新型花形聚合物前药载体的设计、合成及其肿瘤靶向性能研究

Covalent conjugation of anticancer drug to polymer backbone forms so-called "polymeric prodrug". This provides a powerful means for drug modification and represents a better approach for the construction of polymer therapeutics, motivating increasing attention for improved cancer chemotherapy with reducing off-site toxicity. Dendrimers are considered to be one of the ideal candidates for the construction of polymeric prodrug because of their low dispersity, nanosize, hyper-branched structure, and multiple functional groups on the surface for drug conjugation. But their progress has been hampered by several significant drawbacks. Synthesis of dendrimers is complex and multi-step, resulting low yield, restriction to smaller constructs, batch-to-batch variations, and difficulties in scale-up. Higher generations of dendrimers (>8) are difficult to prepare and drug conjugation efficiency is low due to increasing steric hindrance. In addition, conjugation of hydrophobic drugs to the dendrimer periphery have been reported to induce aggregation between dendrimer molecules resulting in dramatic increases in particle size. The goal of this project is to develop a new class of materials, called "sunflower polymeric prodrug" for tumor-targeted chemotherapy. Sunflower polymers are synthesized by using controlled living radical polymerization from a cyclic macro-initiator template from which "rays" are polymerized that radiate from the cyclic core. Sunflower polymers therefore combine the structural complexity displayed by dendrimers with the relative ease of synthesis of traditional linear polymers. We hypothesize that sunflower polymers can be optimized as drug carriers to provide preferential tumor delivery while maintaining effective tumor penetration. Anti-cancer drug, doxorubicin (DOX) is readily conjugated via pH-cleavable hydrazone linkages to functional monomers in the sunflower core, and targeting ligands, folic acid is decorated to the termini of polymer "rays" to increase uptake in cancer cells. We propose to optimize the synthesis condition, to prepare sunflower polymers of various sizes, to investigate hierarchical self-assembly behaviors of sunflower polymers, to determine optimal composition and size for tumor accumulation and penetration, and to functionalize the polymers for tumor-targeted chemotherapy delivery in vitro and in vivo. Successful completion of this project would lead to a delivery system that could be easily synthesized with controlled size and surface properties, functionalized with a range of targeting ligands, and conjugated to one or even multiple drug entities. This versatility allows the material to be tailored for specific cancer applications. Importantly, these materials will be well-characterized and easily scaled, facilitating eventual manufacturing and clinical translation.

抗癌药物和聚合物通过化学键合得到的聚合物前药载体，在癌症治疗方面显示出高效和低毒副作用的优势，有希望成为癌症治疗的新途径。而树枝形高分子具有的超支化结构和多功能化表面使其成为聚合物前药载体的理想候选材料之一，但其复杂多步的制备过程、高代数树枝形高分子因空间位阻效应引起的低药物键合率、表面修饰疏水药物导致的分子间聚集等缺点大大限制了其应用。本项目拟合成新型花形聚合物前药载体，它以环状聚合物为内核，以辐射状的高分子链段为臂，利用对肿瘤酸性pH敏感的腙键，将抗癌药物键合到其环状内核上，同时将对肿瘤具有良好靶向性的配体键合到其臂的末端，实现前药载体对肿瘤细胞的主动靶向。本项目将优化合成条件，研究花形聚合物多级组装行为，筛选出同时具有长循环半衰期和在肿瘤组织处良好渗透能力的花形聚合物的最优化组成和尺寸，揭示花形聚合物前药载体在体外和体内的抗癌效果，为发展一类新型前药载体奠定技术基础。

为了解决传统超支化聚合物复杂多步的制备工艺等限制其临床应用和转化的重要瓶颈，本项目以发展具有超支化拓扑结构的新型花形（环状刷形）聚合物主要研究目标，（1）分别制备了对肿瘤局部高热（40 oC）和还原微环境敏感的环状刷形聚合物；（2）基于二元嵌段共聚物的环状模板首次合成了含有异相聚合物刷的环状刷形聚合物；（3）合成了具有环状亲水链段的蝌蚪状两亲性嵌段共聚物；（4）设计和合成了一系列具有交替亲、疏水刷的瓶刷形共轭聚合物；（5）通过可逆加成碎片链转移-自缩合乙烯基聚合技术，制备了基于超支化嵌段-无序共聚物的喜树碱（CPT）聚合物前药；（6）基于一种全功能化的链转移单体通过一步法制备了pH和还原双重敏感性的超支化聚合物前药。研究发现（1）对肿瘤微环境敏感的环状刷形聚合物兼具细胞外的稳定性和肿瘤细胞内的有效去稳定化，实现所负载药物在细胞内的快速释放；（2）环状刷形聚合物具有比相同组成的甁刷形聚合物更好的稳定性；（3）由于环状拓扑结构更强的空间位阻效应，含异相聚合物刷的环状刷形聚合物具有比相同组成的瓶刷形聚合物更高的药物负载量，其载药胶束也表现出针对癌细胞更强的体外细胞毒性。同时环状拓扑结构可以增强嵌段共聚物自组装胶束的稳定性；（4）含交替亲、疏水刷的瓶刷形共轭聚合物因其独特的相分离结构，能形成稳定单分子胶束，且其在水相中的荧光量子产率（Φ = 0.55）可以媲美于小分子生色团；（5）全功能化的链转移单体为超支化聚合物前药的便捷精准合成提供了高效的方法，在肿瘤弱酸性和还原条件共同作用下，聚合物前药具有比单一刺激条件下更快的药物释放行为。以上研究结果为超支化聚合物的设计、合成及其作为药物载体应用于化疗提供了新思路和理论指导。除以上项目主要研究内容和结果外，我们围绕智能聚合物载体材料的便捷精准合成与功能化，从材料的合成方法，聚合物的拓扑结构以及材料构效关系三个方面开展了一系列原创性的研究工作。