Biology subjects

Sawa, H.

Publications and source records attributed to Sawa, H..

At least 19 recordsLinked to original sources

bioRxiv2026

West Nile virus capsid protein promotes viral replication and pathogenesis through PKCα-dependent lamin phosphorylation and nuclear deformation

The genus Orthoflavivirus comprises several medically important pathogens such as the West Nile virus (WNV), which causes encephalitis in humans. Although viral replication occurs in the cytoplasm, the capsid (C) protein of the orthoflavivirus is localized to both the cytoplasm and nucleus. Nuclear C protein contributes to viral replication and disease progression. However, the underlying mechanisms remain unclear. Here, we investigated whether the WNV C protein induces nuclear deformation and examined the underlying mechanism. We also assessed the contribution of this deformation to viral replication and pathogenesis. WNV infection and C protein expression induced morphological alterations in the nuclear lamina, leading to nuclear deformation. C protein expression enhanced lamin phosphorylation and the disassembly of the polymerized lamin network. In addition, C protein interacted with protein kinase C alpha (PKC) and localized PKC near the nuclear lamina. Downregulation of PKC expression inhibited C protein-induced lamin phosphorylation and nuclear deformation. In addition, both the downregulation of PKC expression and pharmacological inhibition of PKC reduced WNV replication. In contrast, the expression of phosphorylation-deficient lamin mutants attenuated the inhibitory effect of downregulated PKC expression on WNV replication. Furthermore, the pharmacological inhibition of PKC increased the survival rate of WNV-infected mice and suppressed both viral replication and nuclear deformation in the brain. Collectively, these results demonstrate that C protein remodels the nuclear lamina architecture through the PKC-lamin pathway, and that virus-induced nuclear deformation contributes to WNV replication and pathogenesis. Author summaryThe West Nile virus (WNV), a neurotropic orthoflavivirus, causes severe neurological diseases in humans. In host cells, orthoflaviviruses exclusively replicate in the cytoplasm. However, their capsid (C) proteins are localized to both the nucleus and cytoplasm. Although the nuclear C protein has been implicated in viral replication and disease progression, its underlying mechanisms remain unclear. Here, we demonstrate that the WNV C protein induces nuclear deformation, accompanied by the phosphorylation of lamin and disassembly of the nuclear lamina, a structural scaffold that maintains the nuclear shape. The C protein promotes the localization of PKC, a host kinase protein, near the nuclear lamina. Suppression of PKC expression or activity reduces lamin phosphorylation, nuclear deformation, and WNV replication. Importantly, pharmacological inhibition of PKC in WNV-infected mice reduced nuclear deformation and viral replication in the brain and improved survival rates. Collectively, our findings identify the host nucleus as an important site of WNV-host interaction and provide a new perspective that WNV, despite replicating in the cytoplasm, remodels host nuclear architecture to promote viral replication and pathogenesis.

microbiology↗

bioRxiv2026

A surrogate marker of protection confirms the efficacy of an AddaS03-adjuvanted West Nile virus subunit vaccine

West Nile virus (WNV) is the causative agent of fatal West Nile encephalitis. To date, no human vaccine against WNV has been approved. Adjuvants are important for developing effective and affordable vaccines that enhance the immunogenicity and decrease the required antigen doses. In this study, we assessed the efficacy of AddaS03, a synthetic adjuvant analogous to AS03, in a WNV subunit vaccine composed of soluble recombinant envelope protein (sEnv). Using a passive immunization mouse model, we defined the neutralizing antibody titer threshold required for protection against lethal WNV infections and applied this threshold as a surrogate marker to evaluate adjuvant efficacy. AddaS03-adjuvanted formulations elicited markedly higher neutralizing antibody titers compared to Alhydrogel adjuvant 2% (Alhydrogel), even at suboptimal antigen doses, and consistently exceeded the defined protective threshold titer. Moreover, in a sequential challenge mouse model, AddaS03-adjuvanted vaccines completely protected mice from symptomatic WNV infections, whereas Alhydrogel-adjuvanted vaccines failed to confer full protection. Collectively, these findings demonstrate that AddaS03 is a promising adjuvant for WNV subunit vaccine development and highlights the utility of a passive immunization model for defining protective antibody thresholds as a surrogate marker for vaccine evaluation.

microbiology↗

bioRxiv2026

Integrated in vivo and transcriptomic analyses of lethal Oropouche virus infection reveal suppression of pathogenic host responses by antiviral therapy

