The zebrafish, Danio rerio, a small, tropical freshwater species native to Pakistan and India, has become a National Institutes of Health-sanctioned model organism and, due to its many advantages as an experimental vertebrate, it has garnered intense interest from the world's scientific community. Some have labeled the zebrafish, the "vertebrate Drosophila," due to its genetic tractability, small size, low cost, and rapid development. The transparency of the embryo, external development, and the many hundreds of mutant and transgenic lines available add to the allure. Now it appears, the zebrafish can be used for high-throughput screening (HTS) of drug libraries in the discovery process of promising new therapeutics. In this review, various types of screening methods are briefly outlined, as are a variety of screens for different disease models, to highlight the range of zebrafish HTS possibilities. High-content screening (HCS) has been available for cell-based screens for some time and, very recently, HCS is being adapted for the zebrafish. This will allow analysis, at high resolution, of drug effects on whole vertebrates; thus, whole body effects as well as those on specific organs and tissues may be determined.
High-throughput screens (HTS) of compound toxicity against cancer cells can identify thousands of potential new drug-leads. But only limited numbers of these compounds can progress to expensive and labor intensive efficacy studies in mice, creating a ‘bottle-neck’ in the drug development pipeline. Approaches that triage drug-leads for further study are greatly needed. Here, we provide an intermediary platform between HTS and mice by adapting mouse models of pediatric brain tumors to grow as orthotopic xenografts in the brains of zebrafish. Freshly isolated mouse ependymoma, glioma and choroid plexus carcinoma cells expressing red fluorescence protein (RFP) were conditioned to grow at 34°C. Conditioned tumor cells were then transplanted orthotopically into the brains of zebrafish acclimatized to ambient temperatures of 34°C. Live in vivo fluorescence imaging identified robust, quantifiable and reproducible brain tumor growth as well as spinal metastasis in zebrafish. All tumor xenografts in zebrafish retained the histological characteristics of the corresponding parent mouse tumor and efficiently recruited fish endothelial cells to form a tumor vasculature. Finally, by treating zebrafish harboring ERBB2-driven gliomas with an appropriate cytotoxic chemotherapy (5-fluorouracil) or tyrosine kinase inhibitor (Erlotinib), we show that these models can effectively assess drug efficacy. Our data demonstrate, for the first time, that mouse brain tumors can grow orthtopically in fish and serve as a platform to study drug efficacy. Since large cohorts of brain tumor bearing zebrafish can be generated rapidly and inexpensively, these models may serve as a powerful tool to triage drug-leads from HTS for formal efficacy testing in mice.
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