Intracellular Protein Binding of Zr-89 Oxine Cell Labeling for PET Cell Tracking Studies
<b>Background/Objectives</b>: <sup>89</sup>Zr-oxine is an ex vivo cell labeling agent that enables cells to be tracked in vivo by positron emission tomography (PET) over a period of up to two weeks. To better understand where <sup>89</sup>Zr-oxine binds within cel...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-04-01
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| Series: | Pharmaceutics |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1999-4923/17/4/518 |
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| Summary: | <b>Background/Objectives</b>: <sup>89</sup>Zr-oxine is an ex vivo cell labeling agent that enables cells to be tracked in vivo by positron emission tomography (PET) over a period of up to two weeks. To better understand where <sup>89</sup>Zr-oxine binds within cellular components, factors affecting labeling and intracellular distribution of <sup>89</sup>Zr were examined. <b>Methods</b>: Mouse primary T cells, natural killer cells, dendritic cells, and monocytes, and cell lines EL4 (mouse lymphoma), DC2.4 (mouse dendritic cell), Kit225K6 (human T cell leukemia) and MC38 (mouse colon adenocarcinoma) were labeled with <sup>89</sup>Zr-oxine or <sup>111</sup>In-oxine and protein binding within the cellular compartments, the labeling thresholds, and radioactivity retention were subsequently determined. <b>Results</b>: Cell incorporation of <sup>89</sup>Zr-oxine (27.8–71.8 kBq/10<sup>6</sup> cells) positively correlated with cellular size and protein mass. Most (>97%) <sup>89</sup>Zr was protein-bound and primarily localized in the cytoplasm, membrane, and nuclear fractions (>81%) with distribution patterns varying by cell type. By contrast, <sup>111</sup>In-oxine showed lower protein-binding activity of approximately 59–65%, with 62–65% of <sup>111</sup>In localized in the cytoplasm. Autoradiography of electrophoresed subcellular fractionated cell samples indicated stable binding by <sup>89</sup>Zr-oxine to proteins in all subcellular fractions but unstable protein binding by <sup>111</sup>In. Saturation studies showed that <sup>89</sup>Zr-oxine labeling was saturable, and further labeling reduced cellular retention. Biodistribution of dendritic cells labeled with either <sup>89</sup>Zr-oxine or <sup>111</sup>In-oxine indicated greater retention of <sup>89</sup>Zr in the labeled cells in vivo than <sup>111</sup>In. <b>Conclusions</b>: <sup>89</sup>Zr-oxine stably binds many intracellular proteins and shows much higher and more stable protein binding than <sup>111</sup>In-oxine. Intracellular protein binding of <sup>89</sup>Zr accounts for the ability of <sup>89</sup>Zr-oxine labeling to successfully track cells in vivo long-term on PET. |
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| ISSN: | 1999-4923 |