The MYCN oncoprotein as a drug development target

Study on the role of MYCN in retinoblastoma by inhibiting p53 and activating wnt/βcatenin/Fra-1 signaling pathway by reducing DKK3

Retinoblastoma (RB) is a pediatric malignancy, typically diagnosed at birth or during early childhood. The pathogenesis of RB is marked by the amplification of the Basic Helix-Loop-Helix (BHLH) Transcription Factor MYCN, which serves as a transcriptional regulator capable of binding to Dickkopf 3 (DKK3). However, the precise role of DKK3 in the malignant progression of RB cells caused by MYCN remains elusive. In the present study, the expression of MYCN was either overexpressed or interfered in RB cells. Subsequently, the expression level of DKK3 was assessed through quantitative real-time polymerase chain reaction and western blot analysis. Cell proliferation was evaluated using the Cell Counting Kit-8 assay and 5-ethynyl-2'-deoxyuridine staining, while cell cycle progression and apoptosis were analyzed by flow cytometry and western blot analysis, respectively. Additionally, the expression of proteins involved in the Wnt/β-catenin/Fra-1/p53 signaling pathway was evaluated via western blot analysis. To gain further insights, Wnt agonists and the P53 inhibitor PFT-α were introduced into exploration. The current investigation revealed a negative correlation between the expression levels of MYCN and DKK3 in RB cells. Additionally, DKK3 overexpression inhibited cell proliferation, promoted cell apoptosis, and arrested cell cycle in RB cells with high expression of MYCN. Moreover, enhanced DKK3 expression inhibited proliferation, promoted cell cycle arrest and apoptosis of RB cells by modulating the wnt/βcatenin/Fra-1/p53 signaling pathway. Furthermore, in vivo experiments revealed that overexpression of DKK3 inhibits the growth of RB tumors. Collectively, our findings elucidate that MYCN stimulates the Wnt/β-catenin/Fra-1 pathway by suppressing DKK3 expression, ultimately suppressing p53 activity and contributing to malignant progression of RB.

Comprehensive exploration of the involvement of cuproptosis in tumorigenesis and progression of neuroblastoma

BACKGROUND

Copper-induced cell death, or "cuproptosis," as an apoptotic process, has recently received much attention in human diseases. Recent studies on cuproptosis have provided novel insights into the pathogenesis of various diseases, especially cancers. However, the association between neuroblastoma (NB) and cuproptosis in terms of their clinical outcomes, tumorigenesis, and treatment response remains unclear.

METHODS

To determine the role of cuproptosis in NB tumorigenesis and progression, this study employed a systematic technique to explore the characteristic patterns of 10 key cuproptosis-related genes (CUGs) in NB. Consensus clustering analysis of the TARGET and GEO databases divided the NB patients into two subgroups that showed different clinicopathological attributes, molecular patterns, survival outcomes, disease-associated pathways, tumor immune microenvironment (TIME) features, and treatment responses. Moreover, a cuproptosis scoring scheme was established, which divided the patients with NB into two groups with high scores and low scores as per the median score. Furthermore, this research developed a nomogram and risk signature on the basis of this cuproptosis score to better elucidate its function in predicting NB prognosis. In vitro experiments were carried out using Transwell Assay, HLECs tube formation assay, Colony formation assay, Western Blotting Assay, Immunohistochemical (IHC) Staining, Immunofluorescence (IF) Staining and Flow Cytometry Analysis.

RESULTS

The results demonstrated that the established cuproptosis score and prediction model could effectively distinguish between the individuals in low and high-risk groups and had a high predictive value. Lastly, bioinformatics analysis and in vitro experiments enabled the identification of PDHA1, a key CUG, which was involved in both DNA replication-related pathways and the cell cycle. It was also associated with tumorigenesis and progression of NB.

CONCLUSION

Cuproptosis, especially PDHA1, play a crucial role in the TIME characteristics, tumor progression, and long-term prognosis of NB. The patterns of cuproptosis assessed in this research may improve the understanding of the overall concept of NB tumorigenesis, thus facilitating the development of more effective therapeutic interventions.

Identification of a polyamine-related signature and six novel prognostic biomarkers in oral squamous cell carcinoma

Elevated polyamine levels are required for tumor transformation and development; however, expression patterns of polyamines and their diagnostic potential have not been investigated in oral squamous cell carcinoma (OSCC), and its impact on prognosis has yet to be determined. A total of 440 OSCC samples and clinical data were obtained from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO). Consensus clustering was conducted to classify OSCC patients into two subgroups based on the expression of the 17 polyamine regulators. Polyamine-related differentially expressed genes (PARDEGs) among distinct polyamine clusters were determined. To create a prognostic model, PARDEGs were examined in the training cohorts using univariate-Lasso-multivariate Cox regression analyses. Six prognostic genes, namely, "CKS2," "RIMS3," "TRAC," "FMOD," CALML5," and "SPINK7," were identified and applied to develop a predictive model for OSCC. According to the median risk score, the patients were split into high-risk and low-risk groups. The predictive performance of the six gene models was proven by the ROC curve analysis of the training and validation cohorts. Kaplan-Meier curves revealed that the high-risk group had poorer prognosis. Furthermore, the low-risk group was more susceptible to four chemotherapy drugs according to the IC50 of the samples computed by the "pRRophetic" package. The correlation between the risk scores and the proportion of immune cells was calculated. Meanwhile, the tumor mutational burden (TMB) value of the high-risk group was higher. Real-time quantitative polymerase chain reaction was applied to verify the genes constructing the model. The possible connections of the six genes with various immune cell infiltration and therapeutic markers were anticipated. In conclusion, we identified a polyamine-related prognostic signature, and six novel biomarkers in OSCC, which may provide insights to identify new treatment targets for OSCC.

One-Carbon and Polyamine Metabolism as Cancer Therapy Targets

Cancer metabolic reprogramming is essential for maintaining cancer cell survival and rapid replication. A common target of this metabolic reprogramming is one-carbon metabolism which is notable for its function in DNA synthesis, protein and DNA methylation, and antioxidant production. Polyamines are a key output of one-carbon metabolism with widespread effects on gene expression and signaling. As a result of these functions, one-carbon and polyamine metabolism have recently drawn a lot of interest for their part in cancer malignancy. Therapeutic inhibitors that target one-carbon and polyamine metabolism have thus been trialed as anticancer medications. The significance and future possibilities of one-carbon and polyamine metabolism as a target in cancer therapy are discussed in this review.

