Arbidol inhibits HCVpp-mediated lipid mixing. Lipid mixing curves of HCVpp genotype 1b (panel A) and of HApp (panel B) in the absence or presence of ARB, with R18-labeled liposomes (representative of 3 separate experiments). Fourty μl of HCVpp-1b (panel A, solid lines represent 1b-AY for Genbank accession number AY734975, while dotted lines are labeled as 1b-AF for Genbank accession number AF333324) or HApp (panel B) were added to R18-labeled phosphatidylcholine:cholesterol liposomes (15 μM final lipid concentration), in PBS pH 7.4 at 37°C, with or without 1 (ARB 1) or 6 μg/ml (ARB 6) ARB. After a 2-min equilibration, lipid mixing was initiated by decreasing the pH to 5.0 (time 0), and recorded as R18 fluorescence dequenching as a function of time. The 100% fluorescence was obtained by adding 0.1% (v:v; final concentration) Triton X-100 to the suspension.