AT-752, a double prodrug of a guanosine nucleotide analog, inhibits yellow fever virus in a hamster model

Abstract

Yellow fever virus (YFV) is a zoonotic pathogen re-emerging in parts of the world, causing a viral hemorrhagic fever associated with high mortality rates. While an effective vaccine is available, having an effective antiviral against YFV is critical against unexpected outbreaks, or when vaccination is not recommended. We have previously identified AT-281, the free base of AT-752, an orally available double prodrug of a guanosine nucleotide analog, as a potent inhibitor of YFV in vitro, with a 50% effective concentration (EC50) of 0.31 μM. In hamsters infected with YFV (Jimenez strain), viremia rose about 4 log10-fold and serum alanine aminotransferase (ALT) 2-fold compared to sham-infected animals. Treatment with 1000 mg/kg AT-752 for 7 days, initiated 4 h prior to viral challenge, reduced viremia to below the limit of detection by day 4 post infection (pi) and returned ALT to normal levels by day 6 pi. When treatment with AT-752 was initiated 2 days pi, the virus titer and ALT dropped >2 log10 and 53% by day 4 and 6 pi, respectively. In addition, at 21 days pi, 70-100% of the infected animals in the treatment groups survived compared to 0% of the untreated group (p<0.001). Moreover, in vivo formation of the active triphosphate metabolite AT-9010 was measured in the animal tissues, with the highest concentrations in liver and kidney, organs that are vulnerable to the virus. The demonstrated in vivo activity of AT-752 suggests that it is a promising compound for clinical development in the treatment of YFV infection.

Fig 1. AT-752 and its putative metabolic pathway to the pharmacologically active metabolite AT-9010.

Fig 2. Profile of AT-281 and its metabolites in plasma, lung and brain tissue after a single oral dose of AT-752.

Syrian golden male hamsters were administered 500 mg/kg AT-752. Samples were collected up to 24 h post dose and analyzed for AT-281 and its metabolites by LC-MS/MS. Data are expressed as mean ± SD (n = 3 per time point).

Fig 3. Profile of AT-281 and its metabolites in liver and kidney tissue after a single oral dose of AT-752.

Syrian golden male hamsters were administered 500 mg/kg AT-752. Tissue samples were collected up to 24 h post dose and analyzed for AT-281 and its metabolites by LC-MS/MS. Data are expressed as mean ± SD (n = 3 per time point).

Fig 4. Kaplan-Meier survival curves of YFV-infected hamsters treated with AT-752.

Syrian golden hamsters challenged with YFV were administered vehicle (placebo), ribavirin (positive control) or AT-752 four h prior to or 2 d post challenge, followed by BID doses of 1000, 300 or 100 mg/kg for 7 consecutive days starting 1 h post inoculation. Percent survival was calculated up to 21 days post infection. The treated groups were significantly different from vehicle control by one-way ANOVA and Dunnett’s test, ****p<0.0001, ***p<0.001.

Fig 5. Weight change of YFV-infected hamsters treated with AT-752.

Syrian golden hamsters challenged with YFV or sham-infected were administered AT-752, ribavirin (positive control) or vehicle according to Table 2. Body weights were recorded on Day 0 (baseline) and daily from Day 3–18 pi. Weights were compared to Day 0 and presented as percent change. Data expressed as mean ± SD.

Fig 6. Virus titer in YFV-infected hamsters treated with AT-752.

Syrian golden hamsters challenged with YFV were administered 0 (vehicle), 100, 300 or 1000 mg/kg AT-752 four h prior, followed by BID doses for 7 consecutive days starting 1 h post inoculation (pi). Serum was collected 4 d pi, and titers measured by an infectious assay as described in the Methods. The treated groups were significantly different from vehicle by one-way ANOVA and Dunnett’s test, *p<0.05, ***p<0.001. The dashed line (—) represents the assay’s limit of detection. § AT-752 dosing began 2 d post challenge.