Comparative whole transcriptome analysis of gene expression in three canine soft tissue sarcoma types

Soft tissue sarcomas are pleiotropic tumors of mesenchymal cell origin. These tumors are rare in humans but common in veterinary practice, where they comprise up to 15% of canine skin and subcutaneous cancers. Because they present similar morphologies, primary sites, and growth characteristics, they are treated similarly, generally by surgical resection followed by radiation therapy. Previous studies have examined a variety of genetic changes as potential drivers of tumorigenesis and progression in soft tissue sarcomas as well as their use as markers for soft tissue sarcoma subtypes. However, few studies employing next generation sequencing approaches have been published. Here, we have examined gene expression patterns in canine soft tissue sarcomas using RNA-seq analysis of samples obtained from archived formalin-fixed and paraffin-embedded tumors. We provide a computational framework for using resulting data to categorize tumors, perform cross species comparisons and identify genetic changes associated with tumorigenesis. Functional overrepresentation analysis of differentially expressed genes further implicate both common and tumor-type specific transcription factors as potential mediators of tumorigenesis and aggression. Implications for tumor-type specific therapies are discussed. Our results illustrate the potential utility of this approach for the discovery of new therapeutic approaches to the management of canine soft tissue sarcomas and support the view that both common and tumor-type specific mechanisms drive the development of these tumors.

DHODH is an independent prognostic marker and potent therapeutic target in neuroblastoma

Despite intensive therapy, children with high-risk neuroblastoma are at risk of treatment failure. We applied a multiomic system approach to evaluate metabolic vulnerabilities in human neuroblastoma. We combined metabolomics, CRISPR screening, and transcriptomic data across more than 700 solid tumor cell lines and identified dihydroorotate dehydrogenase (DHODH), a critical enzyme in pyrimidine synthesis, as a potential treatment target. Of note, DHODH inhibition is currently under clinical investigation in patients with hematologic malignancies. In neuroblastoma, DHODH expression was identified as an independent risk factor for aggressive disease, and high DHODH levels correlated to worse overall and event-free survival. A subset of tumors with the highest DHODH expression was associated with a dismal prognosis, with a 5-year survival of less than 10%. In xenograft and transgenic neuroblastoma mouse models treated with the DHODH inhibitor brequinar, tumor growth was dramatically reduced, and survival was extended. Furthermore, brequinar treatment was shown to reduce the expression of MYC targets in 3 neuroblastoma models in vivo. A combination of brequinar and temozolomide was curative in the majority of transgenic TH-MYCN neuroblastoma mice, indicating a highly active clinical combination therapy. Overall, DHODH inhibition combined with temozolomide has therapeutic potential in neuroblastoma, and we propose this combination for clinical testing.

CDC27-ODC1 Axis Promotes Metastasis, Accelerates Ferroptosis and Predicts Poor Prognosis in Neuroblastoma

Neuroblastoma (NB) is a devastating malignancy threatening children’s health, and amplification of MYCN is associated with treatment failure and a poor outcome. Here, we aimed to demonstrate the role of cell division cycle 27 (CDC27), an important core subunit of the anaphase-promoting complex, and its clinical significance in NB patients. In functional assays, we illustrated that CDC27 promoted the cell growth, metastasis and sphere-formation ability of NB cells both in vitro and in vivo. To further understand the potential mechanism, SK-N-SH cells were transfected with CDC27 siRNA, and RNA-sequencing was performed. The results revealed that downregulation of CDC27 led to markedly reduced expression of ODC1, which is a well-established direct target of MYCN. Subsequently, we further illustrated that suppression of ODC1 significantly attenuated the promotion effect of CDC27 on the proliferation, metastasis, and sphere-formation ability of NB cells, hinting that CDC27 exerted its biological behavior in NB at least partly in an ODC1-dependent manner. In addition, CDC27 rendered cells more vulnerable to ferroptosis, while knockdown of ODC1 markedly reversed the pro-ferroptotic effect of CDC27. Collectively, our data is the first to report that the CDC27/ODC1 axis promotes tumorigenesis and acts as a positive regulator of ferroptosis in NB, highlighting that CDC27 may represent a novel therapeutic strategy and prognostic biomarker in neuroblastoma.

In Vitro Assessment of the Role of p53 on Chemotherapy Treatments in Neuroblastoma Cell Lines

Neuroblastoma is the most frequent malignant extracranial solid tumor of infancy. The overall objective of this work consists of determining the presence of alterations in the p53/MDM2/p14ARF signaling pathway in neuroblastoma cell lines and deciphering their possible relationship with resistance to known antineoplastic drugs and to differentiation agents. Firstly, we characterized 10 neuroblastoma cell lines for alterations at the p53/MDM2/p14ARF signaling pathway by analysis of TP53 point mutations, MYCN and MDM2 amplification, and p14ARF methylation, homozygous deletions, and expression. Secondly, we chose SK-N-FI (mutated at TP53) and SK-N-Be(2) (wild-type TP53) cell lines, treated them with chemotherapeutic agents (doxorubicin, etoposide, cisplatin, and melphalan) and with two isomers of retinoic acid (RA): (9-cis and all-trans). Finally, we analyzed the distribution of the cell cycle, the induction of apoptosis, and the expression levels of p53, p21, and Bcl-2 in those two cell lines. P14ARF did not present promoter methylation, homozygous deletions, and protein expression in any of the 10 neuroblastoma cell lines. One TP53 point mutation was detected in the SK-N-FI cell line. MYCN amplification was frequent, while most cell lines did not present MDM2 amplification. Treatment of SK-N-FI and SK-N-Be(2) cells with doxorubicin, etoposide, cisplatin, and melphalan increased apoptosis and blocked the cycle in G2/M, while retinoic acid isomers induced apoptosis and decreased the percentage of cells in S phase in TP53 mutated SK-N-FI cells, but not in TP53 wild-type SK-N-Be(2) cells. Treatment with cisplatin, melphalan, or 9-cis RA decreased p53 expression levels in SK-N-FI cells but not in SK-N-Be (2). The expression of p21 was not modified in either of the two cell lines. Bcl-2 levels were reduced only in SK-N-FI cells after treatment with cisplatin. However, treatments with doxorubicin, etoposide, or 9-cis-RA did not modify the levels of this protein in either of the two cell lines. In conclusion, TP53 mutated SK-N-FI cells respond better to the retinoic isomers than TP53 wild-type SK-N-Be(2) cells. Although these are in vitro results, it seems that deciphering the molecular alterations of the p53/MDM2/p14ARF signaling pathway prior to treating patients of neuroblastoma might be useful for standardizing therapies with the aim of improving survival.

