Nigellidine for COVID-19

The novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) responsible for the 2019 coronavirus disease (COVID-19) has caused a global health challenge. The SARS-COV-2 main protease, 3CLpro/Mpro plays a critical role in the viral gene expression and replication and has been a major target for inhibiting viral maturation and enhancing host innate immune responses against COVID-19. In this study, we screened a library of 38 phytochemicals from Nigella sativa (blackseed), Trigonella foenum-graecum (Fenugreek) and Anona muricata (Soursop) potent medicinal plants with reported antiviral properties - in a molecular docking protocol on 3CLpro using Autodock4.0 tool implanted in PyRx followed by docking validation and insilico absorption, distribution, metabolism, excretion, and toxicology (ADMET) evaluations. The docking results were visualized using Accelrys Discovery Studio and Pymol software. Among the 38 ligands screened, 19 showed significant interaction through non-covalent hydrogen bonding, hydrophobic, and electrostatic interactions with binding affinities from -5.3kcal/mol to -8.1kcal/mol indicating significant binding interactions at the active site binding pocket. Another important interaction observed in the study which mostly involve the transfer of charges was pi-interactions such as Pi-Pi interaction, Pi-Alkyl interaction, Pi-Sulfur interaction, Pi- Sigma, and Pi-Pi stacking. The docking results revealed that phytochemicals from T. foenum-graecum showed more 3CLpro inhibitory potential compared to those from N. sativa and A. muricata. Insilico ADMET evaluations for drug-like and lead-like characteristics however demonstrated that only 8 ligands - apigenin, kaempferol, luteolin, dithymoquinone, naringenine, nornuciferine, quercetin and nigellidine were actually drug-like; showed best activities against 3CLpro, and lack hepatotoxicity effects while none was lead-like. Insilico results of this study further suggested that drug repurposing candidates, remdesivir, indinavir,hydroxychloroquine, chloroquine and ritonavir,exhibited various interactions with 3CLpro. Hence, further in vitro and in vivo studies are proposed.

COVID-19 has been a threat to the entire world for more than two years since its outbreak in December 2019 in Wuhan city of China. SARS-CoV-2, the causative agent, had been reported to mutate over time exposing new variants. To date, no impeccable cure for the disease has been unveiled. This study outlines an extensive in silico approach to scrutinize certain phytochemical compounds of Nigella sativa (mainly the black cumin seeds) targeting the spike protein and the main protease (Mpro) enzyme of the Omicron variant of SARS-CoV-2. The objective of this study is to investigate the extracted compounds with a view to developing a potential inhibitor against the concerned SARS-CoV-2 variant. The investigation contemplates drug-likeness analysis, molecular docking study, ADME and toxicity prediction, and molecular dynamics simulation which have been executed to elucidate different phytochemical and pharmacological properties of the tested compounds. Based on drug-likeness parameters, a total of 96 phytochemical compounds from N. sativa have been screened in the study. Interestingly, Nigelladine A among the compounds exhibited the highest docking score with both the targets with the same binding affinity which is −7.8 kcal/mol. However, dithymoquinone, kaempferol, Nigelladine B, Nigellidine, and Nigellidine sulphate showed mentionable docking scores. Molecular dynamics up to 100 nanoseconds were simulated under GROMOS96 43a1 force field for the protein-ligand complexes exhibiting the top-docking score. The root mean square deviations (RMSD), root mean square fluctuations (RMSF), radius of gyration (Rg), solvent accessible surface area (SASA), and the number of hydrogen bonds have been evaluated during the simulation. From the findings, the present study suggests that Nigelladine A showed the most promising results among the selected molecules. This framework, however, interprets only a group of computational analyses on selected phytochemicals. Further investigations are required to validate the compound as a promising drug against the selected variant of SARS-CoV-2.