The use of the previously known anti-viral drugs and their derivatives is promising until a permanent treatment is available. In this study, docking studies were performed over the five potential target sites or binding pockets of SARS-CoV-2 to find the potential binding molecule to combat the life-threatening coronavirus disease. Table 1 summarizes the top five lead molecules which bind with strong affinity with their respective target proteins. Among the 52 screened drugs against the SARS-CoV-2 almost 16 molecules have been shown inhibiting potential. The molecular docking with 5 potential target proteins of SARS-CoV-2 revealed the anti-viral potential of these 16 lead molecules against COVID-19 infection with some common target interactions (Table1).
Table 1
List of potential lead molecules against SARS-CoV-2 proteins [Binding energy MMGBSA] and Binding affinity (XP G Score) of selected anti-viral drugs
Protein PDB ID | Ligand ID | Name | XP G Score | MMGBSA |
6M71 (SARS-CoV-2 RNA-dependent RNA polymerase) | 60855 | Zanamivir | -9.572 | -46.38 |
| 154234 | Peramivir | -8.855 | -4.37 |
| 5280544 | Herbacetin | -7.85 | -50.43 |
| 5362119 | Lisinopril | -8.561 | -35.48 |
| 54892 | Quinapril | -8.102 | -14.16 |
6M0J-RBD (Spike receptor-binding domain) | 5280544 | Herbacetin | -4.836 | -46.24 |
| 60855 | Zanamivir | -4.582 | -32.88 |
| 168849 | Pectolinarin | -4.459 | -39.42 |
| 37542 | Ribavirin | -4.275 | -43.06 |
| 10445549 | Galidesivir BCX4430 | -4.106 | -23.66 |
6LU7 (SARS-CoV-2 main protease) | 5280544 | Herbacetin | -8.691 | -54.54 |
| 121304016 | Remdesivir | -8.377 | -110.02 |
| 5282150 | Rhoifolin | -7.627 | -71.41 |
| 168849 | Pectolinarin | -6.889 | -67.8 |
| 45375808 | Sofosbuvir | -6.808 | -82.04 |
1R4L (Inhibitor Bound Human ACE-Related Carboxypeptidase (ACE2)) | 60172 | Adefovir | -10.296 | -58.26 |
| 5291 | Imatinib | -9.046 | -108.81 |
| 56640146 | Dasabuvir | -8.294 | -79.08 |
| 60855 | Zanamivir | -8.196 | -35.08 |
| 5282150 | Rhoifolin | -7.989 | -63.46 |
6W01 (NSP15 Endoribonuclease from SARS-CoV-2) | 37542 | Ribavirin | -8.081 | -26.36 |
| 60855 | Zanamivir | -6.502 | -32.95 |
| 188323 | Cirsimaritin | -5.425 | -38.62 |
| 87718162 | 2H-Cyclohepta[b] thiophene-3-carboxamide | -4.905 | -35.2 |
| 121304016 | Remdesivir | -4.798 | -66.74 |
Table 2
ADME properties for the lead molecules
PDB ID | Ligand no. | Chemical Name | Mol wt. | SASA | HB donor | HB acceptor | QPlog Po/w | QPlog S | PSA | N & O | Rule of 5 | Ring atoms | Rule of 3 |
6M71 | 60855 | Zanamivir | 332.313 | 584.151 | 9 | 12.35 | -2.766 | -0.985 | 223.322 | 11 | 2 | 6 | 1 |
