Fig. 4: GRL-1720 and 5h exert potent activity against SARS-CoV-2WK-521 but shikonin, nelfinavir, and atazanavir, reportedly active against SARS-CoV-2, failed to block the infection by SARS-CoV-2WK-521.
VeroE6 cells were exposed to SARS-CoV-2WK-521 for 1 h, the viruses were washed out, and the virus-exposed cells were cultured in the presence or absence of various concentrations of each test compound for 3 days. Immunocytochemistry was then performed using an IgG fraction prepared from COVID-19-convalescent plasma as a primary antibody. Viral breakthrough was observed in the cells cultured in the presence of remdesivir at 100 µM, while in the cells cultured with 100 µM GRL-1720 and 5h, no such virus breakthrough was found. Arrows denote the cells infected by the virus in the presence of high concentrations of remdesivir. Such breakthrough cells (stained in green) are often seen in clusters. SARS-CoV-2 antigens, F-actin, and nuclei are stained in green, red, and blue, respectively. Representative images from three independently conducted experiments are shown. Scale bar = 100 µm.
