A Kegin-type polyoxometalate, PM-523, in combination with ribavirin, was tested for its therapeutic effectiveness against influenza virus (FluV) A (H1N1) infection in tissue culture and in mice, PM-523 {(PriNH(3))(6)H [PTi2W10O38(O-2)(2)]. H2O, where Pri is isopropanol} and ribavirin individually inhibited FluV A-induced cytopathic effects in Madin-Darby canine kidney (MDCK) cells at median effective concentrations (EC(50)s) of 30 and 34 mu M, respectively, and at 70% effective concentrations (EC(70)s) of 48 and 72 mu M, respectively, On the other hand, a combination of PM-523 and ribavirin at a ratio of 1:16 exhibited lower EC(50)s and EC(70)s than each compound used singly, and combination indices were less than 1, A wide range of combinations of PM-523 and ribavirin at ratios of from 1:128 to 1:1 exhibited additive or synergistic anti-FluV effects in MDCK cells, When these compounds were tested for their anti-FluV A activities in vivo by aerosol exposure of mice which had been infected with a lethal dose of FluV A by an intranasal route, a 1:16 combination of PM-523 and ribavirin was found to have a significantly better therapeutic effect than a single dose of either compound used singly with respect to both the survival rate of the mice and the virus titer in the lungs of the infected mice, PM-523 was effective for the treatment of experimental FluV infection, and in combination with ribavirin, PM-523 exhibited enhanced anti-FluV effects in vitro and in vivo compared with the effect of PM-523 alone.
