Student: Vittorio De Santis
1. To develop 89Zr-macrophage labelling methodologies based on new peptide/protein cell delivery vehicles, improving radiolabelling efficiencies and minimising 89Zr efflux from macrophages.
2. To undertake PET imaging of 89Zr-macrophages in preclinical tumour models to determine macrophage biodistribution at different disease stages.
3. To determine in preclinical tumour models whether 89Zr-macrophage biodistribution correlates with cancer therapy outcome.
Macrophages are tissue-resident components of the innate and adaptive immune systems, and perform a variety of functions in host defence and maintenance of homeostasis. As such they are crucial in the progress and resolution of a variety of pathological conditions, including cancer, autoimmunity, atherosclerosis and rejection of transplanted organs. In oncology, the density of tumour-associated macrophages is associated with poor prognosis. Being able to image macrophage location and migration would (i) aid in the development of novel tumour-associated macrophage-targeted drugs and (ii) provide clinically useful information on disease pathology. Macrophage imaging also has applications in other diseases – for instance, it would allow monitoring of the immune response of organ transplant recipients. Recent research has been successfully carried out with antibodies targeting macrophages labelled with SPECT radionuclides. In preclinical models of cancer (Figure 1), arthritis (Figure 2) and heart transplants macrophage SPECT imaging can be used to monitor therapy response. For example, 111In-anti-F4/80 is a protein that targets macrophages. Using 111In-anti-F4/80, a heterogeneous distribution of macrophages can be visualised in a tumour microenvironment (Figure 1) in mice with breast cancer xenografts. In mouse models of arthritis, treatment with therapeutic etanercept reduces not only the inflammation in joints, but also the accumulation of 111In-anti-F4/80 in those joints (Figure 2).
PET imaging provides higher resolution, sensitivity and quantifiability compared to SPECT, and thus is advantageous for imaging small populations of macrophage cells migrating to small tumour lesions. The PET isotope, zirconium-89 (89Zr) (half-life = 78h), allows PET imaging up to two weeks post-injection. Recent work4 at KCL has demonstrated that metastable lipophilic complexes that deliver 89Zr4+ across macrophage cell membranes and release it within cells can be used to label cells. However, labelling efficiency and efflux of 89Zr from cells is variable. New peptide/protein vehicles that deliver their cargo efficiently and quantitatively to the cell cytosol are likely to provide improved 89Zr uptake.
This project aims to radiolabel macrophages with new 89Zr-protein vehicles ex vivo, providing populations of 89Zr-macrophages. Prior to in vivo studies, the 89Zr-macrophages will be tested to ensure that they remain viable, and that their phenotype is still typical of the native, unmodified cell. The 89Zr-macrophages will be assessed in vivo using PET imaging, in both tumour-bearing and healthy mice, to determine how macrophage biodistribution differs in diseased and healthy mice. The biodistribution of 89Zr-macrophages will also be assessed in tumour-bearing mice that receive therapy (chemotherapy, radiotherapy or antibody therapy) to assess whether 89Zr-macrophage biodistribution correlates with cancer therapy outcome. Ultimately, these studies will help answer the following question: Can 89Zr-macrophage PET imaging be used as a predictor of disease prognosis and therapy outcome?
(1) Terry, S. Y. A., et al. (2015) 111In-anti-F4/80-A3-1 antibody: a novel tracer to image macrophages. Eur. J. Nucl. Med. Mol. Imaging 42, 1430.
(2) Terry, S. Y. A., et al. (2016) Monitoring Therapy Response of Experimental Arthritis with Radiolabeled Tracers Targeting Fibroblasts, Macrophages, or Integrin αvβ3. J. Nucl. Med. 57, 467.
(3) O’Neill, A. S. G., Terry, S. Y. A., et al. (2015) Non-invasive molecular imaging of inflammatory macrophages in allograft rejection. EJNMMI Res. 5, 69.
(4) Charoenphun, P., et al. (2015) 89[Zr]Oxinate4 for long-term in vivo cell tracking by positron emission tomography. Eur. J. Nucl. Med. Mol. Imaging 42, 278-87.
(5) Dixon, J. E., et al. (2016) Highly efficient delivery of functional cargoes by the synergistic effect of GAG binding motifs and cell-penetrating peptides. Proc. Natl. Acad. Sci. 113, E291-E99.