Automated, quantitative screening assay for antiangiogenic compounds using transgenic zebrafish

A novel imaging-based high-throughput screening approach to anti-angiogenic drug discovery

The successful progression to the clinic of angiogenesis inhibitors for cancer treatment has spurred interest in developing new classes of anti-angiogenic compounds. The resulting surge in available candidate therapeutics highlights the need for robust, high-throughput angiogenesis screening systems that adequately capture the complexity of new vessel formation while providing quantitative evaluation of the potency of these agents. Available in vitro angiogenesis assays are either cumbersome, impeding adaptation to high-throughput screening formats, or inadequately model the complex multistep process of new vessel formation. We therefore developed an organotypic endothelial-mural cell co-culture assay system that reflects several facets of angiogenesis while remaining compatible with high-throughput/high-content image screening. Co-culture of primary human endothelial cells (EC) and vascular smooth muscle cells (vSMC) results in assembly of a network of tubular endothelial structures enveloped with vascular basement membrane proteins, thus, comprising the three main components of blood vessels. Initially, EC are dependent on vSMC-derived VEGF and sensitive to clinical anti-angiogenic therapeutics. A subsequent phenotypic VEGF-switch renders EC networks resistant to anti-VEGF therapeutics, demarcating a mature vascular phenotype. Conversely, mature EC networks remain sensitive to vascular disrupting agents. Therefore, candidate anti-angiogenic compounds can be interrogated for their relative potency on immature and mature networks and classified as either vascular normalizing or vascular disrupting agents. Here, we demonstrate that the EC-vSMC co-culture assay represents a robust high-content imaging high-throughput screening system for identification of novel anti-angiogenic agents. A pilot high-throughput screening campaign was used to define informative imaging parameters and develop a follow-up dose-response scheme for hit characterization. High-throughput screening using the EC-vSMC co-culture assay establishes a new platform to screen for novel anti-angiogenic compounds for cancer therapy.

The genetics of cardiovascular disease: new insights from emerging approaches

The prospect that sequencing the human genome would see rapid translation of a greater understanding of cardiovascular genetics into novel diagnostics and therapeutics has so far met with only limited success. However, diverse technological advances and exploitation of novel animal models of cardiovascular development and disease are providing ever more insight into cardiovascular diseases and development, and bring closer the prospect of 'post-genomic' diagnostics and therapies. Here we review some of these emerging approaches (genome wide association studies, deep sequencing, microRNA regulation, and zebrafish as a model of cardiovascular disease and development) and discuss their potential for finally fulfilling the promise of application to clinical cardiovascular medicine.

Analysis of the retina in the zebrafish model

The zebrafish is one of the leading models for the analysis of the vertebrate visual system. A wide assortment of molecular, genetic, and cell biological approaches is available to study zebrafish visual system development and function. As new techniques become available, genetic analysis and imaging continue to be the strengths of the zebrafish model. In particular, recent developments in the use of transposons and zinc finger nucleases to produce new generations of mutant strains enhance both forward and reverse genetic analysis. Similarly, the imaging of developmental and physiological processes benefits from a wide assortment of fluorescent proteins and the ways to express them in the embryo. The zebrafish is also highly attractive for high-throughput screening of small molecules, a promising strategy to search for compounds with therapeutic potential. Here we discuss experimental approaches used in the zebrafish model to study morphogenetic transformations, cell fate decisions, and the differentiation of fine morphological features that ultimately lead to the formation of the functional vertebrate visual system.

The application of phenotypic high-throughput screening techniques to cardiovascular research

In traditional pure protein high-throughput drug screens, also called in vitro screens, individual compounds from a small molecule collection are tested to determine whether they inhibit the enzymatic activity or binding properties of a purified target protein. In contrast, phenotypic high-throughput drug screens, also called chemical genetic or in vivo screens, investigate the ability of individual compounds from a collection to inhibit a biological process or disease model in live cells or intact organisms. In this review, the role of phenotypic screening techniques to identify novel therapeutic agents for the treatment of cardiovascular disease will be discussed.