Oropouche virus (OROV) is an emerging arbovirus responsible for large outbreaks of febrile illness in Central and South America, with increasing reports of severe neurological disease and fatal outcomes. Despite its growing public health impact, no approved antiviral therapies or vaccines are currently available. Here, we show that favipiravir, a broad-spectrum nucleoside analogue, robustly suppresses OROV replication and disease in vivo. In a lethal Syrian hamster model, favipiravir treatment provided complete protection against OROV infection, preventing viral dissemination to peripheral organs and the central nervous system, and remained highly effective when administration was initiated after infection. In contrast, insufficient antiviral control resulted in viral neuroinvasion and fatality. To define host responses associated with OROV pathogenesis and their modulation by antiviral therapy, we performed transcriptomic profiling of liver and brain tissues. OROV infection induced interferon-driven inflammatory programs accompanied by marked disruption of metabolic and tissue homeostatic pathways, whereas these transcriptional signatures were largely abrogated by favipiravir treatment. Together, our findings identify favipiravir as a potent antiviral candidate against OROV and provide the first in vivo, tissue-resolved transcriptomic framework of OROV infection, linking effective viral suppression with the prevention of neuroinvasion and pathogenic host responses. These results highlight antiviral intervention as a viable strategy to mitigate OROV-associated disease and mortality.

microbiology↗

bioRxiv2026

A lethal mouse model of Oz virus infection reveals hepatic involvement and enables evaluation of antiviral and vaccine efficacy

Oz virus (OZV), a member of the genus Thogotovirus in the family Orthomyxoviridae, is an emerging tick-borne virus reported in Japan. A fatal human case and seroepidemiological evidence of widespread exposure among wild animals and humans suggest its potential public health significance. However, no animal models suitable for pathogenic studies or evaluation of countermeasures are available for OZV. Here, we have established a lethal mouse model of OZV infection using cell-adapted virus and mice lacking type I interferon signaling (B6 Ifnar1 KO mice). OZV infection resulted in 100% mortality and was characterized by robust viral replication in the liver and spleen, severe hepatitis, and acute liver injury. Using this model, we also demonstrated that oral administration of T-705, an antiviral drug widely used against RNA viruses, as well as immunization with an inactivated whole virus particle vaccine, protected B6 Ifnar1 KO mice from lethal OZV infection by mitigating the acute hepatitis. The present study provides critical insights into OZV pathogenesis and establishes a practical in vivo platform for the development of countermeasures against OZV infection. Significance statementEmerging tick-borne viruses pose a growing public health concern, yet progress in understanding their pathogenesis and in developing countermeasures is often limited by the lack of relevant animal models. Oz virus (OZV), a recently identified thogotovirus associated with a fatal human case, exemplifies this challenge. Here, we establish a lethal mouse model of OZV infection that reveals pronounced hepatic involvement as a central pathological feature. Using this model, we demonstrate effective protection by both an antiviral drug and an inactivated vaccine against lethal OZV challenge. This study provides a practical in vivo platform for investigating OZV pathogenesis and for accelerating the development of medical countermeasures against this emerging tick-borne virus.

microbiology↗

bioRxiv2025

Differential functions of multiple Wnts and receptors in cell polarity regulation in C. elegans

Metazoan species possess multiple Wnt ligands and receptor genes that regulate diverse developmental processes. Because these genes often act redundantly, analysis of single-gene mutants does not necessarily reveal the full roles of Wnt signaling. In C. elegans, three Wnt genes (cwn-1, egl-20, and cwn-2) and three receptor genes (lin-17/Fzd, mom-5/Fzd, and cam-1/Ror) redundantly regulate the polarity of asymmetrically dividing seam cells. Here, we comprehensively analyzed genetic interactions among these Wnt and receptor genes. In mom-5 mutant backgrounds, additional mutations in Wnt genes disrupted cell polarization. In contrast, in cam-1 mutant backgrounds, Wnt mutations frequently caused abnormal polarity orientation. These findings indicate that MOM-5 and CAM-1 play distinct roles in establishing cell polarization and determining its orientation, respectively. lin-17 mutations suppressed polarity reversal in multiple Wnt compound mutants, suggesting that LIN-17 may function as a molecular switch for polarity orientation. Although all three Wnt genes regulate polarity orientation in a gradient-independent manner in the absence of receptor mutations, in lin-17 mutant backgrounds, reversing the expression gradients of cwn-1 and egl-20, but not cwn-2, enhanced polarity reversal. This suggests that cwn-1 and egl-20 act not only permissively but also instructively to regulate polarity orientation. Together, our results reveal distinct and cooperative functions of multiple Wnt ligands and receptors that ensure robust control of cell polarity.

