Acid sphingomyelinase (ASM) and COVID-19: A review of the potential use of ASM inhibitors against SARS-CoV-2.

In the last 2 years, different pharmacological agents have been indicated as potential inhibitors of SARS-CoV-2 in vitro. Specifically, drugs termed as functional inhibitors of acid sphingomyelinase (FIASMAs) have proved to inhibit the SARS-CoV-2 replication using different types of cells. Those therapeutic agents share several chemical structure characteristics and some well-known representatives are fluoxetine, escitalopram, fluvoxamine, and others. Most of the FIASMAs are primarily used as effective therapeutic agents to treat different pathologies, therefore, they are natural drug candidates for repositioning strategy. In this review, we summarize the two main proposed mechanisms mediating acid sphingomyelinase (ASM) inhibition and how they can explain the inhibition of SARS-CoV-2 replication by FIASMAs. The first mechanism implies a disruption in the lysosomal pH fall as the endosome-lysosome moves toward the interior of the cell. In fact, changes in cholesterol levels in endosome-lysosome membranes, which are associated with ASM inhibition is thought to be mediated by lysosomal proton pump (ATP-ase) inactivation. The second mechanism involves the formation of an extracellular ceramide-rich domain, which is blocked by FIASMAs. The ceramide-rich domains are believed to facilitate the SARS-CoV-2 entrance into the host cells.

In silico analysis of the antidepressant fluoxetine and similar drugs as inhibitors of the human protein acid sphingomyelinase: a related SARS-CoV-2 inhibition pathway.

Acid Sphingomyelinase (ASM) is a human phosphodiesterase that catalyzes the metabolism of sphingomyelin (SM) to ceramide and phosphocholine. ASM is involved in the plasma membrane cell repair and is associated with the lysosomal inner lipid membrane by nonbonding interactions. The disruption of those interaction would result in ASM release into the lysosomal lumen and consequent degradation of its structure. Furthermore, SARS-CoV-2 infection has been linked with ASM activation and with a ceramide domain formation in the outer leaflet of the plasma membrane that is thought to be crucial for the viral particles recognition by the host cells. In this study, we have explored in silico the behavior of fluoxetine and related drugs as potential inhibitors of ASM. Theoretically, these drugs would be able to overpass lysosomal membrane and reach the interactions that sustain ASM structure, breaking them and inhibiting the ASM. The analyses of docking data indicated that fluoxetine allocated mainly in the N-terminal saposin domain via nonbonding interactions, mostly of hydrophobic nature. Similar results were obtained for venlafaxine, citalopram, atomoxetine, nisoxetine and fluoxetine's main metabolite norfluoxetine. In conclusion, it was observed that the saposin allocation may be a good indicative of the drugs inhibition mechanism, once this domain is responsible for the binding of ASM to lysosomal membrane and some of those drugs have previously been reported to inhibit the phosphodiesterase by releasing its structure in the lysosomal lumen. Our MD data also provides some insight about natural ligand C18 sphingomyelin conformations on saposin.Communicated by Ramaswamy H. Sarma.

In Silico Analysis of the Antidepressant Fluoxetine and Related Drugs at SARS-CoV-2 Main Protease (Mpro) and Papain-like Protease (PLpro).

BACKGROUND: SARS-CoV-2 main protease (Mpro or 3CLpro) and papain-like protease (PLpro) are common viral targets for repurposed drugs to combat COVID-19 disease. Recently, several antidepressants (such as fluoxetine, venlafaxine and citalopram) belonging to the Selective Serotonin Reuptake Inhibitors (SSRIs) and the Serotonin-Norepinephrine Reuptake Inhibitors (SNRI) classes have been shown to in vitro inhibit viral replication. AIM: Investigate a possible action of fluoxetine and derivatives on SARS-CoV-2 protease sites. METHODS: Molecular docking was performed using AutoDock Vina. Both protease structures and different drug conformations were used to explore the possibility of SARS-CoV-2 inhibition on a Mpro or PLpro related pathway. Drug structures were obtained by optimization with the Avogadro software and MOPAC using the PM6 method. Results were analysed on Discovery Studio Visualizer. RESULTS: The results indicated that Mpro interacted in a thermodynamically favorable way with fluoxetine, venlafaxine, citalopram, atomoxetine, nisoxetine and norfluoxetine in the region of the active site, whether PLpro conformers did not come close to the active site. CONCLUSION: In an in silico perspective, it is likely that the SSRIs and other anti-depressants could interact with Mpro and cause the enzyme to malfunction. Unfortunately, the same drugs did not present similar results on PLpro crystal, therefore, no inhibition is expected in an in vitro trial. Anyway, in vitro tests are necessary for a better understanding of the links between SARS-CoV-2 proteases and antidepressants.

