## 4 Discussion  
One of the lignans isolated from _S. chinensis_, saucerneol, exhibits various pharmacological activities. In this study, we identified saucerneol as an effective antiviral compound against EV71, CVA16, and CVB3 in vitro and confirmed its antiviral efficacy against CVB3 in vivo. Currently, no antiviral agents are clinically approved for the treatment of hand, foot, and mouth diseases caused by enteric viruses. The development of new antiviral drugs against these viruses is an urgent challenge. Pleconaril is a broad-spectrum antiviral compound that inhibits enterovirus and human rhinovirus capsid proteins [28]. However, owing to inconsistent results in the treatment of enteroviral infections and limited clinical efficacy against the common cold caused by HRV, clinical development of pleconaril was halted in 2002 [29]. Rupintrivir, a 3C protease inhibitor of enteroviruses, exhibits broad-spectrum antiviral activity against members of the Picornaviridae family. Nevertheless, a V104I-resistant mutation was identified within the 3C protease of enterovirus D68 [30; 31; 32; 33]. Envivocrine, which targets the host protein phosphatidylinositol-4-kinase III \(\beta\) (PI4 KIII\(\beta\)), is the only enterovirus replication inhibitor that has undergone clinical evaluation [34]. However, it was discontinued in clinical phase II owing to the toxicity observed in clinical trials evaluating its use for the treatment of the common cold associated with HRV [35]. Ribavirin, in the form of ribavirin triphosphate, can serve as a base analog for either ATP or GTP. The antiviral potency of ribavirin has been demonstrated against various RNA viruses, both in vitro and in vivo, including EV71 [36]. However, a recent study showed that ribavirin failed to protect 1-day-old mice infected with EV71 [6]. Furthermore, ribavirin did not significantly prevent EV71 infection in Vero cells and even exhibited high levels of cytotoxicity [37]. This highlights the potential significance of developing new antiviral agents for the treatment of EV71 infections. Our research has revealed that saucerneol exhibits potent antiviral activity, inhibiting more than 80% of EV71, CVA16, and CVB3 at a concentration of 2 ug/mL. The cytotoxicity of saucerneol on Vero cells was not observed up to 10 ug/mL, indicating the absence of cytotoxicity at saucerneol concentrations below 10 ug/mL. No significant difference in body weight was observed compared to mice that did not receive saucerneol. Notably, no significant toxicity was observed at the administered dose of 2 mg/kg of saucerneol, even in the in vivo setting, during the 9 days of treatment. Double-stranded DNA generated through viral infection or cellular stress can induce the assembly of cGAS oligomers, leading to the enzymatic activation of cGAS and the production of 2\({}^{\prime}\)3\({}^{\prime}\) cyclic GMP-AMP (cGAMP). Subsequently, cGAMP binds to the stimulator of interferon genes (STING) located on the endoplasmic reticulum (ER) membrane, initiating a downstream cascade. cGAMP-bound STING recruits TANK-binding kinase 1 (TBK1), which facilitates the phosphorylation of TBK1 and STING at Ser366. This leads to the recruitment of interferon regulatory factor 3 (IRF3), which, upon phosphorylation by TBK1, undergoes dimerization and translocates to the nucleus. These events trigger the expression of type I interferons, interferon-stimulated genes (ISGs), inflammatory mediators, pro-apoptotic genes, and chemokine genes [38]. Proper activation of this IFNAR signaling cascade is critical for controlling viral replication in the context of EV71, CVB3, CVA16, and related viral infections [39]. However, it is evident that certain viruses have evolved mechanisms to suppress the activation of the IFNAR signaling pathway. Therefore, various strategies can be devised to stimulate these pathways and enhance the effectiveness of antiviral agents. mROS can disrupt mitochondrial transcription factor A (TFAM) and mtDNA stability, leading to mtDNA release and mitochondrial dysfunction [40].