CTSL and COVID-19: The cellular entry of SARS-CoV-2 also shows a dependence on cathepsin L enzymatic activity via the endosomal pathway, so cathepsin L inhibitors were also identified as a novel target to inhibit COVID-19 entry into the host cell.24 Herein, we highlight some of the potent cathepsin L inhibitors which show least interference with the cleavage of a host protein-derived peptide (pro-neuropeptide Y) such as SSAA09E1.