An inducible kras(V12) transgenic zebrafish model for liver tumorigenesis and chemical drug screening

Multisite Assembly of Gateway Induced Clones (MAGIC): a flexible cloning toolbox with diverse applications in vertebrate model systems

Here we present the Multisite Assembly of Gateway Induced Clones (MAGIC) system, which harnesses site-specific recombination-based cloning via Gateway technology for rapid, modular assembly of between 1 and 3 "Entry" vector components, all into a fourth, standard high copy "Destination" plasmid backbone. The MAGIC toolkit spans a range of in vitro and in vivo uses, from directing tunable gene expression, to driving simultaneous expression of microRNAs and fluorescent reporters, to enabling site-specific recombinase-dependent gene expression. All MAGIC system components are directly compatible with existing multisite gateway Tol2 systems currently used in zebrafish, as well as existing eukaryotic cell culture expression Destination plasmids, and available mammalian lentiviral and adenoviral Destination vectors, allowing rapid cross-species experimentation. Moreover, herein we describe novel vectors with flanking piggyBac transposon elements for stable genomic integration in vitro or in vivo when used with piggyBac transposase. Collectively, the MAGIC system facilitates transgenesis in cultured mammalian cells, electroporated mouse and chick embryos, as well as in injected zebrafish embryos, enabling the rapid generation of innovative DNA constructs for biological research due to a shared, common plasmid platform.

Amphiphilic hydroxyethyl starch-based nanoparticles carrying linoleic acid modified berberine inhibit the expression of krasv12 oncogene in zebrafish

Cancer is one of the most lethal diseases all over the world. Despite that many drugs have been developed for cancer therapy, they still suffer from various limitations including poor treating efficacy, toxicity to normal human cells, and the emergence of multidrug resistance. In this study, the amphiphilic LHES polymers were prepared using hydroxyethyl starch (HES) and linoleic acid as starting materials. The content and substitution degree of linoleic acid groups in LHES polymers were analyzed. The LHES polymers were used for fabricating LHES-B nanoparticles carrying a linoleic acid modified berberine derivative (L-BBR). The LHES-B nanoparticles showed high drug loading efficiency (29%) and could quickly release L-BBR under acidic pH condition (pH = 4.5). Biological investigations revealed that LHES-B nanoparticles significantly inhibited the proliferation of HepG2 cells and exhibited higher cytotoxicity than L-BBR. In a transgenic Tg(fabp10:rtTA2s-M2; TRE2:EGFP-krasv12) zebrafish model, LHES-B nanoparticles obviously inhibited the expression of krasv12 oncogene. These results indicated that LHES carriers could improve the anticancer activity of L-BBR, and the synthesized LHES-B nanoparticles showed great potential as anticancer drug.

Water-soluble red fluorescent protein dimers for hypoxic two-photon photodynamic therapy

In this study, two water-soluble red fluorescent protein (RFP) dimers, FP2R' and FP2R'', were synthesized by linking two phenothiazine-based RFP chromophore analogues through alkyl chains or alkoxy chains for hypoxic two-photon photodynamic therapy. RFP dimers are heavy-atom-free two-photon photosensitizers in which the intersystem crossing process is boosted by S and N heteroatoms. In terms of the aqueous solubility, the saturation concentration of FP2R'' was 3.5 mM, the emission wavelength was 677 nm, the singlet oxygen yield was 18%, and the two-photon absorption coefficient (β) was 2.1 × 10-11 cm W-1. Further, the RFP dimer FP2R'' showed excellent biocompatibility, negligible dark toxicity, and could produce 1O2 and O2˙- simultaneously. Under 460 nm illumination, the photosensitizer FP2R'' showed high phototoxicity with an IC50 value of 4.08 μM in an hypoxia environment, indicating that the photosensitizer FP2R'' has an excellent anti-hypoxia ability. In addition, the photosensitizer FP2R'' demonstrated a precise localization ability to lysosomes and its Pearson's colocalization coefficient was 0.94, which could guide the aggregation of photosensitizers in the lysosomes of tumor cells to effectively improve its photodynamic therapy (PDT) effect. In particular, when exposed to 800 nm two-photon excitation, FP2R'' effectively produced 1O2 and O2˙- in zebrafish and exhibited a bright two-photon fluorescence imaging capability. At the same time, the efficacy of two-photon photodynamic therapy mediated by the photosensitizer FP2R'' was verified in the tumor zebrafish model, and the growth of tumor cells in zebrafish was significantly inhibited under a two-photon laser irradiation. The water-soluble two-photon photosensitizer FP2R'' that was reasonably constructed in this study can be used as a high-efficiency hypoxic two-photon photosensitizer to inhibit deep tumor tissues.

Methods to Study Liver Disease Using Zebrafish Larvae

Liver disease affects millions of people worldwide, and the high morbidity and mortality is attributed in part to the paucity of treatment options. In many cases, liver injury self-resolves due to the remarkable regenerative capacity of the liver, but in cases when regeneration cannot compensate for the injury, inflammation and fibrosis occur, creating a setting for the emergence of liver cancer. Whole animal models are crucial for deciphering the basic biological underpinnings of liver biology and pathology and, importantly, for developing and testing new treatments for liver disease before it progresses to a terminal state. The cellular components and functions of the zebrafish liver are highly similar to mammals, and zebrafish develop many diseases that are observed in humans, including toxicant-induced liver injury, fatty liver, fibrosis, and cancer. Therefore, the widespread use of zebrafish larvae for studying the mechanisms of these pathologies and for developing potential treatments necessitates the optimization of experimental approaches to assess liver disease in this model. Here, we describe protocols using staining methods, imaging, and gene expression analysis to assess liver injury, fibrosis, and preneoplastic changes in the liver of larval zebrafish.

Amino acid modified OCMC-g-Suc-β-CD nanohydrogels carrying lapatinib and ginsenoside Rg1 exhibit high anticancer activity in a zebrafish model

Nanohydrogels show great potential as efficient drug carriers due to their biocompatibility, low toxicity, and high water absorbability. In this paper, we prepared two O-carboxymethylated chitosan (OCMC)-based polymers functionalized with β-cyclodextrin (β-CD) and amino acid. The structures of the polymers were characterized by Fourier Transform Infrared (FTIR) Spectroscopy. Morphological study was carried out on a Transmission Electron Microscope (TEM), and the results indicated that the two polymers had irregular spheroidal structure with some pores distributed on their surface. The average particle diameter was below 500 nm, and the zeta potential was above +30 mV. The two polymers were further used for preparing nanohydrogels loaded with anticancer drugs lapatinib and ginsenoside Rg1, and the resulting nanohydrogels showed high drug loading efficiency and pH-sensitive (pH = 4.5) drug release behavior. In vitro cytotoxicity investigation revealed that the nanohydrogels exhibited high cytotoxicity against lung cancer (A549) cells. In vivo anticancer investigation was performed in a transgenic Tg(fabp10:rtTA2s-M2; TRE2:EGFP-kras ^V12) zebrafish model. The results showed that the synthesized nanohydrogels significantly inhibited the expression of EGFP-kras ^v12 oncogene in zebrafish liver, and the L-arginine modified OCMC-g-Suc-β-CD nanohydrogels loading lapatinib and ginsenoside Rg1 showed the best results.

