Wild-type ALK and activating ALK-R1275Q and ALK-F1174L mutations upregulate Myc and initiate tumor formation in murine neural crest progenitor cells

ALK upregulates POSTN and WNT signaling to drive neuroblastoma

Neuroblastoma is the most common extracranial solid tumor of childhood. While MYCN and mutant anaplastic lymphoma kinase (ALKF1174L) cooperate in tumorigenesis, how ALK contributes to tumor formation remains unclear. Here, we used a human stem cell-based model of neuroblastoma. Mis-expression of ALKF1174L and MYCN resulted in shorter latency compared to MYCN alone. MYCN tumors resembled adrenergic, while ALK/MYCN tumors resembled mesenchymal, neuroblastoma. Transcriptomic analysis revealed enrichment in focal adhesion signaling, particularly the extracellular matrix genes POSTN and FN1 in ALK/MYCN tumors. Patients with ALK-mutant tumors similarly demonstrated elevated levels of POSTN and FN1. Knockdown of POSTN, but not FN1, delayed adhesion and suppressed proliferation of ALK/MYCN tumors. Furthermore, loss of POSTN reduced ALK-dependent activation of WNT signaling. Reciprocally, inhibition of the WNT pathway reduced expression of POSTN and growth of ALK/MYCN tumor cells. Thus, ALK drives neuroblastoma in part through a feedforward loop between POSTN and WNT signaling.

Targeted treatment of refractory primitive neuroectodermal tumor arising from an immature teratoma with crizotinib leading to a sustained response

Here we present a case of metastatic PNET which arose from an immature teratoma that was refractory to standard Ewing sarcoma chemotherapy. This PNET was determined to have elevated levels of ALK protein via IHC. The patient was treated with crizotinib on a palliative basis with a sustained response.

Fragment-based discovery of novel phenyltriazolyl derivatives as allosteric type-I1/2 ALK inhibitors with promising antitumor effects

Based on the high-throughput screening hit BY-1, a series of phenyltriazolyl derivatives were developed. Satisfyingly, most compounds were detected moderate to excellent antitumor effects against Karpas299 and H2228 cells. Among them, 12k bearing 4‑hydroxypiperidinyl group exhibited the optimal activities against tested cells with IC₅₀ values of 51 nM and 175 nM, as well as promising inhibitory effects on ALK^WT (3.7 nM) and ALK^L1196M (6.8 nM). Unlike the conventional type-I ALK inhibitors, molecular models identified 12k as an allosteric type-I^1/2 inhibitor by forming key interactions in both the ATP binding region and the hydrophobic back pocket of ALK. Intriguingly, 12k could dose-dependently induce apoptosis on H2228 cell and inhibit colony formation and tumor cell migration. Taken together, the rationalization of 12k may shed new light on the identification of novel allosteric type-I^1/2 ALK inhibitors.

A Focus on Regulatory Networks Linking MicroRNAs, Transcription Factors and Target Genes in Neuroblastoma

Neuroblastoma (NB) is a tumor of the peripheral sympathetic nervous system that substantially contributes to childhood cancer mortality. NB originates from neural crest cells (NCCs) undergoing a defective sympathetic neuronal differentiation and although the starting events leading to the development of NB remain to be fully elucidated, the master role of genetic alterations in key oncogenes has been ascertained: (1) amplification and/or over-expression of MYCN, which is strongly associated with tumor progression and invasion; (2) activating mutations, amplification and/or over-expression of ALK, which is involved in tumor initiation, angiogenesis and invasion; (3) amplification and/or over-expression of LIN28B, promoting proliferation and suppression of neuroblast differentiation; (4) mutations and/or over-expression of PHOX2B, which is involved in the regulation of NB differentiation, stemness maintenance, migration and metastasis. Moreover, altered microRNA (miRNA) expression takes part in generating pathogenetic networks, in which the regulatory loops among transcription factors, miRNAs and target genes lead to complex and aberrant oncogene expression that underlies the development of a tumor. In this review, we have focused on the circuitry linking the oncogenic transcription factors MYCN and PHOX2B with their transcriptional targets ALK and LIN28B and the tumor suppressor microRNAs let-7, miR-34 and miR-204, which should act as down-regulators of their expression. We have also looked at the physiologic role of these genetic and epigenetic determinants in NC development, as well as in terminal differentiation, with their pathogenic dysregulation leading to NB oncogenesis.

