Professor Josef Penninger. Credit: Paul Joseph for LSI.

Angiotensin-converting enzyme 2 (ACE2) the receptor used by the SARS-CoV-2 virus as a gateway to enter and infect host cells has garnered significant attention for the wrong reasons over recent months. But could it also point towards an exit route out of this pandemic? In an interview with Technology Networks, the renowned immunologist Professor Josef Penninger nicknamed "Mr ACE2" explains why he thinks so, and discusses the latest clinical data obtained from testing the soluble ACE2 receptor, APN01.

Before the Nature paper was published, the researchers discovered that ACE2 was also expressed in the lung, a curious finding which "didn't make any sense".1 They wanted to get to the bottom of it. "All of my postdocs worked on models for intensive care units for mice so that we could study acute lung injury. At that time, between 20002003, there were maybe two or three groups on the planet which did this. The reason being it was difficult to create stable and reproducible models. My postdocs worked for many years to get the model going and then we studied ACE2 using it. We found that when we delete ACE2 in animal models the lung injury got much worse. The reninangiotensin unit is a critical component of lung injury."2

What role does ACE2 play in the body?In 2020, thanks to the contribution of Penninger and others, we now have a more thorough understanding of the role ACE2 plays in human physiology. ACE2 is an enzyme that is expressed on the membranes of cells, located in several places throughout the body, including the heart, lungs, arteries, kidneys and intestines. It is a critical component of a biochemical pathway known as the reninangiotensin system. In this pathway, ACE2 helps to modulate a protein called angiotensin II which increases blood pressure and inflammation, causing damage to blood vessels and other tissue injuries. ACE2 catalyzes the hydrolysis of angiotensin II into other molecules that counteract its harmful effects.3

However, in 2005, the World Health Organization (WHO) declared that SARS was contained. "Of course, now everyone was saying who cares. It's beautiful work but it has no relevance because there is no SARS," Penninger recalls. Fast-forward to 2020, the novel coronavirus SARS-CoV-2 has brought life to a screeching halt, and the irony of this research being declared "irrelevant" leaves a sour taste.

I asked Penninger what his initial thoughts were when the news broke of the novel coronavirus outbreak. He recalls: "It immediately clicked in my brain that ACE2 must be the target receptor for SARS-CoV-2 because of the similarities between the Spike protein of SARS and SARS-CoV-2." Sure enough, he was right. As the number of COVID-19 fatalities began to rapidly climb, scientists, industry leaders and global authorities assembled to search for an effective therapeutic against the virus.In April 2020, Apeiron announced it had received regulatory approvals in Austria, Germany and Denmark to initiate a Phase II clinical trial of APN01 in 200 severely infected COVID-19 patients. The announcement followed preclinical testing of APN01 in SARS-CoV-2 cell models and human-derived organoids. Often referred to as "mini-organs", organoids are three-dimensional cell cultures that can recapitulate, to a certain degree, the complexity of an organ.

How does APN01 work in the context of SARS-CoV-2?As APN01 imitates the ACE2 receptor, SARS-CoV-2 binds to it instead of the human form of the receptor. Consequently, the virus cannot enter and infect cells, so APN01 acts as a neutralizing agent and decoy. In parallel, APN01 reduces the inflammatory reactions in the lungs and protects against ARDS.

The preclinical data, published in Cell, reports that APN01 can "reduce viral growth in Vero E6 cells by a factor of 1,0005,000" and that "human blood vessel organoids and kidney organoids can be readily infected with SARS-CoV-2, which can be "significantly inhibited by human recombinant ACE2 at the early stage of infection."6Penninger believes that APN01 is probably "one of the most rational therapies you can think of" which goes beyond antibody therapies that work to neutralize the virus. In a press release, Professor Henning Bundgaard, principal investigator of the clinical trial and professor at the Faculty of Health and Medical Sciences at the University of Copenhagen said: We are eager to participate in this very promising and critical study. APN01 is an advanced drug candidate with a very strong dual rationale that may provide an important therapeutic contribution to fight the COVID-19 pandemic."

Infusion of APN01 was correlated with a gradual reduction in the levels of several diseas relevant mediators over the nine-day period, in addition to a rapid loss of viremia, and a delayed reduction in viral titers from tracheal samples and nasopharyngeal swabs.

Furthermore, infusion of APN01 did not adversely impact the patient's adaptive immune response, which was a huge factor of consideration, as Penninger told Technology Networks: "You could argue that if our molecule binds to the virus, it could divert the virus somehow so that immunity cannot kick in, making the disease even worse. Now we know the answer to this question and it looks very good."

Of course this data is obtained from just one patient, which must be considered. However, it's a positive start, and the Phase II APN01 clinical trial is still recruiting.

Peter Llewellyn-Davies, CEO of APEIRON Biologics, said in a press release: "We are delighted our drug candidate APN01 may have helped this patient to overcome the life-threatening disease and are confident to confirm these positive results in our ongoing and progressing pivotal clinical Phase II trial. The further scientific validation by this renowned journal encourages us in our efforts to providing an efficacious therapy against COVID-19 for the benefit of patients and society."

When asked whether he feels optimistic about the future of APN01, Penninger immediately responds: "Absolutely. The science here, that me and other companies are doing, points in the same direction. It will be interesting to see how this [APN01] plays out, in terms of viral load and the protecting of organs. As we know COVID-19 has other long-term effects in tissues around the body. ACE2 explains this distribution."

Penninger sounds confident, but not arrogant. It is evident that he truly believes in the science behind APN01; after all, he has committed many years of his research career to exploring it, discounting critics along the way. But in the context of the global pandemic, the clinical data is everything.

"What we do not know is: What dose should we use? Which timing for therapy is right? Should we start earlier? The clinical trial is testing the drug in severe COVID-19 patients. Would it work better when tested in patients for which the disease is not severe? These are the questions we have, and that's why we do careful clinical testing," he says. "I am totally confident about the science, but the clinical outcome let's see what the data tells us."Josef Penninger was speaking to Molly Campbell, Science Writer for Technology Networks.References:

1. Crackower MA, Sarao R, Oudit GY, et al. Angiotensin-converting enzyme 2 is an essential regulator of heart function. Nature. 2002;417(6891):822-828. doi:10.1038/nature00786.

2. Imai Y, Kuba K, Rao S, et al. Angiotensin-converting enzyme 2 protects from severe acute lung failure. Nature. 2005;436(7047):112-116. doi:10.1038/nature03712.

3. Fountain JH, Lappin SL. Physiology, Renin Angiotensin System. Treasure Island (FL): StatPearls Publishing; 2020. https://www.ncbi.nlm.nih.gov/books/NBK470410/. Accessed September 24, 2020.

4. Li W, Moore MJ, Vasilieva N, et al. Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature. 2003;426(6965):450-454. doi:10.1038/nature02145.

5. Khan A, Benthin C, Zeno B, et al. A pilot clinical trial of recombinant human angiotensin-converting enzyme 2 in acute respiratory distress syndrome. Critical Care. 2017;21(1):234. doi:10.1186/s13054-017-1823-x

6. Monteil V, Kwon H, Prado P, et al. Inhibition of SARS-CoV-2 infections in engineered human tissues using clinical-grade soluble human ACE1. Cell. 2020;181(4):905-913.e7. doi:10.1016/j.cell.2020.04.004.

7. Zoufaly A, Poglitsch M, Aberle JH, et al. Human recombinant soluble ACE2 in severe COVID-19. The Lancet Respiratory Medicine. doi:10.1016/S2213-2600(20)30418-5

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A Conversation With Professor Josef Penninger on the Journey to a COVID-19 Therapeutic - Technology Networks