Novel amphiphilic hydroxyethyl starch-based nanoparticles loading camptothecin exhibit high anticancer activity in HepG2 cells and zebrafish

Camptothecin is a naturally occurred anticancer drug but exhibits limitations including poor aqueous solubility, low bioavailability, and high level of adverse drug reactions on normal organs. To overcome these problems, this paper developed a novel amphiphilic Lau-Leu-HES carrier using hydroxyethyl starch, lauric acid, and L-leucine as starting materials. The carrier was successfully applied to prepare Lau-Leu-HES nanoparticles loading camptothecin. The drug loading efficiency and encapsulation efficiency of the nanoparticles were calculated to be 29.04% and 81.85%, respectively. The nanoparticles exhibited high zeta potential (-15.51 mV) and small hydrodynamic diameter (105.4 nm). Camptothecin in nanoparticles could be rapidly released under acidic condition (pH = 4.5), thereby indicating the high sensitivity under cancer microenvironments. Anticancer investigation revealed that the nanoparticles could inhibit the proliferation of HepG2 cells in vitro. Compared with commercial available drug doxorubicin, the nanoparticles could significantly inhibit the expression of kras^v12 oncogene in transgenic Tg (EGFP-kras^V12) zebrafish. These results indicate that the camptothecin-loaded Lau-Leu-HES nanoparticles are expected to be a potential candidate for cancer therapy.

A multidimensional metabolomics workflow to image biodistribution and evaluate pharmacodynamics in adult zebrafish

An integrated evaluation of the tissue distribution and pharmacodynamic properties of a therapeutic is essential for successful translation to the clinic. To date, however, cost-effective methods to measure these parameters at the systems level in model organisms are lacking. Here, we introduce a multidimensional workflow to evaluate drug activity that combines mass spectrometry-based imaging, absolute drug quantitation across different biological matrices, in vivo isotope tracing and global metabolome analysis in the adult zebrafish. As a proof of concept, we quantitatively determined the whole-body distribution of the anti-rheumatic agent hydroxychloroquine sulfate (HCQ) and measured the systemic metabolic impacts of drug treatment. We found that HCQ distributed to most organs in the adult zebrafish 24 h after addition of the drug to water, with the highest accumulation of both the drug and its metabolites being in the liver, intestine and kidney. Interestingly, HCQ treatment induced organ-specific alterations in metabolism. In the brain, for example, HCQ uniquely elevated pyruvate carboxylase activity to support increased synthesis of the neuronal metabolite, N-acetylaspartate. Taken together, this work validates a multidimensional metabolomics platform for evaluating the mode of action of a drug and its potential off-target effects in the adult zebrafish. This article has an associated First Person interview with the first author of the paper.

Systematic Characterization of the Disruption of Intestine during Liver Tumor Progression in the xmrk Oncogene Transgenic Zebrafish Model

The crosstalk between tumors and their local microenvironment has been well studied, whereas the effect of tumors on distant tissues remains understudied. Studying how tumors affect other tissues is important for understanding the systemic effect of tumors and for improving the overall health of cancer patients. In this study, we focused on the changes in the intestine during liver tumor progression, using a previously established liver tumor model through inducible expression of the oncogene xmrk in zebrafish. Progressive disruption of intestinal structure was found in the tumor fish, displaying villus damage, thinning of bowel wall, increase in goblet cell number, decrease in goblet cell size and infiltration of eosinophils, most of which were observed phenotypes of an inflammatory intestine. Intestinal epithelial cell renewal was also disrupted, with decreased cell proliferation and increased cell death. Analysis of intestinal gene expression through RNA-seq suggested deregulation of genes related to intestinal function, epithelial barrier and homeostasis and activation of pathways in inflammation, epithelial mesenchymal transition, extracellular matrix organization, as well as hemostasis. Gene set enrichment analysis showed common gene signatures between the intestine of liver tumor fish and human inflammatory bowel disease, the association of which with cancer has been recently noticed. Overall, this study represented the first systematic characterization of the disruption of intestine under the liver tumor condition and suggested targeting intestinal inflammation as a potential approach for managing cancer cachexia.

Notch–Sox9 Axis Mediates Hepatocyte Dedifferentiation in KrasG12V-Induced Zebrafish Hepatocellular Carcinoma

Liver cancer is one of the most prevalent cancers in humans. Hepatocytes normally undergo dedifferentiation after the onset of hepatocellular carcinoma, which in turn facilitates the progression of cancer. Although the process of hepatocellular carcinoma dedifferentiation is of significant research and clinical value, the cellular and molecular mechanisms underlying it are still not fully characterized. We constructed a zebrafish liver cancer model based on overexpression of the oncogene krasG12V to investigate the hepatocyte dedifferentiation in hepatocellular carcinoma. We found that, after hepatocarcinogenesis, hepatocytes dedifferentiated and the Notch signaling pathway was upregulated in this progress. Furthermore, we found that inhibition of the Notch signaling pathway or deficiency of sox9b both prevented hepatocyte dedifferentiation following hepatocellular carcinoma induction, reducing cancer metastasis and improving survival. In conclusion, we found that hepatocytes undergo dedifferentiation after hepatocarcinogenesis, a process that requires Notch signaling and likewise the activation of Sox9.

Sustained experimental activation of FGF8/ERK in the developing chicken spinal cord models early events in ERK-mediated tumorigenesis

The MAPK/ERK pathway regulates a variety of physiological cellular functions, including cell proliferation and survival. It is abnormally activated in many types of human cancers in response to driver mutations in regulators of this pathway that trigger tumor initiation. The early steps of oncogenic progression downstream of ERK overactivation are poorly understood due to a lack of appropriate models. We show here that ERK1/2 overactivation in the trunk neural tube of the chicken embryo through expression of a constitutively active form of the upstream kinase MEK1 (MEK1ca), rapidly provokes a profound change in the transcriptional signature of developing spinal cord cells. These changes are concordant with a previously established role of the tyrosine kinase receptor ligand FGF8 acting via the ERK1/2 effectors to maintain an undifferentiated state. Furthermore, we show that MEK1ca-transfected spinal cord cells lose neuronal identity, retain caudal markers, and ectopically express potential effector oncogenes, such as AQP1. MEK1ca expression in the developing spinal cord from the chicken embryo is thus a tractable in vivo model to identify the mechanisms fostering neoplasia and malignancy in ERK-induced tumorigenesis of neural origins.

Inducible Liver Cancer Models in Transgenic Zebrafish to Investigate Cancer Biology

Primary liver cancer is one of the most prevalent and deadly cancers, which incidence continues to increase while treatment response remains poor; thus, in-depth understanding of tumour events is necessary to develop more effective therapies. Animal models for liver cancer are powerful tools to reach this goal. Over the past decade, our laboratory has established multiple oncogene transgenic zebrafish lines that can be robustly induced to develop liver cancer. Histological, transcriptomic and molecular analyses validate the use of these transgenic zebrafish as experimental models for liver cancer. In this review, we provide a comprehensive summary of our findings with these inducible zebrafish liver cancer models in tumour initiation, oncogene addiction, tumour microenvironment, gender disparity, cancer cachexia, drug screening and others. Induced oncogene expression causes a rapid change of the tumour microenvironment such as inflammatory responses, increased vascularisation and rapid hepatic growth. In several models, histologically-proven carcinoma can be induced within one week of chemical inducer administration. Interestingly, the induced liver tumours show the ability to regress when the transgenic oncogene is suppressed by the withdrawal of the chemical inducer. Like human liver cancer, there is a strong bias of liver cancer severity in male zebrafish. After long-term tumour progression, liver cancer-bearing zebrafish also show symptoms of cancer cachexia such as muscle-wasting. In addition, the zebrafish models have been used to screen for anti-metastasis drugs as well as to evaluate environmental toxicants in carcinogenesis. These findings demonstrated that these inducible zebrafish liver cancer models provide rapid and convenient experimental tools for further investigation of fundamental cancer biology, with the potential for the discovery of new therapeutic approaches.