Defining Pathological Activities of ALK in Neuroblastoma, a Neural Crest-Derived Cancer

Neuroblastoma is a common extracranial solid tumour of childhood, responsible for 15% of cancer-related deaths in children. Prognoses vary from spontaneous remission to aggressive disease with extensive metastases, where treatment is challenging. Tumours are thought to arise from sympathoadrenal progenitor cells, which derive from an embryonic cell population called neural crest cells that give rise to diverse cell types, such as facial bone and cartilage, pigmented cells, and neurons. Tumours are found associated with mature derivatives of neural crest, such as the adrenal medulla or paraspinal ganglia. Sympathoadrenal progenitor cells express anaplastic lymphoma kinase (ALK), which encodes a tyrosine kinase receptor that is the most frequently mutated gene in neuroblastoma. Activating mutations in the kinase domain are common in both sporadic and familial cases. The oncogenic role of ALK has been extensively studied, but little is known about its physiological role. Recent studies have implicated ALK in neural crest migration and sympathetic neurogenesis. However, very few downstream targets of ALK have been identified. Here, we describe pathological activation of ALK in the neural crest, which promotes proliferation and migration, while preventing differentiation, thus inducing the onset of neuroblastoma. Understanding the effects of ALK activity on neural crest cells will help find new targets for neuroblastoma treatment.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumours that originate from cells of neural crest (NC) origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage. Therapeutic resistance, post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell (CSC)-like subpopulations, which through their self-renewing capacity, intermittent and slow cell cycles, drug-resistant and reversibly adaptive plastic phenotypes, represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs. In this review, dedicated to NB CSCs and the prospects for their therapeutic eradication, we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction, specification, epithelial to mesenchymal transition and migratory behaviour, in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB. We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs, before providing a comprehensive review of the salient molecules, signalling pathways, mechanisms, tumour microenvironmental and therapeutic conditions involved in promoting, selecting and maintaining NB CSC subpopulations, and that underpin their therapy-resistant, self-renewing metastatic behaviour. Finally, we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance, post-therapeutic relapse and metastatic progression.

Anaplastic Lymphoma Kinase Overexpression Is Associated with Aggressive Phenotypic Characteristics of Ovarian High-Grade Serous Carcinoma

Deregulated full-length anaplastic lymphoma kinase (ALK) overexpression has been found in some primary solid tumors, but little is known about its role in ovarian high-grade serous carcinoma (HGSC). Herein, we focused on the functional roles of ALK in HGSC. Cytoplasmic ALK immunoreactivity without chromosomal rearrangement and gene mutations was significantly higher in HGSC compared with non-HGSC type ovarian carcinomas, and was significantly associated with several unfavorable clinicopathologic factors and poor prognosis. HGSC cell lines stably overexpressing ALK exhibited increased cell proliferation, enhanced cancer stem cell features, and accelerated cell mobility, whereas these phenotypes were abrogated in ALK-knockdown cells. Expression of the nervous system-associated gene, ELAVL3, and the corresponding protein (commonly known as HuC) was significantly increased in cells overexpressing ALK. There was increased expression of Sox2 and Sox3 (genes associated with the neural progenitor population) in ALK-overexpressing but not ALK-knockdown cells. Furthermore, overexpression of Sox2 or Sox3 enhanced both ALK and ELAVL3 promoter activities, suggesting the existence of ALK/Sox/HuC signaling loops. Finally, ALK overexpression was due to increased expression of neuroendocrine markers, including synaptophysin, CD56, and BCL2, in HGSC tissues. These findings suggest that overexpression of full-length ALK may influence the biological behavior of HGSC through cooperation with ELAVL3 and Sox factors, leading to establishment and maintenance of the aggressive phenotypic characteristics of HGSC.

Anaplastic lymphoma kinase (alk), a neuroblastoma associated gene, is expressed in neural crest domains during embryonic development of Xenopus

Neuroblastoma is a neural crest-derived paediatric cancer that is the most common and deadly solid extracranial tumour of childhood. It arises when neural crest cells fail to follow their differentiation program to give rise to cells of the sympathoadrenal lineage. These undifferentiated cells can proliferate and migrate, forming tumours mostly found associated with the adrenal glands. Activating mutations in the kinase domain of anaplastic lymphoma kinase (ALK) are linked to high-risk cases, where extensive therapy is ineffective. However, the role of ALK in embryonic development, downstream signal transduction and in metastatic transformation of the neural crest is poorly understood. Here, we demonstrate high conservation of the ALK protein sequences among vertebrates. We then examine alk mRNA expression in the frog models Xenopus laevis and Xenopus tropicalis. Using in situ hybridisation of Xenopus embryos, we show that alk is expressed in neural crest domains throughout development, suggesting a possible role in neuroblastoma initiation. Lastly, RT-qPCR analyses show high levels of alk expression at tadpole stages. Collectively, these data may begin to elucidate how alk functions in neural crest cells and how its deregulation can result in tumorigenesis.

