Cilnidipine exerts antiviral effects in vitro and in vivo by inhibiting the internalization and fusion of influenza A virus

Background Influenza A virus (IAV) is a major cause of seasonal and global pandemics, posing serious health risks. Repositioning approved drugs offers an efficient antiviral strategy, particularly as calcium (Ca 2 ⁺) is crucial for IAV infection, making Ca 2 ⁺ channel blockers (CCBs) promising candidates for antiviral agents. Methods The in vitro antiviral activity of cilnidipine was evaluated using MTT assays, qRT-PCR, plaque assays, and western blotting. Mechanistic studies involved time-of-addition, viral internalization, pseudovirus neutralization, and HA (hemagglutinin) syncytium assays. For in vivo analysis, BALB/c mice were intranasally infected to evaluate the effects of cilnidipine on viral titer, lung index, pulmonary inflammatory mediators, and survival rate. Results In vitro, cilnidipine exhibits antiviral activity against IAV during the early stages of infection. It disrupts clathrin- and caveolin-mediated endocytosis to inhibit the internalization of IAV and interacts with the viral HA2 subunit to impede virus membrane fusion. Additionally, cilnidipine suppresses the PI3K-AKT and p38 MAPK pathways activated by IAV infections. In vivo, cilnidipine reduces virus titers and lung index, ameliorates lung pathology, and inhibits pulmonary inflammatory mediator expression, improving survival rates. Conclusions These findings highlight the promising anti-IAV properties of cilnidipine both in vitro and in vivo, suggesting its potential as a clinical agent for emergencies against influenza outbreaks.