Long lived PET tracers for tracking labelled cells

Cell tracking is important because the information it provides is required to inform cell based treatment development. Additionally, it has a diagnostic purpose for detecting infection/inflammation diseases with labelled cells, a technique that has become part of routine clinical practice. Currently only gamma emitting radiotracers for single photon emission computed tomography (SPECT) are available to label cells for routine service. PET (positron emission tomography) exhibits better resolution than SPECT and its use in cell tracking would improve image quality, detectability and quantification for smaller lesions.The studies presented in this thesis report on development of cell labelling techniques with positron emitting radionuclides. The production and characterisation of complexes of copper-64 with dithiocarbamate (DTC) analogues and bis(thiosemicarbazones) (BTSCs) are described. Their labelling efficacies and stabilities were investigated. Although efficient and rapid extraction of 64Cu (DEDTC)2 and 64Cu-GTSM were observed, a high percentage of the radiotracer leakage from the labelled cells was still problematic. Efflux kinetics were similar for all the complexes used suggesting that the efflux mechanism was the same in all cases. In an alternative approach, a novel lipophilic complex of the long lived PET isotope, zirconium-89, was synthesised and characterised. [89Zr]-Zr(oxinate)4 showed good retention in the labelled cells 24 hr after labelling as well as moderate uptake in many types of cells including human leucocytes and mouse multiple myeloma (MM) cells (eGFP-5T33). In vivo imaging and ex vivo tissues counting was used to compare cell tracking with [89Zr]-Zr(oxinate)4 and [111In]-In(oxinate)3 labelled MM cells. The main organs of the homing radiolabelled cells were similar in MM model. However, mice injected [111In]-In(oxinate)3 labelled MM cells. The main organs of the homing radiolabelled cells were similar in MM model. However, mice injected [111In-In(oxinate)3 labelled cells showed higher accumulation of activity in the kidneys thanthose of [89Zr]-Zr(oxinate)4 that might indicate the greater release and metabolism of the 111In radiotracer released from the labelled cells. The localisation of [89Zr]-Zr(oxinate)4 in labelled MM cells was confirmed by sorting of homing organ (liver, spleen, bone marrow) homogenates based on green fluorescence protein (GFP) expression up to 7 days post inoculation, which showed that radioactivity remained predominantly in GFP-positive cells confirming that radionuclide loss from the labelled cells was minimal and that the cells remained alive at 7 days post injection. In addition we demonstrated that mice inoculated [89Zr]-Zr(oxinate)4 labelled cells can be tracked by PET imaging for 14 days after inoculation.It was concluded that while Cu-64 radiolabelling of cells was ineffective because the majority of radioactivity was lost from cells by 24 hr, the novel complex [89Zr]-Zr(oxinate)4 can be successfully synthesised with acceptable quality and very promising long lived PET tracer for tracking labelled cells for up to weeks