Favipiravir (T-705) inhibits Junín virus infection and reduces mortality in a guinea pig model of Argentine hemorrhagic fever

Abstract

Background: Junín virus (JUNV), the etiologic agent of Argentine hemorrhagic fever (AHF), is classified by the NIAID and CDC as a Category A priority pathogen. Presently, antiviral therapy for AHF is limited to immune plasma, which is readily available only in the endemic regions of Argentina. T-705 (favipiravir) is a broadly active small molecule RNA-dependent RNA polymerase inhibitor presently in clinical evaluation for the treatment of influenza. We have previously reported on the in vitro activity of favipiravir against several strains of JUNV and other pathogenic New World arenaviruses.

Methodology/principal findings: To evaluate the efficacy of favipiravir in vivo, guinea pigs were challenged with the pathogenic Romero strain of JUNV, and then treated twice daily for two weeks with oral or intraperitoneal (i.p.) favipiravir (300 mg/kg/day) starting 1-2 days post-infection. Although only 20% of animals treated orally with favipiravir survived the lethal challenge dose, those that succumbed survived considerably longer than guinea pigs treated with placebo. Consistent with pharmacokinetic analysis that showed greater plasma levels of favipiravir in animals dosed by i.p. injection, i.p. treatment resulted in a substantially higher level of protection (78% survival). Survival in guinea pigs treated with ribavirin was in the range of 33-40%. Favipiravir treatment resulted in undetectable levels of serum and tissue viral titers and prevented the prominent thrombocytopenia and leucopenia observed in placebo-treated animals during the acute phase of infection.

Conclusions/significance: The remarkable protection afforded by i.p. favipiravir intervention beginning 2 days after challenge is the highest ever reported for a small molecule antiviral in the difficult to treat guinea pig JUNV challenge model. These findings support the continued development of favipiravir as a promising antiviral against JUNV and other related arenaviruses.

Figure 1. Survival outcome following oral treatment of JUNV-infected guinea pigs with favipiravir.

Guinea pigs (n = 10/group) were challenged i.p. with 1300 PFU of JUNV. They were dosed by instillation of favipiravir, ribavirin, or carrot baby food vehicle (placebo) into the back of the oral cavity. Treatments (Tx) with the indicated concentrations of drugs were initiated 24 h post-infection (p.i.) and administered twice daily for 14 days (capped hashed line). A) survival, B) mean body weight (relative to initial starting weight), and C) temperature were monitored for 40 days. ***P<0.001 compared to placebo-treated animals by the log-rank test.

Figure 2. PK analysis of favipiravir in male Hartley guinea pigs dosed by oral instillation or intraperitoneal (i.p.) injection.

Favipiravir (100 mg/kg) was administered orally in carrot baby food vehicle or by i.p. injection in 2.9% sodium bicarbonate. Longitudinal plasma favipiravir levels are shown from 3 animals per treatment group at 15 and 30 minutes, and 1, 2, and 4 h after treatment. Data points represent the mean and standard error of the mean.

Figure 3. Survival outcome following i.p. treatment of JUNV-infected guinea pigs with favipiravir.

Guinea pigs (n = 12/experimental group) were challenged i.p. with 750 PFU of JUNV and dosed i.p. with favipiravir (300 mg/kg/d), ribavirin (50 mg/kg/d), or 2.9% sodium bicarbonate vehicle (placebo) beginning 48 h post-infection (p.i.). Treatments (Tx) were administered twice daily for 14 days (capped hashed line). A) survival (n = 9/group), and B) mean body weight (relative to initial starting weight) and C) temperature were monitored in all surviving animals for 42 days. **P<0.01, ***P<0.001 compared to placebo-treated animals by the log-rank test.

Figure 4. Effect of i.p. favipiravir treatment on day 14 viral loads in JUNV-challenged guinea pigs.

Animals were infected and treated as described in Figure 3. Three pre-designated animals in each treatment group were sacrificed on day 14 post-infection for analysis of A) serum, B) brain, C) heart, D) kidney, E) liver, F) lung and G) spleen virus titers. Two serum samples and 1 liver sample collected from 2 moribund animals from the placebo group euthanized on days 12 and 14 were also included in the analysis. Unique symbols in each treatment group represent values for the same animal across all parameters and hashed lines indicate the assay limits of detection in tissue samples. **P<0.01, ***P<0.001 compared to placebo.