Measurement and relevance of neuroblastoma DNA copy number changes in the post-genome era

Association between chromosomal aberration of COX8C and tethered spinal cord syndrome: array-based comparative genomic hybridization analysis

Copy number variations have been found in patients with neural tube abnormalities. In this study, we performed genome-wide screening using high-resolution array-based comparative genomic hybridization in three children with tethered spinal cord syndrome and two healthy parents. Of eight copy number variations, four were non-polymorphic. These non-polymorphic copy number variations were associated with Angelman and Prader-Willi syndromes, and microcephaly. Gene function enrichment analysis revealed that COX8C, a gene associated with metabolic disorders of the nervous system, was located in the copy number variation region of Patient 1. Our results indicate that array-based comparative genomic hybridization can be used to diagnose tethered spinal cord syndrome. Our results may help determine the pathogenesis of tethered spinal cord syndrome and prevent occurrence of this disease.

High genomic instability predicts survival in metastatic high-risk neuroblastoma

We aimed to identify novel molecular prognostic markers to better predict relapse risk estimate for children with high-risk (HR) metastatic neuroblastoma (NB). We performed genome- and/or transcriptome-wide analyses of 129 stage 4 HR NBs. Children older than 1 year of age were categorized as "short survivors" (dead of disease within 5 years from diagnosis) and "long survivors" (alive with an overall survival time ≥ 5 years). We reported that patients with less than three segmental copy number aberrations in their tumor represent a molecularly defined subgroup with a high survival probability within the current HR group of patients. The complex genomic pattern is a prognostic marker independent of NB-associated chromosomal aberrations, i.e., MYCN amplification, 1p and 11q losses, and 17q gain. Integrative analysis of genomic and expression signatures demonstrated that fatal outcome is mainly associated with loss of cell cycle control and deregulation of Rho guanosine triphosphates (GTPases) functioning in neuritogenesis. Tumors with MYCN amplification show a lower chromosome instability compared to MYCN single-copy NBs (P = .0008), dominated by 17q gain and 1p loss. Moreover, our results suggest that the MYCN amplification mainly drives disruption of neuronal differentiation and reduction of cell adhesion process involved in tumor invasion and metastasis. Further validation studies are warranted to establish this as a risk stratification for patients.

Genetic stratification of neuroblastoma for treatment tailoring

Neuroblastoma is the most common extracranial tumor of childhood. The clinical behavior is variable, ranging from spontaneous regression to fatal progression despite aggressive therapy. The most highly statistically significant and clinically relevant factors that are currently used for classification include stage, age, histopathologic category, MYCN oncogene status, chromosome 11q status and DNA ploidy. These genetic markers were analyzed separately by classical methods until recently: mainly fluorescence in situ hybridization or loss of heterozygosity. The development of genome-wide techniques such as comparative genomic hybridization, array comparative genomic hybridization and single nucleotide polymorphism allows the analysis of copy number variations through the whole genome in one step. This enabled the investigators to refine different genetic subtypes for the better comprehension of neuroblastoma tumor behavior and reach the conclusion that these data together with a genomic profile based on gene expression should be included in future treatment stratification.

2p24 Gain region harboring MYCN gene compared with MYCN amplified and nonamplified neuroblastoma: biological and clinical characteristics

Although the role of MYCN amplification in neuroblastoma is well established, the biological and clinical characteristics of the 2p gain region harboring the MYCN gene remain unclear. The aim of this study was to compare the biological and clinical characteristics of these tumors with MYCN amplified and nonamplified neuroblastoma and to determine their impact on disease outcome. Samples from 177 patients were analyzed by fluorescence in situ hybridization, including MYCN, 1p, 17q, and 11q regions; 2p gain was identified in 25 patients, MYCN amplification in 31, and no amplification in 121 patients. Patients with 2p gain had a significantly worse 5-year event-free survival rate than patients with no MYCN amplified (P < 0.001), and an intermediate 5-year overall survival rate difference existed between the MYCN amplified tumors (P = 0.025) and nonamplified (P = 0.003) groups. All of the 2p gain samples were associated with segmental and/or numerical alterations in the other tested regions. The presence of segmental alterations with or without MYCN amplification was recently found to be the strongest predictor of relapse in a multivariate analysis. The results of the present study suggest that the determination of MYCN gene copy number relative to chromosome 2, when evaluating MYCN status at diagnosis, may help to reveal the underlying genetic pattern of these tumors and better understand their clinical behavior.

Transcribed-Ultra Conserved Region expression is associated with outcome in high-risk neuroblastoma

Background

Neuroblastoma is the most common, pediatric, extra-cranial, malignant solid tumor. Despite multimodal therapeutic protocols, outcome for children with a high-risk clinical phenotype remains poor, with long-term survival still less than 40%. Hereby, we evaluated the potential of non-coding RNA expression to predict outcome in high-risk, stage 4 neuroblastoma.

Methods

We analyzed expression of 481 Ultra Conserved Regions (UCRs) by reverse transcription-quantitative real-time PCR and of 723 microRNAs by microarrays in 34 high-risk, stage 4 neuroblastoma patients.

