Prussian Blue Nanoparticles as Cellular T1 MRI Contrast Agents

描述（由申请人提供）：该提案旨在开发普鲁士蓝纳米颗粒（PBNP）作为新一代T1加权MRI造影剂（CA），具有高弛豫率、长血液循环时间和穿透细胞膜的能力。普鲁士蓝（PB）是一种铁氰化物，分子式为Fe 4 III [Fe II（CN）6] 3·nH 2 O（n=14-16），其中两个不同的铁中心，Fe 3+（高自旋S=5/2）和Fe 2+（低自旋S=0）通过CN-基团桥接。在PB的晶体结构中，四分之一（25%）的FeII（CN）6单元不在晶格中，在结构内部产生了一个充满水分子的大空腔。缺失的Fe II（CN）6单元也导致Fe 3+中心被一个水分子和五个CN-基团配位，从而产生用于增强T1弛豫的活性内球弛豫机制。由于强配体场效应和CN-基团同时与扩展的3D网络中的Fe 3+和Fe 2+中心配位，CN-配体和Fe 3 +/Fe 2+离子完全锁定在其晶格位置并且不能从结构中释放。因此，PB具有对任何化合物测量的最低溶度积常数（Ksp=10-41）。我们已经发现，用Mn 2+或/和Gd 3+离子替换晶格中的一些Fe 3+离子可以形成掺入锰或钆的纳米颗粒，Mn@ PBNP和Gd@ PBNP，其具有显著增加的r1弛豫率。此外，与小分子Gd 3+螯合物相比，PBNP在溶液中的结构刚性和降低的翻滚速率可以有助于这种新的纳米平台中的额外的T1加权MRI对比度增强。我们的目标是：（i）探索通过调整纳米颗粒尺寸、Mn 2+或/和Gd 3+掺杂水平以及用小分子或聚合物进行表面涂覆来优化r1弛豫率的方法;（ii）系统地研究细胞摄取和细胞成像的特性以及图像引导药物递送应用的潜力;和（iii）同时掺入Mn 2+或/和Gd 3+离子沿着放射性核素Ga-67或Ga-68用于MRI-SPECT和MRI-PET双峰成像应用。 我们将奋进测试以下四个假设：1）普鲁士蓝纳米粒子，当适当的定制和工程，将有效地减少质子从散装水的纵向弛豫时间。将Mn 2+或/和Gd 3+掺入到该纳米平台中将显著增加r1弛豫率; 2）普鲁士蓝纳米颗粒将被细胞内化，表现出无毒性并且在细胞成像和递送小分子试剂中有效; 3）普鲁士蓝纳米颗粒将是体内有效的T1加权MRI造影剂;和4）将锰（II）或/和钆（III）的顺磁性离子沿着放射性核素Ga-67或Ga-68同时掺入普鲁士蓝纳米颗粒中将产生用于体外和体内MRI-SPECT和MRI-PET成像的有效双峰造影剂。 影响 我们探索PBNPs作为新型T1加权MRI的方法是前所未有的，代表了新一代CA设计的范式转变。从这项拟议的研究中出现的新范式将被证明是革命性的，而不是在一类新的颗粒T1加权MRI CA中增加r1弛豫率的进化，因此将有很大的潜力在MRI诊断成像中产生重大突破，甚至可能完全改变这一领域的研究景观。 公共卫生相关性：普鲁士蓝纳米颗粒作为细胞T1 MRI造影剂我们的目标是开发适用于癌细胞细胞成像的新型普鲁士蓝纳米颗粒T1加权MRI造影剂。这样的试剂将穿透细胞膜，不表现出细胞毒性，并且可以将成像和递送能力整合到用于图像引导的药物递送的单个平台中。从这项研究中开发的设计范例将被证明是变革性的，并有可能显着影响诊断磁共振成像。

DESCRIPTION (provided by applicant): This proposal is aimed at developing Prussian blue nanoparticles (PBNPs) as a new generation of T1-weighted MRI contrast agents (CAs) with high relaxivity, long blood circulation times and ability to penetrate the cell membrane. Prussian blue (PB) is iron(III) hexacyanoferrate(II) with anidealized formula Fe4III[FeII(CN)6]3.nH2O (n=14-16) in which two different iron centers, Fe3+ (high-spin S=5/2) and Fe2+ (low-spin S=0) are bridged by the CN- groups. In the crystal structure of PB, a quarter (25%) of the FeII(CN)6 unit is absent from the crystal lattice, creating a large cavity inside the structure that is filled with water molecules. The missing FeII(CN)6 unit also causes the Fe3+ center to be coordinated by one water molecule and five CN- groups, thus giving rise to an active inner-sphere relaxation mechanism for enhancing the T1 relaxation. Due to the strong ligand-field effect and simultaneous coordination of the CN- group to both the Fe3+ and Fe2+ centers in the extended 3D network, the CN- ligand and the Fe3+/Fe2+ ions are completely locked in their lattice positions and cannot be released from the structure. As a result, PB has the lowest solubility product constant ever measured for any compound (Ksp=10-41). We have found that replacement of some of the Fe3+ ions with Mn2+ or/and Gd3+ ions in the crystal lattice can form