PHOX2B is a novel and specific marker for minimal residual disease testing in neuroblastoma

Neuroblastoma mRNAs predict outcome in children with stage 4 neuroblastoma: a European HR-NBL1/SIOPEN study

PURPOSE

To evaluate the hypothesis that detection of neuroblastoma mRNAs by reverse transcriptase quantitative polymerase chain reaction (RTqPCR) in peripheral blood (PB) and bone marrow aspirates (BM) from children with stage 4 neuroblastoma are clinically useful biomarkers of risk.

METHODS

RTqPCR for paired-like homeobox 2b (PHOX2B), tyrosine hydroxylase (TH), and doublecortin (DCX) mRNA in PB and BM of children enrolled onto the High-Risk Neuroblastoma Trial-1 of the European Society of Pediatric Oncology Neuroblastoma Group (HR-NBL1/SIOPEN) was performed at diagnosis and after induction therapy.

RESULTS

High levels of TH, PHOX2B, or DCX mRNA in PB or BM at diagnosis strongly predicted for worse event-free survival (EFS) and overall survival (OS) in a cohort of 290 children. After induction therapy, high levels of these mRNAs predicted worse EFS and OS in BM but not in PB. Combinations of mRNAs in BM did not add to the predictive power of any single mRNA. However, in the original (n = 182) and validation (n = 137) PB cohorts, high TH (log10TH > 0.8) or high PHOX2B (log10PHOX2B > 0.28) identify 19% of children as ultrahigh risk, with 5-year EFS and OS rates of 0%; OS rate was 25% (95% CI, 16% to 36%) and EFS rate was 38% (95% CI, 28% to 49%) in the remaining children. The magnitude of reduction in mRNA level between diagnosis and postinduction therapy in BM or PB was not of additional predictive value.

CONCLUSION

High levels of TH and PHOX2B mRNA in PB at diagnosis objectively identify children with ultrahigh-risk disease who may benefit from novel treatment approaches. The level of TH, PHOX2B, and DCX mRNA in BM and/or PB at diagnosis might contribute to an algorithm to improve stratification of children for treatment.

Early negative minimal residual disease in bone marrow after immunotherapy is less predictive of late or non-marrow relapse among patients with high-risk stage 4 neuroblastoma

Molecular detection of minimal residual disease (MRD) measured by quantitative reverse transcription-polymerase chain reaction using a four-marker panel in the bone marrow (BM) after only two treatment cycles of anti-GD2 immunotherapy was a strong independent outcome predictor among high-risk patients with stage 4 neuroblastoma in first remission. While 32 of 46 MRD-negative patients relapsed within 2 years from immunotherapy, only four had marrow relapse; in three of these four patients, MRD turned positive in the subsequent BM. We conclude that negative MRD in the post-cycle two BM was rarely associated with BM relapse, but it did not exclude recurrences at other sites.

Polymorphisms in the calcium-sensing receptor gene are associated with clinical outcome of neuroblastoma

Background

Neuroblastic tumors include the neuroblastomas, ganglioneuroblastomas, and ganglioneuromas. Clinical behavior of these developmental malignancies varies from regression to aggressive growth with metastatic dissemination. Several clinical, histological, genetic, and biological features are associated with this diversity of clinical presentations. The calcium-sensing receptor (CaSR) is a G-protein coupled receptor with a key role in calcium homeostasis. We have previously reported that it is expressed in benign, differentiated neuroblastic tumors, but silenced by genetic and epigenetic events in unfavorable neuroblastomas. We have now analyzed three functionally relevant polymorphisms clustered at the signal transduction region of the CaSR (rs1801725, rs1042636 and rs1801726) to assess if genetic variants producing a less active receptor are associated with more aggressive disease course.

Methods

Polymorphisms were analyzed in DNA samples from 65 patients using specific Taqman Genotyping Assays.

