Researchers are studying the antiviral potential of acriflavine against SARS-CoV-2

Acriflavine has traditionally been used as a topical antiseptic, although it has recently been incorporated as an antiviral agent at low doses, possibly by stimulating interferon production. In a new study it was recently uploaded to the bioRxiv* preprint server, the use of the drug to SARS-CoV-2 infection is being investigated, showing widespread activity towards a range of other betacoronaviruses.

Detecting drug directions against SARS-CoV-2

Replacement of known drugs may be of paramount importance in coronary heart disease pandemic 2019 (COVID-19). Because they have already studied toxic images in detail, they have the potential to be used quickly without adhering to the typically long clinical development timeline. In an effort to find appropriate drug drivers, the group identified several essential and highly conserved proteins encoded by the SARS-CoV-2 genome. The papase-like protease cysteine ​​(PL^PRO) belongs to unstructured protein 3, and is essential for virus protein maturation while it is identified to reduce host interferon response, making it an attractive drug target.

High-throughput screening method towards detection of PL protectors^PRO recruited, exhibiting a protease assay with a fluorescent tag to nearly 6,000 known and approved small molecular compounds. At this stage, acriflavine has already been observed to generate the greatest inhibition of the fertilizers tested, and the effect of the drug on enzymatic activity has been studied using acriflavine recording with fluorescent against natural PL^PRO, providing IC₅₀ of 1.66 µM and 1.46 µM in each test, respectively. Specificity of the drug towards PL^PRO it was also shown in comparison to a structure and function-related protease, which exhibited inhibition of less than 50% at high concentrations of 100 µM.

More characters with NMR and X-ray crystals showed the way acriflavine binds to PL^PRO, without affecting the overall coherence of the protein and thus tend to bind in a local spatial location. Two molecules of dechlorinated acriflavine (proflavine) are capable of stacking inside a PL binding pocket^PRO, promotes a major conformal change characterized by rotation and movement of the adjacent BL2 loop, a reserved area around coronaviruses which, when distorted in this way, prevents entry into the enzyme active site. Commercial acriflavine contains a mixture of structure-like molecules, some of which carry the named chloride ion, and others by methylation. Several other binding sites were found that contributed to the inhibition of enzyme uptake, both in more hydrophilic and hydrophobic pockets that were thus used by the more or less polar forms of the drug. The group noted that it was a much more potent inhibitor than pure proflavine, suggesting that the total distortion from multiple binding sites on PL^PRO that’s best disrupted protein activity.

Testing for antiviral activity

To further test the efficacy and toxicity of the drug against SARS-CoV-2 infection in vitro evaluations were performed in human cells. Cell cytotoxicity A 50% density was found in the range of about 3–12 µM over the various exposed human cells, and IC₅₀ values ​​towards SARS-CoV-2 were around 50 nM. Applying the drug at later intervals was equally effective in virus inhibition, further supporting that inhibition at the stage of virus reproduction and does not affect cell entry.

Human airway with SARS-CoV-2 infection ex vivo a model then compared acriflavine with remdesivir, a broad-spectrum antiviral, showing much greater inhibition at concentrations as low as 500 nM compared with 10 µM of the latter. Two additional betacoronaviruses SARS-CoV-2 – MERS-CoV and HCoV-OC43 – as well as two alphacoronaviruses, were then tested against acriflavine. All betacoronaviruses showed comparable IC₅₀ values ​​to SARS-CoV-2, while the drug was completely ineffective in slowing the replication of alphacoronaviruses.

Finally, a murine model was used to compare acriflavine with remdesivir, administered in equal doses over 6 days, with SARS-CoV-2 challenge introduced on the latter. RT-qPCR subsequently showed that the virus was present in the lungs and brain of the untreated body, common due to the high frequency of the ACE2 receptor at these sites. Remdesivir reduced the viral load in the brain by about 2 orders of magnitude, while acriflavine did that by about 5 fold. Viral loading in the lungs was not significantly reduced by any means, although oral administration of acriflavine was more effective than intramuscular injection.

Acriflavine could be used as a useful broad-spectrum betacoronavirus drug despite a short retention time in vivo. The group points out that the fragrant ring structure that allows the drug to stack within the PL^PRO pocket binding and inhibition of protein activity are generally associated with DNA interaction and mutagenesis, so there may be some concerns regarding long-term use. That said, that history has not yet revealed concerns about restricted use in humans.

* Important message

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding clinical practice / health-related behaviors, or be treated as fixed information.