Student: Peter Gawne
This project is ideally suited to a student who wants to carry out synthetic chemistry, alongside radiochemistry and biological cell assays and analysis.
The favoured oxidation state of zirconium is 4+ (compared to 3+ for indium), but the parallels between the two metals in reactivity and preferred ligand types suggest that the mechanism exploited to label cells with 111In (i.e. lipophilic metastable chelates entering cells and subsequently dissociating) might be exploited in the case of 89Zr. Tetravalent zirconium forms ZrL4 complexes with monobasic bidentate ligands such as oxinate, tropolonate and hydroxamates, analogous to InL3. On this basis we developed the first synthesis of [89Zr]-Zr(oxinate)4, and compared it with [111In]-In(oxinate)3 for labelling several cell lines and human donor leukocyte, and tracking GFP-5T33 myeloma cells in mice. The resulting efficiency of labelling with Zr-89 was similar to that of In-111, but the Zr-89 showed reduced loss of radiolabel from cells over several days post labelling, both in vitro and in vivo, and initial comparison of toxic effects showed no notable differences (Figure 1).1 In addition, preliminary work by the Torres group (unpublished) has shown that the oxine complex can label liposomes with 89Zr, with 45% efficiency with stability for at least 48h in human serum.
Figure 1. Distribution of Zr-89-labelled myeloma cells 2 days and 7 days after injection into mice. Uptake in the liver, spleen and bone marrow is seen as expected.
We therefore propose to convert this preliminary methodology into a clinical translatable PET cell-tracking tool. This requires a survey of the most effective chelating agents to improve on the current use of oxine, both to improve the synthesis of the initial complex and to improve the efficiency of radiolabelling cells (this part of the project has the potential to generate new IP); Torres has begun this process by demonstrating that an isomer of oxine, 2-hydroxyquinoline, is superior to oxine in complexing 89Zr and incorporating it into liposomes (Figure 2, unpublished).
Figure 2. Structure of 2-hydroxyquinoline (top) and 8-hydroxoquinoline (oxine, bottom)
Using fundamental principles of coordination chemistry, the student will design new candidate ligands for Zr-89. At Imperial College, within the Long group, he/she will synthesise “non-radioactive or cold” zirconium complexes with the aim of characterising their coordination and physicochemical properties (solubility, stability). The student will gain skills in synthetic inorganic chemistry and characterisation (X-ray, MS, IR, etc)
The student will then synthesise and characterise the complexes using Zr-89, available at the labs at St. Thomas’ and test their properties (stability, lipophilicity), gaining skills in radiochemistry under the supervision of Torres and Blower. Further evaluation will be conducted of the retention/efflux of radioactivity in labelled cells in a variety of human cell types including neutrophils, eosinophils, lymphocytes (including engineered T-cells), dendritic cells, stem cells and other transplantable cells, and liposomal drug carriers provided by our collaborator Prof. A. Gabizon (Jerusalem). He is a renowned scientist and clinician in the field of nanomedicine and cancer therapy and co-inventor of Doxil®, a successful liposomal anticancer drug; and a full evaluation of the effects of radiolabelling on survival and differentiation/phenotype in vitro and in vivo behaviour of the cells, to ensure that the trafficking observed by PET truly reflects the behaviour of the cells. This will provide the requisite data for selecting the first human evaluation of the Zr-89 PET cell tracking method, which will be planned first in patient cohorts currently imaged by SPECT-isotope (Tc-99m, In-111) labelled cells in order to confirm that the new method matches gold standard technology, then in new more demanding settings such as atherosclerosis where the smaller size of lesions and smaller cell numbers severely limit the utility of current SPECT methods and highlighting the advantages of PET (resolution, sensitivity, quantification).
1 (a) Charoenphun P, Meszaros LK, Chuamsaamarkkee K, Sharif-Paghaleh E, Ballinger JR, Ferris TJ, Went MJ, Mullen GED, Blower PJ. [89Zr]-Zr(oxinate)4 for long term in vivo cell tracking by positron emission tomography. Eur J Nucl Med Mol Imaging 2014; DOI 10.1007/s00259-014-2945-x. (b) Ferris TJ, Charoenphun P, Meszaros LK, Mullen GED, Blower PJ, Went MJ. Synthesis and characterisation of zirconium complexes for cell tracking with Zr-89 by positron emission tomography. Dalton Trans 2014;43:14851–14857.