Wider research context / theoretical framework: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus which causes coronavirus disease 2019 (COVID-19), uses membrane-bound angiotensin-converting enzyme 2 (ACE2) as its functional receptor to gain cellular entry and infect cells. ACE2 is part of the Renin- Angiotensin-Aldosterone System, a cascade of vasoactive peptides which can be therapeutically targeted to control blood pressure. There is a currently ongoing debate whether antihypertensive drugs (i.e. angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors) can increase the expression of ACE2 in the lungs and thereby increase the risk of viral infection. However, this is based on either indirect evidence from human studies or on preclinical data (ACE2 expression/activity in the heart and kidney of rats). As of yet no data is available regarding the effect of antihypertensive medication on ACE2 expression in the respiratory tractand the lungs, the primary sites of viral infection.
Hypotheses / research questions / objectives: We hypothesize that positron emission tomography (PET) imaging with radiolabelled derivatives of the highly potent ACE2-selective inhibitor MLN-4760, administered intratracheally as an aerosol into the airways, will allow measuring the effect of treatment with antihypertensive drugs on lung-specific ACE2 expression in rats.
Approach / methods: We will synthesize novel derivatives of MLN-4760, which can be straightforwardly labelled with the PET radionuclides 18F and 11C, and compare their potency for ACE2 inhibition with authentic MLN-4760. The suitability of novel radiotracers to visualize pulmonary ACE2 will be assessed in rats without and with co-administration of unlabelled MLN-4760 and in wild-type and Ace2 knockout mice. Once an effective ACE2 radiotracer is available it will be used to compare pulmonary ACE2 expression in groups of rats treated with losartan or lisinopril with an untreated control group. PET measures of pulmonary ACE2 expression will be correlated with semiquantitative measures of ACE2 expression obtained from immunohistochemical staining of lung tissue slices using an anti-ACE2 antibody.
Level of originality / innovation: So far the measurement of ACE2 expression in the lungs has been limited to ex vivo analysis (PCR, Western blot or immunohistochemistry), which is difficult to perform in a clinical setting. PET imaging with ACE2-specific radiotracers will enable non-invasive measurement of ACE2 expression in the lungs of patients, which is important to better understand the role of this protein in the pathogenesis and pathophysiology of COVID-19 and to aid in the development of novel drugs targeting ACE2.
