Abstract
Assessing the retention of cell therapies following implantation is vital and often achieved by labelling cells with 2′-[18F]-fluoro-2′-deoxy-D-glucose (18F-FDG). However, this approach is limited by local retention of cell-effluxed radiotracer. Here, in a preclinical model of critical limb ischemia, we assessed a novel method of cell tracking using 3′-deoxy-3′-L-[18F]-fluorothymidine (18F-FLT); a clinically available radiotracer which we hypothesise will result in minimal local radiotracer reuptake and allow a more accurate estimation of cell retention. Human endothelial cells (HUVECs) were incubated with 18F-FDG or 18F-FLT and cell characteristics were evaluated. Dynamic positron emission tomography (PET) images were acquired post-injection of free 18F-FDG/18F-FLT or 18F-FDG/18F-FLT-labelled HUVECs, following the surgical induction of mouse hind-limb ischemia. In vitro, radiotracer incorporation and efflux was similar with no effect on cell viability, function or proliferation under optimised conditions (5 MBq/mL, 60 min). Injection of free radiotracer demonstrated a faster clearance of 18F-FLT from the injection site vs. 18F-FDG (p ≤ 0.001), indicating local cellular uptake. Using 18F-FLT-labelling, estimation of HUVEC retention within the engraftment site 4 hr post-administration was 24.5 ± 3.2%. PET cell tracking using 18F-FLT labelling is an improved approach vs. 18F-FDG as it is not susceptible to local host cell reuptake, resulting in a more accurate estimation of cell retention.
Highlights
One of the most commonly applied clinical positron emission tomography (PET) cell tracking approaches in cardiovascular studies uses direct cell labelling with 2′-[18F]-fluoro-2′-deoxy-D-glucose (18F-FDG)8,9,11–16. 18F-FDG is a glucose analogue which becomes phosphorylated and trapped intracellularly and can be used as a marker of metabolic activity as well as for cell tracking
As part of our efforts to translate the use of human embryonic stem cell-derived endothelial cells into the clinic for treatment of critical limb ischemia[22], we aimed to optimise and develop methods for the accurate assessment of cell tracking post-implantation
This investigation addressed the hypothesis that any 18F-FLT effluxed from labelled cells would not be incorporated at the site of injection by host cells, providing an improved method for tracking endothelial cell fate in an in vivo model of ischemia-induced angiogenesis compared to 18F-FDG labelling
Summary
One of the most commonly applied clinical PET cell tracking approaches in cardiovascular studies uses direct cell labelling with 2′-[18F]-fluoro-2′-deoxy-D-glucose (18F-FDG)8,9,11–16. 18F-FDG is a glucose analogue which becomes phosphorylated and trapped intracellularly and can be used as a marker of metabolic activity as well as for cell tracking. As part of our efforts to translate the use of human embryonic stem cell-derived endothelial cells into the clinic for treatment of critical limb ischemia[22], we aimed to optimise and develop methods for the accurate assessment of cell tracking post-implantation. This investigation addressed the hypothesis that any 18F-FLT effluxed from labelled cells would not be incorporated at the site of injection by host cells, providing an improved method for tracking endothelial cell fate in an in vivo model of ischemia-induced angiogenesis compared to 18F-FDG labelling. The key aims were to determine; 1) whether cells could be labelled with 18F-FLT and how this compared to 18F-FDG labelling, 2) the effect of radiolabelling human umbilical vein endothelial cells (HUVECs) with 18F-FDG and 18F-FLT on cell viability, proliferation and function in vitro, and 3) if 18F-FLT cell labelling is an improved approach compared with 18F-FDG for assessing cell fate in vivo due to the absence of local re-uptake of effluxed radiotracer
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