8. Overview of Docking Studies of the Metal Complexes against COVID-19
Abbas et al. (2022) modified four additional heterocyclic of ferrocene derivatives—L1 = N-(2–hydroxy-5-biphenyl) ferrocylideneamine (Ferrocencarboxaldehyde), L2 = N-(2–hydroxy-5-nitrophenyl) ferrocylideneamine, L3 = N-(2–hydroxy-5-sulfonylphenyl) ferrocylideneamine, and L4 = N-(2–hydroxy-5-chlorophenyl) ferrocylideneamine)—which have been synthesized through reacting with an aqueous solution containing the amount of the L4, phenyl-, sulfonyl-, and nitro with 0.5 mmol ferrocenecarboxaldehyde and 0.5 mmol chloro-modified aminophenol in ethanol as just a solvent. The composition and structure of the ferrocene derivatives were identified by FT-IR, 1HNMR, electronic spectroscopy, and mass spectrometry. The composition of L4 was furthermore characterized through X-ray diffraction (single-crystal) [
83]. The composition of the SARS-CoV-2 (6LU7 proteins) has been submitted to the Global Protein Database. Autodock or a model describing the MOE-docking investigation of molecules as well as controlled treatments were used to refine the (6LU7 protein) structure.
Table 1 displayed the energy of binding values among ligands and proteins. It shows the binding energy relations between ligands and binding sites in the tested complexes and SARS-CoV-2 (6LU7 proteins). The interacting between hydrogen of a ligand and hydroxyl of CYS145 was determined to also be 2.40 A in L1 and 2.70 A between hydrogen of GLY143 and oxygen of the ligand. In L2, hydrogen bonding between TRP218’s keto oxygen and the ligand’s hydroxyl showed to be 2.60 A, and connection among hydrogen of ARG222 and the ligand’s O—N—O was shown to be 2.20 A. For hydrogen bonding among both the keto O of ARG279 as well as the HSO
3 of the tested ligand has been determined as being 2.70 A in molecule L3, while the cross- linking among the keto (oxygen) of GLY278 and the HSO
3 of the tested ligand has been determined as being 2.30 A. The molecular dynamic data for L1-L4 revealed which L1 may be more anti-COVID19 and anti-oxidant than its competitors. In comparison to the reference medications, the calculation analysis shows that L1 inhibits SARSCoV-2 more effectively. This discovery opens the way for more research into L1 and its possible use in the preventive care of SARS-CoV-2.
El-Gammal et al, (2022) synthesized (HL) the ligand of hydrazone by refluxing for 2 h in a 1:1 M ratio of the mixture of 2- Acetylpyridine (6 mmol) & (20 mL) hot ethanol of 4-(3-cyano-4,6-dimethylpyridin-2-ylamino) benzohydrazide (6 mmol) that was prepared and then acidified with glacial Ac OH drops [
84,
85,
86]. The product was obtained and filtered, and the bright yellow filter was rinsed with Et OH before solvent extraction. This was eventually dehydrated with anhydrous CaCl
2 in a vacuum desiccator. Cu(II) and Ni(II) and Co(II) complexes (1–3) were created by combining a hot Et OH solution of the metal salts Ni(NO
3)
2 6H
2O (1.0 mmol) and Cu(NO
3)
2 3H
2O (1.0 mmol) and Co(NO
3)
2. 6H
2O (1.0 mmol), with a heated EtOH solution of HL (1.0 mmol) in a molar ratio (1 M:1 HL). Reflux for 3 h was the reaction solution. The yield was filtered off then washed with hot EtOH and dried through adding drops of petroleum ether over anhydrous CaCl
2 and eventually dehydrated with dehydrated CaCl
2 in desiccators [
84]. The Schiff base and its Ni(II), Cu(II), and Co(II) metal complexes (1–3) as shown in (
Figure S2) were characterized with different analytical and spectroscopic techniques, such as UV–Visible, FT-IR, CHN, magnetic measures,
13C NMR,
1 H NMR, magnetic, electronic spectrum, and TGA and XRD analysis. The molecular modeling using the DFT technique displays bond angles and quantum chemical factors and bond lengths and dioxygen stimulation in features of phenoxazinone included was thoroughly investigated using o-aminophenol as a standard data activated by tested complexes. The docking binding site linkages were assessed by connecting with major protease (SARS-CoV-2) that was provided from the RCSB pdb database (PDB ID: 6 W41) to predict the effect of HL in opposing COVID-19. As a result, additional preclinical and practice trials into HL as a potentially COVID-19 disease [
87]. We applied docking to study the interaction of the (HL) to (6 W41). The findings suggested that HL and protein 6 W41 may be organized. The data obtained from docking relieved that a favorable interaction between HL and 6 W41 proteins target (
Figure S2) with the energy calculated in (
Table 2). The HB plot’s curve shows that there are intra-molecular hydrogen contacts between (HL) and the sensor, as well as reduced binding energies (kCal/mole) between both the COVID-19 (6 W41) binding site and HL. The computed results are acceptable. When AutoDock’s Ki value was matched to an experiment Ki value, Gibbs was negative. The binding site between the HL and (6W41) protein surface of COVID-19 used H-bonding via electrostatic and van der Waals interactions, with the HL exhibiting a binding affinity of –5.88 and the H-bond exhibiting binding energy of –5.88. Associations with protein residues and tested complex scoring were revealed to be possible (HL) and inhibitors of the 6W41-main proteins with just a restricted access protein surface COVID-19. As a result, we can deduce that HL has the minimum binding affinity and highest binding ability (–5.17 and –5.88 kCal/mol, respectively) [
87].