| 154234 | Peramivir | 328.411 | 570.353 | 6 | 7.2 | 0.542 | -1.892 | 161.383 | 8 | 1 | 5 | 1 |
| 5280544 | Herbacetin | 302.24 | 518.017 | 4 | 5.25 | 0.429 | -2.89 | 142.141 | 7 | 0 | 16 | 1 |
| 5362119 | Lisinopril | 405.493 | 723.035 | 5 | 9.5 | -1.204 | -1.371 | 149.231 | 8 | 0 | 11 | 2 |
| 54892 | Quinapril | 438.522 | 711.294 | 2 | 8.5 | 1.225 | -3.618 | 110.196 | 7 | 0 | 16 | 1 |
6M0J-RBD | 5280544 | Herbacetin | 302.24 | 518.017 | 4 | 5.25 | 0.429 | -2.89 | 142.141 | 7 | 0 | 16 | 1 |
| 60855 | Zanamivir | 332.313 | 584.151 | 9 | 12.35 | -2.766 | -0.985 | 223.322 | 11 | 2 | 6 | 1 |
| 168849 | Pectolinarin | 622.579 | 839.584 | 6 | 19.8 | -0.73 | -2.846 | 226.481 | 15 | 3 | 28 | 2 |
| 37542 | Ribavirin | 244.207 | 426.928 | 5 | 12.3 | -2.564 | -1.485 | 156.493 | 9 | 0 | 10 | 1 |
| 10445549 | Galidesivir BCX4430 | 265.271 | 480.902 | 7 | 9.1 | -2.151 | -0.725 | 146.442 | 8 | 1 | 14 | 1 |
6LU7 | 5280544 | Herbacetin | 302.24 | 518.017 | 4 | 5.25 | 0.429 | -2.89 | 142.141 | 7 | 0 | 16 | 1 |
| 121304016 | Remdesivir | 602.583 | 836.121 | 5 | 16.65 | 0.943 | -4.184 | 200.319 | 14 | 2 | 20 | 1 |
| 5282150 | Rhoifolin | 578.526 | 858.839 | 7 | 19.05 | -1.506 | -3.456 | 233.943 | 14 | 3 | 28 | 2 |
| 168849 | Pectolinarin | 622.579 | 839.584 | 6 | 19.8 | -0.73 | -2.846 | 226.481 | 15 | 3 | 28 | 2 |
| 45375808 | Sofosbuvir | 529.458 | 748.602 | 3 | 14.9 | 1.249 | -3.347 | 173.576 | 12 | 2 | 17 | 0 |
1R4L | 60172 | Adefovir | 273.188 | 465.498 | 4 | 10.7 | -0.415 | -1.135 | 137.267 | 9 | 0 | 9 | 1 |
| 5291 | Imatinib | 493.61 | 890.127 | 2 | 10.5 | 3.581 | -4.873 | 89.54 | 8 | 0 | 30 | 1 |
| 56640146 | dasabuvir | 493.576 | 797.927 | 2 | 8.75 | 3.555 | -6.692 | 129.501 | 8 | 0 | 22 | 1 |
| 60855 | Zanamivir | 332.313 | 584.151 | 9 | 12.35 | -2.766 | -0.985 | 223.322 | 11 | 2 | 6 | 1 |
| 5282150 | Rhoifolin | 578.526 | 858.839 | 7 | 19.05 | -1.506 | -3.456 | 233.943 | 14 | 3 | 28 | 2 |
6W01 | 37542 | Ribavirin | 244.207 | 426.928 | 5 | 12.3 | -2.564 | -1.485 | 156.493 | 9 | 0 | 10 | 1 |
| 60855 | Zanamivir | 332.313 | 584.151 | 9 | 12.35 | -2.766 | -0.985 | 223.322 | 11 | 2 | 6 | 1 |
| 188323 | Cirsimaritin | 314.294 | 550.603 | 1 | 4.5 | 2.664 | -4.018 | 91.451 | 6 | 0 | 16 | 0 |
| 87718162 | 2H-Cyclohepta[b]thiophene-3-carboxamide | 191.247 | 385.9 | 2 | 3 | 1.381 | -2.292 | 50.593 | 2 | 0 | 10 | 0 |
| 121304016 | Remdesivir | 602.583 | 836.121 | 5 | 16.65 | 0.943 | -4.184 | 200.319 | 14 | 2 | 20 | 1 |
Table 3
The details of possible proposed lead molecules as a potential anti-SARS-CoV-2 drug.