Results

First, the comparison of 8 short- versus 12 long-term survivors showed that 54 UCRs were significantly (P < 0.0491) over-expressed in the former group. For 48 Ultra Conserved Region (UCRs) the expression levels above the cut-off values defined by ROC curves were strongly associated with good-outcome (OS: 0.0001 <P < 0.0185, EFS: 0.0001 <P < 0.0491). Then we tested the Transcribed-UCR (T-UCR) threshold risk-prediction model on an independent cohort of 14 patients. The expression profile of 28 T-UCRs was significantly associated to prognosis and at least 15 up-regulated T-UCRs are needed to discriminate (P < 0.0001) short- from long-survivors at the highest sensitivity and specificity (94.12%). We also identified a signature of 13 microRNAs differently expressed between long- and short-surviving patients. The comparative analysis of the two classes of non-coding RNAs disclosed that 9 T-UCRs display their expression level that are inversely correlated with expression of 5 complementary microRNAs of the signature, indicating a negative regulation of T-UCRs by direct interaction with microRNAs. Moreover, 4 microRNAs down-regulated in tumors of long-survivors target 3 genes implicated in neuronal differentiation, that are known to be over-expressed in low-risk tumors.

Conclusions

Our pilot study suggests that a deregulation of the microRNA/T-UCR network may play an important role in the pathogenesis of neuroblastoma. After further validation on a larger independent set of samples, such findings may be applied as the first T-UCR prognostic signature for high-risk neuroblastoma patients.

High-resolution array copy number analyses for detection of deletion, gain, amplification and copy-neutral LOH in primary neuroblastoma tumors: four cases of homozygous deletions of the CDKN2A gene

Background

Neuroblastoma is a very heterogeneous pediatric tumor of the sympathetic nervous system showing clinically significant patterns of genetic alterations. Favorable tumors usually have near-triploid karyotypes with few structural rearrangements. Aggressive stage 4 tumors often have near-diploid or near-tetraploid karyotypes and structural rearrangements. Whole genome approaches for analysis of genome-wide copy number have been used to analyze chromosomal abnormalities in tumor samples. We have used array-based copy number analysis using oligonucleotide single nucleotide polymorphisms (SNP) arrays to analyze the chromosomal structure of a large number of neuroblastoma tumors of different clinical and biological subsets.

Results

Ninety-two neuroblastoma tumors were analyzed with 50 K and/or 250 K SNP arrays from Affymetrix, using CNAG3.0 software. Thirty percent of the tumors harbored 1p deletion, 22% deletion of 11q, 26% had MYCN amplification and 45% 17q gain. Most of the tumors with 1p deletion were found among those with MYCN amplification. Loss of 11q was most commonly seen in tumors without MYCN amplification. In the case of MYCN amplification, two types were identified. One type displayed simple continuous amplicons; the other type harbored more complex rearrangements. MYCN was the only common gene in all cases with amplification. Complex amplification on chromosome 12 was detected in two tumors and three different overlapping regions of amplification were identified. Two regions with homozygous deletions, four cases with CDKN2A deletions in 9p and one case with deletion on 3p (the gene RBMS3) were also detected in the tumors.

Conclusion

SNP arrays provide useful tools for high-resolution characterization of significant chromosomal rearrangements in neuroblastoma tumors. The mapping arrays from Affymetrix provide both copy number and allele-specific information at a resolution of 10–12 kb. Chromosome 9p, especially the gene CDKN2A, is subject to homozygous (four cases) and heterozygous deletions (five cases) in neuroblastoma tumors.

Molecular biology of neuroblastoma

Neuroblastoma is one of the most frequently occurring solid tumours in children, especially in the first year of life, when it accounts for 50% of all tumours. It is the second most common cause of death in children, only preceded by accidents. The most peculiar characteristic of neuroblastoma is its clinical heterogeneity. Approximately half of the cases are classified as high risk, with overall survival rates around 40% despite intensive multimodal therapy. Nevertheless, other subsets of neuroblastomas will undergo spontaneous regression and others will show very slow progression. Despite many advances in the past three decades, neuroblastoma has remained an enigmatic challenge to clinical and basic scientists. Elucidation of the exact molecular pathways of neuroblastoma will enable researchers and clinicians to stratify the disease and adapt therapy to the risk of relapse or progression. This review focuses on recent advances in our understanding of the biology of this complex paediatric tumour. Neuroblastoma is already one of the first examples for the use of tumoral genetic markers as a tool for defining tumour behaviour and to aid clinical staging.