Small molecule screen for compounds that affect vascular development in the zebrafish retina

Blood vessel formation in the vertebrate eye is a precisely regulated process. In the human retina, both an excess and a deficiency of blood vessels may lead to a loss of vision. To gain insight into the molecular basis of vessel formation in the vertebrate retina and to develop pharmacological means of manipulating this process in a living organism, we further characterized the embryonic zebrafish eye vasculature, and performed a small molecule screen for compounds that affect blood vessel morphogenesis. The screening of approximately 2000 compounds revealed four small molecules that at specific concentrations affect retinal vessel morphology but do not produce obvious changes in trunk vessels, or in the neuronal architecture of the retina. Of these, two induce a pronounced widening of vessel diameter without a substantial loss of vessel number, one compound produces a loss of retinal blood vessels accompanied by a mild increase of their diameter, and finally one other generates a severe loss of retinal vessels. This work demonstrates the utility of zebrafish as a screening tool for small molecules that affect eye vasculature and presents several compounds of potential therapeutic importance.

High-throughput screen for novel antimicrobials using a whole animal infection model

The nematode Caenorhabditis elegans is a unique whole animal model system for identifying small molecules with in vivo anti-infective properties. C. elegans can be infected with a broad range of human pathogens, including Enterococcus faecalis, an important human nosocomial pathogen. Here, we describe an automated, high-throughput screen of 37,200 compounds and natural product extracts for those that enhance survival of C. elegans infected with E. faecalis. Using a robot to dispense live, infected animals into 384-well plates and automated microscopy and image analysis, we identified 28 compounds and extracts not previously reported to have antimicrobial properties, including six structural classes that cure infected C. elegans animals but do not affect the growth of the pathogen in vitro, thus acting by a mechanism of action distinct from antibiotics currently in clinical use.

Combination of reverse and chemical genetic screens reveals angiogenesis inhibitors and targets

We combined reverse and chemical genetics to identify targets and compounds modulating blood vessel development. Through transcript profiling in mice, we identified 150 potentially druggable microvessel-enriched gene products. Orthologs of 50 of these were knocked down in a reverse genetic screen in zebrafish, demonstrating that 16 were necessary for developmental angiogenesis. In parallel, 1280 pharmacologically active compounds were screened in a human cell-based assay, identifying 28 compounds selectively inhibiting endothelial sprouting. Several links were revealed between the results of the reverse and chemical genetic screens, including the serine/threonine (S/T) phosphatases ppp1ca, ppp1cc, and ppp4c and an inhibitor of this gene family; Endothall. Our results suggest that the combination of reverse and chemical genetic screens, in vertebrates, is an efficient strategy for the identification of drug targets and compounds that modulate complex biological systems, such as angiogenesis.

Targeting angiogenesis via a c-Myc/hypoxia-inducible factor-1alpha-dependent pathway in multiple myeloma

Bone marrow angiogenesis is associated with multiple myeloma (MM) progression. Here, we report high constitutive hypoxia-inducible factor-1alpha (Hif-1alpha) expression in MM cells, which is associated with oncogenic c-Myc. A drug screen for anti-MM agents that decrease Hif-1alpha and c-Myc levels identified a variety of compounds, including bortezomib, lenalidomide, enzastaurin, and adaphostin. Functionally, based on transient knockdowns and overexpression, our data delineate a c-Myc/Hif-1alpha-dependent pathway mediating vascular endothelial growth factor production and secretion. The antiangiogenic activity of our tool compound, adaphostin, was subsequently shown in a zebrafish model and translated into a preclinical in vitro and in vivo model of MM in the bone marrow milieu. Our data, therefore, identify Hif-1alpha as a novel molecular target in MM and add another facet to anti-MM drug activity.

