Rational Design, Synthesis and Preliminary Evaluation of Novel Fusarinine C-Based Chelators for Radiolabeling with Zirconium-89

Fusarinine C (FSC) has recently been shown to be a promising and novel chelator for 89Zr. Here, FSC has been further derivatized to optimize the complexation properties of FSC-based chelators for 89Zr-labeling by introducing additional carboxylic groups. These were expected to improve the stability of 89Zr-complexes by saturating the 8-coordination sphere of [ 89Zr] Zr 4+, and also to introduce functionalities suitable for conjugation to targeting vectors such as monoclonal antibodies. For proof of concept, succinic acid derivatization at the amine groups of FSC was carried out, resulting in FSC(succ) 2 and FSC(succ) 3. FSC(succ) 2 was further derivatized to FSC(succ) 2 AA by reacting with acetic anhydride (AA). The Zr 4+ complexation properties of these chelators were studied by reacting with ZrCl 4. Partition coefficient, protein binding, serum stability, acid dissociation, and transchelation studies of 89Zr-complexes were carried out in vitro and the results were compared with those for 89Zr-desferrioxamine B ([ 89Zr]Zr-DFO) and 89Zr-triacetylfusarinine C ([ 89Zr]Zr-TAFC). The in vivo properties of [ 89Zr]Zr-FSC(succ) 3 were further compared with [ 89Zr]Zr-TAFC in BALB/c mice using micro-positron emission tomography/computer tomography (microPET/CT) imaging. Fusarinine C (succ) 2AA and FSC(succ) 3 were synthesized with satisfactory yields. Complexation with ZrCl 4 was achieved using a simple strategy resulting in high-purity Zr-FSC(succ) 2AA and Zr-FSC(succ) 3 with 1:1 stoichiometry. Distribution coefficients of 89Zr-complexes revealed increased hydrophilic character compared to [ 89Zr]Zr-TAFC. All radioligands showed high stability in phosphate buffered saline (PBS) and human serum and low protein-bound activity over a period of seven days. Acid dissociation and transchelation studies exhibited a range of in vitro stabilities following the order: [ 89Zr]Zr-FSC(succ) 3 > [ 89Zr]Zr-TAFC > [ 89Zr]Zr-FSC(succ) 2AA >> [ 89Zr]Zr-DFO. Biodistribution studies of [ 89Zr]Zr-FSC(succ) 3 revealed a slower excretion pattern compared to [ 89Zr]Zr-TAFC. In conclusion, [ 89Zr]Zr-FSC(succ) 3 showed the best stability and inertness. The promising results obtained with [ 89Zr]Zr-FSC(succ) 2AA highlight the potential of FSC(succ) 2 as a monovalent chelator for conjugation to targeted biomolecules, in particular, monoclonal antibodies. View Full-Tex