中文摘要：

二乙烯三胺（DETA）修饰生物可降解的聚乙二醇（PEG）-聚天冬氨酸（PAsp）两嵌段聚合物PEG-PAsp，并通过配体交换将PEG-PAsp（DETA）修饰到磁共振（MR）对比剂SPIO表面，阳离子嵌段PAsp（DETA）可负载核酸分子siRNA，从而获得兼具MR显像和核酸传输功能的生物可降解载体．细胞毒性研究证实该载体聚合物具有较好的生物安全性，可被肿瘤细胞高效吸收，且使转基因细胞株A549-Luc（恒定表达萤火虫荧光素酶）中荧光素酶的活性下调60％．MR成像也证实，SPIO经载体负载后，其横场弛豫率比游离的水溶性SPIO（WSPIO）提高了3倍以上，达到147Fe（mmol／L）^-1s^-1，显著提高了磁共振的显像效果．

英文摘要：

The lack of effective siRNA delivery vector with low toxicity limited the development of siRNA therapy. The cationic molecule diethylenetriamine （DETA） with low molecular weight was grafted on the block copolymer （PEG-PAsp） of poly （aspartic） （PAsp） and poly （ ethylene glycol） （PEG） to make a ternary copolymer PEG-PAsp （DETA） 30. The MTT analytical results demonstrated that the PEG-PAsp （DETA） 30- SPIONs have lower cytotoxicity. The biodegradable of PEG-PAsp and the low molecular weight of DETA endow the nanocarrier with good biocompatibility. Furthermore,the MR contrast imaging agent SPIO was introduced into copolymer via a ligand exchange method, yielding a MR-visible nanocarrier for imaging siRNA delivery and therapy simultaneously. The SPIONs didn＇ t affect the loading of siRNA. Based on the data of zeta potential and diameter, the N/P = 12 was used to prepare the PEG-PAsp （DETA）30-SPIONs@ siRNA nanoparticle. The MRI-visible polyplexs of N/P = 12 exhibited higher T2 relaxivity （r2 = 147 Fe （mmol/L） ^-1 s^-1） than WSPIO （r2 = 46.4 Fe （mmol/L）^-1 s^-1）, indicating high MRI T2-weighted imaging sensitivity. Using the laser confocal microscope and prussian blue staining,the efficient co-delivery of siRNA and SPIO was confirmed in the present study. Moreover, the luciferase gene-specific siRNA delivered with vector could effectively inhibit the firefly luciferase gene expression in cancer cells. SPIO co-delivered with siRNA provides a real-time and noninvasive approach to guide the optimization of the properties of siRNA delivery vector.