In Vitro and In Silico study showing that all-trans retinoic acid is a potent SARS-CoV-2 3CLpro inhibitor, inhibits SARS-CoV-2 replication in VeroE6/TMPRSS2 cells, and is effective against alpha, beta, gamma, and delta variants in Calu-3 cells.
Morita et al., 8/23/2021, peer-reviewed, 9 authors.
In Vitro studies are an important part of preclinical research, however results may be very different in vivo.