Abstract
Respiratory viral infections continue to pose a significant global health burden, highlighting the urgent need for broad-spectrum antiviral therapeutics. In this study, we identified ECDD-S16, an arylnaphthalene lignan derivative, as a potent broad-spectrum antiviral. ECDD-S16 exhibited dose-dependent antiviral activity against influenza A (H1N1 and H3N2), influenza B, SARS-CoV-2, and respiratory syncytial virus (RSV) in mammalian cell cultures, with selectivity indices (SI) up to 3,194 against H1N1, representing a marked improvement over the parent arylnaphthalene lignans. Using influenza A (H1N1) as a mechanistic model, we show that ECDD-S16 acts during the early stage of the viral life cycle. Time-of-addition analysis localized its activity predominantly to the first hour of infection, while LysoTracker staining demonstrated that ECDD-S16 markedly reduced the accumulation of acidic vesicles. Co-localization analyses with the early and late endosomal markers EEA1 and LAMP1 further revealed altered association of viral antigen with endosomal compartments. Nevertheless, bypassing endosomal acidification by triggering fusion at the plasma membrane restored infection only partially, and ECDD-S16 also inhibited HA-mediated fusion when the acidic trigger was supplied externally. Collectively, these findings identify ECDD-S16 as a promising broad-spectrum antiviral candidate that interferes with an early, pH-dependent step of influenza virus entry. These results establish ECDD-S16 as a promising broad-spectrum antiviral candidate for further development against respiratory viral infections.