Evaluation of Angiotensin-Converting Enzyme 2 Expression In Vivo with Novel 68 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 1 to A 9 ) were designed, synthesized and connected with a chelator, 1,4,7-triazacyclononane- N,N',N' '-triacetic acid (NOTA). NOTA-A 1 , NOTA-A 2 , NOTA-A 4 , NOTA-A 5 , and NOTA-A 8 were successfully labeled with [ ⁶⁸ Ga]Ga ³⁺ and were used for biological evaluation. [ ⁶⁸ Ga]Ga-NOTA-A 2 , [ ⁶⁸ Ga]Ga-NOTA-A 5 , and [ ⁶⁸ Ga]Ga-NOTA-A 8 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 [ ⁶⁸ Ga]Ga-NOTA-A 2 , [ ⁶⁸ Ga]Ga-NOTA-A 5 , or [ ⁶⁸ Ga]Ga-NOTA-A 8 . These peptides also accumulated in the organs with high-level ACE2 expression, confirmed by immunohistochemical stain. Among them, [ ⁶⁸ Ga]Ga-NOTA-A 5 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 [ ⁶⁸ Ga]Ga-NOTA-A 5 was evaluated with positron emission tomography/computed tomography (PET/CT) in three participants without adverse events. ⁶⁸ Ga-labeled peptides originated from the coronavirus RBD, with [ ⁶⁸ Ga]Ga-NOTA-A 5 as a typical representative, seem to be safe and effective for the evaluation of ACE2 expression in vivo with PET/CT, facilitating further mechanism investigation and clinical evaluation of ACE2-related diseases.
Competing Interests: The authors declare the following competing financial interest(s): L. L., G. H., Z. J. and Z. Z hold the patent rights for [68Ga]Ga-NOTA-A2/5/8 and related technology. Other authors declare no other conflict of interests.
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