Targeting spike glycans to inhibit SARS-CoV2 viral entry

Lectins in oncology and virology: Mechanisms of anticancer activity and SARS-CoV-2 inhibition

Lectins are proteins or glycoproteins of non-immune origin with carbohydrate-binding properties. They are found both prokaryotic and eukaryotic organisms. The most abundant source of the lectins are plants. Many lectins have anticancer effects by directly exerting cytotoxic effects on malignant cells or indirectly activating the immune system. Lectins also have antiviral activities. These proteins can recognise glycoproteins on the surface of enveloped viruses and bind to them. This creates a physical barrier between them and the corresponding receptors on the surface of the host cell, which prevents the virus from entering the cell and can thus effectively inhibit the replication of the virus. In this review, we focus on the anticancer activities of selected lectins and the underlying mechanisms. We also discuss different types of lectins with antiviral activity. We have paid special attention to lectins with inhibitory activity against SARS-CoV-2. Finally, we outline the challenges of using lectins in therapy and suggest future research directions.

Inhibition of SARS-CoV-2 infection and replication by Petasites hybridus CO2-extract (Ze 339)

BACKGROUND

The intensified search for low-threshold herbal anti-viral drugs would be of great advantage in prevention of early stages of infection. Since the SARS-CoV-2 Omicron variant has prevailed in western countries, the course has only been mild, but there are still no widely available drugs that can alleviate or shorten disease progression and counteract the development of Long-COVID. This study aimed to investigate the antiviral effects of a CO2-extract from Petasites hybridus (Ze 339).

METHODS

We analyzed the infection and replication rate of SARS-CoV-2 in primary normal human bronchial epithelial cells (NHBEs) using a GFP-expressing version of the wild-type SARS-CoV-2 virus and live cell imaging. Upon infection with a clinical isolate of the Omicron variant, viral RNA content was quantified, and plaque assays were performed. In addition, the human transcriptome was analyzed after 4- and 24-hours post infection using whole genome microarrays.

RESULTS

Ze 339 had a protective effect on primary airway epithelial cells during SARS-CoV-2 infection and impeded SARS-CoV-2 infection and replication in NHBE. Notably, Ze 339 inhibited the expression of infection-induced IFNA10 by 8.6-fold (p < 0.05) and additionally reduced a wide range of other interferons (IFNA6, IFNA7, IFNA8, IFNA21, IFNE, IFNW1).

CONCLUSION

Thereby, Ze 339 attenuated epithelial infection by SARS-CoV-2 and modeled the IFN response. In conclusion, this study highlights Ze 339 as a potential treatment option for COVID-19 that limits infection-associated cell intrinsic immune responses.

The Antiviral Activity of the Lectin Griffithsin against SARS-CoV-2 Is Enhanced by the Presence of Structural Proteins

Although COVID-19 transmission has been reduced by the advent of vaccinations and a variety of rapid monitoring techniques, the SARS-CoV-2 virus itself has shown a remarkable ability to mutate and persist. With this long track record of immune escape, researchers are still exploring prophylactic treatments to curtail future SARS-CoV-2 variants. Specifically, much focus has been placed on the antiviral lectin Griffithsin in preventing spike protein-mediated infection via the hACE2 receptor (direct infection). However, an oft-overlooked aspect of SARS-CoV-2 infection is viral capture by attachment receptors such as DC-SIGN, which is thought to facilitate the initial stages of COVID-19 infection in the lung tissue (called trans-infection). In addition, while immune escape is dictated by mutations in the spike protein, coronaviral virions also incorporate M, N, and E structural proteins within the particle. In this paper, we explored how several structural facets of both the SARS-CoV-2 virion and the antiviral lectin Griffithsin can affect and attenuate the infectivity of SARS-CoV-2 pseudovirus. We found that Griffithsin was a better inhibitor of hACE2-mediated direct infection when the coronaviral M protein is present compared to when it is absent (possibly providing an explanation regarding why Griffithsin shows better inhibition against authentic SARS-CoV-2 as opposed to pseudotyped viruses, which generally do not contain M) and that Griffithsin was not an effective inhibitor of DC-SIGN-mediated trans-infection. Furthermore, we found that DC-SIGN appeared to mediate trans-infection exclusively via binding to the SARS-CoV-2 spike protein, with no significant effect observed when other viral proteins (M, N, and/or E) were present. These results provide etiological data that may help to direct the development of novel antiviral treatments, either by leveraging Griffithsin binding to the M protein as a novel strategy to prevent SARS-CoV-2 infection or by narrowing efforts to inhibit trans-infection to focus on DC-SIGN binding to SARS-CoV-2 spike protein.