ODC1 is a critical determinant of MYCN oncogenesis and a therapeutic target in neuroblastoma

Neuroblastoma: paradigm for precision medicine

Neuroblastoma (NB) is the third most common pediatric cancer. Although NB accounts for 7% of pediatric malignancies, it is responsible for more than 10% of childhood cancer-related mortality. Prognosis and treatment are determined by clinical and biological risk factors. Estimated 5-year survival rates for patients with non-high-risk and high-risk NB are more than 90% and less than 50%, respectively. Recent clinical trials have continued to reduce therapy for patients with non-high-risk NB, including the most favorable subsets who are often followed with observation approaches. In contrast, high-risk patients are treated aggressively with chemotherapy, radiation, surgery, and myeloablative and immunotherapies.

Polyamine metabolism is sensitive to glycolysis inhibition in human neuroblastoma cells

Polyamines are essential for cell proliferation, and their levels are elevated in many human tumors. The oncogene n-myc is known to potentiate polyamine metabolism. Neuroblastoma, the most frequent extracranial solid tumor in children, harbors the amplification of n-myc oncogene in 25% of the cases, and it is associated with treatment failure and poor prognosis. We evaluated several metabolic features of the human neuroblastoma cell lines Kelly, IMR-32, and SK-N-SH. We further investigated the effects of glycolysis impairment in polyamine metabolism in these cell lines. A previously unknown linkage between glycolysis impairment and polyamine reduction is unveiled. We show that glycolysis inhibition is able to trigger signaling events leading to the reduction of N-Myc protein levels and a subsequent decrease of both ornithine decarboxylase expression and polyamine levels, accompanied by cell cycle blockade preceding cell death. New anti-tumor strategies could take advantage of the direct relationship between glucose deprivation and polyamine metabolism impairment, leading to cell death, and its apparent dependence on n-myc. Combined therapies targeting glucose metabolism and polyamine synthesis could be effective in the treatment of n-myc-expressing tumors.

Expression quantitative trait loci and receptor pharmacology implicate Arg1 and the GABA-A receptor as therapeutic targets in neuroblastoma

The development of targeted therapeutics for neuroblastoma, the third most common tumor in children, has been limited by a poor understanding of growth signaling mechanisms unique to the peripheral nerve precursors from which tumors arise. In this study, we combined genetics with gene-expression analysis in the peripheral sympathetic nervous system to implicate arginase 1 and GABA signaling in tumor formation in vivo. In human neuroblastoma cells, either blockade of ARG1 or benzodiazepine-mediated activation of GABA-A receptors induced apoptosis and inhibited mitogenic signaling through AKT and MAPK. These results suggest that ARG1 and GABA influence both neural development and neuroblastoma and that benzodiazepines in clinical use may have potential applications for neuroblastoma therapy.

MycN promotes TRPM7 expression and cell migration in neuroblastoma through a process that involves polyamines

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MycN expression correlates with TRPM7 expression in neuroblastoma (NB) tumors.

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Expression of the transmembrane protein TRPM7 correlates with lower overall survival in NB tumors.

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MycN promotes TRPM7 mRNA and protein expression and increases TRPM7 channel activity.

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TRPM7 regulates NB cell migration.

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Polyamines regulate TRPM7 expression.

Neuroblastoma is an extra-cranial solid cancer in children. MYCN gene amplification is a prognostic indicator of poor outcome in neuroblastoma. Recent studies have shown that the multiple steps involved in cell migration are dependent on the availability of intracellular calcium (Ca²⁺). Although significant advances have been made in understanding the role of Ca²⁺ during migration, little has been achieved towards understanding its impact on the progression of diseases such as cancer. Interestingly, previous studies showed that cancer cell migration is regulated by TRPM7, a calcium-permeable ion channel. The objective of the current study was to elucidate the mechanism by which MycN promotes NB cell migration and the mechanism regulating TRPM7 expression. The results showed that MycN increased TRPM7 expression, induced TRPM7 channel activity, increased intracellular Ca²⁺ signaling, and promoted cell migration in NB cells. The results also showed that inhibition or down-regulation of ornithine decarboxylase (ODC) inhibited TRPM7 expression, a process that was reversed by spermidine. Overall, this study provides evidence that MycN promotes TRPM7 expression and cell migration through a mechanism that involves ODC synthesis of polyamines.

Deoxyhypusine synthase (DHPS) inhibitor GC7 induces p21/Rb-mediated inhibition of tumor cell growth and DHPS expression correlates with poor prognosis in neuroblastoma patients

PURPOSE

Neuroblastoma (NB) is an aggressive pediatric malignancy that typically occurs in infants and children under the age of 5 years. High-stage tumors relapse frequently even after aggressive multimodal treatment, resulting in therapy resistance and eventually in patient death. Clearly, new biologically-targeted drugs are needed that more efficiently suppress tumor growth and prevent relapse. We and others previously showed that polyamines such as spermidine play an essential role in NB tumorigenesis and that DFMO, an inhibitor of the central polyamine synthesis gene ODC, is effective in vitro and in vivo, prompting its evaluation in NB clinical trials. However, the specific molecular actions of polyamines remain poorly defined. Spermidine and deoxyhypusine synthase (DHPS) are essential components in the hypusination-driven post-translational activation of eukaryotic initiation factor 5A (eIF5A).

METHODS

We assessed the role of DHPS in NB and the impact of its inhibition by N(1)-guanyl-1,7-diaminoheptane (GC7) on tumor cell growth using cell proliferation assays, Western blot, immunofluorescence microscopy, and Affymetrix micro-array mRNA expression analyses in NB tumor samples.

RESULTS

We found that GC7 inhibits NB cell proliferation in a dose-dependent manner, through induction of the cell cycle inhibitor p21 and reduction of total and phosphorylated Rb proteins. Strikingly, high DHPS mRNA expression correlated significantly with unfavorable clinical parameters, including poor patient survival, in a cohort of 88 NB tumors (all P < 0.04).

CONCLUSIONS

These results suggest that spermidine and DHPS are key contributing factors in NB tumor proliferation through regulation of the p21/Rb signaling axis.

An unexpected role for caspase-2 in neuroblastoma

Caspase-2 has been implicated in various cellular functions, including cell death by apoptosis, oxidative stress response, maintenance of genomic stability and tumor suppression. The loss of the caspase-2 gene (Casp2) enhances oncogene-mediated tumorigenesis induced by E1A/Ras in athymic nude mice, and also in the Eμ-Myc lymphoma and MMTV/c-neu mammary tumor mouse models. To further investigate the function of caspase-2 in oncogene-mediated tumorigenesis, we extended our studies in the TH-MYCN transgenic mouse model of neuroblastoma. Surprisingly, we found that loss of caspase-2 delayed tumorigenesis in the TH-MYCN neuroblastoma model. In addition, tumors from TH-MYCN/Casp2^−/− mice were predominantly thoracic paraspinal tumors and were less vascularized compared with tumors from their TH-MYCN/Casp2^+/+ counterparts. We did not detect any differences in the expression of neuroblastoma-associated genes in TH-MYCN/Casp2^−/− tumors, or in the activation of Ras/MAPK signaling pathway that is involved in neuroblastoma progression. Analysis of expression array data from human neuroblastoma samples showed a correlation between low caspase-2 levels and increased survival. However, caspase-2 levels correlated with clinical outcome only in the subset of MYCN-non-amplified human neuroblastoma. These observations indicate that caspase-2 is not a suppressor in MYCN-induced neuroblastoma and suggest a tissue and context-specific role for caspase-2 in tumorigenesis.