Biological categories of neuroblastoma based on the international neuroblastoma pathology classification for treatment stratification

The International Neuroblastoma Pathology Classification (INPC), which distinguishes a favorable histology (FH) and an unfavorable histology (UH), is one of the most powerful prognostic factors in patients with neuroblastoma. FH that shows spontaneous regression or age-appropriate tumor differentiation/maturation, is common in infants and has mutual interaction with Schwann cells via the NGF/NTRK1 pathway and gain of whole chromosome 17. In contrast, UH is prevalent in older children and is molecularly heterogeneous. MYCN amplification is the most frequent genomic abnormality in tumors with UH. MYCN-amplified tumors demonstrate characteristic histology, the same as MYC-positive neuroblastoma. Chromosome 1pLOH is often associated with MYCN amplification, but on the other hand, chromosome 11qLOH rarely occurs in combination with MYCN amplification. 11qLOH has an inferior prognostic impact in UH without MYCN amplification. The high expression of ALK protein is a negative prognostic factor in both ALK mutated or amplified tumors and FH, but not in UH. Abnormal maintenance/elongation of telomeres; overexpression of telomerase reverse transcriptase (TERT) and the alternative lengthening of telomeres (ALT) phenotype due to ATRX mutation, are another molecular event in UH. The INPC, incorporating immunohistochemistry for MYCN, MYC, ALK, TERT and ATRX, represents a practical and implementable approach to create the biological category for the future management of patients with this unique disease.

In vitro Modeling of Embryonal Tumors

A subset of pediatric tumors affects very young children and are thought to arise during fetal life. A common theme is that these embryonal tumors hijack developmental programs, causing a block in differentiation and, as a consequence, unrestricted proliferation. Embryonal tumors, therefore typically maintain an embryonic gene signature not found in their differentiated progeny. Still, the processes underpinning malignant transformation remain largely unknown, which is hampering therapeutic innovation. To gain more insight into these processes, in vitro and in vivo research models are indispensable. However, embryonic development is an extremely dynamic process with continuously changing cellular identities, making it challenging to define cells-of-origin. This is crucial for the development of representative models, as targeting the wrong cell or targeting a cell within an incorrect developmental time window can result in completely different phenotypes. Recent innovations in in vitro cell models may provide more versatile platforms to study embryonal tumors in a scalable manner. In this review, we outline different in vitro models that can be explored to study embryonal tumorigenesis and for therapy development.

Lineage-restricted sympathoadrenal progenitors confer neuroblastoma origin and its tumorigenicity

Neuroblastoma (NB) is the most common cancer in infants and it accounts for six percent of all pediatric malignancies. There are several hypotheses proposed on the origins of NB. While there is little genetic evidence to support this, the prevailing model is that NB originates from neural crest stem cells (NCSCs). Utilizing in vivo mouse models, we demonstrate that targeting MYCN oncogene to NCSCs causes perinatal lethality. During sympathoadrenal (SA) lineage development, SOX transcriptional factors drive the transition from NCSCs to lineage-specific progenitors, characterized by the sequential activation of Sox9/Sox10/Sox4/Sox11 genes. We find the NCSCs factor SOX10 is not expressed in neuroblasts, but rather restricted to the Schwannian stroma and is associated with a good prognosis. On the other hand, SOX9 expression in NB cells was associated with several key biological processes including migration, invasion and differentiation. Moreover, manipulating SOX9 gene predominantly affects lineage-restricted SA progenitors. Our findings highlight a unique molecular SOX signature associated with NB that is highly reminiscent of SA progenitor transcriptional program during embryonic development, providing novel insights into NB pathobiology. In summary, we provide multiple lines of evidence suggesting that multipotent NCSCs do not contribute to NB initiation and maintenance.

Differences in Genomic Profiles and Outcomes Between Thoracic and Adrenal Neuroblastoma

BACKGROUND

Neuroblastoma is a biologically and clinically heterogeneous disease. Based on recent studies demonstrating an association between the primary tumor site, prognosis, and commonly measured tumor biological features, we hypothesized that neuroblastomas arising in different sites would show distinct genomic features reflective of the developmental biology of the sympathicoadrenal nervous system.

METHODS

We first compared genomic and epigenomic data of primary diagnostic neuroblastomas originating in the adrenal gland (n = 646) compared to thoracic sympathetic ganglia (n = 118). We also evaluated association of common germline variation with these primary sites in 1027 European-American neuroblastoma patients.

