Supramolecular Nanoparticle-Based PET Probes for Pretargeted Tumor Imaging

描述（由申请人提供）：该 R21 提案的长期目标是开发一种新型基于纳米颗粒 (NP) 的正电子发射断层扫描 (PET) 探针，以实现高性能肿瘤成像。我们建议采用预靶向成像策略，将 NP 成分与其相应的放射性标记记者分离。首先，通过合理的分子设计分别合成一对肿瘤靶向的纳米颗粒成分和具有所需PK的放射性标记报告基因。然后，我们将调节其他实验变量（例如注射时间和剂量）之间的相互作用，以实现最佳 PET 成像结果。成功预靶向成像的先决条件是在体内实现肿瘤靶向纳米粒子和顺序注射的放射性标记报告物的选择性和不可逆偶联。因此，我们利用基于一对反应基序（即反式环辛烯（TCO）和四嗪（Tz））的生物正交共轭化学，其具有快速反应动力学和生物稳定性。 PET 成像的未来进展将涉及设计优先在肿瘤中积累的分子成像探针。除了基于小分子和亲和配体的 PET 成像探针外，纳米颗粒表现出独特的增强渗透性和保留 (EPR) 效应，代表了一类新的 PET 探针，能够被动靶向渗漏脉管系统——这是大多数实体瘤观察到的普遍特征。虽然多种 NP PET 探针已在临床前环境中进行了检查，但进一步提高肿瘤摄取并减少其他器官中的非特异性分布仍然存在挑战。 在我们的分子设计中，TCO 基序共价连接到超分子纳米颗粒 (SNP) 的聚合物构建块上。分子构件的自组装导致 TCO 的封装，产生 TCO 封装的 SNP (TCO?SNP) 作为肿瘤靶向 NP 成分。此外，放射性标记的报道分子由互补的Tz基序和18F-标签组成。在拟议的 PET 成像研究中，首先将 TCO?SNP 施用于动物。当 TCO?SNP 接近其在肿瘤中的最佳积累时，然后注射放射性标记的报告基因。体内生物正交反应瞬间发生，产生高对比度 PET 成像。我们的联合团队有一些初步数据支持这种新型 NP PET 成像探针的可行性。我们将实现以下两个具体目标来完成我们的研究工作：1) 准备和选择具有最佳 PK 的 TCO?SNP 和放射性标记记者，2) 使用成对的 TCO?SNP 和放射性标记记者进行预靶向 PET 成像的体内演示。 该提案汇集了四个研究小组（PI 和 3 位联合研究员）的专业知识，涵盖超分子化学、纳米颗粒、放射化学、分子成像和癌症生物学领域。我们预计，我们提出的研究的成功论证可能会改变当前肿瘤 PET 成像的范式，并为预靶向药物输送开辟新的机会。

DESCRIPTION (provided by applicant): The long-term objective of this R21 proposal is to develop a new class of nanoparticle (NP)-based positron emission tomography (PET) probes that enable high-performance tumor imaging. We propose to adopt a pretargeted imaging strategy to decouple the NP components from their corresponding radiolabeled reporters. First, a pair of tumor-targeting NP component and radiolabeled reporter with desired PKs will be synthesized separately via rational molecular designs. We will then modulate the interplay between other experimental variables such as injection times and dosage in order to achieve optimal PET imaging outcomes. A prerequisite to successful pretargeted imaging is to accomplish selective and irreversible coupling of the tumor- targeting NP and sequentially injected radiolabeled reporter in vivo. We thus exploit the use of a bioorthogonal conjugation chemistry based on a pair of reactive motifs, i.e., trans-cyclooctene (TCO) and tetrazine (Tz), which have fast reaction kinetics and biological stability. Future progress in PET imaging will involve designing molecular imaging probes that preferentially accumulate in tumors. Aside from small molecule and affinity ligand-based PET imaging probes, NPs exhibiting unique enhanced permeability and retention (EPR) effects represent a new category of PET probes capable of passively targeting leaky vasculature - a universal characteristic observed for most solid tumors. While a variety of NP PET probes have been examined in pre-clinical setting, challenges remain to further improve tumor uptake and reduce nonspecific distribution in other organs. In our molecular design, the TCO motif is covalently attached onto a polymer building block of supra-molecular nanoparticle (SNP). Self-assembly of the molecular building blocks leads to encapsulation of TCO to yield TCO-encapsulated SNP (TCO?SNP) as the tumor-targeting NP component. Further, the radiolabeled reporter is composed of the complementary Tz motif and 18F-tag. In the proposed PET imaging study, TCO?SNP is first administered to an animal. When the TCO?SNPs approach their optimal accumulation in tumor, the radiolabeled reporter is then injected. In vivo bio-orthogonal reaction occurs instantaneously, resulting in high-contras PET imaging. Our joint team has some preliminary data supporting the feasibility of this new class of NP PET imaging probes. We will implement the following two Specific Aims to accomplish our research endeavors, 1) Prepare and select TCO?SNPs and radiolabeled reporters with optimal PKs, and 2) In vivo demonstration of pretargeted PET imaging using pairs of TCO?SNPs and radiolabeled reporters. This proposal brings together the expertise of four research groups (PI and 3 co-investigators) covering the fields of supramolecular chemistry, nanoparticle, radiochemistry, molecular imaging and cancer biology. We envision that the successful demonstration of our proposed research could change current paradigm in oncologic PET imaging, and open up new opportunities for pretargeted drug delivery.