developmental biology↗

bioRxiv2025

Application of the CPER reverse genetics system for genetic engineering of rabies virus

Reverse genetics (RG) systems are essential tools for basic virological studies and applied studies using engineered recombinant viruses in various research fields. While the circular polymerase extension reaction (CPER) has been widely applied to prepare a full-length infectious complementary DNA (cDNA) of positive-sense RNA viruses, its use for negative-sense RNA viruses (mononegaviruses) remains limited. Here, we report the first CPER-based RG system for rabies virus (RABV), a member of mononegaviruses. Infectious RABV was successfully rescued from cells transfected with helper plasmids and the CPER product, the assembled overlapping DNA fragments encoding the full-length viral genome cDNA and regulatory elements. Using this system, we generated wild-type, point-mutant, reporter-expressing, and chimeric RABVs, all of which retained their expected biological properties. Deep sequencing revealed that CPER-derived viruses occasionally harbor low-frequency mutations undetectable by Sanger sequencing, highlighting PCR-related artifacts as a limitation. In addition, CPER products with a pUC19 backbone could be directly applied for E. coli transformation and cloning of RABV full genome cDNA plasmids, offering a flexible, ligase-free cloning strategy for conventional RG. Our work establishes CPER as a versatile platform for engineering recombinant RABVs, facilitating rapid generation and genetic manipulation of RABV with potential applications for research on other mononegaviruses.

microbiology↗

bioRxiv2025

Detection and genetic characterization of pigeon gammacoronavirus

Most members of the genus Gammacoronavirus infect avian hosts, but far fewer viruses have been characterized than in the other coronavirus genera, leaving their diversity largely unclear. Pigeon gammacoronaviruses were previously detected by consensus PCR, but only partial sequences were determined. In this study, we comprehensively analyzed public RNA-seq datasets and reconstructed two nearly complete genomes of pigeon gammacoronaviruses. Molecular evolutionary analyses showed pigeon gammacoronaviruses belong to the subgenus Igacovirus, and their pairwise distances to the members of this subgenus meet the International Committee on Taxonomy of Viruses (ICTV) species demarcation criteria, supporting their designation as a novel species in this subgenus. Notably, although nucleotide sequences are highly conserved gammacoronaviruses, their 3'-genomic region exhibited differences in gene organization among pigeon coronavirus variants. These findings expand our knowledge of the diversity of gammacoronaviruses.

microbiology↗

bioRxiv2025

Simple and quantitative detection of double-stranded RNA as a signature of pan-virus infections using a luciferase-based biosensor

Viral infections produce double-stranded RNA (dsRNA) during replication, which trigger host innate immune responses. Immunoassays using anti-dsRNA antibodies have been widely employed to detect viral dsRNA. In this study, we used a luciferase-based dsRNA biosensor which consists of protein kinase R (PKR)-derived dsRNA binding domains fused to split luciferase subunits. Here, we demonstrate the use of the dsRNA biosensor to measure viral dsRNA in RNA specimens extracted from cells infected with Japanese encephalitis virus (JEV). Moreover, the biosensor reacts to a broad-spectrum of dsRNAs from infection with representatives of various viral families including positive- and negative-sense single-stranded RNA (ssRNA) viruses, dsRNA viruses, and DNA viruses. We validated the specific interaction between the dsRNA biosensor and viral RNA including subgenomic flavivirus RNA (sfRNA) through RNA immunoprecipitation. Additionally, we observed luminescence signals directly from lysates of JEV-infected cells after cell lysis and phase separation with Triton X-114. Finally, we used the biosensor to assess the activity of antiviral compounds. In summary, our results demonstrate that the luciferase-based dsRNA biosensor offers a simple, homogeneous, and high-throughput platform for quantifying viral replication, presenting a promising alternative to antibody-based dsRNA detection methods.

microbiology↗

bioRxiv2025

Discovery of The Clinical Candidate S-892216: A Second-Generation of SARS-CoV-2 3CL Protease Inhibitor for Treating COVID-19

