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

描述(申请人提供)：组织的局部pH变化通常与许多病理情况有关--包括损伤、炎症和缺血，以及各种癌症。虽然已经取得了进展，但创建能够检测pH但也满足所有所需特性的磁共振成像(MRI)试剂--包括高灵敏度、低剂量、高生物兼容性和不依赖浓度的pH响应--仍然是一个长期的挑战。基于作为原始区域R15支持的一部分所做的工作，在此更新申请中提出的工作的总体目标是开发一种新型的基于树枝状功能化的超顺磁性氧化铁纳米颗粒(‘树枝状-SPIONS’)的MRI造影剂，它将在生理相关的区域中提供高度敏感的pH响应，并表征这些pH敏感响应的性质。据认为，大多数pH响应是由Spion表面电荷密度和溶液离子强度之间的相互作用调制的树枝状SPION的瞬时可逆聚集造成的。相应地，该提案有两个具体的目标：(1)合成和表征新型树状分子功能化的SPION，旨在在生理相关的区域(在pH~6-8之间变化)产生强烈的pH敏感MR响应；(2)在化学均相和现实的细胞环境中对这些新型树枝状SPION进行基础研究，以更好地了解这种pH敏感反应的起源。为了支持(1)，将合成各种新的树枝状SPION(通过多步有机合成和通过配体交换方法与纳米晶Spion核的共价树枝状连接)，其树枝状功能被设计为在~6-8之间的给定位置提供峰值pH敏感性；树枝状物生成的变化应该允许对给定树枝状Spion的pH拐点的大小和位置进行微调。对水中1H自旋松弛速率(r1，r2，r2*)随Spion负载的变化进行MR测量，可以系统地测量和表征给定树枝状Spion在不同条件(包括pH，离子强度和磁场)下的弛豫度。为了支持(2)，我们将研究给定的MR响应和物理Spion行为之间的相关性。取决于回声时间的有效R2值的CPMG MR测量将提供在给定条件下存在的Spion聚集程度的指示；这些结果将在理论模型(正在开发中)的背景下进行解释，以及通过透射电子显微镜(TEM)和动态光散射(DLS)获得的补充结果。此外，对支持(2)的pH敏感反应的更多了解自然将被用作设计和合成为支持(1)而创建的下一代pH敏感SPION的反馈。最后，涉及细胞培养的实验将允许直接比较在多隔室、类似组织的环境中获得的结果与在化学均质环境中获得的结果。 公共卫生相关性：组织pH值的局部变化通常与一系列疾病有关，包括许多癌症。一旦成功，这项拟议的工作将为一类新型pH感应剂的设计和作用机制提供新的见解，并进一步直接导致新型磁共振造影剂的开发，这种造影剂将允许详细绘制体内的pH梯度图，以改进各种恶性肿瘤的可视化、诊断和治疗(也可以预见对其他可能存在pH变化的临床情况的影响)。例如，预计癌症治疗中的积极治疗措施将首先表现为局部新陈代谢的变化，因为与此类疾病相关的pH值变化是由局部新陈代谢问题引起的。因此，与简单的基于卡尺的肿瘤尺寸测量(可能需要更长的时间才能显现)相比，探测组织酸碱度对治疗的反应有望提供更快的反馈。

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).