The kinase ALK stimulates the kinase ERK5 to promote the expression of the oncogene MYCN in neuroblastoma

ALK in cancer: from function to therapeutic targeting

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) that acts as an oncogenic driver in solid and haematological malignancies in both children and adults. Although ALK-expressing (ALK+) tumours show strong initial responses to the series of ALK inhibitors currently available, many patients will develop resistance. In this Review, we discuss recent advances in ALK oncogenic signalling, together with existing and promising new modalities to treat ALK-driven tumours, including currently approved ALK-directed therapies, namely tyrosine kinase inhibitors, and novel approaches such as ALK-specific immune therapies. Although ALK inhibitors have changed the management and clinical history of ALK+ tumours, they are still insufficient to cure most of the patients. Therefore, more effort is needed to further improve outcomes and prevent the tumour resistance, recurrence and metastatic spread that many patients with ALK+ tumours experience. Here, we outline how a multipronged approach directed against ALK and other essential pathways that sustain the persistence of ALK+ tumours, together with potent or specific immunotherapies, could achieve this goal. We envision that the lessons learned from treating ALK+ tumours in the clinic could ultimately accelerate the implementation of innovative combination therapies to treat tumours driven by other tyrosine kinases or oncogenes with similar properties.

Targeting the MYCN-MDM2 pathways for cancer therapy: Are they druggable?

Targeting oncogenes and their interactive partners is an effective approach to developing novel targeted therapies for cancer and other chronic diseases. We and others have long suggested the MDM2 oncogene being an excellent target for cancer therapy, based on its p53-dependent and -independent oncogenic activities in a variety of cancers. The MYC family proteins are transcription factors that also regulate diverse biological functions. Dysregulation of MYC, such as amplification of MYCN, is associated with tumorigenesis, especially for neuroblastoma. Although the general survival rate of neuroblastoma patients has significantly improved over the past few decades, high-risk neuroblastoma still presents a poor prognosis. Therefore, innovative and more potent therapeutic strategies are needed to eradicate these aggressive neoplasms. This review focuses on the oncogenic properties of MYCN and its molecular regulation and summarizes the major therapeutic strategies being developed based on preclinical findings. We also highlight the potential benefits of targeting both the MYCN and MDM2 oncogenes, providing preclinical evidence of the efficacy and safety of this approach. In conclusion, the development of effective small molecules that inhibit both MYCN and MDM2 represents a promising new strategy for the treatment of neuroblastoma and other cancers.

Anaplastic Lymphoma Kinase signaling stabilizes SLC3A2 expression via MARCH11 to promote neuroblastoma cell growth

Solute Carrier Family 3, Member 2 (SLC3A2 or 4F2hc) is a multifunctional glycoprotein that mediates integrin-dependent signaling, acts as a trafficking chaperone for amino acid transporters, and is involved in polyamine transportation. We identified SLC3A2 as a potential Anaplastic Lymphoma Kinase (ALK) interacting partner in a BioID-proximity labeling screen in neuroblastoma (NB) cells. In this work we show that endogenous SLC3A2 and ALK interact in NB cells and that this SLC3A2:ALK interaction was abrogated upon treatment with the ALK inhibitor lorlatinib. We show here that loss of ALK activity leads to decreased SLC3A2 expression and reduced SLC3A2 protein stability in a panel of NB cell lines, while stimulation of ALK with ALKAL2 ligand resulted in increased SLC3A2 protein levels. We further identified MARCH11, an E3 ligase, as a regulator of SLC3A2 ubiquitination downstream of ALK. Further, knockdown of SLC3A2 resulted in inhibition of NB cell growth. To investigate the therapeutic potential of SLC3A2 targeting, we performed monotreatment of NB cells with AMXT-1501 (a polyamine transport inhibitor), which showed only moderate effects in NB cells. In contrast, a combination lorlatinib/AMXT-1501 treatment resulted in synergistic inhibition of cell growth in ALK-driven NB cell lines. Taken together, our results identify a novel role for the ALK receptor tyrosine kinase (RTK), working in concert with the MARCH11 E3 ligase, in regulating SLC3A2 protein stability and function in NB cells. The synergistic effect of combined ALK and polyamine transport inhibition shows that ALK/MARCH11/SLC3A2 regulation of amino acid transport is important for oncogenic growth and survival in NB cells.

HDAC6-MYCN-CXCL3 axis mediates allergic inflammation and is necessary for allergic inflammation-promoted cellular interactions

Histone deacetylase 6 (HDAC6) has been shown to play an important role in allergic inflammation. This study hypothesized that novel downstream targets of HDAC6 would mediate allergic inflammation. Experiments employing HDAC6 knock out C57BL/6 mice showed that HDAC6 mediated passive cutaneous anaphylaxis (PCA) and passive systemic anaphylaxis (PSA). Antigen stimulation increased expression of N-myc (MYCN) and CXCL3 in an HDAC6-dependent manner in the bone marrow-derived mast cells. MYCN and CXCL3 were necessary for both PCA and PSA. The role of early growth response 3 (EGR3) in the regulation of HDAC6 expression has been reported. ChIP assays showed EGR3 as a direct regulator of MYCN. miR-34a-5p was predicted to be a negative regulator of MYCN. Luciferase activity assays showed miR-34a-5p as a direct regulator of MYCN. miR-34a-5p mimic negatively regulated PCA and PSA. MYCN decreased miR-34a-5p expression in antigen-stimulated rat basophilic leukemia cells (RBL2H3). MYCN was shown to bind to the promoter sequence of CXCL3. In an IgE-independent manner, recombinant CXCL3 protein increased expression of HDAC6, MYCN, and β-hexosaminidase activity in RBL2H3 cells. Mouse recombinant CXCL3 protein enhanced the angiogenic potential of the culture medium of RBL2H3. CXCL3 was necessary for the enhanced angiogenic potential of the culture medium of antigen-stimulated RBL2H3. The culture medium of RBL2H3 was able to induce M2 macrophage polarization in a CXCL3-dependent manner. Recombinant CXCL3 protein also increased the expression of markers of M2 macrophage. Thus, the identification of the novel role of HDAC6-MYCN-CXCL3 axis can help better understand the pathogenesis of anaphylaxis.

Human iPSC modeling recapitulates in vivo sympathoadrenal development and reveals an aberrant developmental subpopulation in familial neuroblastoma

Studies defining normal and disrupted human neural crest cell development have been challenging given its early timing and intricacy of development. Consequently, insight into the early disruptive events causing a neural crest related disease such as pediatric cancer neuroblastoma is limited. To overcome this problem, we developed an in vitro differentiation model to recapitulate the normal in vivo developmental process of the sympathoadrenal lineage which gives rise to neuroblastoma. We used human in vitro pluripotent stem cells and single-cell RNA sequencing to recapitulate the molecular events during sympathoadrenal development. We provide a detailed map of dynamically regulated transcriptomes during sympathoblast formation and illustrate the power of this model to study early events of the development of human neuroblastoma, identifying a distinct subpopulation of cell marked by SOX2 expression in developing sympathoblast obtained from patient derived iPSC cells harboring a germline activating mutation in the anaplastic lymphoma kinase (ALK) gene.