Cirri et al. (2020) revealed that metal-based medicines have a wide range of chemical structures and relativities that are strictly related to the nature of the metal core and the surrounding ligands. Because of their wide chemical diversity, metal compounds are clearly a rich source of novel medicinally beneficial substances; as a result, we strongly propose that metal-based medications be included as much as possible in new drug development screening programs. This may be especially important in the hunt for innovative drugs to treat COVID-19 disease, a severe and quickly spreading disease for which medicinal treatments are currently unavailable and desperately needed. There are two basic approaches to developing metal-based medicines as anti-COVID-19 agents: medication repurposing and new drug development. Regarding the first approach, some extremely encouraging in vitro results for auranofin, a gold compound in clinical use for the treatment of rheumatoid arthritis, have been described. Similarly, several bismuth compounds appear to be highly promising. The second technique is, undoubtedly, more complex and time-intensive, but it may provide more options; it may be aided by pathway-driven or target-driven discovery considerations. The advantages and disadvantages of the two drug-discovery methodologies are examined and debated [
88]. In this context, the effectiveness of early micronutrient supplementation, with an emphasis on zinc, selenium, and vitamin D, in reducing COVID-19 escalation has also been revised [
89].
Mir et al. (2021) investigated the search for possible preventative and therapeutic antiviral techniques that are of special and urgent relevance in light of the growing COVID-19 pandemic caused by the SARS-CoV-2 virus. Zinc is known to impact antimicrobial and antioxidant immunity as well as regulate the late inflammatory response [
90]. Meanwhile, the intensity of COVID-19 is linked to the problems listed above, for which Schiff base complexes have been found to be excellent candidates. However, as recently shown (
Figure 2) the participation of co-ligands, such as CO, NO, and H
2S, may enhance anti-coronavirus activity [
91,
92]. To consider a substance as an anti-covid medication, stimulation receptor interaction and slowing replication of coronavirus genetic code are required. Consequently, complexes depend on the nature of metals may play a significant role in the development of metallodrugs to treat this infection [
93].
Ahmed et al. (2022) combined 2,2-(ethylenedioxy)bis(ethylamine) with imidazole-2-carboxaldehyde in a 1:2 ratio for the preparation of Schiff base ligand and its metal chelates with Fe(III), Mn(II), Cr(III), Ni(II), Co(II), Cd(II), and Cu(II). The metals were prepared in a 1:1 ratio. The ligand and its complexes were identified using a variety of approaches. To help further comprehend the complicated structure, classification performances, for example, FT-IR, UV, and 1H NMR spectral testing, CHN, magnetic characteristics, conductivity, TGA, BET surface area, and theoretically by DFT were applied. Docking studies in the drug development process, docking is a suitable system for predicting the good stability of a receptor–ligand interaction in order to better identify interaction features. This strategy is commonly used in the early stages of drug design and development as a virtual searching technique [
94,
95,
96]. The researchers wanted to observe how the complexes interacted with the crystal structure of the SARS-CoV-2 basic protease with an unliganded active site (2019-nCoV, coronavirus illness 2019, COVID-19) (PDB ID: 6Y84) proteins. The compounds reacted strongly with the protein’s acceptors. When we used 6Y84 docking to examine the activation energies of binding (G) Fe(III), Mn(II), Cr(III), Ni(II), Co(II), Cu(II), and Cd(II), the best results revealed that the free energies of binding (G) were, −7.6, −6.0, −10.1, −5.9, −8.5, −7.7, −4.6, and −6.1 kcal/mol, respectively. With 3.03, 3.07, 2.99, 3.06, 2.98, 302, 2.95, and 3.07 Å distances, all tested compounds connect over H-donor, excepting ligand, which binds through H-acceptor [
97,
98]. Our molecules have high binding energies, indicating that may affect the metabolic changes of this protein. (Mn(L) H
2O Cl) Cl. 3H
2O had the strongest binding while having the lowest energy (−10.10 kcal/mol) [
99,
100].
