A randomized trial of 13-Cis retinoic acid in children with advanced neuroblastoma after high-dose therapy

SLIT3-mediated intratumoral crosstalk induces neuroblastoma differentiation via a spontaneous regression-like program

BACKGROUND

Neuroblastoma, the most common pediatric extracranial solid tumor, has heterogeneous clinical outcomes ranging from malignant progression to spontaneous regression. With the highest frequency of the elusive spontaneous regression, low-risk INSS Stage 4S neuroblastoma represents an ideal model for mechanistic investigation. Spontaneous regression is often accompanied by tumor differentiation, but the mechanisms underlying this process remain largely unclear.

METHODS

Single-nucleus transcriptomics (snRNA-seq) data of neuroblastoma samples were obtained from the Synapse repository to investigate the composition of heterogeneous tumor cell clusters. The feature of the Stage 4S-specific tumor cell subpopulation was revealed through differential expression analysis, pathway enrichment analysis and pseudotime analysis, followed by clinical significance validation on public cohort datasets. The biological function of secreted SLIT3 was validated using multiple in vitro models, including recombinant protein treatment, conditioned medium treatment, and cell lines coculture, to confirm the intratumoral crosstalk effect. Orthotopic and subcutaneous xenograft models were established to verify SLIT3's in vivo function. Cellular bulk RNA-seq analysis was performed with or without SLIT3 recombinant protein treatment to discover the downstream pathways activated by SLIT3, followed by validation with specific pathway inhibitors.

RESULTS

Analysis of snRNA-seq revealed a distinct subpopulation of tumor cells within INSS Stage 4S neuroblastoma, characterized by a spontaneous regression-like program progressing toward differentiation. Activated SLIT-ROBO signaling was found in the Stage 4S-specific tumor cell subpopulation, which strongly correlated with favorable prognosis. Further investigation into the secreted ligands in SLIT-ROBO related pathways revealed that SLIT3 displayed the most potent enrichment in Stage 4S tumors and the strongest differentiation-inducing effect. In vitro experiments using recombinant SLIT3 protein, conditioned medium, and cell lines coculture consistently demonstrated the capacity of SLIT3 to induce neuroblastoma cell differentiation via intratumoral crosstalk, as evidenced by increased neurite outgrowth and elevated expression of neuronal differentiation markers. Both orthotopic xenograft and subcutaneous xenograft models demonstrated that SLIT3 expression suppressed tumor growth, leading to in vivo tumor differentiation. Mechanistically, PLCβ/PKC signaling mediates the SLIT3-induced neuroblastoma cell differentiation.

CONCLUSIONS

Stage 4S-specific tumor cell subpopulation exhibits a spontaneous regression-like program, from which SLIT3 mediates intratumoral crosstalk and promotes neuroblastoma differentiation via PLCβ/PKC signaling. These findings provide new insights into the mechanism of spontaneous regression in neuroblastoma and offer novel therapeutic targets for differentiation-based treatment strategies.

GPOH Guidelines for Diagnosis and First-line Treatment of Patients with Neuroblastic Tumors, update 2025

The clinical course of neuroblastoma is more heterogeneous than any other malignant disease. Many low-risk patients experience regression after limited or even no chemotherapy. However, more than half of high-risk patients die from disease despite intensive multimodal treatment. Precise disease characterization for each patient at diagnosis is key for risk-adapted treatment. The guidelines presented here incorporate results from national and international clinical trials to produce recommendations for diagnosing and treating neuroblastoma patients in German hospitals outside of clinical trials.

Defining neuroblastoma: From origin to precision medicine

Neuroblastoma (NB), a heterogenous pediatric tumor of the sympathetic nervous system, is the most common and deadly extracranial solid malignancy diagnosed in infants. Numerous efforts have been invested in understanding its origin and in development of novel curative targeted therapies. Here, we summarize the recent advances in the identification of the cell of origin and the genetic alterations occurring during development that contribute to NB. We discuss current treatment regimens, present and future directions for the identification of novel therapeutic metabolic targets, differentiation agents, as well as personalized combinatory therapies as potential approaches for improving the survival and quality of life of children with NB.

Impact of risk-based therapy on late morbidity and mortality in neuroblastoma survivors: a report from the Childhood Cancer Survivor Study

BACKGROUND

Early efforts at risk-adapted therapy for neuroblastoma are predicted to result in differential late effects; the magnitude of these differences has not been well described.

METHODS

Late mortality, subsequent malignant neoplasms (SMNs), and severe/life-threatening chronic health conditions (CHCs), graded according to CTCAE v4.03, were assessed among 5-year Childhood Cancer Survivor Study (CCSS) survivors of neuroblastoma diagnosed 1987-1999. Using age, stage at diagnosis, and treatment, survivors were classified into risk groups (low [n = 425]; intermediate [n = 252]; high [n = 245]). Standardized mortality ratios (SMRs) and standardized incidence ratios (SIRs) of SMNs were compared with matched population controls. Cox regression models estimated hazard ratios (HRs) and 95% confidence intervals for CHC compared with 1029 CCSS siblings.

RESULTS

Among survivors (49.8% male; median age = 21 years, range = 7-42; median follow-up = 19.3 years, range = 5-29.9), 80% with low-risk disease were treated with surgery alone, whereas 79.1% with high-risk disease received surgery, radiation, chemotherapy ± autologous stem cell transplant (ASCT). All-cause mortality was elevated across risk groups (SMRhigh = 27.7 [21.4-35.8]; SMRintermediate = 3.3 [1.7-6.5]; SMRlow = 2.8 [1.7-4.8]). SMN risk was increased among high- and intermediate-risk survivors (SIRhigh = 28.0 [18.5-42.3]; SIRintermediate = 3.7 [1.2-11.3]) but did not differ from the US population for survivors of low-risk disease. Compared with siblings, survivors had an increased risk of grade 3-5 CHCs, particularly among those with high-risk disease (HRhigh = 16.1 [11.2-23.2]; HRintermediate = 6.3 [3.8-10.5]; HRlow = 1.8 [1.1-3.1]).

CONCLUSION

Survivors of high-risk disease treated in the early days of risk stratification carry a markedly elevated burden of late recurrence, SMN, and organ-related multimorbidity, whereas survivors of low/intermediate-risk disease have a modest risk of late adverse outcomes.

Retinoid Therapy for Neuroblastoma: Historical Overview, Regulatory Challenges, and Prospects

Retinoids are vitamin A derivatives and include trans-retinoic acid, isotretinoin, tamibarotene, and bexarotene, all of which are currently available for clinical use. The clinical development of retinoid therapy for neuroblastoma has a history spanning more than four decades. The most promising agent is isotretinoin, which can contribute to improving event-free survival in patients with high-risk neuroblastoma by approximately 10% when administered over six months as maintenance therapy. Although isotretinoin is regarded as an essential component in the standard clinical management of high-risk neuroblastoma, its use for this purpose in the US and EU is off-label. To promote isotretinoin use in Japan as a treatment for neuroblastoma, our clinical research team is planning to launch an investigator-initiated, registration-directed clinical trial. The present review article discusses the basic science behind retinoid therapy, pre-clinical/clinical evidence on neuroblastoma, the concept of the proposed clinical trial, and prospects for this therapy.

Mitochondrial uncoupler and retinoic acid synergistically induce differentiation and inhibit proliferation in neuroblastoma

Neuroblastoma is a leading cause of death in childhood cancer cases. Unlike adult malignancies, which typically develop from aged cells through accumulated damage and mutagenesis, neuroblastoma originates from neural crest cells with disrupted differentiation. This distinct feature provides novel therapeutic opportunities beyond conventional cytotoxic methods. Previously, we reported that the mitochondrial uncoupler NEN (niclosamide ethanolamine) activated mitochondria respiration to reprogram the epigenome, promoting neuronal differentiation. In the current study, we further combine NEN with retinoic acid (RA) to promote neural differentiation both in vitro and in vivo. The treatment increased the expression of RA signaling and neuron differentiation-related genes, resulting in a global shift in the transcriptome towards a more favorable prognosis. Overall, these results suggest that the combination of a mitochondrial uncoupler and the differentiation agent RA is a promising therapeutic strategy for neuroblastoma.

