Hydroxychloroquine (HCQ) Exhibits Better Binding to the Main Protease (M^pro) Compared to Spike Protein (S protein) of SARS-CoV-2: An In-silico Analysis

Background: Despite various efforts in preventing and treating SARS-CoV-2 infections; transmission and mortality have been increasing at alarming rates globally. Since its first occurrence in Wuhan, China, in December 2019, the number of cases and deaths due to SARS-CoV- -2 infection continues to increase across 220 countries. Currently, there are about 228 million cases and 4.6 million deaths recorded globally. Although several vaccines/drugs have been reported to prevent or treat SARS-CoV-2, their efficacy to protect against emerging variants and duration of protection are not fully known. Hence, more emphasis is given to repurpose the existing pharmacological agents to manage the infected individuals. One such agent is hydroxychloroquine (HCQ), which is a more soluble derivative of antimalarial drug chloroquine. HCQ has been tested in clinical trials to mitigate SARS-CoV-2 infection-induced complications while reducing the time to clinical recovery (TTCR). However, several concerns and questions about the utility and efficacy of HCQ for treating SARS-CoV-2 infected individuals still persist. Identifying key proteins regulated by HCQ is likely to provide vital clues required to address these concerns. Objective: The objective of this study is to identify the ability of HCQ for binding to the most widely studied molecular targets of SARS-CoV-2 viz., spike glycoprotein (S protein), and main protease (Mpro, also referred as chymotrypsin like protease) using molecular docking approaches and correlate the results with reported mechanisms of actions of HCQ. Methods: X-ray crystallographic structures of spike glycoprotein and main protease of SARSCoV- 2 were retrieved from Research Collaboratory for Structural Bioinformatics (RCSB) Protein Data Bank (PDB). The structure of Hydroxychloroquine was retrieved from the PubChem compound database. The binding interactions of the HCQ with target proteins were predicted using CDocker algorithm, and visualized using Discovery studio visualizer. Results: Data from molecular docking studies showed very strong binding of HCQ to the main protease compared to spike glycoprotein. Conclusion: The antiviral activity of HCQ is attributed to its ability to bind to the main protease compared to surface glycoprotein. Therefore, future studies should focus more on developing a combination agent/strategy for targeting surface glycoprotein and main protease together.