Givinostat rescues folding of cystathionine beta-synthase and ameliorates murine homocystinuria

Homocystinuria (HCU) is an inherited metabolic disorder caused by missense mutations in the cystathionine beta-synthase (CBS) gene, leading to protein misfolding and degradation. Pharmacological chaperones, which stabilize native protein conformations, offer a promising therapeutic strategy, but tools for their identification are lacking. We developed a cell-based CBS folding reporter assay using split-fluorescent protein complementation, focusing on the common HCU-causing CBS I278T variant. In addition to proteasome inhibitors investigated as potential treatment for HCU, screening of chemical libraries identified several histone deacetylase inhibitors, with givinostat showing the highest recovery of CBS I278T folding and activity. Givinostat binds CBS, but also acts indirectly by modulating the proteostasis network and protein degradation pathways. Short-term treatment of HCU mice expressing CBS I278T partially restored hepatic CBS expression and reduced serum homocysteine levels. This study presents a novel tool, which lead to identification of new class of potential pharmacological chaperones for HCU, paving the way for personalized assays targeting different pathogenic variants and adaptations for other protein misfolding disorders.