An orthotopic glioblastoma animal model suitable for high-throughput screenings

Developing a zebrafish xenograft model of diffuse midline glioma

Diffuse midline glioma (DMG) is a highly aggressive brain tumor that predominantly affects children. Conventional treatments such as radiation therapy can control progression for a time, but DMG kills nearly 100 percent of patients. Although murine models have provided critical insights into the biology of DMG and in assessing new therapeutic strategies, they are not suitable for high-throughput screening to identify and profile novel therapies due to technical challenges, ethical considerations and high cost. Zebrafish ( Danio rerio ) is an established vertebrate model for large-scale drug screening, and zebrafish have demonstrated the ability to replicate the key biological and pathlogical aspects of human malignancies. Here, we developed a novel method for transplanting human DMG cells into large numbers of zebrafish embyros to speed the assessment of anti-tumor drug efficacy in vivo and thereby facilitate the development of novel therapeutics for clinical translation. We transplanted red fluorescent protein (RFP)-labeled, patient-derived DMG cell lines into zebrafish blastulas. Remarkably, many DMG cells migrate into the developing brain and are present in the midline of the brain 24 hours after blastula injection. Tumor cell burden was monitored by measuring RFP fluorescence intensity changes over time. Time-course images of transplanted tumor cell volumes were acquired, and the interactions between transplanted DMG cells and microglial cells were further analyzed using Imaris software. We have developed a simple and rapid transplantation protocol to establish a zebrafish xenograft model of DMG. Our method involves transplanting DMG cells into the blastula stage (1000 cell stage) of zebrafish embryos, which does not require complex surgical techniques. This approach allows for the transplantation of hundreds of embryos per hour, significantly increasing the efficiency of creating DMG zebrafish xenografts that are suitable for high-throughput drug and gene discovery screens.

Development of an orthotopic medulloblastoma zebrafish model for rapid drug testing

BACKGROUND

Medulloblastoma (MB) is one of the most common malignant brain tumors in children. Current preclinical in vivo model systems for MB have increased our understanding of molecular mechanisms regulating MB development. However, they may not be suitable for large-scale studies. The aim of this study was to investigate if a zebrafish-based xenograft model can recapitulate MB growth and enable rapid drug testing.

METHODS

Nine different MB cell lines or patient-derived cells were transplanted into blastula-stage zebrafish embryos. Tumor development and migration were then monitored using live imaging. RNA sequencing was performed to investigate transcriptome changes after conditioning cells in a neural stem cell-like medium. Furthermore, drug treatments were tested in a 96-well format.

RESULTS

We demonstrate here that transplantation of MB cells into the blastula stage of zebrafish embryos leads to orthotopic tumor growth that can be observed within 24 h after transplantation. Importantly, the homing of transplanted cells to the hindbrain region and the aggressiveness of tumor growth are enhanced by pre-culturing cells in a neural stem cell-like medium. The change in culture conditions rewires the transcriptome toward a more migratory and neuronal phenotype, including the expression of guidance molecules SEMA3A and EFNB1, both of which correlate with lower overall survival in MB patients. Furthermore, we highlight that the orthotopic zebrafish MB model has the potential to be used for rapid drug testing.

CONCLUSIONS

Blastula-stage zebrafish MB xenografts present an alternative to current MB mouse xenograft models, enabling quick evaluation of tumor cell growth, neurotropism, and drug efficacy.

Small Fish, Big Answers: Zebrafish and the Molecular Drivers of Metastasis

Cancer metastasis is a leading cause of cancer-related deaths and represents one of the most challenging processes to study due to its complexity and dynamic nature. Zebrafish (Danio rerio) have become an invaluable model in metastasis research, offering unique advantages such as optical transparency, rapid development, and the ability to visualize tumor interactions with the microenvironment in real time. This review explores how zebrafish models have elucidated the critical steps of metastasis, including tumor invasion, vascular remodeling, and immune evasion, while also serving as platforms for drug testing and personalized medicine. Advances such as patient-derived xenografts and innovative genetic tools have further established zebrafish as a cornerstone in cancer research, particularly in understanding the molecular drivers of metastasis and identifying therapeutic targets. By bridging the experimental findings with clinical relevance, zebrafish continue transforming our understanding of cancer biology and therapy.

Inhibition of GPR68 kills glioblastoma in zebrafish xenograft models

OBJECTIVE

Inhibition and knockdown of GPR68 negatively affects glioblastoma cell survival in vitro by inducing ferroptosis. Herein, we aimed to demonstrate that inhibition of GPR68 reduces the survival of glioblastoma cells in vivo using two orthotopic larval xenograft models in Danio rerio, using GBM cell lines U87-MG and U138-MG. In vivo survival of the cancer cells was assessed in the setting of GPR68 inhibition or knockdown.

RESULTS

In vitro, shRNA-mediated knockdown of GPR68 inhibition demonstrated potent cytotoxic effects against U87 and U138 glioblastoma cell lines. This effect was associated with increased intracellular lipid peroxidation, suggesting ferroptosis as the underlying mechanism of cell death. Translating these findings in vivo, we established a novel xenograft model in zebrafish by successfully grafting fluorescently labeled human glioblastoma cells, which were previously shown to overexpress GPR68. shRNA knockdown of GPR68 significantly reduced the viability of grafted GBM cells within this model. Additionally, treatment with ogremorphin (OGM), a highly specific small molecule inhibitor of GPR68, also reduced the viability of grafted GBM cells with limited toxicity to the developing zebrafish embryos. This study suggests that therapeutic targeting of GPR68 with small molecules like OGM represents a promising approach for the treatment of GBM.