Exacerbation of Liver Tumor Metastasis in twist1a+/xmrk+ Double Transgenic Zebrafish following Lipopolysaccharide or Dextran Sulphate Sodium Exposure

The poor prognosis for patients with hepatocellular carcinoma (HCC) is related directly to metastasis. The Twist1 gene encodes for a transcription factor essential to embryogenesis. It has also been shown to promote epithelial-to-mesenchymal transition (EMT), invasion, and metastasis; however, there is currently no in vivo evidence that Twist1 plays a role in the metastasis of liver tumors. Zebrafish are increasingly being used as an alternative cancer model. In the current study, an adult-stage zebrafish HCC model was used to examine the synergistic effects of twist1a and xmrk, a well characterized oncogene, during HCC metastasis. We also examined the effects of two inflammatory agents, lipopolysaccharides (LPS) and dextran sulfate sodium (DSS), on the hepatocyte-specific expression of transgenic twist1a and xmrk. The conditional overexpression of twist1a and xmrk was shown to promote liver tumor metastasis in zebrafish, resulting in increased apoptosis and cell proliferation as well as tumor maintenance and propagation independent of the inherent EMT-inducing activity of xmrk. Exposing twist1a+/xmrk+ transgenic zebrafish to LPS or DSS was shown to promote metastasis, indicating that the overexpression of twist1a and xmrk led to crosstalk between the signaling pathways involved in EMT. This study provides important evidence pertaining to the largely overlooked effects of signaling crosstalk between twist1a and xmrk in regulating HCC metastasis. Our results also suggest that the co-expression of twist1a/xmrk in conjunction with exposure to LPS or DSS enhances HCC metastasis, and provides a valuable in vivo platform by which to investigate tumor initiation and metastasis in the study of liver cancer.

Experimental Models of Hepatocellular Carcinoma-A Preclinical Perspective

Hepatocellular carcinoma (HCC), the most frequent form of primary liver carcinoma, is a heterogenous and complex tumor type with increased incidence, poor prognosis, and high mortality. The actual therapeutic arsenal is narrow and poorly effective, rendering this disease a global health concern. Although considerable progress has been made in terms of understanding the pathogenesis, molecular mechanisms, genetics, and therapeutical approaches, several facets of human HCC remain undiscovered. A valuable and prompt approach to acquire further knowledge about the unrevealed aspects of HCC and novel therapeutic candidates is represented by the application of experimental models. Experimental models (in vivo and in vitro 2D and 3D models) are considered reliable tools to gather data for clinical usability. This review offers an overview of the currently available preclinical models frequently applied for the study of hepatocellular carcinoma in terms of initiation, development, and progression, as well as for the discovery of efficient treatments, highlighting the advantages and the limitations of each model. Furthermore, we also focus on the role played by computational studies (in silico models and artificial intelligence-based prediction models) as promising novel tools in liver cancer research.

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.

Zebrafish as a Model for Anticancer Nanomedicine Studies

Nanomedicine is a new approach to fight against cancer by the development of anticancer nanoparticles (NPs) that are of high sensitivity, specificity, and targeting ability to detect cancer cells, such as the ability of Silica NPs in targeting epithelial cancer cells. However, these anticancer NPs require preclinical testing, and zebrafish is a useful animal model for preclinical studies of anticancer NPs. This model affords a large sample size, optical imaging, and easy genetic manipulation that aid in nanomedicine studies. This review summarizes the numerous advantages of the zebrafish animal model for such investigation, various techniques for inducing cancer in zebrafish, and discusses the methods to assess cancer development in the model and to test for the toxicity of the anticancer drugs and NPs. In addition, it summarizes the recent studies that used zebrafish as a model to test the efficacy of several different anticancer NPs in treating cancer.

Zebrafish, an In Vivo Platform to Screen Drugs and Proteins for Biomedical Use

The nearly simultaneous convergence of human genetics and advanced molecular technologies has led to an improved understanding of human diseases. At the same time, the demand for drug screening and gene function identification has also increased, albeit time- and labor-intensive. However, bridging the gap between in vitro evidence from cell lines and in vivo evidence, the lower vertebrate zebrafish possesses many advantages over higher vertebrates, such as low maintenance, high fecundity, light-induced spawning, transparent embryos, short generation interval, rapid embryonic development, fully sequenced genome, and some phenotypes similar to human diseases. Such merits have popularized the zebrafish as a model system for biomedical and pharmaceutical studies, including drug screening. Here, we reviewed the various ways in which zebrafish serve as an in vivo platform to perform drug and protein screening in the fields of rare human diseases, social behavior and cancer studies. Since zebrafish mutations faithfully phenocopy many human disorders, many compounds identified from zebrafish screening systems have advanced to early clinical trials, such as those for Adenoid cystic carcinoma, Dravet syndrome and Diamond-Blackfan anemia. We also reviewed and described how zebrafish are used to carry out environmental pollutant detection and assessment of nanoparticle biosafety and QT prolongation.

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.

Perfluorooctane sulfonate promotes doxycycline-induced liver tumor progression in male Krasv12 transgenic zebrafish

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that has been widely detected in the environment and has caused growing international concern. The liver is the main target organ of PFOS exposure. Animal experiments have shown that PFOS exposure can increase the risk of liver tumorigenesis. However, whether PFOS can accelerate liver tumor progression is still unclear. In this study, transgenic zebrafish Tg(fabp10:rtTA2s-M2; TRE2:EGFP-KRAS^G12V), a hepatocellular carcinoma (HCC) model that can cause liver tumorigenesis by doxycycline (DOX) induction, was used to investigate the effect of PFOS exposure in HCC progression. The male kras^V12 transgenic zebrafish were exposed to 20 mg/L DOX, 500 μg/L PFOS or combined 20 mg/L DOX and 500 μg/L PFOS for 10 d. The results showed that co-treated with PFOS and DOX caused oncogenic Kras-induced liver enlargement, increased the percentages of zebrafish with HCC, and aggravated metabolic reprogramming of liver. To the best of our knowledge, this study for the first proved that PFOS could promote liver tumor progression. Decreased vitamin D level and increased fatty acid intake caused by PFOS might be responsible for the tumor-promoting effects. The results suggest that attention should be paid to the tumor-promoting effects of PFOS when assessing its environmental health risks, and these findings provide new insights into the toxicity of PFOS.

Application of Animal Models in Cancer Research: Recent Progress and Future Prospects

Animal models refers to the animal experimental objects and related materials that can simulate human body established in medical research. As the second-largest disease in terms of morbidity and mortality after cardiovascular disease, cancer has always been the focus of human attention all over the world, which makes it a research hotspot in the medical field. At the same time, more and more animal models have been constructed and used in cancer research. With the deepening of research, the construction methods of cancer animal models are becoming more and more diverse, including chemical induction, xenotransplantation, gene programming, and so on. In recent years, patient-derived xenotransplantation (PDX) model has become a research hotspot because it can retain the microenvironment of the primary tumor and the basic characteristics of cells. Animal models can be used not only to study the biochemical and physiological processes of the occurrence and development of cancer in objects but also for the screening of cancer drugs and the exploration of gene therapy. In this paper, several main tumor animal models and the application progress of animal models in tumor research are systematically reviewed. Finally, combined with the latest progress and development trend in this field, the future research of tumor animal model was prospected.

Reeling in the Zebrafish Cancer Models

Zebrafish are rapidly becoming a leading model organism for cancer research. The genetic pathways driving cancer are highly conserved between zebrafish and humans, and the ability to easily manipulate the zebrafish genome to rapidly generate transgenic animals makes zebrafish an excellent model organism. Transgenic zebrafish containing complex, patient-relevant genotypes have been used to model many cancer types. Here we present a comprehensive review of transgenic zebrafish cancer models as a resource to the field and highlight important areas of cancer biology that have yet to be studied in the fish. The ability to image cancer cells and niche biology in an endogenous tumor makes zebrafish an indispensable model organism in which we can further understand the mechanisms that drive tumorigenesis and screen for potential new cancer therapies.

