Evaluating the <i>in Vitro</i> Efficacy of Quassinoids from <i>Eurycoma longifolia</i> and <i>Eurycoma harmandiana</i> against Common Cold Human Coronavirus OC43 and SARS-CoV-2 Using In-Cell Enzyme-Linked Immunosorbent Assay.
Choonong R, Ruangdachsuwan S, Churod T, Palabodeewat S, Punyahathaikul S, Juntarapornchai S, Ketsuwan K, Komaikul J, Masrinoul P, Kitisripanya T, Juengwatanatrakul T, Yusakul G, Kanchanapoom T, Putalun W.
Coronavirus disease-2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, has become a pandemic and public health crisis. SARS-CoV-2 and the seasonal common cold coronavirus (HCoV-OC43) belong to the beta genus of human coronaviruses (HCoVs). In-cell ELISA assays were performed using HCoV-OC43 and SARS-CoV-2 and evaluated the antiviral activity of herbal plants. <i>Eurycoma longifolia</i> (EL) and <i>Eurycoma harmandiana</i> (EH) roots (antipyretic properties) and their constituent quassinoids, especially chaparrinone and eurycomalactone, showed potent anti-HCoV-OC43 and SARS-CoV-2 activities, and the low IC<sub>50</sub> values of the mentioned constituents were observed in the range of 0.32-0.51 μM. Eurycomanone and 13β,21-dihydroeurycomanone may contribute to the antiviral activity of EL, whereas chaparrinone is the major and active antiviral constituent of EH root. The content of quassinoids, β<i>-</i>carboline, and canthin-6-one alkaloids and the cytotoxicity profile of EL and EH extracts were varied regarding extraction solvents. The boiled water and 50% EtOH extractions of both plants were less toxic than those with 95% EtOH as the extraction solvent. Our research suggests that quassinoids, which come from EL and EH roots and are anti-coronavirus compounds, are potential treatment candidates for COVID-19 and merit further <i>in vivo</i> investigations.