Measuring circulating neuroblastoma cells by quantitative reverse transcriptase-polymerase chain reaction analysis

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.

Liquid biomarkers for the management of paediatric neuroblastoma: an approach to personalised and targeted cancer therapy

Background:

Neuroblastoma is the most common extracranial solid tumour of infancy and accounts for about 6–10% of paediatric cancers. It has a biologically and clinically heterogeneous behaviour that ranges from spontaneous regression to cases of highly aggressive metastatic disease that could be unresponsive to standard therapy. In recent years, there have been several investigations into the development of various diagnostic, predictive and prognostic biomarkers towards personalised and targeted management of the disease.

Materials and Methods:

This paper reports on the review of current clinical and emerging biomarkers used in risk assessment, screening for early detection and diagnosis, prognostication and monitoring of the response of treatment of neuroblastoma in paediatric patients.

Conclusions:

Tumour markers can significantly improve diagnosis; however, the invasive, unpleasant and inconvenient nature of current tissue biopsies limits their applications, especially in paediatric patients. Therefore, the development of a non-invasive, reliable high accurate and personalised diagnostic tool capable of early detection and rapid response is the most promising step towards advanced cancer management from tumour diagnosis, therapy to patient monitoring and represents an important step towards the promise of precision, personalised and targeted medicine. Liquid biopsy assay with wide ranges of clinical applications is emerging to hold incredible potential for advancing cancer treatment and has greater promise for diagnostic purposes, identification and tracking of tumour-specific alterations during the course of the disease and to guide therapeutic decisions.

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.

The ionic charge of copper-64 complexes conjugated to an engineered antibody affects biodistribution

The development of biomolecules as imaging probes requires radiolabeling methods that do not significantly influence their biodistribution. Sarcophagine (Sar) chelators form extremely stable complexes with copper and are therefore a promising option for labeling proteins with (64)Cu. However, initial studies using the first-generation sarcophagine bifunctional chelator SarAr to label the engineered antibody fragment ch14.18-ΔCH2 (MW 120 kDa) with (64)Cu showed high tracer retention in the kidneys, presumably because the high local positive charge on the Cu(II)-SarAr moiety resulted in increased binding of the labeled protein to the negatively charged basal cells of the glomerulus. To test this hypothesis, ch14.18-ΔCH2 was conjugated with a series of Sar derivatives of decreasing positive charge and three commonly used macrocyclic polyaza polycarboxylate (PAC) bifunctional chelators (BFC). The immunoconjugates were labeled with (64)Cu and injected into mice, and PET/CT images were obtained at 24 and 48 h postinjection (p.i.). At 48 h p.i., ex vivo biodistribution was assessed. In addition, to demonstrate the potential of metastasis detection using (64)Cu-labeled ch14.18-ΔCH2, a preclinical imaging study of intrahepatic neuroblastoma tumors was performed. Reducing the positive charge on the Sar chelators decreased kidney uptake of Cu-labeled ch14.18-ΔCH2 by more than 6-fold, from >45 to <6% ID/g, whereas the uptake in most other tissues, including liver, was relatively unchanged. However, despite this dramatic decrease, the renal uptake of the PAC BFCs was generally lower than that of the Sar derivatives, as was the liver uptake. Uptake of (64)Cu-labeled ch14.18-ΔCH2 in neuroblastoma hepatic metastases was detected using PET.

Minimal residual disease is a prognostic marker for neuroblastoma with bone marrow infiltration

OBJECTIVE

This pilot study focused on whether flow cytometry (FCM) detection of minimal residual disease in bone marrow (BM) could predict the outcome of patients with advanced neuroblastoma (NB).

PATIENTS AND METHODS

Fifty-seven stage 4 NB patients with BM infiltration were enrolled in this study. All of them received NB-2001 protocol. BM samples were examined for tumor cell contamination by both morphology and FCM with CD45-FITC/CD81-PE/CD56-PECy5 monoclonal antibodies cocktail at diagnosis and after 4 courses of chemotherapy.

RESULTS

BM samples of all patients were positive at diagnosis by FCM, and samples from 30 patients became negative after 4 courses of chemotherapy, 10 patients relapsed (33.3%) in mean 45.5 months, range 7 to 69. Another 27 patients remained positive, and 20 of them relapsed (74.1%) in mean 24.2 months, range 8 to 48. There was a statistically significant difference in event-free survival between the 2 groups (P = 0.002).

CONCLUSIONS

Persistence of minimal residual disease in BM may work as a chemotherapy response marker and predict the prognosis in advanced NB.

Consensus criteria for sensitive detection of minimal neuroblastoma cells in bone marrow, blood and stem cell preparations by immunocytology and QRT-PCR: recommendations by the International Neuroblastoma Risk Group Task Force

Disseminating disease is a predictive and prognostic indicator of poor outcome in children with neuroblastoma. Its accurate and sensitive assessment can facilitate optimal treatment decisions. The International Neuroblastoma Risk Group (INRG) Task Force has defined standardised methods for the determination of minimal disease (MD) by immunocytology (IC) and quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) using disialoganglioside G(D2) and tyrosine hydroxylase mRNA respectively. The INRG standard operating procedures (SOPs) define methods for collecting, processing and evaluating bone marrow (BM), peripheral blood (PB) and peripheral blood stem cell harvest by IC and QRT-PCR. Sampling PB and BM is recommended at diagnosis, before and after myeloablative therapy and at the end of treatment. Peripheral blood stem cell products should be analysed at the time of harvest. Performing MD detection according to INRG SOPs will enable laboratories throughout the world to compare their results and thus facilitate quality-controlled multi-centre prospective trials to assess the clinical significance of MD and minimal residual disease in heterogeneous patient groups.

