An integrated in silico and ex vivo study identifies quinazolinedione L134716 as a potential inhibitor of infectious bronchitis virus.

Infectious Bronchitis Virus (IBV) poses a persistent threat to poultry health and productivity, resulting in substantial economic losses. Despite the deployment of live attenuated and inactivated vaccines, effective control of IBV remains challenging, emphasizing the need for alternative strategies to manage infections. This study identifies dual inhibitors targeting the main protease (Mpro) and papain-like protease (PLpro) of infectious bronchitis virus (IBV) using a combinatorial in silico and ex vivo approach. Screening of the MyriaScreen Diversity Library II, comprising 10,000 diverse small molecules, resulted in the selection of two promising compounds, ST092577 and L134716, based on their strong and stable interactions with both proteases. Molecular dynamics (MD) simulations further confirmed the stability of these complexes, with their binding interactions validated through MM-PBSA binding free energy calculations. Ex vivo validation utilizing tracheal organ cultures and quantitative PCR demonstrated that 50 µM of L134716 (4-(4-(benzyloxy)ph)-7,7-dimethyl-4,6,7,8-tetrahydro-2,5(1 H,3 H)-quinazolinedione) significantly reduced the IBV genome load in infected tracheal rings. This reduction in viral load was further corroborated by immunohistochemical analysis. These findings underscore the promising potential of targeting key viral proteases Mpro and PLpro as part of alternative therapeutic strategies against IBV infections in poultry. While the results are encouraging, additional in ovo and in vivo studies are necessary to validate these findings and further explore the efficacy of L134716 in practical applications.