biostudies-literatureFalke SHelmholtz-GemeinschaftDeutsche ForschungsgemeinschaftHelmholtz AssociationJavna Agencija za Raziskovalno Dejavnost RSEuropean CommissionBundesministerium für Bildung und Forschung7048-7067https://www.ebi.ac.uk/biostudies/studies/S-EPMC11089505biostudies-literatureUnknown67(9)Emerging RNA viruses, including SARS-CoV-2, continue to be a major threat. Cell entry of SARS-CoV-2 particles via the endosomal pathway involves cysteine cathepsins. Due to ubiquitous expression, cathepsin L (CatL) is considered a promising drug target in the context of different viral and lysosome-related diseases. We characterized the anti-SARS-CoV-2 activity of a set of carbonyl- and succinyl epoxide-based inhibitors, which were previously identified as inhibitors of cathepsins or related cysteine proteases. Calpain inhibitor XII, MG-101, and CatL inhibitor IV possess antiviral activity in the very low nanomolar EC₅₀ range in Vero E6 cells and inhibit CatL in the picomolar <i>K_i</i> range. We show a relevant off-target effect of CatL inhibition by the coronavirus mJournal of medicinal chemistryStructural Elucidation and Antiviral Activity of Covalent Cathepsin L Inhibitors.PMC11089505P1-0048SFragXFISCOVInternLabs-0011-HIR3X16GW0277KA1-Co-06 â??CORAEROâ?&#157;EFRE-REACTSFB-TRR353 (project 471011418)031B0405DIO-0048Falke SUsenik ATurk DLoboda JDretnik KLieske JHerrmann ASekirnik AMeents ATurk VReinke PYAEwert WHinrichs WLindic NTsuge HGunther SKarnicar KChapman HNEbert GfalseStructural Elucidation and Antiviral Activity of Covalent Cathepsin L Inhibitors.Emerging RNA viruses, including SARS-CoV-2, continue to be a major threat. Cell entry of SARS-CoV-2 particles via the endosomal pathway involves cysteine cathepsins. Due to ubiquitous expression, cathepsin L (CatL) is considered a promising drug target in the context of different viral and lysosome-related diseases. We characterized the anti-SARS-CoV-2 activity of a set of carbonyl- and succinyl epoxide-based inhibitors, which were previously identified as inhibitors of cathepsins or related cysteine proteases. Calpain inhibitor XII, MG-101, and CatL inhibitor IV possess antiviral activity in the very low nanomolar EC₅₀ range in Vero E6 cells and inhibit CatL in the picomolar <i>K_i</i> range. We show a relevant off-target effect of CatL inhibition by the coronavirus m2024-01-01T00:00:00Z2024 May2026-04-08T19:50:52.032Z2026-04-08T14:33:23.408ZS-EPMC110895053863016510.1021/acs.jmedchem.3c02351