the manganese- or gadolinium-incorporated nanoparticles, Mn@PBNPs and Gd@PBNPs with significantly increased r1 relaxivity. Besides, the structural rigidity and reduced tumbling rates of PBNPs in solution, as compared to the small molecular Gd3+-chelates, can contribute to additional T1-weighted MRI contrast enhancement in this new nanoplatform. Our goals are: (i) to explore methods for optimizing the r1 relaxivity by adjusting the nanoparticle size, level of Mn2+- or/and Gd3+-doping, and surface coating with small molecules or polymers; (ii) to systematically investigate the characteristics of cellular uptake and cellular imaging as well as potential for image-guided drug delivery applications; and (iii) to simultaneously incorporate Mn2+ or/and Gd3+ ions along with the radionuclide Ga-67 or Ga-68 for MRI-SPECT and MRI-PET bimodal imaging applications. We will endeavor to test the following four hypotheses: 1) Prussian blue nanoparticles, when properly tailored and engineered, will be effective in reducing the longitudinal relaxation time of protons from bulk water. Incorporation of Mn2+ or/and Gd3+ into this nanoplatform will significantly increase the r1 relaxivity; 2) Prussian blue nanoparticles will be internalized by cells, exhibit no toxicity and be effective in cellular imaging and in delivering small-molecular agents; 3) Prussian blue nanoparticles will be effective T1-weighted MRI contrast agents in vivo; and 4) Simultaneous incorporation of paramagnetic ions of manganese(II) or/and gadolinium(III) along with the radionuclide Ga-67 or Ga-68 into Prussian blue nanoparticles will produce effective bimodal contrast agents for in vitro and in vivo MRI-SPECT and MRI-PET imaging. Impact Our approach to exploring PBNPs as novel T1-weighted MRI is unprecedented and represents a paradigm shift in the design of new-generation CAs. The new paradigm that will emerge from this proposed research will prove to be revolutionary rather than evolutionary for increasing r1 relaxivity in a novel class of particulate T1-weighted MRI CAs, and thus will have high potential to produce a major breakthrough in MRI diagnostic imaging and may even completely change the landscape in this area of research. PUBLIC HEALTH RELEVANCE: Prussian Blue Nanoparticles as Cellular T1 MRI Contrast Agents We aim to develop novel Prussian blue nanoparticulate T1-weighted MRI contrast agents suitable for cellular imaging of cancer cells. Such agents will penetrate the cell membrane, exhibit no cytotoxicity, and can integrate imaging and delivering capabilities into a single platform for image- guided drug delivery. The design paradigm developed from this research will prove to be transformative and have potential to significantly impact the diagnostic MR imaging.