Novel 89 Zr cell labeling approach for PET-based cell trafficking studies

Background With the recent growth of interest in cell-based therapies and radiolabeled cell products, there is a need to develop more robust cell labeling and imaging methods for in vivo tracking of living cells. This study describes evaluation of a novel cell labeling approach with the positron emission tomography (PET) isotope 89 Zr ( T 1/2 = 78.4 h). 89 Zr may allow PET imaging measurements for several weeks and take advantage of the high sensitivity of PET imaging. Methods A novel cell labeling agent, 89 Zr-desferrioxamine-NCS ( 89 Zr-DBN), was synthesized. Mouse-derived melanoma cells (mMCs), dendritic cells (mDCs), and human mesenchymal stem cells (hMSCs) were covalently labeled with 89 Zr-DBN via the reaction between the NCS group on 89 Zr-DBN and primary amine groups present on cell surface membrane protein. The stability of the label on the cell was tested by cell efflux studies for 7 days. The effect of labeling on cellular viability was tested by proliferation, trypan blue, and cytotoxicity/apoptosis assays. The stability of label was also studied in in vivo mouse models by serial PET scans and ex vivo biodistribution following intravenous and intramyocardial injection of 89 Zr-labeled hMSCs. For comparison, imaging experiments were performed after intravenous injections of 89 Zr hydrogen phosphate ( 89 Zr(HPO 4 ) 2 ). Results The labeling agent, 89 Zr-DBN, was prepared in 55% ± 5% decay-corrected radiochemical yield measured by silica gel iTLC. The cell labeling efficiency was 30% to 50% after 30 min labeling depending on cell type. Radioactivity concentrations of labeled cells of up to 0.5 MBq/10 6 cells were achieved without a negative effect on cellular viability. Cell efflux studies showed high stability of the radiolabel out to 7 days. Myocardially delivered 89 Zr-labeled hMSCs showed retention in the myocardium, as well as redistribution to the lung, liver, and bone. Intravenously administered 89 Zr-labeled hMSCs also distributed primarily to the lung, liver, and bone, whereas intravenous 89 Zr(HPO 4 ) 2 distributed to the liver and bone with no activity in the lung. Thus, the in vivo stability of the radiolabel on the hMSCs was evidenced. Conclusions We have developed a robust, general, and biostable 89 Zr-DBN-based cell labeling strategy with promise for wide applications of PET-based non-invasive in vivo cell trafficking.