MagA基因修饰间充质干细胞介导的肿瘤转移灶磁共振检测及磁热疗

The detection and the targeted therapy of metastatic tumor is very important to the patient.To increase detection rate of metastatic tumors and improve targeted therapy, the mesenchymal stem cells (MSCs) which can specifically migrate to tumor is used as a gene delivery in this study. We'll make the animal metastatic tumor model in rat liver. MSCs will gain the expression of MagA gene by lentivirus and then contain the superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs would be enriched specifically in the metastatic tumors with MSCs migration after transplant. These SPIONs would enhance contrast between metastatic tumors and normal tissue by the T2*WI signal reduction. The enhanced contrast can help us to find metastatic tumors more accurately. These SPIONs in metastatic tumors can also be remotely heated upon exposure to an external alternating magnetic field.And the temperature of metastatic tumor areas will be rised specifically. The targeted magnetic hyperthermia therapy would lead to apoptosis and necrosis of cells. So the metastatic tumors and the transplant MSCs would be eliminated. The results of this study would be helpful to the detection of metastatic tumors and to the targeted therapy.

恶性肿瘤转移灶的发现对病情评估至关重要，而目前对转移灶的特异性治疗也存在困难。本课题以大鼠血行肝转移模型为例。将磁共振报告基因MagA基因转染入间充质干细胞，在间充质干细胞内持续形成内生性超顺磁性氧化铁纳米颗粒（SPIONs, superparamagnetic iron oxide nanoparticles）。利用间充质干细胞对肿瘤转移灶特异性归巢的性质，将间充质干细胞内含的SPIONs特异性运送至肿瘤转移灶部位，使其在肿瘤转移灶内持续性富集。这些SPIONs降低磁共振T2*WI信号的特性，将会增强转移灶与周围组织对比度，达到增加肿瘤转移灶检出率的目的。并利用SPIONs在交变磁场下产热效应，特异性的在肿瘤转移灶内形成相对高热，致肿瘤细胞凋亡及坏死，达到特异性消除肿瘤转移灶的目的，同时也消除移植间充质干细胞的生物效应。为发现和特异性治疗恶性肿瘤转移灶提供新的方法模式及坚实的实验基础。

本课题组人工合成超顺磁性氧化铁纳米微粒（superparamagnetic iron oxide nanoparticles，SPIONs），并将其顺利转染入间充质肝细胞（MSCs，mesenchymal stem cells）内，普鲁士蓝染色及电镜检测均在细胞内找到含铁颗粒。检测转染后MSCs，其内携铁量为（23.73±3.59）pg/cell，符合磁热疗需要浓度。体外证实，该浓度SPIONs不影响MSCs向肿瘤归巢的能力。同时我们也成功建立了胶质瘤肝血行转移模型。将SPIONs转染后MSCs注入建模裸鼠尾静脉后，7.0T磁共振（Magnatic Resonance Imaging，MRI）检测发现肿瘤转移灶信号较对照组明显降低，提示SPIONs转染后MSCs能顺利归巢于肿瘤转移灶，将SPIONs富集于转移灶，并冰冻切片普鲁士蓝染色证实。为肿瘤转移灶的MRI检测及磁热疗提供了坚实的实验基础。最后本课题组证实，SPION-MSCs归巢于肿瘤转移灶后进行磁热疗，对于早期较小的肿瘤灶能部分抑制其生长，但对晚期较大的肿瘤灶效果欠佳。推测可能与SPION-MSCs归巢数量及磁热疗时的肿瘤大小有关，在早期SPION-MSCs相对于肿瘤细胞较多，而晚期SPION-MSCs相对于肿瘤细胞较少。提高SPION-MSCs归巢效率及磁热疗频率可能会有效解决上述问题。