Repurposing Cilnidipine as an Entry Inhibitor Against Crimean–Congo Haemorrhagic Fever Pseudovirus Infection

Crimean-Congo haemorrhagic fever virus (CCHFV), a tick-borne pathogen of the Nairoviridae family, is classified as a high-risk biosafety level-4 (BSL-4) agent, which restricts its handling and limits mechanistic investigations. To overcome these challenges, we developed a CCHFV pseudovirus as a safe and reliable surrogate for studying viral entry and evaluating antiviral candidates. Pseudovirus-based systems have proven valuable tools for elucidating viral infection mechanisms, conducting neutralization assays, and screening small-molecule inhibitors. In the present study, a lentiviral packaging system incorporating CCHFV envelope glycoproteins (Gn and Gc) was established in HEK293T cells to generate infectious pseudovirions. Viral infectivity was quantified using a luciferase reporter assay. Cilnidipine, a clinically approved dual L-type and N-type calcium channel blocker with established antihypertensive activity, was investigated for its potential to inhibit CCHFV pseudovirus entry in HEK293T and Huh-7 cells. Treatment with cilnidipine resulted in a marked, dose-dependent reduction in luciferase signal, suggesting potent inhibition of pseudovirus entry at micromolar concentrations. Co-treatment assays further confirmed its inhibitory action at the early stages of infection. Overall, this study highlights cilnidipine as a promising repurposed antiviral candidate targeting viral entry pathways. The findings provide a foundation for future mechanistic and preclinical evaluations aimed at developing effective therapeutics against CCHFV.