Ghasemi et al. (2021) synthesized two novel mixed-ligand complexes by using a NN’O type antisymmetric tridentate ligand as the major ligand with pyridine (1) or 2,2 -dimethyl-4,4—bithiazole (BTZ) (2) as co-ligands. All crystal structures were identified with various analytical and spectroscopic techniques. Docking of macromolecules was employed to investigate how well the tested compounds interacted with 6LU7 as the receptor protein. Comparing the relative energy levels (ΔG binding) displayed that complex (2) was more efficient than (1) and favipiravir as a reference drug. Such binding energies were high quality (2) > (1) > (SB) > (BTZ). This shows the surface of the protein receptor interacted between both the tested complexes and favipiravir with 6LU7. Three hydrogen bonding relating a few of the NH
2 group’s H atoms, and also the H15 and H16 to ASN142, and GLU166, were discovered at 1.91, 2.12, and 2.06 in complex (1). C–H bonding was also discovered at 3.24 with C pyridine and ASN142. At 5.24, alkyl hydrophobic connecting in between phenyl ring from of the aldehyde molecule and MET165 was discovered, as is another alkyl hydrophobic connection to HIS163. The interaction between Br and ASP 187 was estimated to be 3.53. At 2.69, 2.51, 2.22, 2.20, 2.13, and 2.10, six hydrogen bondings among NH
2, H18, and H19 to ASN142, GLU166, and BTZ were identified in complex (2). Around 4.88 a d 5.73 Å, two π -sulfur bondings to HIS163 and HIS172 were discovered, as well as two π -alkyl polar bondings to HIS41 at 4.51 and 5.38 Å. Five hydrogen bondings among oxygen and hydrogen ligand atoms to SYS156, LYS100, ASP33 (two), and N of ligand have been discovered at 3.73, 1.77, 2.00, 1.69, and 1.77 Å. In the (SB) ligand at 2.99 Å, one π -lone pair-bonding in between the ligand ring and TYR101 was identified. At 4.24 and 4.75 Å, one alkyl Hyd and π -alkyl Hyd to LYS102 were discovered. The C–H bond between the N atom and VAL18 was determined to be 3.78 Å in the (BTZ) ligand. At 2.37 Å, one π -donor-H bond was discovered between such a ring of ligand and GLY71. A single π -lone pair connection to MET17 was discovered. At 3.49 and 5.40 Å, two alkyl Hyd. bonding here between C atom and ALA70 and VAL18 were discovered. At 4.71 and 4.77 Å, two π-alkyl Hyd. links to ALA70 and TRP31 were discovered. All of the analyzed materials [
101,
102] had a visual analysis of molecular docking, which involved drugs–receptor H. connection contacts, 2D-ligand–receptor hydrogen bond connection, and receptor side surfaces hydrogen bond connection. These tested complexes have greater negative binding energies than other tested Cu-complexes described in the literature [
103], which might be related to the and BTZ moieties and acceptor groups of the aldehyde [
104].
El-Lateef et al. (2022) prepared several salphen compounds and their Fe
3+ studied chelates were synthesized besides fully characterized through several spectroscopic and physicochemical tools, such as CHN, IR, NMR, UV-Vis spectra, vibration spectra, magnetic moment, and TGA. Additionally, the modifications of the tested structures were studied by theoretical calculations. The relationship among all results displays that CPBS and PDBS ligands interact as tetra-dentate binding through deprotonated azomethine (two) and two-(OH) groups to form octahedral complexes with Fe
3+ ions. The free binding energies of tested CPBS and PDBS ligands and complexes with the coronavirus receptor main protein (PDB ID: 6lu7) were reported toward being −6.9, −4.6, −18.0, and −13.3, and kcal/mol for CPBS, PDBS, (FeCPBS (H
2O) NO
3), and (FePDBS (H
2O) NO
3), respectively, as revealed in (
Table 3) [
105]. The further negative the binding energy, the greater the interaction. So, the connections are in the demand of PDBS < CPBS < (FePDBS (H
2O) NO
3) < (FeCPBS(H
2O)NO
3).
Figure 3 and
Figure 4 show 2D and 3D plots of CPBS, PDBS, (FeCPBS (H
2O) NO
3), and (FePDBS H
2O)NO
3) associations with the binding site of the coronavirus receptor protein (PDB ID: 6lu7).
Mohamed et al. (2021) used a tridentate ligand, 4-((1-(5-acetyl-2,4-dihydroxyphenyl)ethylidene)amino)-1,5-dimethyl 2-phenyl-1H-pyrazol-3(2H)-one, to form mononuclear chelates of Cr(III), Cu(II), Fe(III), Zn(II), Ni(II), and Mn(II). The tridentate coordination behavior of the ligand was demonstrated in all complexes from an azomethine N
2 and O
2 atoms, as indicated by IR spectrum analyses. The M to L ratio was confirmed to be 1:1, as indicated by elemental analysis and described by spectroscopic methods. For molecules and pharmaceuticals employed in prescriptions for the management of COVID-19, computer estimations of antimicrobial activities were made [
105,
106]. The target of the docking studies tests was to simulate the binding possibilities for H
2L ligand and its chelates to the crystalline structure of the SARS CoV-2 major protein in association with inhibition UAW247 (6XBH). Shows the least many free binding energy of both ligand and their complexes estimated through 6XBH. The interaction models of H
2L and their related complexes against protein were represented in 3D interaction maps. It was determined that all of the drugs tested interacted via hydrogen bonds (
Table 4). Ligand, Fe(III), Cr(III), and Ni(II) complexes interact via H-donor to (Glu 166) glutamic acid ad (Met 49) methionine, whereas Cu(II), Mn(II), Zn(II), and Cd(II) complexes bind via H-acceptor to glutamine (Gln 189), glycine (Gly 143), and Glu 166, respectively, with 2.88, 3.38, 3.77, 2.86, 3.31, 3.08, 3.06, and 3.34 Å distances, respectively [
106,
107]. The interaction energies indicated that the Cr(III) complex has a much more constant connection and low activation energy. Then the binding energy for the novel coronavirus demonstrates substantial interactions with its targets. This could explain the formation of hydrogen bonds between Met165 and Gln166 amino acid residues. The studied complex is protected by pi-H connections with Glu189 receptors [
108,
109,
110,
111].
