Huang Guofeng, Zhou Zhongmin, Srinivasan Rekha, Penn Marc S, Kottke-Marchant Kandice, Marchant Roger E, Gupta Anirban S
Department of Biomedical Engineering, Case Western Reserve University, Wickenden Building, 10900 Euclid Avenue, Cleveland, OH 44106-7207, USA.
Biomaterials. 2008 Apr;29(11):1676-85. doi: 10.1016/j.biomaterials.2007.12.015. Epub 2008 Jan 14.
Platelet adhesion, activation and fibrinogen-mediated aggregation are primary events in vascular thrombosis and occlusion. An injectable delivery system that can carry thrombolytics selectively to the sites of active platelet aggregation has immense potential in minimally invasive targeted therapy of vascular occlusion. To this end we are studying liposomes surface-modified by fibrinogen-mimetic RGD motifs that can selectively target and bind integrin GPIIb-IIIa on activated platelets. Here we report liposome surface-modification with a conformationally constrained high affinity cyclic RGD motif to modulate the GPIIb-IIIa-binding capability of the liposomes. Such affinity enhancement is important for practical in vivo applications to compete with native fibrinogen towards binding GPIIb-IIIa. The platelet-binding of RGD-modified liposomes was studied by fluorescence and scanning electron microscopy, and flow cytometry, in vitro. Binding of RGD-modified liposomes was also tested in vivo in a rat carotid injury model and analyzed ex vivo by fluorescence microscopy. The results from all experiments show that cyclic RGD-liposomes bind activated platelets significantly higher compared to linear RGD-liposomes. Hence, the results establish the feasibility of modulating the platelet-targeting and binding ability of vascularly targeted liposomes by manipulating the affinity of surface-modifying ligands.
血小板黏附、激活以及纤维蛋白原介导的聚集是血管血栓形成和阻塞中的主要事件。一种能够将溶栓剂选择性地输送到活跃血小板聚集部位的可注射给药系统在血管阻塞的微创靶向治疗中具有巨大潜力。为此，我们正在研究用模拟纤维蛋白原的RGD基序进行表面修饰的脂质体，该基序能够选择性地靶向并结合活化血小板上的整合素GPIIb-IIIa。在此，我们报道用构象受限的高亲和力环状RGD基序对脂质体进行表面修饰，以调节脂质体与GPIIb-IIIa的结合能力。这种亲和力的增强对于实际体内应用很重要，以便与天然纤维蛋白原竞争结合GPIIb-IIIa。通过荧光、扫描电子显微镜和流式细胞术在体外研究了RGD修饰脂质体与血小板的结合。还在大鼠颈动脉损伤模型中对RGD修饰脂质体的体内结合进行了测试，并通过荧光显微镜进行离体分析。所有实验结果表明，与线性RGD脂质体相比，环状RGD脂质体与活化血小板的结合显著更高。因此，这些结果证实了通过操纵表面修饰配体的亲和力来调节血管靶向脂质体的血小板靶向和结合能力的可行性。