Retinoids in cancer chemoprevention and therapy: Meta-analysis of randomized controlled trials

Retinoids, natural and synthetic derivatives of vitamin A, have many regulatory functions in human body, including regulating cellular proliferation, differentiation, apoptosis. Moreover, retinoids have been used successfully for the treatment of certain malignancies, especially acute promyelocytic leukemia (APL) in adults and neuroblastoma in children. However, retinoids have not yet been translated into effective systemic treatments for most solid cancers. Some recent studies have shown that retinoids promote tumorigenesis. Therefore, we performed this meta-analysis to systematically evaluate the efficacy of retinoids in the chemoprevention and treatment of cancers. We performed literature search of several electronic databases, including PubMed, Embase and Cochrane Library from 2000 January to 2021 November. Various outcomes were applied to investigate the potential of retinoids for prevention and treatment of cancers. The primary outcomes in this study were disease recurrence and clinical response. The secondary outcomes included overall survival (OS), cancer development, disease progression and event-free survival. We identified 39 randomized controlled trials with 15,627 patients in this study. Our results showed that lower recurrence rate and better clinical response were obtained in retinoids treated patients with cancer or premalignancy as compared with control. The differences were statistically significant (RR = 0.85, 95% CI = 0.74-0.96, p = 0.01; RR = 1.24, 95% CI = 1.03-1.49, p = 0.02, respectively). Retinoids treatment was not associated with improvement in overall survival, cancer development, disease progression or event-free survival. Subgroup analysis conducted based on cancer type showed that patients benefited from retinoids treatment in APL, renal cell carcinoma, hepatocellular carcinoma, lung cancer, Kaposi sarcoma, and complete hydatidiform mole. No significant therapeutic effect was noted in head and neck cancer, acute myeloid leukemia (AML), melanoma, breast cancer, bladder cancer, cervical intraepithelial neoplasia (CIN) or cervical carcinoma. Subgroup analysis based on tumor classification demonstrated that retinoids group obtained a lower recurrence rate and better clinical response than control group in solid cancers. In conclusion, clinical application of retinoids was associated with reduction in disease recurrence and improvement in clinical response, illustrating that retinoids play a key role in cancer prevention and therapy. Further research is needed to broaden the utility of retinoids in other types of cancers. Systematic Review Registration: PROSPERO, identifier CRD42022296706.

Hypercalcemia is a frequent side effect of 13-cis-retinoic acid treatment in patients with high-risk neuroblastoma

PURPOSE

13-cis-Retinoic acid (13-cisRA) is used as a postconsolidation treatment in patients with high-risk neuroblastoma. Hypercalcemia is a known side effect of retinoids. Frequency, symptoms, treatment, and risk factors for hypercalcemia were analyzed.

PATIENTS

Data were retrospectively analyzed for 350 patients registered in the German Neuroblastoma trials NB97 and NB04 who were treated with high-risk protocols-including myeloablative chemotherapy with autologous stem cell transplantation (SCT) or maintenance therapy-and had received 13-cisRA between January 1, 2000 and December 31, 2010.

RESULTS

Hypercalcemia was reported in 78 patients (22.3%), and 37 patients (10.6%) developed Common Terminology Criteria for Adverse Events (CTCAE) grade 3 or 4 hypercalcemia. The calcium levels were 2.5-4.6 mmol/L (median 3.1 mmol/L). Patients with a single kidney were at a higher risk of developing hypercalcemia (p = .001). Regarding postinduction treatment, 69 of 280 patients with SCT (24.6%) and nine of 70 patients without SCT (12.9%) developed hypercalcemia during 13-cisRA treatment (p = .037). Most patients developed hypercalcemia in the first cycle of 13-cisRA, and only in a single cycle. Hypercalcemia symptoms were frequent but moderate. In most patients, treatment with 13-cisRA was continued without dose reduction in subsequent cycles.

CONCLUSION

In this cohort, grades 3 and 4 hypercalcemia were observed more often than previously reported. A single kidney and pretreatment with myeloablative chemotherapy with stem cell transplantation were identified as potential risk factors for the development of hypercalcemia.

Therapeutically targeting oncogenic CRCs facilitates induced differentiation of NB by RA and the BET bromodomain inhibitor

Retinoic acids (RAs) are the most successful therapeutics for cancer differentiation therapy used in high-risk neuroblastoma (NB) maintenance therapy but are limited in effectiveness. This study identifies a strategy for improving efficacy through disruption of cancer cell identity via BET inhibitors. Mutations that block development are theorized to cause NB through retention of immature cell identities contributing to oncogenesis. NB has two interchangeable cell identities, maintained by two different core transcriptional regulatory circuitries (CRCs): a therapy-resistant mesenchymal/stem cell state and a proliferative adrenergic cell state. MYCN amplification is a common mutation of high-risk NB and recently found to block differentiation by driving high expression of the adrenergic CRC transcription factor ASCL1. We investigated whether disruption of immature CRCs can promote RA-induced differentiation since only a subset of NB patients responds to RA. We found that silencing ASCL1, a critical member of the adrenergic CRC, or global disruption of CRCs with the BET inhibitor JQ1, suppresses gene expression of multiple CRC factors, improving RA-mediated differentiation. Further, JQ1 and RA synergistically decrease proliferation and induce differentiation in NB cell lines. Our findings support preclinical studies of RA and BET inhibitors as a combination therapy in treating NB.

Differentiating Neuroblastoma: A Systematic Review of the Retinoic Acid, Its Derivatives, and Synergistic Interactions

A neuroblastoma (NB) is a solid paediatric tumour arising from undifferentiated neuronal cells. Despite the recent advances in disease management and treatment, it remains one of the leading causes of childhood cancer deaths, thereby necessitating the development of new therapeutic agents and regimens. Retinoic acid (RA), a vitamin A derivative, is a promising agent that can induce differentiation in NB cells. Its isoform, 13-cis RA or isotretinoin, is used in NB therapy; however, its effectiveness is limited to treating a minimal residual disease as maintenance therapy. As such, research focuses on RA derivatives that might increase the anti-NB action or explores the potential synergy between RA and other classes of drugs, such as cellular processes mediators, epigenetic modifiers, and immune modulators. This review summarises the in vitro, in vivo, and clinical data of RA, its derivatives, and synergising compounds, thereby establishing the most promising RA derivatives and combinations of RA for further investigation.

Immunomodulator polyinosinic-polycytidylic acid enhances the inhibitory effect of 13-cis-retinoic acid on neuroblastoma through a TLR3-related immunogenic-apoptotic response

High-risk neuroblastoma is associated with low long-term survival rates due to recurrence or metastasis. Retinoids, including 13-cis-retinoic acid (13cRA), are commonly used for the treatment of high-risk neuroblastoma after myeloablative therapy; however, there are significant side effects and resistance rates. In this study, we demonstrated that 13cRA has a better antiproliferative effect in MYCN-amplified neuroblastoma cells than in MYCN-nonamplified neuroblastoma cells. In MYCN-amplified SK-N-DZ cells, 13cRA induced significant upregulation of toll-like receptor 3 (TLR3) and mitochondrial antiviral-signaling protein (MAVS) expression in a time-dependent manner. Furthermore, poly (I:C), a synthetic agonist of TLR3, effectively synergized with 13cRA to enhance antiproliferative effects through upregulation of the innate immune signaling and the mitochondrial stress response, leading to augmentation of the apoptotic response in 13cRA-responsive cancer cells. In addition, the 13cRA/poly (I:C) combination induced neural differentiation through activation of retinoic acid receptors beta (RAR-β), restoring expression of α-thalassemia/mental retardation syndrome X-linked (ATRX) protein, and inhibiting vessel formation, leading to retarded tumor growth in a mouse xenograft model. These results suggest that the combination of poly (I:C) and RA may provide synergistic therapeutic benefits for treatment of patients with high-risk neuroblastoma.

Retinoic acid postconsolidation therapy for high-risk neuroblastoma patients treated with autologous haematopoietic stem cell transplantation

BACKGROUND

Neuroblastoma is a rare malignant disease and mainly affects infants and very young children. The tumours mainly develop in the adrenal medullary tissue, with an abdominal mass as the most common presentation. About 50% of patients have metastatic disease at diagnosis. The high-risk group is characterised by metastasis and other features that increase the risk of an adverse outcome. High-risk patients have a five-year event-free survival of less than 50%. Retinoic acid has been shown to inhibit growth of human neuroblastoma cells and has been considered as a potential candidate for improving the outcome of patients with high-risk neuroblastoma. This review is an update of a previously published Cochrane Review.

