Integration of computational and experimental techniques for the discovery of PLpro covalent inhibitors. When large virtual screening and rational design meet

Papain-like protease (PL pro ) and 3-chymotrypsin-like protease (3CL pro or Mpro) are viral enzymes essential for the replication of SARS-CoV-2, the virus causing coronavirus disease of 2019 (COVID-19) infection. While 3CL pro has been the main target of many potential antivirals including nirmatrelvir (active ingredient of Paxlovid), PL pro has proven to be more challenging to target and only a handful of inhibitors have been disclosed. However, PL pro inhibitors would enrich the therapeutic arsenal against COVID-19 resistant strains to 3CL pro inhibitors and in future coronavirus pandemics. Combining our experience with 3CL pro covalent inhibitors with our expertise in structure-based covalent drug discovery, we rationally designed PL pro inhibitors achieving a maximum potency (IC 50 ) of 13 μM through fusion of GRL0617 and VIR-251 PL pro inhibitors. In parallel, we launched an integrated large scale virtual screening/experimental approach, identifying four novel chemical series active at micromolar concentrations against PL pro . We report herein our investigations including rational design, virtual screening, synthesis of selected structures and in vitro assays leading to novel PL pro inhibitors. Surprisingly, these two very distinct approaches led to similar structures.