Speeding up Glioblastoma Cancer Research: Highlighting the Zebrafish Xenograft Model

Glioblastoma multiforme (GBM) is a very aggressive and lethal primary brain cancer in adults. The multifaceted nature of GBM pathogenesis, rising from complex interactions between cells and the tumor microenvironment (TME), has posed great treatment challenges. Despite significant scientific efforts, the prognosis for GBM remains very poor, even after intensive treatment with surgery, radiation, and chemotherapy. Efficient GBM management still requires the invention of innovative treatment strategies. There is a strong necessity to complete cancer in vitro studies and in vivo studies to properly evaluate the mechanisms of tumor progression within the complex TME. In recent years, the animal models used to study GBM tumors have evolved, achieving highly invasive GBM models able to provide key information on the molecular mechanisms of GBM onset. At present, the most commonly used animal models in GBM research are represented by mammalian models, such as mouse and canine ones. However, the latter present several limitations, such as high cost and time-consuming management, making them inappropriate for large-scale anticancer drug evaluation. In recent years, the zebrafish (Danio rerio) model has emerged as a valuable tool for studying GBM. It has shown great promise in preclinical studies due to numerous advantages, such as its small size, its ability to generate a large cohort of genetically identical offspring, and its rapid development, permitting more time- and cost-effective management and high-throughput drug screening when compared to mammalian models. Moreover, due to its transparent nature in early developmental stages and genetic and anatomical similarities with humans, it allows for translatable brain cancer research and related genetic screening and drug discovery. For this reason, the aim of the present review is to highlight the potential of relevant transgenic and xenograft zebrafish models and to compare them to the traditionally used animal models in GBM research.

Challenges and Promise for Glioblastoma Treatment through Extracellular Vesicle Inquiry

Glioblastoma (GB) is a rare but extremely aggressive brain tumor that significantly impacts patient outcomes, affecting both duration and quality of life. The protocol established by Stupp and colleagues in 2005, based on radiotherapy and chemotherapy with Temozolomide, following maximum safe surgical resection remains the gold standard for GB treatment; however, it is evident nowadays that the extreme intratumoral and intertumoral heterogeneity, as well as the invasiveness and tendency to recur, of GB are not compatible with a routine and unfortunately ineffective treatment. This review article summarizes the main challenges in the search for new valuable therapies for GB and focuses on the impact that extracellular vesicle (EV) research and exploitation may have in the field. EVs are natural particles delimited by a lipidic bilayer and filled with functional cellular content that are released and uptaken by cells as key means of cell communication. Furthermore, EVs are stable in body fluids and well tolerated by the immune system, and are able to cross physiological, interspecies, and interkingdom barriers and to target specific cells, releasing inherent or externally loaded functionally active molecules. Therefore, EVs have the potential to be ideal allies in the fight against GB and to improve the prognosis for GB patients. The present work describes the main preclinical results obtained so far on the use of EVs for GB treatment, focusing on both the EV sources and molecular cargo used in the various functional studies, primarily in vivo. Finally, a SWOT analysis is performed, highlighting the main advantages and pitfalls of developing EV-based GB therapeutic strategies. The analysis also suggests the main directions to explore to realize the possibility of exploiting EVs for the treatment of GB.

Glioblastoma research on zebrafish xenograft models: a systematic review

Glioblastoma (GBM) constitutes the most common primary brain tumor in adults. The challenges in GBM therapeutics have shed light on zebrafish used as a promising animal model for preclinical GBM xenograft studies without a standardized methodology. This systematic review aims to summarize the advances in zebrafish GBM xenografting, compare research protocols to pinpoint advantages and underlying limitations, and designate the predominant xenografting parameters. Based on the PRISMA checklist, we systematically searched PubMed, Scopus, and ZFIN using the keywords "glioblastoma," "xenotransplantation," and "zebrafish" for papers published from 2005 to 2022, available in English. 46 articles meeting the review criteria were examined for the zebrafish strain, cancer cell line, cell labeling technique, injected cell number, time and site of injection, and maintenance temperature. Our review designated that AB wild-type zebrafish, Casper transparent mutants, transgenic Tg(fli1:EGFP), or crossbreeding of these predominate among the zebrafish strains. Orthotopic transplantation is more commonly employed. A number of 50-100 cells injected at 48 h post-fertilization in high density and low infusion volume is considered as an effective xenografting approach. U87 cells are used for GBM angiogenesis studies, U251 for GBM proliferation studies, and patient-derived xenograft (PDX) to achieve clinical relevance. Gradual acclimatization to 32-33 °C can partly address the temperature differential between the zebrafish and the GBM cells. Zebrafish xenograft models constitute valuable tools for preclinical studies with clinical relevance regarding PDX. The GBM xenografting research requires modification based on the objective of each research team. Automation and further optimization of the protocol parameters could scale up the anticancer drug trials.

Pediatric low-grade glioma models: advances and ongoing challenges

Pediatric low-grade gliomas represent the most common childhood brain tumor class. While often curable, some tumors fail to respond and even successful treatments can have life-long side effects. Many clinical trials are underway for pediatric low-grade gliomas. However, these trials are expensive and challenging to organize due to the heterogeneity of patients and subtypes. Advances in sequencing technologies are helping to mitigate this by revealing the molecular landscapes of mutations in pediatric low-grade glioma. Functionalizing these mutations in the form of preclinical models is the next step in both understanding the disease mechanisms as well as for testing therapeutics. However, such models are often more difficult to generate due to their less proliferative nature, and the heterogeneity of tumor microenvironments, cell(s)-of-origin, and genetic alterations. In this review, we discuss the molecular and genetic alterations and the various preclinical models generated for the different types of pediatric low-grade gliomas. We examined the different preclinical models for pediatric low-grade gliomas, summarizing the scientific advances made to the field and therapeutic implications. We also discuss the advantages and limitations of the various models. This review highlights the importance of preclinical models for pediatric low-grade gliomas while noting the challenges and future directions of these models to improve therapeutic outcomes of pediatric low-grade gliomas.

