Minimal residual disease monitoring in neuroblastoma patients based on the expression of a set of real-time RT-PCR markers in tumor-initiating cells

A comprehensive overview of liquid biopsy applications in pediatric solid tumors

Liquid biopsies are emerging as an alternative source for pediatric cancer biomarkers with potential applications during all stages of patient care, from diagnosis to long-term follow-up. While developments within this field are reported, these mainly focus on dedicated items such as a specific liquid biopsy matrix, analyte, and/or single tumor type. To the best of our knowledge, a comprehensive overview is lacking. Here, we review the current state of liquid biopsy research for the most common non-central nervous system pediatric solid tumors. These include neuroblastoma, renal tumors, germ cell tumors, osteosarcoma, Ewing sarcoma, rhabdomyosarcoma and other soft tissue sarcomas, and liver tumors. Within this selection, we discuss the most important or recent studies involving liquid biopsy-based biomarkers, anticipated clinical applications, and the current challenges for success. Furthermore, we provide an overview of liquid biopsy-based biomarker publication output for each tumor type based on a comprehensive literature search between 1989 and 2023. Per study identified, we list the relevant liquid biopsy-based biomarkers, matrices (e.g., peripheral blood, bone marrow, or cerebrospinal fluid), analytes (e.g., circulating cell-free and tumor DNA, microRNAs, and circulating tumor cells), methods (e.g., digital droplet PCR and next-generation sequencing), the involved pediatric patient cohort, and proposed applications. As such, we identified 344 unique publications. Taken together, while the liquid biopsy field in pediatric oncology is still behind adult oncology, potentially relevant publications have increased over the last decade. Importantly, steps towards clinical implementation are rapidly gaining ground, notably through validation of liquid biopsy-based biomarkers in pediatric clinical trials.

Distinct Expression Profiles of Neuroblastoma-Associated mRNAs in Peripheral Blood and Bone Marrow of Non-High-Risk and High-Risk Neuroblastoma Patients

Non-high-risk (non-HR) neuroblastoma (NB) patients have excellent outcomes, with more than a 90% survival rate, whereas HR NB patients expect less than a 50% survival rate. Metastatic disease is the principal cause of death among both non-HR and HR NB patients. Previous studies have reported the significant but limited prognostic value of quantitative PCR (qPCR)-based assays, measuring overlapping but different sets of neuroblastoma-associated mRNAs (NB-mRNAs), to detect metastatic disease in both non-HR and HR patient samples. A droplet digital PCR (ddPCR)-based assay measuring seven NB-mRNAs (CRMP1, DBH, DDC, GAP43, ISL1, PHOX2B, and TH mRNAs) was recently developed and exhibited a better prognostic value for HR patient samples than qPCR-based assays. However, it remained to be tested on non-HR patient samples. In the present study, we employed the ddPCR-based assay to study peripheral blood (PB) and bone marrow (BM) samples collected at diagnosis from eight non-HR and eleven HR cases and characterized the expression profiles of NB-mRNAs. The most highly expressed NB-mRNAs in PB and BM differed between non-HR and HR cases, with the CRMP1 mRNA being predominant in non-HR cases and the GAP43 mRNA in HR cases. The levels of NB-mRNAs in PB and BM were 5 to 1000 times lower in non-HR cases than in HR cases. The PB to BM ratio of NB-mRNAs was 10 to 100 times higher in non-HR cases compared to HR cases. The present case series suggests that non-HR and HR NB patients have the distinct expression profiles of NB-mRNAs in their PB and BM.

Advances in liquid biopsy in neuroblastoma

Even with intensive treatment of high-risk neuroblastoma (NB) patients, half of high-risk NB patients still relapse. New therapies targeting the biological characteristics of NB have important clinical value for the personalized treatment of NB. However, the current biological markers for NB are mainly analyzed by tissue biopsy. In recent years, circulating biomarkers of NB based on liquid biopsy have attracted more and more attention. This review summarizes the analytes and methods for liquid biopsy of NB. We focus on the application of liquid biopsy in the diagnosis, prognosis assessment, and monitoring of NB. Finally, we discuss the prospects and challenges of liquid biopsy in NB.

