Optimisation of the Synthesis and Cell Labelling Conditions for [89Zr]Zr-oxine and [89Zr]Zr-DFO-NCS: a Direct In Vitro Comparison in Cell Types with Distinct Therapeutic Applications

Abstract

Background: There is a need to better characterise cell-based therapies in preclinical models to help facilitate their translation to humans. Long-term high-resolution tracking of the cells in vivo is often impossible due to unreliable methods. Radiolabelling of cells has the advantage of being able to reveal cellular kinetics in vivo over time. This study aimed to optimise the synthesis of the radiotracers [⁸⁹Zr]Zr-oxine (8-hydroxyquinoline) and [⁸⁹Zr]Zr-DFO-NCS (p-SCN-Bn-Deferoxamine) and to perform a direct comparison of the cell labelling efficiency using these radiotracers.

Procedures: Several parameters, such as buffers, pH, labelling time and temperature, were investigated to optimise the synthesis of [⁸⁹Zr]Zr-oxine and [⁸⁹Zr]Zr-DFO-NCS in order to reach a radiochemical conversion (RCC) of >95 % without purification. Radio-instant thin-layer chromatography (iTLC) and radio high-performance liquid chromatography (radio-HPLC) were used to determine the RCC. Cells were labelled with [⁸⁹Zr]Zr-oxine or [⁸⁹Zr]Zr-DFO-NCS. The cellular retention of ⁸⁹Zr and the labelling impact was determined by analysing the cellular functions, such as viability, proliferation, phagocytotic ability and phenotypic immunostaining.

Results: The optimised synthesis of [⁸⁹Zr]Zr-oxine and [⁸⁹Zr]Zr-DFO-NCS resulted in straightforward protocols not requiring additional purification. [⁸⁹Zr]Zr-oxine and [⁸⁹Zr]Zr-DFO-NCS were synthesised with an average RCC of 98.4 % (n = 16) and 98.0 % (n = 13), respectively. Cell labelling efficiencies were 63.9 % (n = 35) and 70.2 % (n = 30), respectively. ⁸⁹Zr labelling neither significantly affected the cell viability (cell viability loss was in the range of 1-8 % compared to its corresponding non-labelled cells, P value > 0.05) nor the cells' proliferation rate. The phenotype of human decidual stromal cells (hDSC) and phagocytic function of rat bone-marrow-derived macrophages (rMac) was somewhat affected by radiolabelling.

Conclusions: Our study demonstrates that [⁸⁹Zr]Zr-oxine and [⁸⁹Zr]Zr-DFO-NCS are equally effective in cell labelling. However, [⁸⁹Zr]Zr-oxine was superior to [⁸⁹Zr]Zr-DFO-NCS with regard to long-term stability, cellular retention, minimal variation between cell types and cell labelling efficiency.

Keywords: 89Zr; Cell labelling; Cell tracking; Deferoxamine; Imaging; Oxine; PET.