Mitigators of Radiation-Induced Endovascular Injury: Targeting Tie2 and Thrombocytopenia

项目摘要 大规模核事件造成的辐射暴露可能会产生灾难性的后果。显著 发病率和死亡率可由血管内皮损伤引起。内皮细胞是所有 辐射诱导的血管内损伤可能导致急性和迟发性器官毒性，例如 急性肺损伤、肺纤维化和造血功能受损。这些结果来自于几个 对内皮的病理影响，其开始为内皮屏障破坏和血管渗漏。 内皮完整性和屏障功能在很大程度上受内皮受体酪氨酸激酶的调节 领带2。Tie 2通过其激动剂配体血管生成素-1（Ang-1）激活，促进血管完整性，防止血管生成。 由炎症引起的血管渗漏。相反，Ang-2，一种Tie 2拮抗剂，抑制了 Ang-1，从而在多种病理条件下促进血管渗漏，如败血症和化学-血管生成。 导致肺损伤。重要的是，血管紧张素-2的表达在暴露于辐射后的内皮细胞中增加， 提示Tie 2活性降低是辐射诱导的血管内损伤的重要因素。在 除Ang-2外，Tie 2还受血管内皮蛋白酪氨酸磷酸酶（VE-PTP）负调控。 我们的研究小组已经测试了一种高度选择性的VE-PTP小分子抑制剂AKB-9785，它可以作为一种药物， 药理学Tie 2激活剂，并显示其在临床前模型中促进内皮屏障功能。 通过靶向这一途径，我们可以增加Tie 2活性，防止放射后血管渗漏，并改善 结果。除了Tie 2，血小板也通过占据内皮细胞的间隙来调节内皮屏障功能。 内皮细胞衬里;释放可溶性因子（包括Ang-1），增强屏障功能;促进生长 维持内皮细胞的超微结构。血小板缺乏（即，辐射诱导 血小板减少症）可能介导血管渗漏和其它下游效应。虽然血小板减少症可能 通过输血解决，供体血小板供应有限，可能无法在大规模辐射中获得 活动为了满足这一需求，我们开发了纤维蛋白原包被纳米颗粒（FCN）作为一种新的治疗药物 战略成像研究表明，FCN与内皮细胞结合，起到物理存在的作用（即，堵塞 间隙），并将剩余的血小板募集到需要的部位。因此，FCN可以具有两种直接效果（改善的 止血）和对内皮的间接作用（Ang-1/Tie 2活化），以及在小鼠中的初步研究 辐射诱导的血小板减少模型表明，FCN改善生存。而AKB-9785和FCN 可能出现靶向不同的途径，Ang-1的作用是一个重要的重叠点。所以我们 建议进一步描述辐射对肺内皮细胞的急性和延迟效应， 骨髓，重点是内皮Tie 2信号通路和血小板减少症作为可能的介质， 辐射损伤我们还提出了针对这些新的对策（AKB-9785，FCN）的研究 途径，以减轻辐射诱导的内皮损伤的影响。

PROJECT SUMMARY Radiation exposure from a large-scale nuclear incident could have catastrophic consequences. Significant morbidity and mortality may result from damage to the vascular endothelium. Endothelial cells are central to all organs, and radiation-induced endovascular injury may result in both acute and delayed organ toxicity, such as acute lung injury, pulmonary fibrosis, and impaired hematopoiesis. These outcomes result from several pathological effects on the endothelium, which begin with endothelial barrier disruption and vascular leak. Endothelial integrity and barrier function are regulated in large part by the endothelial receptor tyrosine kinase Tie2. Tie2 activation by its agonist ligand, angiopoietin-1 (Ang-1), promotes vascular integrity, preventing vascular leak induced by inflammation. In contrast, Ang-2, a Tie2 antagonist, inhibits the stabilizing effects of Ang-1, thereby promoting vascular leak in a variety of pathological conditions, such as sepsis and chemical- induced lung injury. Importantly, Ang-2 expression is increased in endothelial cells after exposure to radiation, suggesting that decreased Tie2 activity is an important factor in radiation-induced endovascular injury. In addition to Ang-2, Tie2 is negatively regulated by vascular endothelial-protein tyrosine phosphatase (VE-PTP). Our group has tested a highly selective small molecule inhibitor of VE-PTP, AKB-9785, which acts as a pharmacological Tie2 activator, and shown that it promotes endothelial barrier function in preclinical models. By targeting this pathway, we may increase Tie2 activity, prevent vascular leak after radiation, and improve outcomes. In addition to Tie2, platelets also regulate endothelial barrier function by occupying gaps in the endothelial lining; releasing soluble factors (including Ang-1) to enhance barrier function; promoting the growth of endothelial cells; and maintaining the endothelial ultrastructure. Paucity of platelets (i.e., radiation-induced thrombocytopenia) may mediate vascular leak and other downstream effects. Though thrombocytopenia may be addressed via transfusion, donor platelets are limited in supply and may not be available in a mass radiation event. To meet this need, we have developed fibrinogen-coated nanoparticles (FCN) as a novel therapeutic strategy. Imaging studies suggest that FCN bind to endothelial cells, serving a physical presence (i.e., plugging gaps), and recruit the remaining platelets to sites of need. Thus, FCN may have both direct effects (improved hemostasis) and indirect effects (Ang-1/Tie2 activation) on the endothelium, and preliminary studies in murine models of radiation-induced thrombocytopenia suggest that FCN improve survival. While AKB-9785 and FCN may appear to target different pathways, the role of Ang-1 is an important point of overlap. Therefore, we propose to further characterize the acute and delayed effects of radiation on endothelial cells in the lung and bone marrow, focusing on the endothelial Tie2 signaling pathway and thrombocytopenia as likely mediators of radiation damage. We also propose study to novel countermeasures (AKB-9785, FCN) targeting these pathways to mitigate the effects of radiation-induced endothelial injury.