Circulating Tumor DNA in Pediatric Cancer

The measurement of circulating tumor DNA (ctDNA) has gained increasing prominence as a minimally invasive tool for the detection of cancer-specific markers in plasma. In adult cancers, ctDNA detection has shown value for disease-monitoring applications including tumor mutation profiling, risk stratification, relapse prediction, and treatment response evaluation. To date, there are ctDNA tests used as companion diagnostics for adult cancers and it is not understood why the same cannot be said about childhood cancer, despite the marked differences between adult and pediatric oncology. In this review, we discuss the current understanding of ctDNA as a disease monitoring biomarker in the context of pediatric malignancies, including the challenges associated with ctDNA detection in liquid biopsies. The data and conclusions from pediatric cancer studies of ctDNA are summarized, highlighting treatment response, disease monitoring and the detection of subclonal disease as applications of ctDNA. While the data from retrospective studies highlight the potential of ctDNA, large clinical trials are required for ctDNA analysis for routine clinical use in pediatric cancers. We outline the requirements for the standardization of ctDNA detection in pediatric cancers, including sample handling and reproducibility of results. With better understanding of the advantages and limitations of ctDNA and improved detection methods, ctDNA analysis may become the standard of care for patient monitoring in childhood cancers.

Investigation of patient factors associated with the number of transfusions required during chemotherapy for high-risk neuroblastoma

BACKGROUND

Blood transfusion is an important supportive care for high-risk neuroblastoma. When the number of transfusions increases, transfusion-associated adverse reactions may be more problematic. However, the factors determining the degree of myelosuppression and the number of transfusions during chemotherapy for high-risk neuroblastoma remain unclear.

MATERIALS AND METHODS

We investigated patient factors determining the number of required transfusions in 15 high-risk neuroblastoma patients who received five courses of chemotherapy. Clinical data, cytokine profile and colony-forming assay with bone marrow samples at diagnosis were analysed.

RESULTS

The required number of transfusions of both platelets and erythrocytes decreased once in the second course and then increased as the course progressed. The variability among cases increased as the chemotherapy course progressed. In cases of low peripheral blood platelet count and lower fibrinogen level at diagnosis, the number of platelet transfusions was higher during chemotherapy. In contrast, there was a negative correlation between the forming ability of granulocyte-macrophage or erythroid colonies and the number of erythrocyte transfusions in the latter period.

CONCLUSION

In the early stages of chemotherapy, bone marrow infiltration in neuroblastoma and/or coagulopathy complication may cause thrombocytopenia and requirement of platelet transfusion; conversely, in the later stages, the number of erythrocyte transfusions may be defined by the patient's inherent hematopoietic ability. These factors may be useful in predicting the required number of transfusions.

Discovery of Spatial Peptide Signatures for Neuroblastoma Risk Assessment by MALDI Mass Spectrometry Imaging

Simple Summary

The childhood tumor, neuroblastoma, has a broad clinical presentation. Risk assessment at diagnosis is particularly difficult in molecularly heterogeneous high-risk cases. Here we investigate the potential of imaging mass spectrometry to directly detect intratumor heterogeneity on the protein level in tissue sections. We show that this approach can produce discriminatory peptide signatures separating high- from low- and intermediate-risk tumors, identify 8 proteins aassociated with these signatures and validate two marker proteins using tissue immunostaining that have promise for further basic and translational research in neuroblastoma. We provide proof-of-concept that mass spectrometry-based technology could assist early risk assessment in neuroblastoma and provide insights into peptide signature-based detection of intratumor heterogeneity.

Abstract

Risk classification plays a crucial role in clinical management and therapy decisions in children with neuroblastoma. Risk assessment is currently based on patient criteria and molecular factors in single tumor biopsies at diagnosis. Growing evidence of extensive neuroblastoma intratumor heterogeneity drives the need for novel diagnostics to assess molecular profiles more comprehensively in spatial resolution to better predict risk for tumor progression and therapy resistance. We present a pilot study investigating the feasibility and potential of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to identify spatial peptide heterogeneity in neuroblastoma tissues of divergent current risk classification: high versus low/intermediate risk. Univariate (receiver operating characteristic analysis) and multivariate (segmentation, principal component analysis) statistical strategies identified spatially discriminative risk-associated MALDI-based peptide signatures. The AHNAK nucleoprotein and collapsin response mediator protein 1 (CRMP1) were identified as proteins associated with these peptide signatures, and their differential expression in the neuroblastomas of divergent risk was immunohistochemically validated. This proof-of-concept study demonstrates that MALDI-MSI combined with univariate and multivariate analysis strategies can identify spatially discriminative risk-associated peptide signatures in neuroblastoma tissues. These results suggest a promising new analytical strategy improving risk classification and providing new biological insights into neuroblastoma intratumor heterogeneity.

