In vitro and in vivo activities of anti-influenza virus compound T-705

Abstract

T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) has been found to have potent and selective inhibitory activity against influenza virus. In an in vitro plaque reduction assay, T-705 showed potent inhibitory activity against influenza A, B, and C viruses, with 50% inhibitory concentrations (IC(50)s) of 0.013 to 0.48 microg/ml, while it showed no cytotoxicity at concentrations up to 1,000 microg/ml in Madin-Darby canine kidney cells. The selectivity index for influenza virus was more than 2,000. It was also active against a neuraminidase inhibitor-resistant virus and some amantadine-resistant viruses. T-705 showed weak activity against non-influenza virus RNA viruses, with the IC(50)s being higher for non-influenza virus RNA viruses than for influenza virus, and it had no activity against DNA viruses. Orally administered T-705 at 100 mg/kg of body weight/day (four times a day) for 5 days significantly reduced the mean pulmonary virus yields and the rate of mortality in mice infected with influenza virus A/PR/8/34 (3 x 10(2) PFU). These results suggest that T-705 may be a compound that is useful and highly selective against influenza virus infections and that has a mode of action different from those of commercially available drugs, such as amantadine, rimantadine, and neuraminidase inhibitors.

FIG. 1.

Structure of T-705.

FIG. 2.

Effect of oral administration of T-705 on prevention of death in influenza virus-infected mice. Mice were infected with influenza virus A/PR/8/34 at 3 × 10² PFU/mouse as described in Materials and Methods. Mice were treated q.i.d. with oral doses of T-705 at 50 (▪), 100 (▴), or 200 (•) mg/kg/day or with methylcellulose solution as a control (○) for 5 days beginning 1 h after infection. The results presented here were obtained from a single representative experiment. ∗, P < 0.0125 compared to the results for 0.5% methylcellulose solution-treated controls (log rank test).

FIG. 3.

Effect of oral administration of T-705 on lung virus yield in influenza virus-infected mice. Mice were infected with influenza virus A/PR/8/34 at 3 × 10² PFU/mouse, and lung virus yields were determined as described in Materials and Methods. Mice were treated q.i.d. with oral doses of T-705 at 50, 100, or 200 mg/kg/day or with methylcellulose solution as a control for 5 days beginning 1 h after infection. The results presented here were obtained from a single representative experiment. The numbers in parentheses represent the number of mice whose lung virus titers were less than the limit of detection (2 × 10² PFU/lung). ∗, P < 0.05 compared to the results for 0.5% methylcellulose solution-treated controls (nonparametric Dunnett's test); ∗∗, P < 0.01 compared to the results for 0.5% methylcellulose solution-treated controls (nonparametric Dunnett's test).