Jamal Guenoun MD, Presenter: Nothing to Disclose

Gerben A. Koning PhD, Abstract Co-Author: Nothing to Disclose

Piotr Alfred Wielopolski PhD, Abstract Co-Author: Nothing to Disclose

Gabriela Natalia Doeswijk BSc, Abstract Co-Author: Nothing to Disclose

Gabriel P. Krestin MD, PhD, Abstract Co-Author: Consultant, General Electric Company Research grant, General Electric Company Research grant, Bayer AG Research grant, Siemens AG

Monique R. Bernsen PhD, Abstract Co-Author: Nothing to Disclose

To develop an optimized labeling protocol for mesenchymal stem cells with Gd-liposomes that allows for sensitive and longitudinal tracking of cell fate in vivo.

Gd-DTPA was incorporated in the water phase of cationic liposomes containing cholesterol, DOTAP and DPPC at molar ratios 2.35:1.65:1.0. Rat mesenchymal stem cells (MSCs; Millipore, Billerica, MA, USA) were labeled with 125, 250, 500 or 1000 µM lipid, corresponding to 52±3, 104±6, 209±13 and 420±25 µM Gd respectively. Control cells were incubated with HEPES-containing liposomes. Labeling was performed for 1h, 4h or 24h. The cellular Gd load, cellular toxicity, cell proliferation rate and cell differentiation were determined as a function of labeling time and lipid dosage. Intracellular retention of Gd was assessed over time (20d). The intracellular fate of Gd-liposomes was studied with confocal microscopy, using fluorescent dyes in the water-core and bilayer. MRI visualization of Gd-labeled cells was performed on a 1.5T as well as a 3.0T clinical scanner. For in vivo experiments, cells were transplanted in skeletal muscle and imaged for at least 3 weeks. At several time-points animals were sacrificed and histology was performed to correlate MRI contrast to the presence of Gd-liposome labeled cells.

Labeling for 4h with 125 µM lipid is the most preferred labeling strategy, combining time-efficiency with a sufficient cellular Gd uptake (30±2.5 pg Gd cell-1), without significant effects on cell viability, proliferation and cell differentiation. Gd-liposomes were retained well intracellularly, in an endosomal distribution pattern. MSCs labeled with Gd-liposomes were imaged with MRI at both 1.5T and 3.0T, resulting in excellent visualization both in vitro and in vivo. At least 10.000 Gd-MSCs could be detected. Histology showed the liposomes to be still present at the site of injection, inside the labeled cells. Prolonged in vivo imaging of 500,000 Gd-labeled cells was possible for at least two weeks (3.0T).

In conclusion, Gd-loaded cationic liposomes are an excellent candidate to label MSCs, without detrimental effects on cell viability, proliferation and differentiation allowing sensitive and longitudinal visualization by MRI.

Cell labeling with Gd-liposomes might prove valuable for cell tracking in vivo in a clinical setting, for example as a therapy evaluation of stem cell therapy.

Guenoun, J, Koning, G, Wielopolski, P, Doeswijk, G, Krestin, G, Bernsen, M, Optimizing the Cell Labeling Strategy with Cationic Gd-liposomes: Longitudinal in Vivo Follow-up of Gd-labeled MSCs.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11010095.html