Skeletal Biology and Disease Modeling in Zebrafish

Zebrafish are teleosts (bony fish) that share with mammals a common ancestor belonging to the phylum Osteichthyes, from which their endoskeletal systems have been inherited. Indeed, teleosts and mammals have numerous genetically conserved features in terms of skeletal elements, ossification mechanisms, and bone matrix components in common. Yet differences related to bone morphology and function need to be considered when investigating zebrafish in skeletal research. In this review, we focus on zebrafish skeletal architecture with emphasis on the morphology of the vertebral column and associated anatomical structures. We provide an overview of the different ossification types and osseous cells in zebrafish and describe bone matrix composition at the microscopic tissue level with a focus on assessing mineralization. Processes of bone formation also strongly depend on loading in zebrafish, as we elaborate here. Furthermore, we illustrate the high regenerative capacity of zebrafish bones and present some of the technological advantages of using zebrafish as a model. We highlight zebrafish axial and fin skeleton patterning mechanisms, metabolic bone disease such as after immunosuppressive glucocorticoid treatment, as well as osteogenesis imperfecta (OI) and osteopetrosis research in zebrafish. We conclude with a view of why larval zebrafish xenografts are a powerful tool to study bone metastasis. © 2021 American Society for Bone and Mineral Research (ASBMR).

Benefits of Zebrafish Xenograft Models in Cancer Research

As a promising in vivo tool for cancer research, zebrafish have been widely applied in various tumor studies. The zebrafish xenograft model is a low-cost, high-throughput tool for cancer research that can be established quickly and requires only a small sample size, which makes it favorite among researchers. Zebrafish patient-derived xenograft (zPDX) models provide promising evidence for short-term clinical treatment. In this review, we discuss the characteristics and advantages of zebrafish, such as their transparent and translucent features, the use of vascular fluorescence imaging, the establishment of metastatic and intracranial orthotopic models, individual pharmacokinetics measurements, and tumor microenvironment. Furthermore, we introduce how these characteristics and advantages are applied other in tumor studies. Finally, we discuss the future direction of the use of zebrafish in tumor studies and provide new ideas for the application of it.

Stimulation of hepatocarcinogenesis by activated cholangiocytes via Il17a/f1 pathway in kras transgenic zebrafish model

It has been well known that tumor progression is dependent on secreted factors not only from tumor cells but also from other surrounding non-tumor cells. In the current study, we investigated the role of cholangiocytes during hepatocarcinogenesis following induction of oncogenic kras^V12 expression in hepatocytes using an inducible transgenic zebrafish model. Upon induction of carcinogenesis in hepatocytes, a progressive cell proliferation in cholangiocytes was observed. The proliferative response in cholangiocytes was induced by enhanced lipogenesis and bile acids secretion from hepatocytes through activation of Sphingosine 1 phosphate receptor 2 (S1pr2), a known cholangiocyte receptor involving in cholangiocyte proliferation. Enhancement and inhibition of S1pr2 could accelerate or inhibit cholangiocyte proliferation and hepatocarcinogenesis respectively. Gene expression analysis of hepatocytes and cholangiocytes showed that cholangiocytes stimulated carcinogenesis in hepatocytes via an inflammatory cytokine, Il17a/f1, which activated its receptor (Il17ra1a) on hepatocytes and enhanced hepatocarcinogenesis via an ERK dependent pathway. Thus, the enhancing effect of cholangiocytes on hepatocarcinogenesis is likely via an inflammatory loop.

The Role of Feed in Aquatic Laboratory Animal Nutrition and the Potential Impact on Animal Models and Study Reproducibility

Feed plays a central role in the physiological development of terrestrial and aquatic animals. Historically, the feeding practice of aquatic research species derived from aquaculture, farmed, or ornamental trades. These diets are highly variable, with limited quality control, and have been typically selected to provide the fastest growth or highest fecundity. These variations of quality and composition of diets may affect animal/colony health and can introduce confounding experimental variables into animal-based studies that impact research reproducibility.

Transgenic zebrafish for modeling hepatocellular carcinoma

Liver cancer is the third leading cause of cancer‐related deaths throughout the world, and more than 0.6 million people die from liver cancer annually. Therefore, novel therapeutic strategies to eliminate malignant cells from liver cancer patients are urgently needed. Recent advances in high‐throughput genomic technologies have identified de novo candidates for oncogenes and pharmacological targets. However, testing and understanding the mechanism of oncogenic transformation as well as probing the kinetics and therapeutic responses of spontaneous tumors in an intact microenvironment require in vivo examination using genetically modified animal models. The zebrafish (Danio rerio) has attracted increasing attention as a new model for studying cancer biology since the organs in the model are strikingly similar to human organs and the model can be genetically modified in a short time and at a low cost. This review summarizes the current knowledge of epidemiological data and genetic alterations in hepatocellular carcinoma (HCC), zebrafish models of HCC, and potential therapeutic strategies for targeting HCC based on knowledge from the models.

Genetic Engineering of Zebrafish in Cancer Research

Zebrafish (Danio rerio) is an excellent model to study a wide diversity of human cancers. In this review, we provide an overview of the genetic and reverse genetic toolbox allowing the generation of zebrafish lines that develop tumors. The large spectrum of genetic tools enables the engineering of zebrafish lines harboring precise genetic alterations found in human patients, the generation of zebrafish carrying somatic or germline inheritable mutations or zebrafish showing conditional expression of the oncogenic mutations. Comparative transcriptomics demonstrate that many of the zebrafish tumors share molecular signatures similar to those found in human cancers. Thus, zebrafish cancer models provide a unique in vivo platform to investigate cancer initiation and progression at the molecular and cellular levels, to identify novel genes involved in tumorigenesis as well as to contemplate new therapeutic strategies.

Zebrafish In Vivo Models of Cancer and Metastasis

Metastasis, the dispersal of cancer cells from a primary tumor to secondary sites within the body, is the leading cause of cancer-related death. Animal models have been an indispensable tool to investigate the complex interactions between the cancer cells and the tumor microenvironment during the metastatic cascade. The zebrafish (Danio rerio) has emerged as a powerful vertebrate model for studying metastatic events in vivo. The zebrafish has many attributes including ex-utero development, which facilitates embryonic manipulation, as well as optically transparent tissues, which enables in vivo imaging of fluorescently labeled cells in real time. Here, we summarize the techniques which have been used to study cancer biology and metastasis in the zebrafish model organism, including genetic manipulation and transgenesis, cell transplantation, live imaging, and high-throughput compound screening. Finally, we discuss studies using the zebrafish, which have complemented and benefited metastasis research.

Zebrafish: An emerging model system to study liver diseases and related drug discovery

The zebrafish has emerged as a powerful vertebrate model for studying liver-associated disorders. Liver damage is a crucial problem in the process of drug development and zebrafish have proven to be an important tool for the high-throughput screening of drugs for hepatotoxicity. Although the structure of the zebrafish liver differs to that of mammals, the fundamental physiologic processes, genetic mutations and manifestations of pathogenic responses to environmental insults exhibit much similarity. The larval transparency of the zebrafish is a great advantage for real-time imaging in hepatic studies. The zebrafish has a broad spectrum of cytochrome P450 enzymes, which enable the biotransformation of drugs via similar pathways as mammals, including oxidation, reduction and hydrolysis reactions. In the present review, we appraise the various drugs, chemicals and toxins used to study liver toxicity in zebrafish and their similarities to the rodent models for liver-related studies. Interestingly, the zebrafish has also been effectively used to study the pathophysiology of nonalcoholic and alcoholic fatty liver disease. The genetic models of liver disorders and their easy manipulation provide great opportunity in the area of drug development. The zebrafish has proven to be an influential model for the hepatic system due to its invertebrate-like advantages coupled with its vertebrate biology. The present review highlights the pivotal role of zebrafish in bridging the gap between cell-based and mammalian models.

