Introduction: Canine distemper virus (CDV) and canine coronavirus (CCoV) are two highly contagious viruses that primarily affect dogs, causing disease in the gastrointestinal and respiratory systems, and sometimes the neurological system. Despite advances in vaccines and antiviral therapies, many viruses remain difficult to treat, underscoring the need for innovative control strategies. This study explores the antiviral activity of two antimicrobial peptides, pantinin-1 and pantinin-2, derived from the venom of the scorpion Pandinus imperator, against CDV and CCoV.

Methods: The peptides were prepared via solid-phase peptide chemical synthesis and assessed for their cytotoxicity in canine fibrosarcoma cells (A-72), and Vero/hSLAM cells, using MTT assay. Non-cytotoxic concentrations of both peptides were tested for antiviral activity primarily through plaque reduction assays and tissue culture infective dose (TCID₅₀), alongside quantification of viral N gene expression levels. Furthermore, peptide conformations were examined in aqueous buffer and in a membrane/mimetic environment (trifluoroethanol (TFE)/H₂O) using circular dichroism (CD) and NMR analyses.

Results: The results show that both pantinins exert antiviral effects within a concentration range from 6 µM to 50 µM against both viruses. Peptides affect viral particles by exerting a virucidal effect and preventing the fusion and entry of the virus into host cells. These results were confirmed by means of qPCR, showing complete suppression of N viral gene expression at the highest concentration of both pantinins (50 μM). In TFE/H₂O, both peptides shift to α-helical structures, which are often associated with membrane interaction and significantly influence antiviral activity.

Conclusion: These findings show that pantinin-1 and pantinin-2 have promising antiviral properties, supporting their potential as therapeutic agents against CDV and CCoV infections.

Further studies are needed to explore their mechanism, optimise antiviral potency, and assess safety in animal models.