MR Tracking Of Magnetized Labeled Placental Mesenchymal Stem Cells Targeting Colorectal Cancer

Objective To investigate the effect of human placental mesenchymal stem cells(PMSCs)on the growth of colorectal cancer,explore the feasibility of magnetic labeling PMSCs imaging under 3.0T MR and its rule in vitro and in vivo.Methods Using poly-L-lysine(PLL)as transfection agent and ultramicro superparamagnetic iron oxide particles(USPIO)to form different concentrations of PLL-USPIO complex to label PMSCs.USPIO labeling efficiency and the biological characteristics such as the survival rate,proliferation ability and apoptosis rate of PMSCs were investigated to determine the optimal label concentration.Agarose gel models of different orders of magnitude were prepared,T2 WI,T2mapping and T2*mapping sequences were performed under 3.0 T magnetic resonance to observe the imaging patterns of labeled cells and the minimum number of cells that could be visualized.The nude mice of HT-29 subcutaneous xenograft were randomly divided into experimental group and control group,after 14 days,the experimental group was injected with magnetically labeled PMSCs,the growth of the transplanted tumor and MR signal changes of the two groups were observed,and the quality of the image of magnetized labeled cells under different sequences was compared.After scanning,two groups of transplanted tumor was taken for he staining and immunohistochemical analysis.Results The labeling rates were all>95% when USPIO labeling concentration ?10?g/ml,and the concentration range of 5~15?g/ml had no obvious effect on the biological characteristics,such as PMSCs activity,proliferative ability and apoptosis rate(P >0.05).When the final concentration of USPIO labeling is 10?g/ml,104 PMSCs can be displayed in the 3.0T MR on T2* mapping sequence,and the contrast of T2* mapping sequence for the tracking of USPIO-labeled labeled cells is better than that of T2 WI and T2 mapping sequences.The local low signal in colorectal tumors was seen on the first day under 3.0T MR in the experimental group,and the low signal range decreased with increasing time from the third day,there was no significant difference compared with control group on the 14 th day.The T2 and T2* values gradually increased and the tumor volume decreased,but the tumor volume and weight of the experimental group and the control group were not statistically significant(P> 0.05),and the CD31,CD34 and Ki67 positive rates were not significant between the two groups(P>0.05).Conclusion 3.0T MR can safely and effectively perform molecular imaging of PMSCs in vitro and vivo,T2*mapping sequence is superior to T2 WI and T2 mapping sequence in USPIO-labeled cells.PMSCs may have a delayed effect on the growth rate of colorectal tumors,but the specific mechanism remains to be studied.