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 (89Zr) 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 89Zr. The corresponding [89Zr]­Zr-labeled chelators were evaluated for complex stability in human serum. All new chelating agents rapidly bound to 89Zr in excellent radiolabeling efficiency at room temperature. Among the new [89Zr]­Zr-labeled chelators evaluated, [89Zr]­Zr-NODHA showed the highest stability in human serum without losing 89Zr, and [89Zr]­Zr-NODHA-PY released a considerable amount of 89Zr in human serum. [89Zr]­Zr-NODHA, [89Zr]­Zr-NODHA-PY, and [89Zr]­Zr-DFO were comparatively evaluated for in vivo complex stability by performing biodistribution studies using normal mice. [89Zr]­Zr-DFO had the lowest bone uptake at all time points, while [89Zr]­Zr-NODHA-PY showed poor stability in mice as evidenced by high bone accumulation at the 24 h time point. [89Zr]­Zr-NODHA exhibited better renal clearance but higher bone uptake than [89Zr]­Zr-DFO.