Single-cell profiling and zebrafish avatars reveal LGALS1 as immunomodulating target in glioblastoma

Glioblastoma (GBM) remains the most malignant primary brain tumor, with a median survival rarely exceeding 2 years. Tumor heterogeneity and an immunosuppressive microenvironment are key factors contributing to the poor response rates of current therapeutic approaches. GBM-associated macrophages (GAMs) often exhibit immunosuppressive features that promote tumor progression. However, their dynamic interactions with GBM tumor cells remain poorly understood. Here, we used patient-derived GBM stem cell cultures and combined single-cell RNA sequencing of GAM-GBM co-cultures and real-time in vivo monitoring of GAM-GBM interactions in orthotopic zebrafish xenograft models to provide insight into the cellular, molecular, and spatial heterogeneity. Our analyses revealed substantial heterogeneity across GBM patients in GBM-induced GAM polarization and the ability to attract and activate GAMs-features that correlated with patient survival. Differential gene expression analysis, immunohistochemistry on original tumor samples, and knock-out experiments in zebrafish subsequently identified LGALS1 as a primary regulator of immunosuppression. Overall, our work highlights that GAM-GBM interactions can be studied in a clinically relevant way using co-cultures and avatar models, while offering new opportunities to identify promising immune-modulating targets.

Preclinical glioma models in neuro-oncology: enhancing translational research

PURPOSE OF REVIEW

Gliomas represent approximately 25% of all primary brain and other central nervous system (CNS) tumors and 81% of malignant tumors. Unfortunately, standard treatment approaches for most CNS cancers have shown limited improvement in patient survival rates.

RECENT FINDINGS

The current drug development process has been plagued by high failure rates, leading to a shift towards human disease models in biomedical research. Unfortunately, suitable preclinical models for brain tumors have been lacking, hampering our understanding of tumor initiation processes and the discovery of effective treatments. In this review, we will explore the diverse preclinical models employed in neuro-oncology research and their contributions to translational science.

SUMMARY

By utilizing a combination of these preclinical models and fostering interdisciplinary collaborations, researchers can deepen their understanding of glioma brain tumors and develop novel therapeutic strategies to combat these devastating diseases. These models offer promising prospects for personalized and efficacious treatments for these challenging malignancies. Although it is unrealistic to fully replicate the complexity of the human body in vitro, the ultimate goal should be to achieve the closest possible resemblance to the clinical context.

Actionable cancer vulnerability due to translational arrest, p53 aggregation and ribosome biogenesis stress evoked by the disulfiram metabolite CuET

Drug repurposing is a versatile strategy to improve current therapies. Disulfiram has long been used in the treatment of alcohol dependency and multiple clinical trials to evaluate its clinical value in oncology are ongoing. We have recently reported that the disulfiram metabolite diethyldithiocarbamate, when combined with copper (CuET), targets the NPL4 adapter of the p97VCP segregase to suppress the growth of a spectrum of cancer cell lines and xenograft models in vivo. CuET induces proteotoxic stress and genotoxic effects, however important issues concerning the full range of the CuET-evoked tumor cell phenotypes, their temporal order, and mechanistic basis have remained largely unexplored. Here, we have addressed these outstanding questions and show that in diverse human cancer cell models, CuET causes a very early translational arrest through the integrated stress response (ISR), later followed by features of nucleolar stress. Furthermore, we report that CuET entraps p53 in NPL4-rich aggregates leading to elevated p53 protein and its functional inhibition, consistent with the possibility of CuET-triggered cell death being p53-independent. Our transcriptomics profiling revealed activation of pro-survival adaptive pathways of ribosomal biogenesis (RiBi) and autophagy upon prolonged exposure to CuET, indicating potential feedback responses to CuET treatment. The latter concept was validated here by simultaneous pharmacological inhibition of RiBi and/or autophagy that further enhanced CuET's tumor cytotoxicity, using both cell culture and zebrafish in vivo preclinical models. Overall, these findings expand the mechanistic repertoire of CuET's anti-cancer activity, inform about the temporal order of responses and identify an unorthodox new mechanism of targeting p53. Our results are discussed in light of cancer-associated endogenous stresses as exploitable tumor vulnerabilities and may inspire future clinical applications of CuET in oncology, including combinatorial treatments and focus on potential advantages of using certain validated drug metabolites, rather than old, approved drugs with their, often complex, metabolic profiles.

Zebrafish: A Relevant Genetic Model for Human Primary Immunodeficiency (PID) Disorders?

Primary immunodeficiency (PID) disorders, also commonly referred to as inborn errors of immunity, are a heterogenous group of human genetic diseases characterized by defects in immune cell development and/or function. Since these disorders are generally uncommon and occur on a variable background profile of potential genetic and environmental modifiers, animal models are critical to provide mechanistic insights as well as to create platforms to underpin therapeutic development. This review aims to review the relevance of zebrafish as an alternative genetic model for PIDs. It provides an overview of the conservation of the zebrafish immune system and details specific examples of zebrafish models for a multitude of specific human PIDs across a range of distinct categories, including severe combined immunodeficiency (SCID), combined immunodeficiency (CID), multi-system immunodeficiency, autoinflammatory disorders, neutropenia and defects in leucocyte mobility and respiratory burst. It also describes some of the diverse applications of these models, particularly in the fields of microbiology, immunology, regenerative biology and oncology.

