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 promotes tumorigenesis and contributes to drug resistance. Increased expression of the kinases discoidin domain receptor 2 (DDR2), RET Proto-Oncogene (RET), Platelet Derived Growth Factor Receptor Alpha (PDGFRA), KIT Proto-Oncogene (KIT), MET Proto-Oncogene (MET), and anaplastic lymphoma kinase (ALK) independently correlate with decreased overall survival and event free survival 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 N-Myc proto-oncogene (MYCN), ALK, or 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 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.

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.

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.

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.

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

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

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.

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.

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

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

Minichromosome maintenance protein MCM7 is a direct target of the MYCN transcription factor in neuroblastoma.

The MYCN oncogene is amplified in approximately 25% of neuroblastoma tumors and is the most significant negative prognostic factor. The direct transcriptional targets of MYCN in MYCN-amplified tumors have not been defined. Microarray analysis of RNA from neuroblastoma primary cell cultures revealed 10-fold higher MCM7 expression in MYCN-amplified versus nonamplified tumors. MCM7 is an essential component of DNA replication licensing factor, a hexameric protein complex that regulates DNA synthesis during the cell cycle, preventing rereplication and ensuring maintenance of DNA euploidy. Additional experiments demonstrated markedly increased expression of MCM7 RNA and protein in MYCN-amplified neuroblastoma tumors and cell lines. Induction of MYCN in conditional cell lines results in increased expression of endogenous MCM7 mRNA and a 3-fold increase in protein levels. In addition, luciferase activity from MCM7 promoter/luciferase gene reporter constructs was significantly increased under MYCN-induced conditions. Specific electrophoretic mobility shifts of MCM7 promoter sequences are detected in extracts of MYCN-amplified cells. These findings demonstrate that in neuroblastoma, the MYCN oncogene directly activates genes required for DNA replication, and this may contribute to neoplastic transformation of these MYCN-amplified tumors.

Anti-gene peptide nucleic acid specifically inhibits MYCN expression in human neuroblastoma cells leading to cell growth inhibition and apoptosis.

We developed an anti-gene peptide nucleic acid (PNA) for selective inhibition of MYCN transcription in neuroblastoma cells, targeted against a unique sequence in the antisense DNA strand of exon 2 of MYCN and linked at its NH(2) terminus to a nuclear localization signal peptide. Fluorescence microscopy showed specific nuclear delivery of the PNA in six human neuroblastoma cell lines: GI-LI-N and IMR-32 (MYCN-amplified/overexpressed); SJ-N-KP and NB-100 (MYCN-unamplified/low-expressed); and GI-CA-N and GI-ME-N (MYCN-unamplified/unexpressed). Antiproliferative effects were observable at 24 hours (GI-LI-N, 60%; IMR-32, 70%) and peaked at 72 hours (GI-LI-N, 80%; IMR-32, 90%; SK-N-KP, 60%; NB-100, 50%); no reduction was recorded for GI-CA-N and GI-ME-N (controls). In MYCN-amplified/overexpressed IMR-32 cells and MYCN-unamplified/low-expressed SJ-N-KP cells, inhibition was recorded of MYCN mRNA (by real-time PCR) and N-Myc (Western blotting); these inhibitory effects increased over 3 days after single treatment in IMR-32. Anti-gene PNA induced G(1)-phase accumulation (39-53%) in IMR-32 and apoptosis (56% annexin V-positive cells at 24 hours in IMR-32 and 22% annexin V-positive cells at 48 hours in SJ-N-KP). Selective activity of the PNA was shown by altering three point mutations, and by the observation that an anti-gene PNA targeted against the noncoding DNA strand did not exert any effect. These findings could encourage research into development of an anti-gene PNA-based tumor-specific agent for neuroblastoma (and other neoplasms) with MYCN expression.

Transmembrane adaptor protein PAG1 is a novel tumor suppressor in neuroblastoma.