Limited correlation between tumor markers and minimal residual disease detected by seven neuroblastoma-associated mRNAs in high-risk neuroblastoma patients

Vanillylmandelic acid (VMA), homovanillic acid (HVA), neuron-specific enolase (NSE) and lactate dehydrogenase (LDH) are classical tumor markers and are used as standard clinical evaluations for patients with neuroblastoma (NB). Minimal residual disease (MRD) can be monitored by quantifying several sets of NB-associated mRNAs in the bone marrow (BM) and peripheral blood (PB) of patients with NB. Although MRD in BM and PB has been revealed to be a strong prognostic factor that is independent of standard clinical evaluations, its interrelation with tumor markers remains uncharacterized. The present study determined the levels of tumor markers (VMA, HVA, NSE and LDH) and MRD (BM-MRD and PB-MRD) in 133 pairs of concurrently collected BM, PB and urine samples from 19 patients with high-risk NB. The patients were evaluated during the entire course of treatment, which included 10 diagnoses, 32 treatments, 36 post-treatment, 9 relapses and 46 post-relapse sample pairs. The level of BM-MRD and PB-MRD was determined by quantifying 7 NB-mRNAs (collapsin response mediator protein 1, dopamine beta-hydroxylase, dopa decarboxylase, growth-associated protein 43, ISL LIM homeobox 1, pairedlike homeobox 2b and tyrosine hydroxylase) using droplet digital PCR. In overall sample pairs, tumor markers (VMA, HVA, NSE and LDH) demonstrated weak but significant correlations (P<0.011) with BM-MRD and PB-MRD. In subgroups according to each patient evaluation, the degree of correlation between tumor markers and MRD became stronger in patients with adrenal gland tumors, BM metastasis at diagnosis and relapse/regrowth compared with overall sample pairs. In contrast, tumor markers demonstrated variable correlations with MRD in subgroups according to each sample evaluation (BM infiltration at sampling, collection time point and disease status). The results suggested that tumor markers may demonstrate limited correlation with MRD in patients with high-risk NB.

The Application of and Factors Influencing, the NB5 Assay in Neuroblastomas

Purpose

The NB5 assay was performed in bone marrow (BM) and peripheral blood (PB) to detect neuroblastomas (NBs) with micrometastases. The sensitivity and factors influencing the NB5 assay were preliminarily evaluated.

Methods

The NB5 assay uses RT-PCR to detect the co-expression of five mRNAs from the neuroblastoma-associated genes, CHGA, DCX, DDC, PHOX2B, and TH. We enrolled 180 cases of neuroblastoma and 65 cases of non-neuroblastoma. Bone marrow and peripheral blood were collected from every patient. The gold standard for the diagnosis of NB was pathological evaluation of solid tumor specimens or bone marrow biopsies (BMBs) from hematological tumors. STATA version 15 and SPSS version 17 software were used for analysis.

Results

We found that 17 patients were BMB (+), and they were diagnosed as the International Neuroblastoma Staging System (INSS) stage IV and the high-risk group. All 17 patients were BM (+), while 15 patients were PB (+) (15/17, 88.2%). Among the 163 children who were BMB (-), 56 were BM (+), 40 were PB (+), and 36 were BM (+) and PB (+). The sensitivity of the NB5 assay in BM (40.5%) and PB (30.5%) was significantly higher than the sensitivity of BMB (9.4%, P = 0.000). In the non-NB group, four cases were BM (+) and one case was PB (+). The specificity of the NB5 assay in BM and PB was 93.8% and 98.5%, respectively. The sensitivity of the NB5 assay in both BM and PB in INSS stage IV patients was significantly higher than that in INSS stage I-II patients (P <0.05). The sensitivity of the NB5 assay in both BM and PB in the high-risk group was significantly higher than that in the middle-low-risk groups (P = 0.0001). Logistic regression analyses indicated that liver metastases and bone metastases were the primary factors influencing the sensitivity of the NB5 assay in BM and PB (P <0.05).

Conclusions

The NB5 assay had significantly higher sensitivity than the pathological analysis of BMB in detecting NB with micrometastases. The NB5 assay had higher sensitivity in INSS stage IV or the high-risk group. Liver metastases and bone metastases were the primary factors that affected the sensitivity of the NB5 assay.

