Investigation of Novel Bis- and Tris-tetraazamacrocycles for Use in the Copper-64 (⁶⁴Cu) Radiolabeling of Antibodies with Potential To Increase the Therapeutic Index for Drug Targeting

Abstract

The (64)Cu complexes of a series of mono-, bis-, and tris-tetraazamacrocycles have been prepared, and their stability in human sera has been assessed. The ligands forming the most stable Cu(2+) complexes were then conjugated to the B72.3 antibody (mAb). Conditions for conjugation of the ligands to the mAb were optimized for the concentration of protein, ligand, pH, temperature, and time. The optimum moles of Cu(2+) attached to the mAb were as high as 3.5 for L2 and 5.5 or 2.7 for L5, and the immunoreactivity was > or =80%. Biodistribution of the radioimmunoconjugates showed good tumor localization and target-to-background ratios that were significantly enhanced compared to those achieved with monotetraazamacrocyclic derivatives.

Enhancing PET Signal at Target Tissue in Vivo: Dendritic and Multimeric Tris(hydroxypyridinone) Conjugates for Molecular Imaging of αvβ3 Integrin Expression with Gallium-68

“… 42 − 44 In these cases, the functionalized/radiolabeled biomolecule retained affinity for receptor targets in vitro 40 , 41 , 44 and in vivo. 38 , 39 , 42 , 43 Additionally, when compared to bioconjugates containing fewer chelating groups, dendrimer or multichelator conjugated proteins demonstrated higher specific activity—that is, a higher number of radionuclides were bound per bioconjugate compared to homologues containing a single chelator. 38 , 41 − 43 In some cases, this resulted in higher concentrations of radioactivity at target tissue (tumors) in vivo.…”

DOTA-Functionalized Polylysine: A High Number of DOTA Chelates Positively Influences the Biodistribution of Enzymatic Conjugated Anti-Tumor Antibody chCE7agl

“…By comparing the novel antibody-dendrimer conjugates with conventionally produced immunoconjugates containing high numbers of single chelating molecules at multiple sites, they found that the number of conjugation sites had a dramatic effect on the immunoreactivity of the antibody, whereas dendrimer size did not influence the immunoreactivity of the derivatized antibody with comparable derivatization sites per molecule. In a recently published study, Ramli et al have designed a tris-tetraazamacrocycle comprising three chelating moieties in order to increase the specific activity of a RIC [17]. In comparison to an analogous mono-tetraazamacrocycle, the tris-tetraazamacrocycle immunoconjugate showed higher specific activity upon radiolabeling with 64 Cu.…”

Radiolabeling of Nanomaterials: Advantages and Challenges

“…However, inappropriate choice in linkage and the local low pH may lead to the detachment of radiometals from NMs in the following cases: 1) The protonation of chelator’s carboxyl and amine groups may compromise the in vivo stability of the chelation ( Figures 1A, i . ( Liu and Edwards, 2001 ; Ramli et al, 2009 ). 2) The newly formed bond between the linkage group of bifunctional chelating agent and the NMs is too weak to maintain stability in vivo (like some ether bonds or ester bonds, Figure 1Aii ).…”

“…1) The protonation of chelator’s carboxyl and amine groups may compromise the in vivo stability of the chelation ( Figures 1A, i . ( Liu and Edwards, 2001 ; Ramli et al, 2009 ).…”