No | Name | Active against | Mechanism | References |
1. | Zanamivir | Influenza viruses | Neuraminidase inhibitor | [29] |
2. | Peramivir | Influenza virus | Neuraminidase inhibitor | [30] |
3. | Herbacetin | SARS CoV | Inhibitor | [31] |
4. | Lisinopril | Acute myocardial infarction, hypertension | ACE inhibitor | [32] |
5. | Quinapril | Influenza | ACE inhibitor, RNA polymerase | [33] |
6. | Pectolinarin | HSV-1, VACV‐WR and DENV‐2 | Tyrosinase inhibitor | [34] |
7. | Ribavirin | Hepatitis C | Synthetic guanosine analog | [35] |
8. | Galidesivir BCX4430 | Hepatitis C | Adenosine analog | [36] |
9. | Remdesivir | Ebola virus, Respiratory syncytial virus | Viral RNA polymerase | [36] |
10. | Rhoifolin | | | [37] |
11. | Sofosbuvir | Yellow fever, Zika virus, Dengue, Hepatitis C, Chikungunya viruses | Inhibitor of viral RNA synthesis by inhibiting NS5B protein | [34] |
12. | Adefovir | HIV | Reverse transcriptase inhibitor | [38] |
13. | Imatinib | SARS CoV and MERS CoV | Tyrosine kinase inhibitor | [39] |
14. | Dasabuvir | Hepatitis C virus | Non-nucleoside inhibitor, Inhibits the action of NS5B polymerase | [38] |
15. | Cirsimaritin | Influenza virus | Downregulating the NF-κb signal transduction pathway | [40] |
16. | 2H-Cyclohepta[b]thiophene-3-carboxamide | HIV-1 | Ribonuclease inhibitors | [41] |
In light of present findings Zanamivir, Peramivir, Herbacetin, Lisinopril, Quinapril are the top five molecules that showed the potential to bind with SARS-CoV-2 RNA-dependent RNA polymerase (6M71). Similarly, Herbacetin, Zanamivir. Pectolinarin, Ribavirin, Galidesivir BCX4430 are the top five molecules that exhibited the high binding potential to bind with SARS-CoV-2 spike receptor-binding domain protein (6M0J-RBD). Further, Herbacetin, Remdesivir, Rhoifolin, Pectolinarin, Sofosbuvir are the top potential drugs that bind with SARS-CoV-2 main protease (6LU7). Apart from this, Adefovir, Imatinib, Dasabuvir, Zanamivir, Rhoifolin are the drugs, which showed the possible strong interaction on the 1R4L site. However, Ribavirin, Zanamivir, Cirsimaritin, 2H-Cyclohepta[b]thiophene-3-carboxamide, Remdesivir display the possible affinity to bind with NSP15 Endoribonuclease of SARS-CoV-2 (Table 1).
Among the tested drugs in this in-silico study, the present finding suggests the highest binding potential of Remedesivir, Imatinib, Herbacetin, Zanamivir, Ribavirin, Dasabuvir, Rhoifolin, Sofosbuvir, Cirsimaritin, and 2H-Cyclohepta[b]thiophene-3-carboxamide for their respective protein targets. The results showed efficient binding of the potential targets of SARS-CoV-2 with these lead molecules as the best active binders. These interactions suggest their probable mechanism for anti-viral effects against SARS-CoV-2. Our results predict a strong therapeutic potential of these proposed drugs against SARS-CoV-2 infection.
Herbacetine and Rhoifoloin are polyphenolic drugs. polyphenolic drugs are natural antioxidant boosters that contribute to anti-viral therapies since ancient times [42]. Herbal formulations used for alternative therapies have remains a popular choice among clinicians due to their least toxic nature. The potential of Plant Bioactive Compounds was also tested for anti-SARS-CoV-2 potency [43, 44]. Polyphenols have a high affinity to proteins via hydrogen bonding formation that helps them to inhibit the viral proteases involved in viral replication. Molecular docking studies prove the inhibitory action of polyphenolic compounds against SARS-CoV-2 main protease (Mpro) and spike (S) glycoprotein inhibitors [45, 46].
The docking of the proposed ligand molecules with the active site of a receptor determines the orientation of binding capacity, formation of bridges, and possible hydrophilic, hydrophobic interactions along with the amount of energy liberated that refers to the stability of the ligand-receptor complex [47, 48]. In search of the potential lead inhibitor molecules, we have tested various anti-viral candidates for repositioning as SARS-CoV-2 inhibitors. Figure 1 depicts the best docking poses of Proteins with the top docked ligand showing the highest docking score. For instance, 6M71 have shown the highest docking score with Zanamivir (Figure 1a), 6M0J-RBD, and 6LU7 with Herbacetin (Figure 1b&C), 1R4L with Adefovir (Figure 1d), and 6W01 with Ribavirin (Figure 1e). Various interactions between the protein with respective docked ligands such as hydrogen bonds, pi-pi interaction have been displayed in Figure 1a-e respectively. Figure 2 represents the structures of Zanamivir (Figure 2a), Herbacetin (Figure 2b), 1R4L with Adefovir (Figure 2c), and Ribavirin (Figure 2d).