MYCN in Neuroblastoma: "Old Wine into New Wineskins"

MYCN Proto-Oncogene, BHLH Transcription Factor (MYCN) has been one of the most studied genes in neuroblastoma. It is known for its oncogenetic mechanisms, as well as its role in the prognosis of the disease and it is considered one of the prominent targets for neuroblastoma therapy. In the present work, we attempted to review the literature, on the relation between MYCN and neuroblastoma from all possible mechanistic sites. We have searched the literature for the role of MYCN in neuroblastoma based on the following topics: the references of MYCN in the literature, the gene's anatomy, along with its transcripts, the protein's anatomy, the epigenetic mechanisms regulating MYCN expression and function, as well as MYCN amplification. MYCN plays a significant role in neuroblastoma biology. Its functions and properties range from the forming of G-quadraplexes, to the interaction with miRNAs, as well as the regulation of gene methylation and histone acetylation and deacetylation. Although MYCN is one of the most primary genes studied in neuroblastoma, there is still a lot to be learned. Our knowledge on the exact mechanisms of MYCN amplification, etiology and potential interventions is still limited. The knowledge on the molecular mechanisms of MYCN in neuroblastoma, could have potential prognostic and therapeutic advantages.

Metabolism and function of polyamines in cancer progression

Polyamines are essential for the proliferation, differentiation, and development of eukaryotes. They include spermine, spermidine, and the diamine precursor putrescine, and are low-molecular-weight, organic polycations with more than two amino groups. Their intracellular concentrations are strictly maintained within a specific physiological range through several regulatory mechanisms in normal cells. In contrast, polyamine metabolism is dysregulated in many neoplastic states, including cancer. In various types of cancer, polyamine levels are elevated, and crosstalk occurs between polyamine metabolism and oncogenic pathways, such as mTOR and RAS pathways. Thus, polyamines might have potential as therapeutic targets in the prevention and treatment of cancer. The molecular mechanisms linking polyamine metabolism to carcinogenesis must be unraveled to develop novel inhibitors of polyamine metabolism. This overview describes the nature of polyamines, their association with carcinogenesis, the development of polyamine inhibitors and their potential, and the findings of clinical trials.

Heterogeneity in retinoblastoma: a tale of molecules and models

Retinoblastoma, an intraocular pediatric cancer, develops in the embryonic retina following biallelic loss of RB1. However, there is a wide range of genetic and epigenetic changes that can affect RB1 resulting in different clinical outcomes. In addition, other transformations, such as MYCN amplification, generate particularly aggressive tumors, which may or may not be RB1 independent. Recognizing the cellular characteristics required for tumor development, by identifying the elusive cell-of-origin for retinoblastoma, would help us understand the development of these tumors. In this review we summarize the heterogeneity reported in retinoblastoma on a molecular, cellular and tissue level. We also discuss the challenging heterogeneity in current retinoblastoma models and suggest future platforms that could contribute to improved understanding of tumor initiation, progression and metastasis in retinoblastoma, which may ultimately lead to more patient-specific treatments.

Investigational drugs in phase II clinical trials for the treatment of neuroblastoma

INTRODUCTION

Neuroblastoma (NB) is an embryonal tumor originating from undifferentiated neural crest cell, highly heterogeneous ranging from spontaneous regression to progression despite multimodal treatments. Approximately, 20% of patients are refractory to frontline therapy and 50% will relapse/progress after an initial response. The overall five year survival for high-risk neuroblastoma ranges from 35-45%. Despite enhanced understanding of NB biology and the addition of myeloablative chemotherapy, isotretinoin and immunotherapy, survival for high risk NB remains less than 50%. Areas covered: This review summarizes and gives a critical overview of phase II trials investigating therapies for relapsed-refractory and high risk neuroblastoma. Expert opinion: Several novel molecules have been developed and are currently under investigation for the treatment of NB. The trend of novel targeted agents is one towards individualized, tailored therapy, based on the molecular and biological differences that characterize tumors that seem similar based solely on histological analysis. The task of developing new molecules is particularly difficult for NB, given the recurrent development of new patterns of drug resistance. However, even if current research is focused towards identifying the best treatments for each children and young adult with a NB defined disease, a deeper knowledge of the molecular biology and genetics is needed.

Functional prediction of miR-3144-5p in human cardiac myocytes based on transcriptome sequencing and bioinformatics

BACKGROUND

RAN guanine nucleotide release factor (RANGRF) encoding protein MOG1 plays an important role in cardiac arrhythmia, so we intended to investigate the regulatory miRNA of RANGRF and explore its potential regulatory mechanism in arrhythmogenesis.

METHODS

Based on bioinformatic analysis, miR-3144-5p was predicted to be a regulatory miRNA of RANGRF, which were then validated through a dual-luciferase reporter plasmid assay. Subsequently, the expression level of miR-3144-5p in human cardiac myocytes (HCMs) was detected, followed by cell transfection with miR-3144-5p mimics. Transcriptome sequencing was then performed in HCMs with or without transfection. The sequencing results were subjected to bioinformatic analyses, including differentially expressed gene (DEG) analysis, functional enrichment analysis, protein-protein interaction (PPI) network analysis, miRNA-target gene analysis, and miRNA-transcription factor (TF)-target gene coregulatory network analysis.

RESULTS

There really existed a regulatory relation between miR-3144-5p and RANGRF. The expression level of miR-3144-5p was low in HCMs. After cell transfection, miR-3144-5p expression level significantly increased in HCMs. Bioinformatic analyses of the transcriptome sequencing results identified 300 upregulated and 271 downregulated DEGs between miR-3144-5p mimic and control group. The upregulated genes ISL1 and neuregulin 1 (NRG1) were significantly enriched in cardiac muscle cell myoblast differentiation (GO:0060379). CCL21 was one of the hub genes in the PPI network and also a target gene of miR-3144-5p. Moreover, the TF of v-Myc avian myelocytomatosis viral oncogene neuroblastoma-derived homolog (MYCN) was involved in the miR-3144-5p-TF-target gene coregulatory network and interacted with the target genes of miR-3144-5p.

CONCLUSION

ISL1, NRG1, CCL21, and MYCN were differentially expressed in the miR-3144-5p mimic group, suggesting that miR-3144-5p overexpression plays a role in HCMs by regulating these genes and TF. This study may provide new insight into the mechanisms behind the progression of cardiac arrhythmia.

Current Chemotherapy and Potential New Targets in Uterine Leiomyosarcoma

A variety of chemotherapeutic agents have been used for treating recurrent or advanced stage uterine leiomyosarcoma (ULMS). The response rates of these current agents are disappointing, with partial response rates varying from 0% to 33%, and complete response rates varying from 0% to 8%. Recent studies have documented many molecular changes in ULMSs. Prominent amongst these are gains of growth factors C-MYC, Bcl-2, K-ras, and Ki-67, and losses in tumor suppressors p16, p53, Rb1, ING2 and D14S267. Various techniques that have been used to target these molecules are presented. Targeting specific therapies at these underlying molecular changes could potentially yield better response rates with fewer side effects.