RESULTS

We observed higher rates of MYCN amplification, chromosome 1q gain, and chromosome 11q deletion among adrenal tumors, which were highly predictive of functional RNA signatures. Surprisingly, thoracic neuroblastomas were more likely to harbor ALK driver mutations than adrenal cases among all cases (odds ratio = 1.89, 95% confidence interval = 1.04 to 3.43), and among cases without MYCN amplification (odds ratio = 2.86, 95% confidence interval = 1.48 to 5.49). Common germline single nucleotide polymorphisms (SNPs) in BARD1 (previously associated with high-risk neuroblastoma) were found to be strongly associated with predisposition for origin at adrenal, rather than thoracic, sites.

CONCLUSIONS

Neuroblastomas arising in the adrenal gland are more likely to harbor structural DNA aberrations including MYCN amplification, whereas thoracic tumors show defects in mitotic checkpoints resulting in hyperdiploidy. Despite the general association of ALK mutations with high-risk disease, thoracic tumors are more likely to harbor gain-of-function ALK aberrations. Site of origin is likely reflective of stage of sympathetic nervous system development when malignant transformation occurs and is a surrogate for underlying tumor biology.

Expression of the Neuroblastoma-Associated ALK-F1174L Activating Mutation During Embryogenesis Impairs the Differentiation of Neural Crest Progenitors in Sympathetic Ganglia

Neuroblastoma (NB) is an embryonal malignancy derived from the abnormal differentiation of the sympathetic nervous system. The Anaplastic Lymphoma Kinase (ALK) gene is frequently altered in NB, through copy number alterations and activating mutations, and represents a predisposition in NB-genesis when mutated. Our previously published data suggested that ALK activating mutations may impair the differentiation potential of neural crest (NC) progenitor cells. Here, we demonstrated that the expression of the endogenous ALK gene starts at E10.5 in the developing sympathetic ganglia (SG). To decipher the impact of deregulated ALK signaling during embryogenesis on the formation and differentiation of sympathetic neuroblasts, Sox10-Cre;LSL-ALK-F1174L embryos were produced to restrict the expression of the human ALK-F1174L transgene to migrating NC cells (NCCs). First, ALK-F1174L mediated an embryonic lethality at mid-gestation and an enlargement of SG with a disorganized architecture in Sox10-Cre;LSL-ALK-F1174L embryos at E10.5 and E11.5. Second, early sympathetic differentiation was severely impaired in Sox10-Cre;LSL-ALK-F1174L embryos. Indeed, their SG displayed a marked increase in the proportion of NCCs and a decrease of sympathetic neuroblasts at both embryonic stages. Third, neuronal and noradrenergic differentiations were blocked in Sox10-Cre;LSL-ALK-F1174L SG, as a reduced proportion of Phox2b⁺ sympathoblasts expressed βIII-tubulin and almost none were Tyrosine Hydroxylase (TH) positive. Finally, at E10.5, ALK-F1174L mediated an important increase in the proliferation of Phox2b⁺ progenitors, affecting the transient cell cycle exit observed in normal SG at this embryonic stage. Altogether, we report for the first time that the expression of the human ALK-F1174L mutation in NCCs during embryonic development profoundly disturbs early sympathetic progenitor differentiation, in addition to increasing their proliferation, both mechanisms being potential crucial events in NB oncogenesis.

The roles played by the MYCN, Trk, and ALK genes in neuroblastoma and neural development

Neuroblastoma is one of the most frequent, yet distinctive and challenging childhood tumors. The uniqueness of this tumor depends on its biological markers, which classify neuroblastomas into favorable and unfavorable, with 5-year survival rates ranging from almost 100-30%. In this review, we focus on some biological factors that play major roles in neuroblastoma: MYCN, Trk, and ALK. The MYCN and Trk family genes have been studied for decades and are known to be crucial for the tumorigenesis and progression of neuroblastoma. ALK gene mutations have been recognized recently to be responsible for familial neuroblastomas. Each factor plays an important role in normal neural development, regulating cell proliferation or differentiation by activating several signaling pathways, and interacting with each other. These factors have been studied not only as prognostic factors, but also as targets of neuroblastoma therapy, and some clinical trials are ongoing. We review the basic aspects of MYCN, Trk, and ALK in both neural development and in neuroblastoma.

PRIMA-1MET-induced neuroblastoma cell death is modulated by p53 and mycn through glutathione level

Background

Neuroblastoma is the most common extracranial solid tumor in children. This cancer has a low frequency of TP53 mutations and its downstream pathway is usually intact. This study assessed the efficacy of the p53 activator, PRIMA-1^MET, in inducing neuroblastoma cell death.

