Inhibition of Ebola Virus by a Molecularly Engineered Banana Lectin

Ebolaviruses cause an often rapidly fatal syndrome known as Ebola virus disease (EVD), with average case fatality rates of similar to 50%. There is no licensed vaccine or treatment for EVD, underscoring the urgent need to develop new anti-ebolavirus agents, especially in the face of an ongoing outbreak in the Democratic Republic of the Congo and the largest ever outbreak in Western Africa in 2013-2016. Lectins have been investigated as potential antiviral agents as they bind glycans present on viral surface glycoproteins, but clinical use of them has been slowed by concerns regarding their mitogenicity, i.e. ability to cause immune cell proliferation. We previously engineered a banana lectin (BanLec), a carbohydrate-binding protein, such that it retained antiviral activity but lost mitogenicity by mutating a single amino acid, yielding H84T BanLec (H84T). H84T shows activity against viruses containing high-mannose N-glycans, including influenza A and B, HIV-1 and -2, and hepatitis C virus. Since ebolavirus surface glycoproteins also contain many high-mannose N-glycans, we assessed whether H84T could inhibit ebolavirus replication. H84T inhibited Ebola virus (EBOV) replication in cell cultures. In cells, H84T inhibited both virus-like particle (VLP) entry and transcription/replication of the EBOV mini-genome at high micromolar concentrations, while inhibiting infection by transcription- and replication-competent VLPs, which measures the full viral life cycle, in the low micromolar range. H84T did not inhibit assembly, budding, or release of VLPs. These findings suggest that H84T may exert its anti-ebolavirus effect(s) by blocking both entry and transcription/replication. In a mouse model, H84T partially (maximally, similar to 50-80%) protected mice from an otherwise lethal mouse-adapted EBOV infection. Interestingly, a single dose of H84T pre-exposure to EBOV protected similar to 80% of mice. Thus, H84T shows promise as a new anti-ebolavirus agent with potential to be used in combination with vaccination or other agents in a prophylactic or therapeutic regimen. Author summary There are no approved vaccines or treatments to combat infections with ebolaviruses, which cause Ebola virus disease (EVD), an often rapidly fatal disease characterized by fever and bleeding that results in death in up to similar to 90% of cases. Ebolaviruses are among the most pathogenic viruses that cause human disease and represent a threat to global public health. Outbreaks of EVD occur periodically in African countries and can be exported elsewhere, with recent outbreaks including one ongoing in the Democratic Republic of the Congo and the largest ever in Western Africa in 2013-2016. There is therefore a great need to develop new vaccines and treatments that target ebolaviruses. We examined whether a lectin (carbohydrate-binding protein), predicted to bind to carbohydrates present on the surface of many viruses and thereby interfere with infection, could block ebolavirus infection and be used for prevention and/or treatment of EVD. We found that the protein blocked ebolavirus infection in cell cultures and, moreover, protected a significant proportion of ebolavirus-infected mice from death, even when administered only once before exposure to virus as a preventive. The protein hence shows promise as a potential agent to prevent and/or treat EVD.