Virtual Screening and Zebrafish Phenotype‐Based Evaluation Argues Against Repurposing 4‐Phenylbutyrate for STXBP1 ‐Related Disorders

Syntaxin‐binding protein 1 ( STXBP1 ) mutations lead to severe epilepsy, intellectual disability, developmental delay, and movement disorder. Effective treatments for these conditions do not exist. Recent studies in Munc18‐1 ( STXBP1 ) C. elegans models demonstrate that 4‐phenylbutyrate (4‐PBA) or related pharmacological chaperones stabilize Munc18‐1 protein levels and rescue locomotion deficits. These studies suggest a novel treatment strategy for these patients. Here, we used a stxbp1a zebrafish model with a profound movement disorder to screen 4‐PBA and alternative structural analogs identified using artificial intelligence (AI)‐based screening. Automated locomotion assays conducted on larval stxbp1a mutant zebrafish at 5 days post‐fertilization (dpf) confirm and extend the movement disorder endophenotype. Drug treatment (4‐PBA or 16 identified candidates) failed to rescue the stxbp1a mutant zebrafish locomotion deficit. Electrophysiology studies in a stxbp1b zebrafish model characterized by spontaneous seizure activity (i.e., epilepsy) failed to detect a reduction in ictal‐like events with 4‐PBA treatment. Taken together, our results suggest caution in repurposing 4‐PBA or related compounds for the treatment of STXBP1 disorders.