Minimal residual disease in high-risk neuroblastoma shows a dynamic and disease burden-dependent correlation between bone marrow and peripheral blood

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Bone marrow is the most frequent site of metastasis and relapse for neuroblastoma.

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Minimal residual disease has been identified in bone marrow and peripheral blood (BM-MRD and PB-MRD) by quantifying several sets of neuroblastoma-associated mRNAs.

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BM-MRD has significant prognostic information for high-risk neuroblastoma.

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BM-MRD and PB-MRD show a dynamic and disease burden-dependent correlation in high-risk neuroblastoma.

Neuroblastoma (NB) is the most common extracranial solid tumor in children and originates from sympathoadrenal or Schwann cell precursors derived from neural crest. These neural crest derivatives also constitute the hematopoietic and mesenchymal stem cells in bone marrow (BM) that is the most frequent site of NB metastasis and relapse. In NB patients, NB cells have been pathologically detected in BM and peripheral blood (PB), and minimal residual disease (MRD) in BM and PB (BM-MRD and PB-MRD) can be monitored by quantitating several sets of NB-associated mRNAs (NB-mRNAs). Although previous studies have shown varying degrees of correlation between BM-MRD and PB-MRD, the underlying factors and/or mechanisms remains unknown. In the present study, we determined the levels of BM-MRD and PB-MRD by quantitating seven NB-mRNAs in 133 pairs of concurrently collected BM and PB samples from 19 high-risk NB patients with clinical disease evaluation, and examined their correlation in overall and subgroups of sample pairs. The levels of BM-MRD and PB-MRD were moderately (r = 0.418, p < 0.001) correlated with each other in overall sample pairs. The correlation became strong (r = 0.725, p < 0.001), weak (r = 0.284, p = 0.008), and insignificant (p = 0.194) in progression, stable, and remission subgroups of sample pairs, respectively. It also became stronger in subgroups of sample pairs with poor treatment responses and poor prognostic factors. Present study suggests that MRD in high-risk NB shows a dynamic and disease burden-dependent correlation between BM and PB.

Kalirin-RAC controls nucleokinetic migration in ADRN-type neuroblastoma

The migrational propensity of neuroblastoma is affected by cell identity, but the mechanisms behind the divergence remain unknown. Using RNAi and time-lapse imaging, we show that ADRN-type NB cells exhibit RAC1- and kalirin-dependent nucleokinetic (NUC) migration that relies on several integral components of neuronal migration. Inhibition of NUC migration by RAC1 and kalirin-GEF1 inhibitors occurs without hampering cell proliferation and ADRN identity. Using three clinically relevant expression dichotomies, we reveal that most of up-regulated mRNAs in RAC1- and kalirin-GEF1-suppressed ADRN-type NB cells are associated with low-risk characteristics. The computational analysis shows that, in a context of overall gene set poverty, the upregulomes in RAC1- and kalirin-GEF1-suppressed ADRN-type cells are a batch of AU-rich element-containing mRNAs, which suggests a link between NUC migration and mRNA stability. Gene set enrichment analysis-based search for vulnerabilities reveals prospective weak points in RAC1- and kalirin-GEF1-suppressed ADRN-type NB cells, including activities of H3K27- and DNA methyltransferases. Altogether, these data support the introduction of NUC inhibitors into cancer treatment research.

Bottom up proteomics identifies neuronal differentiation pathway networks activated by cathepsin inhibition treatment in neuroblastoma cells that are enhanced by concurrent 13-cis retinoic acid treatment

Neuroblastoma is the second most common pediatric cancer involving the peripheral nervous system in which stage IVS metastatic tumors regress due to spontaneous differentiation. 13-cis retinoic acid (13-cis RA) is currently used in the clinic for its differentiation effects and although it improves outcomes, relapse is seen in half of high-risk patients. Combinatorial therapies have been shown to be more effective in oncotherapy and since cathepsin inhibition reduces tumor growth, we explored the potential of coupling 13-cis RA with a cathepsin inhibitor (K777) to enhance therapeutic efficacy against neuroblastoma. Shotgun proteomics was used to identify proteins affected by K777 and dual (13-cis RA/K777) treatment in neuroblastoma SK-N-SH cells. Cathepsin inhibition was more effective in increasing proteins involved in neuronal differentiation and neurite outgrowth than 13-cis RA alone, but the combination of both treatments enhanced the neuronal differentiation effect. SIGNIFICANCE: As neuroblastoma can spontaneously differentiate, determining which proteins are involved in differentiation can guide development of more accurate diagnostic markers and more effective treatments. In this study, we established a differentiation proteomic map of SK-N-SH cells treated with a cathepsin inhibitor (K777) and K777/13-cis RA (dual). Bioinformatic analysis revealed these treatments enhanced neuronal differentiation and axonogenesis pathways. The most affected proteins in these pathways may become valuable biomarkers of efficacy of drugs designed to enhance differentiation of neuroblastoma [1].

