SARS-CoV-2 variant of concern type and biological sex affect efficacy of molnupiravir in dwarf hamster model of severe COVID-19

Summary ParagraphSARS-CoV-2 variants of concern (VOC) have triggered distinct infection waves in the coronavirus disease 2019 (COVID-19) pandemic, culminating in currently all-time high incidence rates of VOC omicron. Orally available direct-acting antivirals such as molnupiravir promise to improve disease management and limit SARS-CoV-2 spread. However, molnupiravir efficacy against VOC delta was questioned based on clinical trial results and its potency against omicron is unknown. This study evaluates molnupiravir against a panel of relevant VOC in three efficacy models: primary human airway epithelium organoids, the ferret model of upper respiratory disease, and a lethal Roborovski dwarf hamster efficacy model of severe COVID-19-like acute lung injury. All VOC were equally efficiently inhibited by molnupiravir in cultured cells and organoids. Treatment consistently reduced upper respiratory VOC shedding in ferrets and prevented viral transmission. Pathogenicity in the dwarf hamsters was VOC-dependent and highest for gamma, omicron, and delta with fulminant lung histopathology. Oral molnupiravir started 12 hours after infection resulted in complete survival of treated dwarf hamsters independent of challenge VOC. However, reduction in lung virus differed VOC-dependently, ranging from one (delta) to four (gamma) orders of magnitude compared to vehicle-treated animals. Dwarf hamsters infected with VOC omicron showed significant individual variation in response to treatment. Virus load reduction was significant in treated males, but not females. The dwarf hamster model recapitulates mixed efficacy of molnupiravir seen in human trials and alerts that therapeutic benefit of approved antivirals must be continuously reassessed in vivo as new VOC emerge.

A bifluorescent-based assay for the identification of neutralizing antibodies against SARS-CoV-2 variants of concern in vitro and in vivo

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged at the end of 2019 and has been responsible for the still ongoing coronavirus disease 2019 (COVID-19) pandemic. Prophylactic vaccines have been authorized by the United States (US) Food and Drug Administration (FDA) for the prevention of COVID-19. Identification of SARS-CoV-2 neutralizing antibodies (NAbs) is important to assess vaccine protection efficacy, including their ability to protect against emerging SARS- CoV-2 variants of concern (VoC). Here we report the generation and use of a recombinant (r)SARS-CoV-2 USA/WA1/2020 (WA-1) strain expressing Venus and a rSARS-CoV-2 expressing mCherry and containing mutations K417N, E484K, and N501Y found in the receptor binding domain (RBD) of the spike (S) glycoprotein of the South African (SA) B.1.351 (beta, {beta}) VoC, in bifluorescent-based assays to rapidly and accurately identify human monoclonal antibodies (hMAbs) able to neutralize both viral infections in vitro and in vivo. Importantly, our bifluorescent-based system accurately recapitulated findings observed using individual viruses. Moreover, fluorescent- expressing rSARS-CoV-2 and the parental wild-type (WT) rSARS-CoV-2 WA-1 had similar viral fitness in vitro, as well as similar virulence and pathogenicity in vivo in the K18 human angiotensin converting enzyme 2 (hACE2) transgenic mouse model of SARS-CoV-2 infection. We demonstrate that these new fluorescent-expressing rSARS- CoV-2 can be used in vitro and in vivo to easily identify hMAbs that simultaneously neutralize different SARS-CoV-2 strains, including VoC, for the rapid assessment of vaccine efficacy or the identification of prophylactic and/or therapeutic broadly NAbs for the treatment of SARS-CoV-2 infection.

SARS-CoV-2 B.1.1.7 and B.1.351 variants of concern induce lethal disease in K18-hACE2 transgenic mice despite convalescent plasma therapy

SARS-CoV-2 variants of concern (VoCs) are impacting responses to the COVID-19 pandemic. Here we present a comparison of the SARS-CoV-2 USA-WA1/2020 (WA-1) strain with B.1.1.7 and B.1.351 VoCs and identify significant differences in viral propagation in vitro and pathogenicity in vivo using K18-hACE2 transgenic mice. Passive immunization with plasma from an early pandemic SARS-CoV-2 patient resulted in significant differences in the outcome of VoC-infected mice. WA-1-infected mice were protected by plasma, B.1.1.7-infected mice were partially protected, and B.1.351-infected mice were not protected. Serological correlates of disease were different between VoC-infected mice, with B.1.351 triggering significantly altered cytokine profiles than other strains. In this study, we defined infectivity and immune responses triggered by VoCs and observed that early 2020 SARS-CoV-2 human immune plasma was insufficient to protect against challenge with B.1.1.7 and B.1.351 in the mouse model.

4'-Fluorouridine is a broad-spectrum orally efficacious antiviral blocking respiratory syncytial virus and SARS-CoV-2 replication

The COVID-19 pandemic has underscored the critical need for broad-spectrum therapeutics against respiratory viruses. Respiratory syncytial virus (RSV) is a major threat to pediatric patients and the elderly. We describe 4-fluorouridine (4-FlU, EIDD-2749), a ribonucleoside analog that inhibits RSV, related RNA viruses, and SARS-CoV-2 with high selectivity index in cells and well-differentiated human airway epithelia. Polymerase inhibition in in vitro RdRP assays established for RSV and SARS-CoV-2 revealed transcriptional pauses at positions i or i+3/4 post-incorporation. Once-daily oral treatment was highly efficacious at 5 mg/kg in RSV-infected mice or 20 mg/kg in ferrets infected with SARS-CoV-2 WA1/2020 or variant-of-concern (VoC) isolate CA/2020, initiated 24 or 12 hours after infection, respectively. These properties define 4-FlU as a broad-spectrum candidate for the treatment of RSV, SARS-CoV-2 and related RNA virus infections. One-Sentence Summary4-Fluorouridine is an orally available ribonucleoside analog that efficiently treats RSV and SARS-CoV-2 infections in vivo.