ESI09 blocks the early stage of vesicular stomatitis virus expressing EBOV glycoprotein (EGP-VSV) infection in endothelial cells. (A) The number of EGP-VSV viral RNA copies detected at 24 h p.i. in the Vehicle-, ESI09-, ESI09+ I942-, and I942-pretreated HUVECs. N = 3 for each group. * p < 0.05 compared to the Vehicle group, ** p < 0.05 compared to the ESI09 group. (B–G) EM detection of EGP-VSV particles in HUVECs pretreated with DMSO (B–E) and ESI09 (F–G) at 6 h p.i. with EGP-VSV (at an MOI of 200). Arrows highlight EGP-VSV particles in cross-sections, and asterisks indicate particles in longitudinal sections. Scale bar, B–G, 2 µM. (H) The number of viral RNA copies detected in the membrane-bound fractions from the binding assay of Vehicle- and ESI09-pretreated HUVECs at 15 min p.i. with EGP-VSV at an MOI of 20. N = 3 for each group. (I) Confirmation of the qualities of the samples from the membrane and early endosome fractionations. (J) The number of EGP-VSV viral RNA copies detected at 1 h p.i. at an MOI of 200 in the membrane fractions of Vehicle- and ESI09-pretreated HUVECs. N = 3 for each group. (K) The number of EGP-VSV viral RNA copies detected at 1 h p.i. at an MOI of 200 in the early endosome fractions of Vehicle- and ESI09-pretreated HUVECs. N = 3 for each group. * p < 0.001 compared to the Vehicle group.