Spiperone, identified through compound screening, activates calcium-dependent chloride secretion in the airway

Cystic fibrosis (CF) is caused by mutations in the gene producing the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR functions as a Cl^- channel. Its dysfunction limits Cl^- secretion and enhances Na⁺ absorption, leading to viscous mucus in the airway. Ca²⁺-activated Cl^- channels (CaCCs) are coexpressed with CFTR in the airway surface epithelia. Increases in cytosolic Ca²⁺ activate the epithelial CaCCs, which provides an alternative Cl^- secretory pathway in CF. We developed a screening assay and screened a library for compounds that could enhance cytoplasmic Ca²⁺, activate the CaCC, and increase Cl^- secretion. We found that spiperone, a known antipsychotic drug, is a potent intracellular Ca²⁺ enhancer and demonstrated that it stimulates intracellular Ca²⁺, not by acting in its well-known role as an antagonist of serotonin 5-HT₂ or dopamine D₂ receptors, but through a protein tyrosine kinase-coupled phospholipase C-dependent pathway. Spiperone activates CaCCs, which stimulates Cl^- secretion in polarized human non-CF and CF airway epithelial cell monolayers in vitro and in CFTR-knockout mice in vivo. In conclusion, we have identified spiperone as a new therapeutic platform for correction of defective Cl^- secretion in CF via a pathway independent of CFTR.