Comparative Assessment of Complex Stabilities of Radiocopper Chelating Agents by a Combination of Complex Challenge and in vivo Experiments

Abstract

For (64) Cu radiolabeling of biomolecules to be used as in vivo positron emission tomography (PET) imaging agents, various chelators are commonly applied. It has not yet been determined which of the most potent chelators--NODA-GA ((1,4,7-triazacyclononane-4,7-diyl)diacetic acid-1-glutaric acid), CB-TE2A (2,2'-(1,4,8,11-tetraazabicyclo[6.6.2]hexadecane-4,11-diyl)diacetic acid), or CB-TE1A-GA (1,4,8,11-tetraazabicyclo[6.6.2]hexadecane-4,11-diyl-8-acetic acid-1-glutaric acid)--forms the most stable complexes resulting in PET images of highest quality. We determined the (64) Cu complex stabilities for these three chelators by a combination of complex challenge and an in vivo approach. For this purpose, bioconjugates of the chelating agents with the gastrin-releasing peptide receptor (GRPR)-affine peptide PESIN and an integrin αv β3 -affine c(RGDfC) tetramer were synthesized and radiolabeled with (64) Cu in excellent yields and specific activities. The (64) Cu-labeled biomolecules were evaluated for their complex stabilities in vitro by conducting a challenge experiment with the respective other chelators as challengers. The in vivo stabilities of the complexes were also determined, showing the highest stability for the (64) Cu-CB-TE1A-GA complex in both experimental setups. Therefore, CB-TE1A-GA is the most appropriate chelating agent for *Cu-labeled radiotracers and in vivo imaging applications.

Hybrid Multimodal Imaging Synthons for Chemoselective and Efficient Biomolecule Modification with Chelator and Near-Infrared Fluorescent Cyanine Dye

“…When combining PET and NIR-OI, the PET-radionuclide in the molecular probe defines the synthetic strategy, because radiolabeling will always be the last step for molecules prepared for diagnostic PET imaging [ 7 ]. In this study, we chose to apply 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODA-GA) as chelating agent as it allows the very efficient, mild and stable introduction of both positron emitters, 68 Ga and 64 Cu [ 16 , 17 ], exhibiting half-lives of 68 min and 12.7 h, therefore being appropriate for most PET imaging studies. As NIR fluorescent dyes, we chose to use three different cyanine dyes based on the parent compound indocyanine green (ICG), which has been in use for medical diagnosis over the last 60 years [ 5 , 18 ].…”

Targeted 64Cu‐labeled gold nanoparticles for dual imaging with positron emission tomography and optical imaging

“…As liberated 64 Cu 2+ is mainly deposited in the liver, limiting the usefulness of this followed DOTA approach, [31][32][33] we used NODAGA (1,4,7-triazacyclononane,1-glutaric acid-4,7acetic acid) as chelating agent for the design of our AuNPs to enable a more stable copper complexation. 34,35 To achieve target-specific accumulation of our AuNPs in prostate carcinomas, we further functionalized them with bombesin 7-14 (BBN (7)(8)(9)(10)(11)(12)(13)(14) ) and the Lys-urea-glu motif (LUG). 36,37 2 | RESULTS AND DISCUSSION The AuNPs (3 ± 2 nm) were synthesized by the Brust-Schiffrin method 9 with thiol-PEG 3 -OH used as the stabilizing ligand and for biocompatibility and was further functionalized via ligand exchange with furan-protected maleimide-PEG 4 -thiol.…”

Inhibition of Rho-Associated Kinase 1/2 Attenuates Tumor Growth in Murine Gastric Cancer

“…A dynamic scan starting 60 p.i. was performed over 30 min, and a subsequent CT image was acquired using a tri-modal Bruker Albira II small-animal PET/SPECT/CT (Bruker Biospin GmbH) [35], [36]. Thereafter, mice were sacrificed and organs snap-frozen or fixed in formalin for paraffin embedding.…”

“…Thereafter, mice were sacrificed and organs snap-frozen or fixed in formalin for paraffin embedding. 3D-reconstruction software and calculation of standard uptake volume (SUV) and tumor volume (in cm 3 ) within the region of interest (ROI) was conducted reconstructing images with 35 iterations and using PMOD v.3.608 for data analysis (PMOD, Zurich, Switzerland) as published [35], [36]. To reduce reader bias, the images were analyzed rater-blinded.…”