Heparan sulfate promotes ACE2 super-cluster assembly to enhance SARS-CoV-2-associated syncytium formation.

The mechanism of syncytium formation, caused by spike-induced cell-cell fusion in severe COVID-19, is largely unclear. Here we combine chemical genetics with 4D confocal imaging to establish the cell surface heparan sulfate (HS) as a critical host factor exploited by SARS-CoV-2 to enhance spike’s fusogenic activity. HS binds spike to facilitate ACE2 clustering, generating synapse-like cell-cell contacts to promote fusion pore formation. ACE2 clustering, and thus, syncytium formation is significantly mitigated by chemical or genetic elimination of cell surface HS, while in a cell-free system consisting of purified HS, spike, and lipid-anchored ACE2, HS directly induces ACE2 clustering. Importantly, the interaction of HS with spike allosterically enables a conserved ACE2 linker in receptor clustering, which concentrates spike at the fusion site to overcome fusion-associated activity loss. This fusion-boosting mechanism can be effectively targeted by an investigational HS-binding drug, which reduces syncytium formation in vitro and viral infection in mice.

Bisubstrate Inhibitors of Severe Acute Respiratory Syndrome Coronavirus-2 Nsp14 Methyltransferase.

Taking advantage of the uniquely constricted active site of SARS-CoV-2 Nsp14 methyltransferase, we have designed bisubstrate inhibitors interacting with the SAM and RNA substrate binding pockets. Our efforts have led to nanomolar inhibitors including compounds 3 and 10. As a prototypic inhibitor, compound 3 also has an excellent selectivity profile over a panel of human methyltransferases. Remarkably, C-nucleoside 10 exhibits high antiviral activity and low cytotoxicity, leading to a therapeutic index (CC50/EC50) greater than 139. Furthermore, a brief metabolic profiling of these two compounds suggests that they are less likely to suffer from major metabolic liabilities. Moreover, computational docking studies point to protein-ligand interactions that can be exploited to enhance inhibitory activity. In short, discovery of inhibitor 10 clearly demonstrates that potent and selective anti-SARS-CoV-2 activity can be achieved by targeting the Nsp14 methyltransferase. Therefore, the current work strongly supports the continued pursuit of Nsp14 methyltransferase inhibitors as COVID-19 therapeutics.

Bisubstate Inhibitors of Severe Acute Respiratory Syndrome Coronavirus-2 Nsp14 Methyltransferase

Taking advantage of the uniquely constricted active site of SARS-CoV-2 Nsp14 methyltransferase, we have designed bisubstrate inhibitors interacting with the SAM and RNA substrate binding pockets. Our efforts have led to nanomolar inhibitors including compounds 3 and 10. As a prototypic inhibitor, compound 3 also has an excellent selectivity profile over a panel of human methyltransferases. Remarkably, C-nucleoside 10 exhibits high antiviral activity and low cytotoxicity, leading to a therapeutic index (CC50/EC50) greater than 139. Furthermore, a brief metabolic profiling of these two compounds suggests that they are less likely to suffer from major metabolic liabilities. Moreover, computational docking studies point to protein–ligand interactions that can be exploited to enhance inhibitory activity. In short, discovery of inhibitor 10 clearly demonstrates that potent and selective anti-SARS-CoV-2 activity can be achieved by targeting the Nsp14 methyltransferase. Therefore, the current work strongly supports the continued pursuit of Nsp14 methyltransferase inhibitors as COVID-19 therapeutics.

A recombinant spike protein subunit vaccine confers protective immunity against SARS-CoV-2 infection and transmission in hamsters.

Multiple safe and effective vaccines that elicit immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are necessary to respond to the ongoing coronavirus disease 2019 (COVID-19) pandemic. Here, we developed a protein subunit vaccine composed of spike ectodomain protein (StriFK) plus a nitrogen bisphosphonate-modified zinc-aluminum hybrid adjuvant (FH002C). StriFK-FH002C generated substantially higher neutralizing antibody titers in mice, hamsters, and cynomolgus monkeys than those observed in plasma isolated from COVID-19 convalescent individuals. StriFK-FH002C also induced both TH1- and TH2-polarized helper T cell responses in mice. In hamsters, StriFK-FH002C immunization protected animals against SARS-CoV-2 challenge, as shown by the absence of virus-induced weight loss, fewer symptoms of disease, and reduced lung pathology. Vaccination of hamsters with StriFK-FH002C also reduced within-cage virus transmission to unvaccinated, cohoused hamsters. In summary, StriFK-FH002C represents an effective, protein subunit-based SARS-CoV-2 vaccine candidate.

A SCID mouse-human lung xenograft model of SARS-CoV-2 infection.

SARS-CoV-2 infection, which is responsible for the current COVID-19 pandemic, can cause life-threatening pneumonia, respiratory failure and even death. Characterizing SARS-CoV-2 pathogenesis in primary human target cells and tissues is crucial for developing vaccines and therapeutics. However, given the limited access to clinical samples from COVID-19 patients, there is a pressing need for in vitro/in vivo models to investigate authentic SARS-CoV-2 infection in primary human lung cells or tissues with mature structures. The present study was designed to evaluate a humanized mouse model carrying human lung xenografts for SARS-CoV-2 infection in vivo. Methods: Human fetal lung tissue surgically grafted under the dorsal skin of SCID mice were assessed for growth and development after 8 weeks. Following SARS-CoV-2 inoculation into the differentiated lung xenografts, viral replication, cell-type tropism and histopathology of SARS-CoV-2 infection, and local cytokine/chemokine expression were determined over a 6-day period. The effect of IFN-α treatment against SARS-CoV-2 infection was tested in the lung xenografts. Results: Human lung xenografts expanded and developed mature structures closely resembling normal human lung. SARS-CoV-2 replicated and spread efficiently in the lung xenografts with the epithelial cells as the main target, caused severe lung damage, and induced a robust pro-inflammatory response. IFN-α treatment effectively inhibited SARS-CoV-2 replication in the lung xenografts. Conclusions: These data support the human lung xenograft mouse model as a useful and biological relevant tool that should facilitate studies on the pathogenesis of SARS-CoV-2 lung infection and the evaluation of potential antiviral therapies.

Gender associates with both susceptibility to infection and pathogenesis of SARS-CoV-2 in Syrian hamster.

Epidemiological studies of the COVID-19 patients have suggested the male bias in outcomes of lung illness. To experimentally demonstrate the epidemiological results, we performed animal studies to infect male and female Syrian hamsters with SARS-CoV-2. Remarkably, high viral titer in nasal washings was detectable in male hamsters who presented symptoms of weight loss, weakness, piloerection, hunched back and abdominal respiration, as well as severe pneumonia, pulmonary edema, consolidation, and fibrosis. In contrast with the males, the female hamsters showed much lower shedding viral titers, moderate symptoms, and relatively mild lung pathogenesis. The obvious differences in the susceptibility to SARS-CoV-2 and severity of lung pathogenesis between male and female hamsters provided experimental evidence that SARS-CoV-2 infection and the severity of COVID-19 are associated with gender.