Promising bifunctional chelators for copper 64-PET imaging: practical 64Cu radiolabeling and high in vitro and in vivo complex stability

Abstract

Positron emission tomography (PET) using copper-64 is a sensitive and non-invasive imaging technique for diagnosis and staging of cancer. A bifunctional chelator that can present rapid radiolabeling kinetics and high complex stability with 64Cu is a critical component for targeted PET imaging. Bifunctional chelates 3p-C-NE3TA, 3p-C-NOTA, and 3p-C-DE4TA were evaluated for complexation kinetics and stability with 64Cu in vitro and in vivo. Hexadentate 3p-C-NOTA and heptadentate 3p-C-NE3TA possess a smaller TACN-based macrocyclic backbone, while nonadentate 3p-C-DE4TA is constructed on a larger CYCLEN-based ring. The frequently explored chelates of 64Cu, octadentate C-DOTA and hexadentate C-NOTA were also comparatively evaluated. Radiolabeling kinetics of bifunctional chelators with 64Cu was assessed under mild conditions. All bifunctional chelates instantly bound to 64Cu in excellent radiolabeling efficiency at room temperature. C-DOTA was less efficient in binding 64Cu than all other chelates. All 64Cu-radiolabeled bifunctional chelates remained stable in human serum without any loss of 64Cu for 2 days. When challenged by an excess amount of EDTA, 64Cu complexes of 3p-C-NE3TA and 3p-C-NOTA were shown to be more stable than 64Cu-C-DOTA and 64Cu-C-DE4TA. 3p-C-NE3TA and 3p-C-NOTA displayed comparable in vitro and in vivo complex stability to 64Cu-C-NOTA. In vivo biodistribution result indicates that the 64Cu-radiolabeled complexes of 3p-C-NOTA and 3p-C-NE3TA possess excellent in vivo complex stability, while 64Cu-3p-C-DE4TA was dissociated as evidenced by high renal and liver retention in mice. The results of in vitro and in vivo studies suggest that the bifunctional chelates 3p-C-NOTA and 3p-C-NE3TA offer excellent chelation chemistry with 64Cu for potential PET imaging applications.

Radiolabelling of Extracellular Vesicles for PET and SPECT imaging

“…Using the same (or less) amount of sEVs (~ 106 nm) as Banerjee and his group, they achieved considerably higher RLY (91.2 ± 0.2% vs. ~ 20%). This could be the result of the well-known high radiochemical stability of [ 64 Cu]Cu-NOTA complexes 109 , 110 . PEGylation had the desired effect of increased sEV circulation, decreased liver uptake and increased tumour uptake, particularly after 24 h (Fig.…”

Imaging Neurotensin Receptor in Prostate Cancer With 64Cu-Labeled Neurotensin Analogs

“…It is well-known that the radiometal chelators could have significant effect on probe distribution in vivo. [34][35][36] Therefore, in this report, 3 radiometal chelators are conjugated to NT peptides (DOTA-NT, NOTA-NT, and AmBaSar-NT) aiming to select the most potent one for in vivo imaging applications. After conjugation, cell binding assay confirmed that addition of the chelate on the C-terminal lysine has minimal effect on NTR binding capacity.…”

New Insights in the Design of Bioactive Peptides and Chelating Agents for Imaging and Therapy in Oncology

“…NOTA and derivatives are well-known to form a very stable complexes with 68 Ga and with 64 Cu [ 100 , 101 ]. Coordination of 68 Ga with DOTA derivatives is less efficient, often requiring heating (80–100°C).…”