Methods

CellTiter 2.0 was used to study susceptibility and specificity of NB cell lines to PRIMA-1^MET. Real-time PCR and western blot were used to assess the most common p53 transactivation targets. Induction of p53 and Noxa, and inhibition of Cas3/7, were used to assess impact on cell death after PRIMA-1^MET treatment. Flow cytometry was used to analyze cell cycle phase and induction of apoptosis, reactive oxygen species, and the collapse of mitochondrial membrane potential.

Results

Neuroblastoma cell lines were at least four times more susceptible to PRIMA-1^MET than were primary fibroblasts and keratinocyte cell lines. PRIMA-1^MET induced cell death rapidly and in all cell cycle phases. Although PRIMA-1^MET activated p53 transactivation activity, p53’s role is likely limited because its main targets remained unaffected, whereas pan-caspase inhibitor demonstrated no ability to prevent cell death. PRIMA-1^MET induced oxidative stress and modulated the methionine/cysteine/glutathione axis. Variations of MYCN and p53 modulated intracellular levels of GSH and resulted in increased/decreased sensitivity of PRIMA-1^MET. PRIMA-1^MET inhibited thioredoxin reductase, but the effect of PRIMA-1^MET was not altered by thioredoxin inhibition.

Conclusions

PRIMA-1^MET could be a promising new agent to treat neuroblastoma because it demonstrated good anti-tumor action. Although p53 is involved in PRIMA-1^MET-mediated cell death, our results suggest that direct interaction with p53 has a limited role in neuroblastoma but rather acts through modulation of GSH levels.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1066-6) contains supplementary material, which is available to authorized users.

Differentiation of Human Embryonic Stem Cells to Sympathetic Neurons: A Potential Model for Understanding Neuroblastoma Pathogenesis

Background and Aims

Previous studies modelling human neural crest differentiation from stem cells have resulted in a low yield of sympathetic neurons. Our aim was to optimise a method for the differentiation of human embryonic stem cells (hESCs) to sympathetic neuron-like cells (SN) to model normal human SNS development.

Results

Using stromal-derived inducing activity (SDIA) of PA6 cells plus BMP4 and B27 supplements, the H9 hESC line was differentiated to neural crest stem-like cells and SN-like cells. After 7 days of PA6 cell coculture, mRNA expression of SNAIL and SOX-9 neural crest specifier genes and the neural marker peripherin (PRPH) increased. Expression of the pluripotency marker OCT 4 decreased, whereas TP53 and LIN28B expression remained high at levels similar to SHSY5Y and IMR32 neuroblastoma cell lines. A 5-fold increase in the expression of the catecholaminergic marker tyrosine hydroxylase (TH) and the noradrenergic marker dopamine betahydroxylase (DBH) was observed by day 7 of differentiation. Fluorescence-activated cell sorting for the neural crest marker p75, enriched for cells expressing p75, DBH, TH, and PRPH, was more specific than p75 neural crest stem cell (NCSC) microbeads. On day 28 post p75 sorting, dual immunofluorescence identified sympathetic neurons by PRPH and TH copositivity cells in 20% of the cell population. Noradrenergic sympathetic neurons, identified by copositivity for both PHOX2B and DBH, were present in 9.4% ± 5.5% of cells.

Conclusions

We have optimised a method for noradrenergic SNS development using the H9 hESC line to improve our understanding of normal human SNS development and, in a future work, the pathogenesis of neuroblastoma.

A new ALK isoform transported by extracellular vesicles confers drug resistance to melanoma cells

Background

Drug resistance remains an unsolved clinical issue in oncology. Despite promising initial responses obtained with BRAF and MEK kinase inhibitors, resistance to treatment develops within months in virtually all melanoma patients.

Methods

Microarray analyses were performed in BRAF inhibitor-sensitive and resistant cell lines to identify changes in the transcriptome that might play a role in resistance. siRNA approaches and kinase inhibitors were used to assess the involvement of the identified Anaplastic Lymphoma Kinase (ALK) in drug resistance. The capability of extracellular vesicles (EVs) to transfer drug resistant properties was investigated in co-culture assays.

Results

Here, we report a new mechanism of acquired drug resistance involving the activation of a novel truncated form of ALK. Knock down or inhibition of ALK re-sensitised resistant cells to BRAF inhibition and induced apoptosis. Interestingly, truncated ALK was also secreted into EVs and we show that EVs were the vehicle for transferring drug resistance.

Conclusions

To our knowledge, this is the first report demonstrating the functional involvement of EVs in melanoma drug resistance by transporting a truncated but functional form of ALK, able to activate the MAPK signalling pathway in target cells. Combined inhibition of ALK and BRAF dramatically reduced tumour growth in vivo. These findings make ALK a promising clinical target in melanoma patients.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0886-x) contains supplementary material, which is available to authorized users.

