基于NaGdF4纳米晶体的磁共振分子影像探针的构建与性质研究

Magnetic resonance imaging (MRI) is a robust analytical technology in many areas of biomedical research, and diagnosis of diseases such as cancer. To meet the sensitivity requirement of the technique, contrast agents are always used in MRI assays. Gd-DTPA is a widely used MRI contrast agent in current clinical diagnosis. However, there are some drawbacks such as too short metabolism cycle and obvious side effects, which will limit the application of this small molecular contrast agent. To overcome these drawbacks, developing new contrast agents with appropriate retention time in body, low toxicity and tumor targeting, has received increasing attention. This proposal describes research on the synthesis, characterization and biofunctionalization of a new contrast agent to be employed in MRI of tumor. We propose to synthesize narrow distribution sodium gadolinium tetrafluoride (NaGdF4) nanocrystals with different diameters and functionalized PEG ligands, and to transform the hydrophobic NaGdF4 nanocrystals into the hydrophilic via ligand exchange. For targeted attaching with tumor, we also propose to develop the synthetic methodology to attach the nanocrystals to monoclonal antibody. The contrast effect of the NaGdF4 nanocrystal will be evaluated by in vitro and in vivo MRI detections. The effect of nanocrystal size on bio-distribution of nanocrystal, metabolism process, targeted attaching with tumor will also be investigated. The overall goal of this proposal is to develop a new T1-weighted MRI probe based on paramagnetic NaGdF4 nanocrystal.

磁共振成像技术是目前生物医学检测及肿瘤临床诊断的主要手段之一，为提高成像对比度，磁共振成像造影剂被广泛使用。然而，Gd-DTPA等顺磁离子络合物小分子造影剂存在血液代谢时间短，释放顺磁离子毒副作用高等缺点。因此，发展新型高灵敏度磁共振造影剂，进而构建分子影像探针已经成为全世界科学家所关注的热点。本项目拟以顺磁性NaGdF4纳米晶体作为T1加权磁共振分子影像探针的应用为背景，探索尺寸可控的单分散性NaGdF4纳米晶体和功能化的PEG配体的制备方法，并通过表面配体交换获得具有高水相分散性、胶体稳定性的顺磁性PEG-NaGdF4纳米晶体，然后通过与抗体耦联，获得具有抗体靶向的分子影像探针。进一步结合动物成像实验，系统研究NaGdF4纳米晶体尺寸和表面配体化学结构对纳米材料磁学性质、生物体内分布与代谢过程及与肿瘤靶向识别的影响，以期构建抗体靶向的NaGdF4纳米晶体磁共振影像探针。

本项目以构建基于稀土纳米颗粒的高灵敏肿瘤分子影像探针为目标，系统研究了稀土纳米晶体的尺寸控制合成、表面生物相容性修饰、肿瘤分子影像探针构建及成像应用方法，对推动稀土纳米材料在肿瘤分子影像诊断中的应用具有重要的科学意义。本项目取得的创新性成果如下：1）揭示了反应条件与稀土纳米晶体成核与生长动力学关系，建立了窄粒径分布的顺磁性NaGdF4纳米晶体及顺磁性/上转换光学NaGdF4:Yb,Er纳米晶体的可控制备方法；2）设计并合成了与稀土纳米晶体结合力强的功能化生物相容性PEG配体，通过配体置换制备了在磷酸缓冲液等生理缓冲液中具有长期胶体稳定性的生物相容性纳米颗粒；3）建立了温和、高效的纳米颗粒与抗体耦联方法，构建了高灵敏磁共振及磁共振/上转换光学肿瘤分子影像探针；4）构建了小鼠结直肠癌皮下肿瘤模型及腹腔肿瘤转移模型，利用所构建的探针开展了肿瘤在体磁共振及磁共振/上转换光学成像，成功实现了直径小于2 mm肿瘤的成像检测；5）利用稀土元素自然丰度低的属性，深入研究了纳米晶体尺寸依赖的体内分布行为。在项目执行期间，共发表学术论文11篇，申请专利1项，圆满完成项目计划任务。