Alshammari et al. (2021) prepared a chain of N-substituted-2-quinolonylacetohydrazides with the goal of testing their effectiveness against SARS-CoV-2. Mass spectra, NMR, IR, and CHN all verified the structures of the observed molecules. Most of the drugs studied had a good binding affinity to the SARS-CoV-2 major protease (M
pro), which was equivalent to Remdesivir, according to molecular docking calculations. Molecular modeling simulations have been done using Autodock software (version 4.2.6) to identify the binding mechanism and sensitivities of the prepared molecules (4a–k) of the SARS-CoV-2 main protein (Mpro). (
Table 5) shows the estimated docking values and the interacting properties of compounds 4a–k with Mpro. (
Table 5) shows the estimated docking tests and the binding properties of molecules 4a–k through Mpro receptor. The computed docking scores in
Table 5 revealed that compounds 4a–k had good interaction binding for M
pro, through values ranging from 7.5 to 9.7 kcal/mol. Conversely, MOE modeling of Remdesivir gave interacting energy of −8.5 kcal/mol by M
pro (
Table 5). Assessment of the interacting abilities exposed which molecule 4d exhibited the highest interacting abilities to M
pro with results of −9.7 kcal/mol. The great interacting energies of molecule 4d towards M
pro may be qualified to generate four important hydrogen bonds with measurements of 2.07, 2.22, 2.02, and 1.83 Å with GLU166, SER144, LEU141, and HIS163 amino acids, respectively. 2D LigPlus models of contacts of molecules 4a–k interacted with vital protein sites of SARS-CoV-2 M
pro. Overall, the molecular modeling data might test the theory that the synthesized molecules can be effective SARS-CoV-2 M
pro inhibitors [
112].
Ali et al. (2021) prepared Cu chelates of two ligands, hydroxychloroquine, and chloroquine and described through X-ray diffraction, electronic spectra, and TGA, and these were screened using an in silico technique. More strategies and available techniques are often used in a study of the treatment and its target molecule. As an example of analyzing potential drug candidates before entering the laboratory, we use theoretical investigations on previously described biologically active complex compounds. On some COVID-19-related proteins, we performed DFT calculation studies for structure elucidation and modification, as well as molecular docking experiments. According to our findings, drug development really should be computer-aided. [
113] In comparison to the parent medication, the data showed that both polar and non-polar groups within metal chelates were balanced. The metallodrug interactions here with the receptor of the viral ADP-ribose-1 monophosphatase enzyme are promoted by this structural equilibrium. As a result, the enzyme’s activity is blocked, which is the intended effect of COVID-19 infection prevention [
114].
Almalki et al. (2021) used in silico analysis molecular docking to describe the production of Cu (II) and Co (II) thiazole chelates as well as the activity enhancers for contact with COVID-19 [
115]. We also used CHN, electronic, and spectral studies to confirm the preparation of binuclear ligand complexes (Cu(II), Ni(II), Co(II), and Zn(II)). Molecular modeling was used to screen the generated medicinal metal complexes for biological assessments. Refat et al. (2021) showed that Ni(II) complex has higher binding effectiveness for COVID-19 protease (6LU7), according to molecular docking experiments [
116]. In addition, they developed a novel COVID-19 medications method based on simulation investigations, including transition metal (Fe, Cr, and Ni) loaded fullerenes–favipiravir chelates [
117].
Hecel et al. (2020) showed that Zn(II) is an immune enhancer and a virus regulator (RNA-dependent RNA polymerase inhibitor). The impact of internal Zn(II) content on both RNA and DNA viruses, mainly that affect the respiratory system, including such pi coronaviruses, and respiratory syncytial virus and influenza have been described in several investigations. One of the modes of action for chloroquine and hydroxychloroquine’s efficacy in treating COVID-19 is its ability to act as a Zn(II) ionophore, delivering more Zn(II) into the cells. Consequently, Zn(II) is one of the attractive and viable options for a suppressive effect impact on the SARS-CoV-2 replicative cycle amongst transition metals [
118]. Poupaert et al. (2020) showed that various research papers back up Zn(II) as the gold standard for COVID-19 medications. The studies used quantum mechanics molecular simulations to demonstrate Zn
2+ interactions at the molecular level. They suggest that first- and second-generation medicaments, like azithromycin (Zn
++-antibiotic combination), could be used to treat COVID-19 [
119].