Increased plasma concentration of cell-free DNA precedes disease recurrence in children with high-risk neuroblastoma

Background

Neuroblastoma is the most common extracranial solid tumor of childhood. The high rate of recurrence is associated with a low survival rate for patients with high-risk neuroblastoma. There is thus an urgent need to identify effective predictive biomarkers of disease recurrence.

Methods

A total of 116 patients with high-risk neuroblastoma were recruited at Beijing Children’s Hospital between February 2015 and December 2017. All patients received multidisciplinary treatment, were evaluated for the therapeutic response, and then initiated on maintenance treatment. Blood samples were collected at the beginning of maintenance treatment, every 3 months thereafter, and at the time of disease recurrence. Plasma levels of cell-free DNA (cfDNA) were quantified by qPCR. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the ability of plasma cfDNA concentration to predict recurrence.

Results

Of the 116 patients, 36 (31.0%) developed recurrence during maintenance treatment. The median time to recurrence was 19.00, 9.00, and 8.00 months for patients who had achieved complete response (n = 6), partial response (n = 25), and stable disease (n = 5), respectively, after multidisciplinary treatment. The median plasma cfDNA concentration at the time of recurrence was significantly higher than the concentration in recurrence-free patients throughout maintenance treatment (29.34 ng/mL vs 10.32 ng/mL). Patients recorded a plasma cfDNA level ≥ 29 ng/mL an average of 0.55 months before diagnosis of disease recurrence. ROC analysis of the power of plasma cfDNA to distinguish between patients with or without recurrence yielded an area under the curve of 0.825, with optimal sensitivity and specificity of 80.6 and 71.3%, respectively, at a cfDNA level of 12.93 ng/mL.

Conclusions

High plasma cfDNA concentration is a potential molecular marker to signal disease recurrence in patients with high-risk neuroblastoma.

The pitfalls and promise of liquid biopsies for diagnosing and treating solid tumors in children: a review

Cell-free DNA profiling using patient blood is emerging as a non-invasive complementary technique for cancer genomic characterization. Since these liquid biopsies will soon be integrated into clinical trial protocols for pediatric cancer treatment, clinicians should be informed about potential applications and advantages but also weaknesses and potential pitfalls. Small retrospective studies comparing genetic alterations detected in liquid biopsies with tumor biopsies for pediatric solid tumor types are encouraging. Molecular detection of tumor markers in cell-free DNA could be used for earlier therapy response monitoring and residual disease detection as well as enabling detection of pathognomonic and therapeutically relevant genomic alterations.Conclusion: Existing analyses of liquid biopsies from children with solid tumors increasingly suggest a potential relevance for molecular diagnostics, prognostic assessment, and therapeutic decision-making. Gaps remain in the types of tumors studied and value of detection methods applied. Here we review the current stand of liquid biopsy studies for pediatric solid tumors with a dedicated focus on cell-free DNA analysis. There is legitimate hope that integrating fully validated liquid biopsy-based innovations into the standard of care will advance patient monitoring and personalized treatment of children battling solid cancers.What is Known:• Liquid biopsies are finding their way into routine oncological screening, diagnosis, and disease monitoring in adult cancer types fast.• The most widely adopted source for liquid biopsies is blood although other easily accessible body fluids, such as saliva, pleural effusions, urine, or cerebrospinal fluid (CSF) can also serve as sources for liquid biopsiesWhat is New:• Retrospective proof-of-concept studies in small cohorts illustrate that liquid biopsies in pediatric solid tumors yield tremendous potential to be used in diagnostics, for therapy response monitoring and in residual disease detection.• Liquid biopsy diagnostics could tackle some long-standing issues in the pediatric oncology field; they can enable accurate genetic diagnostics in previously unbiopsied tumor types like renal tumors or brain stem tumors leading to better treatment strategies.

