Identification and evaluation of a novel tribenzamide derivative as an inhibitor targeting the entry of the respiratory syncytial virus

Human respiratory syncytial virus (RSV) is the leading cause of severe lower respiratory tract infections in infants, the elderly, and the immunocompromised, yet no licensed vaccine and only limited therapeutic options for prevention and treatment are available, which poses a global health challenge and emphasizes the urgent medical need for novel antiviral agents. In the current study, a novel potent small molecule inhibitor of RSV was identified by performing a screening and structure optimization campaign, wherein a naturally occurring dicaffeoylquinic acid (DCQA) compound served as a chemical starting point. The reported benzamide derivative inhibitor, designated as 2f, was selected for its improved stability and potent antiviral activity from a series of investigated structurally related compounds. 2f was well tolerated by cells and able to inhibit RSV infection with a half maximal inhibitory concentration (IC50) of 35 nM and a favorable selectivity index (SI) of 3742. Although the exact molecular target for 2f is not known, in vitro mechanism of action investigations revealed that the compound inhibits the early stage of infection by interacting with RSV virion and interferes primarily with the attachment and potentially with the virus-cell fusion step. Moreover, intranasal administration of 2f to mice simultaneously or prior to intranasal infection with RSV significantly decreased viral load in the lungs, pointing to the in vivo potential of the compound. Our results suggest that 2f is a viable candidate for further preclinical development and evaluation as an antiviral agent against RSV infections.