Genes proximal and distal to MYCN are highly expressed in human neuroblastoma as visualized by comparative expressed sequence hybridization

MYCN amplification is associated with poor prognosis in neuroblastoma disease. To improve our understanding of the influence of the MYCN amplicon and its corresponding expression, we investigated the 2p expression pattern of MYCN amplified (n = 13) and nonamplified (n = 4) cell lines and corresponding primary tumors (n = 3) using the comparative expressed sequence hybridization technique. All but one MYCN amplified cell line displayed overexpression at 2p. Expression peaks were observed frequently at 2pter and less frequently at 2p24 (MYCN locus), 2p23.3-23.2, and/or 2p23.1. Importantly, cell lines and two corresponding primary tumors displayed expression peaks at similar loci. No significant 2p24 expression level was observed for those cell lines displaying a low amplification rate (n = 3) by comparative genomic hybridization. Only the cell lines with an enhanced peak at 2p23.2-23.3 displayed coamplification of the ALK gene (2p23.2), reported to be associated with unfavorable prognosis. Finally, two of four cell lines without MYCN amplification, both derived from patients with poor outcome, also showed an expression peak at 2p23.2. These data indicate that, besides MYCN, other genes proximal and distal to MYCN are highly expressed in neuroblastoma. The prognostic significance of expression peaks at 2p23.2-23.3, independent of MYCN and ALK status, remains to be investigated.

Influence of 17q gain and promoter polymorphisms on mRNA expression of somatostatin receptor type 2 in neuroblastoma

BACKGROUND

Neuroblastoma, the most frequent solid extracranial tumor in children, is characterized by a wide spectrum of clinical behaviours. We previously reported that high expression of somatostatin receptor type-2 (sst2) mRNA is associated to increased overall and event free survival. Several genetic abnormalities are detected in neuroblastomas, frequently involving balanced and/or unbalanced gain on the long arm on chromosome 17, the same region containing sst2 gene.

METHODS

In this study we detected balanced and/or unbalanced 17q gain in 50 neuroblastomas. Since two polymorphisms in sst2 promoter (-57 C>G and -83 A>G) were previously described as responsible for an in vitro reduction of sst2 mRNA expression, promoter sequencing was also performed in the same samples. The results were compared to sst2 mRNA expression, measured by real-time RT-PCR.

RESULTS

The frequency of 17q gain (14/50 neuroblastomas) was significantly associated to sst2 mRNA over-expression (Fischer's exact test: p=0.0012). The sst2 expression was significant higher both in balance and unbalance 17q amplifications (ANOVA: p=0.04). Conversely, we found a reduction of sst2 mRNA in neuroblastomas with -57 C>G promoter polymorphism (ANOVA: p=0.03).

CONCLUSION

We highlighted that 17q gain and promoter polymorphisms can play a role into the regulation of sst2 expression in neuroblastomas.

Neuroblastoma

The clinical hallmark of neuroblastoma is heterogeneity, with the likelihood of cure varying widely according to age at diagnosis, extent of disease, and tumour biology. A subset of tumours will undergo spontaneous regression while others show relentless progression. Around half of all cases are currently classified as high-risk for disease relapse, with overall survival rates less than 40% despite intensive multimodal therapy. This Seminar focuses on recent advances in our understanding of the biology of this complex paediatric solid tumour. We outline plans for the development of a uniform International Neuroblastoma Risk Group (INRG) classification system, and summarise strategies for risk-based therapies. We also update readers on new discoveries related to the underlying molecular pathogenesis of this tumour, with special emphasis on advances that are translatable to the clinic. Finally, we discuss new approaches to treatment, including recently discovered molecular targets that might provide more effective treatment strategies with the potential for less toxicity.

High-resolution analysis of allelic imbalance in neuroblastoma cell lines by single nucleotide polymorphism arrays

Genomic copy number changes are detectable in many malignancies, including neuroblastoma, using techniques such as comparative genomic hybridization (CGH), microsatellite analysis, conventional karyotyping, and fluorescence in situ hybridization (FISH). We report the use of 10K single nucleotide polymorphism (SNP) microarrays to detect copy number changes and allelic imbalance in six neuroblastoma cell lines (IMR32, SHEP, NBL-S, SJNB-1, LS, and SKNBE2c). SNP data were generated using the GeneChip DNA Analysis and GeneChip chromosome copy number software (Affymetrix). SNP arrays confirmed the presence of all previously reported cytogenetic abnormalities in the cell lines, including chromosome 1p deletion, MYCN amplification, gain of 17q and 11q, and 14q deletions. In addition, the SNP arrays revealed several chromosome gains and losses not detected by CGH or karyotyping; these included gain of 8q21.1 approximately 24.3 and gain of chromosome 12 in IMR-32 cells; loss at 4p15.3 approximately 16.1 and loss at 16p12.3 approximately 13.2, 11q loss with loss of heterozygosity (LOH) at 11q14.3 approximately 23.3 in SJNB-1 cells; and loss at 8p21.2 approximately 23.3 and 9p21.3 approximately 22.1 with corresponding LOH in SHEP cells. The SNP arrays refined the mapping of the 2p amplicons in LS, BE2c, and IMR-32 cell lines, the 12q amplicon in LS cells, and also identified an 11q13 amplicon in LS cells. There was good concordance among SNP arrays, CGH, and karyotyping. SNP array analysis is a powerful tool for the detection of allelic imbalance in neuroblastoma and also allows identification of LOH without changes in copy number (uniparental disomy).