M. C. Vlasiou and K. S. Pafti (2021) used one of the most widely structure-based design techniques, MOE-docking. We selected to do studies with various binding proteins to coronavirus, as described in the overview, including at least one blood transport protein so the ligand was being tested also as a therapeutic target for coronavirus. Docking tests revealed that the VXn codified receptor had the binding interactions score for BSA protein of any ligand, followed by Xn which has a binding free energy of −10.872 kcal/mol. It forms a hydrogen bridge with TYR147, ASP108, ILE455, and PRO146 (four H bonds) and interacts with BSA by van der Waals forces, which has a binding free energy of −9.323 kcal/mol. The compound Vbicah has a binding energy of −10.888 kcal/mol for the N-terminal RNA-binding domain of the SARS-CoV-2 nucleocapsid glycoprotein (6YI3), followed by VXn with −10.523kcal/mol. The maximum energy contact of an Xn with 6YI3 is connected to the amino acid glutamate, whereas the highest energy interaction of VXn through the same protein is associated with the intracellular domain. Remarkably, both Vbdeah and Vbicah exciting force with the 6YI3 amino acid asparagine. Proceeding with SARS-CoV-2 RNA-dependent polymerase (6M71), beginning through compound that has the greatest reactivity for protein, Vbicah(−10.266 kcal/mol) > Vtocdea (−9.891 kcal/mol) > Vtocdpa (−9.706 kcal/mol) > Xn (−9.603 kcal/mol) > VXn (−9.364 kcal/mol) > Vbdea (−8.647 kcal/mol). The % interaction energies of the enzyme’s active site 6YI3 on the tested compounds are shown in (
Figure 5). The maximum energy interface of an Xn compound for 6YI3 is connected to the protein glutamine, whereas the greatest energy interaction of VXn with the same protein is associated with the amino acid arginine. Remarkably, both Vbdeah and Vbicah interact better with the 6YI3 amino acid asparagine. Finally, in terms of complex formation with COVID-19 basic protease (6M03), Vtocdea and VXn are among the greatest compounds. Vtocdea interacts with other organisms via hydrogen bonding. Vtocdea connects with both (SER255, and PRO322) via hydrogen bonds, while VXn connects with the proteins (GLN110, and THR111) via hydrogen bonds. The electrostatic interactions had a limited impact on such connections. Surface charges are only visible between Vtocdea and 6M03 (−0.029 Kcal/mol), Vtocdpa and BSA (−0.162 Kcal/mol), Vtocdpa and 6M71 (−0.294 Kcal/mol), Vtocdea and BSA (0.042 Kcal/mol), and Vtocdpa and 6M03 (−0.018 Kcal/mol). The electrostatic attraction of Vtocdea and Vtocdpa is consistent with previous research [
113,
120], demonstrating that these compounds have anti-cancer potential by disrupting the charge transfer series in mitochondria. Considering the theoretical research, we believe that compounds like Vtocdea and VXn are promising candidates for in vitro and in vivo testing of the COVID-19 virus [
121].
R. K. Hussein and H. M. Elkhair (2021) presented various efforts made to identify therapeutic prescriptions for treating this virus. As a result of the absence of a significant publication for such a suitable therapy to treat COVID-19, the use of zinc chelates as a supplement to chloroquine/hydroxychloroquine in the treatment of COVID-19, the investigations show highlighted molecular docking and molecular dynamics methodology as effective tools for developing effective treatments to control the COVID-19 pandemic. Some zinc-CQ/HCQ complexes have still been identified to target COVID-19’s Mpro basic protease. According to molecular docking simulations, Zn(QC)Cl
2(H
2O) and Zn(HQC)Cl
2(H
2O) had the lowest binding affinity (−7.70 Kcal/mol and −7.54), respectively. The hydrogen bonds detected have been in the greatest range of H Bond group distances. The analysis of binding site contacts indicated that Zn(QC)Cl
2(H
2O) forms 3 hydrogen bonds with the basic protease receptor, but Zn(HQC)Cl
2(H
2O) forms 8 hydrogen bonds with the basic protease receptor. The observed study of RMSD and RMSF pathways in MOE dynamics simulations revealed the remarkable binding mode and physical properties of Mpro-Zn(CQ/HCQ) Cl
2H
2O chelates. It is possible to deduce that Zn (CQ/HCQ) Cl
2H
2O has a high potential as a COVID-19 Mpro inhibitor, as represented in
Figure 6 [
122].