The activation of type 1 corticotropin releasing factor receptor (CRF-R1) inhibits proliferation and promotes differentiation of neuroblastoma cells in vitro via p27(Kip1) protein up-regulation and c-Myc mRNA down-regulation

Our group has previously shown that corticotropin releasing factor (CRF) inhibits proliferation of human endocrine-related cancer cell lines via the activation of CRF type-1 receptors (CRF-R1). Tumors originating from the nervous system also express CRF receptors but their role on neoplastic cell proliferation was poorly investigated. Here we investigated the effect of CRF receptor stimulation on nervous system-derived cancer cells, using the SK-N-SH (N) human neuroblastoma cell line as an experimental model. We found that SK-N-SH (N) cells express functionally active CRF-R1, whose activation by CRF and the cognate peptide urocortin (UCN) is associated to reduced cell proliferation and motility, as well as neuronal-like differentiation. UCN did not interfere with cell viability and cell-cycle arrest. Those effects seem to be mediated by a mechanism involving the activation of cAMP/PKA/CREB pathway and the subsequent downstream increase in p27(Kip1) and underphosphorylated retinoblastoma protein levels, as well as reduced c-Myc mRNA accumulation.

A Phase I Trial of DFMO Targeting Polyamine Addiction in Patients with Relapsed/Refractory Neuroblastoma

BACKGROUND

Neuroblastoma (NB) is the most common cancer in infancy and most frequent cause of death from extracranial solid tumors in children. Ornithine decarboxylase (ODC) expression is an independent indicator of poor prognosis in NB patients. This study investigated safety, response, pharmacokinetics, genetic and metabolic factors associated with ODC in a clinical trial of the ODC inhibitor difluoromethylornithine (DFMO) ± etoposide for patients with relapsed or refractory NB.

METHODS AND FINDINGS

Twenty-one patients participated in a phase I study of daily oral DFMO alone for three weeks, followed by additional three-week cycles of DFMO plus daily oral etoposide. No dose limiting toxicities (DLTs) were identified in patients taking doses of DFMO between 500-1500 mg/m2 orally twice a day. DFMO pharmacokinetics, single nucleotide polymorphisms (SNPs) in the ODC gene and urinary levels of substrates for the tissue polyamine exporter were measured. Urinary polyamine levels varied among patients at baseline. Patients with the minor T-allele at rs2302616 of the ODC gene had higher baseline levels (p=0.02) of, and larger decreases in, total urinary polyamines during the first cycle of DFMO therapy (p=0.003) and had median progression free survival (PFS) that was over three times longer, compared to patients with the major G allele at this locus although this last result was not statistically significant (p=0.07). Six of 18 evaluable patients were progression free during the trial period with three patients continuing progression free at 663, 1559 and 1573 days after initiating treatment. Median progression-free survival was less among patients having increased urinary polyamines, especially diacetylspermine, although this result was not statistically significant (p=0.056).

CONCLUSIONS

DFMO doses of 500-1500 mg/m2/day are safe and well tolerated in children with relapsed NB. Children with the minor T allele at rs2302616 of the ODC gene with relapsed or refractory NB had higher levels of urinary polyamine markers and responded better to therapy containing DFMO, compared to those with the major G allele at this locus. These findings suggest that this patient subset may display dependence on polyamines and be uniquely susceptible to therapies targeting this pathway.

TRIAL REGISTRATION

Clinicaltrials.gov NCT#01059071.

Exploration of the selective recognition of the G-quadruplex in the N-myc oncogene by electrospray ionization mass spectrometry

RATIONALE

The N-myc gene is a member of the MYC family and its amplification is highly correlated with the pathophysiology of cancers. The G-rich sequence, d(AG3CG3AG3AG3A), in the first intron of N-myc can form a G-quadruplex structure. Small molecules binding to it with high affinity and selectivity may provide a potential approach to modulate the expression of the N-myc gene.

METHODS

Electrospray ionization (ESI) mass spectrometry was used to analyze the G-quadruplex formation of the d(AG3CG3AG3AG3A) sequence, and to evaluate the binding affinities and selectivities of natural small molecules with the N-myc G-quadruplex.

RESULTS

Enniatin B was found to have the highest binding affinity with this G-quadruplex within the 12 small molecules. Moreover, it also showed a biased selectivity toward the N-myc G-quadruplex compared with the other five G-quadruplexes derived from C-myc, Bcl2, Chl1, c-kit promoters and telomere G-rich sequences.

CONCLUSIONS

In this study, we found a natural small molecule, enniatin B, which could bind to the G-quadruplex of the d(AG3CG3AG3AG3A) sequence from the first intron of the N-myc gene with high affinity and selectivity, which may lead to a potential modulation of the N-myc gene.

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.

AMXT-1501, a novel polyamine transport inhibitor, synergizes with DFMO in inhibiting neuroblastoma cell proliferation by targeting both ornithine decarboxylase and polyamine transport

Neuroblastoma (NB) is associated with MYCN oncogene amplification occurring in approximately 30% of NBs and is associated with poor prognosis. MYCN is linked to a number of genes including ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis. ODC expression is elevated in many forms of cancer including NB. Alpha-difluoromethylornithine (DFMO), an ODC inhibitor, is currently being used in a Phase I clinical trial for treatment of NB. However, cancer cells treated with DFMO may overcome their polyamine depletion by the uptake of polyamines from extracellular sources. A novel polyamine transport inhibitor, AMXT-1501, has not yet been tested in NB. We propose that inhibiting ODC with DFMO, coupled with polyamine transport inhibition by AMXT-1501 will result in enhanced NB growth inhibition. Single and combination drug treatments were conducted on three NB cell lines. DFMO IC50 values ranged from 20.76 to 33.3 mM, and AMXT-1501 IC50 values ranged from 14.13 to 17.72 µM in NB. The combination treatment resulted in hypophosphorylation of retinoblastoma protein (Rb), suggesting growth inhibition via G1 cell cycle arrest. Increased expression of cleaved PARP and cleaved caspase 3 in combination-treated cells starting at 48 hr suggested apoptosis. The combination treatment depleted intracellular polyamine pools and decreased intracellular ATP, further verifying growth inhibition. Given the current lack of effective therapies for patients with relapsed/refractory NB and the preclinical effectiveness of DFMO with AMXT-1501, this combination treatment provides promising preclinical results. DFMO and AMXT-1501 may be a potential new therapy for children with NB.

Cidofovir selectivity is based on the different response of normal and cancer cells to DNA damage

Background

Cidofovir (CDV) proved efficacious in treatment of human papillomaviruses (HPVs) hyperplasias. Antiproliferative effects of CDV have been associated with apoptosis induction, S-phase accumulation, and increased levels of tumor suppressor proteins. However, the molecular mechanisms for the selectivity and antitumor activity of CDV against HPV-transformed cells remain unexplained.

Methods

We evaluated CDV drug metabolism and incorporation into cellular DNA, in addition to whole genome gene expression profiling by means of microarrays in two HPV⁺ cervical carcinoma cells, HPV^- immortalized keratinocytes, and normal keratinocytes.

