A promising therapeutic solution to COVID-19 - using ACE2 decoy

[Ygggdrasil]

As noted in this thread, I have been following the development of APN01 (hrsACE2) by Apeiron. How does the nano-particle capsule improve delivery of the ACE2 decoy molecule over the human recombinant soluble version, hrsACE2?

The evACE2 contents appears to be essentially the same molecule (presumably without the part that makes hrsACE2 soluble) but with a different delivery system. The nano particle delivery system is used to allow intra-cellular delivery e.g. they are used by mRNA vaccines to allow the vaccine particles to pass through human cell membranes and deliver the mRNA contents into the cell. But, as I understand it, the decoy molecule remains in the extra-cellular environment to attach to the spike proteins of the virus and prevent attachment of the virus to the ACE2 receptor which is essential for the virus to gain entry to the cell. Perhaps @Ygggdrasil may wish to comment.

AM

Here's the citation to the evACE2 paper, since this has not yet been linked in the thread:

Circulating ACE2-expressing extracellular vesicles block broad strains of SARS-CoV-2
https://www.nature.com/articles/s41467-021-27893-2

Abstract:

The severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) has caused the pandemic of the Coronavirus induced disease 2019 (COVID-19) with evolving variants of concern. It remains urgent to identify novel approaches against broad strains of SARS-CoV-2, which infect host cells via the entry receptor angiotensin-converting enzyme 2 (ACE2). Herein, we report an increase in circulating extracellular vesicles (EVs) that express ACE2 (evACE2) in plasma of COVID-19 patients, which levels are associated with severe pathogenesis. Importantly, evACE2 isolated from human plasma or cells neutralizes SARS-CoV-2 infection by competing with cellular ACE2. Compared to vesicle-free recombinant human ACE2 (rhACE2), evACE2 shows a 135-fold higher potency in blocking the binding of the viral spike protein RBD, and a 60- to 80-fold higher efficacy in preventing infections by both pseudotyped and authentic SARS-CoV-2. Consistently, evACE2 protects the hACE2 transgenic mice from SARS-CoV-2-induced lung injury and mortality. Furthermore, evACE2 inhibits the infection of SARS-CoV-2 variants (α, β, and δ) with equal or higher potency than for the wildtype strain, supporting a broad-spectrum antiviral mechanism of evACE2 for therapeutic development to block the infection of existing and future coronaviruses that use the ACE2 receptor.

As to your questions about the paper, a few quick notes:
1) One element of the paper is that the evACE2 molecules were found to be naturally produced by the body (e.g. they were not designed in the lab as a therapeutic).

2) While vesicles and lipid nanoparticles allow intracellular delivery, in this case the ACE2 molecules are in vesicles presumably because of the opposite process: ACE2 molecules from cells being secreted out of the cell in extracellular vesicles.

3) As noted in the abstract of the article, the researchers compared the efficacy of evACE2 to recombinant human ACE2 in blocking SARS-CoV-2 infection. They conclude: "Compared to vesicle-free recombinant human ACE2 (rhACE2), evACE2 shows a 135-fold higher potency in blocking the binding of the viral spike protein RBD, and a 60- to 80-fold higher efficacy in preventing infections by both pseudotyped and authentic SARS-CoV-2." However, it is unclear how this would compare to the soluble hrsACE2 (presumably the rhACE2 was ineffective because it was not soluble or stable in the body).

4) In general, delivery systems are very important parts of drugs and can have profound effects on the efficacy of drugs. For example, there could be differences in how stable hrsACE2 vs evACE2 are in the body, which can affect dosing and how often the drug would have to be administered. One method or the other could allow greater amounts of the ACE2 molecule in the body, which could affect how well they are able to block infection. Delivery could also affect the distribution of the drug to different sites of the body (given that SARS-CoV-2 infection begins in the respiratory tract, efficient delivery of the drug to that site would be important in preventing disease and preventing transmission while delivery to other sites of the body is important for treating severe disease). It's difficult to know which approach is better in the absence of any data comparing the two drugs.

5) Another consideration is ease of manufacture. It is likely much easier to produce hrsACE2 as a drug vs an evACE2.

 

[Andrew Mason]

Thanks @Ygggdrasil for your very helpful post and the link to the paper.

Just a few observations/comments on the paper:

1. It appears that the existence of these evACE2 exosomes was previously unknown. Apparently the SARS-CoV-2 virus triggers a response in certain cells to produce these evACE2s:

"Consistently, SARS-CoV-2 infection triggered secretion of ACE2+TSG101+ EVs by human pneumocyte A549 cells overexpressing ACE2 (Supplementary Fig. 1e), implying that upregulated production of ACE2+ EVs is part of the innate response to SARS-CoV-2 infection in COVID-19 patients."

2. It appears that the evACE2 exosome includes the transmembrane protein with each ACE2 receptor (which, as I understand, is not part of hrsACE2) - and each EV presents 20-40 of such ACE2 complexes on its surface:

"Based on the molecular weight of ACE2 and the number of EV particles detected in isolated HEK-ev1 and HeLa-ev2 respectively, each EV might present 20–40 ACE2 molecules. Collectively, our results demonstrate that the SARS-CoV-2 entry receptor ACE2 protein is expressed on EVs, most likely as a full-length transmembrane protein."

My understanding is that the hrsACE2 (human recombinant soluble ACE2) is just the extra-cellular part of the whole ACE2 transmembrane protein as shown here¹:

¹ ACE2: The Key Molecule for Understanding the Pathophysiology of Severe and Critical Conditions of COVID-19: Demon or Angel?,Li Xiao, Hiroshi Sakagami and Nobuhiko Miwa, Viruses 2020, 12, 491; 28Apr20,

I am trying to understand why the evACE2 would be so much more effective than hrsACE2 in acting as a decoy for the virus. I note that in a cell that expresses ACE2, the TMPRSS2 protease is required in order for the virus to pass through the cell membrane. If the evACE2 exosome also presents the TMPRSS2 protease, could the evACE2 act by ingesting viruses? Since the evACE2 has dozens of receptors, each EV could ingest dozens of viruses that would be otherwise able to infect a cell. Since the EV has no machinery for translating proteins, the virus would not be able to reproduce.

Otherwise, if the evACE2 just allows the extracellular receptor portion to attach to the virus I don't see why it should that much more effective than hrsACE2 in blocking the virus.

AM