Andrographolide and Deoxyandrographolide Inhibit Protease and IFN-Antagonist Activities of Foot-and-Mouth Disease Virus 3C.

Foot-and mouth-disease (FMD) caused by the FMD virus (FMDV) is highly contagious and negatively affects livestock worldwide. The control of the disease requires a combination of measures, including vaccination; however, there is no specific treatment available. Several studies have shown that plant-derived products with antiviral properties were effective on viral diseases. Herein, antiviral activities of andrographolide (AGL), deoxyandrographolide (DAG), and neoandrographolide (NEO) against FMDV serotype A were investigated using an in vitro cell-based assay. The results showed that AGL and DAG inhibited FMDV in BHK-21 cells. The inhibitory effects of AGL and DAG were evaluated by RT-qPCR and exhibited EC50 values of 52.18 ± 0.01 µM (SI = 2.23) and 36.47 ± 0.07 µM (SI = 9.22), respectively. The intracellular protease assay revealed that AGL and DAG inhibited FMDV 3C with IC50 of 67.43 ± 0.81 and 25.58 ± 1.41 µM, respectively. Additionally, AGL and DAG significantly interfered with interferon (IFN) antagonist activity of the 3C by derepressing interferon-stimulating gene (ISGs) expression. The molecular docking confirmed that the andrographolides preferentially interacted with the 3C active site. However, NEO had no antiviral effect in any of the assays. Conclusively, AGL and DAG inhibited FMDV serotype A by interacting with the 3C and hindered its protease and IFN antagonist activities.