9. In Vitro and In Vivo Potency of Metallo-Compounds against SARS-CoV-2
Yuan et al. (2020) employed metal chelates as antibiotic agents in the past. Unfortunately, their antiviral properties have not been well investigated. Bismuth medicines and similar compounds have been exposed to have strong antivirus effectiveness against SARS-CoV [
123] in previous experiments. On the basis of these findings, we chose six metal compounds: two bismuth(iii) (Bi(TPP) (TPP, tetraphenylporphyrinate) and two bismuth(iii) citrate-based drugs (colloidal bismuth subcitrate (CBS) and RBC) and Bi(TPyP) (TPyP, tetra(4-pyridyl) porphy. As represented in (
Figure S2). In monkey kidney Vero E6 cells, the (CC50) 50% cytotoxic activity concentrations of the tested complexes were calculated to be 2243 ± 43 μM for RBC, 3254 ± 21 μM for CBS, >400 M for both Bi(TPyP) and Bi(TPP), 13.5 ± 1.8 μM for Au(PEt3) Cl, and 14.2 ± 1.3 μM for auranofin. Because of their auspiciously lower cytotoxicity compared to Au(i)-based therapies, the four bismuth(ii) molecules were picked for more examination on potential CC50 rates in human colorectal Caco-2 cells, relieving similar CC50 data rates greater from 400 to 3740 M. As represented in
Figure S3. The ½ efficient dosages (EC50) of the bismuth(iii) complexes were evaluated at little µm values and then were observed to be 2.3 ± 0.5 µM in RBC and 4.6 ± 0.4 µM and CBS, 7.5 ± 0.9 µM for Bi(TPyP), and 3.9 ± 1.2 µM for Bi(TPP). Interestingly, adding all four bismuth(ii) complexes to Caco-2 cells and Vero E6 at 1 h after infection (h.p.i.) reduced viral genome levels in a daily dosage mode (
Figure S3). RBC and CBS had more strong anti-coronavirus activity than Bi(TPyP) and Bi(TPP) at non-toxic doses, as demonstrated by the optimum ~2-log versus 1-log dosage decreased in Vero E6 cell suspension
Figure S3a–d, ~3-log towards ~2-log decrease in Caco-2 cell suspension
Figure S3e–h, and ~4-log towards ~3-log decrease in Vero E6 and Caco-2 cell lines medium
Figure S3i–l,m–p. Interestingly, Bi(iii) drugs/complexes significantly reduced SARS-CoV-2, also demonstrated through significantly lower virus nucleocapsid production in drug-treated control cells in comparison to DMSO-treated cells
Figure S4a–f. Toward found out that stages of the SARS-CoV-2 transcription and replication were disrupted through drug complexes, which used a period test, which involved handling virus-infected cells for each complex at various intervals, then assessing viral titer after 9 h post-infection, once the first round of virus replication was observable in the culturing medium.
Figure S4g,h. Bi(TPyP) was found to considerably inhibit virus reproduction during co-incubation of cells, but no action was seen after Bi(TPyP) was sustained once virus assembly, that Bi(TPyP) may interact with SARS-CoV-2 attachment to the surface of the cell. When RBC was added during the pre-incubation step, it had no effect on virus replication, but when it was added during the co-incubation and post-entry periods, it reduced viral loads by ~2 log, implying that RBC is a multi-target therapy that acts during virus entrance or initial occurrences when virus replication. The inhibition of virus entry by RBC and Bi(TPyP) was verified through a system that gave a virus infection test, which revealed that RBC and Bi(TPyP) reduced the percentage of virus entrance by ~45% and 53%, respectively (
Figure S4i). Both CBS and Bi(TPP) work correctly only at the post-entry stage. Briefly, SARS-CoV-2 shows a sensitive effect on therapy with bismuth(ii)-based medicines [
124].
Grazia Martina et al. (2021) estimated the antiviral potency of the tested molecules towards coronavirus, a DYRA, association with cells infection in the appearance of repeated therapy dilutions, has been employed as earlier defined, towards slight variations. The bithiazole chemotype is a promising substrate for the design of BSAAs by targeting the host kinase machinery (PI4KIII) or certain targets, as seen here with SARS-CoV-2. As detailed, the bithiazole chemotype can be modified to produce multitarget equivalents that act on many targets involved in various diseases (for example, cystic fibrosis and associated viral infections). The findings in this research may serve to assist the development of tailored bithiazoles with increased broad-spectrum antiviral efficacy by effectively inhibiting various targets involved in virus propagation. More investigations upon the class of BSAAs are being carried out to analyze their mechanism of action and antiviral potential [
125].