Molecular profiling of childhood cancer: Biomarkers and novel therapies

BACKGROUND

Technological advances including high-throughput sequencing have identified numerous tumor-specific genetic changes in pediatric and adolescent cancers that can be exploited as targets for novel therapies.

SCOPE OF REVIEW

This review provides a detailed overview of recent advances in the application of target-specific therapies for childhood cancers, either as single agents or in combination with other therapies. The review summarizes preclinical evidence on which clinical trials are based, early phase clinical trial results, and the incorporation of predictive biomarkers into clinical practice, according to cancer type.

MAJOR CONCLUSIONS

There is growing evidence that molecularly targeted therapies can valuably add to the arsenal available for treating childhood cancers, particularly when used in combination with other therapies. Nonetheless the introduction of molecularly targeted agents into practice remains challenging, due to the use of unselected populations in some clinical trials, inadequate methods to evaluate efficacy, and the need for improved preclinical models to both evaluate dosing and safety of combination therapies.

GENERAL SIGNIFICANCE

The increasing recognition of the heterogeneity of molecular causes of cancer favors the continued development of molecularly targeted agents, and their transfer to pediatric and adolescent populations.

Targeting RNA polymerase I to treat MYC-driven cancer

The MYC oncoprotein and transcription factor is dysregulated in a majority of human cancers and is considered a major driver of the malignant phenotype. As such, developing drugs for effective inhibition of MYC in a manner selective to malignancies is a 'holy grail' of transcription factor-based cancer therapy. Recent advances in elucidating MYC biology in both normal cells and pathological settings were anticipated to bring inhibition of tumorigenic MYC function closer to the clinic. However, while the extensive array of cellular pathways that MYC impacts present numerous fulcrum points on which to leverage MYC's therapeutic potential, identifying the critical target(s) for MYC-specific cancer therapy has been difficult to achieve. Somewhat unexpectedly, MYC's fundamental role in regulating the 'housekeeping' process of ribosome biogenesis, one of the most ubiquitously required and conserved cell functions, may provide the Achilles' heel for therapeutically targeting MYC-driven tumors.

Therapeutic targets for neuroblastomas

INTRODUCTION

Neuroblastoma (NB) is the most common and deadly solid tumor in children. Despite recent improvements, the long-term outlook for high-risk NB is still < 50%. Further, there is considerable short- and long-term toxicity. More effective, less toxic therapy is needed, and the development of targeted therapies offers great promise.

AREAS COVERED

Relevant literature was reviewed to identify current and future therapeutic targets that are critical to malignant transformation and progression of NB. The potential or actual NB therapeutic targets are classified into four categories: i) genes activated by amplification, mutation, translocation or autocrine overexpression; ii) genes inactivated by deletion, mutation or epigenetic silencing; iii) membrane-associated genes expressed on most NBs but few other tissues; or iv) common target genes relevant to NB as well as other tumors.

EXPERT OPINION

Therapeutic approaches have been developed to some of these targets, but many remain untargeted at the present time. It is unlikely that single targeted agents will be sufficient for long-term cure, at least for high-risk NBs. The challenge will be how to integrate targeted agents with each other and with conventional therapy to enhance their efficacy, while simultaneously reducing systemic toxicity.

Quantitative analysis of BTF3, HINT1, NDRG1 and ODC1 protein over-expression in human prostate cancer tissue

Prostate carcinoma is the most common cancer in men with few, quantifiable, biomarkers. Prostate cancer biomarker discovery has been hampered due to subjective analysis of protein expression in tissue sections. An unbiased, quantitative immunohistochemical approach provided here, for the diagnosis and stratification of prostate cancer could overcome this problem. Antibodies against four proteins BTF3, HINT1, NDRG1 and ODC1 were used in a prostate tissue array (> 500 individual tissue cores from 82 patients, 41 case pairs matched with one patient in each pair had biochemical recurrence). Protein expression, quantified in an unbiased manner using an automated analysis protocol in ImageJ software, was increased in malignant vs non-malignant prostate (by 2-2.5 fold, p<0.0001). Operating characteristics indicate sensitivity in the range of 0.68 to 0.74; combination of markers in a logistic regression model demonstrates further improvement in diagnostic power. Triple-labeled immunofluorescence (BTF3, HINT1 and NDRG1) in tissue array showed a significant (p<0.02) change in co-localization coefficients for BTF3 and NDRG1 co-expression in biochemical relapse vs non-relapse cancer epithelium. BTF3, HINT1, NDRG1 and ODC1 could be developed as epithelial specific biomarkers for tissue based diagnosis and stratification of prostate cancer.

Novel interaction of ornithine decarboxylase with sepiapterin reductase regulates neuroblastoma cell proliferation

Ornithine decarboxylase (ODC) is the sentinel enzyme in polyamine biosynthesis. Both ODC and polyamines regulate cell division, proliferation, and apoptosis. Sepiapterin reductase (SPR) catalyzes the last step in the biosynthesis of tetrahydrobiopterin (BH4), an essential cofactor of nitric oxide synthase, and has been implicated in neurological diseases but not yet in cancer. In this study, we present compelling evidence that native ODC and SPR physically interact, and we defined the individual amino acid residues involved in both enzymes using in silico protein-protein docking simulations. The resulting heterocomplex is a surprisingly compact structure, featuring two energetically and structurally equivalent binding modes both in monomer and in dimer conformations. The novel interaction between ODC and SPR proteins was confirmed under physiological conditions by co-immunoprecipitation and co-localization in neuroblastoma (NB) cells. Importantly, we showed that siRNA (small interfering RNA)-mediated knockdown of SPR expression significantly reduced endogenous ODC enzyme activity in NB cells, thus demonstrating the biological relevance of the ODC-SPR interaction. Finally, in a cohort of 88 human NB tumors, we found that high SPR mRNA expression correlated significantly with poor survival prognosis using a Kaplan-Meier analysis (log-rank test, P=5 × 10(-4)), suggesting an oncogenic role for SPR in NB tumorigenesis. In conclusion, we showed that ODC binds SPR and thus propose a new concept in which two well-characterized biochemical pathways converge via the interaction of two enzymes. We identified SPR as a novel regulator of ODC enzyme activity and, based on clinical evidence, present a model in which SPR drives ODC-mediated malignant progression in NB.

Molecular Pathways: Targeting MYC-induced metabolic reprogramming and oncogenic stress in cancer

MYC is a multifunctional transcription factor that is deregulated in many human cancers. MYC impacts a collaborative genetic program that orchestrates cell proliferation, metabolism, and stress responses. Although the progression of MYC-amplified tumors shows robust dependence on MYC activity, directly targeting MYC as a therapeutic method has proven to be technically difficult. Therefore, alternative approaches are currently under development with a focus on interference with MYC-mediated downstream effects. To fuel rapid cell growth, MYC reprograms cancer cell metabolism in a way that is substantially different from normal cells. The MYC-induced metabolic signature is characterized by enhanced glucose and glutamine uptake, increased lactate production, and altered amino acid metabolism. Targeting MYC-reprogrammed cancer cell metabolism is considered to be promising based on multiple preclinical studies. In addition, the increased biosynthetic demand of MYC-driven tumors coupled with limited nutrient access within tumor microenvironments create multiple levels of oncogenic stress, which can also be used as tumor-specific targets for pharmacologic intervention. Presumably, the best therapeutic strategy for treating MYC-amplified tumors is combined targeting of multiple MYC-mediated pathways, especially those involved in regulating cell proliferation, metabolism, and oncogenic stress.

