RR:C19 Evidence Scale rating by reviewer:
Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.
This manuscript presents a study on the ability of a dimeric lipopeptide fusion inhibitor to block SARS-CoV-2 infection in a cell-cell fusion assay, in vitro infection, and the ferret as an in vivo animal transmission model of infection. The authors claim that the lipopeptides are highly stable, non-toxic, and able to block SARS-CoV-2 infection and transmission in the ferret are very well-supported by the data and multiple methods used. Decision-makers should consider the claims in this study actionable with only minor limitations.
The studies are presented in a very clear and well-written, easy-to-understand format. The study is based on sound theory and prior data backing up the logical approach. In short, several monomeric and dimeric forms of inhibitory peptide formulations are tested in a cell-cell fusion assay to select the strongest candidate. These and subsequent in vitro and in vivo experiments are well controlled and the constructs are tested in addition in an assay for cellular toxicity. Importantly, the authors test the lipopeptide against known S protein variants and the SARS-CoV-1 and MERS-CoV S proteins, finding equal and significant inhibitory potential, respectively, suggesting potential broad-scale use against coronavirus (why not test against common cold CoV?). The lipopeptide performed well in VeroE6 cell infection assays and completely blocked ferret transmission in an experiment with 2 susceptible animals exposed for 24 hours to shedding animals. The proposed construct being stable, non-toxic, and inexpensive seems a strong candidate to have a potential high impact on public health implementation during the current pandemic.
The suitability of the ferret model for transmission studies of SARS-CoV-2 is debatable considering the dose required to initiate infection in contact animals and the lack of clinical signs observed in infected hosts. In addition, the authors cite the outbreak in mink populations as evidence for mustelid species in general being competent and highly susceptible and transmitting hosts. In fact, the American mink and the ferret are relatively distant on the mustelid phylogeny and the one should not be used to imply the others’ suitability as a model, particularly considering the potential adaptability of the SARS-CoV-2 virus within hosts.
The authors do not comment on what seems like peculiarly different IC50 curves for SARS-CoV-2 infection in VeroE6 vs VeroE6-TMPRSS expressing cells, which might have been expected to have a higher IC50. Why are these curves different and does it imply uncertainty about the IC50 for implementation in animal hosts, particularly humans?