肿瘤微环境敏感的靶向给药系统的作用机制与分子设计

Malignant tumor is a killer threatening human health. Chemotherapy plays an important role in the treatment of tumor, but the actual curative effect is not very satisfactory. One of the important reasons is the lack of selectivity for in vivo distribution of chemotherapy drugs on tumor tissue. The tumor cell targeting efficiency based on various passive and active targeting strategies is not satisfactory. Therefore, how to improve the selectivity of the drugs on tumor cells, to achieve high efficient intracellular drug delivery, to gain high drug concentration in tumor cells, is the long-term important issue for tumor treatment. At present, studies on the targeting drug-delivery systems based on tumor microenvironment sensitivity are mainly the experiments on the drug targeting effect. There are very few works involving mechanism, interaction and molecular simulations. Molecular simulation is the connection bridge across micro and macro, and is a strong supplement to the experiments. Its advantage is it can provide much microscopic information which is difficult to obtain in practical experiments. This project adopts molecular simulation method to study the interactions among activatable cell-penetrating peptides, matrix metalloproteinases and cell membrane, understanding the molecular mechanism of tumor-targeted drug delivery and the mechanism of enzyme cleavage reaction, revealing the relationship between the structures of targeting carrier and improving the drug targeting, providing new ideas for optimization and design of tumor-targeted drug delivery systems.

恶性肿瘤是威胁人类健康的头号杀手，化疗在肿瘤治疗中具有重要作用，但实际疗效不甚理想。重要原因之一是化疗药物在体内的分布对肿瘤组织缺乏选择性，当前各种被动和主动靶向策略的肿瘤细胞内靶向效率并不理想。因此，如何提高药物对肿瘤细胞的选择性，实现胞内高效药物递送，获得肿瘤细胞内较高的药物浓度，长期以来都是肿瘤治疗面临的重大科学问题。目前，基于肿瘤微环境敏感的靶向给药系统的研究，主要是药物靶向性效果实验方面的工作，涉及机理、相互作用本质和分子模拟方面的研究几乎没有。分子模拟是联系微观与宏观之间的桥梁，是对实验的有力补充，其优势是可以为我们提供许多实际实验难以获得的微观信息。本项目采用分子模拟的方法研究可活化细胞穿膜肽、基质金属蛋白酶及细胞膜之间的相互作用，深入了解肿瘤给药靶向性的分子作用机制及其酶切反应机理，揭示靶向载体结构与提高药物靶向性之间的关系，为肿瘤靶向给药系统的优化设计提供新的思路。

化疗是目前治疗癌症的主要方法之一，但如何将药物高效地递送到肿瘤组织并进入肿瘤细胞仍未得到很好解决。基于MMP-2/9在肿瘤细胞高表达，因此设计可被MMP-2/9识别、激活、利用细胞穿膜肽（CPP）作为胞内递送载体的可激活细胞穿膜肽（ACPP）靶向递送系统对肿瘤成像与治疗具有重要的科学意义与实际价值。本项目利用分子动力学模拟、伞状取样、QM/MM等计算方法，并辅以圆二色谱表征研究了ACPP的结构特征与构效关系，探究了MMP-2/9识别并水解底物肽的分子机理与水解产物的释放机制，探讨了CPP跨膜过程的关键因素和内含的定量关系。结果表明，底物肽结合于MMP-2/9的催化凹槽，底物肽P1和P1’位点处的残基对结合构型至关重要。但P1位点残基所在位置而非其种类使得底物肽与蛋白间有很强的相互作用，P1’位点通常为Leu或Ile，可与蛋白S1’疏水孔形成“锁-钥识别”。MMP-2/9水解底物肽的机理是水介导的亲核进攻，反应第一步是水解过程的决速步骤。P1位点残基种类的改变会影响水解速率，但水解反应仍可以发生。在底物肽水解产物的释放过程中，连接CPP的N-产物解离常数为268nM，远大于C-产物的0.00335nM。因此比起C-产物，N-产物更容易离开MMP-9，这更有利于其下一步携带药物进入靶向细胞。在探究CPP的跨膜机制中，发现胍鎓离子-PO4之间形成的盐桥是富含精氨酸的CPP跨膜形成水孔过程的主要驱动力，CPP残基侧链的氢原子的偏电荷分布、磷脂双层的负电荷密度、疏水屏障等均会影响CPP的跨膜过程。本项目从分子水平上阐明了MMP的构效关系、选择性识别与水解机制，将对基于MMP的新药开发大有裨益。对CPP跨膜传递过程的研究将有助于设计下一代胞内递送载体，提高药物递送效率，为胞内递送系统的发展打下理论基础。