type solid tumors.

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.

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.