Fig 5.

Inhibitory effect of L-742,001 on viral RNA synthesis is situated after viral entry. Light gray bars indicate that the test compound L-742,001 (50 μM), EGCG (50 μM), ribavirin (20 μM), or SA-19 (20 μM) was added to MDCK cells, and after 30 min incubation at 35°C, influenza virus A/PR/8/34 was added. Dark gray bars indicate that virus was added first and allowed to enter during 1 h of incubation, after which the compounds were added at the same concentrations as those described for the light gray bars. In both conditions, total cellular RNA was extracted at 10 h p.i. VC, untreated virus control. The number of vRNA copies was quantified by two-step real-time RT-PCR. On the y axis, the fold increase in vRNA copies is shown relative to the viral copy number added at time zero. Ribavirin and L-742,001 remain fully effective when added after virus entry. In contrast, the reported entry inhibitor SA-19 (33) as well as EGCG are inactive when added at 1 h p.i. Data shown are the means ± SEM from two independent tests.