Results

Determination of the metabolism and drug incorporation of CDV into genomic DNA demonstrated a higher rate of drug incorporation in HPV⁺ tumor cells and immortalized keratinocytes compared to normal keratinocytes. Gene expression profiling clearly showed distinct and specific drug effects in the cell types investigated. Although an effect on inflammatory response was seen in all cell types, different pathways were identified in normal keratinocytes compared to immortalized keratinocytes and HPV⁺ tumor cells. Notably, Rho GTPase pathways, LXR/RXR pathways, and acute phase response signaling were exclusively activated in immortalized cells. CDV exposed normal keratinocytes displayed activated cell cycle regulation upon DNA damage signaling to allow DNA repair via homologous recombination, resulting in genomic stability and survival. Although CDV induced cell cycle arrest in HPV^- immortalized cells, DNA repair was not activated in these cells. In contrast, HPV⁺ cells lacked cell cycle regulation, leading to genomic instability and eventually apoptosis.

Conclusions

Taken together, our data provide novel insights into the mechanism of action of CDV and its selectivity for HPV-transformed cells. The proposed mechanism suggests that this selectivity is based on the inability of HPV⁺ cells to respond to DNA damage, rather than on a direct anti-HPV effect. Since cell cycle control is deregulated by the viral oncoproteins E6 and E7 in HPV⁺ cells, these cells are more susceptible to DNA damage than normal keratinocytes. Our findings underline the therapeutic potential of CDV for HPV-associated malignancies as well as other neoplasias.

Cell survival signaling in neuroblastoma

Neuroblastoma is the most common extracranial solid tumor of childhood and is responsible for over 15% of pediatric cancer deaths. Neuroblastoma tumorigenesis and malignant transformation is driven by overexpression and dominance of cell survival pathways and a lack of normal cellular senescence or apoptosis. Therefore, manipulation of cell survival pathways may decrease the malignant potential of these tumors and provide avenues for the development of novel therapeutics. This review focuses on several facets of cell survival pathways including protein kinases (PI3K, AKT, ALK, and FAK), transcription factors (NF-κB, MYCN and p53), and growth factors (IGF, EGF, PDGF, and VEGF). Modulation of each of these factors decreases the growth or otherwise hinders the malignant potential of neuroblastoma, and many therapeutics targeting these pathways are already in the clinical trial phase of development. Continued research and discovery of effective modulators of these pathways will revolutionize the treatment of neuroblastoma.

Oncolytic adenovirus armed with shRNA targeting MYCN gene inhibits neuroblastoma cell proliferation and in vivo xenograft tumor growth

PURPOSE

MYCN amplification and p53 inactivation are two typical characteristics of aggressive neuroblastomas and are strongly associated with cancer progression and treatment failure. In an effort to develop new therapeutic agents to treat the aggressive neuroblastomas, we constructed ZD55-shMYCN, an oncolytic adenovirus ZD55 carrying short hairpin RNA (shRNA) targeting MYCN gene, and investigated the effects on proliferation of the p53-null and MYCN-amplified neuroblastoma cell line LA1-55N in vitro and in vivo by ZD55-shMYCN.

METHODS

In this study, we used ZD55-shMYCN to treat p53-null and MYCN-amplified neuroblastoma cells. To confirm the ability of selective replication of the ZD55-shMYCN, we examined the expression of E1A protein by western blotting. We used quantitative real-time PCR analysis and western blotting analysis to determine the inhibitory effect of ZD55-shMYCN on MYCN expression. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] cell proliferation assay and xenograft mouse model were used to test the antigrowth efficacy of ZD55-shMYCN.

RESULTS

The results showed that ZD55-shMYCN selectively replicated and significantly downregulated the MYCN expression in LA1-55N cells. ZD55-shMYCN effectively inhibited the proliferation in LA1-55N cells in vitro and significantly inhibited tumor growth in vivo xenograft tumor in nude mice.

CONCLUSIONS

ZD55-shMYCN provides a novel agent for treating MYCN-amplified and p53-inactive aggressive neuroblastoma, representing a promising approach for further clinical development.

A call to ARMS: targeting the PAX3-FOXO1 gene in alveolar rhabdomyosarcoma

INTRODUCTION

Expression of fusion oncoproteins generated by recurrent chromosomal translocations represents a major tumorigenic mechanism characteristic of multiple cancers, including one-third of all sarcomas. Oncogenic fusion genes provide novel targets for therapeutic intervention. The PAX3-FOXO1 oncoprotein in alveolar rhabdomyosarcoma (ARMS) is presented as a paradigm to examine therapeutic strategies for targeting sarcoma-associated fusion genes.

AREAS COVERED

This review discusses the role of PAX3-FOXO1 in ARMS tumors. Besides evaluating various approaches to molecularly target PAX3-FOXO1 itself, this review highlights therapeutically attractive downstream genes activated by PAX3-FOXO1.

EXPERT OPINION

Oncogenic fusion proteins represent desirable therapeutic targets because their expression is specific to tumor cells, but these fusions generally characterize rare malignancies. Full development and testing of potential drugs targeted to these fusions are complicated by the small numbers of patients in these disease categories. Although efforts to develop targeted therapies against fusion proteins should continue, molecular targets that are applicable to a broader tumor landscape should be pursued. A shift of the traditional paradigm to view therapeutic intervention as target-specific rather than tumor-specific will help to circumvent the challenges posed by rare tumors and maximize the possibility of developing successful new treatments for patients with these rare translocation-associated sarcomas.

Antitumor activity of sustained N-myc reduction in rhabdomyosarcomas and transcriptional block by antigene therapy

PURPOSE

Rhabdomyosarcomas are a major cause of cancer death in children, described with MYCN amplification and, in the alveolar subtype, transcription driven by the PAX3-FOXO1 fusion protein. Our aim was to determine the prevalence of N-Myc protein expression and the potential therapeutic effects of reducing expression in rhabdomyosarcomas, including use of an antigene strategy that inhibits transcription.

EXPERIMENTAL DESIGN

Protein expression was assessed by immunohistochemistry. MYCN expression was reduced in representative cell lines by RNA interference and an antigene peptide nucleic acid (PNA) oligonucleotide conjugated to a nuclear localization signal peptide. Associated gene expression changes, cell viability, and apoptosis were analyzed in vitro. As a paradigm for antigene therapy, the effects of systemic treatment of mice with rhabdomyosarcoma cell line xenografts were determined.

RESULTS

High N-Myc levels were significantly associated with genomic amplification, presence of the PAX3/7-FOXO1 fusion genes, and proliferative capacity. Sustained reduction of N-Myc levels in all rhabdomyosarcoma cell lines that express the protein decreased cell proliferation and increased apoptosis. Positive feedback was shown to regulate PAX3-FOXO1 and N-Myc levels in the alveolar subtype that critically decrease PAX3-FOXO1 levels on reducing N-Myc. Pharmacologic systemic administration of the antigene PNA can eliminate alveolar rhabdomyosarcoma xenografts in mice, without relapse or toxicity.

