Danhier Pierre, Magat Julie, Levêque Philippe, De Preter Géraldine, Porporato Paolo E, Bouzin Caroline, Jordan Bénédicte F, Demeur Gladys, Haufroid Vincent, Feron Olivier, Sonveaux Pierre, Gallez Bernard
Louvain Drug Research Institute, Biomedical Magnetic Resonance Research Group, Université catholique de Louvain, Brussels, Belgium.
NMR Biomed. 2015 Mar;28(3):367-75. doi: 10.1002/nbm.3259. Epub 2015 Jan 22.
Cell tracking could be useful to elucidate fundamental processes of cancer biology such as metastasis. The aim of this study was to visualize, using MRI, and to quantify, using electron paramagnetic resonance (EPR), the entrapment of murine breast cancer cells labeled with superparamagnetic iron oxide particles (SPIOs) in the mouse brain after intracardiac injection. For this purpose, luciferase-expressing murine 4 T1-luc breast cancer cells were labeled with fluorescent Molday ION Rhodamine B SPIOs. Following intracardiac injection, SPIO-labeled 4 T1-luc cells were imaged using multiple gradient-echo sequences. Ex vivo iron oxide quantification in the mouse brain was performed using EPR (9 GHz). The long-term fate of 4 T1-luc cells after injection was characterized using bioluminescence imaging (BLI), brain MRI and immunofluorescence. We observed hypointense spots due to SPIO-labeled cells in the mouse brain 4 h after injection on T2 *-weighted images. Histology studies showed that SPIO-labeled cancer cells were localized within blood vessels shortly after delivery. Ex vivo quantification of SPIOs showed that less than 1% of the injected cells were taken up by the mouse brain after injection. MRI experiments did not reveal the development of macrometastases in the mouse brain several days after injection, but immunofluorescence studies demonstrated that these cells found in the brain established micrometastases. Concerning the metastatic patterns of 4 T1-luc cells, an EPR biodistribution study demonstrated that SPIO-labeled 4 T1-luc cells were also entrapped in the lungs of mice after intracardiac injection. BLI performed 6 days after injection of 4 T1-luc cells showed that this cell line formed macrometastases in the lungs and in the bones. Conclusively, EPR and MRI were found to be complementary for cell tracking applications. MRI cell tracking at 11.7 T allowed sensitive detection of isolated SPIO-labeled cells in the mouse brain, whereas EPR allowed the assessment of the number of SPIO-labeled cells in organs shortly after injection.
细胞追踪对于阐明癌症生物学的基本过程（如转移）可能是有用的。本研究的目的是利用磁共振成像（MRI）进行可视化，并利用电子顺磁共振（EPR）进行定量，以观察心内注射后标记有超顺磁性氧化铁颗粒（SPIO）的小鼠乳腺癌细胞在小鼠脑内的滞留情况。为此，用荧光莫尔戴离子罗丹明B SPIO标记表达荧光素酶的小鼠4T1-luc乳腺癌细胞。心内注射后，使用多个梯度回波序列对SPIO标记的4T1-luc细胞进行成像。使用EPR（9GHz）对小鼠脑内的氧化铁进行离体定量。注射后4T1-luc细胞的长期命运通过生物发光成像（BLI）、脑MRI和免疫荧光进行表征。注射后4小时，在T2 *加权图像上观察到小鼠脑内由于SPIO标记的细胞而出现的低信号点。组织学研究表明，SPIO标记的癌细胞在递送后不久就定位在血管内。SPIO的离体定量显示，注射后不到1%的注射细胞被小鼠脑摄取。MRI实验未显示注射后数天小鼠脑内出现大转移灶，但免疫荧光研究表明，在脑内发现的这些细胞形成了微转移灶。关于4T1-luc细胞的转移模式，一项EPR生物分布研究表明，心内注射后，SPIO标记的4T1-luc细胞也滞留在小鼠肺部。注射4T1-luc细胞6天后进行的BLI显示，该细胞系在肺部和骨骼中形成了大转移灶。总之，发现EPR和MRI在细胞追踪应用中具有互补性。11.7T的MRI细胞追踪能够灵敏地检测小鼠脑内孤立的SPIO标记细胞，而EPR能够在注射后不久评估器官内SPIO标记细胞的数量。
