Long-term non-invasive drug treatments for adult zebrafish

SUMMARY Zebrafish embryos are widely used for drug-discovery however administering drugs to adult zebrafish is limited by current protocols that can cause stress. Here, we develop a drug formulation and administration method for adult zebrafish by producing food-based drug pellets which are consumed voluntarily. We apply this to zebrafish with BRAF-mutant melanoma, a model that has significantly advanced our understanding of melanoma progression, but not of drug resistance due to the limitations of current treatment methods. Short-term, precise, and daily dosing with drug-pellets made with the BRAF V600E inhibitor, vemurafenib, led to tumour regression. On-target drug efficacy was determined by phospho-ERK staining. Continued drug treatment led to the emergence, for the first time in zebrafish, of acquired drug resistance and melanoma relapse, modelling the responses seen in melanoma patients. This method presents a controlled, non-invasive approach that permits long-term drug studies, and can be widely applied to any adult zebrafish model. SUMMARY STATEMENT This drug-pellet approach is a precise dosing method to administer short or long-term drug treatments to adult zebrafish, that is stress-free for the fish and requires minimal animal handling. We use this method to develop new drug-resistant models of melanoma in zebrafish, opening new doors for modelling and screening drug treatments in adult zebrafish.