Direct blue 53, a biological dye, inhibits SARS-CoV-2 infection by blocking ACE2 and spike interaction in vitro and in vivo.

COVID-19 is a global health problem caused by SARS-CoV-2, which has led to over 600 million infections and 6 million deaths. Developing novel antiviral drugs is of pivotal importance to slow down the epidemic swiftly. In this study, we identified five azo compounds as effective antiviral drugs to SARS-CoV-2, and mechanism study revealed their targets for impeding viral particles' ability to bind to host receptors. Direct Blue 53, which displayed the strongest inhibitory impact, inhibited five mutant strains at micromole. In vitro, mechanism study demonstrated Direct Blue 53 inhibited viral infection through interaction with the spike of SARS-CoV-2. And 25 mg/kg/d compound treatment showed 50% or 60% survival protection against lethal Delta or Omicron BA.2 infection in vivo. Taken together, our results demonstrate that azo compounds with dimethyl-biphenyl-diyl-bis(azo)bis structure may be promising anti-SARS-CoV-2 drug candidates, which provide practicable therapies with the aid of structural optimizations and further research.