An indium-111-labelled membrane-targeted peptide for cell tracking with radionuclide imaging.

Cell labelling agents that enable longitudinal in vivo tracking of administered cells will support the clinical development of cell-based therapies. Radionuclide imaging with gamma and positron-emitting radioisotopes can provide quantitative and longitudinal mapping of cells in vivo . To make this widely accessible and adaptable to a range of cell types, new, versatile and simple methods for directly radiolabelling cells are required. We have developed [ 111 In]In-DTPA-CTP, the first example of a radiolabelled peptide that binds to the extracellular membrane of cells, for tracking cell distribution in vivo using Single Photon Emission Computed Tomography (SPECT). [ 111 In]In-DTPA-CTP consists of (i) myristoyl groups for insertion into the phospholipid bilayer, (ii) positively charged lysine residues for electrostatic association with negatively charged phospholipid groups at the cell surface and (iii) a diethylenetriamine pentaacetate derivative that coordinates the γ-emitting radiometal, [ 111 In]In 3+ . [ 111 In]In-DTPA-CTP binds to 5T33 murine myeloma cells, enabling qualitative SPECT tracking of myeloma cells' accumulation in lungs immediately after intravenous administration. This is the first report of a radiolabelled cell-membrane binding peptide for use in cell tracking.