Investigating the potential of natural compounds as novel inhibitors of SARS-CoV-2 RdRP using computational approaches.

COVID-19 is a highly contagious disease caused by SARS-CoV-2. Currently, no vaccines or antiviral treatments are available to combat this deadly virus; however, precautions and some repurposed medicines are available to contain COVID-19. RNA-dependent RNA polymerase (RdRP) plays an important role in the replication or transcription of viral mechanisms. Approved antiviral drug such as Remdesivir has shown inhibitory activity against SARS-CoV-2 RdRP. The purpose of this study was to carry out a rational screening of natural products against SARS-CoV-2 RdRP, which may serve as a basis to develop a treatment option against COVID-19. For this purpose, a protein and structure conservation analysis of SARS-CoV-2 RdRP was performed to check mutations. A library of 15,000 phytochemicals was developed from literature review, ZINC database, PubChem and MPD3 database; and was used to performed molecular docking and molecular dynamics simulation (MD) analysis. The top-ranked compounds were subjected to pharmacokinetic and pharmacological studies. Among them, top 7 compounds (Spinasaponin A, Monotropane, Neohesperidoe, Posin, Docetaxel, Psychosaponin B2, Daphnodrine M, and Target Remedesvir) were noticed to interact with the active site residues. MD simulation in aqueous solution suggested conformational flexibility of loop regions in the complex to stabilize the docked inhibitors. Our study revealed that the studied compounds have potential to bind to the active site residues of SARS-CoV-2 RdRP. Although, this computational work is not experimentally determined but the structural information and selected compounds might help in the design of antiviral drugs targeting SAR-CoV-2 by inhibiting the activity of SARS-CoV-2 RdRP.

Genetic conservation of SARS-CoV-2 RNA replication complex in globally circulating isolates and recently emerged variants from humans and minks suggests minimal pre-existing resistance to remdesivir.

Remdesivir (RDV) exhibits potent antiviral activity against SARS-CoV-2 and is currently the only drug approved for the treatment of COVID-19. However, little is currently known about the potential for pre-existing resistance to RDV and the possibility of SARS-CoV-2 genetic diversification that might impact RDV efficacy as the virus continue to spread globally. In this study, >90,000 SARS-CoV-2 sequences from globally circulating clinical isolates, including sequences from recently emerged United Kingdom and South Africa variants, and >300 from mink isolates were analyzed for genetic diversity in the RNA replication complex (nsp7, nsp8, nsp10, nsp12, nsp13, and nsp14) with a focus on the RNA-dependent RNA polymerase (nsp12), the molecular target of RDV. Overall, low genetic variation was observed with only 12 amino acid substitutions present in the entire RNA replication complex in ≥0.5% of analyzed sequences with the highest overall frequency (82.2%) observed for nsp12 P323L that consistently increased over time. Low sequence variation in the RNA replication complex was also observed among the mink isolates. Importantly, the coronavirus Nsp12 mutations previously selected in vitro in the presence of RDV were identified in only 2 isolates (0.002%) within all the analyzed sequences. In addition, among the sequence variants observed in ≥0.5% clinical isolates, including P323L, none were located near the established polymerase active site or sites critical for the RDV mechanism of inhibition. In summary, the low diversity and high genetic stability of the RNA replication complex observed over time and in the recently emerged SARS-CoV-2 variants suggests a minimal global risk of pre-existing SARS-CoV-2 resistance to RDV.

The Novel Coronavirus Enigma: Phylogeny and Analyses of Coevolving Mutations Among the SARS-CoV-2 Viruses Circulating in India.

BACKGROUND: The RNA genome of the emerging novel coronavirus is rapidly mutating, and its human-to-human transmission rate is increasing. Hence, temporal dissection of their evolutionary dynamics, the nature of variations among different strains, and understanding the single nucleotide polymorphisms in the endemic settings are crucial. Delineating the heterogeneous genomic constellations of this novel virus will help us understand its complex behavior in a particular geographical region. OBJECTIVE: This is a comprehensive analysis of 95 Indian SARS-CoV-2 genome sequences available from the Global Initiative on Sharing All Influenza Data (GISAID) repository during the first 6 months of 2020 (January through June). Evolutionary dynamics, gene-specific phylogeny, and the emergence of the novel coevolving mutations in 9 structural and nonstructural genes among circulating SARS-CoV-2 strains across 12 different Indian states were analyzed. METHODS: A total of 95 SARS-CoV-2 nucleotide sequences submitted from India were downloaded from the GISAID database. Molecular Evolutionary Genetics Analysis, version X software was used to construct the 9 phylogenetic dendrograms based on nucleotide sequences of the SARS-CoV-2 genes. Analyses of the coevolving mutations were done in comparison to the prototype SARS-CoV-2 from Wuhan, China. The secondary structure of the RNA-dependent RNA polymerase/nonstructural protein NSP12 was predicted with respect to the novel A97V mutation. RESULTS: Phylogenetic analyses revealed the evolution of "genome-type clusters" and adaptive selection of "L"-type SARS-CoV-2 strains with genetic closeness to the bat severe acute respiratory syndrome-like coronaviruses. These strains were distant to pangolin or Middle East respiratory syndrome-related coronavirus strains. With regard to the novel coevolving mutations, 2 groups have been seen circulating in India at present, the "major group" (66/95, 69.4%) and the "minor group" (21/95, 22.1%) , harboring 4 and 5 coexisting mutations, respectively. The "major group" mutations fall in the A2a clade. All the minor group mutations, except 11083G>T (L37F, NSP6 gene), were unique to the Indian isolates. CONCLUSIONS: This study highlights the rapidly evolving SARS-CoV-2 virus and the cocirculation of multiple clades and subclades. This comprehensive study is a potential resource for monitoring the novel mutations in the viral genome, interpreting changes in viral pathogenesis, and designing vaccines or other therapeutics.