Disruption of serotonin homeostasis in intestinal organoids provides insights into drug-induced gastrointestinal toxicity

Drug-induced gastrointestinal toxicity is a frequent clinical adverse event that needs to be carefully monitored and managed to ensure patient compliance. While preclinical assessment of drug-induced gastrointestinal toxicity mostly relies on animal experimentation, intestinal organoids have gained increasing attention to identify gastrointestinal toxicants in vitro. Nonetheless, current in vitro protocols primarily assess structural alterations induced by drugs, whereas gastrointestinal adverse events can often stem from functional disturbances. Disruption of serotonin signaling in the gastrointestinal tract is associated with impaired motility, as well as nausea and vomiting. We aimed to investigate alterations of serotonin homeostasis in organoids derived from the canine small intestine as a driver of drug-induced gastrointestinal toxicity. Treatment of the organoids with a compound (NVS-1) inducing acute gastrointestinal toxicity in dogs as well as with three tyrosine kinase inhibitors with known preclinical and clinical gastrointestinal adverse effects (afatinib, crizotinib and vandetanib) led to increased supernatant serotonin levels. Mechanistic assays showed that, while NVS-1 and afatinib stimulate serotonin release, crizotinib and vandetanib inhibit serotonin re-uptake via direct inhibition of the serotonin re-uptake transporter. Using a data mining approach, we further suggest that inhibition of serotonin re-uptake could contribute to gastrointestinal toxicity observed with multiple marketed drugs. In conclusion, we present the implementation of a novel in vitro gastrointestinal toxicity endpoint that could complement current methods and serve as a mechanistic and predictive/screening tool for drug-induced gastrointestinal toxicity.