Objective  To investigate the in vitro antiviral effects of synthetic allicin against herpes simplex virus type 1 (HSV-1) and its underlying mechanism.

Methods Network pharmacology and molecular docking were employed to predict the potential targets of allicin. The cytotoxicity of synthetic allicin was assessed using the cell counting kit-8 (CCK-8) assay, and its direct virucidal activity and inhibitory effects on viral adsorption and penetration were evaluated by the plaque formation assay to determine its in vitro anti-HSV-1 activity. Real-time quantitative PCR (RT-qPCR) was performed to assess changes in the expression of key viral genes at different time points after treatment and to identify the critical molecular targets involved in the antiviral activity of synthetic allicin.

Results Molecular docking analysis suggested that thymidine kinase and DNA polymerase might be key potential targets through which allicin exerts its antiviral effects. In addition, in vitro experiments showed that the 50% cytotoxic concentration (CC₅₀) of synthetic allicin in Vero cells was 51.26 mmol/L, and its median effective concentration‌ (EC₅₀) against HSV-1 was 35.10 μmol/L, with a selection index (SI) of 1460.40. Synthetic allicin inhibited HSV-1 adsorption (EC₅₀ = 328.70 μmol/L) and penetration (EC₅₀ = 31.10 μmol/L) and directly inactivated viral particles (EC₅₀ = 195.0 μmol/L). The time-of-addition assay indicated that synthetic allicin primarily acted during the early stages of viral infection (≤ 8 h). RT-qPCR results demonstrated that synthetic allicin significantly downregulated the transcription of HSV-1 immediate-early genes (UL54/ICP27), early genes (UL23/TK and UL39/RR1), and the late gene (US6/gD) (P < 0.05).

Conclusion Synthetic allicin exhibits anti-HSV-1 activity at multiple stages of the viral life cycle, with particularly pronounced inhibitory effects at the viral penetration stage. This effect may be associated with its interference with the replication of early genes (UL54/ICP27, UL23/TK, and UL39/RR1) and the transcription of the late gene US6/gD.