A sinomenine derivative protects life-threatening inflammatory injuries via covalently binding to a novel allosteric inhibition site of IRF3

The severe inflammation associated with infectious or inflammatory diseases significantly contributes to mortality. Interferon regulatory factor 3 (IRF3) represents a potential anti-inflammatory target, but the development of IRF3 inhibitors has not yielded satisfactory results to date. In this study, we established a phenotype-based high-throughput screening system to conduct activity-guided hierarchical screening of clinical frequently used anti-inflammatory and anti-rheumatic herbal extracts and compounds. Employing a Gaussia-luciferase reporter system driven by the IFNB1 promoter, we identified sinomenine as a potent type I interferon (IFN) inhibitor from a set of 28 anti-inflammatory herbal products. Furthermore, among 24 synthesized sinomenine derivatives modified by various electrophilic groups, Sim-9 (2.5–10 μM) dose-dependently inhibited IFN responses triggered by TLRs, RLRs, and STING activation in mouse RAW264.7 cells and in human THP-1 cells, HT-29 cells and A549 cells. We demonstrated that Sim-9, by covalently binding to Cys222, induced a conformational change in the pLxIS motif-binding surface of IRF3, thus blocking its interaction with upstream adapters, including TRIF, MAVS and STING, and subsequent homodimerization of IRF3 itself, which were all essential for activation of type I IFN responses. In in vivo experiments, we showed that injection of Sim-9 (30, 60 mg/kg, i.p.) effectively protected against devastating inflammation in cecal ligation and puncture (CLP)-induced sepsis in mice, and improved cerulein-induced pancreatitis by inhibiting IRF3. Our study discovers Sim-9 as a novel covalent allosteric inhibitor of IRF3 and reveals that the pLxIS motif binding surface represents a previously uncharacterized druggable target for IRF3 activation, providing a promising therapeutic strategy for the treatment of severe inflammatory injuries.