Potential of 6'‑hydroxy justicidin B from Justicia procumbens as a therapeutic agent against coronavirus disease 2019

Since the onset of the coronavirus disease 2019 (COVID-19) pandemic, remarkable advances have been made in vaccine development to reduce mortality. However, therapeutic interventions for COVID-19 are comparatively limited despite these intensive efforts. Furthermore, the rapid mutation capability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a characteristic of its RNA structure, has led to the emergence of multiple variants, necessitating a shift from a predominantly vaccine-centric approach to one that encompasses therapeutic strategies. 6'-Hydroxy justicidin B (6'-HJB), an arylnaphthalene lignan isolated from Justicia procumbens, a traditional Chinese medicine, is known for its antiviral properties.

The aim of the present study was to assess the effectiveness and safety of 6'-HJB against SARS-CoV-2 in order to determine its potential as a therapeutic agent against COVID-19.

The efficacy of 6'-HJB was evaluated both in vitro using Vero and Calu-3 cell lines and in vivo using ferrets. The safety assessment included toxicokinetics, safety pharmacology, and Good Laboratory Practice (GLP)-compliant toxicity evaluations following single- and repeated-dose toxicity studies in dogs.

The anti-SARS-CoV-2 efficacy of 6'-HJB was evaluated through dose-response curve (DRC) analysis using immunofluorescence; 6'-HJB demonstrated superior inhibition of SARS-CoV-2 growth and lower cytotoxicity than remdesivir. In SARS-CoV-2-infected ferret, 6'-HJB showed efficacy comparable to that of the positive control, Truvada. Further GLP toxicity studies corroborated the safety profile of 6'-HJB. Single-dose and 4-week repeated oral toxicity studies in Beagle dogs demonstrated minimal harmful effects at the highest dosages. The lethal dose of 6'-HJB exceeded 2,000 mg kg^-1 in Beagle dogs. Toxicokinetic and GLP safety pharmacology studies demonstrated no adverse effects of 6'-HJB on metabolic processes, respiratory or central nervous systems, or cardiac functions.

This research highlights both the antiviral efficacy and safety profile of 6'-HJB, underscoring its potential as a novel COVID-19 treatment option. The potential of 6'-HJB was demonstrated using modern scientific methodologies and standards.