低氧靶向控释磁性聚合物药物载体的构建及作用机制研究

Nanoparticles-based drug carrier systems focusing on targeted delivery and stimuli-responsive controlled release for tumor therapy have attracted a great of attentions; however, the triggers that are utilized to affect targeting and release behaviors of carrier systems are limited to tumor-associated molecules, tumor acidic microenvironment, and external physical stimuli despite of intensive research efforts..It is well-known that hypoxia is a characteristic feature of almost all solid tumors, and therefore, there is an urgent need to development novel carrier systems that target hypoxia. In this work, a multifunctional magnetic polymer carrier system is fabricated, consisting of magnetic nanoparticles (magnetic orientation induces the accumulation of carrier in the region of hypoxic tumor) as cores, hypoxia-targeted (hypoxic cells aggressively uptake positively charged carrier) and hypoxia-responsive (the polymer is transformed to release drug inside hypoxic cells) polymer as coating layer, and loaded drug. Firstly, the controllable synthesis of multifunctional magnetic polymer carrier system is achieved, and its chemical and physical properties are characterized. Secondly，the effects of oxygen microenvironment on targeted uptake of carrier by cells and controlled release behavior of carrier inside cells will be systematically investigated. Thirdly, in vivo biological effects of carrier system as well as its therapeutic effectiveness on hypoxic tumor are determined. Generally, the purpose of this work is to bulid a smart carrier system for hypoxic tumor therapy, and to provide new ideas and new approaches for the development of tumor hypoxic microenvironment targeted and/or responsive theranostics.

靶向和控释是抗肿瘤纳米载药体系研究中两个重要的方向。目前，纳米载药体系靶向和控释功能主要是通过肿瘤细胞相关的生物分子、肿瘤酸性微环境或者外部因素的作用来实现。根据实体瘤普通存在低氧现象这一特征，本课题首次构建以低氧为单一作用靶点，靶向和控释一体的新型纳米载药体系。该载药体系是具有低氧靶向功能（低氧肿瘤细胞选择性吞噬正电荷纳米载体）、低氧响应功能（在低氧细胞内聚合物构型发生变化从而释放药物）的聚合物同时负载磁性纳米颗粒（磁定位诱导载药体系在低氧肿瘤区域富集）和药物形成的磁性聚合物颗粒。实现多功能磁性聚合物载药体系的可控制备；着重考察该载药体系与低氧肿瘤细胞的靶向作用、在细胞内低氧刺激下的药物释放行为，明确氧环境对载体靶向、药物控释行为的影响；在活体水平系统地评价该载药体系生物学效应以及对低氧肿瘤的治疗效果，为发展以低氧为靶点的肿瘤诊疗手段提供新思路和新方法。

靶向和控释是纳米药物载体研究中两个重要的方向。目前，纳米载药体系的靶向和控释功能主要通过肿瘤微环境相关的一些生物分子或生物信号来实现，如一些过表达的受体或酶、氧化还原能以及酸性pH等。低氧与许多疾病息息相关，同时也是肿瘤微环境的显著特征之一，它存在于肿瘤发生和发展的各个阶段，却很少出现在正常组织中。因此，本课题的目标是发展以低氧为作用靶点的低氧响应纳米载药体系并用于肿瘤以及其它低氧相关疾病的治疗。经过三年的研究，完成了课题的预定目标。第一，将低氧响应分子2-硝基咪唑衍生化之后插入脂质体磷脂双分子层中，得到了低氧响应脂质药物载体并负载药物，用于肿瘤治疗。结果表明：（1）该载体与传统脂质体一样，都具有较好的稳定性以及较高的药物包封率；（2）该载体带有正电荷，在低氧下能够被更多的细胞吞噬，具有低氧靶向性；（3）该载体具有较高的低氧响应敏感性，不但能响应模拟的低氧环境，甚至能响应单个以及几个低氧细胞；（4）该载体能够在体内响应肿瘤组织，能够比传统脂质体更快地释放药物，因而有更好的治疗效果。第二，以另一种低氧响应分子偶氮苯类化合物为基底合成低氧响应聚合物，制备得到不同的低氧响应聚合物药物载体，分别用于糖尿病和肿瘤的治疗。结果表明：（1）由于偶氮苯类化合物中偶氮键在低氧下会断裂，因此相比于基于2-硝基咪唑的载体，此类载体的低氧响应敏感性更高，能够更快地释放药物；（2）此类载体生物安全性好；（3）在糖尿病动物模型中，通过葡萄糖氧化酶与血液中高浓度的血糖反应形成低氧的条件，该载体能够快速地释放胰岛素，从而降低体内血糖浓度，并更长时间地将血糖浓度稳定在一个较低的水平。本课题的结果表明，低氧响应纳米药物载体能够快速响应低氧，因而在肿瘤以及其它低氧相关疾病的治疗中有广阔的应用前景。