Germline Mutations in Mtap Cooperate with Myc to Accelerate Tumorigenesis in Mice

Objective

The gene encoding the methionine salvage pathway methylthioadenosine phosphorylase (MTAP) is a tumor suppressor gene that is frequently inactivated in a wide variety of human cancers. In this study, we have examined if heterozygosity for a null mutation in Mtap (Mtap^lacZ) could accelerate tumorigenesis development in two different mouse cancer models, Eμ-myc transgenic and Pten^+/−.

Methods

Mtap Eμ-myc and Mtap Pten mice were generated and tumor-free survival was monitored over time. Tumors were also examined for a variety of histological and protein markers. In addition, microarray analysis was performed on the livers of Mtap^lacZ/+ and Mtap^+/+ mice.

Results

Survival in both models was significantly decreased in Mtap^lacZ/+ compared to Mtap^+/+ mice. In Eµ-myc mice, Mtap mutations accelerated the formation of lymphomas from cells in the early pre-B stage, and these tumors tended to be of higher grade and have higher expression levels of ornithine decarboxylase compared to those observed in control Eµ-myc Mtap^+/+ mice. Surprisingly, examination of Mtap status in lymphomas in Eµ-myc Mtap^lacZ/+ and Eµ-myc Mtap^+/+ animals did not reveal significant differences in the frequency of loss of Mtap protein expression, despite having shorter latency times, suggesting that haploinsufficiency of Mtap may be playing a direct role in accelerating tumorigenesis. Consistent with this idea, microarray analysis on liver tissue from age and sex matched Mtap^+/+ and Mtap^lacZ/+ animals found 363 transcripts whose expression changed at least 1.5-fold (P<0.01). Functional categorization of these genes reveals enrichments in several pathways involved in growth control and cancer.

Conclusion

Our findings show that germline inactivation of a single Mtap allele alters gene expression and enhances lymphomagenesis in Eµ-myc mice.

Children's Oncology Group's 2013 blueprint for research: neuroblastoma

Estimated 5-year survival rates for patients with non-high-risk and high-risk neuroblastoma are 90% and 50%, respectively. Recent clinical trials have shown excellent outcomes with reduced therapy for non-high-risk disease. For patients with high-risk neuroblastoma treated with chemoradiotherapy, surgery, and stem cell transplantation, the addition of anti-disialoganglioside (GD2) immunotherapy plus cytokines improves survival. Upcoming trials will study the incorporation of targeted radionuclide therapy prior to myeloablative chemotherapy into high-risk treatment. Phase 2 trials will investigate druggable target(s) including mTOR inhibition and GD2-directed therapy in combination with chemotherapy for patients with recurrent neuroblastoma, and ALK inhibition for those with ALK-aberrant tumors.

Increased polyamines alter chromatin and stabilize autoantigens in autoimmune diseases

Polyamines are small cations with unique combinations of charge and length that give them many putative interactions in cells. Polyamines are essential since they are involved in replication, transcription, translation, and stabilization of macro-molecular complexes. However, polyamine synthesis competes with cellular methylation for S-adenosylmethionine, the methyl donor. Also, polyamine degradation can generate reactive molecules like acrolein. Therefore, polyamine levels are tightly controlled. This control may be compromised in autoimmune diseases since elevated polyamine levels are seen in autoimmune diseases. Here a hypothesis is presented explaining how polyamines can stabilize autoantigens. In addition, the hypothesis explains how polyamines can inappropriately activate enzymes involved in NETosis, a process in which chromatin is modified and extruded from cells as extracellular traps that bind pathogens during an immune response. This polyamine-induced enzymatic activity can lead to an increase in NETosis resulting in release of autoantigenic material and tissue damage.

Changes in MYCN expression in human neuroblastoma cell lines following cisplatin treatment may not be related to MYCN copy numbers

Neuroblastoma is a tumor accounting for approximately 10% of all childhood malignancies and 50% of all childhood cancer-related deaths. MYCN gene copy number variation represents the most important prognostic factor in neuroblastoma. Prognostic significance of MYCN gene expression is more complicated and may depend on other factors such as MYCN gene copy number status. In the present study, we assessed MYCN gene expression using real-time RT-PCR following cisplatin treatment in three human neuroblastoma cell lines (UKF-NB-3, UKF-NB-4 and SK-N-AS) and their cisplatin-resistant counterparts. We also examined MYCN gene status and copy number (gain and amplification) variations using interphase and metaphase fluorescent in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA). Only cisplatin-sensitive UKF-NB-4 cells exhibited decreased MYCN expression following treatment with cisplatin. Other sensitive neuroblastoma cells did not exhibit a change in MYCN expression. In contrast, cisplatin-resistant UKF-NB-4 and SK-N-AS cells exhibited increased MYCN expression irrespective of the number of MYCN copies or concentration of cisplatin in the medium. In MYCN-amplified neuroblastoma cells we did not observe any significant change in the number of MYCN copies after cisplatin treatment, whereas MYCN-non-amplified SK-N-AS cells revealed during cisplatin treatment an increased number of MYCN gene copies caused by 2p gain in the majority of cells by FISH. We postulated that cisplatin treatment does not result directly in altered transcription of MYCN. A functional change in MYCN mRNA levels and increased MYCN expression in cisplatin-resistant neuroblastoma cells do not have a clear relationship to MYCN copy numbers. These findings may further contribute to the understanding of cisplatin chemotherapy in connection with MYCN expression, and the possible copy number variations in MYCN neuroblastoma cells may be of importance since targeting of MYCN is being tested as neuroblastoma therapy.

DFMO/eflornithine inhibits migration and invasion downstream of MYCN and involves p27Kip1 activity in neuroblastoma

Neuroblastoma (NB) is the most common extracranial pediatric tumor. NB patients over 18 months of age at the time of diagnosis are often in the later stages of the disease, present with widespread dissemination, and often possess MYCN tumor gene amplification. MYCN is a transcription factor that regulates the expression of a number of genes including ornithine decarboxylase (ODC), a rate-limiting enzyme in the biosynthesis of polyamines. Inhibiting ODC in NB cells produces many deleterious effects including G₁ cell cycle arrest, inhibition of cell proliferation, and decreased tumor growth, making ODC a promising target for drug interference. DFMO treatment leads to the accumulation of the cyclin-dependent kinase inhibitor p27^Kip1 protein and causes p27^Kip1/Rb-coupled G₁ cell cycle arrest in MYCN-amplified NB tumor cells through a process that involves p27^Kip1 phosphorylation at residues Ser10 and Thr198. While p27^Kip1 is well known for its role as a cyclin-dependent kinase inhibitor, recent studies have revealed a novel function of p27^Kip1 as a regulator of cell migration and invasion. In the present study we found that p27^Kip1 regulates the migration and invasion in NB and that these events are dependent on the state of phosphorylation of p27^Kip1. DFMO treatments induced MYCN protein downregulation and phosphorylation of Akt/PKB (Ser473) and GSK3-β (Ser9), and polyamine supplementation alleviated the DFMO-induced effects. Importantly, we provide strong evidence that p27^Kip1 mRNA correlates with clinical features and the survival probability of NB patients.