IGF1R Contributes to Cell Proliferation in ALK-Mutated Neuroblastoma with Preference for Activating the PI3K-AKT Signaling Pathway

Aberrant activation of anaplastic lymphoma kinase (ALK) by activating point mutation or amplification drives 5-12% of neuroblastoma (NB). Previous work has identified the involvement of the insulin-like growth factor 1 receptor (IGF1R) receptor tyrosine kinase (RTK) in a wide range of cancers. We show here that many NB cell lines exhibit IGF1R activity, and that IGF1R inhibition led to decreased cell proliferation to varying degrees in ALK-driven NB cells. Furthermore, combined inhibition of ALK and IGF1R resulted in synergistic anti-proliferation effects, in particular in ALK-mutated NB cells. Mechanistically, both ALK and IGF1R contribute significantly to the activation of downstream PI3K-AKT and RAS-MAPK signaling pathways in ALK-mutated NB cells. However, these two RTKs employ a differential repertoire of adaptor proteins to mediate downstream signaling effects. We show here that ALK signaling led to activation of the RAS-MAPK pathway by preferentially phosphorylating the adaptor proteins GAB1, GAB2, and FRS2, while IGF1R signaling preferentially phosphorylated IRS2, promoting activation of the PI3K-AKT pathway. Together, these findings reveal a potentially important role of the IGF1R RTK in ALK-mutated NB and that co-targeting of ALK and IGF1R may be advantageous in clinical treatment of ALK-mutated NB patients.

The significance of ERK5 catalytic-independent functions in disease pathways

Extracellular signal-regulated kinase 5 (ERK5), also known as BMK1 or MAPK7, represents a recent addition to the classical mitogen-activated protein kinase (MAPK) family. This family includes well-known members such as ERK1/2, c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38 MAPK), as well as atypical MAPKs such as ERK3, ERK4, ERK7 (ERK8), and Nemo-like kinase (NLK). Comprehensive reviews available elsewhere provide detailed insights into ERK5, which interested readers can refer to for in-depth knowledge (Nithianandarajah-Jones et al., 2012; Monti et al., Cancers (Basel), 2022, 14). The primary aim of this review is to emphasize the essential characteristics of ERK5 and shed light on the intricate nature of its activation, with particular attention to the catalytic-independent functions in disease pathways.

Etiopathogenic role of ERK5 signaling in sarcoma: prognostic and therapeutic implications

Sarcomas constitute a heterogeneous group of rare and difficult-to-treat tumors that can affect people of all ages, representing one of the most common forms of cancer in childhood and adolescence. Little is known about the molecular entities involved in sarcomagenesis. Therefore, the identification of processes that lead to the development of the disease may uncover novel therapeutic opportunities. Here, we show that the MEK5/ERK5 signaling pathway plays a critical role in the pathogenesis of sarcomas. By developing a mouse model engineered to express a constitutively active form of MEK5, we demonstrate that the exclusive activation of the MEK5/ERK5 pathway can promote sarcomagenesis. Histopathological analyses identified these tumors as undifferentiated pleomorphic sarcomas. Bioinformatic studies revealed that sarcomas are the tumors in which ERK5 is most frequently amplified and overexpressed. Moreover, analysis of the impact of ERK5 protein expression on overall survival in patients diagnosed with different sarcoma types in our local hospital showed a 5-fold decrease in median survival in patients with elevated ERK5 expression compared with those with low expression. Pharmacological and genetic studies revealed that targeting the MEK5/ERK5 pathway drastically affects the proliferation of human sarcoma cells and tumor growth. Interestingly, sarcoma cells with knockout of ERK5 or MEK5 were unable to form tumors when engrafted into mice. Taken together, our results reveal a role of the MEK5/ERK5 pathway in sarcomagenesis and open a new scenario to be considered in the treatment of patients with sarcoma in which the ERK5 pathway is pathophysiologically involved.

Modulation of ERK5 Activity as a Therapeutic Anti-Cancer Strategy

The extracellular signal-regulated kinase 5 (ERK5) signaling pathway is one of four conventional mitogen-activated protein (MAP) kinase pathways. Genetic perturbation of ERK5 has suggested that modulation of ERK5 activity may have therapeutic potential in cancer chemotherapy. This Miniperspective examines the evidence for ERK5 as a drug target in cancer, the structure of ERK5, and the evolution of structurally distinct chemotypes of ERK5 kinase domain inhibitors. The emerging complexities of ERK5 pharmacology are discussed, including the confounding phenomenon of paradoxical ERK5 activation by small-molecule ERK5 inhibitors. The impact of the recent development and biological evaluation of potent and selective bifunctional degraders of ERK5 and future opportunities in ERK modulation are also explored.

Clinical Significance and Regulation of ERK5 Expression and Function in Cancer

Extracellular signal-regulated kinase 5 (ERK5) is a unique kinase among MAPKs family members, given its large structure characterized by the presence of a unique C-terminal domain. Despite increasing data demonstrating the relevance of the ERK5 pathway in the growth, survival, and differentiation of normal cells, ERK5 has recently attracted the attention of several research groups given its relevance in inflammatory disorders and cancer. Accumulating evidence reported its role in tumor initiation and progression. In this review, we explore the gene expression profile of ERK5 among cancers correlated with its clinical impact, as well as the prognostic value of ERK5 and pERK5 expression levels in tumors. We also summarize the importance of ERK5 in the maintenance of a cancer stem-like phenotype and explore the major known contributions of ERK5 in the tumor-associated microenvironment. Moreover, although several questions are still open concerning ERK5 molecular regulation, different ERK5 isoforms derived from the alternative splicing process are also described, highlighting the potential clinical relevance of targeting ERK5 pathways.

Combined Detection of Copy Number Variations of MYCN and ALK using Droplet Digital Polymerase Chain Reaction to Identify High-Risk Patients with Neuroblastoma

OBJECTIVE

The current study sought to explore the significance of copy number variations (CNVs) of MYCN (v-myc myelocytomatosis viral related oncogene, neuroblastoma derived [avian]) and ALK (anaplastic lymphoma kinase) genes individually as well as their combined impact on clinical outcome and overall survival of patients with neuroblastoma (NB).

METHODS

A total 71 individuals including healthy controls (n = 11), circulating DNA (n = 11), and primary tumors (n = 49) were evaluated to detect CNVs of MYCN and ALK genes using droplet digital polymerase chain reaction. Data were correlated with univariate and multivariate survival analysis.

RESULTS

CNVs of MYCN and ALK were detected in 27% and 18.2% from circulating DNA samples. A statistically significant difference in CNVs was noted between healthy controls and circulating DNA samples for MYCN (P = 0.001) and ALK (P = 0.004) genes. Further, we noted >70% concordance in CNVs of MYCN (P = 0.030) and ALK (P = 0.040) from primary tumors and concordant plasma samples of patients with NB. Multivariate survival analysis for disease-free survival (P = 0.031) and overall survival (P = 0.011) showed that CNVs of both genes emerged at step 1 and thus remained as significant markers for predicting early recurrence and shorter survival, respectively, for patients with NB.

