Evaluation of Angiotensin-Converting Enzyme 2 Expression with Novel Ga-Labeled Peptides Originated from the Coronavirus Receptor-Binding Domain.

Angiotensin-converting enzyme 2 (ACE2) is not only a key to the renin-angiotensin-aldosterone system and related diseases, but also the main entry point on cell surfaces for certain coronaviruses, including severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2. By analyzing the different key binding sites from the receptor-binding domain (RBD) of SARS-CoV and SARS-CoV-2, nine new ACE2-targeting peptides (A to A) were designed, synthesized and connected with a chelator, 1,4,7-triazacyclononane-'-triacetic acid (NOTA). NOTA-A, NOTA-A, NOTA-A, NOTA-A, and NOTA-A were successfully labeled with [Ga]Ga and were used for biological evaluation. [Ga]Ga-NOTA-A, [Ga]Ga-NOTA-A, and [Ga]Ga-NOTA-A showed specific binding to ACE2 via cell assays, and their binding sites and binding capacity were calculated by molecular docking and molecular dynamics simulations. In tumor-bearing mice, A549 tumors were visualized 60 min postinjection of [Ga]Ga-NOTA-A, [Ga]Ga-NOTA-A, or [Ga]Ga-NOTA-A. These peptides also accumulated in the organs with high-level ACE2 expression, confirmed by immunohistochemical stain. Among them, [Ga]Ga-NOTA-A exhibited the highest tumor uptake and tumor/background ratio, and it successfully tracked the increased ACE2 levels in mice tissues after excessive Losartan treatment. In a first-in-human study, the distribution of [Ga]Ga-NOTA-A was evaluated with positron emission tomography/computed tomography (PET/CT) in three participants without adverse events. Ga-labeled peptides originated from the coronavirus RBD, with [Ga]Ga-NOTA-A as a typical representative, seem to be safe and effective for the evaluation of ACE2 expression with PET/CT, facilitating further mechanism investigation and clinical evaluation of ACE2-related diseases.