DnaJ-PKAc fusion induces liver inflammation in a zebrafish model of fibrolamellar carcinoma

Fibrolamellar carcinoma (FLC) is a rare liver cancer that affects adolescents and young adults. Genomic analysis of FLC has revealed a 400 kb deletion in chromosome 19 that leads to the chimeric transcript DNAJB1-PRKACA (DnaJ-PKAc), comprised of the first exon of heat shock protein 40 (DNAJB1) and exons 2-10 of the catalytic subunit of protein kinase A (PRKACA). Here, we report a new zebrafish model of FLC induced by ectopic expression of zebrafish Dnaja-Pkaca (zfDnaJa-Pkaca) in hepatocytes that is amenable to live imaging of early innate immune inflammation. Expression of zfDnaJa-Pkaca in hepatocytes induces hepatomegaly and increased hepatocyte size. In addition, FLC larvae exhibit early innate immune inflammation characterized by early infiltration of neutrophils and macrophages into the liver microenvironment. Increased Caspase-a (the zebrafish homolog for human caspase-1) activity was also found in the liver of FLC larvae, and pharmacological inhibition of Tnfα and caspase-a decreased liver size and inflammation. Overall, these findings show that innate immune inflammation is an early feature in a zebrafish model of FLC and that pharmacological inhibition of TNFα or caspase-1 activity might be targets to treat inflammation and progression in FLC patients.This article has an associated First Person interview with the first author of the paper.

Inflammatory Responses during Tumour Initiation: From Zebrafish Transgenic Models of Cancer to Evidence from Mouse and Man

The zebrafish is now an important model organism for cancer biology studies and provides unique and complementary opportunities in comparison to the mammalian equivalent. The translucency of zebrafish has allowed in vivo live imaging studies of tumour initiation and progression at the cellular level, providing novel insights into our understanding of cancer. Here we summarise the available transgenic zebrafish tumour models and discuss what we have gleaned from them with respect to cancer inflammation. In particular, we focus on the host inflammatory response towards transformed cells during the pre-neoplastic stage of tumour development. We discuss features of tumour-associated macrophages and neutrophils in mammalian models and present evidence that supports the idea that these inflammatory cells promote early stage tumour development and progression. Direct live imaging of tumour initiation in zebrafish models has shown that the intrinsic inflammation induced by pre-neoplastic cells is tumour promoting. Signals mediating leukocyte recruitment to pre-neoplastic cells in zebrafish correspond to the signals that mediate leukocyte recruitment in mammalian tumours. The activation state of macrophages and neutrophils recruited to pre-neoplastic cells in zebrafish appears to be heterogenous, as seen in mammalian models, which provides an opportunity to study the plasticity of innate immune cells during tumour initiation. Although several potential mechanisms are described that might mediate the trophic function of innate immune cells during tumour initiation in zebrafish, there are several unknowns that are yet to be resolved. Rapid advancement of genetic tools and imaging technologies for zebrafish will facilitate research into the mechanisms that modulate leukocyte function during tumour initiation and identify targets for cancer prevention.

E2f5 is a versatile transcriptional activator required for spermatogenesis and multiciliated cell differentiation in zebrafish

E2f5 is a member of the E2f family of transcription factors that play essential roles during many cellular processes. E2f5 was initially characterized as a transcriptional repressor in cell proliferation studies through its interaction with the Retinoblastoma (Rb) protein for inhibition of target gene transcription. However, the precise roles of E2f5 during embryonic and post-embryonic development remain incompletely investigated. Here, we report that zebrafish E2f5 plays critical roles during spermatogenesis and multiciliated cell (MCC) differentiation. Zebrafish e2f5 mutants develop exclusively as infertile males. In the mutants, spermatogenesis is arrested at the zygotene stage due to homologous recombination (HR) defects, which finally leads to germ cell apoptosis. Inhibition of cell apoptosis in e2f5;tp53 double mutants rescued ovarian development, although oocytes generated from the double mutants were still abnormal, characterized by aberrant distribution of nucleoli. Using transcriptome analysis, we identified dmc1, which encodes an essential meiotic recombination protein, as the major target gene of E2f5 during spermatogenesis. E2f5 can bind to the promoter of dmc1 to promote HR, and overexpression of dmc1 significantly increased the fertilization rate of e2f5 mutant males. Besides gametogenesis defects, e2f5 mutants failed to develop MCCs in the nose and pronephric ducts during early embryonic stages, but these cells recovered later due to redundancy with E2f4. Moreover, we demonstrate that ion transporting principal cells in the pronephric ducts, which remain intercalated with the MCCs, do not contain motile cilia in wild-type embryos, while they generate single motile cilia in the absence of E2f5 activity. In line with this, we further show that E2f5 activates the Notch pathway gene jagged2b (jag2b) to inhibit the acquisition of MCC fate as well as motile cilia differentiation by the neighboring principal cells. Taken together, our data suggest that E2f5 can function as a versatile transcriptional activator and identify novel roles of the protein in spermatogenesis as well as MCC differentiation during zebrafish development.

Evidence for immortality and autonomy in animal cancer models is often not provided, which causes confusion on key issues of cancer biology

Modern research into carcinogenesis has undergone three phases. Surgeons and pathologists started the first phase roughly 250 years ago, establishing morphological traits of tumors for pathologic diagnosis, and setting immortality and autonomy as indispensable criteria for neoplasms. A century ago, medical doctors, biologists and chemists started to enhance "experimental cancer research" by establishing many animal models of chemical-induced carcinogenesis for studies of cellular mechanisms. In this second phase, the two-hit theory and stepwise carcinogenesis of "initiation-promotion" or "initiation-promotion-progression" were established, with an illustrious finding that outgrowths induced in animals depend on the inducers, and thus are not authentically neoplastic, until late stages. The last 40 years are the third incarnation, molecular biologists have gradually dominated the carcinogenesis research fraternity and have established numerous genetically-modified animal models of carcinogenesis. However, evidence has not been provided for immortality and autonomy of the lesions from most of these models. Probably, many lesions had already been collected from animals for analyses of molecular mechanisms of "cancer" before the lesions became autonomous. We herein review the monumental work of many predecessors to reinforce that evidence for immortality and autonomy is essential for confirming a neoplastic nature. We extrapolate that immortality and autonomy are established early during sporadic human carcinogenesis, unlike the late establishment in most animal models. It is imperative to resume many forerunners' work by determining the genetic bases for initiation, promotion and progression, the genetic bases for immortality and autonomy, and which animal models are, in fact, good for identifying such genetic bases.

Quantifying Liver Size in Larval Zebrafish Using Brightfield Microscopy

In several transgenic zebrafish models of hepatocellular carcinoma (HCC), hepatomegaly can be observed during early larval stages. Quantifying larval liver size in zebrafish HCC models provides a means to rapidly assess the effects of drugs and other manipulations on an oncogene-related phenotype. Here we show how to fix zebrafish larvae, dissect the tissues surrounding the liver, photograph livers using bright-field microscopy, measure liver area, and analyze results. This protocol enables rapid, precise quantification of liver size. As this method involves measuring liver area, it may underestimate differences in liver volume, and complementary methodologies are required to differentiate between changes in cell size and changes in cell number. The dissection technique described herein is an excellent tool to visualize the liver, gut, and pancreas in their natural positions for myriad downstream applications including immunofluorescence staining and in situ hybridization. The described strategy for quantifying larval liver size is applicable to many aspects of liver development and regeneration.