CONCLUSIONS

Our study showed that the analysis of circulating DNA by droplet digital polymerase chain reaction is a helpful technique to identify high-risk patients for aggressive therapy at an early stage of disease. We also concluded that codetection of MYCN and ALK is a more powerful tool for identifying high-risk patients with NB. Thus, this study showed a novel coordinately significant prognostic role of MYCN and ALK CNVs.

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.

Clinical, genetic and pharmacological data support targeting the MEK5/ERK5 module in lung cancer

Despite advances in its treatment, lung cancer still represents the most common and lethal tumor. Because of that, efforts to decipher the pathophysiological actors that may promote lung tumor generation/progression are being made, with the final aim of establishing new therapeutic options. Using a transgenic mouse model, we formerly demonstrated that the sole activation of the MEK5/ERK5 MAPK route had a pathophysiological role in the onset of lung adenocarcinomas. Given the prevalence of that disease and its frequent dismal prognosis, our findings opened the possibility of targeting the MEK5/ERK5 route with therapeutic purposes. Here we have explored such possibility. We found that increased levels of MEK5/ERK5 correlated with poor patient prognosis in lung cancer. Moreover, using genetic as well as pharmacological tools, we show that targeting the MEK5/ERK5 route is therapeutically effective in lung cancer. Not only genetic disruption of ERK5 by CRISPR/Cas9 caused a relevant inhibition of tumor growth in vitro and in vivo; such ERK5 deficit augmented the antitumoral effect of agents normally used in the lung cancer clinic. The clinical correlation studies together with the pharmacological and genetic results establish the basis for considering the targeting of the MEK5/ERK5 route in the therapy for lung cancer.

Small molecule ERK5 kinase inhibitors paradoxically activate ERK5 signalling: be careful what you wish for…

ERK5 is a protein kinase that also contains a nuclear localisation signal and a transcriptional transactivation domain. Inhibition of ERK5 has therapeutic potential in cancer and inflammation and this has prompted the development of ERK5 kinase inhibitors (ERK5i). However, few ERK5i programmes have taken account of the ERK5 transactivation domain. We have recently shown that the binding of small molecule ERK5i to the ERK5 kinase domain stimulates nuclear localisation and paradoxical activation of its transactivation domain. Other kinase inhibitors paradoxically activate their intended kinase target, in some cases leading to severe physiological consequences highlighting the importance of mitigating these effects. Here, we review the assays used to monitor ERK5 activities (kinase and transcriptional) in cells, the challenges faced in development of small molecule inhibitors to the ERK5 pathway, and classify the molecular mechanisms of paradoxical activation of protein kinases by kinase inhibitors.

BioID-Screening Identifies PEAK1 and SHP2 as Components of the ALK Proximitome in Neuroblastoma Cells

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) that is mutated in approximately 10% of pediatric neuroblastoma (NB). To shed light on ALK-driven signaling processes, we employed BioID-based in vivo proximity labeling to identify molecules that interact intracellularly with ALK. NB-derived SK-N-AS and SK-N-BE(2) cells expressing inducible ALK-BirA* fusion proteins were generated and stimulated with ALKAL ligands in the presence and absence of the ALK tyrosine kinase inhibitor (TKI) lorlatinib. LC/MS-MS analysis identified multiple proteins, including PEAK1 and SHP2, which were validated as ALK interactors in NB cells. Further analysis of the ALK-SHP2 interaction confirmed that the ALK-SHP2 interaction as well as SHP2-Y542 phosphorylation was dependent on ALK activation. Use of the SHP2 inhibitors, SHP099 and RMC-4550, resulted in inhibition of cell growth in ALK-driven NB cells. In addition, we noted a strong synergistic effect of combined ALK and SHP2 inhibition that was specific to ALK-driven NB cells, suggesting a potential therapeutic option for ALK-driven NB.

Concurrent targeting of MAP3K3 and BRD4 by miR-3140-3p overcomes acquired resistance to BET inhibitors in neuroblastoma cells

Neuroblastoma (NB) harboring MYCN amplification is a refractory disease with a poor prognosis. As BRD4, an epigenetic reader belonging to the bromodomain and extra terminal domain (BET) family, drives transcription of MYCN in NB cells, BET inhibitors (BETis) are considered useful for NB therapy. However, clinical trials of BETis suggested that early acquired resistance to BETis limits their therapeutic benefit. MicroRNAs are small non-coding RNAs that mediate post-transcriptional silencing of target genes. We previously identified miR-3140-3p as a potent candidate for nucleic acid therapeutics for cancer, which directly targets BRD4. We demonstrated that miR-3140-3p suppresses tumor cell growth in MYCN-amplified NB by downregulating MYCN and MYC through BRD4 suppression. We established BETi-acquired resistant NB cells to evaluate the mechanism of resistance to BETi in NB cells. We revealed that activated ERK1/2 stabilizes MYCN protein by preventing ubiquitin-mediated proteolysis via phosphorylation of MYCN at Ser62 in BETi-acquired resistant NB cells, thereby attenuating the effects of BETi in these cells. miR-3140-3p efficiently downregulated MYCN expression by directly targeting the MAP3K3-ERK1/2 pathway in addition to BRD4 suppression, inhibiting tumor cell growth in BETi-acquired resistant NB cells. This study suggests that miR-3140-3p has the potential to overcome resistance to BETi in NB.

Playing the Whack-A-Mole Game: ERK5 Activation Emerges Among the Resistance Mechanisms to RAF-MEK1/2-ERK1/2- Targeted Therapy

Molecularly tailored therapies have opened a new era, chronic myeloid leukemia being the ideal example, in the treatment of cancer. However, available therapeutic options are still unsatisfactory in many types of cancer, and often fail due to the occurrence of resistance mechanisms. With regard to small-molecule compounds targeting the components of the Mitogen-Activated Protein Kinase (MAPK) cascade RAF-MEK1/2-ERK1/2, these drugs may result ineffective as a consequence of the activation of compensatory pro-survival/proliferative signals, including receptor tyrosine kinases, PI3K, as well as other components of the MAPK family such as TPL2/COT. The MAPK ERK5 has been identified as a key signaling molecule in the biology of several types of cancer. In this review, we report pieces of evidence regarding the activation of the MEK5-ERK5 pathway as a resistance mechanism to RAF-MEK1/2-ERK1/2 inhibitors. We also highlight the known and possible mechanisms underlying the cross-talks between the ERK1/2 and the ERK5 pathways, the characterization of which is of great importance to maximize, in the future, the impact of RAF-MEK1/2-ERK1/2 targeting. Finally, we emphasize the need of developing additional therapeutically relevant MEK5-ERK5 inhibitors to be used for combined treatments, thus preventing the onset of resistance to cancer therapies relying on RAF-MEK1/2-ERK1/2 inhibitors.