Physical interaction between MYCN oncogene and polycomb repressive complex 2 (PRC2) in neuroblastoma: functional and therapeutic implications

CLU (clusterin) is a tumor suppressor gene that we have previously shown to be negatively modulated by the MYCN proto-oncogene, but the mechanism of repression was unclear. Here, we show that MYCN inhibits the expression of CLU by direct interaction with the non-canonical E box sequence CACGCG in the 5'-flanking region. Binding of MYCN to the CLU gene induces bivalent epigenetic marks and recruitment of repressive proteins such as histone deacetylases and Polycomb members. MYCN physically binds in vitro and in vivo to EZH2, a component of the Polycomb repressive complex 2, required to repress CLU. Notably, EZH2 interacts with the Myc box domain 3, a segment of MYC known to be essential for its transforming effects. The expression of CLU can be restored in MYCN-amplified cells by epigenetic drugs with therapeutic results. Importantly, the anticancer effects of the drugs are ablated if CLU expression is blunted by RNA interference. Our study implies that MYC tumorigenesis can be effectively antagonized by epigenetic drugs that interfere with the recruitment of chromatin modifiers at repressive E boxes of tumor suppressor genes such as CLU.

Focal DNA copy number changes in neuroblastoma target MYCN regulated genes

Neuroblastoma is an embryonic tumor arising from immature sympathetic nervous system cells. Recurrent genomic alterations include MYCN and ALK amplification as well as recurrent patterns of gains and losses of whole or large partial chromosome segments. A recent whole genome sequencing effort yielded no frequently recurring mutations in genes other than those affecting ALK. However, the study further stresses the importance of DNA copy number alterations in this disease, in particular for genes implicated in neuritogenesis. Here we provide additional evidence for the importance of focal DNA copy number gains and losses, which are predominantly observed in MYCN amplified tumors. A focal 5 kb gain encompassing the MYCN regulated miR-17∼92 cluster as sole gene was detected in a neuroblastoma cell line and further analyses of the array CGH data set demonstrated enrichment for other MYCN target genes in focal gains and amplifications. Next we applied an integrated genomics analysis to prioritize MYCN down regulated genes mediated by MYCN driven miRNAs within regions of focal heterozygous or homozygous deletion. We identified RGS5, a negative regulator of G-protein signaling implicated in vascular normalization, invasion and metastasis, targeted by a focal homozygous deletion, as a new MYCN target gene, down regulated through MYCN activated miRNAs. In addition, we expand the miR-17∼92 regulatory network controlling TGFß signaling in neuroblastoma with the ring finger protein 11 encoding gene RNF11, which was previously shown to be targeted by the miR-17∼92 member miR-19b. Taken together, our data indicate that focal DNA copy number imbalances in neuroblastoma (1) target genes that are implicated in MYCN signaling, possibly selected to reinforce MYCN oncogene addiction and (2) serve as a resource for identifying new molecular targets for treatment.

Critical roles of Myc-ODC axis in the cellular transformation induced by myeloproliferative neoplasm-associated JAK2 V617F mutant

The acquired mutation (V617F) of Janus kinase 2 (JAK2) is observed in the majority of patients with myeloproliferative neoplasms (MPNs). In the screening of genes whose expression was induced by JAK2 (V617F), we found the significant induction of c-Myc mRNA expression mediated by STAT5 activation. Interestingly, GSK-3β was inactivated in transformed Ba/F3 cells by JAK2 (V617F), and this enhanced the protein expression of c-Myc. The enforced expression of c-Myc accelerated cell proliferation but failed to inhibit apoptotic cell death caused by growth factor deprivation; however, the inhibition of GSK-3β completely inhibited the apoptosis of cells expressing c-Myc. Strikingly, c-Myc T58A mutant exhibited higher proliferative activity in a growth-factor-independent manner; however, this mutant failed to induce apoptosis. In addition, knockdown of c-Myc significantly inhibited the proliferation of transformed cells by JAK2 (V617F), suggesting that c-Myc plays an important role in oncogenic activity of JAK2 (V617F). Furthermore, JAK2 (V617F) induced the expression of a target gene of c-Myc, ornithine decarboxylase (ODC), known as the rate-limiting enzyme in polyamine biosynthesis. An ODC inhibitor, difluoromethylornithine (DFMO), prevented the proliferation of transformed cells by JAK2 (V617F). Importantly, administration of DFMO effectively delayed tumor formation in nude mice inoculated with transformed cells by JAK2 (V617F), resulting in prolonged survival; therefore, ODC expression through c-Myc is a critical step for JAK2 (V617F)-induced transformation and DFMO could be used as effective therapy for MPNs.

Evaluation of clinically translatable MR imaging biomarkers of therapeutic response in the TH-MYCN transgenic mouse model of neuroblastoma

PURPOSE

To evaluate noninvasive and clinically translatable magnetic resonance (MR) imaging biomarkers of therapeutic response in the TH-MYCN transgenic mouse model of aggressive, MYCN-amplified neuroblastoma.

MATERIALS AND METHODS

All experiments were performed in accordance with the local ethical review panel and the UK Home Office Animals Scientific Procedures Act 1986 and with the UK National Cancer Research Institute guidelines for the welfare of animals in cancer research. Multiparametric MR imaging was performed of abdominal tumors found in the TH-MYCN model. T2-weighted MR imaging, quantitation of native relaxation times T1 and T2, the relaxation rate R2*, and dynamic contrast-enhanced MR imaging were used to monitor tumor response to cyclophosphamide (25 mg/kg), the vascular disrupting agent ZD6126 (200 mg/kg), or the antiangiogenic agent cediranib (6 mg/kg, daily). Any significant changes in the measured parameters, and in the magnitude of the changes after treatment between treated and control cohorts, were identified by using Student two-tailed paired and unpaired t test, respectively, with a 5% level of significance.

RESULTS

Treatment with cyclophosphamide or cediranib induced a 54% or 20% reduction in tumor volume at 48 hours, respectively (P < .005 and P < .005, respectively; P < .005 and P < .005 versus control, respectively). Treatment with ZD6126 induced a 45% reduction in mean tumor volume 24 hours after treatment (P < .005; P < .005 versus control). The antitumor activity of cyclophosphamide, cediranib, and ZD6126 was consistently associated with a decrease in tumor T1 (P < .005, P < .005, and P < .005, respectively; P < .005, P < .005, and P < .005 versus control, respectively) and with a correlation between therapy-induced changes in native T1 and changes in tumor volume (r = 0.56; P < .005). Tumor response to cediranib was also associated with a decrease in the dynamic contrast-enhanced MR imaging-derived volume transfer constant (P = .07; P < .05 versus control) and enhancing fraction (P < .05; P < .01 versus control), and an increase in R2* (P < .005; P < .05 versus control).

CONCLUSION

The T1 relaxation time is a robust noninvasive imaging biomarker of response to therapy in tumors in TH-MYCN mice, which emulate high-risk neuroblastoma in children. T1 measurements can be readily implemented on clinical MR systems and should be investigated in translational clinical trials of new targeted therapies for pediatric neuroblastoma.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120128/-/DC1.

