Surface-functionalized SPIONs for pH-sensitive MRI contrast in physiologically-re

描述（由申请人提供）：组织pH值的局部变化通常与许多病理状况有关，包括损伤、炎症、缺血以及各种癌症。虽然取得了进展，但创造能够感知pH值但同时满足所有期望特性的磁共振成像（MRI）试剂-包括高灵敏度，低最小剂量，高生物相容性和浓度无关的pH反应-仍然是一个持续的挑战。基于作为原始AREA R15支持的一部分所做的工作，本更新申请中提出的工作的总体目标是开发一类基于树突功能化超顺磁性氧化铁纳米颗粒（“树突- SPIONs”）的新型MRI造影剂，该造影剂将在生理相关的制度下提供高度敏感的pH响应，并表征这些pH敏感响应的性质。我们认为，大多数pH响应是由树突-SPION的瞬态可逆聚集引起的，这是由SPION表面电荷密度和溶液离子强度之间的相互作用所调节的。相应地，该提案有两个具体目标：(1)合成和表征新型树突功能化SPIONs，设计用于在生理相关环境（pH值在6-8之间变化）中产生强烈的pH敏感MR反应；(2)在化学均质和现实细胞环境中对这些新型树突-旋子进行基础研究，以更深入地了解这种ph敏感反应的起源。为了支持(1)，将合成各种新的树突-SPION（通过多步骤有机合成和通过配体交换方法与纳米晶体SPION核心的共价树突连接），其树突功能被设计为在~6-8之间的给定位置提供峰值pH灵敏度；树突世代的变化应该允许对给定树突- spion的pH值变化的幅度和位置进行微调。MR测量水溶液1H自旋弛豫率（R1, R2, R2*）作为SPION载荷的函数，将允许在各种条件下（包括pH，离子强度和磁场）对给定树突-SPION进行系统的弛豫测量和表征。为了支持(2)，将研究给定MR响应与SPION物理行为之间的相关性。有效R2值的回波时间相关CPMG MR测量将提供在给定条件下存在的SPION聚类程度的指示；这些结果将在理论模型（正在开发中）的背景下进行解释，并通过透射电子显微镜（TEM）和动态光散射（DLS）获得补充结果。此外，在支持(2)中获得的对ph敏感响应的更好理解将自然地被用作设计和合成支持(1)的下一代ph传感SPIONs的反馈。最后，涉及细胞培养的实验将允许直接比较在多室、组织样环境中获得的结果与在化学均匀环境中获得的结果。

DESCRIPTION (provided by applicant): Local variations in tissue pH are often associated with many pathological conditions-including injury, inflammation, and ischemia, as well as a variety of cancers. While progress has been made, the creation of magnetic resonance imaging (MRI) agents capable of sensing pH but that also meet all of the desired traits- including high sensitivity, low minimum dose, high biological compatibility, and concentration-independent pH response-remains a persistent challenge. Based upon the work performed as part of the original AREA R15 support, the overall goal of the work proposed in this renewal application is to develop a novel class of MRI contrast agents based on dendron-functionalized super paramagnetic iron oxide nanoparticles ('dendron- SPIONs') that will provide highly sensitive pH responses in physiologically-relevant regimes, and to characterize the nature of those pH-sensitive responses. It is believed that most of the pH response results from transient, reversible clustering of the dendron-SPIONs modulated by an interplay between the SPION surface charge density and the solution ionic strength. Correspondingly, the Proposal has two Specific Aims: (1) to synthesize and characterize novel dendron-functionalized SPIONs designed to give strong pH-sensitive MR responses in physiologically relevant regimes (with varying values between pH~6-8); and (2) to perform fundamental studies of these novel dendron-SPIONs-in both chemically homogeneous and realistic cellular environments-to obtain a greater understanding of the origins of such pH-sensitive responses. In support of (1), a variety of new dendron-SPIONs will be synthesized (via multi-step organic synthesis and covalent dendron linkage to the nanocrystallite SPION cores via ligand-exchange methods) whose dendron functionalities with be designed to provide peak pH sensitivity at a given location between ~6-8; variation of the dendron generation should allow fine tuning of the magnitude and position of the pH inflection for a given dendron-SPION. MR measurements of aqueous 1H spin relaxation rates (R1, R2, R2*) as functions of SPION loading will allow systematic relaxivity measurement and characterization for a given dendron-SPION under various conditions (including pH, ionic strength, and magnetic field). In support of (2), the correlation between a given MR response and the physical SPION behavior will be studied. Echo-time dependent CPMG MR measurements of effective R2 values will provide an indication of the degree of SPION clustering present under a given set of conditions; these results will be interpreted in the context of a theoretical model (under development) and complimentary results obtained by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Furthermore, greater understanding of the pH-sensitive responses obtained in support of (2) will naturally be used as feedback for design and synthesis of next-generation pH-sensing SPIONs created in support of (1). Finally, experiments involving cell cultures will allow direct comparison of results obtained in multi-compartment, tissue-like environments with those obtained in chemically homogeneous environments. PUBLIC HEALTH RELEVANCE: Local variations in tissue pH are often associated with a range of diseases, including many cancers. Once successful, the proposed work should provide new insight into the design and mechanism-of-action of a novel class of pH-sensing agents, and furthermore, should lead directly to the development of novel MRI contrast agents that would allow the detailed mapping of pH gradients in the body for the improved visualization, diagnosis, and treatment of various malignancies (impact for other clinical situations where pH variance may be present is also envisioned). For example, it is anticipated that positive therapeutic measures in the treatment of cancers will manifest themselves first as changes in local metabolism, since the pH variance associated with such diseases is caused by problems with local metabolism. Thus, the ability to probe tissue pH in response to therapy promises to provide more rapid feedback than simple 'caliper-based' measurements of tumor dimensions (which can take much longer to manifest).