Reactivity and binding mode of disulfiram, its metabolites, and derivatives in SARS-CoV-2 PLpro: insights from computational chemistry studies.

The papain-like protease (PLpro) from SARS-CoV-2 is an important target for the development of antivirals against COVID-19. The safe drug disulfiram (DSF) presents antiviral activity inhibiting PLpro in vitro, and it is under clinical trial studies, indicating to be a promising anti-COVID-19 drug. In this work, we aimed to understand the mechanism of PLpro inhibition by DSF and verify if DSF metabolites and derivatives could be potential inhibitors too. Molecular docking, DFT, and ADMET techniques were applied. The carbamoylation of the active site cysteine residue by DSF metabolite (DETC-MeSO) is kinetically and thermodynamically favorable (ΔG‡ = 3.15 and ΔG = - 12.10 kcal mol-1, respectively). Our results strongly suggest that the sulfoxide metabolites from DSF are promising covalent inhibitors of PLpro and should be tested in in vitro and in vivo assays to confirm their antiviral action.

In silico studies of Mpro and PLpro from SARS-CoV-2 and a new class of cephalosporin drugs containing 1,2,4-thiadiazole.

The SARS-CoV-2 proteases Mpro and PLpro are important targets for the development of antivirals against COVID-19. The functional group 1,2,4-thiadiazole has been indicated to inhibit cysteinyl proteases, such as papain and cathepsins. Of note, the 1,2,4-thiadiazole moiety is found in a new class of cephalosporin FDA-approved antibiotics: ceftaroline fosamil, ceftobiprole, and ceftobiprole medocaril. Here we investigated the interaction of these new antibiotics and their main metabolites with the SARS-CoV-2 proteases by molecular docking, molecular dynamics (MD), and density functional theory (DFT) calculations. Our results indicated the PLpro enzyme as a better in silico target for the new antibacterial cephalosporins. The results with ceftaroline fosamil and the dephosphorylate metabolite compounds should be tested as potential inhibitor of PLpro, Mpro, and SARS-CoV-2 replication in vitro. In addition, the data here reported can help in the design of new potential drugs against COVID-19 by exploiting the S atom reactivity in the 1,2,4-thiadiazole moiety. Supplementary Information: The online version contains supplementary material available at 10.1007/s11224-022-02036-5.

In silico Studies on the Interaction between Mpro and PLpro From SARS-CoV-2 and Ebselen, its Metabolites and Derivatives.

The COVID-19 pandemic caused by the SARS-CoV-2 has mobilized scientific attention in search of a treatment. The cysteine-proteases, main protease (Mpro) and papain-like protease (PLpro) are important targets for antiviral drugs. In this work, we simulate the interactions between the Mpro and PLpro with Ebselen, its metabolites and derivatives with the aim of finding molecules that can potentially inhibit these enzymes. The docking data demonstrate that there are two main interactions between the thiol (-SH) group of Cys (from the protease active sites) and the electrophilic centers of the organoselenium molecules, i. e. the interaction with the carbonyl group (O=C… SH) and the interaction with the Se moiety (Se… SH). Both interactions may lead to an adduct formation and enzyme inhibition. Density Functional Theory (DFT) calculations with Ebselen indicate that the energetics of the thiol nucleophilic attack is more favorable on Se than on the carbonyl group, which is in accordance with experimental data (Jin et al. Nature, 2020, 582, 289-293). Therefore, organoselenium molecules should be further explored as inhibitors of the SARS-CoV-2 proteases. Furthermore, we suggest that some metabolites of Ebselen (e. g. Ebselen diselenide and methylebselenoxide) and derivatives ethaselen and ebsulfur should be tested in vitro as inhibitors of virus replication and its proteases.