Prophylactic and therapeutic remdesivir (GS-5734) treatment in the rhesus macaque model of MERS-CoV infection

Abstract

The continued emergence of Middle East Respiratory Syndrome (MERS) cases with a high case fatality rate stresses the need for the availability of effective antiviral treatments. Remdesivir (GS-5734) effectively inhibited MERS coronavirus (MERS-CoV) replication in vitro, and showed efficacy against Severe Acute Respiratory Syndrome (SARS)-CoV in a mouse model. Here, we tested the efficacy of prophylactic and therapeutic remdesivir treatment in a nonhuman primate model of MERS-CoV infection, the rhesus macaque. Prophylactic remdesivir treatment initiated 24 h prior to inoculation completely prevented MERS-CoV-induced clinical disease, strongly inhibited MERS-CoV replication in respiratory tissues, and prevented the formation of lung lesions. Therapeutic remdesivir treatment initiated 12 h postinoculation also provided a clear clinical benefit, with a reduction in clinical signs, reduced virus replication in the lungs, and decreased presence and severity of lung lesions. The data presented here support testing of the efficacy of remdesivir treatment in the context of a MERS clinical trial. It may also be considered for a wider range of coronaviruses, including the currently emerging novel coronavirus 2019-nCoV.

Keywords: MERS-CoV; animal model; antiviral; remdesivir; therapy.

Fig. 1.

Study outline. To test the prophylactic and therapeutic efficacy of remdesivir treatment in the rhesus macaque model of MERS-CoV infection, three groups of six rhesus macaques were inoculated with MERS-CoV strain HCoV-EMC/2012; one group was administered 5 mg/kg remdesivir starting at 24 h before inoculation (black circles), and one group was administered 5 mg/kg remdesivir starting at 12 h after inoculation (red circles). One group of six control animals was i.v.-administered 1 mL/kg vehicle solution, with three animals receiving vehicle solution according to the prophylactic treatment schedule, and three animals receiving it according to the therapeutic treatment schedule. Treatment was continued once daily until 6 dpi, when all animals were euthanized. At 0, 1, 3, 5, and 6 dpi, clinical examinations were performed to monitor the health status of the animals.

Fig. 2.

Clinical findings in rhesus macaques inoculated with MERS-CoV and treated with remdesivir. Three groups of six rhesus macaques were inoculated with MERS-CoV strain HCoV-EMC/2012; one group was i.v.-administered 1 mL/kg vehicle solution (vehicle control; gray circles), one group was administered 5 mg/kg remdesivir starting at 24 h before inoculation (prophylactic remdesivir; black squares), and one group was administered 5 mg/kg remdesivir starting at 12 h after inoculation (therapeutic remdesivir; red triangles). After inoculation, the animals were observed twice daily for clinical signs of disease and scored using a predetermined clinical scoring system (A). On 0, 1, 3, 5 and 6 dpi, clinical examinations were performed during which respiration rate was determined (B), and radiographs were taken. Radiographs were used to score individual lung lobes for severity of pulmonary infiltrates by a clinical veterinarian according to a standard scoring system (0: normal; 1: mild interstitial pulmonary infiltrates; 2: moderate pulmonary infiltrates perhaps with partial cardiac border effacement and small areas of pulmonary consolidation; 3: serious interstitial infiltrates, alveolar patterns and air bronchograms); the cumulative X-ray score is the sum of the scores of the six individual lung lobes per animal; scores shown are from 6 dpi (C). Asterisks indicate statistically significant difference in a two-way (A and B) or one-way (C) ANOVA with Dunnett’s multiple comparisons; black asterisks indicate statistical significance between the vehicle control and prophylactic remdesivir groups, and red asterisks indicate statistical significance between the vehicle control and therapeutic remdesivir groups. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.

Fig. 3.

Viral loads in respiratory tract tissues of rhesus macaques inoculated with MERS-CoV and treated with remdesivir. Three groups of six rhesus macaques were inoculated with MERS-CoV strain HCoV-EMC/2012; one group was i.v.-administered 1 mL/kg vehicle solution (vehicle control; gray circles), one group was administered 5 mg/kg remdesivir starting at 24 h before inoculation (prophylactic remdesivir; black squares), and one group was administered 5 mg/kg remdesivir starting at 12 h after inoculation (therapeutic remdesivir; red triangles). Treatment was continued once daily until 6 dpi, when all animals were euthanized and necropsies were performed. At necropsy, tissue samples were collected from all six lung lobes, RNA was extracted, and viral load was determined as TCID50 equivalents per gram tissue. Individual animals and lung lobes are indicated (A), and averages and SDs per group (B). Similarly, viral loads were determined in additional tissues from the respiratory tract of each animal (C). R: right; L: left. Asterisks indicate statistically significant differences in a two-way ANOVA with Dunnett’s multiple comparisons. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.

Fig. 4.

Pathological findings in the lungs of rhesus macaques inoculated with MERS-CoV and treated with remdesivir. Three groups of six rhesus macaques were inoculated with MERS-CoV strain HCoV-EMC/2012; one group was i.v.-administered 1 mL/kg vehicle solution (vehicle control; gray circles), one group was administered 5 mg/kg remdesivir starting at 24 h before inoculation (prophylactic remdesivir; black squares), and one group was administered 5 mg/kg remdesivir starting at 12 h after inoculation (therapeutic remdesivir; red triangles). Treatment was continued once daily until 6 dpi, when all animals were euthanized and necropsies were performed. At necropsy, the percentage of each lung lobe affected by gross lesions was estimated by a board-certified veterinary pathologist (A). Lung samples were collected and stained with H&E and analyzed for the presence of lesions by a board-certified veterinary pathologist. Each lung was given a score from 0 to 4 based on the abundance of lesions; the cumulative histology score is the sum of the scores of the six individual lung lobes per animal (B). One representative H&E image was chosen for each group (magnification: 100×) (C). Lung samples were also stained with a polyclonal α-MERS-CoV antibody; one representative image was chosen for each group (magnification: 200×) (D). Images in C and D were chosen as representative images of lung lesions and antigen expression, respectively, rather than being images from consecutive tissue slides. Asterisks indicate statistically significant differences in a two-way ANOVA with Dunnett’s multiple comparisons. **P < 0.01; ****P < 0.0001.