OBJECTIVES

To evaluate the efficacy and safety of additional retinoic acid as part of a postconsolidation therapy after high-dose chemotherapy (HDCT) followed by autologous haematopoietic stem cell transplantation (HSCT), compared to placebo retinoic acid or to no additional retinoic acid in people with high-risk neuroblastoma (as defined by the International Neuroblastoma Risk Group (INRG) classification system).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library (2016, Issue 11), MEDLINE in PubMed (1946 to 24 November 2016), and Embase in Ovid (1947 to 24 November 2016). Further searches included trial registries (on 22 December 2016), conference proceedings (on 23 March 2017) and reference lists of recent reviews and relevant studies. We did not apply limits by publication year or languages.

SELECTION CRITERIA

Randomised controlled trials (RCTs) evaluating additional retinoic acid after HDCT followed by HSCT for people with high-risk neuroblastoma compared to placebo retinoic acid or to no additional retinoic acid. Primary outcomes were overall survival and treatment-related mortality. Secondary outcomes were progression-free survival, event-free survival, early toxicity, late toxicity, and health-related quality of life.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

The update search did not identify any additional studies. We identified one RCT that included people with high-risk neuroblastoma who received HDCT followed by autologous HSCT (N = 98) after a first random allocation and who received retinoic acid (13-cis-retinoic acid; N = 50) or no further therapy (N = 48) after a second random allocation. These 98 participants had no progressive disease after HDCT followed by autologous HSCT. There was no clear evidence of difference between the treatment groups either in overall survival (hazard ratio (HR) 0.87, 95% confidence interval (CI) 0.46 to 1.63; one trial; P = 0.66) or in event-free survival (HR 0.86, 95% CI 0.50 to 1.49; one trial; P = 0.59). We calculated the HR values using the complete follow-up period of the trial. The study also reported overall survival estimates at a fixed point in time. At the time point of five years, the survival estimate was reported to be 59% for the retinoic acid group and 41% for the no-further-therapy group (P value not reported). We did not identify results for treatment-related mortality, progression-free survival, early or late toxicity, or health-related quality of life. We could not rule out the possible presence of selection bias, performance bias, attrition bias, and other bias. We judged the evidence to be of low quality for overall survival and event-free survival, downgraded because of study limitations and imprecision.

AUTHORS' CONCLUSIONS

We identified one RCT that evaluated additional retinoic acid as part of a postconsolidation therapy after HDCT followed by autologous HSCT versus no further therapy in people with high-risk neuroblastoma. There was no clear evidence of a difference in overall survival and event-free survival between the treatment alternatives. This could be the result of low power. Information on other outcomes was not available. This trial was performed in the 1990s, since when many changes in treatment and risk classification have occurred. Based on the currently available evidence, we are therefore uncertain about the effects of retinoic acid in people with high-risk neuroblastoma. More research is needed for a definitive conclusion.

Retinoic acid post consolidation therapy for high-risk neuroblastoma patients treated with autologous hematopoietic stem cell transplantation

BACKGROUND

Neuroblastoma is a rare malignant disease and mainly affects infants and very young children. The tumors mainly develop in the adrenal medullary tissue and an abdominal mass is the most common presentation. About 50% of patients have metastatic disease at diagnosis. The high-risk group is characterized by metastasis and other characteristics that increase the risk for an adverse outcome. High-risk patients have a five-year event-free survival of less than 50%. Retinoic acid has been shown to inhibit growth of human neuroblastoma cells and has been considered as a potential candidate for improving the outcome of patients with high-risk neuroblastoma.

OBJECTIVES

To evaluate efficacy and adverse events of retinoic acid after consolidation with high-dose chemotherapy followed by bone marrow transplantation as compared to placebo or no therapy in patients with high-risk neuroblastoma (as defined by the International Neuroblastoma Risk Group (INRG) classification system). Our outcomes of interest were overall survival and treatment-related mortality as primary outcomes; and progression- and event-free survival, early and late toxicity, and health-related quality of life as secondary outcomes.

SEARCH METHODS

We searched the electronic databases CENTRAL (2014, Issue 8) on The Cochrane Library, MEDLINE (1946 to October 2014), and EMBASE (1947 to October 2014). Further searches included trial registries, conference proceedings, and reference lists of recent reviews and relevant articles. We did not apply limits on publication year or languages.

SELECTION CRITERIA

Randomized controlled trials (RCTs) evaluating retinoic acid post consolidation therapy for high-risk neuroblastoma patients treated with autologous hematopoietic stem cell transplantation (HSCT) compared to placebo or no further treatment.

DATA COLLECTION AND ANALYSIS

Two review authors performed the study selection, extracted the data on study and patient characteristics and assessed the risk of bias independently. We resolved differences by discussion or by appeal to a third review author. We performed analyses according to the guidelines of the Cochrane Handbook for Systematic Reviews of Interventions. The authors of the included study did not report the results specifically for the treatment groups relevant to this Cochrane Review. Therefore, we deduced the appropriate survival data from the published survival curves and calculated a hazard ratio (HR) based on the deduced data.

MAIN RESULTS

We identified one RCT (CCG-3891) that included patients with high-risk neuroblastoma who received high-dose chemotherapy followed by autologous HSCT (N = 98) after a first random allocation and who received retinoic acid (13-cis-retinoic acid; N = 50) or no further therapy (N = 48) after a subsequent second random allocation. These patients had no progressive disease after consolidation therapy. There was no clear evidence of difference between the treatment groups in both overall survival (HR 0.87, 95% CI 0.46 to 1.63; one trial; P = 0.66, low quality of evidence) and event-free survival (HR 0.86, 95% CI 0.50 to 1.49; one trial; P = 0.59, low quality of evidence). We calculated these HR values using the complete follow-up period of the trial. The study also reported five-year overall survival rates: 59% for the retinoic acid group and 41% for the no further therapy group (P value not reported). We did not identify results for treatment-related mortality, progression-free survival, early or late toxicity, or health-related quality of life. Also, we could not rule out the possible presence of selection bias, performance bias, attrition bias, and other bias.

AUTHORS' CONCLUSIONS

We identified one RCT that evaluated retinoic acid as a consolidation therapy versus no further therapy after high-dose chemotherapy followed by bone-marrow transplantation in patients with high-risk neuroblastoma. The difference in overall survival and event-free survival between both treatment alternatives was not statistically significantly different. This could be the result of low power. Information on other outcomes was not available. This trial was performed in the 1990s, since then many changes in for example treatment and risk classification have occurred. Therefore, based on the currently available evidence, we are uncertain about the effects of retinoic acid in patients with high-risk neuroblastoma. More research is needed for a definitive conclusion.

Selective HDAC1/HDAC2 inhibitors induce neuroblastoma differentiation

While cytotoxic chemotherapy remains the hallmark of cancer treatment, intensive regimens fall short in many malignancies, including high-risk neuroblastoma. One alternative strategy is to therapeutically promote tumor differentiation. We created a gene expression signature to measure neuroblast maturation, adapted it to a high-throughput platform, and screened a diversity oriented synthesis-generated small-molecule library for differentiation inducers. We identified BRD8430, containing a nine-membered lactam, an ortho-amino anilide functionality, and three chiral centers, as a selective class I histone deacetylase (HDAC) inhibitor (HDAC1 > 2 > 3). Further investigation demonstrated that selective HDAC1/HDAC2 inhibition using compounds or RNA interference induced differentiation and decreased viability in neuroblastoma cell lines. Combined treatment with 13-cis retinoic acid augmented these effects and enhanced activation of retinoic acid signaling. Therefore, by applying a chemical genomic screening approach, we identified selective HDAC1/HDAC2 inhibition as a strategy to induce neuroblastoma differentiation.

Adaptive dosing approaches to the individualization of 13-cis-retinoic acid (isotretinoin) treatment for children with high-risk neuroblastoma

PURPOSE

To investigate the feasibility of adaptive dosing and the impact of pharmacogenetic variation on 13-cis-retinoic acid (13-cisRA) disposition in high-risk patients with neuroblastoma.

