SARS-CoV emerged from a zoonotic reservoir and couple with cytokine, chemokine, and Interferon Stimulated Gene (ISG) responses in patients provided evidence that SARS-CoV pathogenesis is partially controlled by innate immune signaling [25]. Dysregulation of inflammatory cytokines such as tumor necrosis factor (TNF)‐α, interleukin (IL)‐1β, IL‐6, IL‐10] and polymorphonuclear neutrophil (PMN); and chemokine IL‐8 are responsible for the indication of viral infection, which may be due to activation of transcription factor nuclear factor (NF)‐κB, activator protein (AP)‐1 and activating factor‐2 (ATF‐2) [26-29]. This is also observed in SARS-CoV-2. Thus, identifying specific molecules to destroy the immune evasion of SARS-CoV-2 is very crucial.
Scoping or systematic reviews of preclinical have served as a robust form of knowledge synthesis to evaluate transparently experimental therapies for more than a decade [30]. Our findings from the meta-analysis indicated the effects of the selected compounds in the reduction of the virus titer. The treatment efficacy is represented by the midpoint and the length of each segment in the forest plot while the diamond shape showed the combined effect (Figure. 3). Further, results from meta-analysis, in vivo and molecular docking studies corroborate three compounds, which are EIDD-2801, GS-5734 and amodiaquine. The histopathology and immunological findings of all the compounds against the SARS-CoV virus are shown in Table 1.
The understanding of the similarity between the 3CLpro main protease of SAR-CoV and COVID-19 which is very important in the viral life cycle has highlighted the protease as an attractive potential target for anti-coronavirus drug development [31-33]. In addition, they both have catalytic dyad composed of conserved residues His41 and Cys145. Considering the in vivo activity, of the investigated compounds, their molecular affinity in the binding pocket of COVID-19 main protease was evaluated. Only, seven out of the compounds showed good binding energy. They bind with COVID-19 protease via multiple hydrogen bonding and hydrophobic contacts. Residues Phe140, 185 Leu141, His163, Met165, Glu166, and His172 form hydrophobic interactions, whilst Asn142, Gly143, and Cys145 form intermolecular H-bond with the ligands. The binding mode indicates useful clues to the possible molecular basis of these compounds.
Table 1: Results obtained in infected mice treated with the selected compounds [19-24]
Authors
|
Treatment
|
Lung virus titer
|
Histopathology and immunological findings
|
Bernard et al. 2006a
|
Nelfinavir
|
Weakly effective
In effective
|
-
|
|
β-D-N4-hydroxycytidine
|
-
|
|
Calpain inhibitor VI
|
Weakly effective
|
-
|
|
Pentoxifylline
|
Weakly effective
|
-
|
|
Chloroquine
|
Weakly effective
|
-
|
|
Amodiaquine
|
Weakly effective
|
-
|
|
3-Deazaneplanocin
|
Ineffective
|
-
|
Bernard et al. 2006b
|
Mycophenolic acid
|
Ineffective
|
Increase in viral replication
|
|
Ribavirin
EICAR
Mizoribine
|
Ineffective
Ineffective
Ineffective
|
Inhibit macrophage production of pro-inflammatory cytokines and Th2 cytokines while preserving Th1 cytokine.
Increase in viral replication
Increase in viral replication
|
Barnard et al. 2008
|
Promazine
|
Ineffective
|
Reduction in RANTES expression promoting neutrophil migration to the SARS-CoV infection site. Promazine and its prodrugs should not be considered potential therapies for SARS infections.
|
Craig et.al 2009
|
Ribavirin
|
Weakly effective
|
Allowed continual stimulation of the inflammatory response, which may contribute to pathogenesis. Decreased IL-6 expression
|
|
Dipeptidyl glutaminyl fluoromethylketone (EP128533)
|
Ineffective
|
Neither effective in preventing death nor reduced the disease signs measured. No evidence of toxicity and lack of activity may be likely due to bioavailability. May be a foundation for development of an effective antiviral prodrug that is soluble and bioavailable
|
Sheahan et al. 2017
|
Remdesivir (GS-5734)
|
Effective
|
Therapeutic administration of GS-5734 reduced disease and suppressed replication of SARS-COV during an ongoing infection. Improve pulmonary function, reduce viral loads, with no development in disease outcomes, thus not clinically beneficial.
|
Sheahan et al. 2020
|
β -D-N4-hydroxycytidine-5′-isopropyl ester (EIDD-2801)
|
Effective
|
Significantly reduced lung viral loads and improved pulmonary function and weight loss.
|
As shown in Figure 5, the oxygen atom of the primary hydroxyl functional group of nucleoside unit EIDD-1931 (B.E = 6.5 kcal/mol) is H-bonded to Cys145 with bond distance of 2.59 Å and bond angle of 127.7 and 100.5o, respectively, while, the hydrogen atom is H-bonded Ser144 and Le141 (bond distance = 2.73 and 2.68 Å; bond angle = 129.1, 114.7, 127.7 and 100.5o, respectively). The conserved amino acid His41 is sandwiched between the pyrimidinone ring and the hydroxy amino group via H-bonding and hydrophobic interaction.
