Simplified 89Zr-Labeling Protocol of Oxine (8-Hydroxyquinoline) Enabling Prolonged Tracking of Liposome-Based Nanomedicines and Cells

In this work, a method for the preparation of the highly lipophilic labeling synthon [Zr-89]Zr(oxinate)(4) was optimized for the radiolabeling of liposomes and human induced pluripotent stem cells (hiPSCs). The aim was to establish a robust and reliable labeling protocol for enabling up to one week positron emission tomography (PET) tracing of lipid-based nanomedicines and transplanted or injected cells, respectively. [Zr-89]Zr(oxinate)(4) was prepared from oxine (8-hydroxyquinoline) and [Zr-89]Zr(OH)(2)(C2O4). Earlier introduced liquid-liquid extraction methods were simplified by the optimization of buffering, pH, temperature and reaction times. For quality control, thin-layer chromatography (TLC), size-exclusion chromatography (SEC) and centrifugation were employed. Subsequently, the Zr-89-complex was incorporated into liposome formulations. PET/CT imaging of Zr-89-labeled liposomes was performed in healthy mice. Cell labeling was accomplished in PBS using suspensions of 3 x 10(6) hiPSCs, each. [Zr-89]Zr(oxinate)(4) was synthesized in very high radiochemical yields of 98.7% (96.8% +/- 2.8%). Similarly, high internalization rates (>= 90%) of [Zr-89]Zr(oxinate)(4) into liposomes were obtained over an 18 h incubation period. MicroPET and biodistribution studies confirmed the labeled nanocarriers' in vivo stability. Human iPSCs incorporated the labeling agent within 30 min with similar to 50% efficiency. Prolonged PET imaging is an ideal tool in the development of lipid-based nanocarriers for drug delivery and cell therapies. To this end, a reliable and reproducible Zr-89 radiolabeling method was developed and tested successfully in a model liposome system and in hiPSCs alike.

Automated summary

This study optimized a method for the preparation of the highly lipophilic labeling synthon [Zr-89]Zr(oxinate)(4) for radiolabeling of liposomes and human induced pluripotent stem cells. The developed labeling protocol demonstrated high radiochemical yields and efficient cell internalization rates. Prolonged PET imaging confirmed the stability of labeled nanocarriers in vivo, emphasizing the potential of the method for drug delivery and cell therapy applications.