Molecular Mechanisms of Epithelial to Mesenchymal Transition Regulated by ERK5 Signaling

Extracellular signal-regulated kinase (ERK5) is an essential regulator of cancer progression, tumor relapse, and poor patient survival. Epithelial to mesenchymal transition (EMT) is a complex oncogenic process, which drives cell invasion, stemness, and metastases. Activators of ERK5, including mitogen-activated protein kinase 5 (MEK5), tumor necrosis factor α (TNF-α), and transforming growth factor-β (TGF-β), are known to induce EMT and metastases in breast, lung, colorectal, and other cancers. Several downstream targets of the ERK5 pathway, such as myocyte-specific enhancer factor 2c (MEF2C), activator protein-1 (AP-1), focal adhesion kinase (FAK), and c-Myc, play a critical role in the regulation of EMT transcription factors SNAIL, SLUG, and β-catenin. Moreover, ERK5 activation increases the release of extracellular matrix metalloproteinases (MMPs), facilitating breakdown of the extracellular matrix (ECM) and local tumor invasion. Targeting the ERK5 signaling pathway using small molecule inhibitors, microRNAs, and knockdown approaches decreases EMT, cell invasion, and metastases via several mechanisms. The focus of the current review is to highlight the mechanisms which are known to mediate cancer EMT via ERK5 signaling. Several therapeutic approaches that can be undertaken to target the ERK5 pathway and inhibit or reverse EMT and metastases are discussed.

Combined Replenishment of miR-34a and let-7b by Targeted Nanoparticles Inhibits Tumor Growth in Neuroblastoma Preclinical Models

Neuroblastoma (NB) tumor substantially contributes to childhood cancer mortality. The design of novel drugs targeted to specific molecular alterations becomes mandatory, especially for high-risk patients burdened by chemoresistant relapse. The dysregulated expression of MYCN, ALK, and LIN28B and the diminished levels of miR-34a and let-7b are oncogenic in NB. Due to the ability of miRNA-mimics to recover the tumor suppression functions of miRNAs underexpressed into cancer cells, safe and efficient nanocarriers selectively targeted to NB cells and tested in clinically relevant mouse models are developed. The technology exploits the nucleic acids negative charges to build coated-cationic liposomes, then functionalized with antibodies against GD₂ receptor. The replenishment of miR-34a and let-7b by NB-targeted nanoparticles, individually and more powerfully in combination, significantly reduces cell division, proliferation, neoangiogenesis, tumor growth and burden, and induces apoptosis in orthotopic xenografts and improves mice survival in pseudometastatic models. These functional effects highlight a cooperative down-modulation of MYCN and its down-stream targets, ALK and LIN28B, exerted by miR-34a and let-7b that reactivate regulatory networks leading to a favorable therapeutic response. These findings demonstrate a promising therapeutic efficacy of miR-34a and let-7b combined replacement and support its clinical application as adjuvant therapy for high-risk NB patients.

Extracellular signal regulated kinase 5 promotes cell migration, invasion and lung metastasis in a FAK-dependent manner

This study was designed to evaluate ERK5 expression in lung cancer and malignant melanoma progression and to ascertain the involvement of ERK5 signaling in lung cancer and melanoma. We show that ERK5 expression is abundant in human lung cancer samples, and elevated ERK5 expression in lung cancer was linked to the acquisition of increased metastatic and invasive potential. Importantly, we observed a significant correlation between ERK5 activity and FAK expression and its phosphorylation at the Ser⁹¹⁰ site. Mechanistically, ERK5 increased the expression of the transcription factor USF1, which could transcriptionally upregulate FAK expression, resulting in FAK signaling activation to promote cell migration. We also provided evidence that the phosphorylation of FAK at Ser⁹¹⁰ was due to ERK5 but not ERK1/2, and we then suggested a role for Ser⁹¹⁰ in the control of cell motility. In addition, ERK5 had targets in addition to FAK that regulate epithelial-to-mesenchymal transition and cell motility in cancer cells. Taken together, our findings uncover a cancer metastasis-promoting role for ERK5 and provide the rationale for targeting ERK5 as a potential therapeutic approach.

Targeted Avenues for Cancer Treatment: The MEK5-ERK5 Signaling Pathway

Twenty years have passed since extracellular signal-regulated kinase 5 (ERK5) and its upstream activator, mitogen-activated protein kinase 5 (MEK5), first emerged onto the cancer research scene. Although we have come a long way in defining the liaison between dysregulated MEK5-ERK5 signaling and the pathogenesis of epithelial and nonepithelial malignancies, selective targeting of this unique pathway remains elusive. Here, we provide an updated review of the existing evidence for a correlation between aberrant MEK5-ERK5 (phospho)proteomic/transcriptomic profiles, aggressive cancer states, and poor patient outcomes. We then focus on emerging insights from preclinical models regarding the relevance of upregulated ERK5 activity in promoting tumor growth, metastasis, therapy resistance, undifferentiated traits, and immunosuppression, highlighting the opportunities, prospects, and challenges of selectively blocking this cascade for antineoplastic treatment and chemosensitization.

Beyond Kinase Activity: ERK5 Nucleo-Cytoplasmic Shuttling as a Novel Target for Anticancer Therapy

The importance of mitogen-activated protein kinases (MAPK) in human pathology is underlined by the relevance of abnormalities of MAPK-related signaling pathways to a number of different diseases, including inflammatory disorders and cancer. One of the key events in MAPK signaling, especially with respect to pro-proliferative effects that are crucial for the onset and progression of cancer, is MAPK nuclear translocation and its role in the regulation of gene expression. The extracellular signal-regulated kinase 5 (ERK5) is the most recently discovered classical MAPK and it is emerging as a possible target for cancer treatment. The bigger size of ERK5 when compared to other MAPK enables multiple levels of regulation of its expression and activity. In particular, the phosphorylation of kinase domain and C-terminus, as well as post-translational modifications and chaperone binding, are involved in ERK5 regulation. Likewise, different mechanisms control ERK5 nucleo-cytoplasmic shuttling, underscoring the key role of ERK5 in the nuclear compartment. In this review, we will focus on the mechanisms involved in ERK5 trafficking between cytoplasm and nucleus, and discuss how these processes might be exploited to design new strategies for cancer treatment.