Results

Mildly inactivating variant rs1801725 was associated with clinical stage 4 (P = 0.002) and the histological subgroup of undifferentiated neuroblastomas (P = 0.046). Patients harboring this polymorphism had significantly lower overall (P = 0.022) and event-free survival (P = 0.01) rates than those who were homozygous for the most common allele among Caucasians. However, this single locus genotype was not independently associated with outcome in multivariate analyses. Conversely, the tri-locus haplotype TAC was independently associated with an increased risk of death in the entire cohort (Hazard Ratio = 2.45; 95% Confidence Interval [1.14–5.29]; P = 0.022) and also in patients diagnosed with neuroblastomas (Hazard Ratio = 2.74; 95% Confidence Interval [1.20–6.25]; P = 0.016).

Conclusions

The TAC haplotype includes the moderately inactivating variant rs1801725 and absence of the gain-of-function rs1042636 polymorphism. Thus, its association with metastatic disease and poor outcome would add to our previous data and further support that inactivation of the CaSR gene is a mechanism associated with neuroblastoma malignant behavior.

PHOX2B immunolabeling: a novel tool for the diagnosis of undifferentiated neuroblastomas among childhood small round blue-cell tumors

Peripheral neuroblastic tumors are the most commonly occurring extracranial tumors in children. Although a reliable diagnosis is achievable in the majority of cases, diagnosis of a minority of peripheral neuroblastic tumor cases (especially undifferentiated neuroblastoma) poses a challenge compared with that of other pediatric small round blue-cell tumors. A panel of immunohistochemical markers and fusion transcripts is available for the diagnosis of such tumors, but the markers for neuroblastoma lack specificity and sensitivity. As the transcription factor PHOX2B is highly specific for the peripheral autonomic nervous system from which peripheral neuroblastic tumors are derived, we have assessed PHOX2B immunolabeling as a diagnostic tool in pediatric small round blue-cell tumors. We observed PHOX2B expression in all peripheral neuroblastic tumors, paragangliomas, and pheochromocytomas tested but in no other pediatric tumors among the 388 cases studied by expression microarray and the 109 cases studied by immunohistochemical analysis. We then assessed the results of PHOX2B immunohistochemistry in 12 cases of undifferentiated pediatric neoplasms: PHOX2B was expressed in 6/6 undifferentiated neuroblastomas and in no other small round blue-cell tumors. Finally, we showed that PHOX2B immunohistochemical analysis improves the diagnosis of undifferentiated neuroblastoma with high specificity and sensitivity.

Neuroblastoma: the impact of biology and cooperation leading to personalized treatments

Neuroblastoma is the most common extra-cranial solid tumor in children. It is a heterogeneous disease, consisting of neural crest-derived tumors with remarkably different clinical behaviors. It can present in a wide variety of ways, including lesions which have the potential to spontaneously regress, or as an extremely aggressive form of metastatic cancer which is resistant to all forms of modern therapy. They can arise anywhere along the sympathetic nervous system. The median age of presentation is approximately 18 months of age. Urinary catecholamines (HVA and VMA) are extremely sensitive and specific tumor markers and are used in diagnosis, treatment response assessment and post-treatment surveillance. The largest national treatment groups from North America, Europe and Japan have formed the International Neuroblastoma Risk Group Task Force (INRG) to identify prognostic factors, to understand the mechanisms of tumorigenesis in this rare disease and to develop multi-modality therapies to improve outcomes and decrease treatment-related toxicities. This international cooperation has resulted in a significant leap in our understanding of the molecular pathogenesis of neuroblastoma. Lower staged disease can be cured if the lesion is resectable. Treatment of unresectable disease (loco-regional and metastatic) is stratified depending on clinical features (age at presentation, staging investigations) and specific tumor biological markers that include histopathological analyses, chromosomal abnormalities and the quantification of expression of an oncogene (MYCN). Modern treatment of high-risk neuroblastoma is the paradigm for the evolution of therapy in pediatric oncology. Outcomes have improved substantially with multi-modality therapy, including chemotherapy, surgery, radiation therapy, myeloablative therapy with stem cell transplant, immunotherapy and differentiation therapy; these comprise the standard of care worldwide. In addition, newer targeted therapies are being tested in phase I/II trials. If successful these agents will be incorporated into mainstream treatment programs.