The application of zebrafish patient-derived xenograft tumor models in the development of antitumor agents

The cost of antitumor drug development is enormous, yet the clinical outcomes are less than satisfactory. Therefore, it is of great importance to develop effective drug screening methods that enable accurate, rapid, and high-throughput discovery of lead compounds in the process of preclinical antitumor drug research. An effective solution is to use the patient-derived xenograft (PDX) tumor animal models, which are applicable for the elucidation of tumor pathogenesis and the preclinical testing of novel antitumor compounds. As a promising screening model organism, zebrafish has been widely applied in the construction of the PDX tumor model and the discovery of antineoplastic agents. Herein, we systematically survey the recent cutting-edge advances in zebrafish PDX models (zPDX) for studies of pathogenesis mechanisms and drug screening. In addition, the techniques used in the construction of zPDX are summarized. The advantages and limitations of the zPDX are also discussed in detail. Finally, the prospects of zPDX in drug discovery, translational medicine, and clinical precision medicine treatment are well presented.

One Host-Multiple Applications: Zebrafish (Danio rerio) as Promising Model for Studying Human Cancers and Pathogenic Diseases

In recent years, zebrafish (ZF) has been increasingly applied as a model in human disease studies, with a particular focus on cancer. A number of advantages make it an attractive alternative for mice widely used so far. Due to the many advantages of zebrafish, modifications can be based on different mechanisms and the induction of human disease can take different forms depending on the research goal. Genetic manipulation, tumor transplantation, or injection of the pathogen are only a few examples of using ZF as a model. Most of the studies are conducted in order to understand the disease mechanism, monitor disease progression, test new or alternative therapies, and select the best treatment. The transplantation of cancer cells derived from patients enables the development of personalized medicine. To better mimic a patient's body environment, immune-deficient models (SCID) have been developed. A lower immune response is mostly generated by genetic manipulation but also by irradiation or dexamethasone treatment. For many studies, using SCID provides a better chance to avoid cancer cell rejection. In this review, we describe the main directions of using ZF in research, explain why and how zebrafish can be used as a model, what kind of limitations will be met and how to overcome them. We collected recent achievements in this field, indicating promising perspectives for the future.

Zebrafish Models of Paediatric Brain Tumours

Paediatric brain cancer is the second most common childhood cancer and is the leading cause of cancer-related deaths in children. Despite significant advancements in the treatment modalities and improvements in the 5-year survival rate, it leaves long-term therapy-associated side effects in paediatric patients. Addressing these impairments demands further understanding of the molecularity and heterogeneity of these brain tumours, which can be demonstrated using different animal models of paediatric brain cancer. Here we review the use of zebrafish as potential in vivo models for paediatric brain tumour modelling, as well as catalogue the currently available zebrafish models used to study paediatric brain cancer pathophysiology, and discuss key findings, the unique attributes that these models add, current challenges and therapeutic significance.

Modeling Brain Tumors: A Perspective Overview of in vivo and Organoid Models

Brain tumors are a large and heterogeneous group of neoplasms that affect the central nervous system and include some of the deadliest cancers. Almost all the conventional and new treatments fail to hinder tumoral growth of the most malignant brain tumors. This is due to multiple factors, such as intra-tumor heterogeneity, the microenvironmental properties of the human brain, and the lack of reliable models to test new therapies. Therefore, creating faithful models for each tumor and discovering tailored treatments pose great challenges in the fight against brain cancer. Over the years, different types of models have been generated, and, in this review, we investigated the advantages and disadvantages of the models currently used.

Orthotopic Transplantation of Human Paediatric High-Grade Glioma in Zebrafish Larvae

Brain tumours are the most common cause of death among children with solid tumours, and high-grade gliomas (HGG) are among the most devastating forms with very poor outcomes. In the search for more effective treatments for paediatric HGG, there is a need for better experimental models. To date, there are no xenograft zebrafish models developed for human paediatric HGG; existing models rely on adult cells. The use of paediatric models is of great importance since it is well known that the genetic and epigenetic mechanisms behind adult and paediatric disease differ greatly. In this study, we present a clinically relevant in vivo model based on paediatric primary glioma stem cell (GSC) cultures, which after orthotopic injection into the zebrafish larvae, can be monitored using confocal imaging over time. We show that cells invade the brain tissue and can be followed up to 8 days post-injection while they establish in the fore/mid brain. This model offers an in vivo system where tumour invasion can be monitored and drug treatments quickly be evaluated. The possibility to monitor patient-specific cells has the potential to contribute to a better understanding of cellular behaviour and personalised treatments in the future.

Real-time evaluation of glioblastoma growth in patient-specific zebrafish xenografts

BACKGROUND

Patient-derived xenograft (PDX) models of glioblastoma (GBM) are a central tool for neuro-oncology research and drug development, enabling the detection of patient-specific differences in growth, and in vivo drug response. However, existing PDX models are not well suited for large-scale or automated studies. Thus, here, we investigate if a fast zebrafish-based PDX model, supported by longitudinal, AI-driven image analysis, can recapitulate key aspects of glioblastoma growth and enable case-comparative drug testing.

METHODS

We engrafted 11 GFP-tagged patient-derived GBM IDH wild-type cell cultures (PDCs) into 1-day-old zebrafish embryos, and monitored fish with 96-well live microscopy and convolutional neural network analysis. Using light-sheet imaging of whole embryos, we analyzed further the invasive growth of tumor cells.