There are five prime virus targets 6M71, 6M0J-RBD, 6LU7, 1R4L, 6W01, NSP15 which play a vital role in the mediation of virulence and pathogenicity. Present results revealed that each target is competitively encountered by a potential lead molecule that possibly inhibits the function of the enzyme and reduces the viral load.
RdRp is the most promising therapeutic drug target as it plays a vital role in viral RNA genome replication. The docking study has shown Zanamivir (332.313 MW) binds with great affinity with the RdRp. In the binding pocket of the enzyme Zanamivir forms various interactions including 7 hydrogen bonds at polar and positive charged residues. The amino acids Arg 553, Arg 555, Thr 556, Asp 623, Asp 760 involved in the formation of hydrogen bonds with Zanamivir (Figure 1a). The highest docking score and binding free energy exhibited by Zanamivir against 6M71 active site residue suggest its potential anti-viral efficacy.
Spike receptor-binding domain is an essential requirement for mediation of SARS-CoV-2 into the host cell [49]. The attachment and entry of virus within the host cell are mediated by spike protein which makes it a suitable target for drugs that can bind and prevent the entry of virus within the host cell. The docking study revealed Herbacetin (302.24 MW) showed a higher potential of binding at the active site of 6M0J-RBD, as this ligand interacts with high affinity within the active site pocket. Here, various interactions of Herbactin with active site amino acid residue of 6M0J-RBD includes the formation of 3 pi cation by Lys 458, Arg 457, Arg454 along and 4 hydrogen bonds with Ser460, Lys 458, and Ser 469 amino acids at positively charged polar regions (Figure 1b).
SARS-CoV-2 encodes two distinct proteases, named papain-like cysteine protease (PLpro) and chymotrypsin-like cysteine protease known as (3C-like protease/ 3CLpro/ Main protease /Mpro). The SARS CoV Mpro is an essential requirement for processing of the polyproteins that are translated from the viral RNA [50]. SARS-CoV-2 Mpro inhibitors are the prime molecules with possible anti-viral efficacy. Therefore, Mpro inhibitory drugs with less toxicity to humans proteases have been considered for virus restriction because no human proteases with a similar cleavage specificity are known [51]. Present molecular docking study showed Herbacetin (302.24 MW) binds in the 6LU7 catalytic site of SARS-CoV-2 were negatively charged and polar residues TYR54, GLU 166, THR 190 in the pocket involved in the formation of 3 hydrogen bonds and HIS 41residue form pi interaction with the drug respectively (Figure 1c). These amino acid residues play an essential role in the catalytic activity of Mpro [50].
ACE2 the negative regulator of the renin-angiotensin system, which is an essential mediator of SARS-CoV-2 infection is widely expressed in the lungs, cardiovascular system, gut, kidneys, central nervous system, and adipose tissue of humans [52, 53]. The interactions between the receptor-binding domain of viral spike (S) protein with surface-expressed human ACE2 is an essential requirement for virus pathophysiological modulations. The present study reveals that Adefovir (273.188 MW) acts as a potential candidate for the inhibition of the 1R4L receptor site. At the active site, the involvement of the amino acid residues HIS 345, PRO 346, HIS 505, ARG 273, ALA 348, ARG 514 which forms 7 hydrogen bonds with Adefovir along with a potential salt bridge with Zn 803 validates its anti-viral efficacy (Figure 1d). Various potential drugs that were proposed as an anti-viral agent (including hydroxychloroquine and chloroquine) against SARS-CoV-2 have the potential ACE2 inhibitory activity [54].
The docking study with NSP15 Endoribonuclease of SARS-CoV-2 reveals the potential biding of the target with the anti-viral drug Ribavirin. Ribavirin (244.207 MW), also known as Tribavirin is an antiviral drug with a possible efficacy against HCV and Flavivirus infection [55].. Ribavirin showed the highest binding affinity for the active site residue of the endoribonuclease. Here, active site residues LYS 290, VAL 292, SER 294, LEU 346 forms 6 hydrogen bonds with ribavirin (Figure 1e).
The physicochemical properties such as molecular weight (MW), surface accessibility (SASA), hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), octanol-water coefficient (Po/w, QPlog S), polar surface area (PSA), number of nitrogen and oxygen atoms, rule of 5, rings atoms and rule of 3 of selected lead molecules were calculated and listed in Table 2. The ADME properties of lead molecules showed their potency as an efficient anti-viral drug against COVID-19.