Speeding Up The Cancer Drug Discovery Process with Zebrafish Disease Models

Cancer is a worldwide disease and one of the leading causes of morbidity and mortality today. Traditionally, mouse models have been used for research as in vivo model organisms. However, the zebrafish (Danio rerio), also known as zebrafish, has emerged as an important new cancer model due to its small size, brood weight, and rapid maturation time, complements models that can traditionally be achieved in mice and cell culture systems. A wide range of assays can be performed in this model, from target discovery, target validation or toxicology studies to tumor generation for corresponding in vivo efficacy testing.

In cancer research, zebrafish models have advantages over traditional cell culture assays because a wider range of phenotypes can be tested. Zebrafish and mammals share common molecular pathways for tumor progression. Likewise, more than 130 different genes in zebrafish liver tumors exhibited expression similar to those characteristic of human liver cancers, correlating with histological tumor type, grade, and stage.

There are several approaches to generate human cancers in zebrafish, such as the development of mutant and transgenic cell lines and transplantation of tumor cells, each with several advantages and disadvantages. The choice of zebrafish stage at which experiments should be performed depends on the purpose of the study, as each developmental stage has some benefits. Embryos are most commonly used when the main purpose of the study is the visualization of specific tumor processes, since their bodies are transparent and allow microscopic observation. Furthermore, cancer developed more rapidly in embryos showing tumor formation 2 days after induction. Therefore, they can be used in projects that need to be fast, such as imaging cancer processes or screening activities.

Mutated cancer driver genes often dominate cancer progression and determine the future of tumorigenesis, however, the initiation process of cancer cannot be observed, and some actionable and time-saving methods are needed to manipulate the zebrafish genome and model cancer initiation and progression. There are different methods to induce cancer in zebrafish, such as chemical mutagenesis, radiation mutagenesis, insertional mutagenesis (which can be transposon-based), or viral vector mutagenesis.

An emerging approach for translational cancer research is patient-derived xenografts in zebrafish embryos (zPDX). Tumor cells from primary or metastatic human cancers collected by surgery or biopsy procedures were transplanted into zebrafish. This approach provides information about the effectiveness of the treatment because the cells share the same molecular, genetic and clinical characteristics as the donor. PDX has been extensively developed in mouse models. However, this model presents some limitations that zPDX overcomes, such as the time it takes to develop a tumor and the required sample size per patient. Models of several cancer types, such as gastric, breast or neuroendocrine cancers, have been developed using this technique.

Due to all the previously described advantages presented by the zebrafish animal model, it has recently come to the fore in the drug discovery process (i) to identify molecules that specifically ameliorate disease phenotypes and (ii) to conduct detailed characterization studies around optimizing compounds with a focus not only on efficacy ( dose-response), but also in toxicity and/or mechanism. Furthermore, with an eye toward precision cancer medicine, personalized therapy is feasible thanks to the development of zPDX.

Small molecule screens are widely used to identify new therapeutics. In this context, cell-based and biochemical drug screens have played an important role in identifying new active molecules from large compound libraries. Nonetheless, in recent years, whole-organism screens have emerged as a promising alternative to testing thousands of molecules. The zebrafish is certainly an interesting approach for this purpose, representing a reliable, low-cost and rapid option for screening large libraries and assessing their direct therapeutic relevance.

Compared with widely used traditional in vitro cell models and in vivo mouse models, zebrafish in vivo models have many advantages in cancer research. The zebrafish has recently become an interesting scientific tool due to its maintenance cost, work feasibility, and simplicity of obtaining cancer phenotypes. In terms of cancer research, zebrafish allow scientists to study processes such as tumor formation, migration, and metastasis, and to flexibly identify optimal molecules or/and known drugs (repositioning) to treat each different tumor type.