An in vivo chemical library screen in Xenopus tadpoles reveals novel pathways involved in angiogenesis and lymphangiogenesis

Angiogenesis and lymphangiogenesis are essential for organogenesis but also play important roles in tissue regeneration, chronic inflammation, and tumor progression. Here we applied in vivo forward chemical genetics to identify novel compounds and biologic mechanisms involved in (lymph)angiogenesis in Xenopus tadpoles. A novel 2-step screening strategy involving a simple phenotypic read-out (edema formation or larval lethality) followed by semiautomated in situ hybridization was devised and used to screen an annotated chemical library of 1280 bioactive compounds. We identified 32 active compounds interfering with blood vascular and/or lymphatic development in Xenopus. Selected compounds were also tested for activities in a variety of endothelial in vitro assays. Finally, in a proof-of-principle study, the adenosine A1 receptor antagonist 7-chloro-4-hydroxy-2-phenyl-1,8-naphthyridine, an inhibitor of blood vascular and lymphatic development in Xenopus, was shown to act also as a potent antagonist of VEGFA-induced adult neovascularization in mice. Taken together, the present chemical library screening strategy in Xenopus tadpoles represents a rapid and highly efficient approach to identify novel pathways involved in (lymph)angiogenesis. In addition, the recovered compounds represent a rich resource for in-depth analysis, and their drug-like features will facilitate further evaluation in preclinical models of inflammation and cancer metastasis.

Automated image-based phenotypic analysis in zebrafish embryos

Presently, the zebrafish is the only vertebrate model compatible with contemporary paradigms of drug discovery. Zebrafish embryos are amenable to automation necessary for high-throughput chemical screens, and optical transparency makes them potentially suited for image-based screening. However, the lack of tools for automated analysis of complex images presents an obstacle to using the zebrafish as a high-throughput screening model. We have developed an automated system for imaging and analyzing zebrafish embryos in multi-well plates regardless of embryo orientation and without user intervention. Images of fluorescent embryos were acquired on a high-content reader and analyzed using an artificial intelligence-based image analysis method termed Cognition Network Technology (CNT). CNT reliably detected transgenic fluorescent embryos (Tg(fli1:EGFP)(y1)) arrayed in 96-well plates and quantified intersegmental blood vessel development in embryos treated with small molecule inhibitors of anigiogenesis. The results demonstrate it is feasible to adapt image-based high-content screening methodology to measure complex whole organism phenotypes.

Zebrafish embryos as models for embryotoxic and teratological effects of chemicals

The experimental virtues of the zebrafish embryo such as small size, development outside of the mother, cheap maintenance of the adult made the zebrafish an excellent model for phenotypic genetic and more recently also chemical screens. The availability of a genome sequence and several thousand mutants and transgenic lines together with gene arrays and a broad spectrum of techniques to manipulate gene functions add further to the experimental strength of this model. Pioneering studies suggest that chemicals can have in many cases very similar toxicological and teratological effects in zebrafish embryos and humans. In certain areas such as cardiotoxicity, the zebrafish appears to outplay the traditional rodent models of toxicity testing. Several pilot projects used zebrafish embryos to identify new chemical entities with specific biological functions. In combination with the establishment of transgenic sensor lines and the further development of existing and new automated imaging systems, the zebrafish embryos could therefore be used as cost-effective and ethically acceptable animal models for drug screening as well as toxicity testing.

Automated analysis of behavior in zebrafish larvae

Zebrafish larvae have become a popular model system to examine genetic and environmental factors that affect behavior. However, studying complex behavior in large numbers of fish larvae can be challenging. The present study describes a novel high-resolution imaging system that is unique in its ability to automatically analyze the location and orientation of zebrafish larvae in multiwell plates. The system revealed behaviors in zebrafish larvae that would have been missed by more manual approaches, including a preference to face a threatening stimulus from a distance and a clockwise orientation in a two-fish assay. The clockwise orientation of the larvae correlates with a clockwise orientation of molecular structures during early development. Larvae with reversed embryonic asymmetries display a counter-clockwise orientation in the two-fish assay, suggesting that embryonic asymmetry and chiral behavior are regulated by the same developmental mechanisms. The developed imaging techniques may be used in large-scale screens to identify genes, pharmaceuticals, and environmental toxicants that influence complex behaviors.

Antiangiogenic activity of Tripterygium wilfordii and its terpenoids

ETHNOPHARMACOLOGICAL RELEVANCE

Tripterygium wilfordii Hook. f. (Celastraceae) has been traditionally used as folk medicine for centuries in China for the treatment of immune-inflammatory diseases.

AIM OF THE STUDY

This study aimed to assess the antiangiogenic activities which support the therapeutic use of Tripterygium wilfordii and its terpenoids for angiogenesis disease such as cancer.