The coronavirus disease 2019 (COVID-19) pandemic crisis has been mitigated by worldwide efforts to develop vaccines and therapeutic drugs. However, there remains concern regarding public health and an unmet need for therapeutic options. Herein, we report the discovery of S-892216, a second-generation SARS-CoV-2 3C-like protease (3CLpro) inhibitor, to treat COVID-19. S-892216 is a reversible covalent 3CLpro inhibitor with highly potent antiviral activity and an EC50 value of 2.48 nM against SARS-CoV-2 infected cells. Structure-based design of a covalent modifier for compound 1 revealed that introducing a nitrile warhead increased 3CLpro inhibition activity by 180-fold. Subsequent optimization efforts yielded S-892216, which combined a favorable pharmacokinetic profile and high off-target selectivity. S-892216 exhibited antiviral activity against diverse SARS-CoV-2 variants, with no cross-resistance to major mutations reducing antiviral activities of nirmatrelvir and ensitrelvir. In SARS-CoV-2-infected mice, S-892216 inhibited viral replication in the lungs similar to ensitrelvir, although at a 30-fold lower dose.

biochemistry↗

bioRxiv2024

Distinct functions of three Wnt proteins control mirror-symmetric organogenesis in the C. elegans gonad

Organogenesis requires the proper production of diverse cell types and their positioning/migration. However, the coordination of these processes during development remains poorly understood. The gonad in C. elegans exhibits a mirror-symmetric structure guided by the migration of distal tip cells (DTCs), which result from asymmetric divisions of somatic gonadal precursors (SGPs; Z1 and Z4). We found that the polarity of Z1 and Z4, which possess mirror-symmetric orientation, is controlled by the redundant functions of the LIN-17/Frizzled receptor and three Wnt proteins (CWN-1, CWN-2, and EGL-20) with distinct functions. In lin-17 mutants, CWN-2 promotes normal polarity in both Z1 and Z4, while CWN-1 promotes reverse and normal polarity in Z1 and Z4, respectively. In contrast, EGL-20 inhibits the polarization of both Z1 and Z4. In lin-17; egl-20 cwn-2 triple mutants with a polarity reversal of Z1, DTCs from Z1 frequently miss-migrate to the posterior side. Our further analysis demonstrates that the mis-positioning of DTCs in the gonad due to the polarity reversal of Z1 leads to mis-migration. Similar mis-migration was also observed in cki-1(RNAi) animals producing ectopic DTCs. These results highlight the role of Wnt signaling in coordinating the production and migration of DTCs to establish a mirror-symmetric organ.

developmental biology↗

bioRxiv2023

Snapshots from Cryo-ET of active SARS-CoV-2 virions

Understanding the molecular properties of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is crucial for tackling future outbreaks. Current structural knowledge of the trimeric spike protein relies on truncated recombinant proteins and/or inactivated full-length forms, which may suffer from overstabilization. Here, we apply cryo-electron tomography (cryo-ET) at a Biosafety Level 3 facility to study the virus structure in its native, active state. The virus particles exhibit variable shapes and sizes with diffusible spikes, with the majority in typical prefusion conformations. Notably, we identified unprecedented, a transient open-trimer prefusion states, revealing a hidden flexibility with opened S1 conformation. Subtomogram averaging of the prefusion spikes indicates a loosely packed trimeric architecture that may facilitate the formation of open-trimer state. A cryo-EM map of recombinant Omicron BA.2.75 spike protein further confirms the presence of this loosely packed trimer as a minor conformational state. The observed dynamics uncover conserved cryptic regions that can be targeted for broadly effective vaccines. Structural analysis of active viruses profoundly impacts our understanding of the overlooked fusion mechanism and vaccine, antibody/drug design.

microbiology↗

bioRxiv2023

Combination therapy with oral antiviral and anti-inflammatory drugs improves the efficacy of delayed treatment in severe COVID-19