Mesenchymal Neuroblastoma Cells Are Undetected by Current mRNA Marker Panels: The Development of a Specific Neuroblastoma Mesenchymal Minimal Residual Disease Panel

Patients with neuroblastoma in molecular remission remain at considerable risk for disease recurrence. Studies have found that neuroblastoma tissue contains adrenergic (ADRN) and mesenchymal (MES) cells; the latter express low levels of commonly used markers for minimal residual disease (MRD). We identified MES-specific MRD markers and studied the dynamics of these markers during treatment.

PATIENTS AND METHODS

Microarray data were used to identify genes differentially expressed between ADRN and MES cell lines. Candidate genes were then studied using real-time quantitative polymerase chain reaction in cell lines and control bone marrow and peripheral blood samples. After selecting a panel of markers, serial bone marrow, peripheral blood, and peripheral blood stem cell samples were obtained from patients with high-risk neuroblastoma and tested for marker expression; survival analyses were also performed.

RESULTS

PRRX1, POSTN, and FMO3 mRNAs were used as a panel for specifically detecting MES mRNA in patient samples. MES mRNA was detected only rarely in peripheral blood; moreover, the presence of MES mRNA in peripheral blood stem cell samples was associated with low event-free survival and overall survival. Of note, during treatment, serial bone marrow samples obtained from 29 patients revealed a difference in dynamics between MES mRNA markers and ADRN mRNA markers. Furthermore, MES mRNA was detected in a higher percentage of patients with recurrent disease than in those who remained disease free (53% v 32%, respectively; P = .03).

CONCLUSION

We propose that the markers POSTN and PRRX1, in combination with FMO3, be used for real-time quantitative polymerase chain reaction-based detection of MES neuroblastoma mRNA in patient samples because these markers have a unique pattern during treatment and are more prevalent in patients with poor outcome. Together with existing markers of MRD, these new markers should be investigated further in large prospective studies.

Bottom up proteomics reveals novel differentiation proteins in neuroblastoma cells treated with 13-cis retinoic acid

Neuroblastoma, a cancer of the sympathetic nervous system, is the second most common pediatric cancer. A unique feature of neuroblastoma is remission in some patients due to spontaneous differentiation of metastatic tumors. 13-cis retinoic acid (13-cis RA) is currently used in the clinic to treat neuroblastoma due to its differentiation inducing effects. In this study, we used shotgun proteomics to identify proteins affected by 13-cis RA treatment in neuroblastoma SK-N-SH cells. Our results showed that 13-cis RA reduced proteins involved in extracellular matrix synthesis and organization and increased proteins involved in cell adhesion and neurofilament formation. These changes indicate that 13-cis RA induces tumor cell differentiation by decreasing extracellular matrix rigidity and increasing neurite overgrowth. Differentially-affected proteins identified in this study may be novel biomarkers of drug efficacy in the treatment of neuroblastoma. SIGNIFICANCE: As neuroblastoma can spontaneously differentiate, determining which proteins are involved in differentiation can guide development of novel treatments. 13-cis retinoic acid is currently used in the clinic as a differentiation inducer. Here we have established a proteome map of SK-N-SH cells treated with 13-cis retinoic acid. Bioinformatic analysis revealed the involvement of development, differentiation, extracellular matrix assembly, collagen biosynthesis, and neurofilament bundle association. This proteome map provides information as to which proteins are important for differentiation and identifies networks that can be targeted by drugs to treat neuroblastoma [1].

Dynamics of Minimal Residual Disease in Neuroblastoma Patients

Neuroblastoma is a common extracranial solid tumor of neural crest (NC) origin that accounts for up to 15% of all pediatric cancer deaths. The disease arises from a transient population of NC cells that undergo an epithelial-mesenchymal transition (EMT) and generate diverse cell-types and tissues. Patients with neuroblastoma are characterized by their extreme heterogeneity ranging from spontaneous regression to malignant progression. More than half of newly diagnosed patients present highly metastatic tumors and are stratified into a high-risk group with dismal outcome. As many as 20% of high-risk patients have residual disease that is refractory or progressive during induction chemotherapy. Although a majority of high-risk patients achieve remission, larger part of those patients has minimal residual disease (MRD) that causes relapse even after additional consolidation therapy. MRD is composed of drug-resistant tumor cells and dynamically presented as cancer stem cells (CSCs) in residual tumors, circulating tumor cells (CTCs) in peripheral blood (PB), and disseminated tumor cells (DTCs) in bone marrow (BM) and other metastatic sites. EMT appears to be a key mechanism for cancer cells to acquire MRD phenotypes and malignant aggressiveness. Due to the restricted availability of residual tumors, PB and BM have been used to isolate and analyze CTCs and DTCs to evaluate MRD in cancer patients. In addition, recent technical advances make it possible to use circulating tumor DNA (ctDNA) shed from tumor cells into PB for MRD evaluation. Because MRD can be detected by tumor-specific antigens, genetic or epigenetic changes, and mRNAs, numerous assays using different methods and samples have been reported to detect MRD in cancer patients. In contrast to the tumor-specific gene-rearrangement-positive acute lymphoblastic leukemia (ALL) and the oncogenic fusion-gene-positive chronic myelogenous leukemia (CML) and several solid tumors, the clinical significance of MRD remains to be established in neuroblastoma. Given the extreme heterogeneity of neuroblastoma, dynamics of MRD in neuroblastoma patients will hold a key to the clinical validation. In this review, we summarize the biology and detection methods of cancer MRD in general and evaluate the available assays and clinical significance of neuroblastoma MRD to clarify its dynamics in neuroblastoma patients.

