DON/DRP‐104 as potent serine protease inhibitors implicated in SARS‐CoV‐2 infection: Comparative binding modes with human TMPRSS2 and novel therapeutic approach

Abstract Human transmembrane serine protease 2 (TMPRSS2) is an important member of the type 2 transmembrane serine protease (TTSP) family with significant therapeutic markings. The search for potent TMPRSS2 inhibitors against severe acute respiratory syndrome coronavirus 2 infection with favorable tissue specificity and off‐site toxicity profiles remains limited. Therefore, probing the anti‐TMPRSS2 potential of enhanced drug delivery systems, such as nanotechnology and prodrug systems, has become compelling. We report the first in silico study of TMPRSS2 against a prodrug, [isopropyl(S)‐2‐((S)‐2‐acetamido‐3‐(1H‐indol‐3‐yl)‐propanamido)‐6‐diazo‐5‐oxo‐hexanoate] also known as DRP‐104 synthesized from 6‐Diazo‐5‐oxo‐ l ‐norleucine (DON). We performed comparative studies on DON and DRP‐104 against a clinically potent TMPRSS2 inhibitor, nafamostat, and a standard serine protease inhibitor, 4‐(2‐Aminoethyl) benzenesulfonyl fluoride (AEBSF) against TMPRSS2 and found improved TMPRSS2 inhibition through synergistic binding of the S1/S1' subdomains. Both DON and DRP‐104 had better thermodynamic profiles than AEBSF and nafamostat. DON was found to confer structural stability with strong positive correlated inter‐residue motions, whereas DRP‐104 was found to confer kinetic stability with restricted residue displacements and reduced loop flexibility. Interestingly, the Scavenger Receptor Cysteine‐Rich (SRCR) domain of TMPRSS2 may be involved in its inhibition mechanics. Two previously unidentified loops, designated X (270−275) and Y (293−296) underwent minimal and major structural transitions, respectively. In addition, residues 273−277 consistently transitioned to a turn conformation in all ligated systems, whereas unique transitions were identified for other transitioning residue groups in each TMPRSS2‐inhibitor complex. Intriguingly, while both DON and DRP‐104 showed similar loop transition patterns, DRP‐104 preserved loop structural integrity. As evident from our systematic comparative study using experimentally/clinically validated inhibitors, DRP‐104 may serve as a potent and novel TMPRSS2 inhibitor and warrants further clinical investigation.