The ETS transcription factor ETV5 is a target of activated ALK in neuroblastoma contributing to increased tumour aggressiveness

Neuroblastoma is an aggressive childhood cancer arising from sympatho-adrenergic neuronal progenitors. The low survival rates for high-risk disease point to an urgent need for novel targeted therapeutic approaches. Detailed molecular characterization of the neuroblastoma genomic landscape indicates that ALK-activating mutations are present in 10% of primary tumours. Together with other mutations causing RAS/MAPK pathway activation, ALK mutations are also enriched in relapsed cases and ALK activation was shown to accelerate MYCN-driven tumour formation through hitherto unknown ALK-driven target genes. To gain further insight into how ALK contributes to neuroblastoma aggressiveness, we searched for known oncogenes in our previously reported ALK-driven gene signature. We identified ETV5, a bona fide oncogene in prostate cancer, as robustly upregulated in neuroblastoma cells harbouring ALK mutations, and show high ETV5 levels downstream of the RAS/MAPK axis. Increased ETV5 expression significantly impacted migration, invasion and colony formation in vitro, and ETV5 knockdown reduced proliferation in a murine xenograft model. We also established a gene signature associated with ETV5 knockdown that correlates with poor patient survival. Taken together, our data highlight ETV5 as an intrinsic component of oncogenic ALK-driven signalling through the MAPK axis and propose that ETV5 upregulation in neuroblastoma may contribute to tumour aggressiveness.

Repotrectinib (TPX-0005), effectively reduces growth of ALK driven neuroblastoma cells

Neuroblastoma is the most commonly diagnosed extracranial tumor in the first year of life. Approximately 9% of neuroblastoma patients present germline or somatic aberrations in the gene encoding for anaplastic lymphoma kinase (ALK). This increases in high-risk neuroblastomas, which have a 14% frequency of ALK aberrations at the time of diagnosis and show increasing numbers at relapse. Abrogating ALK activity with kinase inhibitors is employed as clinical therapy in malignancies such as non-small cell lung cancer and has shown good results in pediatric inflammatory myofibroblastic tumors and anaplastic large cell lymphomas. A phase I clinical trial of the first generation ALK inhibitor, crizotinib, in neuroblastoma patients showed modest results and suggested that further investigation was needed. Continuous development of ALK inhibitors has resulted in the third generation inhibitor repotrectinib (TPX-0005), which targets the active kinase conformations of ALK, ROS1 and TRK receptors. In the present study we investigated the effects of repotrectinib in a neuroblastoma setting in vitro and in vivo. Neuroblastoma cell lines were treated with repotrectinib to investigate inhibition of ALK and to determine its effect on proliferation. PC12 cells transfected with different ALK mutant variants were used to study the efficacy of repotrectinib to block ALK activation/signaling. The in vivo effect of repotrectinib was also analyzed in a neuroblastoma xenograft model. Our results show that repotrectinib is capable of inhibiting signaling activity of a range of ALK mutant variants found in neuroblastoma patients and importantly it exhibits strong antitumor effects in a xenograft model of neuroblastoma.

Pharmacological inhibition of the MEK5/ERK5 and PI3K/Akt signaling pathways synergistically reduces viability in triple-negative breast cancer

Triple-negative breast cancers (TNBCs) represent 15% to 20% of all breast cancers and are often associated with poor prognosis. The lack of targeted therapies for TNBCs contributes to higher mortality rates. Aberrations in the phosphoinositide-3-kinase (PI3K) and mitogen-activated protein kinase pathways have been linked to increased breast cancer proliferation and survival. It has been proposed that these survival characteristics are enhanced through compensatory signaling and crosstalk mechanisms. While the crosstalk between PI3K and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways has been characterized in several systems, new evidence suggests that MEK5/ERK5 signaling is a key component in the proliferation and survival of several aggressive cancers. In this study, we examined the effects of dual inhibition of PI3K/protein kinase B (Akt) and MEK5/ERK5 in the MDA-MB-231, BT-549, and MDA-MB-468 TNBC cell lines. We used the Akt inhibitor ipatasertib, ERK5 inhibitors XMD8-92 and AX15836, and the novel MEK5 inhibitor SC-1-181 to investigate the effects of dual inhibition. Our results indicated that dual inhibition of PI3K/Akt and MEK5/ERK5 signaling was more effective at reducing the proliferation and survival of TNBCs than single inhibition of either pathway alone. In particular, a loss of Bad phosphorylation at two distinct sites was observed with dual inhibition. Furthermore, the inhibition of both pathways led to p21 restoration, decreased cell proliferation, and induced apoptosis. In addition, the dual inhibition strategy was determined to be synergistic in MDA-MB-231 and BT-549 cells and was relatively nontoxic in the nonneoplastic MCF-10 cell line. In summary, the results from this study provide a unique prospective into the utility of a novel dual inhibition strategy for targeting TNBCs.

Alectinib, an Anaplastic Lymphoma Kinase Inhibitor, Abolishes ALK Activity and Growth in ALK-Positive Neuroblastoma Cells

Oncogenic receptor tyrosine kinases including anaplastic lymphoma kinase (ALK) are implicated in numerous solid and hematologic cancers. ALK mutations are reported in an estimated 9% of neuroblastoma and recent reports indicate that the percentage of ALK-positive cases increases in the relapsed patient population. Initial clinical trial results have shown that it is difficult to inhibit growth of ALK positive neuroblastoma with crizotinib, motivating investigation of next generation ALK inhibitors with higher affinity for ALK. Here, alectinib, a potent next generation ALK inhibitor with antitumor activity was investigated in ALK-driven neuroblastoma models. Employing neuroblastoma cell lines and mouse xenografts we show a clear and efficient inhibition of ALK activity by alectinib. Inhibition of ALK activity was observed in vitro employing a set of different constitutively active ALK variants in biochemical assays. The results suggest that alectinib is an effective inhibitor of ALK kinase activity in ALK addicted neuroblastoma and should be considered as a potential future therapeutic option for ALK-positive neuroblastoma patients alone or in combination with other treatments.

Targeting anaplastic lymphoma kinase in neuroblastoma

Over the last decade, anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase (RTK), has been identified as a fusion partner in a diverse variety of translocation events resulting in oncogenic signaling in many different cancer types. In tumors where the full‐length ALK RTK itself is mutated, such as neuroblastoma, the picture regarding the role of ALK as an oncogenic driver is less clear. Neuroblastoma is a complex and heterogeneous tumor that arises from the neural crest derived peripheral nervous system. Although high‐risk neuroblastoma is rare, it often relapses and becomes refractory to treatment. Thus, neuroblastoma accounts for 10–15% of all childhood cancer deaths. Since most cases are in children under the age of 2, understanding the role and regulation of ALK during neural crest development is an important goal in addressing neuroblastoma tumorigenesis. An impressive array of tyrosine kinase inhibitors (TKIs) that act to inhibit ALK have been FDA approved for use in ALK‐driven cancers. ALK TKIs bind differently within the ATP‐binding pocket of the ALK kinase domain and have been associated with different resistance mutations within ALK itself that arise in response to therapeutic use, particularly in ALK‐fusion positive non‐small cell lung cancer (NSCLC). This patient population has highlighted the importance of considering the relevant ALK TKI to be used for a given ALK mutant variant. In this review, we discuss ALK in neuroblastoma, as well as the use of ALK TKIs and other strategies to inhibit tumor growth. Current efforts combining novel approaches and increasing our understanding of the oncogenic role of ALK in neuroblastoma are aimed at improving the efficacy of ALK TKIs as precision medicine options in the clinic.

