Antiviral efficacy and therapeutic potential of the novel nucleoside analog CLEVir-X against feline infectious peritonitis virus in vitro and in vivo.

Feline infectious peritonitis virus (FIPV) is the causative agent of feline infectious peritonitis, a progressive and often fatal disease in cats. Although antiviral therapies have recently become available, the development of effective orally administrable agents remains an important goal for feline coronavirus control. In this study, we evaluated the antiviral efficacy of CLEVir-X, a novel dialdehyde-xanthosine-based nucleoside analogue, against Type II FIPV DF-2 in both in vitro and in vivo models. CLEVir-X exhibited concentration-dependent antiviral activity against FIPV in feline-derived cell lines while maintaining low cytotoxicity. Mechanistic analyses showed that guanosine supplementation partially restored viral replication and that CLEVir-X treatment was associated with moderate induction of interferon-stimulated genes, suggesting possible involvement of host nucleotide modulation and innate antiviral responses. In experimentally infected cats, oral administration of CLEVir-X initiated at 5 dpi was associated with improved survival and stabilization of clinical parameters compared with untreated controls. Hematological and biochemical parameters also showed trends toward baseline values in treated animals. Overall, these findings demonstrate antiviral activity of CLEVir-X in feline-derived cell models and provide preliminary evidence of treatment-associated benefit in experimentally infected cats. The results support further investigation of CLEVir-X as a potential orally administrable therapeutic candidate for feline infectious peritonitis and provide a basis for future studies aimed at defining its precise antiviral mechanism and long-term therapeutic potential.