Design, synthesis, and biological evaluation of first-in-class indomethacin-based PROTACs degrading SARS-CoV-2 main protease and with broad-spectrum antiviral activity

To date, Proteolysis Targeting Chimera (PROTAC) technology has been successfully applied to mediate proteasomal-induced degradation of several pharmaceutical targets mainly related to oncology, immune disorders, and neurodegenerative diseases. On the other hand, its exploitation in the field of antiviral drug discovery is still in its infancy. Recently, we described two indomethacin (INM)-based PROTACs displaying broad-spectrum antiviral activity against coronaviruses. Here, we report the design, synthesis, and characterization of a novel series of INM-based PROTACs that recruit either Von-Hippel Lindau (VHL) or cereblon (CRBN) E3 ligases. The panel of INM-based PROTACs was also enlarged by varying the linker moiety. The antiviral activity resulted very susceptible to this modification, particularly for PROTACs hijacking VHL as E3 ligase, with one piperazine-based compound (PROTAC 6) showing potent anti-SARS-CoV-2 activity in infected human lung cells. Interestingly, degradation assays in both uninfected and virus-infected cells with the most promising PROTACs emerged so far (PROTACs 5 and 6) demonstrated that INM-PROTACs do not degrade human PGES-2 protein, as initially hypothesized, but induce the concentration-dependent degradation of SARS-CoV-2 main protease (Mpro) both in Mpro-transfected and in SARS-CoV-2-infected cells. Importantly, thanks to the target degradation, INM-PROTACs exhibited a considerable enhancement in antiviral activity with respect to indomethacin, with EC50 values in the low-micromolar/nanomolar range. Finally, kinetic solubility as well as metabolic and chemical stability were measured for PROTACs 5 and 6. Altogether, the identification of INM-based PROTACs as the first class of SARS-CoV-2 Mpro degraders demonstrating activity also in SARS-CoV-2-infected cells represents a significant advance in the development of effective, broad-spectrum anti-coronavirus strategies.

Insect protease inhibitors; promising inhibitory compounds against SARS-CoV-2 main protease

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has adversely affected global health since its emergence in 2019. The lack of effective treatments prompted worldwide efforts to immediately develop therapeutic strategies against COVID-19. The main protease (Mpro) of SARS-CoV-2 plays a crucial role in viral replication, and therefore it serves as an attractive target for COVID-19-specific drug development. Due to the richness and diversity of insect protease inhibitors, we docked SARS-CoV-2 Mpro onto 25 publicly accessible insect-derived protease inhibitors using the ClusPro server, and the regions with high inhibitory potentials against Mpro were used to design peptides. Interactions of these inhibitory peptides with Mpro were further assessed by two directed docking programs, AutoDock and Haddock. AutoDock analysis predicted the highest binding energy (-9.39 kcal/mol) and the lowest inhibition constant (130 nM) for the peptide 1KJ0-7 derived from SGCI (Schistocerca gregaria chymotrypsin inhibitor). On the other hand, Haddock analysis resulted in the discovery of a different peptide designated 2ERW-9 from infestin, a serine protease inhibitor of Triatoma infestans, with the best docking score (-131), binding energy (-11.7 kcal/mol), and dissociation constant (2.6E-09 M) for Mpro. Furthermore, using molecular dynamic simulations, 1KJ0-7 and 2ERW-9 were demonstrated to form stable complexes with Mpro. The peptides also showed suitable drug-likeness properties compared to commercially available drugs based on Lipinski's rule. Our findings present two peptides with possible protease inhibitor activities against Mpro and further demonstrate the potential of insect-derived peptides and computer-aided methods for drug discovery.

Molecular mechanism of anti-SARS-CoV2 activity of Ashwagandha-derived withanolides

COVID-19 caused by SARS-CoV-2 corona virus has become a global pandemic. In the absence of drugs and vaccine, and premises of time, efforts and cost required for their development, natural resources such as herbs are anticipated to provide some help and may also offer a promising resource for drug development. Here, we have investigated the therapeutic prospective of Ashwagandha for the COVID-19 pandemic. Nine withanolides were tested in silico for their potential to target and inhibit (i) cell surface receptor protein (TMPRSS2) that is required for entry of virus to host cells and (ii) viral protein (the main protease M^pro) that is essential for virus replication. We report that the withanolides possess capacity to inhibit the activity of TMPRSS2 and M^pro. Furthermore, withanolide-treated cells showed downregulation of TMPRSS2 expression and inhibition of SARS-CoV-2 replication in vitro, suggesting that Ashwagandha may provide a useful resource for COVID-19 treatment.