EXPERIMENTAL DESIGN

13-cisRA (160 mg/m(2) or 5.33 mg/kg/d) was administered to 103 patients ages 21 years or less and plasma concentrations of 13-cisRA and 4-oxo-13-cisRA quantitated on day 14 of treatment. Seventy-one patients were recruited to a dose adjustment group, targeting a 13-cisRA C(max) of 2 μmol/L, with dose increases of 25% to 50% implemented for patients with C(max) values less than 2 μmol/L. A population pharmacokinetic model was applied and polymorphisms in relevant cytochrome P450 genes analyzed.

RESULTS

13-cisRA C(max) values ranged from 0.42 to 11.2 μmol/L, with 34 of 103 (33%) patients failing to achieve a C(max) more than 2 μmol/L. Dose increases carried out in 20 patients in the dose adjustment study group led to concentrations more than 2 μmol/L in 18 patients (90%). Eight of 11 (73%) patients less than 12 kg, receiving a dose of 5.33 mg/kg, failed to achieve a C(max) of 2 μmol/L or more. Significantly, lower C(max) values were observed for patients treated with 5.33 mg/kg versus 160 mg/m(2) (1.9 ± 1.2 vs. 3.1 ± 2.0 μmol/L; mean ± SD; P = 0.023). C(max) was higher in patients who swallowed 13-cisRA capsules as compared with receiving the drug extracted from capsules (4.0 ± 2.2 vs. 2.6 ± 1.8 μmol/L; P = 0.0012). The target C(max) was achieved by 93% (25/27) versus 55% (42/76) of patients in these 2 groups, respectively. No clear relationships were found between genetic variants and 13-cisRA pharmacokinetic parameters.

CONCLUSIONS

Dosing regimen and method of administration have a marked influence on 13-cisRA plasma concentrations. Body weight-based dosing should not be implemented for children less than 12 kg and pharmacologic data support higher doses for children unable to swallow 13-cisRA capsules.

Targeted isotretinoin in neuroblastoma: kinetics, genetics, or absorption

Isotretinoin (13-cis-retinoic acid; 13-cisRA) has been shown to significantly improve survival for children with high-risk neuroblastoma. Pharmacokinetics of isotretinoin may be negatively affected by the mode of drug administration and the dosing formula.

Retinoids in pediatric onco-hematology: the model of acute promyelocytic leukemia and neuroblastoma

Retinoids are lipophilic compounds derived from vitamin A, which have been extensively studied in cancer prevention and therapy. In pediatric oncology, they are successfully used for the treatment of acute promyelocytic leukemia (APL) and high-risk neuroblastoma (HR-NBL). APL is a subtype of acute myeloid leukemia (AML) clinically characterized by a severe bleeding tendency with a highrisk of fatal hemorrhage. The molecular hallmark of this disease is the presence of the promyelocytic leukemia (PML)-retinoic acid receptor-α (RAR α) gene fusion that plays a critical role in promyelocytic leukemogenesis and represents the target of retinoid therapy. The introduction in the late 1980s of all-trans retinoic acid (ATRA) into the therapy of APL radically changed the management and the outcome of this disease. Presently, the standard front-line therapeutic approach for pediatric APL includes anthracycline-based chemotherapy and ATRA, leading to a complete remission in almost 90% of the patients. Neuroblastoma (NBL) is an aggressive childhood tumor derived from the peripheral neural crest. More than half of patients have a high-risk disease, with a poor outcome despite intensive multimodal treatment. Although the exact mechanism of action remains unclear, the introduction of 13-cis-retinoic acid (13-cis-RA) in the therapy of NBL has improved the prognosis of this disease. Currently, the standard treatment for HR-NBL consists of myeloablative therapy followed by autologous hematopoietic stem cell transplantation (HSCT) and maintenance with 13-cis-RA for the treatment of minimal residual disease, leading to a 3-year disease-free survival rate (DFS) of about 50%. In this paper the authors provide a review of the peer-reviewed literature on the role of retinoids in the treatment of pediatric APL and HR-NBL, summarizing the most relevant clinical trial results of the last decades, analyzing the ongoing trials, and investigating future therapeutic perspectives of children affected by these diseases.

The MYCN oncogene and differentiation in neuroblastoma

Childhood neuroblastoma exhibits a heterogeneous clinical behavior ranging from low-risk tumors with the ability to spontaneously differentiate and regress, to high-risk tumors causing the highest number of cancer related deaths in infants. Amplification of the MYCN oncogene is one of the few prediction markers for adverse outcome. This gene encodes the MYCN transcriptional regulator predominantly expressed in the developing peripheral neural crest. MYCN is vital for proliferation, migration and stem cell homeostasis while decreased levels are associated with terminal neuronal differentiation. Interestingly, high-risk tumors without MYCN amplification frequently display increased c-MYC expression and/or activation of MYC signaling pathways. On the other hand, downregulation of MYCN leads to decreased proliferation and differentiation, emphasizing the importance of MYC signaling in neuroblastoma biology. Furthermore, expression of the neurotrophin receptor TrkA is associated with good prognosis, the ability to differentiate and spontaneous regression while expression of the related TrkB receptor is correlated with bad prognosis and MYCN amplification. Here we discuss the role of MYCN in neuroblastoma with a special focus on the contribution of elevated MYCN signaling for an aggressive and undifferentiated phenotype as well as the potential of using MYCN as a therapeutic target.

Neuroblastoma: Therapeutic strategies for a clinical enigma

Neuroblastoma, the most common extracranial pediatric solid tumor remains a clinical enigma with outcomes ranging from cure in >90% of patients with locoregional tumors with little to no cytotoxic therapy, to <30% for those >18months of age at diagnosis with metastatic disease despite aggressive multimodality therapy. Age, stage and amplification of the MYCN oncogene are the most validated prognostic markers. Recent research has shed light on the biology of neuroblastoma allowing more accurate stratification of patients which has permitted reducing or withholding cytotoxic therapy without affecting outcome for low-risk patients. However, for children with high-risk disease, the development of newer therapeutic strategies is necessary. Current surgery and radiotherapy techniques in conjunction with induction chemotherapy have greatly reduced the risk of local relapse. However, refractory or recurrent osteomedullary disease occurs in most patients with high-risk neuroblastoma. Toxicity limits for high-dose chemotherapy appear to have been reached without further clinical benefit. Neuroblastoma is the first pediatric cancer for which monoclonal-antibody-based immunotherapy has been shown to be effective, particularly for metastatic osteomedullary disease. Radioimmunotherapy appears to be a critical component of a recent, successful regimen for treating patients who relapse in the central nervous system, a possible sanctuary site. Efforts are under way to refine and enhance antibody-based immunotherapy and to determine its optimal use. The identification of newer tumor targets and the harnessing of cell-mediated immunotherapy may generate novel therapeutic approaches. It is likely that a combination of therapeutic modalities will be required to improve survival and cure rates.

High-dose chemotherapy and autologous stem cell rescue in patients with high-risk stage 3 neuroblastoma: 10-year experience at a single center

High-dose chemotherapy and autologous stem cell rescue (HDCT/ASCR) was applied to improve the prognosis of patients with high-risk stage 3 neuroblastoma. From January 1997 to December 2006, 28 patients were newly diagnosed as stage 3 neuroblastoma. Nine of 11 patients with N-myc amplification and 5 of 17 patients without N-myc amplification (poor response in 2 patients, persistent residual tumor in 2 and relapse in 1) underwent single or tandem HDCT/ASCR. Patients without high-risk features received conventional treatment modalities only. While 8 of 9 patients underwent single HDCT/ASCR and the remaining one patient underwent tandem HDCT/ASCR during the early study period, all 5 patients underwent tandem HDCT/ASCR during the late period. Toxicities associated with HDCT/ASCR were tolerable and there was no treatment-related mortality. While the tumor relapsed in two of eight patients in single HDCT/ASCR group, all six patients in tandem HDCT/ASCR group remained relapse free. The 5-yr event-free survival (EFS) from diagnosis, in patients with N-myc amplification, was 71.6+/-14.0%. In addition, 12 of 14 patients who underwent HDCT/ASCR remained event free resulting in an 85.1+/-9.7% 5-yr EFS after the first HDCT/ASCR. The present study demonstrates that HDCT/ASCR may improve the survival of patients with high-risk stage 3 neuroblastoma.

