Virtual Screening for SARS-COV-2 Entry Inhibitors by Dual Targeting of TMPRSS2 and CTSL

The COVID-19 pandemic remains to be a global public health crisis due to the emergence of new variants of concern and the scarcity of drug treatments. The cell entry of SARS-CoV-2 requires activation of its spike protein by host proteases TMPRSS2 and CTSL, which triggers membrane fusion and facilitates the endocytic uptake mechanism, respectively. This study employed a structure-based virtual screening technique to identify drugs and natural products that simultaneously target TMPRSS2 and CTSL. Two pharmacophore models were generated from the binding sites of the proteins in complex with their co-crystallized ligands. Both structure-based pharmacophores were used to screen a ligand library composed of 41,775 compounds (10,849 drugs from the ChEMBL database and 30,926 natural products from the NPASS database). A total of 115 compounds (54 drugs and 61 natural products) that fit both TMPRSS2 and CTSL pharmacophore models were identified. The common hits were docked into both proteases to obtain a short list of compounds. Molecular docking filtered 17 compounds (5 drugs and 12 natural products) that have higher binding energy values than the co-crystallized ligands and known inhibitors of both proteins. The top hits were then subjected to ADMET, drug-likeness, and synthetic accessibility filters. Based on docking scores, pharmacokinetics, and drug-likeness, Silibinin was the most promising repurposed drug candidate as a treatment for SARS-CoV-2 infection via dual inhibition of TMPRSS2 and CTSL. Among the natural products, barettin was the best candidate for further development as a novel dual TMPRSS2 and CTSL inhibitor.