Fig. 3: Dose–response relationships of selected antiviral compounds and synergy with remdesivir.

a–c, Vero E6 cells were pre-treated for 16 h with increasing concentrations of the indicated compound and then infected with SARS-CoV-2 at a MOI of 0.1. Twenty-four hours after infection, cells were fixed and analysed by immunofluorescence imaging. For each condition, the percentage of infection was calculated as the ratio of the number of infected cells stained for coronavirus NP to number of cells stained with DAPI. a, Heat map representing normalized infection of the indicated 21 compounds in a dose–response analysis, on a scale from 0 to 1, depicting the average of n = 5 independent experiments. Compounds are grouped in predicted functional clusters. For MDL 28170 and 8-(2-chlorostyryl)caffeine, 0.85 μM was used instead of 1 μM at the second highest dose. Extrapolated EC₅₀ values are listed on the left of the heat map. Asterisks indicate compounds for which EC₅₀ values were calculated on the basis of observed values at the highest concentrations. b, Dose–response analysis of the most potent compounds in a, showing infectivity (black), cell number (red) and cellular EC₅₀ values (see also Extended Data Fig. 6). c, Compounds at indicated doses were combined with 800 nM remdesivir or a negative control (DMSO), and antiviral dose–response relationships were determined in Vero E6 cells using the experimental conditions described in b. Remdesivir alone inhibited viral infection by 20% (black dotted line). The predicted additive combinatorial activity of remdesvir and the indicated compound (see Methods) is denoted by a red dotted line. Observed activity of remdesivir in combination with the indicated compound is shown with a solid red line, and shaded portions of graph indicate the difference between predicted and observed combinatorial activities. EC₅₀ for compound alone (black), and predicted (pink) and observed (red) EC₅₀ for the combined treatment are presented. Data are normalized to mean values for DMSO-treated wells and represent mean ± s.e.m. of n = 3 (apilimod, MDL 28170, Z LVG CHN2, VBY-825 and SL-11128) (b, c) or n = 5 (ONO 5334, clofazimine, DS-6930 and R82913) (b) independent experiments.