Neuroblastoma Origin and Therapeutic Targets for Immunotherapy

Neuroblastoma is a pediatric solid cancer of heterogeneous clinical behavior. The unique features of this type of cancer frequently hamper the process of determining clinical presentation and predicting therapy effectiveness. The tumor can spontaneously regress without treatment or actively develop and give rise to metastases despite aggressive multimodal therapy. In recent years, immunotherapy has become one of the most promising approaches to the treatment of neuroblastoma. Still, only one drug for targeted immunotherapy of neuroblastoma, chimeric monoclonal GD2-specific antibodies, is used in the clinic today, and its application has significant limitations. In this regard, the development of effective and safe GD2-targeted immunotherapies and analysis of other potential molecular targets for the treatment of neuroblastoma represents an important and topical task. The review summarizes biological characteristics of the origin and development of neuroblastoma and outlines molecular markers of neuroblastoma and modern immunotherapy approaches directed towards these markers.

The ALK receptor in sympathetic neuron development and neuroblastoma

The ALK gene encodes a tyrosine kinase receptor characterized by an expression pattern mainly restricted to the developing central and peripheral nervous systems. In 2008, the discovery of ALK activating mutations in neuroblastoma, a tumor of the sympathetic nervous system, represented a breakthrough in the understanding of the pathogenesis of this pediatric cancer and established mutated ALK as a tractable therapeutic target for precision medicine. Subsequent studies addressed the identity of ALK ligands, as well as its physiological function in the sympathoadrenal lineage, its role in neuroblastoma development and the signaling pathways triggered by mutated ALK. This review focuses on these different aspects of the ALK biology and summarizes the various therapeutic strategies relying on ALK inhibition in neuroblastoma, either as monotherapies or combinatory treatments.

Neural crest and cancer: Divergent travelers on similar paths

Neural crest cells are multipotent progenitors that dynamically interpret diverse microenvironments to migrate significant distances as a loosely associated collective and contribute to many tissues in the developing vertebrate embryo. Uncovering details of neural crest migration has helped to inform a general understanding of collective cell migration, including that which occurs during cancer metastasis. Here, we discuss several commonalities and differences of neural crest and cancer cell migration and behavior. First, we focus on some of the molecular pathways required for the initial specification and potency of neural crest cells and the roles of many of these pathways in cancer progression. We also describe epithelial-to-mesenchymal transition, which plays a critical role in initiating both neural crest migration and cancer metastasis. Finally, we evaluate studies that demonstrate myriad forms of cell-cell and cell-environment communication during neural crest and cancer collective migration to highlight the remarkable similarities in their molecular and cell biological regulation.

Combating Drug-Resistant Mutants of Anaplastic Lymphoma Kinase with Potent and Selective Type-I1/2 Inhibitors by Stabilizing Unique DFG-Shifted Loop Conformation

Targeted inhibition of anaplastic lymphoma kinase (ALK) dramatically improved therapeutic outcomes in the treatment of ALK-positive cancers, but unfortunately patients invariably progressed due to acquired resistance mutations in ALK. Currently available drugs are all type-I inhibitors bound to the ATP-binding pocket and are most likely to be resistant in patients harboring genetic mutations surrounding the ATP pocket. To overcome drug resistance, we rationally designed a novel kind of "bridge" inhibitor, which specially bind into an extended hydrophobic back pocket adjacent to the ATP-binding site of ALK. The novel type-I^1/2 inhibitors display excellent antiproliferation activity against ALK-positive cancer cells and appear superior to two clinically used drugs, crizotinib and ceritinib. Structural and molecular modeling analyses indicate that the inhibitor induces dramatic conformational transition and stabilizes unique DFG-shifted loop conformation, enabling persistent sensitivity to different genetic mutations in ALK. These data highlight a rationale for further development of next-generation ALK inhibitors to combat drug resistance.