RESULTS

Our pipeline enables automatic and robust longitudinal observation of tumor growth and survival of individual fish. The 11 PDCs expressed growth, invasion and survival heterogeneity, and tumor initiation correlated strongly with matched mouse PDX counterparts (Spearman R = 0.89, p < 0.001). Three PDCs showed a high degree of association between grafted tumor cells and host blood vessels, suggesting a perivascular invasion phenotype. In vivo evaluation of the drug marizomib, currently in clinical trials for GBM, showed an effect on fish survival corresponding to PDC in vitro and in vivo marizomib sensitivity.

CONCLUSIONS

Zebrafish xenografts of GBM, monitored by AI methods in an automated process, present a scalable alternative to mouse xenograft models for the study of glioblastoma tumor initiation, growth, and invasion, applicable to patient-specific drug evaluation.

Patient-Derived Xenotransplant of CNS Neoplasms in Zebrafish: A Systematic Review

Glioblastoma and neuroblastoma are the most common central nervous system malignant tumors in adult and pediatric populations. Both are associated with poor survival. These tumors are highly heterogeneous, having complex interactions among different cells within the tumor and with the tumor microenvironment. One of the main challenges in the neuro-oncology field is achieving optimal conditions to evaluate a tumor’s molecular genotype and phenotype. In this respect, the zebrafish biological model is becoming an excellent alternative for studying carcinogenic processes and discovering new treatments. This review aimed to describe the results of xenotransplantation of patient-derived CNS tumors in zebrafish models. The reviewed studies show that it is possible to maintain glioblastoma and neuroblastoma primary cell cultures and transplant the cells into zebrafish embryos. The zebrafish is a suitable biological model for understanding tumor progression and the effects of different treatments. This model offers new perspectives in providing personalized care and improving outcomes for patients living with central nervous system tumors.

Clinically relevant orthotopic xenograft models of patient-derived glioblastoma in zebrafish

An accurate prediction of the intracranial infiltration tendency and drug response of individual glioblastoma (GBM) cells is essential for personalized prognosis and treatment for this disease. However, the clinical utility of mouse patient-derived orthotopic xenograft (PDOX) models remains limited given current technical constraints, including difficulty in generating sufficient sample numbers from small tissue samples and a long latency period for results. To overcome these issues, we established zebrafish GBM xenografts of diverse origin, which can tolerate intracranial engraftment and maintain their unique histological features. Subsequent single-cell RNA-sequencing (scRNA-seq) analysis confirmed significant transcriptional identity to that of invading GBM microtumors observed in the proportionally larger brains of model animals and humans. Endothelial scRNA-seq confirmed that the zebrafish blood–brain barrier is homologous to the mammalian blood–brain barrier. Finally, we established a rapid and efficient zebrafish PDOX (zPDOX) model, which can predict long-term outcomes of GBM patients within 20 days. The zPDOX model provides a novel avenue for precision medicine of GBM, especially for the evaluation of intracranial infiltration tendency and prediction of individual drug sensitivity.

Editor's choice: We established zebrafish glioblastoma (GBM) xenograft models that can be used to perform genetic and biological analysis of GBMs, identify blood–brain barrier-penetrating drugs and predict clinical sensitivity to temozolomide in GBM patients.

Heterogeneity and Potency of Peripheral Glial Cells in Embryonic Development and Adults

This review describes the heterogeneity of peripheral glial cell populations, from the emergence of Schwann cells (SCs) in early development, to their involvement, and that of their derivatives in adult glial populations. We focus on the origin of the first glial precursors from neural crest cells (NCCs), and their ability to differentiate into several cell types during development. We also discuss the heterogeneity of embryonic glia in light of the latest data from genetic tracing and transcriptome analysis. Special attention has been paid to the biology of glial populations in adult animals, by highlighting common features of different glial cell types and molecular differences that modulate their functions. Finally, we consider the communication of glial cells with axons of neurons in normal and pathological conditions. In conclusion, the present review details how information available on glial cell types and their functions in normal and pathological conditions may be utilized in the development of novel therapeutic strategies for the treatment of patients with neurodiseases.

Glutaredoxin 2 promotes SP-1-dependent CSPG4 transcription and migration of wound healing NG2 glia and glioma cells: Enzymatic Taoism

Redox regulation of specific cysteines via oxidoreductases of the thioredoxin family is increasingly being recognized as an important signaling pathway. Here, we demonstrate that the cytosolic isoform of the vertebrate-specific oxidoreductase Glutaredoxin 2 (Grx2c) regulates the redox state of the transcription factor SP-1 and thereby its binding affinity to both the promoter and an enhancer region of the CSPG4 gene encoding chondroitin sulfate proteoglycan nerve/glial antigen 2 (NG2). This leads to an increased number of NG2 glia during in vitro oligodendroglial differentiation and promotes migration of these wound healing cells. On the other hand, we found that the same mechanism also leads to increased invasion of glioma tumor cells. Using in vitro (human cell lines), ex vivo (mouse primary cells), and in vivo models (zebrafish), as well as glioblastoma patient tissue samples we provide experimental data highlighting the Yin and Yang of redox signaling in the central nervous system and the enzymatic Taoism of Grx2c.

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CSPG4 promoter binding of the transcription factor SP-1 depends on glutaredoxin 2

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Cytosolic glutaredoxin 2 promotes oligodendrocyte differentiation into NG2 glia

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Migration and wound healing capacity of NG2 glia is increased by glutaredoxin 2

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Glutaredoxin 2 increases invasion of human glioblastoma cells in vitro and in vivo

Preclinical models of glioblastoma: limitations of current models and the promise of new developments

Glioblastoma (GBM) is the most common and aggressive primary brain tumour, yet little progress has been made towards providing better treatment options for patients diagnosed with this devastating condition over the last few decades. The complex nature of the disease, heterogeneity, highly invasive potential of GBM tumours and until recently, reduced investment in research funding compared with other cancer types, are contributing factors to few advancements in disease management. Survival rates remain low with less than 5% of patients surviving 5 years. Another important contributing factor is the use of preclinical models that fail to fully recapitulate GBM pathophysiology, preventing efficient translation from the lab into successful therapies in the clinic. This review critically evaluates current preclinical GBM models, highlighting advantages and disadvantages of using such models, and outlines several emerging techniques in GBM modelling using animal-free approaches. These novel approaches to a highly complex disease such as GBM show evidence of a more truthful recapitulation of GBM pathobiology with high reproducibility. The resulting advancements in this field will offer new biological insights into GBM and its aetiology with potential to contribute towards the development of much needed improved treatments for GBM in future.