New therapeutic targets for the treatment of high-risk neuroblastoma

High-risk neuroblastoma remains a major problem in pediatric oncology, accounting for 15% of childhood cancer deaths. Although incremental improvements in outcome have been achieved with the intensification of conventional chemotherapy agents and the addition of 13-cis-retinoic acid, only one-third of children with high-risk disease are expected to be long-term survivors when treated with current regimens. In addition, the cost of cure can be quite high, as surviving children remain at risk for additional health problems related to long-term toxicities of treatment. Further advances in therapy will require the targeting of tumor cells in a more selective and efficient way so that survival can be improved without substantially increasing toxicity. In this review we summarize ongoing clinical trials and highlight new developments in our understanding of the molecular biology of neuroblastoma, emphasizing potential targets or pathways that may be exploitable therapeutically.

Hypercalcemia and 13-cis-retinoic acid in post-consolidation therapy of neuroblastoma

We report 19 episodes of hypercalcemia in three children treated with 13-cis-retinoic acid (13-cis-RA) as a post-consolidation therapy for high-risk neuroblastoma. There was no concomitant overload in 13-cis-RA blood levels. Blood calcium fell after arrest of 13-cis-RA intake. Half dosage retinoid treatment resumption did not prevent the recurrence of hypercalcemia. Concomitant biological values showed massive bone resorption. Hence, hypercalcemia seemed not secondary to 13-cis-RA overload but rather to inter-individual variability in its interaction with bone metabolism. Current guidelines in case of hypercalcemia are to reduce 13-cis-RA dosage. Instead we propose to maintain the therapeutic dosage, but to shorten the duration of courses.

Long-term results for children with high-risk neuroblastoma treated on a randomized trial of myeloablative therapy followed by 13-cis-retinoic acid: a children's oncology group study

PURPOSE We assessed the long-term outcome of patients enrolled on CCG-3891, a high-risk neuroblastoma study in which patients were randomly assigned to undergo autologous purged bone marrow transplantation (ABMT) or to receive chemotherapy, and subsequent treatment with 13-cis-retinoic acid (cis-RA). PATIENTS AND METHODS Patients received the same induction chemotherapy, with random assignment (N = 379) to consolidation with myeloablative chemotherapy, total-body irradiation, and ABMT versus three cycles of intensive chemotherapy. Patients who completed consolidation without disease progression were randomly assigned to receive no further therapy or cis-RA for 6 months. Results The event-free survival (EFS) for patients randomly assigned to ABMT was significantly higher than those randomly assigned to chemotherapy; the 5-year EFS (mean +/- SE) was 30% +/- 4% versus 19% +/- 3%, respectively (P = .04). The 5-year EFS (42% +/- 5% v 31% +/- 5%) from the time of second random assignment was higher for cis-RA than for no further therapy, though it was not significant. Overall survival (OS) was significantly higher for each random assignment by a test of the log(-log(.)) transformation of the survival estimates at 5 years (P < .01). The 5-year OS from the second random assignment of patients who underwent both random assignments and who were assigned to ABMT/cis-RA was 59% +/- 8%; for ABMT/no cis-RA, it was 41% +/- 8% [corrected]; for continuing chemotherapy/cis-RA, it was 38% +/- 7%; and for chemotherapy/no cis-RA, it was 36% +/- 7%.

CONCLUSION

Myeloablative therapy and autologous hematopoietic cell rescue result in significantly better 5-year EFS than nonmyeloablative chemo therapy; neither myeloablative therapy with [corrected] autologous hematopoietic cell rescue nor cis-RA given after consolidation therapy significantly improved OS.

High-dose rapid and standard induction chemotherapy for patients aged over 1 year with stage 4 neuroblastoma: a randomised trial

BACKGROUND

The current standard treatment for patients with high-risk neuroblastoma includes initial induction chemotherapy with a 21-day interval between induction treatments. We aimed to assess whether an intensive chemotherapy protocol that had a 10-day interval between treatments would improve event-free survival (EFS) in patients aged 1 year or over with high-risk neuroblastoma.

METHODS

Between Oct 30, 1990, and March 18, 1999, patients with stage 4 neuroblastoma who had not received previous chemotherapy were enrolled from 29 centres in Europe. Patients were randomly assigned to rapid treatment (cisplatin [C], vincristine [O], carboplatin [J], etoposide [E], and cyclophosphamide [C], known as COJEC) or standard treatment (vincristine [O], cisplatin [P], etoposide [E], and cyclophosphamide [C], ie, OPEC, alternated with vincristine [O], carboplatin [J], etoposide [E], and cyclophosphamide [C], ie, OJEC). Both regimens used the same total cumulative doses of each drug (except vincristine), but the dose intensity of the rapid regimen was 1.8-times higher than that of the standard regimen. The standard regimen was given every 21 days if patients showed haematological recovery, whereas the rapid regimen was given every 10 days irrespective of haematological recovery. Response to chemotherapy was assessed according to the conventional International Neuroblastoma Response Criteria (INRC). In responders, surgical excision of the primary tumour was attempted, followed by myeloablation (with 200 mg/m2 of melphalan) and haemopoietic stem-cell rescue. Primary endpoints were 3-year, 5-year, and 10-year EFS. Data were analysed by intention to treat. This trial is registered on the clinical trials site of the US National Cancer Institute website, number NCT00365755, and also as EU-20592 and CCLG-NB-1990-11.

FINDINGS

262 patients, of median age 2.95 years (range 1.03-20.97), were randomly assigned-132 patients to standard and 130 patients to rapid treatment. 111 patients in the standard group and 109 patients in the rapid group completed chemotherapy. Chemotherapy doses were recorded for 123 patients in the standard group and 126 patients in the rapid group. 97 of 123 (79%) patients in the standard group and 84 of 126 (67%) patients in the rapid group received at least 90% of the scheduled chemotherapy, and the relative dose intensity was 1.94 compared with the standard regimen. 3-year EFS was 24.2% for patients in the standard group and 31.0% for those in the rapid group (hazard ratio [HR] 0.86 [95% CI 0.66-1.14], p=0.30. 5-year EFS was 18.2% in the standard group and 30.2% in the rapid group, representing a difference of 12.0% (1.8 to 22.3), p=0.022. 10-year EFS was 18.2% in the standard group and 27.1% in the rapid group, representing a difference of 8.9% (-1.2 to 19.0), p=0.085. Myeloablation was given a median of 55 days earlier in patients assigned rapid treatment than those assigned standard treatment. Infective complications (numbers of patients with febrile neutropenia and septicaemia, and if given, time on antibiotic and antifungal treatment) and time in hospital were greater with rapid treatment. Occurrence of fungal infection was the same in both regimens.

INTERPRETATION

Dose intensity can be increased with a rapid induction regimen in patients with high-risk neuroblastoma. There was no significant difference in OS between the rapid and standard regimens at 5 years and 10 years. However, an increasing difference in EFS after 3 years suggests that the efficacy of the rapid regimen is better than the standard regimen. A rapid induction regimen enables myeloablation to be given much earlier, which might contribute to a better outcome.

A phase 2 trial of all-trans-retinoic acid in combination with interferon-alpha2a in children with recurrent neuroblastoma or Wilms tumor: A Pediatric Oncology Branch, NCI and Children's Oncology Group Study

BACKGROUND

The combination of the antiproliferative and differentiation-inducing effects of retinoids together with the antiproliferative, immunostimulatory, and differentiation-potentiating effects of interferon-alpha (IFN-alpha) were the basis for the development of this combination in pediatric patients with refractory neuroblastoma or Wilms tumor.

PROCEDURE

A phase 2 trial of all-trans-retinoic acid (ATRA), administered orally at a dose of 90 mg/m(2)/day in three divided doses for 3 consecutive days per week, and IFN-alpha2a, administered subcutaneously daily at a dose of 3 x 10(6) U/m(2)/day for 5 consecutive days per week, in 4 week cycles was performed. A two-stage design was used for each disease stratum.

RESULTS

Seventeen patients (16 evaluable) with neuroblastoma, median age 9 years, and 15 patients (14 evaluable) with Wilms tumor, median age 6 years, were enrolled. Overall, the combination was well tolerated, with headache being the most common toxicity observed. There were no complete or partial responses. The median number of cycles administered was 1 (range 1-9). Four patients with neuroblastoma had stable disease for 12 or more weeks.

