Antiviral Activity of Medicinal Plant Extracts and Against SARS-CoV-2.

Natural products possess a wide range of biological and biochemical potentials, with plant-derived compounds being significant sources for discovering new drugs. In this study, extracts of and prepared with different solvents were tested for their antiviral activity against the original SARS-CoV-2 Wuhan strain and its variants using plaque assay, quantitative real time RT-PCR, and immunofluorescence assay (IFA). Our results showed that at their maximum non-toxic concentrations, Vitex-Dichloromethane (DCM) and Macaranga extracts significantly inhibited SARS-CoV-2 Wuhan strain growth in Vero E6 cells, showing a 5-log reduction in plaque assay and confirmed by IFA. Meanwhile, Vitex-Hexane showed moderate activity with a 2-log decrease. The inhibition was shown in a dose-dependent manner. The antiviral efficacy of these extracts was further demonstrated against various SARS-CoV-2 variants including Alpha, Beta, Delta, and Omicron. Both Vitex-DCM and Macaranga showed strong virucidal activity. In addition, Vitex-DCM and Macaranga inhibited the transcriptional activity of purified SARS-CoV-2 RdRp, indicating that RdRp inhibition may contribute to viral suppression as shown at the post-infection stage. Furthermore, combining Vitex-DCM or Macaranga with remdesivir showed a synergistic effect against SARS-CoV-2. These results suggest that and extracts are promising candidates for anti-SARS-CoV-2 treatments. Their synergy with remdesivir also underscores the potential of drug combinations in fighting SARS-CoV-2 and preventing the emergence of mutant variants.