New insights into the role of mTORC1 in male fertility in zebrafish

Mechanistic target of rapamycin complex 1 (mTORC1) plays crucial roles in male fertility. In mammals, deregulation of mTORC1 led to disordered spermatogonia proliferation and spermatogenesis, which eventually caused infertility in males. However, its roles in male fertility of non-mammalian species remain unclarified. In the present study, it was found that treatment of rapamycin, an mTORC1 inhibitor, resulted in infertility with decreased milt production and sperm motility in zebrafish. However, it is surprising to find that spermatogenesis was normal in these fish. All types of germ cells were found and the proliferation of spermatogonia and spermatocyte were normal. These results suggested that maturation of sperm may be impaired in males treated with rapamycin. Increased apoptosis was found surrounding the lumen containing spermatozoa, implicating a loss of Sertoli cells in testes treated with rapamycin. Moreover, LH/hCG mediated up-regulation of steroidogenic genes was abolished. The expression of npr and ar induced by LH/hCG was also blocked, which further suppressed the signaling of progestin and androgen. Collectively, mTORC1 maintains male fertility via different mechanisms in fish and mammals. mTORC1 is dispensable for spermatogenesis in zebrafish, but possibly supports the maintenance of Sertoli cells and mediates the signaling of hormones, which are crucial for sperm maturation.

Modeling of Solid-Tumor Microenvironment in Zebrafish (Danio Rerio) Larvae

The zebrafish larvae have emerged as a powerful model for studying tumorigenesis in vivo, with remarkable conservation with mammals in genetics, molecular and cell biology. Zebrafish tumor models bear the significant advantages of optical clarity in comparison to that in the mammalian models, allowing noninvasive investigation of the tumor cell and its microenvironment at single-cell resolution. Here we review recent progressions in the field of zebrafish models of solid tumor diseases in two main categories: the genetically engineered tumor models in which all cells in the tumor microenvironment are zebrafish cells, and xenograft tumor models in which the tumor microenvironment is composed of zebrafish cells and cells from other species. Notably, the zebrafish patient-derived xenograft (zPDX) models can be used for personalized drug assessment on primary tumor biopsies, including the pancreatic cancer. For the future studies, a series of high throughput drug screenings on the library of transgenic zebrafish models of solid tumor are expected to provide systematic database of oncogenic mutation, cell-of-origin, and leading compounds; and the humanization of zebrafish in genetics and cellular composition will make it more practical hosts for zPDX modeling. Together, zebrafish tumor model systems are unique and convenient in vivo platforms, with great potential to serve as valuable tools for cancer researches.

Evolutionarily novel genes are expressed in transgenic fish tumors and their orthologs are involved in development of progressive traits in humans

Abstract

Earlier we suggested a new hypothesis of the possible evolutionary role of hereditary tumors (Kozlov, Evolution by tumor Neofunctionalization, 2014), and described a new class of genes – tumor specifically expressed, evolutionarily novel (TSEEN) genes - that are predicted by this hypothesis (Kozlov, Infect Agents Cancer 11:34, 2016). In this paper we studied evolutionarily novel genes expressed in fish tumors after regression, as a model of evolving organs. As evolutionarily novel genes may not yet have organismal functions, we studied the acquisition of new gene functions by comparing fish evolutionarily novel genes with their human orthologs. We found that many genes involved in development of progressive traits in humans (lung, mammary gland, placenta, ventricular septum, etc.) originated in fish and are expressed in fish tumors and tumors after regression. These findings support a possible evolutionary role of hereditary tumors, and in particular the hypothesis of evolution by tumor neofunctionalization.

Research highlights

Earlier we described a new class of genes that are tumor-specifically expressed and evolutionarily novel (TSEEN). As the functions of TSEEN genes are often uncertain, we decided to study TSEEN genes of fishes so that we could trace the appearance of their new functions in higher vertebrates. We found that many human genes which are involved in development of progressive traits (placenta development, mammary gland and lung development etc.,) originated in fishes and are expressed in fish tumors.

MicroRNAs in Animal Models of HCC

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related mortality. Molecular heterogeneity and absence of biomarkers for patient allocation to the best therapeutic option contribute to poor prognosis of advanced stages. Aberrant microRNA (miRNA) expression is associated with HCC development and progression and influences drug resistance. Therefore, miRNAs have been assayed as putative biomarkers and therapeutic targets. miRNA-based therapeutic approaches demonstrated safety profiles and antitumor efficacy in HCC animal models; nevertheless, caution should be used when transferring preclinical findings to the clinics, due to possible molecular inconsistency between animal models and the heterogeneous pattern of the human disease. In this context, models with defined genetic and molecular backgrounds might help to identify novel therapeutic options for specific HCC subgroups. In this review, we describe rodent models of HCC, emphasizing their representativeness with the human pathology and their usefulness as preclinical tools for assessing miRNA-based therapeutic strategies.

A Novel Zebrafish Model of Metastasis Identifies the HSD11β1 Inhibitor Adrenosterone as a Suppressor of Epithelial-Mesenchymal Transition and Metastatic Dissemination

Metastasis of cancer cells is multi-step process and dissemination is an initial step. Here we report a tamoxifen-controllable Twist1a-ER^T2 transgenic zebrafish line as a new animal model for metastasis research, and demonstrate that this model can serve as a novel platform for discovery of antimetastasis drugs targeting metastatic dissemination of cancer cells. By crossing Twist1a-ER^T2 with xmrk (a homolog of hyperactive form of EGFR) transgenic zebrafish, which develops hepatocellular carcinoma, approximately 80% of the double transgenic zebrafish showed spontaneous cell dissemination of mCherry-labeled hepatocytes from the liver to the entire abdomen region and the tail region. The dissemination is accomplished in 5 days through induction of an epithelial-to-mesenchymal transition. Using this model, we conducted in vivo drug screening and identified three hit drugs. One of them, adrenosterone, an inhibitor for hydroxysteroid (11-beta) dehydrogenase 1 (HSD11β1), has a suppressor effect on cell dissemination in this model. Pharmacologic and genetic inhibition of HSD11β1 suppressed metastatic dissemination of highly metastatic human cell lines in a zebrafish xenotransplantation model. Through downregulation of Snail and Slug, adrenosterone-treated cells recovered expression of E-cadherin and other epithelial markers and lost partial expression of mesenchymal markers compared with vehicle-treated cells. Taken together, our model offers a useful platform for the discovery of antimetastasis drugs targeting metastatic dissemination of cancer cells. IMPLICATIONS: This study describes a transgenic zebrafish model for liver tumor metastasis and it has been successfully used for identification of some drugs to inhibit metastatic dissemination of human cancer cells.

Reversion of tumor hepatocytes to normal hepatocytes during liver tumor regression in an oncogene-expressing transgenic zebrafish model

Tumors are frequently dependent on primary oncogenes to maintain their malignant properties (known as 'oncogene addiction'). We have previously established several inducible hepatocellular carcinoma (HCC) models in zebrafish by transgenic expression of an oncogene. These tumor models are strongly oncogene addicted, as the induced and histologically proven liver tumors regress after suppression of oncogene expression by removal of a chemical inducer. However, the question of whether the liver tumor cells are eliminated or revert to normal cells remains unanswered. In the present study, we generated a novel Cre/loxP transgenic zebrafish line, Tg(fabp10: loxP-EGFP-stop-loxP-DsRed; TRE: CreERT2) (abbreviated to CreER), in order to trace tumor cell lineage during tumor regression after crossing with the xmrk (activated EGFR homolog) oncogene transgenic line, Tg(fabp10: rtTA; TRE: xmrk; krt4: EGFP) We found that, during HCC regression, restored normal liver contained both reverted tumor hepatocytes (RFP+) and newly differentiated hepatocytes (GFP+). RNA sequencing (RNA-seq) analyses of the RFP+ and GFP+ hepatocyte populations after tumor regression confirmed the conversion of tumor cells to normal hepatocytes, as most of the genes and pathways that were deregulated in the tumor stages were found to have normal regulation in the tumor-reverted hepatocytes. Thus, our lineage-tracing studies demonstrated the potential for transformed tumor cells to revert to normal cells after suppression of expression of a primary oncogene. This observation may provide a basis for the development of a therapeutic approach targeting addicted oncogenes or oncogenic pathways.

