Discovery of Pyridazine-3-carboxamide derivatives as potent STING agonists that suppress pseudorabies virus replication.

BACKGROUND

The stimulator of interferon genes (STING) pathway is a critical component of the host defense against viral infections, representing an attractive target for developing broad-spectrum antiviral therapies. While cyclic dinucleotide (CDN)-based STING agonists have been extensively explored, the development of non-CDN small-molecule agonists remains limited, particularly in veterinary applications.

METHODS

To develop STING agonists with micromolar-scale agonistic activity, antiviral activity, stability and safety using a combination strategy. A series of pyridazine-3-carboxamide derivatives were used structure-based approach to modify SR717 with micromolar-scale agonistic activity. The antiviral activity, cytotoxicity, mechanism of action, in vivo safety and effcacy of the analogues were evaluated.

RESULTS

ST26 significantly improved thermally stabilized both human and murine STING (hSTING/mSTING) proteins and elicited potent immunostimulatory effects in THP1 cells, as evidenced by upregulated expression of IFNβ and the proinflammatory chemokine CXCL10, along with phosphorylation of key downstream signaling proteins. ST26 displayed a favorable cytotoxicity profile and conferred notable antiviral activity in vitro. Importantly, ST26 suppressed viral replication in PK15 cells and exhibited robust in vivo efficacy against pseudorabies virus (PRV), a major veterinary pathogen.

CONCLUSION

Mechanistic studies confirmed that ST26 specifically activates the cGAS-STING pathway, inducing potent innate immune responses without observable cytotoxicity in both cellular and animal models. ST26 as a promising host-directed antiviral agent against PRV infection, providing a novel therapeutic strategy for controlling PRV outbreaks in the veterinary medicine.