Therapeutic efficacy of monoclonal antibodies and antivirals against SARS-CoV-2 Omicron BA.1 in Syrian hamsters

Abstract

The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the major antigen stimulating the host's protective immune response. Here we assessed the efficacy of therapeutic monoclonal antibodies (mAbs) against Omicron variant (B.1.1.529) sublineage BA.1 variants in Syrian hamsters. Of the FDA-approved therapeutic mAbs tested (that is, REGN10987/REGN10933, COV2-2196/COV2-2130 and S309), only COV2-2196/COV2-2130 efficiently inhibited BA.1 replication in the lungs of hamsters, and this effect was diminished against a BA.1.1 variant possessing the S-R346K substitution. In addition, treatment of BA.1-infected hamsters with molnupiravir (a SARS-CoV-2 RNA-dependent RNA polymerase inhibitor) or S-217622 (a SARS-CoV-2 protease inhibitor) strongly reduced virus replication in the lungs. These findings suggest that the use of therapeutic mAbs in Omicron-infected patients should be carefully considered due to mutations that affect efficacy, and demonstrate that the antiviral compounds molnupiravir and S-217622 are effective against Omicron BA.1 variants.

Extended Data Fig. 1

Plasma concentration profile of S-217622 after single oral administration to hamsters at 60 mg/kg. S-217622 was orally administered to Syrian hamsters at 60 mg/kg under non-fasted conditions. Blood samples (0.1 mL) were collected at 0.5, 1, 2, 4, 8, and 24 h after dosing and the plasma concentrations of S-217622 were determined. Data are expressed as the mean ± SD (n = 4/group).

Figure 1. Therapeutic effects of monoclonal antibodies on the replication of SARS-CoV-2 Omicron BA.1 and BA.1.1 variants.

a, Schematic diagram of the experimental workflow for assessing the therapeutic effects of monoclonal antibodies. b-d Syrian hamsters were intranasally inoculated with 10³ PFU of D614G (HP095) (b), BA.1 (NC928) (c), or BA.1.1 (NC929) (d). On Day 1 post-infection of D614G (HP095) or BA.1 (NC928), the hamsters were intraperitoneally injected with a single dose of the REGN10987/REGN10933 or COV2–2196/COV2–2130 combination (2.5 mg/kg each), or S309 as monotherapy (5 mg/kg). On Day 1 post-infection with BA.1.1 (NC929), the hamsters were intraperitoneally injected with a single dose of COV2–2130 as monotherapy (5 mg/kg), or with the COV2–2196/COV2–2130 combination (2.5 mg/kg each). As a control, a human monoclonal antibody (1430E3/9) against the hemagglutinin of influenza B virus was injected. Hamsters were euthanized on Day 4 post-infection for virus titration. Sera were also collected at this timepoint, and titers of RBD-specific IgG antibodies in the sera were determined by using ELISAs coated with recombinant RBD derived from the S protein of Wuhan/Hu-1/2019 (GenBank accession #. MN908947). The endpoint titer is defined as the reciprocal of the highest dilution with an OD₄₅₀ cutoff value ≥ 0.1. The detection limit for virus titers was 1.7 log₁₀ (PFU/g). Vertical bars show the mean ± s.e.m. Points indicate data from individual hamsters (b, S309 and REGN10987/REGN10933; n = 4, d, COV2–2196/COV2–2130; n = 3, other groups in b-d, n = 5). The lower limit of detection is indicated by the horizontal dashed line. To compare the lung titers of the different groups in the BA.1 (NC928)-infected hamsters, we used a Kruskal-Wallis test followed by Dunn’s multiple comparisons test. To compare the nasal turbinate and lung titers of the different groups in the D614G (HP095)- or BA.1.1 (NC929)-infected hamsters and the nasal turbinate titers of the different groups in the BA.1 (NC928)-infected hamsters, we used a one-way ANOVA followed by Dunnett’s multiple comparisons test. P values of < 0.05 were considered statistically significant.

Figure 2. Therapeutic effects of antiviral compounds on the replication of the SARS-CoV-2 Omicron /BA.1 variant.

a, Schematic diagram of the experimental workflow for assessing the therapeutic effects of antiviral compounds. b, Syrian hamsters were intranasally inoculated with 10³ PFU of BA.1 (NC928). At 24 h post-infection, hamsters were treated with: 500 mg/kg molnupiravir orally twice daily for 3 days or 60 mg/kg S-217622 orally twice daily for 3 days. Methylcellulose served as a control for oral treatment. Hamsters were euthanized on Days 2, 3, and 4 post-infection for virus titration. Vertical bars show the mean ± s.e.m. Points indicate data from individual hamsters (n = 4/group). c, Schematic diagram of the experimental workflow for investigating the emergence of resistant variants. d and e, Four Syrian hamsters were intranasally inoculated with 10³ PFU of BA.1 (NC928). Cyclophosphamide (CPA) was administered intraperitoneally to hamsters on Days −3, 1, 5, and 9 relative to infection. At 24 h post-infection, hamsters were treated with 500 mg/kg molnupiravir orally twice daily for 5 days or 60 mg/kg S-217622 orally twice daily for 5 days. Methylcellulose served as a control for oral treatment. d, Hamsters were euthanized on Days 7 and 14 post-infection for virus titration. Vertical bars show the mean ± s.e.m. Points indicate data from individual hamsters (n = 4/group). e, Drug susceptibility of viruses. Viruses were isolated from the lungs of immunosuppressed animals treated with molnupiravir, S-217622, or the vehicle control on Days 7 and 14 post-infection. EC₅₀ values of molnupiravir or S-217622 were determined by using the Spearman–Karber formula based on the appearance of visually detectable cytopathic effects (CPE) in quadruplicate experiments. EIDD-1931 is the active form of molnupiravir. -, not applicable. b and d, The lower limit of detection is indicated by the horizontal dashed line. To compare the lung and nasal turbinate titers of the different groups in the BA.1 (NC928)-infected hamsters, we used a Kruskal-Wallis test followed by Dunn’s multiple comparisons test and a one-way ANOVA followed by Dunnett’s multiple comparisons test, respectively. P values of < 0.05 were considered statistically significant.