Combined in vitro and in silico analysis of acyclovir and valacyclovir against Foot-and-Mouth Disease Virus Serotype SAT2

Foot-and-Mouth Disease (FMD) is a highly contagious viral disease of livestock, caused by Foot-and-Mouth Disease Virus (FMDV), having significant economic and animal health impacts across the world. Although vaccination remains the primary control strategy, its limitations, including short-lived and serotype-specific immunity, necessitate alternative antiviral approaches. This study evaluated the antiviral efficacy of acyclovir (ACV) and its prodrug valacyclovir (VACV) against FMDV serotype SAT2 using combined in vitro and in silico methodologies. Cytotoxicity was evaluated in BHK-21 cells via the MTT assay, and non-cytotoxic concentrations (100, 50, and 25 µg/100 µL) were tested under early and late treatment conditions following infection with 108.5 TCID₅₀/mL FMDV SAT2. Antiviral activity was assessed through cytopathic effect (CPE) monitoring and residual infectivity assays. Molecular docking targeting the viral RNA-dependent RNA polymerase (3Dpol) revealed favorable binding interactions. In vitro results demonstrated that acyclovir exhibited limited early-stage inhibition of FMDV SAT2 in BHK-21 cells, whereas valacyclovir showed no antiviral activity. Despite favorable docking interactions, both compounds displayed weak in vitro antiviral efficacy.