CONCLUSION

N-Myc, with its restricted expression in non-fetal tissues, is a therapeutic target to treat rhabdomyosarcomas, and blocking gene transcription using antigene oligonucleotide strategies has therapeutic potential in the treatment of cancer and other diseases that has not been previously realized in vivo.

Differential toll-like receptor 3 (TLR3) expression and apoptotic response to TLR3 agonist in human neuroblastoma cells

Background

Toll-like receptor-3 (TLR-3) is a critical component of innate immune system against dsRNA viruses and is expressed in the central nervous system. However, it remains unknown whether TLR3 may serve as a therapeutic target in human neuroblastoma (NB).

Methods

TLR3 expression in human NB samples was examined by immunohistochemical analysis. Quantitative RT-PCR and western blot was used to determine TLR3 expression in three human NB cell lines. The effect of TLR3 agonist, polyinosinic-polycytidylic acid (poly(I:C)), on the growth of human NB cells was evaluated by WST-1 cell proliferation assay, flow cytometry analysis, and immunoblot analysis. Blockade of TLR3 signaling was achieved using TLR3 neutralizing antibody, small interference RNA, and 2-aminopurine (2-AP), an inhibitor of protein kinase R (PKR), an interferon-induced, double-stranded RNA-activated protein kinase.

Results

In immunohistochemical studies, TLR3 mainly expressed in the cytoplasm of ganglion cells and in some neuroblastic cells, but not in the stromal cells in human NB tissues. Among three human NB cell lines analyzed, TLR3 was significantly up-regulated in SK-N-AS cells at mRNA and protein level compared with other two low TLR3- expressing NB cells. Treatment with poly(I:C) elicited significant growth inhibition and apoptosis only in high TLR3-expressing SK-N-AS cells, but not in low TLR3-expressing SK-N-FI and SK-N-DZ cells. Moreover, poly(I:C) treatment significantly stimulated the activities of PKR, interferon regulatory factor 3 (IRF-3) and caspase-3 in SK-N-AS cells. Application of TLR3 neutralizing antibody or small interference RNA (siRNA) reduced the poly(I:C)-induced inhibition of cell proliferation and apoptosis in SK-N-AS cells. On the contrary, ectopic TLR3 expression enhanced the sensitivity of low TLR3-expressing NB cells to poly(I:C). Finally, application of 2-AP attenuated the poly(I:C)-induced IRF-3 and caspase-3 activation in SK-N-AS cells.

Conclusion

The present study demonstrates that TLR3 is expressed in a subset of NB cells. Besides, TLR3/PKR/IRF-3/capase-3 pathway is implicated in the selective cytotoxicity of TLR3 agonist towards high TLR3-expressing NB cells.

Myogenesis and rhabdomyosarcoma the Jekyll and Hyde of skeletal muscle

Rhabdomyosarcoma, a neoplasm composed of skeletal myoblast-like cells, represents the most common soft tissue sarcoma in children. The application of intensive chemotherapeutics and refined surgical and radiation therapy approaches have improved survival for children with localized disease over the past 3 decades; however, these approaches have not improved the dismal outcome for children with metastatic and recurrent rhabdomyosarcoma. Elegant studies have defined the molecular mechanisms driving skeletal muscle lineage commitment and differentiation, and the machinery that couples differentiation with irreversible cell proliferation arrest. Further, detailed molecular analyses indicate that rhabdomyosarcoma cells have lost the capacity to fully differentiate when challenged to do so in experimental models. We review the intersection of normal skeletal muscle developmental biology and the molecular genetic defects in rhabdomyosarcoma with the underlying premise that understanding how the differentiation process has gone awry will lead to new treatment strategies aimed at promoting myogenic differentiation and concomitant cell cycle arrest.

TCEAL7 inhibition of c-Myc activity in alternative lengthening of telomeres regulates hTERT expression

Replicative senescence forms a major barrier to tumor progression. Cancer cells bypass this by using one of the two known telomere maintenance mechanisms: telomerase or the recombination-based alternative lengthening of telomeres (ALT) mechanism. The molecular details of ALT are currently poorly understood. We have previously shown that telomerase is actively repressed through complex networks of kinase, gene expression, and chromatin regulation. In this study, we aimed to gain further understanding of the role of kinases in the regulation of telomerase expression in ALT cells. Using a whole human kinome small interfering RNA (siRNA) screen, we highlighted 106 kinases whose expression is linked to human telomerase reverse transcriptase (hTERT) promoter activity. Network modeling of transcriptional regulation implicated c-Myc as a key regulator of the 106 kinase hits. Given our previous observations of lower c-Myc activity in ALT cells, we further explored its potential to regulate telomerase expression in ALT. We found increased c-Myc binding at the hTERT promoter in telomerase-positive compared with ALT cells, although no expression differences in c-Myc, Mad, or Max were observed between ALT and telomerase-positive cells that could explain decreased c-Myc activity in ALT. Instead, we found increased expression of the c-Myc competitive inhibitor TCEAL7 in ALT cells and tumors and that alteration of TCEAL7 expression levels in ALT and telomerase-positive cells affects hTERT expression. Lower c-Myc activity in ALT may therefore be obtained through TCEAL7 regulation. Thus, TCEAL7 may present an interesting novel target for cancer therapy, which warrants further investigation.

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.

CDK Inhibitors Roscovitine and CR8 Trigger Mcl-1 Down-Regulation and Apoptotic Cell Death in Neuroblastoma Cells

Neuroblastoma (NB), the most frequent extracranial solid tumor of children accounting for nearly 15% of all childhood cancer mortality, displays overexpression of antiapoptotic Bcl-2 and Mcl-1 in aggressive forms of the disease. The clinical phase 2 drug roscovitine (CYC202, seliciclib), a relatively selective inhibitor of cyclin-dependent kinases (CDKs), and CR8, a recently developed and more potent analog, induce concentration-dependent apoptotic cell death of NB cells (average IC(50) values: 24.2 µM and 0.4 µM for roscovitine and CR8, respectively). Both roscovitine and CR8 trigger rapid down-regulation of the short-lived survival factor Mcl-1 in the 9 investigated human NB cell lines. This effect was further analyzed in the human SH-SY5Y NB cell line. Down-regulation of Mcl-1 appears to depend on inhibition of CDKs rather than on interaction of roscovitine and CR8 with their secondary targets. CR8 is an adenosine triphosphate-competitive inhibitor of CDK9, and the structure of a CDK9/cyclin T/CR8 complex is described. Mcl-1 down-regulation occurs both at the mRNA and protein levels. This effect can be accounted for by a reduction in Mcl-1 protein synthesis, under stable Mcl-1 degradation conditions. Mcl-1 down-regulation is accompanied by a transient increase in free Noxa, a proapoptotic factor. Mcl-1 down-regulation occurs independently of the presence or up-regulation of p53 and of the MYCN status. Taken together, these results suggest that the clinical drug roscovitine and its novel analog CR8 induce apoptotic tumor cell death by down-regulating Mcl-1, a key survival factor expressed in all NB cell lines. CDK inhibition may thus constitute a new approach to treat refractory high-risk NB.

