In vivo imaging of human skeletal muscle cells (HSkMC) biodistribution : comparison between SPET, MRI and BLI

Introduction and aim: The interest about cell-mediated therapy for tissues regeneration is increased in the last few years. Numerous protocols which include implantation of healthy stem cells in diseased models were set up but cell distribution, localization, survival, proliferation and differentiation cannot be evaluated in vivo. Here we compared SPET, MRI and BLI visualization of a human muscle cell line biodistribution proposing the application of these procedures for a better evaluation of muscle stem cell mediated treatments. Methods: Human Skeletal Muscle Cells (HSkMC) were labelled with with Endorem® (0-100-200 µg Fe/mL) for 24 or 48h in presence or not of Poly-L-Lysine (PLL), Protamine Sulfate (PrS), Polybrene (PB) or infected with a lentiviral vector carrying Luciferase gene under control of the Myogenin promoter (pGZ.Myo.L) and then labelled with 111Indium-Oxine (60 µCi/106 cells). Labelled HSkMC were analyzed for viability, iron content, morphology and intrarterially (i.a.) injected into NUDE mice for in-vivo SPET, MRI or BLI. Gamma counting of explanted organ and IHC was performed to validate imaging data. Results: HSkMC incubated for 24h or 48h with 0-100-200µg Fe/mL didn’t show differences, in terms of viability, between labelled/non-labelled cells in the presence or absence of carriers (n=3). The percentage of Iron+ cells increased in proportion to the iron content in the medium; in particular 200ug/mL endorem+PLL was deemed as the ideal cell labelling condition for in vivo MRI giving more than 90% Iron+ cells. Iron loaded or 111Indium- Oxine-luciferase expressing HSkMC were i.a. injected into a murine model of muscle inflammation. MRI permitted to follow over time HSkMC distribution into the injured muscle. SPET and BLI of HSkMC confirmed cell distribution to muscle and revealed an early localisation into the lung. HSkMC infected with pGZ.Myo.L, i.a. injected were detectable in muscle up to 2 months after injection. Interestingly, at this time point, the signal is still present only near the lesion area while disappeared in the rest of the body. Conclusions: Human muscle cells precursors visualization by MRI, SPET or in vivo BLI confirmed the same biodistribution. The different specific protocols will be useful to study the fate and the in vivo behaviour over time of stem cells once injected into recipient animals in a more complete way. It will be possible to use these instruments for the in vivo study of muscular stem cells in restoring skeletal muscles after damage. Acknowledgement: This work was supported by the FP6 Hi-CAM project (LSHC-CT-2006-037737).