Zebrafish as a model to study neuroblastoma development

Neuroblastoma is a pediatric solid tumor arising from embryonic neural crest progenitor cells that normally generate the peripheral sympathetic nervous system. As such, the location of neuroblastoma tumors is correlated with the distribution of major post-ganglionic clusters throughout the sympathetic chain, with the highest incidence in the adrenal medulla or lumbar sympathetic ganglia (~65%). Neuroblastoma is an enigmatic tumor that can spontaneously regress with minimal treatment or become highly metastatic and develop resistance to aggressive treatments, including radiation and high-dose chemotherapy. Age of diagnosis, stage of disease and cellular and genetic features often predict whether the tumor will regress or advance to metastatic disease. Recent efforts using molecular and genomic technologies have allowed more accurate stratification of patients into low-, intermediate- and high-risk categories, thereby allowing for minimal intervention in low-risk patients and providing potential new therapeutic targets, such as the ALK receptor tyrosine kinase, for high-risk or relapsed patients. Despite these advances, the overall survival of high-risk neuroblastoma patients is still less than 50%. Furthermore, next-generation sequencing has revealed that almost two-thirds of neuroblastoma tumors do not contain obvious pathogenic mutations, suggesting that epigenetic mechanisms and/or a perturbed cellular microenvironment may heavily influence neuroblastoma development. Understanding the mechanisms that drive neuroblastoma, therefore, will likely require a combination of genomic, developmental and cancer biology approaches in whole animal systems. In this review, we discuss the contributions of zebrafish research to our understanding of neuroblastoma pathogenesis as well as the potential for this model system to accelerate the identification of more effective therapies for high-risk neuroblastoma patients in the future.

MYCN induces neuroblastoma in primary neural crest cells

Neuroblastoma (NBL) is an embryonal cancer of the sympathetic nervous system (SNS), which causes 15% of pediatric cancer deaths. High-risk NBL is characterized by N-Myc amplification and segmental chromosomal gains and losses. Owing to limited disease models, the etiology of NBL is largely unknown, including both the cell of origin and the majority of oncogenic drivers. We have established a novel system for studying NBL based on the transformation of neural crest cells (NCCs), the progenitor cells of the SNS, isolated from mouse embryonic day 9.5 trunk neural tube explants. Based on pathology and gene expression analysis, we report the first successful transformation of wild-type NCCs into NBL by enforced expression of N-Myc, to generate phenotypically and molecularly accurate tumors that closely model human MYCN-amplified NBL. Using comparative genomic hybridization, we found that NCC-derived NBL tumors acquired copy number gains and losses that are syntenic to those observed in human MYCN-amplified NBL including 17q gain, 2p gain and loss of 1p36. When p53-compromised NCCs were transformed with N-Myc, we generated primitive neuroectodermal tumors with divergent differentiation including osteosarcoma. These subcutaneous tumors were metastatic to regional lymph nodes, liver and lung. Our novel experimental approach accurately models human NBL and establishes a new system with potential to study early stages of NBL oncogenesis, to functionally assess NBL oncogenic drivers and to characterize NBL metastasis.

A genome-wide microRNA profiling indicates miR-424-5p and miR-503-5p as regulators of ALK expression in neuroblastoma

The discovery of missense mutations of ALK gene identified this receptor tyrosine kinase as a therapeutic target in neuroblastoma (NB). Moreover, a high level of ALK protein has been associated with metastatic NB cases and with a worse prognosis, suggesting that also ALK overexpression is involved in NB tumorigenesis. Since miRNAs play key roles in the regulation of gene expression we aimed at identifying those miRNAs that can regulate ALK in NB. We therefore analyzed the genome-wide expression profile of miRNAs in two sample sets of 16 NB cell lines and 22 NB samples by using miRNA microarrays. Both sample sets were then divided into two subgroups showing high (ALK+) or low/absent (ALK-) expression of ALK. Results showed a down-regulation of 30 and 23 miRNAs (p-value <0.05) in the ALK+ group in NB cell lines and samples, respectively. Validation analysis indicated that miR-424-5p and miR-503-5p, belonging to the same cluster, were differentially expressed in both NB cell lines and tumor samples. Although only miR-424-5p showed a direct binding to ALK 3′-UTR, both miRNAs led to a remarkable decreasing of ALK protein as well as to the inhibition of cell viability in ALK+ NB cell lines. In conclusion, our data indicate that both miR-424-5p and miR-503-5p are involved in regulating ALK expression in NB, either by directly targeting ALK receptor or indirectly, and may thus serve as potential therapeutic tools in ALK dependent NBs.

Aldehyde dehydrogenase activity plays a Key role in the aggressive phenotype of neuroblastoma

BACKGROUND

The successful targeting of neuroblastoma (NB) by associating tumor-initiating cells (TICs) is a major challenge in the development of new therapeutic strategies. The subfamily of aldehyde dehydrogenases 1 (ALDH1) isoenzymes, which comprises ALDH1A1, ALDH1A2, and ALDH1A3, is involved in the synthesis of retinoic acid, and has been identified as functional stem cell markers in diverse cancers. By combining serial neurosphere passages with gene expression profiling, we have previously identified ALDH1A2 and ALDH1A3 as potential NB TICs markers in patient-derived xenograft tumors. In this study, we explored the involvement of ALDH1 isoenzymes and the related ALDH activity in NB aggressive properties.