Impact of ERK5 on the Hallmarks of Cancer

Extracellular signal-regulated kinase 5 (ERK5) belongs to the mitogen-activated protein kinase (MAPK) family that consists of highly conserved enzymes expressed in all eukaryotic cells and elicits several biological responses, including cell survival, proliferation, migration, and differentiation. In recent years, accumulating lines of evidence point to a relevant role of ERK5 in the onset and progression of several types of cancer. In particular, it has been reported that ERK5 is a key signaling molecule involved in almost all the biological features of cancer cells so that its targeting is emerging as a promising strategy to suppress tumor growth and spreading. Based on that, in this review, we pinpoint the hallmark-specific role of ERK5 in cancer in order to identify biological features that will potentially benefit from ERK5 targeting.

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.

Dual-Specificity Phosphatases in Neuroblastoma Cell Growth and Differentiation

Dual-specificity phosphatases (DUSPs) are important regulators of neuronal cell growth and differentiation by targeting proteins essential to neuronal survival in signaling pathways, among which the MAP kinases (MAPKs) stand out. DUSPs include the MAPK phosphatases (MKPs), a family of enzymes that directly dephosphorylate MAPKs, as well as the small-size atypical DUSPs, a group of low molecular-weight enzymes which display more heterogeneous substrate specificity. Neuroblastoma (NB) is a malignancy intimately associated with the course of neuronal and neuroendocrine cell differentiation, and constitutes the source of more common extracranial solid pediatric tumors. Here, we review the current knowledge on the involvement of MKPs and small-size atypical DUSPs in NB cell growth and differentiation, and discuss the potential of DUSPs as predictive biomarkers and therapeutic targets in human NB.

Targeting ALK in Cancer: Therapeutic Potential of Proapoptotic Peptides

ALK is a receptor tyrosine kinase, associated with many tumor types as diverse as anaplastic large cell lymphomas, inflammatory myofibroblastic tumors, breast and renal cell carcinomas, non-small cell lung cancer, neuroblastomas, and more. This makes ALK an attractive target for cancer therapy. Since ALK–driven tumors are dependent for their proliferation on the constitutively activated ALK kinase, a number of tyrosine kinase inhibitors have been developed to block tumor growth. While some inhibitors are under investigation in clinical trials, others are now approved for treatment, notably in ALK-positive lung cancer. Their efficacy is remarkable, however limited in time, as the tumors escape and become resistant to the treatment through different mechanisms. Hence, there is a pressing need to target ALK-dependent tumors by other therapeutic strategies, and possibly use them in combination with kinase inhibitors. In this review we will focus on the therapeutic potential of proapoptotic ALK-derived peptides based on the dependence receptor properties of ALK. We will also try to make a non-exhaustive list of several alternative treatments targeting ALK-dependent and independent signaling pathways.

ALK positively regulates MYCN activity through repression of HBP1 expression

ALK mutations occur in 10% of primary neuroblastomas and represent a major target for precision treatment. In combination with MYCN amplification, ALK mutations infer an ultra-high-risk phenotype resulting in very poor patient prognosis. To open up opportunities for future precision drugging, a deeper understanding of the molecular consequences of constitutive ALK signaling and its relationship to MYCN activity in this aggressive pediatric tumor entity will be essential. We show that mutant ALK downregulates the 'HMG-box transcription factor 1' (HBP1) through the PI₃K-AKT-FOXO3a signaling axis. HBP1 inhibits both the transcriptional activating and repressing activity of MYCN, the latter being mediated through PRC2 activity. HBP1 itself is under negative control of MYCN through miR-17~92. Combined targeting of HBP1 by PI₃K antagonists and MYCN signaling by BET- or HDAC-inhibitors blocks MYCN activity and significantly reduces tumor growth, suggesting a novel targeted therapy option for high-risk neuroblastoma.

Integrated proximal proteomics reveals IRS2 as a determinant of cell survival in ALK-driven neuroblastoma

Oncogenic anaplastic lymphoma kinase (ALK) is one of the few druggable targets in neuroblastoma, and therapy resistance to ALK-targeting tyrosine kinase inhibitors (TKIs) comprises an inevitable clinical challenge. Therefore, a better understanding of the oncogenic signaling network rewiring driven by ALK is necessary to improve and guide future therapies. Here, we performed quantitative mass spectrometry-based proteomics on neuroblastoma cells treated with one of three clinically relevant ALK TKIs (crizotinib, LDK378, or lorlatinib) or an experimentally used ALK TKI (TAE684) to unravel aberrant ALK signaling pathways. Our integrated proximal proteomics (IPP) strategy included multiple signaling layers, such as the ALK interactome, phosphotyrosine interactome, phosphoproteome, and proteome. We identified the signaling adaptor protein IRS2 (insulin receptor substrate 2) as a major ALK target and an ALK TKI-sensitive signaling node in neuroblastoma cells driven by oncogenic ALK. TKI treatment decreased the recruitment of IRS2 to ALK and reduced the tyrosine phosphorylation of IRS2. Furthermore, siRNA-mediated depletion of ALK or IRS2 decreased the phosphorylation of the survival-promoting kinase Akt and of a downstream target, the transcription factor FoxO3, and reduced the viability of three ALK-driven neuroblastoma cell lines. Collectively, our IPP analysis provides insight into the proximal architecture of oncogenic ALK signaling by revealing IRS2 as an adaptor protein that links ALK to neuroblastoma cell survival through the Akt-FoxO3 signaling axis.

Phosphoproteome and gene expression profiling of ALK inhibition in neuroblastoma cell lines reveals conserved oncogenic pathways

Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor that is a clinical target of major interest in cancer. Mutations and rearrangements in ALK trigger the activation of the encoded receptor and its downstream signaling pathways. ALK mutations have been identified in both familial and sporadic neuroblastoma cases as well as in 30 to 40% of relapses, which makes ALK a bona fide target in neuroblastoma therapy. Tyrosine kinase inhibitors (TKIs) that target ALK are currently in clinical use for the treatment of patients with ALK-positive non-small cell lung cancer. However, monotherapy with the ALK inhibitor crizotinib has been less encouraging in neuroblastoma patients with ALK alterations, raising the question of whether combinatorial therapy would be more effective. In this study, we established both phosphoproteomic and gene expression profiles of ALK activity in neuroblastoma cells exposed to first- and third-generation ALK TKIs, to identify the underlying molecular mechanisms and identify relevant biomarkers, signaling networks, and new therapeutic targets. This analysis has unveiled various important leads for novel combinatorial treatment strategies for patients with neuroblastoma and an increased understanding of ALK signaling involved in this disease.