CONCLUSIONS

The combination of ATRA and IFN-alpha2a was inactive in children with relapsed or refractory neuroblastoma and Wilms tumor. The lack of activity with this combination in children with refractory neuroblastoma is similar to the disappointing phase 2 results of single agent 13-cis-retinoic-acid (13cRA) and does not support further development of ATRA for children with relapsed neuroblastoma.

Markedly improving survival of neuroblastoma: a 30-year analysis of 1,646 patients

We sought to define current incidence trends and outcomes for pediatric patients with neuroblastoma. The SEER registry was queried from 1973 to 2002. Overall, 1,646 patients with neuroblastoma were identified. The annual incidence has remained unchanged at 0.9 per 100,000. The median age of the population was 1 year, with 42% of patients presenting at <1 year of age. The majority of tumors arose in the retroperitoneum (75.6%) with the remainder located in the mediastinum (15.3%), cervical region (6.6%) and pelvis (2.2%). Markedly improved survival has been noted in each decade (P < 0.002). Sixteen percent of lesions were over 10 cm in greatest dimension, while 84% were high-grade. Disease-specific survival at 1, 2, 5 and 20 years for the entire cohort was 81, 70, 61 and 59%, respectively. Superior survival was observed for infants <1 year of age (P < 0.001). Neuroblastomas in the mediastinum and pelvis had a better prognosis (P < 0.05) while high-grade and lesions over 10 cm carried a worse prognosis (P < 0.022). Surgery but not radiotherapy was associated with improvement in survival (P < 0.001). Multivariate analysis identified age, tumor location, stage, decade of diagnosis and surgical treatment as independent prognostic factors. Neuroblastoma remains a common malignancy with markedly improving patient outcomes. Early diagnosis and surgical therapy continue to provide the best chance for cure. More effective therapies for patients presenting over 1 year of age or those with advanced disease are still needed.

Pharmacokinetics and pharmacogenetics of 13-cis-retinoic acid in the treatment of neuroblastoma

There are a number of factors relating to the clinical pharmacology of 13-cis-Retinoic Acid (13-cisRA) which, taken together, provide a strong case for the potential benefit of a therapeutic monitoring approach to ensure that uniform plasma concentrations of 13-cisRA are achieved in all patients. Firstly, low dose, continuous use of 13-cisRA has been shown to provide limited or no clinical benefit in neuroblastoma patients, whereas a high-dose, intermittent regimen resulted in a significant improvement in event-free survival. This suggests that dose levels and therefore plasma concentrations of drug are important determinants of 13-cisRA efficacy. Secondly, the currently used 13-cisRA dosing regimen of 160 mg/m(2)/day results in a >10-fold variation in plasma concentrations, with plasma concentrations observed in a significant percentage of patients below those required for activity in neuroblastoma cells in vitro. Importantly, there would appear to be limited intra-patient variation in 13-cisRA plasma concentrations, i.e. those patients with lower 13-cisRA plasma concentrations following a single dose of 13-cisRA are likely to have similarly low concentrations following all doses of 13-cisRA on subsequent courses. As 13-cisRA is given as chronic treatment, those patients experiencing lower plasma concentrations on the current dosing regimen will potentially be exposed to sub-therapeutic concentrations of drug for the entire 6 month treatment period. While this type of pharmacokinetic monitoring approach may prove to be beneficial in the short term, an increased knowledge of pharmacogenetic factors influencing to the metabolism of 13-cisRA may ultimately allow us to identify patients who may be less likely to benefit from treatment due to an increased rate of parent drug metabolism. In this respect, pharmacogenetic studies assessing the relative expression levels or mutations in enzymes such as cytochrome P450 (CYP) and particularly CYP26 are needed to assess any potential association with rate of metabolism in vivo.

Pharmacokinetics and metabolism of 13-cis-retinoic acid (isotretinoin) in children with high-risk neuroblastoma - a study of the United Kingdom Children's Cancer Study Group

The administration of 13-cis-retinoic acid (13-cisRA), following myeloablative therapy improves 3-year event-free survival rates in children with high-risk neuroblastoma. This study aimed to determine the degree of inter-patient pharmacokinetic variation and extent of metabolism in children treated with 13-cisRA. 13-cis-retinoic acid (80 mg m⁻² b.d.) was administered orally and plasma concentrations of parent drug and metabolites determined on days 1 and 14 of courses 2, 4 and 6 of treatment. Twenty-eight children were studied. The pharmacokinetics of 13-cisRA were best described by a modified one-compartment, zero-order absorption model combined with lag time. Mean population pharmacokinetic parameters included an apparent clearance of 15.9 l h⁻¹, apparent volume of distribution of 85 l and absorption lag time of 40 min with a large inter-individual variability associated with all parameters (coefficients of variation greater than 50%). Day 1 peak 13-cisRA levels and exposure (AUC) were correlated with method of administration (P<0.02), with 2.44- and 1.95-fold higher parameter values respectively, when 13-cisRA capsules were swallowed as opposed to being opened and the contents mixed with food before administration. Extensive accumulation of 4-oxo-13-cisRA occurred during each course of treatment with plasma concentrations (mean±s.d. 4.67±3.17 μM) higher than those of 13-cisRA (2.83±1.44 μM) in 16 out of 23 patients on day 14 of course 2. Extensive metabolism to 4-oxo-13-cisRA may influence pharmacological activity of 13-cisRA.

Four weeks of oral isotretinoin treatment causes few signs of general toxicity in male and female Sprague–Dawley rats

Despite widespread use of isotretinoin for its anti-acne effects and its current evaluation in clinical trials as a cancer treatment, little is known about its general toxicity in adult nonpregnant animals, particularly after oral administration which mimics the human route. Here, adult male and female Sprague-Dawley rats were gavaged daily with 0 (soy oil), 7.5, or 15 mg/kg isotretinoin for 28 days during which time body weight, food/water intake, and estrous phase were measured. At sacrifice, organ weights were collected and concentrations of dopamine (DA), serotonin and metabolites were measured in frontal cortex, striatum, hippocampus, and diencephalon. Food intake was mildly decreased in both treated groups (approximately 15% in males and 7% in females); however, body weight and water consumption were unaffected. The estrous cycle appeared slightly affected (i.e., lengthened by 15 mg/kg, and both treated groups appeared to have less time in diestrus and more time in estrus). Kidney/body weight ratio was decreased by 7.5 and 15 mg/kg isotretinoin and spleen/body weight ratio was increased in the 7.5 mg/kg group. Males of the 7.5 mg/kg group exhibited significantly higher gonad/body weight ratios than did same-sex controls. Concentrations of monoamine and metabolites in the frontal cortex and diencephalon were unaffected. Nor were striatal DA and DOPAC concentrations affected; however, there were isolated effects on striatal HVA and 5-HIAA. Hippocampal DA concentrations were marginally increased. These data indicate mild effects resulting from oral isotretinoin treatment at doses which likely produce serum levels within the range of humans.

A comparison of current neuroblastoma chemotherapeutics

Neuroblastoma is the most common solid tumour in childhood. Modern management includes a biopsy to perform genetic studies. Based on clinical data and Myc-N amplification (MNA), patients are divided in three prognostic groups: the low-risk (Stage 1, 2, 4S without MNA) has an event-free survival (EFS) of > 90% with surgery alone; the intermediate-risk (Stage 3, > 1 year of age, without MNA and Stage 3 and 4 infants without MNA) has an EFS of approximately 80% with mild chemotherapy and surgery; the high-risk group includes Stage 4, > 1 year of age and any stage and age with MNA. These patients are treated with chemotherapy, surgery, megatherapy, irradiation and 13-cis-retinoic acid. With this complex therapy, a 5-year EFS of 30-50% can be obtained.

Health status of young children during therapy for advanced neuroblastoma

BACKGROUND

The purpose of this study was to describe the health status experienced by young children during various phases of therapy for advanced neuroblastoma.

METHODS

Nineteen patients aged 2.00-4.99 years at the time of diagnosis of neuroblastoma (stages 3 or 4) who received active therapy between 1996 and 2000 were enrolled on the study. Their parents provided proxy assessments of their health status at a maximum of 10 assessment points during therapy using the Comprehensive Health Status Classification System for Pre-school Children (CHSCS-PS), which assesses level of function on 10 separate health domains.

