Repurposing caspofungin as a small-molecule inhibitor of Clostridium perfringens α-toxin for treatment of gas gangrene

BACKGROUND: Among pharmaceuticals currently in clinical use, few drugs directly target bacterial toxins. Clostridium perfringens α-toxin, a phospholipase C (PLC), is a major virulence factor responsible for gas gangrene caused by C. perfringens type A. There is a clinical need for small-molecule compounds that inhibit such bacterial toxins. METHODS: A library of 764 FDA-approved drugs was screened to identify compounds that inhibit the PLC activity of C. perfringens α-toxin. Identified hits were further evaluated for their ability to inhibit α-toxin-induced cytotoxicity in human umbilical vein endothelial cells (HUVECs). Additional in vitro assays were conducted to assess changes in neutrophil activation and cytokine production. In vivo efficacy was evaluated in female C57BL/6J mice (n = 21 or 18 per group) challenged with purified α-toxin or infected with C. perfringens type A. RESULTS: The initial screen identifies 21 compounds that inhibit the PLC activity. Among them, micafungin, an antifungal agent, is the only compound that suppresses α-toxin-induced cell death in HUVECs. Micafungin also reduces α-toxin-induced CD11b expression in neutrophils and cytokine release in HUVECs. Caspofungin, another antifungal with similar properties, also inhibits α-toxin-induced cell death and cytokine production. In mouse models, caspofungin, but not micafungin, significantly reduces lethality caused by α-toxin. Caspofungin also improves survival and mitigates muscle damage in mice infected with C. perfringens type A. CONCLUSIONS: Caspofungin demonstrates promising therapeutic potential as a life-saving treatment for gas gangrene caused by C. perfringens type A, likely through its inhibitory action on α-toxin activity. These findings support the development of new classes of small-molecule therapeutics that directly target bacterial toxins.