Tumor development, growth characteristics and spectrum of genetic aberrations in the TH-MYCN mouse model of neuroblastoma

Background

The TH-MYCN transgenic neuroblastoma model, with targeted MYCN expression to the developing neural crest, has been used to study neuroblastoma development and evaluate novel targeted tumor therapies.

Methods

We followed tumor development in 395 TH-MYCN (129X1/SvJ) mice (125 negative, 206 hemizygous and 64 homozygous mice) by abdominal palpations up to 40 weeks of age. DNA sequencing of MYCN in the original plasmid construct and mouse genomic DNA was done to verify the accuracy. Copy number analysis with Affymetrix® Mouse Diversity Genotyping Arrays was used to characterize acquired genetic aberrations.

Results

DNA sequencing confirmed presence of human MYCN cDNA in genomic TH-MYCN DNA corresponding to the original plasmid construct. Tumor incidence and growth correlated significantly to transgene status with event-free survival for hemizygous mice at 50%, and 0% for homozygous mice. Hemizygous mice developed tumors at 5.6–19 weeks (median 9.1) and homozygous mice at 4.0–6.9 weeks (5.4). The mean treatment window, time from palpable tumor to sacrifice, for hemizygous and homozygous mice was 15 and 5.2 days, respectively. Hemizygous mice developing tumors as early as homozygous mice had a longer treatment window. Age at tumor development did not influence treatment window for hemizygous mice, whereas treatment window in homozygous mice decreased significantly with increasing age. Seven out of 10 analysed tumors had a flat DNA profile with neither segmental nor numerical chromosomal aberrations. Only three tumors from hemizygous mice showed acquired genetic features with one or more numerical aberrations. Of these, one event corresponded to gain on the mouse equivalent of human chromosome 17.

Conclusion

Hemizygous and homozygous TH-MYCN mice have significantly different neuroblastoma incidence, tumor growth characteristics and treatment windows but overlap in age at tumor development making correct early genotyping essential to evaluate therapeutic interventions. Contrasting previous studies, our data show that TH-MYCN tumors have few genetic aberrations.

Integrated genomic analyses identify ARID1A and ARID1B alterations in the childhood cancer neuroblastoma

Neuroblastomas are tumors of peripheral sympathetic neurons and are the most common solid tumor in children. To determine the genetic basis for neuroblastoma we performed whole-genome sequencing (6 cases), exome sequencing (16 cases), genome-wide rearrangement analyses (32 cases), and targeted analyses of specific genomic loci (40 cases) using massively parallel sequencing. On average each tumor had 19 somatic alterations in coding genes (range, 3–70). Among genes not previously known to be involved in neuroblastoma, chromosomal deletions and sequence alterations of chromatin remodeling genes, ARID1A and ARID1B, were identified in 8 of 71 tumors (11%) and were associated with early treatment failure and decreased survival. Using tumor-specific structural alterations, we developed an approach to identify rearranged DNA fragments in sera, providing personalized biomarkers for minimal residual disease detection and monitoring. These results highlight dysregulation of chromatin remodeling in pediatric tumorigenesis and provide new approaches for the management of neuroblastoma patients.

Polyamine pathway inhibition as a novel therapeutic approach to treating neuroblastoma

Polyamines are highly regulated essential cations that are elevated in rapidly proliferating tissues, including diverse cancers. Expression analyses in neuroblastomas suggest that up-regulation of polyamine pro-synthetic enzymes and down-regulation of catabolic enzymes is associated with poor prognosis. Polyamine sufficiency may be required for MYCN oncogenicity in MYCN amplified neuroblastoma, and targeting polyamine homeostasis may therefore provide an attractive therapeutic approach. ODC1, an oncogenic MYCN target, is rate-limiting for polyamine synthesis, and is overexpressed in many cancers including neuroblastoma. Inhibition of ODC1 by difluoromethylornithine (DFMO) decreased tumor penetrance in TH-MYCN mice treated pre-emptively, and extended survival and synergized with chemotherapy in treating established tumors in both TH-MYCN and xenograft models. Efforts to augment DFMO activity, or otherwise maximally reduce polyamine levels, are focused on antagonizing polyamine uptake or augmenting polyamine export or catabolism. Since polyamine inhibition appears to be clinically well tolerated, these approaches, particularly when combined with chemotherapy, have great potential for improving neuroblastoma outcome in both MYCN amplified and non-MYCN amplified neuroblastomas.

Abstract CN04-03: Development of NSAID eflornithine combinations for treating cancer risk factors

Nonsteroidal anti-inflammatory drugs (NSAIDS) have been found to be potent inhibitors of carcinogenesis in both preclinical models and in randomized controlled prospective clinical trials in humans. NSAIDS exert their anti-carcinogenic effects by inhibiting cyclooxygenases (COXs) involved in arachidonic acid metabolism and by COX-independent mechanisms. Empirical data indicates eflornithine (difluoromethylornithine or DFMO), an enzyme-activated inhibitor of ornithine decarboxylase (ODC) (Meyskens and Gerner, 1999), is one of the most potent agents known acting in combination with NSAIDS to inhibit carcinogenesis in rodent models (Steele and Lubet, 2010). At least part of the rationale for combining NSAIDS with eflornithine for inhibition of carcinogenesis is that eflornithine inhibits the activity of ODC, the first enzyme in polyamine synthesis, while NSAIDS activate the spermidine/spermine acetyltransferase (SAT1), which targets polyamines for export by specific solute carrier transporters (Gerner and Meyskens, 2009). Thus, NSAIDS and eflornithine both reduce tissue levels of the growth-associated polyamines, but by complementary mechanisms. A clinical trial of the combination of eflornithine and the NSAID sulindac showed dramatic treatment-associated reductions of metachronous colorectal adenomas in patients with prior sporadic colorectal polyps (Meyskens et al., 2008). Several clinical trials in progress or soon to commence will further test the hypothesis that NSAID eflornithine combinations can successfully treat cancer risk factors in patients with specific cancers, or risk of cancer. One group of clinical trials involves patients with neuroblastoma (NB). Patients with poor prognosis NB often have tumors in which MYCN is overexpressed. Preclinical data indicates that MYCN as well as c-MYC drive expression of ODC and other genes in the polyamine pathway, and that inhibiting this pathway with eflornithine suppressed carcinogenesis in mouse models of NB (Hogarty et al., 2008). Likewise, COX-2 is expressed in NB tumors and cell lines, and COX-2 inhibitors such as celecoxib can suppress the growth of NB xenografts (Ponthan et al., 2007). The Neuroblastoma and Medulloblastoma Translational Research Consortium (NMTRC) and the New Approaches to Neuroblastoma Therapy (NANT) group are conducting clinical trials to evaluate the safety and efficacy of eflornithine alone or in combination with NSAIDS and other agents in patients with high risk NB. The NMTRC is conducting an especially novel prevention trial of eflornithine in patients with high risk NB in remission (NCT01586260). Eflornithine NSAID combinations are also being evaluated in other MYC-associated diseases. Familial adenomatous polyposis (FAP) is a genetic syndrome associated with increased risk of colon cancer and other neoplasia and is caused by mutation/deletions in the adenomatous polyposis coli (APC) tumor suppressor gene. MYC mediates intestinal tumorigenesis (Ignatenko et al., 2006) and combinations of eflornithine and NSAIDS are potent inhibitors of intestinal carcinogenesis (Ignatenko et al., 2008) in murine models of FAP. Notable is the change in clinical management of FAP patients over the past two decades. FAP is now managed primarily by surgery, with duodenal polyposis and desmoid disease constituting two current significant clinical problems. An international consortium will be evaluating the combination of eflornithine and sulindac in adult patients with FAP, using time to FAP-related events as the primary outcome (NCT01483144). This same combination will be evaluated in patients with prior sporadic colon cancer in a study to be conducted by a national cooperative group (S0820, Adenoma and second primary prevention trial, NCT01349881) (Rial et al., 2012). These and other trials have been designed to include assessment of a range of biological correlates, including genetic (Zell et al., 2010), tissue (Thompson et al., 2010) and urinary markers (Hiramatsu et al., 2005) of disease prognosis and prediction of treatment responses, including therapy-associated toxicities.

