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

项目总结 大规模核事故的辐射暴露可能会产生灾难性的后果。意义重大 血管内皮损伤可能导致发病率和死亡率。内皮细胞是急性淋巴细胞白血病的中枢 辐射引起的血管内损伤可能会导致急性和延迟的器官毒性，例如 急性肺损伤、肺纤维化和造血功能受损。这些结果是由几个因素造成的 对内皮的病理影响，从内皮屏障破坏和血管渗漏开始。 内皮完整性和屏障功能在很大程度上由内皮受体酪氨酸激酶调节 铁2.Tie2被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 炎症引起的血管渗漏。相反，Tie2拮抗剂Ang-2抑制血管紧张素转换酶的稳定作用。 Ang-1，从而在各种病理条件下促进血管渗漏，如脓毒症和化学- 致肺损伤。重要的是，血管内皮细胞在辐射后Ang-2的表达增加， 提示Tie2活性降低是放射性血管内损伤的重要因素。在……里面 除Ang-2外，Tie2还受血管内皮细胞酪氨酸磷酸酶(VE-PTP)的负调控。 我们小组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 药理Tie2激活剂，并表明它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Tie2的活性，防止辐射后的血管泄漏，并改善 结果。除Tie2外，血小板还通过占据血管内皮细胞间隙调节内皮屏障功能 内皮衬里；释放可溶性因子(包括血管紧张素-1)，增强屏障功能；促进生长 维持内皮细胞的超微结构。血小板稀少(即辐射引起的 血小板减少症)可能会导致血管渗漏和其他下游效应。尽管血小板减少症可能 通过输血解决，捐献者的血小板供应有限，可能无法在大规模辐射中获得 事件。为了满足这一需求，我们开发了纤维蛋白原包裹纳米粒(Fcn)作为一种新的治疗方法。 策略。成像研究表明，FCN与内皮细胞结合，提供物理存在(即，堵塞 差距)，并将剩余的血小板招募到有需要的地方。因此，FCN可能具有两种直接影响(改进 对血管内皮细胞的间接作用(Ang-1/Tie2激活)，以及对小鼠的初步研究 辐射诱导的血小板减少模型表明，FCN可提高存活率。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。因此，我们 建议进一步表征辐射对肺和肺内皮细胞的急性和延迟影响 骨髓，关注内皮细胞Tie2信号通路和血小板减少作为可能的介质 辐射损伤。我们还提出了针对这些问题的新对策(AKB-9785，FCN)的研究 减轻辐射诱导的内皮损伤影响的途径。

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.