双靶双模态载药分子探针血栓显像与治疗研究

The target selection and the specificity, stability of molecular probes combining with target tissues is the key to achieve efficient molecular imaging. Constructing a molecular probe that responds to the tissue microenvironment significantly improves the specificity of the molecular probe for target tissue, and in combination with the ligand-receptor element, a double-modified, targeted molecular probe can be obtained to increase the contact area between the molecular probe surface and the target tissue, thus solving the problem of molecular probe targeting specificity and binding stability is not strong. In this study, we want to design a thrombin-responsive molecular probe that can be enzymatically digested by thrombin after acute thrombosis to activate the probe binding with the thrombus. In addition, such molecular probes are also linked to fibrin-specific ligands to further enhance their ability to target and bind to thrombus. With double modifications that enable the molecular probes to bind specifically, stably and firmly to the thrombus. At the same time, ultrasound and photoacoustic dual-mode molecular imaging are used to complement each other for the early detection of acute thrombosis. The above-mentioned molecular probes can not only be taken around the thrombus or surface, but also can be absorbed into the deep side of the thrombus mass. Therefore, the thrombolytic drug can be entrapped in the molecular probe for targeted delivery to the thrombus, and the delivery process can be visualized under US and PA imaging. And then using ultrasonic irradiation at the local can promote release of drugs to maximize the effect of thrombolysis and reduce the risk of bleeding, which has potential clinical applications in the future.

靶点选择以及分子探针与靶组织的特异性、稳定结合是实现高效分子成像的关键。构建对组织微环境可响应的分子探针明显提高了分子探针靶向组织的特异性，再结合配体—受体元素可获得双重修饰靶向作用的分子探针，以增加分子探针表面与靶组织接触面积，从而解决分子探针靶向性及结合力不强的问题。本课题针对急性血栓形成后丰富的凝血酶环境设计一种凝血酶响应的分子探针，利用凝血酶酶解分子探针使其激活后靶向结合血栓。另外分子探针还连接纤维蛋白特异性配体，进一步加强靶向结合血栓能力，双重修饰使分子探针特异、稳定、牢固地结合于血栓。同时融合超声及光声双模态分子显像互为补充，有助于急性血栓的早期检出。上述分子探针不仅可被血栓周边或表面摄取，而且可吸收到血栓团块深面，因此可将溶栓药物包载在分子探针中靶向递送至血栓局部，视化递送过程，再于体表加以超声辐照促进药物在局部释放，发挥最大溶栓效应，降低出血风险，具有潜在的临床应用前景。

深静脉血栓虽然通常不致命，但如果缺乏及时诊断和治疗，可能会演变形成血栓后遗症，长时间影响生活质量。而急性血栓由于血管壁有炎症，血栓与管壁黏附不紧，极易发生松弛脱落，进一步引起肺栓塞。因此，临床怀疑急性静脉血栓应早期检查，早期诊断并早期治疗，避免发生严重并发症危及生命。超声是血管血栓的首选和主要检查方法，但当血栓较小或短期内形成的新鲜血栓仅表现为无回声时，极易漏诊，随之也丧失了最佳溶栓时机。本研究针对急性静脉血栓富含凝血酶的微环境特点，通过构建一种安全的基于凝血酶响应、具有液气相变功能的双重靶向血栓的纳米脂质体，用于光声/超声双模态分子显像早期检测急性血栓，并实现实时影像引导下超声溶栓。该纳米脂质体具有高度的生物相容性，被急性血栓局部凝血酶特异性裂解后可双重靶向血栓成分中的红细胞和纤维蛋白，并增强纳米脂质体穿透能力，解决血栓分子探针靶向性及结合力不强的问题。同时LIFU触发脂质体相变后通过增强血栓光声/超声分子显像可检测到常规超声未发现的急性血栓，超声及光声信号强度分别增强了30倍和8倍，提高了对血栓诊断的敏感性。在影像视化下应用LIFU辐照局部血栓，激活纳米脂质体，由声致相变产生的一系列物理爆破作用，实现对静脉血栓的精准溶栓，光声及超声成像显示随时间推移残余血栓面积逐渐减小，直至血栓完全溶解消失，无不良反应。这种非药物性的溶栓策略，规避了全身性用药而引发的一系列严重出血风险，并集可视化诊断为一体，为溶栓治疗提供了一个新的思路。