中文摘要：

目的构建以趋化因子受体4 （C-X-C motif chemokine receptor 4, CXCR4）为祀点的磁共振祀向对比剂并通过体外恶性肿瘤细胞的靶向磁共振成像探讨磁共振信号变化与肿瘤细胞CXCR4表达量的相关性。方法用细胞免疫荧光法和流式细胞计数法分别观察和测定3种恶性肿瘤细胞株（胰腺癌PANC-1、乳腺癌MCF-7和肺癌A549）的CXCR4表达，并验证新型多肤PeP12与3种恶性肿瘤细胞表面的CXCR4特异性结合的能力。化学合成超顺磁性纳米氧化铁颗粒（ultmsmall paramagnetic iron oxide nanoparticle, USPIO-Np）,并与 Pep12 实现共轭联接。动态光散射法测定 Pep12-USPIO 的水和直径；用MTS细胞增殖与毒性检测试剂盒测定其细胞毒性；磁共振成像检测不同浓度PeP12-USPIO溶液的T2/T2^＊信号变化。普鲁士蓝染色验证Pep12-USPIO与3种肿瘤细胞的特异性结合，磁共振成像验证Pep12-USPIO所致磁共振信号变化与3种肿瘤细胞CXCR4表达量的相关性。结果3种恶性肿瘤细胞株均有不同水平的CXCR4表达，流式细胞计数的CXCR4阳性细胞百分比分别为PANC-1： 18.7%; A549： 2.9%; MCF-7： 1.7%。多肽Pep12与3种恶性肿瘤细胞均能特异性结合，并且结合量与CXCR4表达量呈正相关性（r = 0.999，P=0. 027）。自行合成的Pepl2-USPIO在室温下长时间保持稳定的胶体状态，水和直径为（86.60±1.48）nm。Pep12-USPIO细胞毒性较低，铁浓度低于25 μg/ml时，AR2值和AR2＊憧与铁浓度呈现良好的线性正比关系（△R2： R2 =0.996； △R2^＊ ：R^2=0.977）。普鲁士蓝染色证实Pepl2-USPIO能够与3种恶性肿瘤细胞实现靶向结合，磁共振成像证实Pepl2-USPIO能够造成肿瘤细胞悬液磁共振T2/T2 ＊值降低（P 〈0. 01），并且AR2/AR2＊值与肿瘤细胞CXCR4表达水平呈显著的正相关（△R2： r=0. 997, P = 0.050； △R2＊ ： r = 1.000, P =0.019）。结论Pepl2-USPIO物理性质稳定，细胞毒性较低，能够与不同恶性肿?

英文摘要：

Objective To construct a cancer-specific magnetic resonance contrast agent targeting C-X-Cmotif chemokine receptor 4 （CXCR4） on cancer cell surface and to discuss its ability to quantify the CXCR4 ex-pression level of various cancer cells in vitro through the changes of magnetic resonance （ MR） signal. MethodsCellular immunofluorescence and flow cytometry assays were introduced to observe CXCR4 expression pattern andto quantify CXCR4 expression level in 3 different cancer cell lines （ pancreatic cancer cell line PANC-1, breastcancer cell line MCF-7,and lung cancer cell line A549）,respectively. By replacing the CXCR4 monoclonal antibody with a novel peptide, Pep12, we carried out these experiments again in the same condition, to prove itsability to bind to CXCR4 specifically. Ultrasmall paramagnetic iron oxide nanoparticle （ USPIO-Np） was synthesized de novo and conjugated to Pep 12 after surface modification. Dynamic light scattering （ DLS） method was introduced to measure its hydro diameter, MTS assay was performed to test its cell toxicity, and 1. 5T MR scan werecarried out to evaluate the T2/T2 ＊ signal changes. Prussian blue staining was introduced to observe the bindingpattern of Pep12-USPIO to 3 cancer cell lines, and MR scanning of cells cultured with Pep12-USPIO were done toevaluate its ability to quantify the CXCR4 expression level on different cancer cells by T2/T2 ＊ signal changes. Results CXCR4 expression was observed in different patterns and levels in all 3 cancer cell lines. Flow cytome-try showed that the CXCR4 positive cell proportions were 18.1% in PANC-1, 2. 9% in A549, and 1.7% inMCF-7, respectively. Pep 12 was able to bind to all 3 cancer cell lines specifically in a CXCR4 level dependentmanner （r = 0. 999 , P = 0. 027 ） . Pep12-USPIO formed stable aqueous colloid in PBS/water under room tempera-ture. The hydro diameter was （86. 60 ± 1. 48） nm. The cytoxicity of Pep2-USPIO was low. When the concentra-tion of iron was less than 25 ｜xg/ml,the values of AR2 an