MATERIALS AND METHODS

The ethanol extract of Tripterygium wilfordii and subsequent fractions were evaluated on an in vivo antiangiogenic zebrafish embryo model.

RESULTS

Three antiangiogenic terpenoids were isolated by bioassay-guided purification, namely, celastrol (4), cangoronine (5) and triptolide (7). Among them, triptolide manifested the most potent antiangiogenic activity against vessel formation by nearly 50% at 1.2 microM. Semi-quantitative RT-PCR analysis revealed that triptolide dose- and time-dependently reduced the mRNA expression of angiopoietin (angpt)2 and tie2 in zebrafish, indicating the involvement of angpt2/tie2 signaling pathway in the antiangiogenic action of triptolide.

CONCLUSIONS

The discovery of an alternative pathway further confirms the value of ethnopharmacological investigations into traditional botanicals for leads for potential drug development.

Cardio-respiratory control during early development in the model animal zebrafish

Independent of species, the cardiovascular system is the first functioning component of developing vertebrate embryos. One of the main hypotheses is the assumption that larval and juvenile stages of fish and amphibians are not just smaller versions of an adult phenotype. In this review, the cardiovascular and respiratory responses to environmental, genetic and epigenetic perturbations are discussed in detail to understand the relationships between cardiac and respiratory performance, haematopoiesis for embryonic or larval stages with special focus on the popular model animal, the zebrafish. Zebrafish are tiny animals which have many advantages as a model organism in analysis of the cardio-respiratory system. It obtains sufficient amounts of oxygen via bulk diffusion, in contrast to convection-dependent mammals. It is possible to study genetic mutants even with extreme defective phenotypes of the cardio-respiratory system in order to understand its developmental and physiological mechanisms. It has become apparent that the cardio-respiratory system and its control starts functioning very early during development, long before oxygen uptake becomes diffusion limited in zebrafish. Finally, recent improvements in imaging techniques for the use of fish models relevant for developmental physiology and biomedical research are discussed.

Cancer and virus leads by HTS, chemical design and SEA data mining

A variety of medicinal chemistry approaches can be used for the identification of hits, generation of leads and to accelerate the development of drug candidates. The Emory Chemical and Biology Discovery Center (ECBDC) has been an active participant in the NIH's high-throughput screening (HTS) endeavor to identify potent small molecule probes for poorly studied proteins. Several of Emory's projects relate to cancer or virus infection. We have chosen three successful examples including discovery of potent measles virus RNA-dependent RNA polymerase inhibitors, development of Heat Shock Protein 90 (Hsp90) blockers and identification of angiogenesis inhibitors using transgenic Zebrafish as a HTS model. In parallel with HTS, a unique component of the Emory virtual screening (VS) effort, namely, substructure enrichment analysis (SEA) program has been utilized in several cases.

Modeling cardiovascular disease in the zebrafish

The zebrafish possesses a host of advantages that have established it as an excellent model of vertebrate development. These include ease of genetic manipulation and transgenesis, optical clarity, and small size and cost. Biomedical researchers are increasingly exploiting these advantages to model human disease mechanisms. Here we review the use of the zebrafish for cardiovascular research. We summarize previous studies with the use of this organism to model such processes as thrombosis, collateral vessel development, inflammation, cardiomyopathy, and cardiac regeneration, evaluate its promise for novel drug discovery, and consider where the zebrafish fits into the framework of existing cardiovascular models.

Accelerating the development of novel molecular imaging probes: a role for high-throughput screening

Molecular imaging is a rapidly emerging research tool and clinical discipline aimed at noninvasive, quantitative visualization of in vivo molecular processes occurring at cellular and subcellular levels. At present, advancement of the molecular imaging field is driven by the development of improved imaging hardware for use in preclinical and clinical settings, the identification and validation of new, biologically relevant imaging targets, and the development of improved imaging probes derived from novel chemistries. Of these 3 essential facets, which comprise a majority of current molecular imaging research, hardware development and novel target discovery significantly outpace the development and clinical advancement of new molecular imaging probes, particularly with respect to cancer imaging.