METHODS

ALDH activity and ALDH1A1/A2/A3 expression levels were measured using the ALDEFLUOR™ kit, and by real-time PCR, respectively. ALDH activity was inhibited using the specific ALDH inhibitor diethylaminobenzaldehyde (DEAB), and ALDH1A3 gene knock-out was generated through the CRISPR/Cas9 technology.

RESULTS

We first confirmed the enrichment of ALDH1A2 and ALDH1A3 mRNA expression in NB cell lines and patient-derived xenograft tumors during neurosphere passages. We found that high ALDH1A1 expression was associated with less aggressive NB tumors and cell lines, and correlated with favorable prognostic factors. In contrast, we observed that ALDH1A3 was more widely expressed in NB cell lines and was associated with poor survival and high-risk prognostic factors. We also identified an important ALDH activity in various NB cell lines and patient-derived xenograft tumors. Specific inhibition of ALDH activity with diethylaminobenzaldehyde (DEAB) resulted in a strong reduction of NB cell clonogenicity, and TIC self-renewal potential, and partially enhanced NB cells sensitivity to 4-hydroxycyclophosphamide. Finally, the specific knock-out of ALDH1A3 via CRISPR/Cas9 gene editing reduced NB cell clonogenicity, and mediated a cell type-dependent inhibition of TIC self-renewal properties.

CONCLUSIONS

Together our data uncover the participation of ALDH enzymatic activity in the aggressive properties and 4-hydroxycyclophosphamide resistance of NB, and show that the specific ALDH1A3 isoenzyme increases the aggressive capacities of a subset of NB cells.

Mutation-Independent Activation of the Anaplastic Lymphoma Kinase in Neuroblastoma

Activating mutations of anaplastic lymphoma kinase (ALK) have been identified as important players in neuroblastoma development. Our goal was to evaluate the significance of overall ALK activation in neuroblastoma. Expression of phosphorylated ALK, ALK, and its putative ligands, pleiotrophin and midkine, was screened in 289 neuroblastomas and 56 paired normal tissues. ALK was expressed in 99% of tumors and phosphorylated in 48% of cases. Pleiotrophin and midkine were expressed in 58% and 79% of tumors, respectively. ALK activation was significantly higher in tumors than in paired normal tissues, together with ALK and midkine expression. ALK activation was largely independent of mutations and correlated with midkine expression in tumors. ALK activation in tumors was associated with favorable features, including a younger age at diagnosis, hyperdiploidy, and detection by mass screening. Antitumor activity of the ALK inhibitor TAE684 was evaluated in wild-type or mutated ALK neuroblastoma cell lines and xenografts. TAE684 was cytotoxic in vitro in all cell lines, especially those harboring an ALK mutation. TAE684 efficiently inhibited ALK phosphorylation in vivo in both F1174I and R1275Q xenografts but demonstrated antitumor activity only against the R1275Q xenograft. In conclusion, ALK activation occurs frequently during neuroblastoma oncogenesis, mainly through mutation-independent mechanisms. However, ALK activation is not associated with a poor outcome and is not always a driver of cell proliferation and/or survival in neuroblastoma.

Alternative transcription initiation leads to expression of a novel ALK isoform in cancer

Activation of oncogenes by mechanisms other than genetic aberrations such as mutations, translocations, or amplifications is largely undefined. Here we report a novel isoform of the anaplastic lymphoma kinase (ALK) that is expressed in ∼11% of melanomas and sporadically in other human cancer types, but not in normal tissues. The novel ALK transcript initiates from a de novo alternative transcription initiation (ATI) site in ALK intron 19, and was termed ALK(ATI). In ALK(ATI)-expressing tumours, the ATI site is enriched for H3K4me3 and RNA polymerase II, chromatin marks characteristic of active transcription initiation sites. ALK(ATI) is expressed from both ALK alleles, and no recurrent genetic aberrations are found at the ALK locus, indicating that the transcriptional activation is independent of genetic aberrations at the ALK locus. The ALK(ATI) transcript encodes three proteins with molecular weights of 61.1, 60.8 and 58.7 kilodaltons, consisting primarily of the intracellular tyrosine kinase domain. ALK(ATI) stimulates multiple oncogenic signalling pathways, drives growth-factor-independent cell proliferation in vitro, and promotes tumorigenesis in vivo in mouse models. ALK inhibitors can suppress the kinase activity of ALK(ATI), suggesting that patients with ALK(ATI)-expressing tumours may benefit from ALK inhibitors. Our findings suggest a novel mechanism of oncogene activation in cancer through de novo alternative transcription initiation.