Screening of natural compounds from Cyperus rotundus Linn against SARS-CoV-2 main protease (Mpro): An integrated computational approach

Coronavirus disease 2019 (COVID-19) is a viral respiratory disease that has been spreading across the globe. The World Health Organization (WHO) declared it as a public health emergency. The treatment of COVID-19 has been hampered due to the lack of effective therapeutic efforts. Main Protease (M^pro) is a key enzyme in the viral replication cycle and its non-specificity to human protease makes it a potential drug target. Cyperus rotundus Linn, which belongs to the Cyperaceae family, is a traditional herbal medicine that has been widely studied for its antiviral properties. In this study, a computational approach was used to screen natural compounds from C. rotundus Linn using BIOVIA Discovery Suite and novel potential molecules against M^pro of SARS-CoV-2 were predicted. Molecular docking was performed using LibDock protocol and selected ligands were further subjected to docking analysis by CDOCKER. The docking scores of the selected ligands were compared with standard antiretroviral drugs such as lopinavir and ritonavir to assess their binding potentials. Interaction pharmacophore analysis was then performed for the compounds exhibiting good binding scores to evaluate their protein–ligand interactions. The selected protein–ligand complexes were subjected to molecular dynamics simulation for 50 ns. Results of binding free energy analysis revealed that two compounds—β-amyrin and stigmasta-5,22-dien-3-ol—exhibited the best binding interactions and stability. Finally, absorption, distribution, metabolism, excretion, and toxicity (ADMET) studies were performed to understand the pharmacokinetic properties and safety profile of the compounds. The overall results indicate that the phytochemicals from Cyperus rotundus Linn, namely β-amyrin and stigmasta-5,22-dien-3-ol, can be screened as potential inhibitors of SARS-CoV-2 M^pro.

2-Pyridone natural products as inhibitors of SARS-CoV-2 main protease

The disease, COVID-19, is caused by the severe acute respiratory coronavirus 2 (SARS-CoV-2) for which there is currently no treatment. The SARS-CoV-2 main protease (M^pro) is an important enzyme for viral replication. Small molecules that inhibit this protease could lead to an effective COVID-19 treatment. The 2-pyridone scaffold was previously identified as a possible key pharmacophore to inhibit SARS-CoV-2 M^pro. A search for natural, antimicrobial products with the 2-pyridone moiety was undertaken herein, and their calculated potency as inhibitors of SARS-CoV-2 M^pro was investigated. Thirty-three natural products containing the 2-pyridone scaffold were identified from the literature. An in silico methodology using AutoDock was employed to predict the binding energies and inhibition constants (K_i values) for each 2-pyridone-containing compound with SARS-CoV-2 M^pro. This consisted of molecular optimization of the 2-pyridone compound, docking of the compound with a crystal structure of SARS-CoV-2 M^pro, and evaluation of the predicted interactions and ligand-enzyme conformations. All compounds investigated bound to the active site of SARS-CoV-2 M^pro, close to the catalytic dyad (His-41 and Cys-145). Thirteen molecules had predicted K_i values <1 μM. Glu-166 formed a key hydrogen bond in the majority of the predicted complexes, while Met-165 had some involvement in the complex binding as a close contact to the ligand. Prominent 2-pyridone compounds were further evaluated for their ADMET properties. This work has identified 2-pyridone natural products with calculated potent inhibitory activity against SARS-CoV-2 M^pro and with desirable drug-like properties, which may lead to the rapid discovery of a treatment for COVID-19.

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2-pyridone-scaffold is an inhibitory pharmacophore for SARS-CoV-2 M^pro.

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Thirty-three natural, antimicrobial products identified with 2-pyridone moiety.

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All 2-pyridone natural products bind to active site of SARS-CoV-2 M^proin silico.

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Thirteen molecules found to have potent inhibitory activity against SARS-CoV-2 M^pro.

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Inhibition of SARS-CoV-2 by natural 2-pyridones may lead to treatment of COVID-19.

Reckoning a fungal metabolite, Pyranonigrin A as a potential Main protease (Mpro) inhibitor of novel SARS-CoV-2 virus identified using docking and molecular dynamics simulation

The novel SARS-CoV-2 is the etiological agent causing the Coronavirus disease 2019 (COVID-19), which continues to become an inevitable pandemic outbreak. Over a short span of time, the structures of therapeutic target proteins for SARS-CoV-2 were identified based on the homology modelled structure of similar SARS-CoV transmission of 2003. Since the onset of the disease, the research community has been looking for a potential drug lead. Out of all the known resolved structures related to SARS-CoV, Main protease (Mpro) is considered an attractive anti-viral drug target on the grounds of its role in viral replication and probable non-interactive competency to bind to any viral host protein. To the best of our knowledge, till date only one compound has been identified and tested in-vivo as a potent inhibitor of Mpro protein, addressed as N3 (PubChem Compound CID: 6323191) and is known to bind irreversibly to Mpro suppressing its activity. Using computational approach, we intend to identify a probable natural fungal metabolite to interact and inhibit Mpro. After screening various small molecules for molecular docking and dynamics simulation, we propose Pyranonigrin A, a secondary fungal metabolite to possess potent inhibitory potential against the Main protease (Mpro) expressed in SARS-CoV-2 virus.