Development of thrombopoietin mimetic (TPOm) as a mitigator against Radiation-induced endovascular injuries

摘要 放射性血管损伤(Rivi)是急性肾功能衰竭(MOF)的重要组成部分。 全身或局部照射后的辐射综合征(ARS)。急性呼吸窘迫综合征的病理生理学 辐射(IR)对组织干细胞和祖细胞的直接细胞杀伤效应的组合结果 (TSPC)和具有不同辐射敏感性的壁龛细胞。而几种生长和分化药物的靶向 TSPC正被积极用作治疗ARS的药物，显然，快速恢复 干细胞巢细胞中的窦状内皮细胞(SEC)对于提高ARS和ARS的存活率至关重要 改善急性辐射暴露(DEARE)的延迟效应。SECs提供了一条营养和 分泌支持血管周围细胞增殖的血管分泌生长因子，例如， 间充质细胞和TSPC。研究表明，血管成分在急性心肌梗死中的重要作用 辐射对骨髓(BM)和肠道的损伤，以及对肺、肝脏和肾脏的远期影响。在……里面 骨髓、小动脉周围NG2+巢亮周细胞支持造血干细胞(HSC) 静止期，肝窦周围Lepr+雀巢间质细胞促进HSC增殖。跟随 暴露于IR后，BM-SEC退变，窦周龛细胞和肝星状细胞遭到破坏。 VEGFR2介导的骨髓SECs再生是ARS骨髓再生所必需的。 我们正在与Janssen制药公司合作开发一种新的辐射对策， 血栓生成素模拟物(TPOM，又名JNJ-26366821)，它是一种第二阶段就绪的，完全合成的， 聚乙二醇化的TPO受体，c-MPL激动肽，可降低与BM-ARS相关的死亡率和发病率。 TPOM在放射增强剂中是独一无二的，因为有两种不同的药效学效应：(1)减轻 辐射引起的血小板减少、贫血和白细胞减少与c-MPL受体的结合和激活 对巨核细胞和HSC的影响；(2)血管内皮的保护和再生，尤其是SEC。一个 全身照射(WBI)后24小时单次给予TPOm可显著提高小鼠的存活率 多种ARS动物模型，包括小鼠、大鼠、狗和非人灵长类动物(NHP)。TPO也一直被 显示促进血管内皮祖细胞动员到血管损伤部位。因此，我们， 假设除了治疗放射性引起的血小板减少症外，TPOM还将促进 SEC在包括骨髓和肠道在内的多种组织干细胞利基中的再生，从而， 加速辐射暴露后的组织再生。 该提案需要一个循序渐进的计划，以确定TPOM在血管损伤中的放射防护效果。 特定目标下的外周和组织水平1采用急性放射损伤模型。这些研究将集中在 外周血管损伤，造血细胞和血管周围壁龛内皮损伤(H-ARS模型)， 隐窝和绒毛血管内皮细胞损伤(GI-ARS模型)。我们还将验证TPOM的有效性 在小鼠体内，测定其剂量修饰因子及其在特定条件下对炎性细胞因子的影响 目的2.最后，我们将确定其对肺和肾DeARE的影响，确定早期的生物标志物 在系统和组织水平上的内皮损伤，并开发成像技术来评估损伤使用高 对比度微型CT扫描仪。

Abstract Radiation-induced vascular injury (RIVI) is a critical component of the multi-organ failure (MOF) seen in acute radiation syndrome (ARS), following exposure to whole or partial body irradiation. The pathophysiology of ARS results from a combination of direct cytocidal effects of irradiation (IR) on tissue stem and progenitor cells (TSPC) and niche cells with varying radiosensitivity. While several growth and differentiation agents targeting TSPCs are being actively pursued as therapeutics to treat ARS, it is evident that rapid restoration of the sinusoidal endothelial cells (SEC) in the stem cell niche cells is critical for improving survival in ARS and in ameliorating the delayed effects of acute radiation exposure (DEARE). SECs provide a conduit for nutrition and secrete angiocrine growth factors that support the proliferation of perivascular niche cells, such as, mesenchymal cells and TSPCs. Studies have implicated the essential role of the vascular component in acute radiation injuries of the bone marrow (BM) and intestine, as well as, in late effects in lung, liver and kidneys. In the bone marrow, the peri-arteriolar NG2+Nestinbright pericytes support hematopoietic stem cell (HSC) quiescence, while the peri-sinusoidal LepR+Nestindim mesenchymal cells promote HSC proliferation. Following exposure to IR, there is regression of BM-SEC with destruction of peri-sinusoidal niche cells and HSCs. VEGFR2-mediated regeneration of the marrow SECs is necessary for BM regeneration in ARS. We are collaborating with Janssen Pharmaceuticals on the development of a novel radiation countermeasure, thrombopoietin (TPO) mimetic (TPOm, aka JNJ-26366821), which is a Phase II ready, fully synthetic, PEGylated TPO receptor, c-MPL agonist peptide that reduces mortality and morbidity associated with BM-ARS. TPOm is unique amongst radiomitigators because of two distinct pharmacodynamic effects: (1) Mitigation of radiation-induced thrombocytopenia, anemia, and leukopenia upon binding and activation of the c-Mpl receptor on megakaryocytes and HSC, and (2) protection and regeneration of vascular endothelium, particularly SEC. A single dose of TPOm, administered 24 h post-whole body irradiation (WBI) improved survival significantly in multiple animal models of ARS, including mouse, rat, dog and non-human primates (NHP). TPO has also been shown to promote mobilization of vascular endothelial progenitor cells to sites of vascular injury. We, therefore, hypothesize that in addition to treating radiation-induced thrombocytopenia, TPOm would promote regeneration of SEC in multiple tissue stem cell niches, including bone marrow and intestine, thereby, accelerating tissue regeneration after radiation exposure. The proposal entails a step-wise plan to determine the radiomitigating efficacy of TPOm in vascular injuries at peripheral and tissue level under specific aim 1 using acute radiation injury model. These studies will focus on peripheral vascular damage, endothelial injury of the hematopoietic and perivascular niche (H-ARS model), and vascular endothelial injury in the crypt and villi (GI-ARS model). We will also validate the efficacy of TPOm in mice, determine its dose modification factor and its effect of inflammatory cytokine profiles under specific aim 2. Finally, we will determine its effects against DEARE of the lungs and kidney, identify early biomarkers of endothelial injury at systemic and tissue level and develop imaging techniques to assess the injury using high contrast micro-CT scanner.