Drug Repurposing: In Vitro Evaluation of Simeprevir as a Novel Antiviral Drug Against Severe Fever With Thrombocytopenia Syndrome Virus

Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV), a tick‐borne virus with high mortality, currently lacks approved antiviral therapies. In this study, we evaluated the in vitro activity of 19 FDA‐approved drugs against a clinical isolate of SFTSV using cell‐based assays, and immunofluorescence analysis. Simeprevir, Novobiocin, and Levofloxacin hydrochloride demonstrated significant antiviral activity (EC50: 0.009774, 25.12, and 46.30 μM, respectively) with minimal cytotoxicity. Immunofluorescence analysis revealed a dose‐dependent reduction in SFTSV nucleoprotein expression, correlating with decreased viral replication. The remaining 16 drugs exhibited low antiviral efficacy or high cytotoxicity. Although these three small‐molecule drugs show promise for SFTSV treatment, further in vivo studies are necessary to confirm their safety and optimize their structures. Our findings highlight the potential of drug repurposing as a strategy for developing effective therapies against emerging viral infections.