Vicenti et al. (2020) found that anti-Zika (ZIKV) and anti-DENV virus medication development can be accelerated by using practical cell-based assays. Using a pan-flaviviral monoclonal antibody that recognizes a conserved envelope domain, we designed an immunodetection assay (IA). The final procedure incorporates a direct virus yield reduction assay (YRA) in the human Huh7 cell line, followed by supernatant transfer to a separate Huh7 culture to assess late antiviral effects. The IC
50 values for sofosbuvir and ribavirin determined in the secondary YRA were repeatable and identical to those obtained in the direct YRA and plaque reduction assay (PRA). Celgosivir was efficacious against DENV only in the second YRA (IC
50 11.0 1.0 µM) and PRA (IC
50 10.1 1.1 µM), consistent with the suggested mechanism of late action. The assay format solves significant limitations of the gold standard PRA by allowing continuous investigation of potential antiviral drugs against multiple viruses and provides initial data on early versus late antiviral activity. 25,000 Calu-3, pre-seeded in the 96-well plates, were incubated by repeated various concentrations of both tested molecules and cultivated at 37 °C through 5% CO
2. The pathogen sample was introduced at a dose of 250 PFU/well, then after 1 h of adsorbed, the media was withdrawn, and new various concentrations of each tested compound were applied to the cultures. An immune detection assay (IA) was used to measure antimicrobial activities on cell monolayers after a 48-h incubation at 37 °C with 5% CO
2 [
126]. The IA consisted of cell fixation and inhibiting the synthesis, proceeded by 1-h culturing through a specific SARS Ribonucleoprotein. Protein antibody (Milano, cat, Italy, Novus, AP201054), diluted 1:1000 in blocking buffer (PBS) enclosing. After cleaning, structures were treated over 1 h with a monoclonal HRP-coupled anti-mouse IgG tested molecule diluted 1:5000 with delaying buffer (NB7570, Italy, Novus Bio, Milano). After cell wash, the 3, 30, 5, 50-Tetramethylbenzidine substrate (Sigma Aldrich, Darmstadt, Germany) was applied to each well, followed by one liter of sulfuric acid 0.5 M to terminate the reaction. The Absorption Coefficient Module of the GloMax
® exploring Multimode fiber 96-well plate Reader was used to evaluate absorbance around 450 nm optical density (OD450) (Promega). Molecules that have been inactive in DYRA were, subsequently, tested in SYRA to see if they had any late antiviral effects. SYRA was carried out, employing a methodology for SARS-CoV-2 that had previously been described [
126].
Cirri et al. (2021) carried a homogenates microbes created in DYRA were extracted out in each test, reduced, and utilized to transmit 10,000 VERO E6 cells that had been pre-seeded. The viral supernatants were extracted after 1 h of adsorption, new media was applied, and the cell was cultured for 24 h at 37 °C per 5% CO
2. The IA was carried out upon cellular membranes, as previously reported. The ½ inhibition dose (IC50) was estimated using GraphPad Prism software program (version 6.01) and non-linear linear regressions of the dosage curves. Remdesivir has employed a standard drug for SARS-CoV-2 for each test. Carrying the virus and non-infected cells with medicines have been applied to compute virus assembly rates of 100% and 0%, respectively. The proportion of CC50 and IC50 was used to estimate the Sensitivity Index (SI). The upper the SI result, the greater the safety and efficacy which would be noticed while in vivo behavior [
127].
L. R. Bernstein and L. Zhang (2020) provided a culture of African green monkey kidney Vero E6 cells, the American Type Culture Collection (ATCC, CRL-1586), which were verified using a microscopic morphological study and development edge detection. The mycoplasma-free culture was kept in minimum Eagle’s Medium containing (MEM) enriched to 10% foetal bovine serum (FBS) at 37 °C in a temperature-controlled container containing 5% CO
2. A single isolate of SARS-CoV-2 (GISAID EPI ISL 402124 h; CoV-19/Wuhan/WIV04/2019) was cultured in Vero E6 cells and virus intensity was measured using an immunofluorescence test using a 50% tissue culture infective dosage (TCID50). All of the infection studies were carried out in a laboratory with a biosafety level of 3 (BSL-3). Well before Vero E6 cells (5 × 10
4 cells per well) were pre-treated with various concentrations of GaM for 1 h before being infected with the virus at a multiple of infection (MOI) of 0.01. The cells were then cultivated with fresh GaM-containing media after the resulting virus-drug mixture was removed. A volume of 80 mL cell supernatant was obtained from each well 24 h after infection for minimal state opposite polymerase series reaction detection of antibodies RNA (qRT-PCR). All of the tests are carried out in three. Prism software was used to conduct the statistical analysis. GaM inhibited viral replication dose-dependently, with an EC50 (concentration inhibiting viral replication by 50%) of around 14 mM (CI 95% 8.9–22.8 mM) and r214 0.88 for Goodness of Fit and Slope of 0.6 (CI 95% 0.42–0.77) (
Figure S5). At doses up to 200 mM, the gallium maltolate was not hazardous to the cells (the function of cells at 200 mM was 109(3)% compared with the control cells) (
Figure S6). [
128] The EC50 data was estimated by an inhibitor vs. balanced response, movable slope equation:
The repurposing of therapeutic applications metal-based treatments is one example of a straightforward technique. The optimal candidate should be able to combine good antiviral effectiveness with low toxicity. For that purpose, we recommend a quick assessment of auranofin (Ridaura), abbreviated as AF. AF is a medication that was licensed by the FDA in 1985 to treat rheumatoid arthritis. It works by modulating the human immune system. AF has reduced toxicities and is fit for human use. The therapeutic efficacy of AF, which is almost certainly multi-target, is still unknown. However, there is general agreement that the primary target should be thioredoxin reductase 1, resulting in disruption of the basic dehydrogenases pathways, regulation of intracellular redox state, and reactive oxygen species (ROS) induction. Even though ribosome would be an important target, it is nonetheless crucial [
129,
130,
131]. AF has sparked a lot of interest in recent years due to its versatility and ability to be reprocessed for a variety of medicinal applications, including anti-bacterial, anti-cancer, and anti-parasitic agents [
129]. The significant antiretroviral activity was also observed, prompting AF to enter medical testing as an endocrine therapy drug. Its value was noticing which AF was the initiate to be more efficient than hydroxychloroquine and chloroquine in relating to many processes involved in virus-related generation, incubation, and reactivation, as well as in reducing the infected reservoir, in case of HIV infection [
132]. AF, like tocilizumab, has been shown to interfere with interleukin [
133] signaling by blocking JAK1 and STAT3 phosphorylation, inhibiting a small number of proteases, or to interact preferentially to free cysteine in proteins, such as metabolic enzymes [
133]. We endorse the off-label fast estimation of AF in COVID-19 individuals based on these grounds. Surprisingly, an article about AF and COVID-19 was found in the public field through the analysis process of this text [
134].
