Small-molecules that control melanocyte development and movement: a zebrafish approach to identify new research tools and drug-lead discovery

Melanoma is the most lethal form of skin cancer, aggressively killing through rapid metastatic spread. Chemotherapy is ineffective when applied to metastatic melanoma, and early detection is critical to have any hope of cure by surgical excision. Thus, a detailed knowledge of cellular, molecular and genetic knowledge of melanoma progression is highly relevant to diagnosis and developing new therapies. Our strategy to further advance understanding of melanoma is to study melanocytes in situ, within the living zebrafish. Well suited to high-throughput genetic and chemical screening, zebrafish are becoming widely used in the drug-discovery process for target validation, disease modelling, toxicology and target and lead compound discovery. With a specific interest in identifying targetable melanocyte behavior, we have undertaken an in vivo phenotype-based whole organism screen for small molecules that specifically disrupt zebrafish melanocyte behaviour, including growth, development, differentiation, migration and death. Using a focused bioactive library of 1680 Maybridge small molecule screening compounds, over four thousand embryos were collected, and two 3.5-hour post-fertilization (hpf) embryos were arrayed in 96-well plates, each well consisting of 10uM of a specific small molecule. Of the 1680 compounds, 190 compounds affected normal melanocyte development: 84 resulted in pale pigmentation, 93 resulted in complete loss of pigmentation, and 13 affected melanocyte development and patterning.We will present our results discussing how these molecules may act as molecular probes to investigate the individual pathways that control melanin and melanocytes in development, as well as when the system is perturbed, and propose that pharmacological modification of a specific phenotype in an organism is a physiologically relevant approach to understanding the fundamental processes of melanoma development.