Pulmonary infection with SARS-CoV-2 stimulates host immune responses and can also result in the progression of dysregulated and critical inflammation. Throughout the pandemic, the management and treatment of COVID-19 has been continuously updated with a range of antiviral drugs and immunomodulators. Monotherapy with oral antivirals has proven to be effective in the treatment of COVID-19. However, the treatment should be initiated in the early stages of infection to ensure beneficial therapeutic outcomes, and there is still room for further consideration on therapeutic strategies using antivirals. Here, we show that the oral antiviral ensitrelvir combined with the anti-inflammatory corticosteroid methylprednisolone has higher therapeutic effects and better outcomes in a delayed dosing model of SARS-CoV-2 infected hamsters compared to the monotherapy with ensitrelvir or methylprednisolone alone. Combination therapy with these drugs improved respiratory conditions and the development of pneumonia in hamsters even when the treatment was started after 2 days post infection. The combination therapy led to a differential histological and transcriptomic pattern in comparison to either of the monotherapies, with reduced lung damage and down-regulated expressions of genes involved in inflammatory response. Furthermore, we found that the combination treatment is effective in infection with both highly pathogenic delta and circulating omicron variants. Our results demonstrate the advantage of combination therapy with antiviral and corticosteroid drugs in COVID-19 treatment. Since both drugs are available as oral medications, this combination therapy could provide a clinical and potent therapeutic option for COVID-19.

microbiology↗

bioRxiv2022

Morphogenesis of bullet-shaped rabies virus particles requires a functional interplay between the viral matrix protein and ESCRT-I component TSG101

Viral protein assembly and virion budding are tightly regulated to enable the proper formation of progeny virions. At this late stage in the virus life cycle, some enveloped viruses take advantage of the host ESCRT (endosomal sorting complex required for transport) machinery, which contributes to the physiological functions of membrane modulation and abscission. Bullet-shaped viral particles are unique morphological characteristics of rhabdoviruses; however, the involvement of host factors in rhabdovirus infection, and specifically the molecular mechanisms underlying virion formation are not fully understood. In the present study, we used a siRNA screening approach and found that the ESCRT-I component TSG101 contributes to the propagation of rabies virus (RABV). We demonstrated that the matrix protein (M) of RABV interacts with TSG101 via the late-domain containing the PY and YL motifs, which are conserved in various viral proteins. Loss of the YL motif in the RABV M or the downregulation of host TSG101 expression resulted in the intracellular aggregation of viral proteins and abnormal virus particle formation, indicating a defect in the RABV assembly and budding processes. These results indicate that the interaction of the RABV M and TSG101 is pivotal for not only the efficient budding of progeny RABV from infected cells but also for the bullet-shaped virion morphology. ImportanceEnveloped-viruses bud from cells with the host lipid bilayer. Generally, the membrane modulation and abscission are mediated by host ESCRT (endosomal sorting complex required for transport) complexes. Some enveloped-viruses utilize their late (L)-domain to interact with ESCRTs, which promotes viral budding. Rhabdoviruses form characteristic bullet-shaped enveloped-virions, but the underlying molecular mechanisms involved remain elusive. Herein, we showed that TSG101, one of ESCRT components, supports rabies virus (RABV) budding and proliferation. TSG101 interacted with RABV matrix protein via L-domain, and the absence of this interaction resulted in intracellular virion accumulation and distortion of the morphology of progeny virions. Our study reveals that virion formation of RABV is highly regulated by TSG101 and the virus matrix protein.

microbiology↗

bioRxiv2022

2-Thiouridine is a broad-spectrum antiviral nucleoside analogue against positive-strand RNA viruses

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes significant morbidity and mortality worldwide, seriously impacting not only human health but also the global economy. Furthermore, over 1 million cases of newly emerging or re-emerging viral infections, specifically dengue virus (DENV), are known to occur annually. Because no virus-specific and fully effective treatments against these and many other viruses have been approved, they continue to be responsible for large-scale epidemics and global pandemics. Thus, there is an urgent need for novel, effective therapeutic agents. Here, we identified 2-thiouridine (s2U) as a broad-spectrum antiviral nucleoside analogue that exhibited antiviral activity against SARS-CoV-2 and its variants of concern, including the Delta and Omicron variants, as well as a number of other positive-sense single-stranded RNA (ssRNA+) viruses, including DENV. s2U inhibits RNA synthesis catalyzed by viral RNA-dependent RNA polymerase, thereby reducing viral RNA replication, which improved the survival rate of mice infected with SARS-CoV-2 or DENV in our animal models. Our findings demonstrate that s2U is a potential broad-spectrum antiviral agent not only against SARS-CoV-2 and DENV but other ssRNA+ viruses.

