Novel Chelating Agents for Zirconium-89-Positron Emission Tomography (PET) Imaging: Synthesis, DFT Calculation, Radiolabeling, and In Vitro and In Vivo Complex Stability.

We report the synthesis and evaluation of novel chelating agents for zirconium-89 ( 89 Zr) with positron emission tomography (PET) imaging applications. New chelating agents NODHA, NOTHA, and NODHA-PY were constructed on 1,4,7-triazacyclononane (TACN) and possess hydroxamic acid or a pyridine ring as an acyclic binding moiety. The new chelating agents were theoretically studied for complexation with Zr(IV). Structures of Zr(IV)-NODHA, Zr(IV)-NOTHA, and Zr(IV)-NODHA-PY were predicted using density functional methods. NODHA was found to form stronger bonds with Zr(IV) when compared to NOTHA and NODHA-PY. The new chelating agents were evaluated for radiolabeling efficiency in binding 89 Zr. The corresponding [ 89 Zr]Zr-labeled chelators were evaluated for complex stability in human serum. All new chelating agents rapidly bound to 89 Zr in excellent radiolabeling efficiency at room temperature. Among the new [ 89 Zr]Zr-labeled chelators evaluated, [ 89 Zr]Zr-NODHA showed the highest stability in human serum without losing 89 Zr, and [ 89 Zr]Zr-NODHA-PY released a considerable amount of 89 Zr in human serum. [ 89 Zr]Zr-NODHA, [ 89 Zr]Zr-NODHA-PY, and [ 89 Zr]Zr-DFO were comparatively evaluated for in vivo complex stability by performing biodistribution studies using normal mice. [ 89 Zr]Zr-DFO had the lowest bone uptake at all time points, while [ 89 Zr]Zr-NODHA-PY showed poor stability in mice as evidenced by high bone accumulation at the 24 h time point. [ 89 Zr]Zr-NODHA exhibited better renal clearance but higher bone uptake than [ 89 Zr]Zr-DFO.