Scientists T. Marzo and L. Messori (2020) claimed that at a modest µm dose, AF effectively suppresses SARS-CoV-2 multiplication in living organisms, resulting in a 95% decrease in virus RNA. Furthermore, AF was instituted to significantly inhibit the SARS-COV-2-induced cytokines in living cells, which is consistent with prior findings. These clarifications back up our hypothesis, indicating that AF, with its favorable and multitarget mechanism, could be a beneficial medication for limiting the SARS-CoV-2 virus and treating related pneumonia. We suggest that further in vitro analysis of a larger screen of typical metal-based treatment comprising a multiplicity of metal centers, such as Ru and Bi, should be explored and pursued in addition to the definite recommendation of auranofin and related Au complexes. We might reasonably expect that in a few occurrences, such uncommon and distinct metal centers will have significant and beneficial impacts on such novel pathogens that are impossible to predict in advance [
135].
Rothan et al. (2020) examined auranofin’s antiviral efficacy towards coronavirus as well its influence on disease inflammatory response in living organisms. We treated Huh7 cells towards SARS-CoV-2 (USA-WA1/2020) on 2 h at a multitude of invasion (MOI) of 1, and then added 4 M auranofin. As a control, 0.1% DMSO was employed (the solvent was utilized to synthesize drug stock). Huh7 cells were chosen for our investigation because they are very sensitive to SARS-CoV-2 replication. At 24 and 48 h following infection, Culturing supernatants and protein aggregates were obtained. RT-PCR was used to measure virus RNA copies by two different targets, another for the antiviral N1 domain and the other for the viral N
2 region [
136,
137]. Auranofin treatment of cells resulted in a 70% reduction in virus RNA infiltrates relative to DMSO 24 h following the invasion, as seen in (
Figure 7). When compared to DMSO, the virus RNA in the cell medium was reduced by 85% after 48 h. Similarly, as opposed to DMSO-treated cultures, the levels of intracellular viral RNA in auranofin-treated organisms reduced by 85% around 1 d and 95% around 2 d. Both primer sets had essentially identical findings. We then used a plaque test to determine viral titers in the cell culture supernatant. At 48 h after infection, auranofin treatment greatly decreased SARS-CoV-2 infectivity titers in cell culture supernatants (
Figure 7). We used repeated dilutions of auranofin to treat SARS-COV-2 infected Huh7 cells in order to identify the optimum dose of auranofin that suppresses 50% of transcription and replication (EC50). After 2 d from treatment, target RNA was estimated through RT-PCR from supernatants and cell lysates. Non-linear estimation techniques were used to plot the data in graphs (GraphPad software). In auranofin-treated cells, viral RNA activity was decreased in a dose-dependent manner after 48 h. The EC50 values of auranofin therapy against Huh7 cells diseased with SARS-CoV-2 are shown in (
Figure 8). At an EC50 of roughly 1.4 M, auranofin reduced viral multiplication in infected cells. It is worth noting that in comparison to formerly described results on anti-virus activity of hydroxychloroquine, chloroquine, and remdesvir towards SARS-CoV-2 in vitro, we utilized around 20 to 100 times larger pathogen dose (MOI of 1) to attack the cells in our study [
138,
139]. We evaluated the degree of essential proteins in auranofin and DMSO-infected cells at 1 and 2 d after treatment to see how auranofin affected the inflammatory response during SARS-CoV-2 infection [
137]. In Huh7 cells, SARS-CoV-2 transmission causes a substantial upregulation of IL-6, TNF, IL-1, and NF-kB (
Figure 9). In Huh7 cells, auranofin therapy effectively diminished the release of SARS-CoV-2-infected protein. In comparison with mock-infected tissues, SARS-CoV-2 complex combination in a 200-fold spike in IL-6 gene transcription 2 d after transmission. Auranofin-treated cells, on either, only had a 2-fold rise in IL-6 expression. At 2 d after transmission, TNF levels have risen 90-fold on DMSO-preserved, but not in the auranofin-treated organisms, there has been no change in the transcription of IL-1 or NF-kB [
134].