EANM: PET helps track radiolabeled neural stem cells
Neural stem cells can be visualized in vivo using PET and 99mTc-HMPAO for up to 24 hours, according to a presentation made at the European Association of Nuclear Medicine (EANM) Congress in Vienna last week.

The study, conducted by Erik F.J. de Vries, PhD, from the department of nuclear medicine and molecular imaging, University of Groningen in the Netherlands, and colleagues, investigated if C17.2 cells migrate specifically toward gliomas or they also migrate toward other sites of inflammation.

The C17.2 neural stem cell line is known for its migratory potential toward gliomas in-vivo. The researchers used a rat tumor inflammation model and subcutaneously inoculated with glioma cells in the right shoulder and induced sterile inflammation by turpentine injection in the thigh muscle of the left leg.

C17.2 cells were labeled with 18F-FDG, 99mTc-HMPAO or 111In-oxine and intravenously injected in rats and visualized by microPET or planar scintigraphy.

Labeling efficiency of C17.2 cells with 18F-FDG under optimized conditions was 12 percent dose. 99mTc-HMPAO labeling efficiency was 50 percent dose, and 99mTc-HMPAO was well retained inside the cells. Labeling with 111In-oxine caused a toxic response when more than 50 kBq was incorporated, according to Vries and colleagues.

Immediately after tail vein injection, the labeled stem cells were shown to migrate to the site of inflammation as well as the tumor site. However, the majority of cells were trapped in the capillary network of lungs, spleen and liver. While rats treated with free 99mTc-HMPAO showed substantial radioactivity in the brain, rats treated with 99mTc-HMPAO-labeled stem cells showed virtually no radioactivity in the brain. Thus, stem cells do not migrate to the brain in the absence of an inflammatory stimulus, concluded Vries and colleagues.

The researchers also concluded that C17.2 neural stem cells can be visualized in vivo using both PET and planar scintigraphy. However, 18F-FDG shows substantial release from labeled cells, which obscures the migration of the cells in the PET scans. In contrast, 99mTc-HMPAO is a suitable label for in vivo cell tracking for up to 24 hours. For prolonged cell tracking, 111In-oxine is not suitable, since this radiopharmaceutical is toxic to the cells.