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.

The emerging molecular pathogenesis of neuroblastoma: implications for improved risk assessment and targeted therapy

Neuroblastoma is one of the most common solid tumors of childhood, arising from immature sympathetic nervous system cells. The clinical course of patients with neuroblastoma is highly variable, ranging from spontaneous regression to widespread metastatic disease. Although the outcome for children with cancer has improved considerably during the past decades, the prognosis of children with aggressive neuroblastoma remains dismal. The clinical heterogeneity of neuroblastoma mirrors the biological and genetic heterogeneity of these tumors. Ploidy and MYCN amplification have been used as genetic markers for risk stratification and therapeutic decision making, and, more recently, gene expression profiling and genome-wide DNA copy number analysis have come into the picture as sensitive and specific tools for assessing prognosis. The applica tion of new genetic tools also led to the discovery of an important familial neuroblastoma cancer gene, ALK, which is mutated in approximately 8% of sporadic tumors, and genome-wide association studies have unveiled loci with risk alleles for neuroblastoma development. For some of the genomic regions that are deleted in some neuroblastomas, on 1p, 3p and 11q, candidate tumor suppressor genes have been identified. In addition, evidence has emerged for the contribution of epigenetic disturbances in neuroblastoma oncogenesis. As in other cancer entities, altered microRNA expression is also being recognized as an important player in neuroblastoma. The recent successes in unraveling the genetic basis of neuroblastoma are now opening opportunities for development of targeted therapies.

Embryonal neural tumours and cell death

Medulloblastoma and neuroblastoma are malignant embryonal childhood tumours of the central and peripheral nervous systems, respectively, which often show poor clinical prognosis due to resistance to current chemotherapy. Both these tumours have deficient apoptotic machineries adopted from their respective progenitor cells. This review focuses on the specific background for tumour development, and highlights biological pathways that present potential targets for novel therapeutic approaches.

The Myc oncoprotein as a therapeutic target for human cancer

Myc expression is deregulated in a wide range of human cancers and is often associated with aggressive, poorly differentiated tumors. The Myc protein is a transcription factor that regulates a variety of cellular processes including cell growth and proliferation, cell-cycle progression, transcription, differentiation, apoptosis, and cell motility. Potential strategies that either inhibit the growth promoting effect of Myc and/or activate its pro-apoptotic function are presently being explored. In this review, we give an overview of Myc activation in human tumors and discuss current strategies aimed at targeting Myc for cancer treatment. Such therapies could have potential in combination with mechanistically different cytotoxic drugs to combat and eradicate tumors cells.

Current therapy for medulloblastoma

In the past three decades, the survival for patients with medulloblastoma has improved remarkably. Contemporary "standard" therapy for children with medulloblastoma consists of maximal surgical resection followed by craniospinal irradiation with a boost to the posterior fossa, combined with adjuvant chemotherapy. The use of such multimodal therapeutic approaches results in progression-free survival (PFS) rates of 75% to 80% for patients with average-risk disease and approximately 60% for high-risk patients. However, despite the marked improvements in survival, many therapeutic challenges remain. Children with macroscopic metastatic disease (M2/M3) at presentation continue to fare poorly, with the best reports only attaining PFS rates up to 40%. Furthermore, despite intensive multimodal therapy, some patients have disease progression or recurrence, which for most remains incurable. The early recognition of these patients is imperative in order to institute treatment modifications, such as intensification and/or the use of novel experimental therapies. Additionally, the price for cure is clearly evident in survivors, who suffer from significant, often debilitating long-term neurocognitive and neuroendocrine sequela. Using the current clinical stratification system, a significant number of patients are overtreated and unnecessarily subjected to these long-term toxicities. This group of patients would benefit from reductions in therapy. Refinements in patient stratification and further improvement in outcome are unlikely to be achieved without improved knowledge of tumor biology. Several molecular alterations have already been identified, many of which appear to have prognostic significance. Furthermore, the disruption of molecular alterations in signaling pathways involved in the development and maintenance of medulloblastoma using novel molecularly targeted therapies promises to improve outcomes and reduce toxicity for patients with medulloblastoma. It is envisaged that in the near future children diagnosed with medulloblastoma will be more accurately stratified based on a combination of clinical variables and molecular profiles. Improved risk stratification will permit delivery of individualized therapy using conventional treatment modalities in conjunction with novel targeted therapeutic approaches.

MYCN deregulation as a potential target for novel therapies in rhabdomyosarcoma

Rhabdomyosarcoma is the most common soft-tissue sarcoma of childhood. Treatment requires a multimodality approach combining chemotherapy with surgery and radiotherapy. Although overall outcomes have improved considerably, the outlook for patients with high-risk disease, particularly the alveolar subtype, remains bleak and there is a clear need for new chemotherapeutic strategies. This review focuses on the possibilities for interventions targeting myc myelocytomatosis viral related oncogene, neuroblastoma derived (MYCN). The importance of aberrant expression of this oncogene is well established in neuroblastoma and recent data indicate that MYCN deregulation also occurs in up to a quarter of alveolar subtype cases. A range of possible approaches to target MYCN is discussed, including nucleic acid-based and immunotherapy strategies.

Oncogenes as novel targets for cancer therapy (part III): transcription factors

This is the third paper in a four-part serial review on potential therapeutic targeting of oncogenes. The previous parts described the involvement of oncogenes in different aspects of cancer growth and development, and considered the new technologies responsible for the advancement of oncogene identification, target validation, and drug design. Because of such advances, new specific and more efficient therapeutic agents can be developed for cancer. This part of the review continues the exploration of various oncogenes that we have grouped within seven categories: growth factors, tyrosine kinases, intermediate signaling molecules, transcription factors, cell cycle regulators, DNA damage repair genes, and genes involved in apoptosis. Part one discussed growth factors and tyrosine kinases and part two discussed intermediate signaling molecules. This portion of the review covers transcription factors and the various strategies being used to inhibit their expression or decrease their activities.

