(A) Dose response curves for the custom inhibitor Z-AVLD-FMK in a viral infectivity assay in Vero E6 cells. Cell viability values represent the area of cells stained with DRAQ7 DNA dye. Viral infection values were measured as the area of viral plaques visualised by immunofluorescent staining of viral N protein. Data is normalised to DMSO only treated control wells (100%) and plotted as mean and SD, n = 3. EC50 values were determined by non-linear regression and values are given as mean ± SEM. (B) Representative images for the SARS-CoV-2 viral infectivity assay in Vero E6 cells, for Z-AVLD-FMK. Representative wells show Vero E6 cells stained for DNA using DRAQ7 (top panel, labelled cells), and viral N protein immunofluorescence (lower panel, labelled virus).