microbiology↗

bioRxiv2022

Virological characteristics of the SARS-CoV-2 Omicron BA.2.75

SARS-CoV-2 Omicron BA.2.75 emerged in May 2022. BA.2.75 is a BA.2 descendant but is phylogenetically different from BA.5, the currently predominant BA.2 descendant. Here, we showed that the effective reproduction number of BA.2.75 is greater than that of BA.5. While the sensitivity of BA.2.75 to vaccination- and BA.1/2 breakthrough infection-induced humoral immunity was comparable to that of BA.2, the immunogenicity of BA.2.75 was different from that of BA.2 and BA.5. Three clinically-available antiviral drugs were effective against BA.2.75. BA.2.75 spike exhibited a profound higher affinity to human ACE2 than BA.2 and BA.5 spikes. The fusogenicity, growth efficiency in human alveolar epithelial cells, and intrinsic pathogenicity in hamsters of BA.2.75 were comparable to those of BA.5 but were greater than those of BA.2. Our multiscale investigations suggest that BA.2.75 acquired virological properties independently of BA.5, and the potential risk of BA.2.75 to global health is greater than that of BA.5.

microbiology↗

bioRxiv2022

Comparative pathogenicity of SARS-CoV-2 Omicron subvariants including BA.1, BA.2, and BA.5

Unremitting emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants imposes us to continuous control measurement. Given the rapid spread, new Omicron subvariant named BA.5 is urgently required for characterization. Here we analyzed BA.5 with the other Omicron variants BA.1, BA.2, and ancestral B.1.1 comprehensively. Although in vitro growth kinetics of BA.5 is comparable among the Omicron subvariants, BA.5 become much more fusogenic than BA.1 and BA.2. The airway-on-a-chip analysis showed that the ability of BA.5 to disrupt the respiratory epithelial and endothelial barriers is enhanced among Omicron subvariants. Furthermore, in our hamster model, in vivo replication of BA.5 is comparable with that of the other Omicrons and less than that of the ancestral B.1.1. Importantly, inflammatory response against BA.5 is strong compared with BA.1 and BA.2. Our data suggest that BA.5 is still low pathogenic compared to ancestral strain but evolved to induce enhanced inflammation when compared to prior Omicron subvariants.

microbiology↗

bioRxiv2022

Discovery of Chlorofluoroacetamide-Based Covalent Inhibitors for SARS-CoV-2 3CL Protease

The pandemic of coronavirus disease 2019 (COVID-19) has urgently necessitated the development of antiviral agents against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The 3C-like protease (3CLpro) is a promising target for COVID-19 treatment. Here, we report the new class of covalent inhibitors for 3CLpro possessing chlorofluoroacetamide (CFA) as a cysteine reactive warhead. Based on the aza-peptide scaffold, we synthesized the series of CFA derivatives in enantiopure form and evaluated their biochemical efficiencies. The data revealed that 8a (YH-6) with R configuration at the CFA unit strongly blocks the SARS-CoV-2 replication in the infected cells and this potency is comparable to that of nirmatrelvir. The X-ray structural analysis shows that 8a (YH-6) forms a covalent bond with Cys145 at the catalytic center of 3CLpro. The strong antiviral activity and sufficient pharmacokinetics property of 8a (YH-6) suggest its potential as a lead compound for treatment of COVID-19.

biochemistry↗

bioRxiv2022

Oral administration of S-217622, a SARS-CoV-2 main protease inhibitor, decreases viral load and accelerates recovery from clinical aspects of COVID-19

In parallel with vaccination, oral antiviral agents are highly anticipated to act as countermeasures for the treatment of the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Oral antiviral medication demands not only high antiviral activity but also target specificity, favorable oral bioavailability, and high metabolic stability. Although a large number of compounds have been identified as potential inhibitors of SARS-CoV-2 infection in vitro, few have proven to be effective in vivo. Here, we show that oral administration of S-217622, a novel inhibitor of SARS-CoV-2 main protease (Mpro, also known as 3C-like protease), decreases viral load and ameliorates the disease severity in SARS-CoV-2-infected hamsters. S-217622 inhibited viral proliferation at low nanomolar to sub-micromolar concentrations in cells. Oral administration of S-217622 demonstrated eminent pharmacokinetic properties and accelerated recovery from acute SARS-CoV-2 infection in hamster recipients. Moreover, S-217622 exerted antiviral activity against SARS-CoV-2 variants of concern (VOCs), including the highly pathogenic Delta variant and the recently emerged Omicron variant. Overall, our study provides evidence that S-217622, an antiviral agent that is under evaluation in a phase II/III clinical trial, possesses remarkable antiviral potency and efficacy against SARS-CoV-2 and is a prospective oral therapeutic option for COVID-19.

microbiology↗