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The rapid outbreak of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) caused the ongoing coronavirus disease 2019 (COVID-19) pandemic has claimed more than 6.5 million lives worldwide. Although the majority of the SARS-CoV-2 infected individuals experienced mild to moderate symptoms and did not require any special treatment, 20% of the infected population suffered from severe infection, and 5% required intensive care.
Study: The FDA-approved drug Auranofin has a dual inhibitory effect on SARS-CoV-2 entry and NF-κB signaling. Image Credit: NIAID
Severely infected COVID-19 patients suffer multiple organ damage due to inflammatory processes. Apart from the lungs, other organs that are affected by COVID-19 are the liver, heart, and kidney. A strong cytokine release or “cytokine storm” induced by a viral infection and/or secondary infection is the primary cause of death due to COVID-19.
The entry of SARS-CoV-2 in human cells is facilitated by the interaction of the spike (S) protein of the virus with heparan sulfate (HS) and the cleavage of S protein at the S1-S2 junction by Furin. Additionally, the cellular serine protease TMPRSS2 also plays an important role in the viral invasion of the host cell. These enzymes permit their binding to another host factor, namely, the membrane protein neuropilin-1 (NRP1), and induce the merging of cell membranes. Alternatively, the virus can also penetrate host cells via an endocytic pathway within the endosomal-lysosomal compartments, which is processed by the lysosomal Cathepsin L.
Since the beginning of the COVID-19 pandemic, scientists and policymakers have worked at an unprecedented speed to develop effective pharmaceutical and non-pharmaceutical measures to contain the pandemic. Remdesivir, a nucleotide analog targeting the viral RNA-dependent RNA polymerase (RdRp), was recommended for SARS-CoV-2 infected patients who required oxygen support. However, recently, the World Health Organization has advised against the use of this drug to treat COVID-19.
Several COVID-19 antiviral treatments, including Dexamethasone, Lagevrio, and Paxlovid, were found to be effective against the ancestral SARS-CoV-2 strain. However, the effectiveness of these drugs against recently emerged variants has not been evaluated. In addition to these antiviral treatments, monoclonal antibodies have also been used to treat COVID-19 patients. NF-kB inhibitors prevent the incidence of high inflammation caused by the immune responses associated with the high cytokine release due to COVID-19.
In a new ISCIENCE journal study, scientists identified an FDA-approved NF-κB inhibitor, Auranofin, which can also control inflammation. In this study, the FDA-approved drug library, Prestwick Chemical Library, was used for the high throughput screening based on the inhibition of cytokine-induced supramolecular complexes associated with NF-kB activation.
The novelty of the methodology is associated with searching for compounds that can inhibit NF-kB activation events during the early phase of COVID-19, transcriptional activation mediated by NF-kB and upstream of the IKKs activation.
A total of sixty drug candidates were identified after the initial screening process that possessed a high confidence score via statistical analysis. Among these candidates, Phenoxybenzamine, Thimerosal, Parthenolide, and Auranofin were able to inhibit NF-kB361 dependent transcription and development of NF-kB activating complexes.
However, Auranofin, a gold salt, exhibited strong anti-inflammatory properties with fewer side effects. In addition, this compound interfered with NF-kB activity by inhibiting IκB kinase (IKK).
The gold ion associated with Auranofin interacts with enzymes containing sulfur- or nitrogen groups, particularly with the thiol or imidazole groups. Auranofin interacts with a sulfhydryl group of IKK and inhibits upstream enzymatic activity. This drug was approved 33 years ago by the FDA for treating rheumatoid arthritis and is currently undergoing clinical evaluation for its efficacy for cancer treatment.
In 2020, Auranofin was proposed for COVID-19 treatment, and its capacity to inhibit SARS-CoV-2 replication was reported. Additionally, an inhibitory effect on inflammatory cytokine expression was also observed in various in vitro experiments. Interestingly, oral administration of this drug in the Syrian hamster model for therapeutic analysis showed a decrease in lung tissue damage, cell infiltration, inflammation, and IL-6 production.
Compared to all compounds identified via the high throughput screening method, Auranofin was the only compound that could protect cells from SARS-CoV-2 virus invasion. It decreased the number of replication complexes in vitro. Mechanistically, Auranofin blocked the raft-dependent endocytic pathway and enhanced ACE2 mobility at the cell surface, which led to suppressed penetration of SARS-CoV-2 into host cells. In addition, the authors hypothesized that Auranofin disrupts membrane lipids organization, which impacts cellular signaling pathways associated with endocytosis, NF-kB, and ACE2 receptor diffusion.
Proteomic analysis has revealed that Auranofin targets CHORDC1 (Cysteine and Histidine-Rich Domain-Containing 1), TXNRD1 (Thioredoxin Reductase 1), and NFKB2 (Nuclear Factor kappa B p100 subunit). Additionally, this compound also inhibits proteasome-associated deubiquitinases UCHL5 (Ubiquitin C-Terminal Hydrolase L5) and USP14 (Ubiquitin Specific Peptidase 14).
More research based on 3D pulmonary organoid cultures or animal models is required to validate the results and indicate the true therapeutic benefits of Auranofin. In addition, clinical studies using a human cohort are necessary to demonstrate the efficacy of Auranofin against COVID-19 fully.