RESULTS

Eighty-six assessment questionnaires were completed. Maximum morbidity was reported immediately following diagnosis and in the 2-3 weeks following bone marrow transplantation. The greatest morbidity was observed in the pain, self-care, mobility, and emotion domains.

CONCLUSIONS

In addition to facing a high risk of mortality, young children being treated for advanced neuroblastoma also experience considerable morbidity.

Neuroblastoma: evolving therapies for a disease with many faces

Neuroblastoma is the most common extra-cranial solid tumor in children and has a heterogeneous clinical presentation and course. Clinical and biologic features of this disease have been used to develop risk-based therapy. Patients with low-risk disease can be treated with surgery alone. Patients with intermediate-risk features have an excellent prognosis after treatment with surgery and a relatively short course of standard dose chemotherapy. Unfortunately, most children with neuroblastoma present with advanced disease. More than 60% of patients with high-risk features will succumb to their disease despite intensive therapy including a myeloablative consolidation. Research efforts to understand the biologic basis of neuroblastoma and to identify new, more effective therapies are essential to improve the outcome for these children.

Detection and treatment of minimal residual disease in high-risk neuroblastoma

Intensive, myeloablative therapy supported by autologous hematopoietic stem-cell transplantation (AHSCT) has improved the outcome for children with high-risk neuroblastoma. However, >50% of patients develop recurrent neuroblastoma, often from minimal residual disease (MRD). Immunocytological and reverse transcriptase polymerase chain reaction (RT-PCR) for genes highly expressed in neuroblastoma both can detect small amounts of MRD in blood and bone marrow, and detection of MRD at certain levels during therapy has prognostic value. Radionucleotide scans using meta-iodobenzaguanidine (MIBG) imaging allows sensitive detection of neuroblastoma in patients, but whether or not all MIBG-positive disease detected after AHSCT will progress remains to be defined and is complicated by use of post-AHSCT therapy. Selective removal of tumor cells from marrow or blood stem cells harvested for AHSCT could decrease recurrence by preventing infusion of tumorigenic cells with AHSCT. Treating MRD after AHSCT with the differentiation-inducing retinoid 13-cis-retinoic acid significantly /improved EFS of high-risk neuroblastoma patients. Randomized clinical trials in the Children's Oncology Group are testing the value of purging blood stem cells and also whether post-AHSCT therapy with an anti-GD2 monoclonal antibody (combined with cytokines) improves outcome over use of 13-cis-retinoic acid alone. New approaches to treating neuroblastoma MRD that are in early clinical trials include the cytotoxic retinoid fenretinide and the hu14.18-IL2 immunocytokine. It is anticipated that testing novel approaches to treating neuroblastoma MRD will be the subject of future phase-III randomized trials.

Gene and protein expression profiling during differentiation of neuroblastoma cells triggered by 13-cis retinoic acid

PURPOSE

The precise changes in RNA and protein expression that accompany neuroblastoma differentiation remain unknown. The authors used microarray technologies to screen molecules associated with the differentiation of neuroblastoma (NB) cells induced by 13-cis retinoic acid.

METHODS

The authors quantified the expression of 2,061 RNA transcripts related to oncogenesis and of 380 proteins expressed in SK-N-SH and CHP-134 NB cell lines in the presence or absence of 13-cis retinoic acid.

RESULTS

Hierarchical clustering captured gene expression altered during neuroblastoma differentiation induced by 13-cis retinoic acid. Several genes were further abstracted based on P values below 0.0017 or protein chips observed in both NB cell lines. The altered expressions of gene products revealed by both DNA and protein chips were in agreement. The expressions of N-myc, cyclin D3, and Wnt10B were downregulated, whereas those of retinoblastoma (RB) and related genes (p107, RB2/p130, p300/CBP, E2F-1, DP-1) as well as others were upregulated.

CONCLUSIONS

These results suggest that microarray technology can screen for genes that are important in neuroblastoma differentiation.

Clinical and cellular pharmacology in relation to solid tumours of childhood

Our understanding of the clinical and cellular pharmacology of drugs commonly used in the treatment of childhood cancer have increased greatly over the past two decades. However, with the exception of childhood acute lymphoblastic leukaemia (ALL), our current knowledge of factors such as inter-patient pharmacokinetic variability and cellular determinants of chemosensitivity has not been utilized in the design of integrated clinical studies. Recent pre-clinical and clinical evaluation of the topoisomerase I inhibitors topotecan and irinotecan has highlighted the potential importance of pharmacological factors in their effectiveness as cytotoxics. In this review, the clinical and cellular pharmacology of vincristine, actinomycin D, doxorubicin, cyclophosphamide, ifosfamide, cisplatin, carboplatin and etoposide will be discussed in relation to the major paediatric solid tumours. For each disease type, knowledge of the clinical and cellular pharmacology of a candidate drug will be related to pharmacodynamic responses such as response, toxicity and prognosis. For diseases such as Wilms' tumour, osteogenic sarcoma and Ewing's tumour, histological response to initial induction chemotherapy is of prognostic significance, and the depth of response is increasingly recognised as an important determinant of prognosis for high-risk neuroblastoma. For several of these tumour types, the dose-intensity of chemotherapy may be an important variable in determining prognosis. However the relationship between pharmacokinetic variability, cellular pharmacology and the major determinants of chemosensitivity to those drugs employed in first line therapy is unknown. The study of these relationships, by means of up front window studies in children who present with high-risk disease, may be as important as the introduction of new agents. Indeed, the optimisation of current therapies may be required to allow a fully informed selection of those children for whom novel therapies are truly needed. Funding and international collaboration at the clinical and scientific level would be required to achieve these aims.

Retinoid therapy of high-risk neuroblastoma

Retinoids are derivatives of vitamin A that include all trans-retinoic acid (ATRA), 13-cis-retinoic acid, (13-cis-RA), and fenretinide (4-HPR). High levels of either ATRA or 13-cis-RA can cause arrest of cell growth and morphological differentiation of human neuroblastoma cell lines, and phase I trials showed that higher and more sustained drug levels were obtained with 13-cis-RA relative to ATRA. A phase III randomized trial showed that high-dose, pulse therapy with 13-cis-RA given after completion of intensive chemoradiotherapy (with or without autologous bone marrow transplantation) significantly improved event-free survival in high-risk neuroblastoma. The cytotoxic retinoid 4-HPR achieved multi-log cell kills in neuroblastoma cell lines resistant to ATRA and 13-cis-RA, and a pediatric phase I trial has shown it to be well tolerated. Cytotoxicity of 4-HPR is mediated at least in part by increasing tumor cell ceramide levels and combining 4-HPR with ceramide modulators increased anti-tumor activity in pre-clinical models. Thus, further clinical trials of 4-HPR in neuroblastoma, and of 4-HPR in combination with ceramide modulators, are warranted.

In situ photoaffinity labeling of the target protein for lembehyne A, a neuronal differentiation inducer

A C(36) linear acetylene alcohol, lembehyne A (LB-A), induces neuronal differentiation against neuroblastoma cells morphologically and also functionally. The differentiation and cytostatic effect induced by LB-A was specific to neuroblastoma, Neuro 2A cells. To identify the target protein for LB-A, a radioactive photoaffinity probe, [(125)I]18-(2'-azido-5'-iodo-benzoyloxy)-LB-18 ([(125)I]azido-LB-18), was synthesized. As a result of in situ labeling experiments against Neuro 2A cells, a protein of M(r) 30 kDa was photolabeled specifically. This labeling was inhibited in the presence of LB-A or the active analogs of LB-A, whereas the inactive analogs showed no inhibitory effect on this labeling. These results suggest that this protein of M(r) 30 kDa is the target protein for LB-A and may play an important role for the neuronal differentiation in neuroblastoma, Neuro 2A cells.

Pyridoacridine alkaloids inducing neuronal differentiation in a neuroblastoma cell line, from marine sponge Biemna fortis

A new and three known pyridoacridine alkaloids were isolated from the Indonesian marine sponge Biemna fortis as neuronal differentiation inducers against a murine neuroblastoma cell line, Neuro 2A. The chemical structure of the new compound, labuanine A (1), was determined by spectroscopic study and chemical conversion. These pyridoacridine alkaloids induced multipolar neuritogenesis in more than 50% of cells at 0.03-3 micro M concentration. Compound 3, which showed the strongest neuritogenic activity among them, also induced increase of acetylcholinesterase, a neuronal marker in Neuro 2A and arrested cell cycle at the G2/M phase.