Clinical response of the novel activating ALK-I1171T mutation in neuroblastoma to the ALK inhibitor ceritinib

Tumors with anaplastic lymphoma kinase (ALK) fusion rearrangements, including non-small-cell lung cancer and anaplastic large cell lymphoma, are highly sensitive to ALK tyrosine kinase inhibitors (TKIs), underscoring the notion that such cancers are addicted to ALK activity. Although mutations in ALK are heavily implicated in childhood neuroblastoma, response to the ALK TKI crizotinib has been disappointing. Embryonal tumors in patients with DNA repair defects such as Fanconi anemia (FA) often have a poor prognosis, because of lack of therapeutic options. Here we report a child with underlying FA and ALK mutant high-risk neuroblastoma responding strongly to precision therapy with the ALK TKI ceritinib. Conventional chemotherapy treatment caused severe, life-threatening toxicity. Genomic analysis of the initial biopsy identified germline FANCA mutations as well as a novel ALK-I1171T variant. ALK-I1171T generates a potent gain-of-function mutant, as measured in PC12 cell neurite outgrowth and NIH3T3 transformation. Pharmacological inhibition profiling of ALK-I1171T in response to various ALK TKIs identified an 11-fold improved inhibition of ALK-I1171T with ceritinib when compared with crizotinib. Immunoaffinity-coupled LC-MS/MS phosphoproteomics analysis indicated a decrease in ALK signaling in response to ceritinib. Ceritinib was therefore selected for treatment in this child. Monotherapy with ceritinib was well tolerated and resulted in normalized catecholamine markers and tumor shrinkage. After 7.5 mo treatment, the residual primary tumor shrunk, was surgically removed, and exhibited hallmarks of differentiation together with reduced Ki67 levels. Clinical follow-up after 21 mo treatment revealed complete clinical remission including all metastatic sites. Therefore, ceritinib presents a viable therapeutic option for ALK-positive neuroblastoma.

MEKK2 and MEKK3 suppress Hedgehog pathway-dependent medulloblastoma by inhibiting GLI1 function

Hedgehog (Hh) pathway plays a pivotal role in diverse aspects of development and postnatal physiology. Perturbation of Hh signaling and activation of GLI1 (glioma-associated oncogene 1), a dedicated transcription factor for Hh pathway, are highly associated with several cancers, such as medulloblastoma and basal cell carcinoma. Dynamic and precise control of GLI1 activity is thus important to ensure proper homeostasis and tumorigenesis. Here we show that MEKK2 (MAP3K2) and MEKK3 (MAP3K3) inhibit GLI1 transcriptional activity and oncogenic function through phosphorylation on multiple Ser/Thr sites of GLI1, which reduces GLI1 protein stability, DNA-binding ability, and increases the association of GLI1 with SUFU. Interestingly, MEKK2 and MEKK3 are responsible for FGF2-mediated inhibition on Hh signaling. Moreover, expression of MEKK2 and MEKK3 inhibits medulloblastoma cell proliferation and negatively correlates with Hh pathway activity in medulloblastoma clinical samples. Together, these findings reveal a novel noncanonical GLI1 regulation and provide a potential therapeutic target for the treatment of cancers with aberrant Hh pathway activation, such as medulloblastoma.

ALK in Neuroblastoma: Biological and Therapeutic Implications

Neuroblastoma (NB) is the most common and deadly solid tumour in children. Despite the development of new treatment options for high-risk NB, over half of patients relapse and five-year survival remains at 40-50%. Therefore, novel treatment strategies aimed at providing long-term disease remission are urgently sought. ALK, encoding the anaplastic lymphoma kinase receptor, is altered by gain-of-function point mutations in around 14% of high-risk NB and represents an ideal therapeutic target given its low or absent expression in healthy tissue postnatally. Small-molecule inhibitors of Anaplastic Lymphoma Kinase (ALK) approved in ALK fusion-positive lung cancer are currently undergoing clinical assessment in patients with ALK-mutant NB. Parallel pre-clinical studies are demonstrating the efficacy of ALK inhibitors against common ALK variants in NB; however, a complex picture of therapeutic resistance is emerging. It is anticipated that long-term use of these compounds will require combinatorial targeting of pathways downstream of ALK, functionally-related 'bypass' mechanisms and concomitant oncogenic pathways.

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.

ALK is a critical regulator of the MYC-signaling axis in ALK positive lung cancer

A subset of lung cancers is dependent on the anaplastic lymphoma kinase (ALK) oncogene for survival, a mechanism that is exploited by the use of the ALK inhibitor crizotinib. Despite exceptional initial tumor responses to ALK inhibition by crizotinib, durable clinical response is limited and the emergence of drug resistance occurs. Furthermore, intrinsic resistance is frequently observed, where patients fail to respond initially to ALK-inhibitor therapy. These events demonstrate the underlying complexity of a molecularly-defined oncogene-driven cancer and highlights the need to identify compensating survival pathways. Using a loss-of-function whole genome short-hairpin (shRNA) screen, we identified MYCBP as a determinant of response to crizotinib, implicating the MYC signaling axis in resistance to crizotinib-treated ALK+ NSCLC. Further analysis reveals that ALK regulates transcriptional expression of MYC and activates c-MYC transactivation of c-MYC target genes. Inhibition of MYC by RNAi or small molecules sensitizes ALK+ cells to crizotinib. Taken together, our findings demonstrate a dual oncogene mechanism, where ALK positively regulates the MYC signaling axis, providing an additional oncogene target whose inhibition may prevent or overcome resistance.

Brigatinib, an anaplastic lymphoma kinase inhibitor, abrogates activity and growth in ALK-positive neuroblastoma cells, Drosophila and mice

Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor which has been implicated in numerous solid and hematologic cancers. ALK mutations are reported in about 5-7% of neuroblastoma cases but the ALK-positive percentage increases significantly in the relapsed patient population. Crizotinib, the first clinically approved ALK inhibitor for the treatment of ALK-positive lung cancer has had less dramatic responses in neuroblastoma. Here we investigate the efficacy of a second-generation ALK inhibitor, brigatinib, in a neuroblastoma setting. Employing neuroblastoma cell lines, mouse xenograft and Drosophila melanogaster model systems expressing different constitutively active ALK variants, we show clear and efficient inhibition of ALK activity by brigatinib. Similar abrogation of ALK activity was observed in vitro employing a set of different constitutively active ALK variants in biochemical assays. These results suggest that brigatinib is an effective inhibitor of ALK kinase activity in ALK addicted neuroblastoma that should be considered as a potential future therapeutic option for ALK-positive neuroblastoma patients alone or in combination with other treatments.

MEK5/ERK5 signaling inhibition increases colon cancer cell sensitivity to 5-fluorouracil through a p53-dependent mechanism

The MEK5/ERK5 signaling pathway is emerging as an important contributor to colon cancer onset, progression and metastasis; however, its relevance to chemotherapy resistance remains unknown. Here, we evaluated the impact of the MEK5/ERK5 cascade in colon cancer cell sensitivity to 5-fluorouracil (5-FU). Increased ERK5 expression was correlated with poor overall survival in colon cancer patients. In colon cancer cells, 5-FU exposure impaired endogenous KRAS/MEK5/ERK5 expression and/or activation. In turn, MEK5 constitutive activation reduced 5-FU-induced cytotoxicity. Using genetic and pharmacological approaches, we showed that ERK5 inhibition increased caspase-3/7 activity and apoptosis following 5-FU exposure. Mechanistically, this was further associated with increased p53 transcriptional activation of p21 and PUMA. In addition, ERK5 inhibition increased the response of HCT116 p53^+/+ cells to 5-FU, but failed to sensitize HCT116 p53^−/− cells to the cytotoxic effects of this chemotherapeutic agent, suggesting a p53-dependent axis mediating 5-FU sensitization. Finally, ERK5 inhibition using XMD8-92 was shown to increase the antitumor effects of 5-FU in a murine subcutaneous xenograft model, enhancing apoptosis while markedly reducing tumor growth. Collectively, our results suggest that ERK5-targeted in hibition provides a promising therapeutic approach to overcome resistance to 5-FU-based chemotherapy and improve colon cancer treatment.