Stability of PCR targets for monitoring minimal residual disease in neuroblastoma

In neuroblastoma (NB) patients, minimal residual disease (MRD) can be detected by real-time quantitative PCR (qPCR) using NB-specific target genes, such as PHOX2B and TH. However, it is unknown whether the mRNA levels of these targets vary either during treatment or at relapse. If marker genes are not stably expressed, estimation of MRD levels in bone marrow (BM) or peripheral blood will be hampered. We studied the stability of a panel of qPCR markers in primary tumors at diagnosis compared with i) paired metastasis (n = 7), ii) treated (n = 10), and iii) relapse (n = 6) tumors. We also compared relative expression of the targets in iv) primary tumors and BM at diagnosis (n = 17), v) BM and peripheral blood at diagnosis (n = 20), vi) BM at diagnosis and during treatment (n = 26), and vii) BM from different puncture sides (n = 110). Especially at diagnosis, PCR target expression is quite stable. Accurate quantification is possible when expression level can be related to the primary tumor; however, PCR target expression can alter on treatment and at relapse. If the median value of relative expression of a panel of PCR targets is used, most variations due to treatment and outgrowth of subclones level out, allowing for reliable application and quantification of MRD-PCR targets in NB patients.

Multiple target molecular monitoring of bone marrow and peripheral blood samples from patients with localized neuroblastoma and healthy donors

BACKGROUND

Multiple target molecular monitoring of minimal residual disease in neuroblastoma (NB) patients may increase sensitivity and overcome tumor heterogeneity. However, multiple target analysis is costly and time consuming, thus improvement with respect to single target monitoring needs to be achieved.

PROCEDURES

Italian patients with localized NB were evaluated at diagnosis for TH, GD2-s, DDC, DCX, ELAV-4, STX, and Phox2b mRNA expressions. Patients with metastatic NB were tested as positive controls, together with NB primary tumors and cell lines, while healthy donors were tested as negative controls.

RESULTS

All NB-related markers but Phox2b were expressed in healthy donors, and in a high percentage of patients with localized NB without association with clinical events. The introduction of cut-off levels increased marker specificity, although the percentage of positive results was only slightly modified. While TH positivity in PB samples significantly associated with a worse prognosis, a paradox association was found for GD2-s mRNA expression. No correlation and agreement between quantitative and qualitative results obtained with the two assays were found. In the set of samples tested for all markers, no pattern of expression was found to be associated with a specific clinical situation.

CONCLUSION

These findings suggest that positive molecular results may not reflect the presence of disease, and that correlation among different markers is small in condition of low tumor burden. Thus, to reduce cost and amount of precious samples, in addition to TH, whose prognostic value was confirmed, only Phox2b warrants further evaluation in multi-center, prospective studies for high risk patients.

Methylated RASSF1a is the first specific DNA marker for minimal residual disease testing in neuroblastoma

PURPOSE

PCR-based detection of minimal residual disease (MRD) in neuroblastoma (NB) is presently based on NB-specific transcripts. However, the expression of these targets varies between patients and upon treatment, and only PHOX2B is truly specific. RASSF1a is methylated (RASSF1a(M)) in NB, and we investigated whether it can serve as a specific and stable DNA MRD marker.

PATIENTS AND METHODS

The RASSF1a(M)-specific quantitative real-time PCR was tested on control bone marrow (BM; n = 50), on 71 NB tumors, and on 159 clinical BM samples at diagnosis and at follow-up of 77 patients. Results were compared with a panel of RNA markers and correlated with prognosis.

RESULTS

RASSF1a(M) was present in all stage 4 and 4s tumors (n = 50) and in 86% stages 1 to 3 tumors (n = 21). The level of methylation in stage 4 NB was correlated with overall survival (P = 0.02). RASSF1a(M)-PCR was highly specific (only 1 amplification in 50 control samples tested in triplicate) and had a similar sensitivity as the RNA-based PCRs, as shown on clinical samples. Moreover, RASSF1a(M) enabled accurate quantification without need for the original tumor.

CONCLUSIONS

RASSF1a(M) is a novel, highly specific DNA marker for MRD detection in NB, equal to PHOX2B in specificity and sensitivity, and better suitable for MRD quantification. We propose to include RASSF1a(M) in further prospective MRD studies in NB alongside RNA MRD markers. In addition, this assay might also be applicable for detection of circulating tumor cells in patients with other cancers withRASSF1a(M) such as breast or lung cancer.