Citation Format: Eugene W. Gerner. Development of NSAID eflornithine combinations for treating cancer risk factors. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr CN04-03.

Targeting ALK in neuroblastoma--preclinical and clinical advancements

Despite improvements in cancer therapies in the past 50 years, neuroblastoma remains a devastating clinical problem and a leading cause of childhood cancer deaths. Advances in treatments for children with high-risk neuroblastoma have, until recently, involved addition of cytotoxic therapy to dose-intensive regimens. In this era of targeted therapies, substantial efforts have been made to identify optimal targets for different types of cancer. The discovery of hereditary and somatic activating mutations in the oncogene ALK has now placed neuroblastoma among other cancers, such as melanoma and non-small-cell lung cancer (NSCLC), which benefit from therapies with oncogene-specific small-molecule tyrosine kinase inhibitors. Crizotinib, a small-molecule inhibitor of ALK, has transformed the landscape for the treatment of NSCLC harbouring ALK translocations and has demonstrated activity in preclinical models of ALK-driven neuroblastomas. However, inhibition of mutated ALK is complex when compared with translocated ALK and remains a therapeutic challenge. This Review discusses the biology of ALK in the development of neuroblastoma, preclinical and clinical progress with the use of ALK inhibitors and immunotherapy, challenges associated with resistance to such therapies and the steps being taken to overcome some of these hurdles.

Mouse genetics suggests cell-context dependency for Myc-regulated metabolic enzymes during tumorigenesis

c-Myc (hereafter called Myc) belongs to a family of transcription factors that regulates cell growth, cell proliferation, and differentiation. Myc initiates the transcription of a large cast of genes involved in cell growth by stimulating metabolism and protein synthesis. Some of these, like those involved in glycolysis, may be part of the Warburg effect, which is defined as increased glucose uptake and lactate production in the presence of adequate oxygen supply. In this study, we have taken a mouse-genetics approach to challenge the role of select Myc-regulated metabolic enzymes in tumorigenesis in vivo. By breeding λ-Myc transgenic mice, Apc(Min) mice, and p53 knockout mice with mouse models carrying inactivating alleles of Lactate dehydrogenase A (Ldha), 3-Phosphoglycerate dehydrogenase (Phgdh) and Serine hydroxymethyltransferase 1 (Shmt1), we obtained offspring that were monitored for tumor development. Very surprisingly, we found that these genes are dispensable for tumorigenesis in these genetic settings. However, experiments in fibroblasts and colon carcinoma cells expressing oncogenic Ras show that these cells are sensitive to Ldha knockdown. Our genetic models reveal cell context dependency and a remarkable ability of tumor cells to adapt to alterations in critical metabolic pathways. Thus, to achieve clinical success, it will be of importance to correctly stratify patients and to find synthetic lethal combinations of inhibitors targeting metabolic enzymes.

Genetically engineered murine models--contribution to our understanding of the genetics, molecular pathology and therapeutic targeting of neuroblastoma

Genetically engineered mouse models (GEMM) have made major contributions to a molecular understanding of several adult cancers and these results are increasingly being translated into the pre-clinical setting where GEMM will very likely make a major impact on the development of targeted therapeutics in the near future. The relationship of pediatric cancers to altered developmental programs, and their genetic simplicity relative to adult cancers provides unique opportunities for the application of new advances in GEMM technology. In neuroblastoma the well-characterized TH-MYCN GEMM is increasingly used for a variety of molecular-genetic, developmental and pre-clinical therapeutics applications. We discuss: the present and historical application of GEMM to neuroblastoma research, future opportunities, and relevant targets suitable for new GEMM strategies in neuroblastoma. We review the potential of these models to contribute both to an understanding of the developmental nature of neuroblastoma and to improved therapy for this disease.

Evidence of a role for antizyme and antizyme inhibitor as regulators of human cancer

Antizyme and its endogenous antizyme inhibitor have recently emerged as prominent regulators of cell growth, transformation, centrosome duplication, and tumorigenesis. Antizyme was originally isolated as a negative modulator of the enzyme ornithine decarboxylase (ODC), an essential component of the polyamine biosynthetic pathway. Antizyme binds ODC and facilitates proteasomal ODC degradation. Antizyme also facilitates degradation of a set of cell cycle regulatory proteins, including cyclin D1, Smad1, and Aurora A kinase, as well as Mps1, a protein that regulates centrosome duplication. Antizyme has been reported to function as a tumor suppressor and to negatively regulate tumor cell proliferation and transformation. Antizyme inhibitor binds to antizyme and suppresses its known functions, leading to increased polyamine synthesis, increased cell proliferation, and increased transformation and tumorigenesis. Gene array studies show antizyme inhibitor to be amplified in cancers of the ovary, breast, and prostate. In this review, we summarize the current literature on the role of antizyme and antizyme inhibitor in cancer, discuss how the ratio of antizyme to antizyme inhibitor can influence tumor growth, and suggest strategies to target this axis for tumor prevention and treatment.

Regulatory cross-talk of mouse liver polyamine and methionine metabolic pathways: a systemic approach to its physiopathological consequences

Both polyamines and methionine derivatives are nitrogen compounds directly related to the regulation of gene expression. In silico predictions and experimental evidence suggest a cross-talk between polyamine and methionine metabolism in mammalian tissues. Since liver is the major organ that controls nitrogen metabolism of the whole organism, it is the best tissue to further test this hypothesis in vivo. In this work, we studied the effects of the chronic administration of a methionine-supplemented diet (0.5% Met in drinking water for 5 months) on the liver of mice (designated as MET-mice). Metabolic and proteomic approaches were performed and the data obtained were subjected to biocomputational analysis. Results showed that a supplemental methionine intake can indeed regulate biogenic amine metabolism in an in vivo model by multiple mechanisms including metabolic regulation and specific gene demethylation. Furthermore, putative systemic effects were investigated by molecular and cellular biology methods. Among other results, altered expression levels of multiple inflammation and cell proliferation/death balance markers were found and macrophage activation was observed. Overall, the results presented here will be of interest across a variety of biomedical disciplines, including nutrition, orphan diseases, immunology and oncology.

Neuroblastoma genetics and phenotype: a tale of heterogeneity

Cancer is a complex disease driven by multiple genetic and epigenetic alterations. Understanding the (epi-)genetic changes and consequent deregulation of regulatory networks controlling the various normal critical cellular phenotypes that are perturbed in cancer cells can provide clues to new therapeutic opportunities. Moreover, such insights into the molecular pathology of a given cancer type can offer clinical relevant genetic markers or molecular signatures for assessment of prognosis and response to therapy, and prediction of risk for relapse. Therefore, as for many other tumour entities, neuroblastoma (NB) has been the subject of intensive ongoing genomic research. Here we will summarize the current state-of-the-art of these studies with focus on genome wide DNA copy number and gene expression analyses in relation to the relevance for present and future clinical management of NB patients.

