Fig. 1: Drugs inhibiting SARS-CoV-2 spike-induced syncytia.

a, Post-mortem histological analysis of lungs of patients with COVID-19 showing multinucleated syncytia. Original magnification, ×40. Further characterization of these patients has previously been reported¹⁵. b, Formation of syncytia after 24 h expression of spike in Vero cells. Nuclei in white; cell contours in red using wheat-germ agglutinin (WGA); spike protein in green. Scale bars, 200 μm. c, SIA screening. S, spike. d, Image analysis workflow; syncytia were defined as cells showing a cluster of nuclei with an area at least five times larger than the average of the area of non-fused cells. Scale bar, 500 μm. e, Results of SIA screening. The percentage of syncytia normalized on total cells is plotted as a z score. Compounds with a z score ≤ −2.58 (red dotted line, 0.005% tail) are shown in red; those between ≤ −1.96 (0.025% tail, blue dotted line) and −2.58 area in blue. Four drugs that were further studied with viral infection are indicated. CLO, clofazimine; NIC, niclosamide; SAL, salinomycin; SER, sertraline. f, Effect of niclosamide on syncytia. Spike-positive syncytia are in green; nuclei are in blue; cell body is in red using HCS CellMask DeepRed. The percentage of nuclei within in syncytia over total nuclei is shown at the bottom. Scale bar, 500 μm. Numbers on some of the images indicate the screening well. Images are representative of 25 per well; screening was performed in duplicate.