具有嵌段接面交联结构的多功能药物载体研究

Both core-crosslinked and shell-crosslinked micelles have disadvantages, such as low drug loading content and poor mobility, respectively. However, according to spatial structures of micelles, nexus-crosslinking, which happens between hydrophobic and hydrophilic blocks, should demonstrate overwhelming performance compared to the two crosslinking structures mentioned above. Aiming to design delivery carrier for a kind of typical anti-cancer drug, Doxorubicin, this project will focus on synthesis and analysis of aimed product, which presents combined multifunctional characteristics, including cancer cell targeting capability, charge-reversal capability, stimuli-responsibility as well as nexus-crosslinking structure. Nexus-crosslinking structure will be conducted resulting in high drug load and good mobility; blocks consisting of galactose moieties, which have been confirmed to target hepatocytese onto liver surface, will be introduced to present targeting capability; blocks grafted with dimethylmaleic acid can exhibit charge-conversion at tumor （pH≈6.8), which will enhance cellular uptake of delivery to solid tumors, via an adsorptive endocytotic pathway due to the electrostatic interaction between delivery and cells; reduction cleavable crosslinker will be used to lead to controlled release. Preparation and study of characteristics of such new delivery system will provide significant information and reference for engineering novel polymer-based drug delivery vectors.

作为高分子药物载体的核交联及壳交联胶束分别具有药物承载率低及传送性能不佳等缺点。根据胶束的空间结构特性，对介于亲水段及疏水段间的"嵌段接面"进行交联，由于交联部位处于两亲性嵌段的中间部位，则可以改善核交联及壳交联结构的缺点，表现出更加优异的载体性能。本研究针对体内肿瘤的特点采用"嵌段接面"交联结构设计一种新型具有集成功能的药物载体：含有半乳糖基团的嵌段与在肿瘤环境（pH≈6.8）发生电荷反转的"二甲基马来酸修饰的丙烯酰胺"嵌段共同作为胶束外壳，使其成为可被肝癌细胞高效吸收的靶向药物载体；同时具有氧化还原开关响应性的可降解交联剂可以实现药物在细胞内的可控释放。本研究采用阿霉素作为靶药物，研究兼具靶向性、pH响应-电荷反转性、氧化还原开关响应性的新型药物载体，及其在不同"嵌段接面"结构条件下对载药量和药物可控性释放的影响规律，为高分子药物载体结构设计与性能的研究开拓新的方向。

药物载体因其能够改变药物进入体内的方式、分布及控制药物释放而引起了研究者的广泛关注。而高分子聚合物由于其易于设计、制备、改性而成为最常用的药物缓释、控释及靶向运输的材料之一。近年来，具有刺激响应性的“智能”药物载体成为靶向运输及可控释放研究领域的热点。.本课题设计并制备了一种具有刺激响应性的多功能纳米胶束作为抗癌药物阿霉素（DOX）的触发释放载体。结合开环聚合和RAFT聚合方法，制备了PCL36–P [PEGMEA12-(APMAa5-DMMA5)]两亲嵌段聚合物，该聚合物侧链含有对酸敏感的酰胺键，端基为带负电的羧基。当聚合物胶束所处环境pH为6.5时，酰胺键发生水解断裂，侧链端基变为质子化的胺基，聚合物胶束电性由负电转为正电。激光共聚焦显微镜(CLSM)测试结果显示，用不同pH的PCL36–P [PEGMEA12-(APMAa5-DMMA5)]/DOX载药纳米粒溶液培养HepG2细胞， pH6.5时细胞中DOX含量高于pH7.4时细胞中DOX含量；为得到性质更为稳定的药物载体，选用两端带有双键的胱胺化合物作为交联剂将聚合物PCL36–P [PEGMEA12-(APMAa5-DMMA5)]自组装体进行亲水、疏水嵌段界面交联，以保证载药纳米粒在循环过程中的稳定。对DOX的承载实验结果显示，经过嵌段界面交联的聚合物胶束对DOX的承载量和包封率均大于未交联胶束；模拟细胞还原环境的降解实验显示，在一定浓度的谷胱甘肽存在时，交联胶束能够发生降解，且其载药纳米粒子能在较短的时间内实现包载药物的释放，药物释放效率较未交联胶束载药纳米粒子有了明显的提高；体外细胞毒性测试表明，用未交联胶束、交联胶束及其降解产物培养L929细胞，24小时和48小时后细胞的存活率较高且无明显差别。以上结果表明，该聚合物自组装体材料具有良好的生物兼容性、电荷翻转性能、可降解性及药物触发释放性能，作为抗癌药物载体有其广阔的应用前景。