Initial testing (stage 1) of the polyamine analog PG11047 by the pediatric preclinical testing program

BACKGROUND

PG11047 is a novel conformationally restricted analog of the natural polyamine, spermine that lowers cellular endogenous polyamine levels and competitively inhibits natural polyamine functions leading to cancer cell growth inhibition. The activity of PG11047 was evaluated against the PPTP's in vitro and in vivo panels.

PROCEDURES

PG11047 was evaluated against the PPTP in vitro panel using 96 hr exposure at concentrations ranging from 10 nM to 100 µM. It was tested against the PPTP in vivo panels at a dose of 100 mg/kg administered by the intraperitoneal route weekly for 6 weeks.

RESULTS

In vitro PG11047 demonstrated a concentration-response pattern consistent with cytostatic activity. The median EC(50) for PG11047 was 71 nM. Cell lines of the Ewing sarcoma panel had a lower median EC(50) value compared to the remaining cell lines in the panel, while cell lines of the neuroblastoma panel had a higher median EC(50) value. In vivo PG11047 induced significant differences in EFS distribution compared to control in 5 of 32 (15.6%) of the evaluable solid tumor xenografts and in 0 of 7 (0%) of the evaluable ALL xenografts. The single case of tumor regression occurred in an ependymoma xenograft.

CONCLUSIONS

Further pediatric development of PG11047 will require better defining a target population and identifying combinations for which there is a tumor-selective cytotoxic effect. The regression observed for an ependymoma xenograft and the exquisite sensitivity of some Ewing sarcoma cell lines to the antiproliferative effects of PG11047 provide leads for further preclinical investigations.

Identification of novel prognostic markers in relapsing localized resectable neuroblastoma

Patients with localized resectable neuroblastoma (NB) generally have an excellent prognosis and can be treated by surgery alone, but approximately 10% of them develop local recurrences or metastatic progression. The known predictive risk factors are important for the identification of localized resectable NB patients at risk of relapse and/or progression, who may benefit from early and aggressive treatment. These factors, however, identify only a subset of patients at risk, and the search for novel prognostic markers is warranted. This review focuses on the recent advances in the identification of new prognostic markers. Recently we addressed the search of novel genetic prognostic markers in a selected cohort of patients with stroma-poor localized resectable NB who underwent disease relapse or progression (group 1) or complete remission (group 2). High-resolution array-comparative genomic hybridization (CGH) DNA copy-number analysis technology was used. Chromosome 1p36.22p36.32 loss and 1q22qter gain, detected almost exclusively in group 1 patients, were significantly associated with poor event-free survival (EFS). Increasing evidence points to anaplastic lymphoma kinase (ALK) as a fundamental oncogene associated with NB. The immunohistochemical analysis of sporadic NB localized resectable primary tumors (stage 1-2) showed a correlation between aberrant ALK level of expression and tumor progression and clinical outcome. Moreover, other factors that might influence the clinical behavior of these tumors will be reviewed.

Do pharmacokinetic polymorphisms explain treatment failure in high-risk patients with neuroblastoma?

PURPOSE

Neuroblastoma is the most common extracranial solid tumour in childhood. It accounts for 15% of all paediatric oncology deaths. In the last few decades, improvement in treatment outcome for high-risk patients has not occurred, with an overall survival rate <30-40%. Many reasons may account for such a low survival rate. The aim of this review is to evaluate whether pharmacogenetic factors can explain treatment failure in neuroblastoma.

METHODS

A literature search based on PubMed's database Medical Subject Headings (MeSH) was performed to retrieve all pertinent publications on current treatment options and new classes of drugs under investigation. One hundred and fifty-eight articles wer reviewed, and relevant data were extracted and summarised.

RESULTS AND CONCLUSIONS

Few of the large number of polymorphisms identified thus far showed an effect on pharmacokinetics that could be considered clinically relevant. Despite their clinical relevance, none of the single nucleotide polymorphisms (SNPs) investigated can explain treatment failure. These findings seem to reflect the clinical context in which anti-tumour drugs are used, i.e. in combination with multimodal therapy. In addition, many pharmacogenetic studies did not assess (differences in) drug exposure, which could contribute to explaining pharmacogenetic associations. Furthermore, it remains unclear whether the significant activity of new drugs on different neuroblastoma cell lines translates into clinical efficacy, irrespective of resistance or myelocytomatosis viral related oncogene, neuroblastoma derived (MYCN) amplification. Elucidation of the clinical role of pharmacogenetic factors in the treatment of neuroblastoma demands an integrated pharmacokinetic-pharmacodynamic approach to the analysis of treatment response data.

miR-380-5p represses p53 to control cellular survival and is associated with poor outcome in MYCN-amplified neuroblastoma

Inactivation of the p53 tumor suppressor pathway allows cell survival in times of stress and occurs in many human cancers; however, normal embryonic stem cells and some cancers such as neuroblastoma maintain wild-type human TP53 and mouse Trp53 (referred to collectively as p53 herein). Here we describe a miRNA, miR-380-5p, that represses p53 expression via a conserved sequence in the p53 3' untranslated region (UTR). miR-380-5p is highly expressed in mouse embryonic stem cells and neuroblastomas, and high expression correlates with poor outcome in neuroblastomas with neuroblastoma derived v-myc myelocytomatosis viral-related oncogene (MYCN) amplification. miR-380 overexpression cooperates with activated HRAS oncoprotein to transform primary cells, block oncogene-induced senescence and form tumors in mice. Conversely, inhibition of endogenous miR-380-5p in embryonic stem or neuroblastoma cells results in induction of p53, and extensive apoptotic cell death. In vivo delivery of a miR-380-5p antagonist decreases tumor size in an orthotopic mouse model of neuroblastoma. We demonstrate a new mechanism of p53 regulation in cancer and stem cells and uncover a potential therapeutic target for neuroblastoma.

Pleiotropic role for MYCN in medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Sonic Hedgehog (SHH) signaling drives a minority of MB, correlating with desmoplastic pathology and favorable outcome. The majority, however, arises independently of SHH and displays classic or large cell anaplastic (LCA) pathology and poor prognosis. To identify common signaling abnormalities, we profiled mRNA, demonstrating misexpression of MYCN in the majority of human MB and negligible expression in normal cerebella. We clarified a role in pathogenesis by targeting MYCN (and luciferase) to cerebella of transgenic mice. MYCN-driven MB showed either classic or LCA pathologies, with Shh signaling activated in approximately 5% of tumors, demonstrating that MYCN can drive MB independently of Shh. MB arose at high penetrance, consistent with a role for MYCN in initiation. Tumor burden correlated with bioluminescence, with rare metastatic spread to the leptomeninges, suggesting roles for MYCN in both progression and metastasis. Transient pharmacological down-regulation of MYCN led to both clearance and senescence of tumor cells, and improved survival. Targeted expression of MYCN thus contributes to initiation, progression, and maintenance of MB, suggesting a central role for MYCN in pathogenesis.