Chromosome translocations in sarcomas and the emergence of oncogenic transcription factors

A subset of sarcomas is characterised by recurrent chromosome translocations that generate novel fusion oncoproteins. One or both of the genes involved in these translocations often encode transcription factors, and the resulting fusion proteins have aberrant transcriptional function compared to their wild-type counterparts. These fusion transcription factors disrupt multiple biological pathways by altering expression of target genes, and thereby result in a variety of altered cellular properties that contribute to the tumourigenic process. However, experimental data indicate that the fusion gene alone is not sufficient for transformation in primary cells (EWS-FLI1) or tumourigenesis in the mouse (PAX3-FKHR, FUS-CHOP), suggesting that additional collaborating genetic alterations are required. In addition to improving our understanding of the etiology of these tumours, this accumulating knowledge of the oncogenic properties of these fusion proteins, their downstream targets, and cooperating genetic alterations will permit the development of a variety of novel approaches to improve the therapy of these cancers.

Key role for p27Kip1, retinoblastoma protein Rb, and MYCN in polyamine inhibitor-induced G1 cell cycle arrest in MYCN-amplified human neuroblastoma cells

Alpha-difluoromethylornithine (DFMO) inhibits the proto-oncogene ornithine decarboxylase (ODC) and is known to induce cell cycle arrest. However, the effect of DFMO on human neuroblastoma (NB) cells and the exact mechanism of DFMO-induced cell death are largely unknown. Treatment with DFMO in combination with SAM486A, an S-adenosylmethionine decarboxylase (AdoMetDC) inhibitor, has been shown to enhance polyamine pool depletion. Therefore, we analysed the mechanism of action of DFMO and/or SAM486A in two established MYCN-amplified human NB cell lines. DFMO and SAM486A caused rapid cell growth inhibition, polyamine depletion, and G1 cell cycle arrest without apoptosis in cell lines LAN-1 and NMB-7. These effects were enhanced with combined inhibitors and largely prevented by cotreatment with exogenous polyamines. The G1 cell cycle arrest was concomitant with an increase in cyclin-dependent kinase inhibitor p27Kip1. In a similar fashion, DFMO and DFMO/SAM486A inhibited the phosphorylation of the G1/S transition-regulating retinoblastoma protein Rb at residues Ser795 and Ser807/811. Moreover, we observed a dramatic decrease in MYCN protein levels. Overexpression of MYCN induces an aggressive NB phenotype with malignant behavior. We show for the first time that DFMO and SAM486A induce G1 cell cycle arrest in NB cells through p27Kip1 and Rb hypophosphorylation.

13-cis retinoic acid and isomerisation in paediatric oncology--is changing shape the key to success?

Retinoic acid isomers have been used with some success as chemotherapeutic agents, most recently with 13-cis retinoic acid showing impressive clinical efficacy in the paediatric malignancy neuroblastoma. The aim of this commentary is to review the evidence that 13-cis retinoic acid is a pro-drug, and consider the implications of retinoid metabolism and isomerisation for the further development of retinoic acid for cancer therapy. The low binding affinity of 13-cis retinoic acid for retinoic acid receptors, low activity in gene expression assays and the accumulation of the all-trans isomer in cells treated with 13-cis retinoic acid, coupled with the more-favourable pharmacokinetic profile of 13-cis retinoic acid compared to other isomers, suggest that intracellular isomerisation to all-trans retinoic acid is the key process underlying the biological activity of 13-cis retinoic acid. Intracellular metabolism of all-trans retinoic acid by a positive auto-regulatory loop may result in clinical resistance to retinoic acid. Agents that block or reduce the metabolism of all-trans retinoic acid are therefore attractive targets for drug development. Devising strategies to deliver 13-cis retinoic acid to tumour cells and facilitate the intracellular isomerisation of 13-cis retinoic acid, while limiting metabolism of all-trans retinoic acid, may have a major impact on the efficacy of 13-cis retinoic acid in paediatric oncology.

Relationship between MYCN copy number and expression in rhabdomyosarcomas and correlation with adverse prognosis in the alveolar subtype

PURPOSE

Amplification of the transcription factor MYCN is an important molecular diagnostic tool in stratifying treatment for neuroblastoma. Increased copy number and overexpression of MYCN in the pediatric cancer rhabdomyosarcoma has been described in a number of small studies with conflicting conclusions about its association with clinicopathologic characteristics. We aimed to study the phenomenon in the largest series to date.

PATIENTS AND METHODS

Using quantitative polymerase chain reaction, we measured MYCN copy number and expression levels in rhabdomyosarcoma samples from 113 and 92 individuals with a confirmed diagnosis of rhabdomyosarcoma, respectively.

RESULTS

Increased copy number of MYCN was found to be a feature of both the embryonal and alveolar subtypes. The copy number and expression levels were significantly greater in the alveolar subtype, although the range of expression in both subtypes spanned several orders of magnitude. MYCN copy number showed a significant correlation with expression in the alveolar subtype; this relationship between copy number and expression could be modeled as a logarithmic function. It is notable that relatively high expression frequently occurred in embryonal rhabdomyosarcoma without high copy number and that low expression was found in some cases with high copy number. In patients with alveolar rhabdomyosarcoma, overexpression (greater than median) or gain of genomic copies of MYCN were significantly associated with adverse outcome.

CONCLUSION

MYCN deregulation is a feature of rhabdomyosarcoma tumorigenesis, defines groups of patients with a poor prognosis, and is a potential target for novel therapies.

c-Myc as a therapeutic target in cancer

c-Myc is frequently deregulated in human cancers. The c-Myc oncoprotein is a transcription factor, with many of its target genes encoding proteins that initiate and maintain the transformed state. c-Myc is also part of a dynamic network whose members interact selectively with one another and with various transcriptional coregulators and histone-modifying enzymes. This knowledge highlights several points that might be amenable to attack. This review summarizes progress in controlling the extent of c-Myc transcription, translation, interaction with other myc network members, DNA binding and transcriptional activation. Inhibition of c-Myc can be achieved with many of these approaches; however, clinical efficacy will likely require intervention at several levels, perhaps in combination with traditional chemotherapeutic drugs or agents that target other oncoproteins.

Mouse models of childhood cancer of the nervous system

Targeted cancer treatments rely on understanding signalling cascades, genetic changes, and compensatory programmes activated during tumorigenesis. Increasingly, pathologists are required to interpret molecular profiles of tumour specimens to target new treatments. This is challenging because cancer is a heterogeneous disease-tumours change over time in individual patients and genetic lesions leading from preneoplasia to malignancy can differ substantially between patients. For childhood tumours of the nervous system, the challenge is even greater, because tumours arise from progenitor cells in a developmental context different from that of the adult, and the cells of origin, neural progenitor cells, show considerable temporal and spatial heterogeneity during development. Thus, the underlying mechanisms regulating normal development of the nervous system also need to be understood. Many important advances have come from model mouse genetic systems. This review will describe several mouse models of childhood tumours of the nervous system, emphasising how understanding the normal developmental processes, combined with mouse models of cancer and the molecular pathology of the human diseases, can provide the information needed to treat cancer more effectively.