RK424 shows antiviral activity both <i>in vitro</i> and <i>in vivo</i>.

<p>(A) Chemical structure of the RK424. (B) The effects of RK424 on viral replication and MDCK cell viability <i>in vitro</i>. The 50% inhibitory concentration (IC₅₀) and the 50% cytotoxicity concentration (CC₅₀) of RK424 (0–50 μM) were evaluated in a plaque assay and water soluble tetrazolium salt-1 (WST-1) assay, respectively. Data are expressed as the mean ± SD from three samples in each of three independent experiments. (C–H) Inhibitory effect of RK424 <i>in vivo</i>. RK424 (5 mg/kg or 10 mg/kg) was intraperitoneally administered to 6-week-old Balb/c mice 2 h prior to virus exposure and then twice per day for 5 days beginning on the day of infection. PBS and oseltamivir phosphate (Os; 10 mg/kg) were used as a negative and positive controls, respectively. Mice were infected intranasally with ten 50% lethal doses (LD₅₀) of influenza A/WSN/1933 (H1N1) virus. Eight mice per RK424 treated group and seven mice per both negative and positive control group were tested. The body weight of mice from each group was daily monitored (C) and survival rate were also calculated (D). The data were obtained from a single experiment. In the body weight change data, the symbol (*) indicates a statistically significant difference in mean weight between the 10 mg/kg RK424 treated group and the negative control group at that time point. Values are expressed as the mean ± SD and statistical analysis was performed until day 6 post-infection. *; p<0.05. In the survival curve data, the statistically significant difference between the 10 mg/kg RK424 treated group and the negative control is also indicated. *; p<0.01. Three mice from the 10 mg/kg RK424-treated or PBS-treated group were sacrificed on day 6 post-infection and the lungs were harvested to determine viral titers. Plaque images (E) and the viral lung titers (F) in each group are shown. Values are expressed as the mean ± SD of triplicate assays. *; p<0.05. (G and H) Co-administration of RK424 and Os <i>in vivo</i>. K424 (5 mg/kg or 10 mg/kg) and Os (0.02 mg/kg) were intraperitoneally co-administered to 6-week-old Balb/c mice 2 h prior to virus exposure and then twice per day for 5 days beginning on the day of infection. PBS was used as negative control and RK424 (10mg/kg) and Os (0.02mg/kg) were used as monotherapy control, respectively. Eight mice per each group were tested. Body weight change (G) and survival rate (H) of each group were evaluated by a single experiment. In the body weight change data, the symbols (#; 0.02 mg/kg Os, *; 10mg/kg RK424, ×; 0.02mg/kg Os + 5 mg/kg RK424, and △; 0.02 mg/kg Os + 10 mg/kg RK424) indicate a statistically significant difference in mean weight between each compound treated group and the negative control group at that time point. Values are expressed as the mean ± SD and statistical analysis was performed until day 6 post-infection. <b>#</b>,*,×,△; p<0.05, <b>##</b>,××,△△; p<0.005 and <b>###</b>,×××,△△△; p<0.001. In the survival curve data, a statistically significant difference between each compound treated group and the negative control group is also indicated. *; p<0.01 and **; p<0.001.