Zebrafish Models for the Safety and Therapeutic Testing of Nanoparticles with a Focus on Macrophages

New nanoparticles and biomaterials are increasingly being used in biomedical research for drug delivery, diagnostic applications, or vaccines, and they are also present in numerous commercial products, in the environment and workplaces. Thus, the evaluation of the safety and possible therapeutic application of these nanomaterials has become of foremost importance for the proper progress of nanotechnology. Due to economical and ethical issues, in vitro and in vivo methods are encouraged for the testing of new compounds and/or nanoparticles, however in vivo models are still needed. In this scenario, zebrafish (Danio rerio) has demonstrated potential for toxicological and pharmacological screenings. Zebrafish presents an innate immune system, from early developmental stages, with conserved macrophage phenotypes and functions with respect to humans. This fact, combined with the transparency of zebrafish, the availability of models with fluorescently labelled macrophages, as well as a broad variety of disease models offers great possibilities for the testing of new nanoparticles. Thus, with a particular focus on macrophage-nanoparticle interaction in vivo, here, we review the studies using zebrafish for toxicological and biodistribution testing of nanoparticles, and also the possibilities for their preclinical evaluation in various diseases, including cancer and autoimmune, neuroinflammatory, and infectious diseases.

Tipping the Scales With Zebrafish to Understand Adaptive Tumor Immunity

The future of improved immunotherapy against cancer depends on an in-depth understanding of the dynamic interactions between the immune system and tumors. Over the past two decades, the zebrafish has served as a valuable model system to provide fresh insights into both the development of the immune system and the etiologies of many different cancers. This well-established foundation of knowledge combined with the imaging and genetic capacities of the zebrafish provides a new frontier in cancer immunology research. In this review, we provide an overview of the development of the zebrafish immune system along with a side-by-side comparison of its human counterpart. We then introduce components of the adaptive immune system with a focus on their roles in the tumor microenvironment (TME) of teleosts. In addition, we summarize zebrafish models developed for the study of cancer and adaptive immunity along with other available tools and technology afforded by this experimental system. Finally, we discuss some recent research conducted using the zebrafish to investigate adaptive immune cell-tumor interactions. Without a doubt, the zebrafish will arise as one of the driving forces to help expand the knowledge of tumor immunity and facilitate the development of improved anti-cancer immunotherapy in the foreseeable future.

Modeling human brain tumors in flies, worms, and zebrafish: From proof of principle to novel therapeutic targets

For decades, cell biologists and cancer researchers have taken advantage of non-murine species to increase our understanding of the molecular processes that drive normal cell and tissue development, and when perturbed, cause cancer. The advent of whole-genome sequencing has revealed the high genetic homology of these organisms to humans. Seminal studies in non-murine organisms such as Drosophila melanogaster, Caenorhabditis elegans, and Danio rerio identified many of the signaling pathways involved in cancer. Studies in these organisms offer distinct advantages over mammalian cell or murine systems. Compared to murine models, these three species have shorter lifespans, are less resource intense, and are amenable to high-throughput drug and RNA interference screening to test a myriad of promising drugs against novel targets. In this review, we introduce species-specific breeding strategies, highlight the advantages of modeling brain tumors in each non-mammalian species, and underscore the successes attributed to scientific investigation using these models. We conclude with an optimistic proposal that discoveries in the fields of cancer research, and in particular neuro-oncology, may be expedited using these powerful screening tools and strategies.

Cellular and Molecular Mechanisms Underlying Glioblastoma and Zebrafish Models for the Discovery of New Treatments

Glioblastoma (GBM) is the most common of all brain malignant tumors; it displays a median survival of 14.6 months with current complete standard treatment. High heterogeneity, aggressive and invasive behavior, the impossibility of completing tumor resection, limitations for drug administration and therapeutic resistance to current treatments are the main problems presented by this pathology. In recent years, our knowledge of GBM physiopathology has advanced significantly, generating relevant information on the cellular heterogeneity of GBM tumors, including cancer and immune cells such as macrophages/microglia, genetic, epigenetic and metabolic alterations, comprising changes in miRNA expression. In this scenario, the zebrafish has arisen as a promising animal model to progress further due to its unique characteristics, such as transparency, ease of genetic manipulation, ethical and economic advantages and also conservation of the major brain regions and blood-brain-barrier (BBB) which are similar to a human structure. A few papers described in this review, using genetic and xenotransplantation zebrafish models have been used to study GBM as well as to test the anti-tumoral efficacy of new drugs, their ability to interact with target cells, modulate the tumor microenvironment, cross the BBB and/or their toxicity. Prospective studies following these lines of research may lead to a better diagnosis, prognosis and treatment of patients with GBM.

