Cathepsin L is a key host cysteine protease utilized by coronaviruses for cell entry and is a promising drug target for novel antivirals against SARS-CoV-2. The marine natural product gallinamide A and several synthetic analogues were identified as potent inhibitors of cathepsin L with IC50 values in the picomolar range. Lead molecules possessed selectivity over other cathepsins and alternative host proteases involved in viral entry. Gallinamide A directly interacted with cathepsin L in cells and, together with two lead analogues, potently inhibited SARS-CoV-2 infection in vitro, with EC50 values in the nanomolar range. Reduced antiviral activity was observed in cells overexpressing transmembrane protease, serine 2 (TMPRSS2); however, a synergistic improvement in antiviral activity was achieved when combined with a TMPRSS2 inhibitor. These data highlight the potential of cathepsin L as a COVID-19 drug target as well as the likely need to inhibit multiple routes of viral entry to achieve efficacy.
Read MoreContributors: Anneliese S. Ashhurst, Arthur H. Tang, Pavla Fajtová, Michael C. Yoon, Anupriya Aggarwal, Max J. Bedding, Alexander Stoye, Laura Beretta, Dustin Pwee, Aleksandra Drelich, Danielle Skinner, Linfeng Li, Thomas D. Meek, James H. McKerrow, Vivian Hook, Chien-Te Tseng, Mark Larance, Stuart Turville, William H. Gerwick*, Anthony J. O’Donoghue*, and Richard J. Payne*