Neuroblastoma (NB) is the most common extracranial pediatric solid tumor with high mortality rates. The tyrosine kinase c-Src has been known to play an important role in differentiation of NB cells, but the mechanism of c-Src regulation has not been defined. Here, we characterize PAG1 (Cbp, Csk binding protein), a central inhibitor of c-Src and other Src family kinases, as a novel tumor suppressor in NB. Clinical cohort analysis demonstrate that low expression of PAG1 is a significant prognostic factor for high stage disease, increased relapse, and worse overall survival for children with NB. PAG1 knockdown in NB cells promotes proliferation and anchorage-independent colony formation with increased activation of AKT and ERK downstream of c-Src, while PAG1 overexpression significantly rescues these effects. In vivo, PAG1 overexpression significantly inhibits NB tumorigenicity in an orthotopic xenograft model. Our results establish PAG1 as a potent tumor suppressor in NB by inhibiting c-Src and downstream effector pathways. Thus, reactivation of PAG1 and inhibition of c-Src kinase activity represents an important novel therapeutic approach for high-risk NB.

MDM2 as MYCN transcriptional target: implications for neuroblastoma pathogenesis.

MYCN amplification is associated with an exceptionally poor prognosis in neuroblastoma. Furthermore, the crucial effectors of MYCN responsible for this aggressive subset of neuroblastoma await characterization. A critical negative regulator of the p53 tumor suppressor, MDM2, has been recently characterized in neuroblastoma cell lines as a transcriptional target of MYCN. Targeted inhibition of MYCN results in reduced MDM2 expression levels, with concomitant stabilization of p53 and stimulation of apoptosis in MYCN amplified neuroblastoma cell lines. These data suggest the possibility that MYCN-driven expression of MDM2 might play a role in counterbalancing the p53-dependent apoptotic pathways concurrently stimulated by over expression of MYC proteins. Mouse models of lymphoma have demonstrated that MDM2 expression, with decreased p53 activity, is critical for complete MYCC driven tumorigenesis. Our data suggest that a similar situation may apply for MYCN in neuroblastoma. Strategies for pharmacologic and genetic inhibition of MDM2 may prove to be an important new therapeutic approach 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.

WIP1 phosphatase as a potential therapeutic target in neuroblastoma.

The wild-type p53-induced phosphatase 1 (WIP1) is a serine/threonine phosphatase that negatively regulates multiple proteins involved in DNA damage response including p53, CHK2, Histone H2AX, and ATM, and it has been shown to be overexpressed or amplified in human cancers including breast and ovarian cancers. We examined WIP1 mRNA levels across multiple tumor types and found the highest levels in breast cancer, leukemia, medulloblastoma and neuroblastoma. Neuroblastoma is an exclusively TP53 wild type tumor at diagnosis and inhibition of p53 is required for tumorigenesis. Neuroblastomas in particular have previously been shown to have 17q amplification, harboring the WIP1 (PPM1D) gene and associated with poor clinical outcome. We therefore sought to determine whether inhibiting WIP1 with a selective antagonist, GSK2830371, can attenuate neuroblastoma cell growth through reactivation of p53 mediated tumor suppression. Neuroblastoma cell lines with wild-type TP53 alleles were highly sensitive to GSK2830371 treatment, while cell lines with mutant TP53 were resistant to GSK2830371. The majority of tested neuroblastoma cell lines with copy number gains of the PPM1D locus were also TP53 wild-type and sensitive to GSK2830371A; in contrast cell lines with no copy gain of PPM1D were mixed in their sensitivity to WIP1 inhibition, with the primary determinant being TP53 mutational status. Since WIP1 is involved in the cellular response to DNA damage and drugs used in neuroblastoma treatment induce apoptosis through DNA damage, we sought to determine whether GSK2830371 could act synergistically with standard of care chemotherapeutics. Treatment of wild-type TP53 neuroblastoma cell lines with both GSK2830371 and either doxorubicin or carboplatin resulted in enhanced cell death, mediated through caspase 3/7 induction, as compared to either agent alone. Our data suggests that WIP1 inhibition represents a novel therapeutic approach to neuroblastoma that could be integrated with current chemotherapeutic approaches.