Abstract
In this work, a method for the preparation of the highly lipophilic labeling synthon [89Zr]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. [89Zr]Zr(oxinate)4 was prepared from oxine (8-hydroxyquinoline) and [89Zr]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 89Zr-complex was incorporated into liposome formulations. PET/CT imaging of 89Zr-labeled liposomes was performed in healthy mice. Cell labeling was accomplished in PBS using suspensions of 3 × 106 hiPSCs, each. [89Zr]Zr(oxinate)4 was synthesized in very high radiochemical yields of 98.7% (96.8% ± 2.8%). Similarly, high internalization rates (≥90%) of [89Zr]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 ~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 89Zr radiolabeling method was developed and tested successfully in a model liposome system and in hiPSCs alike.
Highlights
The development of nuclear-imaging-guided, liposome-based nanomedicines or nanotheranostics occasionally requires prolonged tracing time due to the slower kinetics, enhanced circulation and excretion time of the candidate compounds
The validity of the established method was verified by positron emission tomography (PET) on a model liposome system and via labeling trials of human induced pluripotent stem cells
~10 million single cells were inoculated in 20 mL Essential 8 medium (E8) + Rhokinase inhibitor (RI) in a 125 mL Erlenmeyer flask and placed on a horizontal shaker rotating at 70 rpm, placed in a conventional incubator at 37 ◦ C, 5% CO2 and 95% RH for 2–3 days to allow human induced pluripotent stem cells (hiPSCs) aggregation and expansion in suspension
Summary
The development of nuclear-imaging-guided, liposome-based nanomedicines or nanotheranostics occasionally requires prolonged tracing time due to the slower kinetics, enhanced circulation and excretion time of the candidate compounds. ([68 Ga]Ga(oxinate)3 , [89 Zr]Zr(oxinate)4 , [111 In]In(oxinate)3 ) are highly lipophilic molecules that can be incorporated into lipid-bilayered nanovesicles (liposomes) and living cells under neutral conditions Using this mechanism, more recent studies disseminated [89 Zr]Zr(oxinate)4 -related cell tracing by applying various labeling protocols from 60% to. 97% labeling efficiency of the prelabeled oxinate [2,3,4,5,6] and complex liposome labeling by combining this method with a liposome-incorporated bifunctional chelator [7]. Based upon these findings, the present study focused on simplifying and optimizing the [89 Zr]Zr(oxinate) production. The established protocols were employed in advanced nanomedicinal and stem cell transplantation studies to be presented elsewhere
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