Disialoganglioside directed immunotherapy of neuroblastoma

Achieving a cure for metastatic neuroblastoma remains a challenge despite sensitivity to chemotherapy and radiotherapy. Most patients achieve remission, but a failure to eliminate minimal residual disease (MRD) often leads to relapse. Immunotherapy is potentially useful for chemotherapy-resistant disease and may be particularly effective for low levels of MRD that are below the threshold for detection by routine radiological and histological methods. Disialoganglioside (GD2), a surface glycolipid antigen that is ubiquitous and abundant on neuroblastoma cells is an ideal target for immunotherapy. Anti-GD2 monoclonal antibodies currently form the mainstay of neuroblastoma immunotherapy and their safety profile has been well-established. Although responses in patients with gross disease have been observed infrequently, histologic responses of bone marrow disease are consistently achieved in >75 percent of patients with primary refractory neuroblastoma. The advent of highly sensitive and specific molecular assays to measure MRD has confirmed the efficacy anti-GD2 antibody immunotherapy in patients with subclinical disease. Such markers will allow further optimization of other anti-MRD therapies. We review the current status of anti-GD2 clinical trials for neuroblastoma and novel preclinical GD2-targeted strategies for this rare but often lethal childhood cancer.

Cyclin D1, a novel molecular marker of minimal residual disease, in metastatic neuroblastoma

Accurate monitoring of minimal residual disease (MRD) is critical for the management of metastatic neuroblastoma (NB). We evaluated cyclin D1 (CCND1), a cell-cycle control gene, as a novel MRD marker of NB. Using quantitative reverse transcriptase-polymerase chain reaction, we studied CCND1 expression in 133 solid tumors of different histological types, including 39 NB tumors, and examined its potential clinical utility as an early response marker in the bone marrows before and after treatment of 118 stage 4 patients enrolled after induction chemotherapy in an immunotherapy protocol. Based on 40 normal marrow and peripheral blood samples, a CCND1 transcript value greater than the mean + 2 SD was defined as positive. Sensitivity of this assay was one NB cell in 10(6) normal mononuclear cells. CCND1 transcript levels were high in NB, breast cancer, and Ewing family tumors. Among the NB patients evaluated, early (2.5 months from protocol entry) marrow response was strongly associated with both progression-free (P=0.0001) and overall survival (P=0.0006). CCND1 response remained predictive of survival among a subset of 66 patients who had no histological evidence of marrow disease before immunotherapy. We conclude that CCND1 has potential clinical utility as a novel molecular marker of MRD in the bone marrow of patients with metastatic NB.

Neuroblastoma-derived secretory protein messenger RNA levels correlate with high-risk neuroblastoma

BACKGROUND/PURPOSE

In advanced-stage neuroblastoma, bulky disease and systemic dissemination can be controlled with intense surgical and medical therapies; however, recurrence rates are very high in this group indicating that residual disease is rarely eradicated. The need to detect residual disease and predict prognosis is critical to planning appropriate treatment regimens for these patients. Recently, neuroblastoma-derived secretory protein (NDSP) was identified and cloned from neuroblastoma.

METHODS

Using quantitative real-time PCR, we tested NDSP messenger RNA (mRNA) expression in 45 neuroblastoma tumor samples and 5 bone marrow samples. Correlation between NDSP expression and age at diagnosis, International Neuroblastoma Staging System, MYCN amplification, and Children's Oncology Group risk stratification was analyzed using Spearman nonparametric correlation.

RESULTS

Neuroblastoma tissue samples show much higher NDSP mRNA levels above control in 43 of 45 samples (96%); moreover, these levels correlate with the Children's Oncology Group neuroblastoma risk group assignment. We also found that bone marrow samples with known tumor infiltration had much higher NDSP mRNA levels than bone marrow from patients without metastasis.

CONCLUSION

From these data, we conclude that NDSP mRNA levels in neuroblastoma tumor tissue correlate with risk group assignment and may serve as a marker for metastasis in bone marrow.

Immunotherapy of neuroblastoma: present, past and future

Neuroblastoma is a neuroectodermal tumor of childhood with poor prognosis and low survival in patients with advanced-stage disease who respond to conventional therapies but unfortunately, often present relapse. Therefore, the search for novel therapeutic strategies is warranted and represents the objective of many investigators. Among the new, innovative approaches, immunotherapy has attracted much interest. However, until recently, little information was available about the immunogenicity of human neuroblastoma.

Detecting minimal residual disease in neuroblastoma patients-the present state of the art

While cyto- and histological screening of bone marrow samples are still accepted as the gold standard for initial staging of neuroblastoma patients, these applications are insufficient during or after therapy because it is not always possible to detect tumour cell infiltration below the level of 1% by morphology alone. For monitoring of minimal residual disease, techniques offering a considerably higher sensitivity have been developed. Immunocytology, RT-PCR and flow cytometry are most frequently used, but differ with regard to targets (single cells, RNA transcripts), measured parameters (tumour cell number, antigen expression, cytomorphology, cytogenetic aberrations, level/number of RNA transcripts), specificity (uni-/multi-parameter analysis) and sensitivity (number of investigated cells). The pros and cons of these methods are reviewed. Precise quantification of residual tumour cells in bone marrow and blood may show a future impact on risk grouping and therapeutic strategies for patients with disseminated disease, but the potential clinical application of these techniques has to be preceded by thorough standardisation and validation in multi-centre studies.