{"doi":"10.3390/pharmaceutics17040518","title":"Intracellular Protein Binding of Zr-89 Oxine Cell Labeling for PET Cell Tracking Studies","abstract":"Background/Objectives: 89Zr-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 89Zr-oxine binds within cellular components, factors affecting labeling and intracellular distribution of 89Zr were examined. Methods: 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 89Zr-oxine or 111In-oxine and protein binding within the cellular compartments, the labeling thresholds, and radioactivity retention were subsequently determined. Results: Cell incorporation of 89Zr-oxine (27.8–71.8 kBq/106 cells) positively correlated with cellular size and protein mass. Most (>97%) 89Zr was protein-bound and primarily localized in the cytoplasm, membrane, and nuclear fractions (>81%) with distribution patterns varying by cell type. By contrast, 111In-oxine showed lower protein-binding activity of approximately 59–65%, with 62–65% of 111In localized in the cytoplasm. Autoradiography of electrophoresed subcellular fractionated cell samples indicated stable binding by 89Zr-oxine to proteins in all subcellular fractions but unstable protein binding by 111In. Saturation studies showed that 89Zr-oxine labeling was saturable, and further labeling reduced cellular retention. Biodistribution of dendritic cells labeled with either 89Zr-oxine or 111In-oxine indicated greater retention of 89Zr in the labeled cells in vivo than 111In. Conclusions: 89Zr-oxine stably binds many intracellular proteins and shows much higher and more stable protein binding than 111In-oxine. Intracellular protein binding of 89Zr accounts for the ability of 89Zr-oxine labeling to successfully track cells in vivo long-term on PET.","journal":"Pharmaceutics","year":2025,"id":536104,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":1,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9647,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":687055,"name":"Yutaka Kurebayashi","orcid":"0000-0003-3773-0851","position":1,"is_corresponding":false},{"id":1420950,"name":"Kingsley O. Asiedu","orcid":null,"position":2,"is_corresponding":false},{"id":110328,"name":"Peter L. Choyke","orcid":"0000-0003-1086-8826","position":3,"is_corresponding":false},{"id":342836,"name":"Noriko Sato","orcid":"0000-0002-9372-1725","position":4,"is_corresponding":false},{"id":944912,"name":"Emmanuel Nyong","orcid":"0009-0006-9718-4433","position":0,"is_corresponding":true}],"reference_count":41,"raw_metadata":null,"created_at":"2026-07-19T02:52:00.885532Z","pmid":"40284513","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}