Opportunities and challenges of circulating biomarkers in neuroblastoma

Molecular analysis of nucleic acid and protein biomarkers is becoming increasingly common in paediatric oncology for diagnosis, risk stratification and molecularly targeted therapeutics. However, many current and emerging biomarkers are based on analysis of tumour tissue, which is obtained through invasive surgical procedures and in some cases may not be accessible. Over the past decade, there has been growing interest in the utility of circulating biomarkers such as cell-free nucleic acids, circulating tumour cells and extracellular vesicles as a so-called liquid biopsy of cancer. Here, we review the potential of emerging circulating biomarkers in the management of neuroblastoma and highlight challenges to their implementation in the clinic.

Circulating microRNA biomarkers for metastatic disease in neuroblastoma patients

In this study, the circulating miRNome from diagnostic neuroblastoma serum was assessed for identification of noninvasive biomarkers with potential in monitoring metastatic disease. After determining the circulating neuroblastoma miRNome, 743 miRNAs were screened in 2 independent cohorts of 131 and 54 patients. Evaluation of serum miRNA variance in a model testing for tumor stage, MYCN status, age at diagnosis, and overall survival revealed tumor stage as the most significant factor impacting miRNA abundance in neuroblastoma serum. Differential abundance analysis between patients with metastatic and localized disease revealed 9 miRNAs strongly associated with metastatic stage 4 disease in both patient cohorts. Increasing levels of these miRNAs were also observed in serum from xenografted mice bearing human neuroblastoma tumors. Moreover, murine serum miRNA levels were strongly associated with tumor volume. These findings were validated in longitudinal serum samples from metastatic neuroblastoma patients, where the 9 miRNAs were associated with disease burden and treatment response.

Early detection of tumor relapse/regrowth by consecutive minimal residual disease monitoring in high-risk neuroblastoma patients

Neuroblastoma is an aggressive pediatric tumor accounting for ~15% of cancer-associated mortalities in children. Despite the current intensive therapy, >50% of high-risk patients experience tumor relapse or regrowth caused by the activation of minimal residual disease (MRD). Although several MRD detection protocols using various reverse transcription-quantitative polymerase chain reaction (RT-qPCR) markers have been reported to evaluate the therapeutic response and disease status of neuroblastoma patients, their clinical significance remains elusive. The present study reports two high-risk neuroblastoma patients, whose MRD was consecutively monitored using 11 RT-qPCR markers (CHRNA3, CRMP1, DBH, DCX, DDC, GABRB3, GAP43, ISL1, KIF1A, PHOX2B and TH) during their course of treatment. The two patients initially responded to the induction therapy and reached MRD-negative status. The patients' MRD subsequently became positive with no elevation of their urinary homovanillic acid, urinary vanillylmandelic acid and serum neuron-specific enolase levels at 13 or 19 weeks prior to the clinical diagnosis of tumor relapse or regrowth. The present cases highlight the possibility of consecutive MRD monitoring using 11 markers to enable an early detection of tumor relapse or regrowth in high-risk neuroblastoma patients.

Polyphenols from marine brown algae target radiotherapy-coordinated EMT and stemness-maintenance in residual pancreatic cancer

INTRODUCTION

Therapy-associated onset of stemness-maintenance in surviving tumor-cells dictates tumor relapse/recurrence. Recently, we recognized the anti-pancreatic cancer (PC) potential of seaweed polyphenol manifolds and narrowed down three superior drug-deliverables that could serve as adjuvants and benefit PC cure. Utilizing the PC- cancer stem cells (PC-CSCs) grown ex vivo and mouse model of residual-PC, we investigated the benefits of seaweed polyphenols in regulating stemness-maintenance.