Effects of sex hormones on liver tumor progression and regression in Myc/xmrk double oncogene transgenic zebrafish

Hepatocellular carcinoma (HCC) shows clear sex disparity with men being more prone to developing HCC and having higher mortality than women. Previous studies have indicated that sex hormones play important roles in HCC initiation and development, but the effects of sex hormones on HCC in clinical trials remain inconsistent. Using zebrafish liver tumor model co-induced by oncogenes Myc and xmrk, we observed similar sex disparity between male and female zebrafish in liver tumor progression and regression; i.e. male Myc/xmrk transgenic zebrafish developed HCC significantly faster and regressed HCC significantly slower than female Myc/xmrk transgenic zebrtafish. To investigate the effects of sex hormones on liver tumor progression and regression, Myc/xmrk fish were treated with either androgen or estrogen, we observed that androgen promoted HCC progression and retarded HCC regression in females, while estrogen attenuated HCC progression and accelerated HCC regression in males. Furthermore, androgen promoted cell proliferation while estrogen inhibited it. Overall, the present study suggested that sex hormones affected liver tumor progression and regression in the Myc/xmrk transgenic zebrafish.

Identification of Novel Anti-Liver Cancer Small Molecules with Better Therapeutic Index than Sorafenib via Zebrafish Drug Screening Platform

Hepatocellular carcinoma (HCC) ranks as the fourth leading cause of cancer-related deaths worldwide. Sorafenib was the only U.S. Food and Drug Administration (FDA) approved drug for treating advanced HCC until recently, so development of new target therapy is urgently needed. In this study, we established a zebrafish drug screening platform and compared the therapeutic effects of two multiple tyrosine kinase inhibitors, 419S1 and 420S1, with Sorafenib. All three compounds exhibited anti-angiogenesis abilities in immersed fli1:EGFP transgenic embryos and the half inhibition concentration (IC₅₀) was determined. 419S1 exhibited lower hepatoxicity and embryonic toxicity than 420S1 and Sorafenib, and the half lethal concentration (LC₅₀) was determined. The therapeutic index (LC₅₀/IC₅₀) for 419S1 was much higher than for Sorafenib and 420S1. The compounds were either injected retro-orbitally or by oral gavage to adult transgenic zebrafish with HCC. The compounds not only rescued the pathological feature, but also reversed the expression levels of cell-cycle-related genes and protein levels of a proliferation marker. Using a patient-derived-xenograft assay, we found that the effectiveness of 419S1 and 420S1 in preventing liver cancer proliferation is better than that of Sorafenib. With integrated efforts and the advantage of the zebrafish platform, we can find more effective and safe drugs for HCC treatment and screen for personalized medicine.

There Is Something Fishy About Liver Cancer: Zebrafish Models of Hepatocellular Carcinoma

The incidence of hepatocellular carcinoma (HCC) and the mortality resulting from HCC are both increasing. Most patients with HCC are diagnosed at advanced stages when curative treatments are impossible. Current drug therapy extends mean overall survival by only a short period of time. Genetic mutations associated with HCC vary widely. Therefore, transgenic and mutant animal models are needed to investigate the molecular effects of specific mutations, classify them as drivers or passengers, and develop targeted treatments. Cirrhosis, however, is the premalignant state common to 90% of HCC patients. Currently, no specific therapies are available to halt or reverse the progression of cirrhosis to HCC. Understanding the genetic drivers of HCC as well as the biochemical, mechanical, hormonal, and metabolic changes associated with cirrhosis could lead to novel treatments and cancer prevention strategies. Although additional therapies recently received Food and Drug Administration approval, significant clinical breakthroughs have not emerged since the introduction of the multikinase inhibitor sorafenib, necessitating alternate research strategies. Zebrafish (Danio rerio) are effective for disease modeling because of their high degree of gene and organ architecture conservation with human beings, ease of transgenesis and mutagenesis, high fecundity, and low housing cost. Here, we review zebrafish models of HCC and identify areas on which to focus future research efforts to maximize the advantages of the zebrafish model system.

[Live-imaging Analyses Using Small Fish Models Reveal New Mechanisms That Regulate Primary Tumorigenesis]

Since the 1980s, zebrafish (Danio rerio) have been used as a valuable model system to investigate developmental processes because they: 1) grow outside their mothers; 2) are transparent during the embryonic stage; and 3) have organs similar to those in humans. Recently, zebrafish have emerged as a powerful model animal for studying not only developmental biology but also human diseases, especially cancer. Owing to the significant advantages of zebrafish, such as low-cost breeding, high efficiency of transgenesis, and ease of in vivo imaging and oncogenic/tumor cell induction, zebrafish offer a unique opportunity to unveil novel mechanisms of cancer progression, invasion, and metastasis. In addition, the small size of zebrafish larvae enables high-throughput chemical screening, and this advantage contributes to generating useful platforms for antitumor drug discovery. Owing to these various merits, which other model animals (such as fly, mouse, and rat) do not possess, zebrafish could achieve a unique status in cancer research. In this review, we discuss the availability of zebrafish for studying cancer and introduce recent cancer studies that have used zebrafish.

Polymerization-Enhanced Two-Photon Photosensitization for Precise Photodynamic Therapy

Two-photon excited photodynamic therapy (2PE-PDT) has attracted great attention in recent years due to its great potential for deep-tissue and highly spatiotemporally precise cancer therapy. Photosensitizers (PSs) with high singlet oxygen (¹O₂) generation efficiency and large two-photon absorption (2PA) cross-sections are highly desirable, but the availability of such PSs is limited by challenges in molecular design. In this work, we report that the polymerization of small-molecule PSs with aggregation-induced emission (AIE) could yield conjugated polymer PSs with good brightness, high ¹O₂ generation efficiency, and large 2PA cross-sections. A pair of conjugated polymer PSs were designed and synthesized, and the corresponding AIE PS dots were prepared by nanoprecipitation, which exhibited outstanding 2PE-PDT performance in in vitro cancer cell ablation and in vivo zebrafish liver tumor treatment. Our work highlights a strategy to design highly efficient PSs for 2PE-PDT.

Transcriptomic profiles of tumor-associated neutrophils reveal prominent roles in enhancing angiogenesis in liver tumorigenesis in zebrafish

We have previously demonstrated the pro-tumoral role of neutrophils using a kras-induced zebrafish hepatocarcinogenesis model. To further illustrate the molecular basis of the pro-tumoral role, Tumor-associated neutrophils (TANs) were isolated by fluorescence-activated cell sorting (FACS) and transcriptomic analyses were carried out by RNA-Seq. Differentially expressed gene profiles of TANs from larvae, male and female livers indicate great variations during liver tumorigenesis, but the common responsive canonical pathways included an immune pathway (Acute Phase Response Signaling), a liver metabolism-related pathway (LXR/RXR Activation) and Thrombin Signaling. Consistent with the pro-tumoral role of TANs, gene module analysis identified a consistent down-regulation of Cytotoxicity module, which may allow continued proliferation of malignant cells. Gene Set Enrichment Analysis indicated up-regulation of several genes promoting angiogenesis. Consistent with this, we found decreased density of blood vessels accompanied with decreased oncogenic liver sizes in neutrophil-depleted larvae. Collectively, our study has indicated some molecular mechanisms of the pro-tumoral roles of TANs in hepatocarcinogenesis, including weakened immune clearance against tumor cells and enhanced function in angiogenesis.

