Highlight article: Use of zebrafish to model chemotherapy and targeted therapy gastrointestinal toxicity

Gastrointestinal toxicity arising from cancer treatment remains a key reason for treatment discontinuation, significantly compromising remission. There are drawbacks to the currently used in vitro and rodent models, and a lack of translatability from in vitro to in vivo work. A screening-amenable alternative in vivo model such as zebrafish would, therefore, find immediate application. This study utilized a transgenic reporter line of zebrafish, Tg(cyp2k18:egfp), that shows eGFP induction as an indicator of drug-induced pathology. Here, we investigate its utility as an alternative vertebrate model to bridge the gap between simple in vitro cellular studies and complex in vivo models for understanding gastrointestinal toxicity induced by chemotherapy and targeted therapy. Transgenic zebrafish larvae were administered afatinib or SN38, and assessed for viability and eGFP induction. Adult zebrafish were administered afatinib via oral gavage, and SN38 via intraperitoneal injection. Fish were killed after 24 h, and had gastrointestinal tracts removed and assessed for histopathological damage, goblet cell changes, and apoptosis. While treatment with either compound did not induce eGFP in the gastrointestinal tract of larvae, SN38 caused histopathological damage to adult intestines. The lack of eGFP induction may be due to poor solubility of the drugs. Chemotherapy agents with high solubility and permeability would be more amenable to these models. Further progress in this area would be greatly facilitated by the generation of robust and reproducible genetic models of zebrafish intestinal toxicity that mimic the known pathobiological pathways in rodents and humans, and can be readily induced in a short time-frame. Impact statement: Gastrointestinal toxicity secondary to cancer treatment remains a major reason for the termination of cancer drug candidates in the development pipeline as well as withdrawal or restrictions of marketed drugs. Current cancer treatment-induced gastrointestinal toxicity models available are limited to in vitro and rodent models that lack translatability and are prohibitively expensive and time consuming. An alternative model to study cancer treatment-induced gastrointestinal toxicity that allows rapid, miniaturized, multi-organ toxicity, screening-amenable testing is therefore warranted. The newly developed Tg(cyp2k18:egfp) zebrafish reporter line was found to induce eGFP in the gastrointestinal tract if toxicity was induced in this area. This paper explored utilizing this reporter line for cancer treatment-induced gastrointestinal toxicity, but found that it was not a useful reporter line in this setting. Further progress in this area would be greatly facilitated by the generation of robust and reproducible genetic models of zebrafish intestinal toxicity that mimic the known pathobiological pathways.