METHODS

ALDH(+)CD44(+)CD24(+) PC-CSCs from Panc-1, Panc-3.27, MiaPaCa-2, or BxPC-3 cells-derived xenografts grown ex vivo were either mock-irradiated, exposed to fractionated irradiation (FIR, 2Gy/D for 5 days), treated with polyphenols (100 μg/ml) of Hormophysa triquerta (HT-EA), Spatoglossum asperum (SA-EA) or Padina tetrastromatica (PT-EA) with/without FIR were examined for cell viability, transcription of 93 stem-cell-related molecules (QPCR profiling). Polyphenol-dependent regulation of FIR-transactivated Oct4, Zic3, EIF4C, Nanog, and LIF (QPCR) and functional translation of Nanog, SOX2, and OCT3/4 (immunoblotting) were examined in Panc-1/Panc-3.27/MiaPaCa-2/BxPC-3-xenografts derived PC-CSCs. Effect of seaweed-polyphenols in the regulation of EMT (N-Cadherin), pluripotency- (SOX2, OCT3/4, Nanog) and stemness-maintenance (PI3KR1, LIF, CD44) in therapy (FIR, 2Gy/D for 5D/wk for 3-weeks) resistant residual tumors were examined by tissue microarray construction and automated immunohistochemistry.

RESULTS

Ex vivo exposure of PC-CSCs to SA-EA, PT-EA and HT-EA exhibit dose-dependent inhibition of cell viability. FIR amplified the transcription of 69, 80, 74 and 77 stem-cell related genes in MiaPaCa-2-, Panc-1-, Panc-3.27- and BXPC3-established xenograft-derived ALDH(+)CD44(+)CD24(+)PC-CSCs. Treatment with SA-EA, PT-EA, or HT-EA completely suppressed FIR-activated stem-cell transcriptional machinery in ALDH(+)CD44(+)CD24(+)PC-CSCs established from MiaPaCa-2, Panc-1, Panc-3.27 and BXPC3 xenografts. QPCR validated EIF4C, OCT3/4, Nanog, LIF, and ZIC3 transcriptional profile outcomes. Nanog, Sox2, and OCT3/4 immunoblotting affirmed the PC-CSC radiosensitizing benefit of seaweed polyphenols. Residual-PC tissues microarrayed and immunostained after in vivo treatments recognized complete regulation of FIR-induced SOX2, OCT3/4, Nanog, LIF, CD44, PIK3R1, N-Cadherin, and E-Cadherin with SA-EA, PT-EA, and HT-EA.

CONCLUSIONS

These data, for the first time, documented the EMT/stemness-maintenance in therapy-resistant PC-CSCs. Further, the data suggest that seaweed polyphenols may inhibit PC relapse/recurrence by targeting therapy-orchestrated stem-cell signaling in residual cells.

Differential expression of minimal residual disease markers in peripheral blood and bone marrow samples from high-risk neuroblastoma patients

Neuroblastoma is an aggressive solid tumor that leads to tumor relapse in more than half of high-risk patients. Minimal residual disease (MRD) is primarily responsible for tumor relapses and may be detected in peripheral blood (PB) and bone marrow (BM) samples. To evaluate the disease status and treatment response, a number of MRD detection protocols based on either common or distinct markers for PB and BM samples have been reported. However, the correlation between the expression of MRD markers in PB and BM samples remains elusive in the clinical samples. In the present study, the expression of 11 previously validated MRD markers (CHRNA3, CRMP1, DBH, DCX, DDC, GABRB3, GAP43, ISL1, KIF1A, PHOX2B and TH) was determined in 23 pairs of PB and BM samples collected from seven high-risk neuroblastoma patients at the same time point, and the sample was scored as MRD-positive if one of the MRD markers exceeded the normal range. Although the number of MRD-positive samples was not significantly different between PB and BM samples, the two most sensitive markers for PB samples (CRMP1 and KIF1A) were different from those for BM samples (PHOX2B and DBH). There was no statistically significant correlation between the expression of MRD markers in the PB and BM samples. These results suggest that MRD markers were differentially expressed in PB and BM samples from high-risk neuroblastoma patients.