Folic acid-nanoscale gadolinium-porphyrin metal-organic frameworks: fluorescence and magnetic resonance dual-modality imaging and photodynamic therapy in hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is the most common primary liver cancer and severely threatens human health. Since the prognosis of advanced HCC remains poor, there is an urgent need to develop new therapeutic approaches. Porphyrin metal-organic frameworks are a class of porous organic-inorganic hybrid functional materials with good biocompatibility.

Methods

Gadolinium-porphyrin metal-organic frameworks were used as a skeleton for folic acid (FA) conjugation to synthesize a novel type of nanoparticle, denoted as folic acid-nanoscale gadolinium-porphyrin metal-organic frameworks (FA-NPMOFs). The FA-NPMOFs were characterized using transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric-differential thermal analysis. The biotoxicity and imaging capability of the FA-NPMOFs were determined using HepG2 cells and embryonic and larval zebrafish. The delivery and photodynamic therapeutic effect of FA-NPMOFs were explored in transgenic zebrafish with doxycycline-induced HCC.

Results

FA-NPMOFs were spherical in structure with good dispersion and water solubility. They showed low biotoxicity, emitted bright red fluorescence, and exhibited an excellent magnetic resonance imaging capability, both in vitro and in vivo. Meanwhile, the FA-NPMOFs exhibited a strong affinity for folate receptor (FR)-expressing cells and were delivered to the tumor site in a targeted manner. Moreover, HCC tumor cells were eliminated following laser irradiation.

Conclusion

FA-NPMOFs can be used for dual-modality imaging and photodynamic therapy in HCC and show promise for use as a carrier in new therapies for HCC and other FR-positive tumors.

Spontaneous Cancers, But Not Many Induced Ones in Animals, Resemble Semi-New Organisms that Possess a Unique Programmed Cell Death Mode Different from Apoptosis, Senescent Death, Necrosis and Stress-Induced Cell Death

There are four basic cell death modes in animals, i.e. physiological senescent death (SD) and apoptosis as well as pathological necrosis and stress-induced cell death (SICD). There have been numerous publications describing “apoptosis” in cancer, mostly focused on killing cancer cells using radio- or chemo-therapy, with few on exploring how cancer cells die naturally without such treatments. Spontaneous benign or malignant neoplasms are immortal and autonomous, but they still retain some allegiance to their parental tissue or organ and thus are still somewhat controlled by the patient's body. Because of these properties of immortality, semi-autonomy, and semi-allegiance to the patient's body, spontaneous tumors have no redundant cells and resemble “semi-new organisms” parasitizing the patients, becoming a unique tissue type possessing a hitherto unannotated cell death mode besides SD, apoptosis, necrosis and SICD. Particularly, apoptosis aims to expunge redundant cells, whereas this new mode does not. In contrast to spontaneous tumors, many histologically malignant tumors induced in experimental animals, before they reach an advanced stage, regress after withdrawal of the inducer. This mortal and non-autonomous nature disqualifies these animal lesions as authentic neoplasms and as semi-new organisms but makes them a good tissue type for apoptosis studies. Ruminating over cell death in spontaneous cancers and many inauthentic tumors induced in animals from these new slants makes us realize that “whether cancer cells undergo apoptosis” is not an easy question with a simple answer. Our answer is that cancer cells have an uncharacterized programmed cell death mode, which is not apoptosis.

Inducible Intestine-Specific Expression of krasV12 Triggers Intestinal Tumorigenesis In Transgenic Zebrafish

KRAS mutations are a major risk factor in colorectal cancers. In particular, a point mutation of KRAS of amino acid 12, such as KRAS^V12, renders it stable activity in oncogenesis. We found that kras^V12 promotes intestinal carcinogenesis by generating a transgenic zebrafish line with inducible kras^V12 expression in the intestine, Tg(ifabp:EGFP-kras^V12). The transgenic fish generated exhibited significant increases in the rates of intestinal epithelial outgrowth, proliferation, and cross talk in the active Ras signaling pathway involving in epithelial-mesenchymal transition (EMT). These results provide in vivo evidence of Ras pathway activation via kras^V12 overexpression. Long-term transgenic expression of kras^V12 resulted in enteritis, epithelial hyperplasia, and tubular adenoma in adult fish. This was accompanied by increased levels of the signaling proteins p-Erk and p-Akt and by downregulation of the EMT marker E-cadherin. Furthermore, we also observed a synergistic effect of kras^V12 expression and dextran sodium sulfate treatment to enhance intestinal tumor in zebrafish. Our results demonstrate that kras^V12 overexpression induces intestinal tumorigenesis in zebrafish, which mimics intestinal tumor formation in humans. Thus, our transgenic zebrafish may provide a valuable in vivo platform that can be used to investigate tumor initiation and anticancer drugs for gastrointestinal cancers.

High-dose acute exposure of paraquat induces injuries of swim bladder, gastrointestinal tract and liver via neutrophil-mediated ROS in zebrafish and their relevance for human health risk assessment

The exact toxicological mechanisms of paraquat (PQ) poisoning are not entirely clear, especially on the high-level acute exposure. To assess the health risk of PQ, especially to suicidal individuals, accidental ingestion eaters, occupational groups, and special multitude, firstly we explored the acute toxic effect and the possible mechanisms of high-level exposure of PQ using zebrafish. The mainly target organs of PQ were swim bladder which is the homolog of the mammalian lung, followed by gastrointestinal tract and liver. Morphological malformations which were further defined by histopathologic examination include smaller size, fibrosis and inflammatory cell invasion for swim bladder; irregularly arranged or dissolved epithelial folds, loss of villous architecture, and ecclasis of mucosal cells in a smaller lumen for gastrointestinal tract; as well as smaller size, degeneration, fibrous proliferation, atrophy for liver. In addition, PQ enhanced leukocyte recruitment (neutrophil migrated first, followed by macrophage) into swim bladder and induced ROS which can be scavenged by glutathione. Moreover, qRT-PCR results showed that PQ increased the expression level of genes involved in the inflammatory response, such as L-1β, IL-6, IL-8, TNF-α, TNF-β, IFN-1, TGF-β, and NF-kB. For the first time, our results demonstrated that acute exposure of PQ induced pulmonary toxicity which was followed by gastrointestinal and hepatic toxicity via neutrophil-mediated ROS in zebrafish. In summary, these findings generated here will contribute to our better understanding of characteristics of PQ acute poisoning and can provide valuable information on better PQ poisoning treatments, occupational disease prevention, and providing theoretical foundation for risk management measures.

Visualizing Photodynamic Therapy in Transgenic Zebrafish Using Organic Nanoparticles with Aggregation-Induced Emission

Photodynamic therapy (PDT) employs accumulation of photosensitizers (PSs) in malignant tumor tissue followed by the light-induced generation of cytotoxic reactive oxygen species to kill the tumor cells. The success of PDT depends on optimal PS dosage that is matched with the ideal power of light. This in turn depends on PS accumulation in target tissue and light administration time and period. As theranostic nanomedicine is driven by multifunctional therapeutics that aim to achieve targeted tissue delivery and image-guided therapy, fluorescent PS nanoparticle (NP) accumulation in target tissues can be ascertained through fluorescence imaging to optimize the light dose and administration parameters. In this regard, zebrafish larvae provide a unique transparent in vivo platform to monitor fluorescent PS bio-distribution and their therapeutic efficiency. Using fluorescent PS NPs with unique aggregation-induced emission characteristics, we demonstrate for the first time the real-time visualization of polymeric NP accumulation in tumor tissue and, more importantly, the best time to conduct PDT using transgenic zebrafish larvae with inducible liver hyperplasia as an example.