MYC in oncogenesis and as a target for cancer therapies

MYC proteins (c-MYC, MYCN, and MYCL) regulate processes involved in many if not all aspects of cell fate. Therefore, it is not surprising that the MYC genes are deregulated in several human neoplasias as a result from genetic and epigenetic alterations. The near "omnipotency" together with the many levels of regulation makes MYC an attractive target for tumor intervention therapy. Here, we summarize some of the current understanding of MYC function and provide an overview of different cancer forms with MYC deregulation. We also describe available treatments and highlight novel approaches in the pursuit for MYC-targeting therapies. These efforts, at different stages of development, constitute a promising platform for novel, more specific treatments with fewer side effects. If successful a MYC-targeting therapy has the potential for tailored treatment of a large number of different tumors.

The polyamine metabolism genes ornithine decarboxylase and antizyme 2 predict aggressive behavior in neuroblastomas with and without MYCN amplification

High polyamine (PA) levels and ornithine decarboxylase (ODC) overexpression are well-known phenomena in many aggressive cancer types. We analyzed the expression of ODC and ODC-activity regulating genes antizymes 1-3 (OAZ1-3) and antizyme inhibitors 1-2 (AZ-IN1-2) in human neuroblastoma (NB) tumors and correlated these with genetic and clinical features of NB. Since ODC is a known target gene of MYCN, the correlation between ODC and MYCN was of special interest. Data were obtained from Affymetrix micro-array analysis of 88 NB tumor samples. In addition, mRNA expression levels of ODC, OAZ2 and MYCN in a MYCN-inducible NB cell line were determined by quantitative real-time reverse-transcriptase polymerase chain reaction (RT-PCR). ODC mRNA expression in NB tumors was significantly predictive of decreased overall survival probability and correlated with several unfavorable clinical NB characteristics (all p < 0.005). Interestingly, high ODC mRNA expression also showed significant correlation with poor survival prognosis in Kaplan-Meier analyses stratified for patients without MYCN amplification, suggesting an additional role for ODC independent of MYCN. Conversely, high OAZ2 mRNA expression correlated with increased survival and with several favorable clinical NB characteristics (all p < 0.003). In addition, we provide first evidence of a role for MYCN-associated transcription factors MAD2 and MAD7 in ODC regulation. In NB cell cultures, ectopic overexpression of MYCN altered ODC but not OAZ2 mRNA levels. In conclusion, these data suggest that elevated ODC and low OAZ2 mRNA expression levels correlate with several unfavorable genetic and clinical features in NB, offering new insights into PA pathways and PA metabolism-targeting therapy in NB.

MYCN oncoprotein targets and their therapeutic potential

The MYCN oncogene encodes a transcription factor which is amplified in up to 40% of high risk neuroblastomas. MYCN amplification is a well-established poor prognostic marker in neuroblastoma, however the role of MYCN expression and the mechanisms by which it acts to promote an aggressive phenotype remain largely unknown. This review discusses the current evidence identifying the direct and indirect downstream transcriptional targets of MYCN from recent studies, with particular reference to how MYCN affects the cell cycle, DNA damage response, differentiation and apoptosis in neuroblastoma.

Chemoprevention of B-cell lymphomas by inhibition of the Myc target spermidine synthase

The oncogenic transcription factor c-Myc (Myc) is frequently overexpressed in human cancers. Myc is known to induce or repress a large set of genes involved in cell growth and proliferation, explaining the selection for mutations in cancer that deregulate Myc expression. Inhibition of ornithine decarboxylase, an enzyme of the polyamine biosynthetic pathway and a Myc target, has been shown to be chemopreventive. In the present study, we have dissected the role of another enzyme in the polyamine biosynthetic pathway, spermidine synthase (Srm), in Myc-induced cancer. We find that Srm is encoded by a Myc target gene containing perfect E-boxes and that it is induced by Myc in a direct manner. RNA interference against Srm shows that it is important for Myc-induced proliferation of mouse fibroblasts but to a lesser extent for transformation. Using the compound trans-4-methylcyclohexylamine, we show that Srm inhibition can delay the onset of B-cell lymphoma development in lambda-Myc transgenic mice. We therefore suggest that inhibition of Srm is an additional chemopreventive strategy that warrants further consideration.

Spermine synthase

Spermine is present in many organisms including animals, plants, some fungi, some archaea, and some bacteria. It is synthesized by spermine synthase, a highly specific aminopropyltransferase. This review describes spermine synthase structure, genetics, and function. Structural and biochemical studies reveal that human spermine synthase is an obligate dimer. Each monomer contains a C-terminal domain where the active site is located, a central linking domain that also forms the lid of the catalytic domain, and an N-terminal domain that is structurally very similar to S-adenosylmethionine decarboxylase. Gyro mice, which have an X-chromosomal deletion including the spermine synthase (SMS) gene, lack all spermine and have a greatly reduced size, sterility, deafness, neurological abnormalities, and a tendency to sudden death. Mutations in the human SMS lead to a rise in spermidine and reduction of spermine causing Snyder-Robinson syndrome, an X-linked recessive condition characterized by mental retardation, skeletal defects, hypotonia, and movement disorders.

Regulation of cellular polyamine levels and cellular proliferation by antizyme and antizyme inhibitor

Polyamines are small aliphatic polycations present in all living cells. Polyamines are essential for cellular viability and are involved in regulating fundamental cellular processes, most notably cellular growth and proliferation. Being such central regulators of fundamental cellular functions, the intracellular polyamine concentration is tightly regulated at the levels of synthesis, uptake, excretion and catabolism. ODC (ornithine decarboxylase) is the first key enzyme in the polyamine biosynthesis pathway. ODC is characterized by an extremely rapid intracellular turnover rate, a trait that is central to the regulation of cellular polyamine homoeostasis. The degradation rate of ODC is regulated by its end-products, the polyamines, via a unique autoregulatory circuit. At the centre of this circuit is a small protein called Az (antizyme), whose synthesis is stimulated by polyamines. Az inactivates ODC and targets it to ubiquitin-independent degradation by the 26S proteasome. In addition, Az inhibits uptake of polyamines. Az itself is regulated by another ODC-related protein termed AzI (antizyme inhibitor). AzI is highly homologous with ODC, but it lacks ornithine-decarboxylating activity. Its ability to serve as a regulator is based on its high affinity to Az, which is greater than the affinity Az has to ODC. As a result, it interferes with the binding of Az to ODC, thus rescuing ODC from degradation and permitting uptake of polyamines.

Pathophysiology of cell phone radiation: oxidative stress and carcinogenesis with focus on male reproductive system

Hazardous health effects stemming from exposure to radiofrequency electromagnetic waves (RF-EMW) emitted from cell phones have been reported in the literature. However, the cellular target of RF-EMW is still controversial. This review identifies the plasma membrane as a target of RF-EMW. In addition, the effects of RF-EMW on plasma membrane structures (i.e. NADH oxidase, phosphatidylserine, ornithine decarboxylase) and voltage-gated calcium channels are discussed. We explore the disturbance in reactive oxygen species (ROS) metabolism caused by RF-EMW and delineate NADH oxidase mediated ROS formation as playing a central role in oxidative stress (OS) due to cell phone radiation (with a focus on the male reproductive system). This review also addresses: 1) the controversial effects of RF-EMW on mammalian cells and sperm DNA as well as its effect on apoptosis, 2) epidemiological, in vivo animal and in vitro studies on the effect of RF-EMW on male reproductive system, and 3) finally, exposure assessment and dosimetry by computational biomodeling.