4.3.2.2. In Vitro Studies
Parallel to in silico studies, in vitro studies, have also been performed to identify potent phytochemical-based anti-SARS-CoV-2 compounds, however, very few phytochemicals have been considered forin vitro analysis. When Homoharringtonine, a plant alkaloid with high antiviral properties, was tested in vitro for its anti-SARS-CoV-2 activity, exhibited SARS-CoV-2 inhibition at an EC50 of 2.10 uM. In addition, Emetine, an isoquinoline derivative that is approved for the treatment of amoebiasis, was also shown to successfully inhibit SARS-CoV-2 at an EC50 of around 0.5 uM. Taking their observations further, the same study tried an approach of combinational drug treatment using Remdesivir and Emetine, and they found that Remdesivir at 6.25 uM and in combination with Emetine at 0.195 uM exhibited 64.9% inhibition of the viral yield . Their study opens avenues for further work to be carried out in the field of combinational therapy using phytoconstituents, which will lead to better clinical outcomes. Another recent in vitro study was conducted specifically to evaluate the anti-SARS-CoV-2 activity of Lycorine, Emetine, and Cephaeline, demonstrated excellent COVID-19 inhibition. However, owing to their biological toxicity, further research needs to be conducted to modify these compounds to make them safer for consumption .
Berberine has already been identified to have good antiviral activity against SARS-CoV-2 through in silico studies, and this is also supported by in vitro studies carried out on Vero E6 cells. The study highlights the potent antiviral activity of Berberine at an EC50 of 9.1 uM, and a continued analysis in infected epithelial cells also reported good viral inhibition at EC50 of 10.7 uM. This study also throws light on the fact Berberine acts on early as well as later stages of COVID-19 infection, and thus represents an excellent candidate for furtherin vivo and clinical studies. Resveratrol, a type of stilbenoid belonging to polyphenols, with abundant medical benefits, was identified as a powerful SARS-CoV-2 inhibitor. A recent biological assay performed on Vero E6 cells demonstrated a reduction in SARS-CoV-2 replication by 3 logs at 25μM, with an EC50 of 4.48 uM. However, the bioavailability of Resveratrol poses a difficulty, which can be overcome if the drug can be administered through the nasotracheal route, and further research followed by clinical trials are required to ascertain the safety and efficiency of Resveratrol.
A series of in vitro studies performed to test the efficiency of Glycyrrhizin which is a triterpene saponin, identified it to be a good inhibitor of Mpro (SARS-CoV2 main viral protease), The antiviral active levels of the drug were within the range of that tolerated by humans, indicating that with further in vivo and clinical validation, Glycyrrhizin could also be one of the potential phytocompound that can be used to treat COVID-19. An in vitro study reported that EGCG expressed potent antiviral activity against Nsp15 of SARS-CoV-2, thus showing that EGCG containing compounds could be excellent inhibitors of viral replication. The study also suggests various methods of administration of EGCG in the form of mouthwashes or nasal washes. EGCG is potent even at very low concentrations. Therefore, this phytocompound is pointed out as a powerful lead for further investigation. The method of in vitro evaluation and analysis of the biological activity of potential drug molecules is shown in Figure 5 .