MEK inhibitor trametinib does not prevent the growth of anaplastic lymphoma kinase (ALK)-addicted neuroblastomas

Activation of the RAS-RAF-MEK-ERK signaling pathway is implicated in driving the initiation and progression of multiple cancers. Several inhibitors targeting the RAS-MAPK pathway are clinically approved as single- or polyagent therapies for patients with specific types of cancer. One example is the MEK inhibitor trametinib, which is included as a rational polytherapy strategy for treating EML4-ALK-positive, EGFR-activated, or KRAS-mutant lung cancers and neuroblastomas that also contain activating mutations in the RAS-MAPK pathway. In addition, in neuroblastoma, a heterogeneous disease, relapse cases display an increased rate of mutations in ALK, NRAS, and NF1, leading to increased activation of RAS-MAPK signaling. Co-targeting ALK and the RAS-MAPK pathway is an attractive option, because monotherapies have not yet produced effective results in ALK-addicted neuroblastoma patients. We evaluated the response of neuroblastoma cell lines to MEK-ERK pathway inhibition by trametinib. In contrast to RAS-MAPK pathway-mutated neuroblastoma cell lines, ALK-addicted neuroblastoma cells treated with trametinib showed increased activation (inferred by phosphorylation) of the kinases AKT and ERK5. This feedback response was mediated by the mammalian target of rapamycin complex 2-associated protein SIN1, resulting in increased survival and proliferation that depended on AKT signaling. In xenografts in mice, trametinib inhibited the growth of EML4-ALK-positive non-small cell lung cancer and RAS-mutant neuroblastoma but not ALK-addicted neuroblastoma. Thus, our results advise against the seemingly rational option of using MEK inhibitors to treat ALK-addicted neuroblastoma.

The role of the ALK receptor in cancer biology

A vast array of oncogenic variants has been identified for anaplastic lymphoma kinase (ALK). Therefore, there is a need to better understand the role of ALK in cancer biology in order to optimise treatment strategies. This review summarises the latest research on the receptor tyrosine kinase ALK, and how this information can guide the management of patients with cancer that is ALK-positive. A variety of ALK gene alterations have been described across a range of tumour types, including point mutations, deletions and rearrangements. A wide variety of ALK fusions, in which the kinase domain of ALK and the amino-terminal portion of various protein partners are fused, occur in cancer, with echinoderm microtubule-associated protein-like 4 (EML4)-ALK being the most prevalent in non-small-cell lung cancer (NSCLC). Different ALK fusion proteins can mediate different signalling outputs, depending on properties such as subcellular localisation and protein stability. The ALK fusions found in tumours lack spatial and temporal regulation, which can also affect dimerisation and substrate specificity. Two ALK tyrosine kinase inhibitors (TKIs), crizotinib and ceritinib, are currently approved in Europe for use in ALK-positive NSCLC and several others are in development. These ALK TKIs bind slightly differently within the ATP-binding pocket of the ALK kinase domain and are associated with the emergence of different resistance mutation patterns during therapy. This emphasises the need to tailor the sequence of ALK TKIs according to the ALK signature of each patient. Research into the oncogenic functions of ALK, and fast paced development of ALK inhibitors, has substantially improved outcomes for patients with ALK-positive NSCLC. Limited data are available surrounding the physiological ligand-stimulated activation of ALK signalling and further research is needed. Understanding the role of ALK in tumour biology is key to further optimising therapeutic strategies for ALK-positive disease.

Novel Molecular Challenges in Targeting Anaplastic Lymphoma Kinase in ALK-Expressing Human Cancers

Targeting anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase receptor initially identified as a potent oncogenic driver in anaplastic large-cell lymphoma (ALCL) in the form of nucleophosmin (NPM)-ALK fusion protein, using tyrosine kinase inhibitors has shown to be a promising therapeutic approach for ALK-expressing tumors. However, clinical resistance to ALK inhibitors invariably occurs, and the molecular mechanisms are incompletely understood. Recent studies have clearly shown that clinical resistance to ALK inhibitors is a multifactorial and complex mechanism. While few of the mechanisms of clinical resistance to ALK inhibitors such as gene mutation are well known, there are others that are not well covered. In this review, the molecular mechanisms of cancer stem cells in mediating resistance to ALK inhibitors as well as the current understanding of the molecular challenges in targeting ALK in ALK-expressing human cancers will be discussed.

Research progress of neuroblastoma related gene variations

Neuroblastoma, the most common extracranial solid tumor among children, is an embryonal tumor originating from undifferentiated neural crest cell. Neuroblastomas are highly heterogeneous, represented by the wide range of clinical presentations and likelihood of cure, ranging from spontaneous regression to relentless progression despite rigorous multimodal treatments. Approximately, 50% of cases are high-risk with overall survival rates less than 40%. With the efforts to collect large numbers of clinically annotated specimens and the advancements in technologies, researchers have revealed numerous genetic alterations that may drive tumor growth. However, the most lack mutations in genes that are recurrently mutated, which inspires researchers to identify disrupted pathways instead of single mutated genes to unearth biological systems perturbed in neuroblastoma. Stratification of patients and target therapy based on their molecular signatures have been the center of focus. This review provides a comprehensive summary of the recent advances in identification of candidate genes variations, targeted approaches to high-risk neuroblastoma and evaluates the methods utilized for detection, which will provide new avenues to develop therapies and further genetic researches.

Immunoassays for the quantification of ALK and phosphorylated ALK support the evaluation of on-target ALK inhibitors in neuroblastoma

Targeted inhibition of anaplastic lymphoma kinase (ALK) is a successful approach for the treatment of many ALK-aberrant malignancies; however, the presence of resistant mutations necessitates both the development of more potent compounds and pharmacodynamic methods with which to determine their efficacy. We describe immunoassays designed to quantitate phosphorylation of ALK, and their use in preclinical models of neuroblastoma, a pediatric malignancy in which gain-of-function ALK mutations predict a poor overall outcome to conventional treatment. Validation of the immunoassays is presented using a panel of neuroblastoma cell lines and evidence of on-target ALK inhibition provided by treatment of a genetically engineered murine model of neuroblastoma with two clinical ALK inhibitors, crizotinib and ceritinib, highlighting the superior efficacy of ceritinib.