可特定解离并高效入胞的高靶向聚合物纳米磁共振造影剂

Magnetic Resonance Imaging (MRI) is a complementary modality for molecular imaging as it provides excellent anatomical details of soft tissues with high spatial resolution. Although various paramagnetic compounds have been evaluated for application within MRI, Gd(III) chelates continue to be the most wildly used T1-weighted contrast agents. Compare to traditional small molecular Gd(III) chelates, polymer nano-contrast agents have demonstrated optimal pharmokinetics and circulation half-life, increased tolerance to enzymatic degradation which improve their therapeutic value. . Activatable cell penetrating peptides (ACPPs) are novel in vivo targeting agents comprised of a polycationic cell penetrating peptides (CPPs) connected via a protease (eg. matrix metalloproteases (MMPs)) cleavable linker to a neutralizing polyanions. ACPPs represent a novel strategy for targeting MR imaging contrast agents for tumor including many traditional xenograft tumor models from different cancer sites, where the gelatinases MMPs are upregulated. In the development of ACPPs conjugated polymer nano-contrast agents, high Mws or large sizes of the deliveries may offer optimal pharmokinetics and circulation half-life, but this will sacrifice the efficiency of cell penetration. There is an equilibrium need to be balanced between the penetration efficiency (preferring low Mw carriers) and long circulation time (preferring big sized carriers).. Herein, in order to address the above points dynamically and develop high efficient MRI nano-contrast agents which can penetrate into tumor cells with higher efficiency (acting as small molecules) while retain the advantages of optimal pharmokinetics and circulation half-life (acting as relative big nano-materials), together with potential abilities of combining multiple modalities on one probe and simultaneous application as drug delivery systems, we propose to develop novel Gd labeled (in the core), protease cleavable, pH-responsive super-lightly-crosslinked, uni-molecular branched copolymer nano-contrast agent conjugated with ACPPs on the corona. On circulating inside the blood , the nano-contrast agents are stable compacted structures (20-60nm) composed of many low Mw linear block copolymer chains, which allow long circulation half-life; Once approaching the tumor cell, the super-lightly-crosslinked nano-particles core will be cleaved very fast by MMPs after acid-induced expansion process. This could result in the formation of low Mw copolymers conjugated with Gd chelates, which can easily penetrate into tumor cell with aid of the outer activated ACPPs, and lead to increasing the relaxivity of contrast agent. This nano-contrast agents will integral advantages of ACPPs, polymer nano-delivery, and low Mw delivery materials together. The successful completion of this project would make a great impact on a new generation of high efficient tumor-targeting cell-penetration imaging for therapies in preclinical and clinical study.

本项目提出构建一种联接可激活细胞穿透肽（ACPPs）的可特定快速解离并能高效入胞的功能性聚合物纳米磁共振（MRI）造影剂。采用活性聚合合成分子量可控的超轻度交联共聚物，再以直接合成方法制备纳米颗粒。结构上为单分子型超支化纳米，核为螯标定的超轻度交联酸碱敏感聚合物, 交联剂主体由特殊多肽构成，外层联接ACPPs，其尺度可控，联接的官能团数目可调。解离前是稳定纳米，通过控制纳米尺寸、核中钆及ACPPs含量等以优化血液半衰期及MRI信号对比度；靠近癌细胞时，纳米核在酸诱导下从疏水转为亲水，处于充分伸张状态，多肽交联剂迅速被基质金属蛋白酶解离成联钆的低分子量线形聚合物，并被外层激活的ACPPs协同快速入胞。调节交联剂的用量及分子量控制涨大行为，释放足够空间以利于酶的有效到达和切断。可同期引入他种诊断剂，实施胞内多种影像联用。项目的成功实施，会对新型高效入胞聚合物纳米造影剂的构建提供新的方向和原理。

本项目合成多种不同尺寸、功能的聚合物纳米材料，用来构建如磁共振（MRI）、荧光等多模态生物影像的纳米探针。同时在此基础上，针对不同的聚合物纳米材料的合成，结构及尺度的调整，功能的引入，以及多领域的应用等方面进行了细致的工作和大胆的探索，拓展了功能性聚合物纳米材料的应用领域。主要进行了以下几项工作：基于超单分子支化聚合物，构建一种联接可激活细胞穿透肽（ACPPs）的可特定快速解离并能高效入胞的功能性聚合物纳米磁共振（MRI）造影剂；构建了基于线性功能聚合物的主动靶向多模态聚合物纳米磁共振造影剂；.进行了环境刺激敏感的新型单分子结构超支化聚合物纳米的合成，及其在药物装载方面的应用研究；进行了新型单分子结构超支化聚合物纳米在协同抗菌领域的应用研究；制备了线性功能聚合物/载银石墨烯复合水凝胶材料，进行了相关抗菌方面的研究等。在相关研究工作中，所合成的纳米材料结构新颖，尺寸可控，可引入多种靶向多肽及官能团。所制备的生物影像探针均具有靶向效果好，能入胞进行成像，成像对比度高，毒性低，生物安全性高等优势。所制备的纳米载药体系具有装载量高，水溶性好，稳定性高，释药可控等特点。所延伸的靶向抗菌体系具有细菌靶向性高，杀菌率高，用量少，不易产生耐药性等优点。制备了具有抗菌和促进伤口愈合功能的热诱导不可逆复合水凝胶PEP-AG，与传统的温度响应型水凝胶可逆的凝胶-溶胶转变性相比，PEP-AG能够快速地在皮肤表面形成凝胶且低温不会变成溶胶；PEP-AG兼具有良好的抗菌性能，能够促进伤口愈合。本项目实施期间，共发表9篇SCI论文，另有3篇在审稿或准备中。申请国家发明专利8项，均已公开实审。共培养5名博士生（含中英联合培养1名），3名硕士生。

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