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.

Lung-residing metastatic and dormant neuroblastoma cells

The mechanism by which dormant tumor cells can begin growing after long periods of inactivity and accelerate disease recurrence is poorly understood. The present study characterizes dormant neuroblastoma (NB) cells, as well as metastatic cells, which reside in the same organ microenvironment. A xenograft model of human NB consisting of variants that generate nonmetastatic local tumors in the orthotopic inoculation site and variants that generate lung metastatic NB (MetNB) cells was developed in our laboratory. The present study shows that lungs of mice inoculated with nonmetastatic NB variants contain disseminated neuroblastoma (DisNB) human cells. Both DisNB and MetNB variants expressed a similar tumorigenicty phenotype in vivo, whereas the MetNB variants produced a heavy metastatic load and the DisNB variants produced no or little metastasis. A comparative in vitro characterization of MetNB and DisNB cells revealed similarities and differences. DisNB, but not MetNB cells, expressed the minimal residual disease markers PHOX2B and TH. MetNB cells demonstrated higher migratory capacity, an elevated matrix metalloproteinase (MMP) secretion, and a higher constitutive phosphorylation of extracellular signal-regulated kinase (ERK) than DisNB cells. We suggest that characteristics common to both MetNB and DisNB cells were acquired relatively early in the metastatic process and the characteristics that differ between these variants were acquired later. We hypothesize that the DisNB cells are metastasis precursors, which may progress toward metastasis under certain microenvironmental conditions.

Detection of human tumor cells by amplicon fusion site polymerase chain reaction (AFS-PCR)

Reliable diagnostic strategies for individuals with cancer demand practical methods for highly sensitive and specific detection of tumor cells. Amplification of genomic regions that include putative oncogenes is common in tumor cells of various types. Genomic array platforms offer the opportunity to identify and precisely map amplified genomic regions (ampGRs). The stable existence of these tumor cell–specific genomic aberrations during and after therapy, in theory, make ampGRs optimal targets for cancer diagnostics. In this study, we mapped ampGRs around the proto-oncogene MYCN of human neuroblastomas using a high-resolution tiling array (HR-TA). Based on the HR-TA data, we were able to precisely describe the telomeric and centromeric borders of the ampGRs and deduce virtual fusion sites of the joined ampGRs (amplicon fusion sites [AFSs]). These AFSs served as blueprints for the subsequent design of AFS bridging PCR assays (AFS-PCRs). Strikingly, these assays were absolutely tumor cell specific and capable of detecting 1 tumor cell in 1 × 10(6) to 8 × 10(6) control cells. We successfully proved the in vivo practicability of AFS-PCR by detecting and quantifying the specific AFS DNA of human MYCN-amplified neuroblastomas in the patients’ corresponding peripheral blood and bone marrow samples. Thus, we believe AFS-PCR could become a powerful and nevertheless feasible personalized diagnostic tool applicable to a large number of cancer patients, including children with MYCN-amplified neuroblastomas.

The prognostic value of fast molecular response of marrow disease in patients aged over 1 year with stage 4 neuroblastoma

BACKGROUND

Quantitative real-time (q)PCR for detection of minimal residual disease (MRD) in children with neuroblastoma (NB) can evaluate molecular bone marrow (BM) response to therapy, but the prognostic value of tumour kinetics in the BM during induction treatment remains to be established. The purpose of this study was to analyse at which time points MRD detection by sequential molecular assessment of BM was prognostic for overall survival (OS).

METHODS

In this single centre study, qPCR was performed with five NB-specific markers: PHOX2B, TH, DDC, GAP43 and CHRNA3, on 106 retrospectively analysed BM samples of 53 patients >1 year with stage 4 neuroblastoma. The prognostic impact of MRD at diagnosis (n = 39), at 3 months after diagnosis (n = 38) and after completing induction chemotherapy (n = 29) was assessed using univariate and bivariate Cox regression analyses.

