Potent, competitive and reversible cysteine, serine and threonine protease inhibitor. Inhibits calpain, kallikrein, trypsin, plasmin, papain and cathepsin B. Does not inhibit pepsin, elastase, renin, cathepsins A and D, thrombin or α-chymotrypsin. Used to protect against hearing loss caused by acoustic overstimulation or the ototoxic antibiotic gentamicin. Shown to inhibit activation-induced programmed cell death. Antioxidant and anti-inflammatory agent. Widely used as a protein purification tool to prevent proteases present in tissue samples from degrading the protein of interest. Molecular docking and molecular dynamics simulation of leupeptin with the transmembrane serine protease TMPRSS2, show strong interactions with the key amino acids Ser186, His41 and Asp180 of catalytic triad present in the active site of TMPRSS2. This interaction causes the inhibition of the function of TMPRSS2, which is essential for SARS-CoV-2 viral entry and infection. As an inhibitor of TMPRSS2 this agent could be repurposed for treatment of COVID-19.