The interactions of 3-Deazaneplanocin (B.E = 6.5 kcal/mol) with the COVID-19 main protease is described in detail in Figure 2. Interestingly, the cyclopentene unit of this compound interacts with Cys145 via H-bonding, whereas, an oxygen atom of the primary hydroxy functional group on cyclopentene ring forms three notable hydrogen bonds with a backbone amino acid residue Gly143 and 145 having the bond distance of 2.59 and 2.25 Å respectively; the hydrogen atom formed H-bond interactions with Ser144 and Leu 141, these interactions were also observed in the docked complex of EP128533. Meanwhile, the amino acid Thr26 is interpolated in between NH2 and NH functional group of imidazo[4,5-c]pyridine moiety. (Figure. 6)
The oxygen atoms on the carbonyl group of fluoromethyl ketone and dimethylamine (EP128533, B.E = 6.9 kcal/mol), dimethylammine forms a H-bond with the side-chain nitrogen of Gly143 and Thr26, while the F atom interacts with Cys145 and Gly143 via another H-bond. The benzyl group in the unit formed interaction with the sulphur of Met165. In addition, the carbamate group fits into a small hydrophobic pocket, which is favorable for π-σ and alkyl interaction between the methylene as well as methyl group and amino acid His41 and Met49 respectively, whereas the amine group H-bonded with Gln189. The increase in the interaction of the inhibitor in the active pocket of COVID-19 protease can be rationalized to be the reason for the increase in the binding affinity of the inhibitor. (Figure.7)
The landscape of amodiaquine docked complex (Fig. 8) was similar to that of EIDD-1931, in the sense that the chloroquinoline group was inserted in the hydrophobic pocket consisting of Met165 and His41. The amino acid Cys145 was H-bonded to the benzyl ring as well as the oxygen atom of the tertiary hydroxyl functional group in the unit. Besides, the hydrogen atom formed H-bond as shown in Figure 4: the first H-bond is from Leu141 (bond distance = 1.90 Å), the second is from Ser144 (bond distance = 2.53 Å). The presence of these two interactions in the binding pocket helps in positioning and stabilizing the docked complex of amodiaquine.
Furthermore, the interactions of nelfinavir (B.E = 8.2 kcal/mol) in the binding pocket of COVID-19 protease are shown in Figure 9. The phenylthiol was deeply inserted within the hydrophobic pocket and interacts to formed: π-π –T stacking contact with amino acid His41, π – alkyl with Met49 and π-sulpur with Met165. Moreover, the –CH3 group on hydroxymethylbenzamide interact with His41 and Leu27 via hydrophobic, while the carbonyl oxygen atom involved in the H-bond network with Gly143. Moreover, Asn142 formed H-bonding with an amine and hydroxyl functional group of isoquinoline carboxamide. It was noted that nelflavir has the highest binding affinity (8.2 kcal·mol-1) which correlates with its highest interaction in the binding pocket of COVID-19 protease, hence confirm its highest stabilization compared to other inhibitors but this lack correlation with meta-analysis and in vivo result, hence the modification of this compound may effectively reduce the virus replication. (Figure. 9)
Interestingly, the predicted binding mode of remdesivir (B.E = 7.5 kcal/mol) in Figure 10 showed interaction with the catalytic dyad. The phenyl moiety formed π-sulphur interaction with catalytic amino acid His41 and π-cation with Met49. All the amines group formed H-bond with amino acid Thr45, Thr25 and Gln149 (b.d = 1.84, 2.34 and 2.53 Å respectively), hydroxyl functional group which is in close proximity with Cys145 accept H-bond from Thr26 (2.38 Å). In addition, the methyl group of methyl pentyl acetate formed hydrophobic interaction with imidazoles of His163 and His172.
β-D-N4-hydroxycytidine-5′-isopropyl ester (EIDD-2801), which is also a nucleoside analog, not only showed high binding but also better interaction compared to β-D-N4-hydroxycytidine. Interestingly, the carbonyl oxygen of EIDD-2801(B.E = 7.2 kcal/mol) accepts H-bond from the backbone of amino acid Gly143, Cys145, and Ser144. The presence of ester in this compound rationalized the increased inhibitory potency of this compound against SARS-CoV-2. The amino acid, Thr190 was H-bonded with hydroxylamine group, meanwhile, the pyrimidinone ring formed hydrophobic interaction with Met165. Further, the oxygen atom in the nucleoside ring, as well as the primary hydroxy functional group interacts with Glu166 and Asn142 via H-bonding. (Figure. 10).