RESULTS

There was no correlation between tumour load at diagnosis and outcome (p = 0.93). Molecular BM remission was observed in 11/38 (29%) of patients at 3 months after diagnosis and associated with favourable outcome (5-y-OS 62 ± 15.0% versus 19 ± 8%; p = 0.009). After completion of induction chemotherapy, BM of 41% (12/29) of the patients was still MRD positive, which was associated with poor outcome (5-y-OS 0% versus 52 ± 12%; p<0.001). For both time points, the prognostic value of molecular response remained significant in bivariate analysis.

CONCLUSIONS

MRD detection measured by a panel of NB specific-PCR targets could identify fast responders, who clear their BM early during treatment. Fast molecular response was a prognostic factor, associated with better outcome. Our data indicate that MRD analysis during induction therapy should be included in prospective MRD studies.

PHOX2B-mediated regulation of ALK expression: in vitro identification of a functional relationship between two genes involved in neuroblastoma

BACKGROUND

Neuroblastoma (NB) is a severe pediatric tumor originating from neural crest derivatives and accounting for 15% of childhood cancer mortality. The heterogeneous and complex genetic etiology has been confirmed with the identification of mutations in two genes, encoding for the receptor tyrosine kinase Anaplastic Lymphoma Kinase (ALK) and the transcription factor Paired-like Homeobox 2B (PHOX2B), in a limited proportion of NB patients. Interestingly, these two genes are overexpressed in the great majority of primary NB samples and cell lines. These observations led us to test the hypothesis of a regulatory or functional relationship between ALK and PHOX2B underlying NB pathogenesis.

METHODOLOGY/PRINCIPAL FINDINGS

Following this possibility, we first confirmed a striking correlation between the transcription levels of ALK, PHOX2B and its direct target PHOX2A in a panel of NB cell lines. Then, we manipulated their expression in NB cell lines by siRNA-mediated knock-down and forced over-expression of each gene under analysis. Surprisingly, PHOX2B- and PHOX2A-directed siRNAs efficiently downregulated each other as well as ALK gene and, consistently, the enhanced expression of PHOX2B in NB cells yielded an increment of ALK protein. We finally demonstrated that PHOX2B drives ALK gene transcription by directly binding its promoter, which therefore represents a novel PHOX2B target.

CONCLUSIONS/SIGNIFICANCE

These findings provide a compelling explanation of the concurrent involvement of these two genes in NB pathogenesis and are going to foster a better understanding of molecular interactions at the base of the disease. Moreover, this work opens new perspectives for NBs refractory to conventional therapies that may benefit from the design of novel therapeutic RNAi-based approaches for multiple gene targets.

Detecting minimal residual disease in neuroblastoma: the superiority of a panel of real-time quantitative PCR markers

BACKGROUND

PCR-based detection of minimal residual disease (MRD) in neuroblastoma (NB) patients can be used for initial staging and monitoring therapy response in bone marrow (BM) and peripheral blood (PB). PHOX2B has been identified as a sensitive and specific MRD marker; however, its expression varies between tumors. Therefore, a panel of markers could increase sensitivity.

METHODS

To identify additional MRD markers for NB, we selected genes by comparing SAGE (serial analysis of gene expression) libraries of healthy and NB tissues followed by extensive real-time quantitative PCR (RQ-PCR) testing in samples of tumors (n = 56), control BM (n = 51), PB (n = 37), and cell subsets. The additional value of a panel was determined in 222 NB samples from 82 Dutch stage 4 NB patients (54 diagnosis BM samples, 143 BM samples during/after treatment, and 25 PB samples).

RESULTS

We identified 2 panels of specific RQ-PCR markers for MRD detection in NB patients: 1 for analysis of BM samples (PHOX2B, TH, DDC, CHRNA3, and GAP43) and 1 for analysis of PB samples (PHOX2B, TH, DDC, DBH, and CHRNA3). These markers all showed high expression in NB tumors and no or low expression in control BM or PB samples. In patients' samples, the PHOX2B marker detected most positive samples. In PB samples, however, 3 of 7 PHOX2B-negative samples were positive for 1 or more markers, and in BM examinations during treatment, 7% (6 of 86) of the PHOX2B-negative samples were positive for another marker.

CONCLUSIONS

Because of differences in the sensitivities of the markers in BM and PB, we advise the use of 2 different panels to detect MRD in these compartments.