Cell-Selective Liposomal Drug Delivery In Restenosis

临床上，接受经皮冠状动脉腔内成形术的患者中有30%以上会发生明显的再狭窄，尽管通过药物干预和使用表面修饰的冠状动脉内支架来抑制新生内膜的形成，但再狭窄的发生率仍然很高。这项拟议研究的总体目标是生物工程新的脂质体药物输送系统，该系统选择性地结合或靶向慢性血管损伤和发展中的再狭窄病变部位表达的细胞表面分子。我们建议研究脂质体的表面修饰：(I)通过利用病变中存在的激活细胞的细胞表面表型的差异，将包裹的药物直接靶向血管损伤部位；以及(Ii)抑制蛋白质在脂质体上的吸附，从而增加循环半衰期。所提出的靶向策略是基于一个中心假设，即刺激的血管细胞的促凝剂和炎症表型包含独特的细胞表面受体，该受体将结合呈现在脂质体表面的内源性配体的仿生结构。通过利用这些配体将长循环脂质体定位到病变部位，局部药物浓度可以提高到治疗水平。具体地说，我们将专注于针对血栓形成和再狭窄中表达的三种细胞表面分子的靶向配体的设计和开发：(1)与活化血小板上的整合素GPIIb-IIIa结合的高亲和力RGD肽；(2)与刺激内皮细胞和平滑肌细胞结合组织因子的第VII因子衍生肽；以及(3)与EC和血小板上的E-和/或P-选择素结合的高亲和力sialyl Lewis x和sialyl Lewis a衍生寡糖。我们将研究配体结构如何调节结合亲和力，并确定这些配体如何影响体外靶细胞对脂质体的结合和摄取，以及在体内球囊诱导的血管损伤大鼠模型中。将研究旨在延长循环寿命的糖脂的物理性质，以确定表面水化和双层稳定性在改变脂质体清除率中的作用。我们将以雷帕霉素和依诺肝素为模型药物，在体内研究长循环、靶向脂质体影响新生内膜形成的能力。通过解决靶向亲和力和特异性，以及延长循环寿命，可以实现有效的药物输送载体，用于管理和预防血栓形成和再狭窄。

Clinically significant restenosis occurs in greater than 30 percent of patients receiving percutaneous transluminal coronary angioplasty, and remains prevalent despite efforts to inhibit neointima formation through pharmacological intervention and the use of surface-modified intracoronary stents. The overall goal of the proposed research is to bioengineer new liposome drug delivery systems that selectively bind, or target, cell surface molecules expressed at sites of chronic vascular injury and developing restenotic lesions. We propose to investigate surface modifications of liposomes that (i) target encapsulated drugs directly to the site of vascular injury, by exploiting differences in cell surface phenotypes characteristic of activated cells present in the lesion; and (ii) inhibit protein adsorption to the liposome, thereby increasing the circulation half-life. The proposed targeting strategies are based on the central hypothesis that procoagulant and inflammatory phenotypes of stimulated vascular cells comprise unique cell surface receptors that will bind biomimetic constructs of endogenous ligands presented on the liposome surface. By utilizing these ligands to localize long-circulating liposomes to the lesion, local drug concentrations can be increased to therapeutic levels. Specifically, we shall focus on the design and development of targeting ligands to three cell surface molecules expressed in thrombosis and restenosis: (1) high affinity RGD peptides that bind integrin GPIIb-IIIa on activated platelets; (2) Factor VII-derived peptides that bind tissue factor on stimulated endothelial cells and smooth muscle cells, and (3) high affinity sialyl Lewis x and sialyl Lewis a - derived oligosaccharides that bind E- and/or P-selectins on EC and platelets. We shall examine how the ligand structures modulate binding affinity, and determine how these ligands affect binding and uptake of liposomes by target cells in vitro, and in a rat model of balloon-induced vascular injury in vivo. The physical properties of glycolipids designed to increase circulation lifetimes will be studied to determine the role of surface hydration and bilayer stability in altering liposomal clearance rates. The ability of long-circulating, targeted liposomes to affect neointima formation will be studied in vivo using rapamycin and enoxaparin as a model encapsulated therapeutic agents. By addressing targeting affinity and specificity, and prolonged circulation lifetime, an effective drug delivery vehicle for the management and prevention of thrombosis and restenosis can be achieved.