Three-dimensional decellularized tumor extracellular matrices with different stiffness as bioengineered tumor scaffolds

In the three-dimensional (3D) tumor microenvironment, matrix stiffness is associated with the regulation of tumor cells behaviors. In vitro tumor models with appropriate matrix stiffness are urgently desired. Herein, we prepare 3D decellularized extracellular matrix (DECM) scaffolds with different stiffness to mimic the microenvironment of human breast tumor tissue, especially the matrix stiffness, components and structure of ECM. Furthermore, the effects of matrix stiffness on the drug resistance of human breast cancer cells are explored with these developed scaffolds as case studies. Our results confirm that DECM scaffolds with diverse stiffness can be generated by tumor cells with different lysyl oxidase (LOX) expression levels, while the barely intact structure and major components of the ECM are maintained without cells. This versatile 3D tumor model with suitable stiffness can be used as a bioengineered tumor scaffold to investigate the role of the microenvironment in tumor progression and to screen drugs prior to clinical use to a certain extent.

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Novel 3D bioengineered tumor scaffolds with different stiffness were developed.

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Cells with different LOX expression levels were used to generate tumor tissue.

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DECM scaffold has good cytocompatibility.

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DECM with high stiffness promotes the resistance of MDA-MB-231 cells to cisplatin.

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DECM with high stiffness increases the expression of Bcl-2 and ABCB1.

Modeling Cancer Using Zebrafish Xenografts: Drawbacks for Mimicking the Human Microenvironment

The first steps towards establishing xenografts in zebrafish embryos were performed by Lee et al., 2005 and Haldi et al., 2006, paving the way for studying human cancers using this animal species. Since then, the xenograft technique has been improved in different ways, ranging from optimizing the best temperature for xenografted embryo incubation, testing different sites for injection of human tumor cells, and even developing tools to study how the host interacts with the injected cells. Nonetheless, a standard protocol for performing xenografts has not been adopted across laboratories, and further research on the temperature, microenvironment of the tumor or the cell-host interactions inside of the embryo during xenografting is still needed. As a consequence, current non-uniform conditions could be affecting experimental results in terms of cell proliferation, invasion, or metastasis; or even overestimating the effects of some chemotherapeutic drugs on xenografted cells. In this review, we highlight and raise awareness regarding the different aspects of xenografting that need to be improved in order to mimic, in a more efficient way, the human tumor microenvironment, resulting in more robust and accurate in vivo results.

Real-time imaging of polymersome nanoparticles in zebrafish embryos engrafted with melanoma cancer cells: Localization, toxicity and treatment analysis

BACKGROUND

The developing zebrafish is an emerging tool in nanomedicine, allowing non-invasive live imaging of the whole animal at higher resolution than is possible in the more commonly used mouse models. In addition, several transgenic fish lines are available endowed with selected cell types expressing fluorescent proteins; this allows nanoparticles to be visualized together with host cells.

METHODS

Here, we introduce the zebrafish neural tube as a robust injection site for cancer cells, excellently suited for high resolution imaging. We use light and electron microscopy to evaluate cancer growth and to follow the fate of intravenously injected nanoparticles.

FINDINGS

Fluorescently labelled mouse melanoma B16 cells, when injected into this structure proliferated rapidly and stimulated angiogenesis of new vessels. In addition, macrophages, but not neutrophils, selectively accumulated in the tumour region. When injected intravenously, nanoparticles made of Cy5-labelled poly(ethylene glycol)-block-poly(2-(diisopropyl amino) ethyl methacrylate) (PEG-PDPA) selectively accumulated in the neural tube cancer region and were seen in individual cancer cells and tumour associated macrophages. Moreover, when doxorubicin was released from PEG-PDPA, in a pH dependant manner, these nanoparticles could strongly reduce toxicity and improve the treatment outcome compared to the free drug in zebrafish xenotransplanted with mouse melanoma B16 or human derived melanoma cells.

INTERPRETATION

The zebrafish has the potential of becoming an important intermediate step, before the mouse model, for testing nanomedicines against patient-derived cancer cells.

FUNDING

We received funding from the Norwegian research council and the Norwegian cancer society.

AXL and CAV-1 play a role for MTH1 inhibitor TH1579 sensitivity in cutaneous malignant melanoma

Cutaneous malignant melanoma (CMM) is the deadliest form of skin cancer and clinically challenging due to its propensity to develop therapy resistance. Reactive oxygen species (ROS) can induce DNA damage and play a significant role in CMM. MTH1 protein protects from ROS damage and is often overexpressed in different cancer types including CMM. Herein, we report that MTH1 inhibitor TH1579 induced ROS levels, increased DNA damage responses, caused mitotic arrest and suppressed CMM proliferation leading to cell death both in vitro and in an in vivo xenograft CMM zebrafish disease model. TH1579 was more potent in abrogating cell proliferation and inducing cell death in a heterogeneous co-culture setting when compared with CMM standard treatments, vemurafenib or trametinib, showing its broad anticancer activity. Silencing MTH1 alone exhibited similar cytotoxic effects with concomitant induction of mitotic arrest and ROS induction culminating in cell death in most CMM cell lines tested, further emphasizing the importance of MTH1 in CMM cells. Furthermore, overexpression of receptor tyrosine kinase AXL, previously demonstrated to contribute to BRAF inhibitor resistance, sensitized BRAF mutant and BRAF/NRAS wildtype CMM cells to TH1579. AXL overexpression culminated in increased ROS levels in CMM cells. Moreover, silencing of a protein that has shown opposing effects on cell proliferation, CAV-1, decreased sensitivity to TH1579 in a BRAF inhibitor resistant cell line. AXL-MTH1 and CAV-1-MTH1 mRNA expressions were correlated as seen in CMM clinical samples. Finally, TH1579 in combination with BRAF inhibitor exhibited a more potent cell killing effect in BRAF mutant cells both in vitro and in vivo. In summary, we show that TH1579-mediated efficacy is independent of BRAF/NRAS mutational status but dependent on the expression of AXL and CAV-1.

