Zebrafish as a Model Organism for the Development of Drugs for Skin Cancer

Abstract

Skin cancer, which includes melanoma and squamous cell carcinoma, represents the most common type of cutaneous malignancy worldwide, and its incidence is expected to rise in the near future. This condition derives from acquired genetic dysregulation of signaling pathways involved in the proliferation and apoptosis of skin cells. The development of animal models has allowed a better understanding of these pathomechanisms, with the possibility of carrying out toxicological screening and drug development. In particular, the zebrafish (Danio rerio) has been established as one of the most important model organisms for cancer research. This model is particularly suitable for live cell imaging and high-throughput drug screening in a large-scale fashion. Thanks to the recent advances in genome editing, such as the clustered regularly-interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) methodologies, the mechanisms associated with cancer development and progression, as well as drug resistance can be investigated and comprehended. With these unique tools, the zebrafish represents a powerful platform for skin cancer research in the development of target therapies. Here, we will review the advantages of using the zebrafish model for drug discovery and toxicological and phenotypical screening. We will focus in detail on the most recent progress in the field of zebrafish model generation for the study of melanoma and squamous cell carcinoma (SCC), including cancer cell injection and transgenic animal development. Moreover, we will report the latest compounds and small molecules under investigation in melanoma zebrafish models.

Keywords: drug development; inhibitor screening; melanoma; skin cancer; squamous cell carcinoma; transgenic zebrafish.

Figure 1

Zebrafish as a relevant model for human disease and cancer therapy. The zebrafish genome shows up to 80% similarity with human disease-associated genes. Moreover, thanks to a well-conserved physiology, the pharmacological behavior and metabolism of several drugs have been screened in zebrafish with effects similar to humans.

Figure 2

Zebrafish model for high-throughput drug screening. Zebrafish is a valuable tool for high-throughput screening assays. In terms of toxicity, zebrafish have been used to evaluate a specific organ or behavior with respect to toxicity. In drug screening, zebrafish is also established as precious platform to multiple systemic phenotype studies simultaneously with metabolic profiles and toxicity reporter lines.

Figure 3

The tumor suppressor hexamethylene bisacetamide inducible 1 (HEXIM1) gene inhibits melanoma in the zebrafish model. HEXIM1 plays an important role as a melanoma tumor suppressor in response to nucleotide stress. HEXIM1 forms a complex with positive transcription elongation factor (P-TEFb) in order to inhibit the kinase to initiate transcription elongation at tumorigenic genes. Alteration of gene expression, in parallel with anti-tumorigenic RNAs binding to HEXIM1, favors the “anti-cancer” gene expression. Pol II: DNA polymerase II; CDK9: cyclin-dependent kinase; CCNT1: Cyclin-T.

Figure 4

Drug development and inhibitor screening using selected MEKi and PI3K/mTOR inhibitors. Zebrafish plays an important role for the screening of compounds targeting MEK/ERK and PI3K/mTOR pathways, both alone and in combination. (A) Example of screening of the FDA library molecules using zebrafish embryos; (B) steps showing hit selection after the screening procedure with different drugs and drug dose response using the melanin assay. At the end of this process, 11 hits were detected to be further evaluated in cell culture. MEKi: mitogen-activated protein kinases inhibitor; PI3K: phosphoinositide 3-kinase; mTOR: mechanistic target of rapamycin.