Synthesis of a new cage ligand, SarAr, and its complexation with selected transition metal ions for potential use in radioimaging†

Abstract

A new hexaazamacrobicyclic cage ligand, 1-N-(4-aminobenzyl)- 3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane-1,8-diamine (SarAr) has been designed for conjugation to proteins. SarAr was synthesised and characterised by microanalyses, 1 H NMR and electrospray mass spectrometry. The complexation of selected transition metal ions (Cu(), Ni() and Co() at 10 Ϫ6 M) by SarAr was complete within 30 min over pH 6 to 8. The [ 64 Cu(SarAr)] 2ϩ complex was investigated with a view to applications in radioimaging. The [ 64 Cu(sar)] 2ϩ complex was found to be stable in human plasma for at least 174 h and biodistribution studies in mice, showed that the [ 64 Cu(SarAr)] 2ϩ complex was rapidly excreted through the renal system unlike the free 64 Cu 2ϩ . Overall, the simple synthesis, ready complexation behaviour of SarAr, the kinetic inertness of the [Cu(SarAr)] 2ϩ complex to dissociation of 64 Cu and its facile elimination from mice make it an attractive prospect for use in nuclear medicine.

Positron emission tomography (PET) imaging of neuroblastoma and melanoma with 64 Cu-SarAr immunoconjugates

“…The [ 64 Cu(SarAr)] 2ϩ complex is rapidly excreted through the kidneys and, in contrast to other chelating agents, was not found to release copper into the liver (13). In the present study, we have extended these findings, showing tumor-specific uptake of SarAr-conjugated 64 Cu-labeled antineuroblastoma antibodies 14.G2a and ch14.…”

“…Earlier work with unconjugated SarAr showed that [ 64 Cu(SarAr)] 2ϩ complexes were stable in plasma, with no significant dissociation of the complex after 174 h (13). The [ 64 Cu(SarAr)] 2ϩ complex is rapidly excreted through the kidneys and, in contrast to other chelating agents, was not found to release copper into the liver (13).…”

“…Preparation of the SarAr chelator has been described in detail (13). The SarAr ligand was conjugated via its primary aromatic amino group to carboxyl groups on the 14.G2a and ch14.18 antibodies, in a reaction mediated by the carbodiimide reagent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC).…”

“…Smith et al (13) have recently developed a derivative of the diamsar ligand, SarAr (Fig. 1), which incorporates an aromatic amine into the cage periphery.…”

Comparison of 64Cu-Complexing Bifunctional Chelators for Radioimmunoconjugation: Labeling Efficiency, Specific Activity, and in Vitro/in Vivo Stability

“…We also included 2-benzyl-3-methylisothiocyanato-diethylenetriaminepentaaceticacid (2B3M-ITC-DTPA) and a sarcophagine ligand, (1-NH 2 -8-NHCO(CH 2 ) 3 CO 2 H)sar where sar = sarcophagine = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane (sar-CO 2 H) 45,46 . Encapsulating hexaamine sarcophagine ligands, first prepared by Sargeson and coworkers [47][48][49][50][51] , form extraordinary stable complexes with copper(II) and benefit from rapid complexation rates 52,53 . Methods have been developed to introduce reactive functional groups to the ligand framework [54][55][56] , to allow the ligands to be conjugated to peptides and antibodies with a goal of synthesizing copper radiopharmaceuticals that benefit from the special properties of sarcophagine ligands 21,45,46,[57][58][59][60][61] .…”