Zebrafish Models of Cancer-New Insights on Modeling Human Cancer in a Non-Mammalian Vertebrate

Zebrafish (Danio rerio) is a valuable non-mammalian vertebrate model widely used to study development and disease, including more recently cancer. The evolutionary conservation of cancer-related programs between human and zebrafish is striking and allows extrapolation of research outcomes obtained in fish back to humans. Zebrafish has gained attention as a robust model for cancer research mainly because of its high fecundity, cost-effective maintenance, dynamic visualization of tumor growth in vivo, and the possibility of chemical screening in large numbers of animals at reasonable costs. Novel approaches in modeling tumor growth, such as using transgene electroporation in adult zebrafish, could improve our knowledge about the spatial and temporal control of cancer formation and progression in vivo. Looking at genetic as well as epigenetic alterations could be important to explain the pathogenesis of a disease as complex as cancer. In this review, we highlight classic genetic and transplantation models of cancer in zebrafish as well as provide new insights on advances in cancer modeling. Recent progress in zebrafish xenotransplantation studies and drug screening has shown that zebrafish is a reliable model to study human cancer and could be suitable for evaluating patient-derived xenograft cell invasiveness. Rapid, large-scale evaluation of in vivo drug responses and kinetics in zebrafish could undoubtedly lead to new applications in personalized medicine and combination therapy. For all of the above-mentioned reasons, zebrafish is approaching a future of being a pre-clinical cancer model, alongside the mouse. However, the mouse will continue to be valuable in the last steps of pre-clinical drug screening, mostly because of the highly conserved mammalian genome and biological processes.

Patient-Derived Glioma Models: From Patients to Dish to Animals

Glioblastoma (GBM) is the most common and malignant primary brain tumor in adults associated with a poor survival. Current standard of care consists of surgical resection followed by radiation and chemotherapy. GBMs are highly heterogeneous, having a complex interaction among different cells within the tumor as well as the tumor microenvironment. One of the main challenges in the neuro-oncology field in general, and GBM in particular, is to find an optimum culture condition that maintains the molecular genotype and phenotype as well as heterogeneity of the original tumor in vitro and in vivo. Established cell lines were shown to be a poor model of the disease, failing to recapitulate the phenotype and harboring non-parental genotypic mutations. Given the growing understanding of GBM biology, the discovery of glioma cancer stem-like cells (GSCs), and their role in tumor formation and therapeutic resistance, scientists are turning more towards patient-derived cells and xenografts as a more representative model. In this review, we will discuss the current state of patient-derived GSCs and their xenografts; and provide an overview of different established models to study GBM biology and to identify novel therapeutics in the pre-clinical phase.

Experimental models and tools to tackle glioblastoma

Glioblastoma multiforme (GBM) is one of the deadliest human cancers. Despite increasing knowledge of the genetic and epigenetic changes that underlie tumour initiation and growth, the prognosis for GBM patients remains dismal. Genome analysis has failed to lead to success in the clinic. Fresh approaches are needed that can stimulate new discoveries across all levels: cell-intrinsic mechanisms (transcriptional/epigenetic and metabolic), cell-cell signalling, niche and microenvironment, systemic signals, immune regulation, and tissue-level physical forces. GBMs are inherently extremely challenging: tumour detection occurs too late, and cells infiltrate widely, hiding in quiescent states behind the blood-brain barrier. The complexity of the brain tissue also provides varied and complex microenvironments that direct cancer cell fates. Phenotypic heterogeneity is therefore superimposed onto pervasive genetic heterogeneity. Despite this bleak outlook, there are reasons for optimism. A myriad of complementary, and increasingly sophisticated, experimental approaches can now be used across the research pipeline, from simple reductionist models devised to delineate molecular and cellular mechanisms, to complex animal models required for preclinical testing of new therapeutic approaches. No single model can cover the breadth of unresolved questions. This Review therefore aims to guide investigators in choosing the right model for their question. We also discuss the recent convergence of two key technologies: human stem cell and cancer stem cell culture, as well as CRISPR/Cas tools for precise genome manipulations. New functional genetic approaches in tailored models will likely fuel new discoveries, new target identification and new therapeutic strategies to tackle GBM.

Xenotransplantation of Human glioblastoma in Zebrafish larvae: in vivo imaging and proliferation assessment

Glioblastoma (GBM) is the most prevalent type of primary brain tumor. Treatment options include maximal surgical resection and drug-radiotherapy combination. However, patient prognosis remains very poor, prompting the search for new models for drug discovery and testing, especially those that allow assessment of in vivo responses to treatment. Zebrafish xenograft models have an enormous potential to study tumor behavior, proliferation and cellular interactions. Here, an in vivo imaging and proliferation assessment method of human GBM xenograft in zebrafish larvae is introduced. Zebrafish larvae microinjected with fluorescently labeled human GBM cells were screened daily using a stereomicroscope and imaged by light sheet fluorescence microscopy (LSFM); volumetric modeling and composite reconstructions were done in single individuals. Larvae containing tumors were enzymatically dissociated, and proliferation of cancer cells was measured using dye dilution by flow cytometry. GBM micro-tumors formed mainly in the zebrafish yolk sac and perivitelline space following injection in the yolk sac, with an engraftment rate of 73%. Daily image analysis suggested cellular division, as micro-tumors progressively grew with differentiated fluorescence intensity signals. Using dye dilution assay by flow cytometry, at least three GBM cells' division cycles were identified. The combination of LSFM and flow cytometry allows assessment of proliferation and tumor growth of human GBM inside zebrafish, making it a useful model to identify effective anti-proliferative agents in a preclinical setting.