FIG. 8.

16677 does not interfere with viral entry and is active late in the replicative cycle. (A) Cell-to-cell fusion induced by transiently expressed MV glycoproteins is not inhibited by the compound. Transfected cells, treated with 15 μM 16677 or DMSO, were photographed after a 24-hour incubation period. For comparison, cells treated with the fusion inhibitor AS-48, cells infected with MV, and mock-transfected/infected cells are shown. (B) Quantification of syncytium formation of transfected cells treated as described for panel A. The values represent averages of four replicates and are expressed as percentages of the syncytium formation observed for DMSO-treated samples. The error bars represent standard deviations. (C) Presence of 16677 during adsorption of virions to target cells does not render particles sensitive to neutralization by a pH 3.0 wash, indicating successful viral entry in the presence of compound. Virions were adsorbed to target cells in the presence of DMSO or 16677, followed by pH 3.0 treatment to neutralize all particles that were in a premembrane fusion state and incubation in the presence of DMSO or 16677 as indicated. Yields of cell-associated viral particles were determined by TCID₅₀ titration. Average values of two experiments are shown, and the error bars represent standard errors of the mean (SEMs). (D) Antiviral activity of 16677 persists to late phases of a replicative cycle. The compound (final concentration, 15 μM) was added at the indicated times postinfection to a one-step replicative cycle. Cell-associated viral particles of compound-treated samples and DMSO-treated controls were harvested 20 h postinfection, and virus yields were determined by TCID₅₀ titration. For comparison, infected cells were treated with the fusion inhibitor AS-48. Average titers of two experiments are shown, and the error bars represent SEMs.