A new approach to discovering a broad-spectrum anti-respiratory virus drug: Tubeimoside II modulates host factor PACT to potentiate the RIG-I antiviral pathway.

PACT (PKR activating protein)/PRKRA is a quintessential double-stranded RNA (dsRNA) binding protein that has recently surfaced as a novel and compelling antiviral target, exhibiting resistance against a spectrum of respiratory viruses. Despite this, no antiviral ligand compounds targeting PACT have been identified to date. In this study, we conducted an extensive screening within natural products, leading to the development of an exceptional PACT-T78 site ligand, tubeimoside II (TBM II). TBM II effectively combats a spectrum of respiratory viruses, including the coronaviruses HCoV-OC43 and SARS-CoV-2, as well as the influenza A H1N1 virus (IAV-H1N1), by reducing viral loads and inhibiting viral replication and proliferation both in vitro and in vivo. Single-cell RNA sequencing demonstrated that TBM II significantly impacts the RIG-I signaling pathway associated with PACT. We found that when PACT was knocked down or when RIG-I, MAVS, or IFN-β were knocked out, the ability of TBM II to activate the RIG-I signaling pathway was diminished, resulting in a corresponding attenuation of its antiviral efficacy. These findings indicated that TBM II targets PACT to activate the RIG-I signaling pathway, thereby increasing the secretion of type I interferon IFN-β, ultimately promoting the innate immune response and achieving antiviral efficacy. In summary, our work identified TBM II as a new generation PACT ligand that activating the RIG-I signaling pathway, achieving broad-spectrum antiviral effects.