Design, synthesis and evaluation of novel bifunctional tetrahydroxamate chelators for PET imaging of 89Zr-labeled antibodies.

Two compact and symmetrical bifunctional tetrahydroxamate chelators, 1 and 2, were synthesized and evaluated for labeling antibodies with 89Zr for imaging with positron emission tomography. Using 2,2'-iminodiacetamide as the backbone, four hydroxamate-containing moieties coupled to the diacetamide nitrogen were used for 89Zr labeling, while a pendant connected to the amino group provided an isothiocyanate group for coupling to the antibody. Both 1- and 2-conjugated Trastuzumab were labeled with 89Zr efficiently (>90% radiolabeling yield), and their 89Zr-labeled products maintained comparable immunoreactivity to Trastuzumab. Compared to 89Zr-labeled deferoxamine-conjugated Trastuzumab, 89Zr-1- and 89Zr-2-Trastuzumab showed faster demetalation in mouse plasma, and also displayed higher bone uptake in mice. Despite suboptimal stability of 89Zr complexes of 1 and 2, our design strategy led to tetrahydroxamate chelators for efficient 89Zr labeling, and could be potentially modified to provide novel chelators with improved stability.