The synthetic retinoid RO 13-6307 induces neuroblastoma differentiation in vitro and inhibits neuroblastoma tumour growth in vivo

Retinoids modulate cell proliferation, differentiation and apoptosis in a variety of tumour cells including leukaemia and neuroblastoma, a childhood tumour of the sympathetic nervous system. 13-cis retinoic acid is in clinical use against minimal residual disease in neuroblastoma, where the effect seems to depend on dose, scheduling and tumour mass. Novel retinoids are searched for, to improve potency and lower toxicity. We investigated the effect of the synthetic retinoid Ro 13-6307 on neuroblastoma growth in vitro on SK-N-BE(2) and SH-SY5Y cells. Furthermore, effects on tumour growth and the toxicity profile were investigated in a rat xenograft model. Effects of Ro 13-6307 were compared to 13-cis RA (retinoic acid) in vitro and in vivo. Neuroblastoma cells treated with 1 microM Ro 13-6307 exhibited neuronal differentiation, decreased proliferation and accumulation of cells in G1 phase in at least the same magnitude as 5 microM 13-cis RA. No apoptosis was detected in vitro. Treatment of nude rats with neuroblastoma using Ro 13-6307, 0.12 mg p.o. daily, decreased neuroblastoma growth in vivo, in terms of tumour volume during treatment and tumour weight at sacrifice (p < 0.05). In contrast, Ro 13-6307, 0.08 mg p.o. daily, resulted in no significant reduction in tumour growth. All rats treated with Ro 13-6307 gained less weight than control rats, but they exhibited no other signs of toxicity. The toxicity profile of Ro 13-6307 was similar to what we found with 13-cis RA. Our preclinical results suggest that Ro 13-6307 may be a candidate retinoid for clinical oral therapy of neuroblastoma in children.

Retinoic acid reduces the cytotoxicity of cyclopentenyl cytosine in neuroblastoma cells

In this paper, it is demonstrated that all-trans, 9-cis and 13-cis retinoic acid (RA) decreased the sensitivity of SK-N-BE(2)c neuroblastoma cells towards the chemotherapeutic agent cyclopentenyl cytosine (CPEC), a potent inhibitor of cytosine-5'-triphosphate synthetase. Retinoic acid attenuated CPEC-induced apoptosis as reflected by a decreased caspase-3 induction. Retinoic acid decreased the accumulation of CPEC, whereas the salvage of cytidine was strongly increased. Metabolic labeling studies using [(3)H]uridine showed a strongly decreased biosynthesis of CTP via CTP synthetase. Retinoic acid likely confers resistance of neuroblastoma cells to CPEC in part by slowing down proliferation, and in part by shifting the synthesis of CTP towards the salvage of cytidine, thereby bypassing CTP synthetase.

Adrenocorticotropic hormone in the aetiology and regression of neuroblastoma

Neuroblastoma is predominantly a paediatric neoplasm of the sympathetic nervous system. Despite the aggressive nature of the disease, spontaneous regression is frequently observed in infants diagnosed under the age of 12 months; especially with a specific stage referred to as stage 4s. Discovering the conditions, the elements, the mechanism and the indices behind this regression phenomenon could have therapeutic potential for prevention and cure. A review of the literature has implicated adrenocorticotropin hormone in both the aetiology and spontaneous regression of neuroblastoma. Manipulation of adrenocorticotropin hormone may offer hope for prevention and cure. Ingestible products such as retinoic acid, glycyrrhizic acid, salsolinol and ketoconazole acting in concert, could represent instrumental tools in a therapeutic manipulation process.

Receptor for advanced glycation end products plays a more important role in cellular survival than in neurite outgrowth during retinoic acid-induced differentiation of neuroblastoma cells

The receptor for advanced glycation end products (RAGE), a member of the immunoglobulin superfamily, is known to interact with amphoterin. This interaction has been proposed to play a role in neurite outgrowth and process elongation during neurodifferentiation. However, there is as yet no direct evidence of the relevance of this pathway to neurodifferentiation under physiological conditions. In this study we have investigated a possible role of RAGE and amphoterin in the retinoic acid-induced differentiation of neuroblastoma cells. The functional inactivation of RAGE by dominant negative and antisense strategies showed that RAGE is not required for process outgrowth or differentiation, although overexpression of RAGE accelerates the elongation of neuritic processes. Using the antisense strategy, amphoterin was shown to be essential for process outgrowth and differentiation, suggesting that amphoterin may interact with other molecules to exert its effect in this context. Interestingly, the survival of the neuroblastoma cells treated with retinoic acid was partly dependent on the expression of RAGE, and inhibition of RAGE function partially blocked the increase in anti-apoptotic protein Bcl-2 following retinoic acid treatment. Based on these results we propose that a combination therapy using RAGE blockers and retinoic acid may prove as a useful approach for chemotherapy for the treatment of neuroblastoma.

Bioavailability and dose-dependent anti-tumour effects of 9-cis retinoic acid on human neuroblastoma xenografts in rat

Neuroblastoma, the most common extracranial solid tumour in children, may undergo spontaneous differentiation or regression, but the majority of metastatic neuroblastomas have poor prognosis despite intensive treatment. Retinoic acid regulates growth and differentiation of neuroblastoma cells in vitro, and has shown activity against human neuroblastomas in vivo. The retinoid 9-cis RA has been reported to induce apoptosis in vitro, and to inhibit the growth of human neuroblastoma xenografts in vivo. However, at given dosage, the treatment with 9-cis RA caused significant toxic side effects. In the present study we investigated the bioavailability of 9-cis RA in rat. In addition, we compared two different dose schedules using 9-cis RA. We found that a lower dose of 9-cis RA (2 mg day(-1)) was non-toxic, but showed no significant effect on tumour growth. The bioavailability of 9-cis RA in rat was 11% and the elimination half-life (t1/2) was 35 min. Considering the short t1/2, we divided the toxic, but tumour growth effective dose 5 mg day(-1) into 2.5 mg p.o. twice daily. This treatment regimen showed no toxicity but only limited effect on tumour growth. Our results suggest that 9-cis RA may only have limited clinical significance for treatment of children with poor prognosis neuroblastoma.

Retinoid therapy of childhood cancer

In vitro studies that showed RA could cause growth arrest and differentiation of myelogenous leukemia and neuroblastoma led to clinical trials of retinoids in APL and neuroblastoma that increased survival for both of those diseases. In the case of APL, ATRA has been the drug of choice, and preclinical and clinical data support direct combinations of ATRA with cytotoxic chemotherapy. For neuroblastoma, a phase I study defined a dose of 13-cis-RA, which was tolerable in patients after myeloablative therapy, and a phase III trial that showed postconsolidation therapy with 13-cis-RA improved EFS for patients with high-risk neuroblastoma. Preclinical studies in neuroblastoma indicate that ATRA or 13-cis-RA can antagonize cytotoxic chemotherapy and radiation, so use of 13-cis-RA in neuroblastoma is limited to maintenance after completion of cytotoxic chemotherapy and radiation. A limitation on the antitumor benefit of ATRA in APL is the marked decrease in drug levels that occurs during therapy as a result of induction of drug metabolism, resulting in a shorter drug half-life and decreased plasma levels. Although early studies sought to overcome the pharmacologic limitations of ATRA therapy in APL, the demonstration that ATO is active against APL in RA-refractory patients has led to a focus on studies employing ATO. Use of 13-cis-RA in neuroblastoma has avoided the decreased plasma levels seen with ATRA. It is likely that recurrent disease seen during or after 13-cis-RA therapy in neuroblastoma is due to tumor cell resistance to retinoid-mediated differentiation induction. Studies in neuroblastoma cell lines resistant to 13-cis-RA and ATRA have shown that they can be sensitive, and in some cases collaterally hypersensitive, to the cytotoxic retinoid fenretinide. Fenretinide induces tumor cell cytotoxicity rather than differentiation, acts independently from RA receptors, and in initial phase I trials has been well tolerated. Clinical trials of fenretinide, alone and in combination with ceramide modulators, are in development.