Figure 1. Migration and accumulation of administered In-111-oxine and SPIO-labeled endothelial progenitor cells in tumors.

Five million In-111-labeled EPCs followed by 5 million magnetically labeled EPCs were administered in tumor-bearing rats. Both In-111- and SPIO-labeled EPCs were injected at the same time in the same animals. Following intravenous administration, SPECT images were obtained on days 0, 1 and 3. MRI images were obtained on day 7 to allow the decay of the radioactivity. SPECT images of the tumor obtained at 3 h (A), 24 h (B) and 72 h (C) showed increased activity at the site of tumor, indicating accumulation of In-111 labeled EPCs. Note a few of the iron-positive cells also make the lining of blood vessels (inset, black arrows). MRI was obtained by a clinical 3T system on day 7 following last SPECT. (D) T₂-weighted image with an echo time of 35 ms, (E) T₂-weighted image with an echo time of 20 ms and corresponding R2* map (F). Note the low signal intensity areas on T₂-weighted image (E, black arrows) and corresponding R2* map (F, yellow arrows) indicating accumulation of iron-positive cells, which is proved by diaminobenzidine-enhanced Prussian blue staining (G). Inset showing the iron-positive cells lining the blood vessels.

EPC: Endothelial progenitor cell.

Reproduced with permission from [101].