Old Arsenal to Combat New Enemy: Repurposing of Commercially Available FDA Approved Drugs Against Main Protease of SARS-CoV2.

In lack of vaccination and therapeutic drugs, the ongoing COVID-19 pandemic affected millions of people, causing 1,018,957 deaths worldwide (World health organization; 1^st October 2020). The conventional drug design pipeline for effective and safer drug development is a costly and time-intensive affair. It takes around ten years in general from identifying a clinical candidate to get the approvals for actual applications. An effective way to cut short drug design pipeline in such emergency cases could be the repurposing of already approved drugs against novel targets. Here in this work, we explored the structure-based drug screening approach to find potential inhibitors of SARS-CoV2 main protease (M^pro) from the library of already FDA approved commercially available drugs. The site-specific and blind docking studies, in combination, suggest three potential inhibitors of M^pro, Ergotamine (ZINC000052955754), Nilotinib (ZINC000006716957) and Naldemedine (ZINC000100378061). Molecular dynamics (MD) simulations and binding free energy calculations using the MMPBSA method further reinforced the efficiency of the screened M^pro inhibitor candidates. The work yields enough evidence to conduct rigorous experimental validation of these drugs before utilizing them for the therapeutic management of SARS-CoV2 infection.