ACE2 nanoparticles prevent cell entry of SARS-CoV-2 (preprint)

We have now been in the grip of the COVID-19 pandemic for over two years with devastating consequences. The continual evolution of the virus has challenged the efficacy of many vaccines and treatment options based on immunotherapies are compromised by this viral escape. One treatment strategy that averts viral escape is the use of constructs based on its entry receptor Angiotensin-Converting Enzyme 2 (ACE2) acting as decoys. Here, we combined full-length human ACE2 with viral vectors commonly used for gene therapy to form nanoparticles that present ACE2 on their surface analogous to human cells. Using cell-based assays and direct, multiscale imaging including cryogenic cellular tomography, we show that these ACE2 nanoparticles are highly efficient in preventing entry of SARS-CoV-2, the virus causing COVID-19, in model cell systems as well as human respiratory tract ex-vivo cultures. Thus, ACE2 nanoparticles have high potential as the next generation therapeutics for addressing the immediate needs of the current pandemic and possible future outbreaks.

SARS-CoV-2 Omicron variant replication in human respiratory tract ex vivo (preprint)

Emergence of SARS-CoV-2 variants of concern (VOC) with progressively increased transmissibility between humans is a threat to global public health. Omicron variant also evades immunity from natural infection or vaccines 1 . It is unclear whether its exceptional transmissibility is due to immune evasion or inherent virological properties.We compared the replication competence and cellular tropism of the wild type (WT) virus, D614G, Alpha, Beta, Delta and Omicron variants in ex vivo explant cultures of human bronchus and lung. Dependence on TMPRSS2 for infection was also evaluated. We show that Omicron replicated faster than all other SARS-CoV-2 in the bronchus but less efficiently in the lung parenchyma. All VOCs had similar cellular tropism as the WT. Delta was more dependent on serine protease than other VOCs tested.Our findings demonstrate that Omicron is inherently able to replicate faster than other variants known to date and this likely contributes to its inherently higher transmissibility, irrespective of its ability to evade antibody immunity. The lower replication competence of Omicron in human lung may be compatible with reduced severity but the determinants of severe disease are multifactorial. These findings provide important biological clues to the transmissibility and pathogenesis of SARS-CoV-2 VOCs.

Simeprevir suppresses SARS-CoV-2 replication and synergizes with remdesivir (preprint)

The outbreak of coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global threat to human health. Using a multidisciplinary approach, we identified and validated the hepatitis C virus (HCV) protease inhibitor simeprevir as an especially promising repurposable drug for treating COVID-19. Simeprevir potently reduces SARS-CoV-2 viral load by multiple orders of magnitude and synergizes with remdesivir in vitro. Mechanistically, we showed that simeprevir inhibits the main protease (Mpro) and unexpectedly the RNA-dependent RNA polymerase (RdRp). Our results thus reveal the viral protein targets of simeprevir, and provide preclinical rationale for the combination of simeprevir and remdesivir for the pharmacological management of COVID-19 patients. One Sentence SummaryDiscovery of simeprevir as a potent suppressor of SARS-CoV-2 viral replication that synergizes with remdesivir.

Tropism of the Novel Coronavirus SARS-CoV-2 in Human Respiratory Tract: An Analysis in Ex Vivo and In Vitro Cultures (preprint)

Background: A novel human coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019, to cause a respiratory disease (COVID-19) of varying severity in Wuhan China, subsequently spreading to other parts of China and beyond. Methods: We infected ex vivo explant cultures of the human conjunctiva, bronchus and lung, and in vitro cultures of primary human alveolar epithelial cells and macrophages with SARS-CoV-2, and assessed viral tropism, replication competence and innate immune responses, in comparison with SARS-CoV, MERS-CoV, and the 2009 pandemic influenza H1N1 (pdmH1N1) virus.Findings: SARS-CoV-2 infected ciliated, mucus secreting and club cells of bronchial epithelium, spindled morphologically type I pneumocytes in the lung, and the conjunctival mucosa. Virus replication competence of SARS-CoV-2 in the bronchus was higher than that of SARS-CoV but lower than pdmH1N1. SARS-CoV-2 replication was comparable with SARS-CoV and pdmH1N1 in the lung but was lower than MERS-CoV. SARS-CoV-2 virus was a less potent inducer of pro-inflammatory cytokines compared with H5N1 and MERS-CoV. Influenza virus infection of alveolar epithelial cells increased ACE2 expression.Interpretation: The conjunctival epithelium and the conducting airways appear to be potential portals of infection of SARS-CoV-2. Both SARS-CoV and SARS-CoV-2 replicated comparably in the alveolar epithelium explaining the progression of infection to a primary viral pneumonia.Funding Statement: US National Institute of Allergy and Infectious Diseases (NIAID) under Centers of Excellence for Influenza Research and Surveillance (CEIRS) contract no. HHSN272201400006C and the Theme Based Research Scheme (Ref: T11-705/14N), Hong Kong Special Administrative Region.Declaration of Interests: There is no conflict of interest for all authors.Ethics Approval Statement: All experiments were carried out in a Bio-safety level 3 (BSL-3) facility. Informed consent was obtained from all subjects and approval was granted by the Institutional Review Board (IRB) of the University of Hong Kong and the Hospital Authority (Hong Kong West) (approval no: UW 20-167).