Magnetic resonance tracking of endothelial progenitor cells labeled with superparamagnetic iron oxide homing to the site of hepatoma

Abstract

Objective To track the migration and incorporation of intravenously injected, magnetically labeled endothelial progenitor cells (EPCs) from mouse bone marrow into the blood vessels in a rapidly growing HCC model by microMR (7.0 T). Methods This study was approved by the Institutional Committee on Animal Research. H22 hepatic ascitic cancer cells was directly injected into the left liver lobe of BALB/c nude mice (n=15). EPCs derived from bone marrow of C57BL/6 mice were isolated and cultured. The third passage EPCs were collected and labeled with 25 μg/ml superparamagnetic iron oxide (SPIO) and poly-l-lysine (PLL) complex (SPIO-PLL). MTT assay and flow cytometry were used to evaluate the difference of growth curve and apoptosis between labeled and unlabeled EPCs. EPCs labeled with SPIO-PLL were injected into mice via tail vein in experiment group (on the 3rd day after establishing HCC model) (n=15) and control group (n=6). The signal changes of tumor (the 1st, 3rd and 7th day after transplantation) were observed by microMR. Prussian blue staining and immunohistochemistry staining of CD31 were performed. MRI findings were confirmed by histomorphology. Two-sample t test was used to analyze the data. Results Single tumor was showed in the liver of all mice 3 d after establishing models. Labeling with SPIO-PLL at a concentration of 25 μg/ml did not alter cell growth curve (measured by MTT assay; t=0.281, P>0.05) and cell apoptosis (analyzed by flow cytometry). The apoptosis rates of SPIO-PLL labeled and unlabled EPCs were (12.31±1.43)% and (11.57±1.24)% in early stage, and (0.55±0.07)% and (0.49±0.05)% in late stage. No significant differences were observed between them (t=0.967, 1.060; both P>0.05). Migration and incorporation of transplanted and labeled cells into tumor were documented with in vivo microMR as low signal intensity at the tumor periphery as early as the 3rd day after EPCs administration in preformed tumors (4/5). Prussian blue staining showed iron-positive cells at the sites corresponding to low signal intensity on MRI. The positive cells expressing CD31 existed in intratumoral and peritumoral vessels. There was no signal change in control group at all time points. Conclusions MRI can demonstrate the incorporation of magnetic labeled mouse EPCs into the implanted hepatoma. It may be helpful for early diagnosis and therapy of liver tumor. Key words: Liver neoplasms; Endothelium; Bone marrow; Superparamagnetic iron oxides; Magnetic resonance imaging