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

摘要 放射性血管损伤（RIVI）是急性放射性损伤后多器官功能衰竭（MOF）的重要组成部分。 辐射综合征（ARS），暴露于全身或部分照射后。ARS的病理生理学 结果来自辐射（IR）对组织干细胞和祖细胞的直接杀细胞作用的组合 （TSPC）和具有不同放射敏感性的小生境细胞。虽然几种生长和分化剂靶向 TSPC正被积极地用作治疗ARS的治疗剂，很明显， 干细胞龛细胞中的窦状内皮细胞（SEC）对于提高ARS患者的存活率至关重要， 改善急性辐射暴露的延迟效应（DEARE）。SECs提供了营养和 分泌支持血管周围小生境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起着重要作用。 骨髓和肠的辐射损伤，以及肺、肝和肾的晚期效应。在 骨髓、动脉周围NG 2 +Nestinbright周细胞支持造血干细胞（HSC） 静止，而窦周LepR+Nestindim间充质细胞促进HSC增殖。以下 暴露于IR，存在BM-SEC的消退，伴随窦周龛细胞和HSC的破坏。 VEGFR 2介导的骨髓SEC再生是ARS中BM再生所必需的。 我们正在与杨森制药公司合作开发一种新的辐射对策， 血小板生成素（TPO）模拟物（TPOm，又名JNJ-26366821），是一种II期就绪，完全合成， 聚乙二醇化TPO受体，c-MPL激动剂肽，可降低BM-ARS相关死亡率和发病率。 TPOm在放射性抑制剂中是独特的，因为有两种不同的药效学作用：（1）减轻放射性抑制剂的毒性。 c-Mpl受体结合和激活后辐射诱导的血小板减少、贫血和白细胞减少 对巨核细胞和HSC的影响;（2）保护和再生血管内皮，特别是SEC。一 全身照射（WBI）后24小时给予单剂量TPOm显著改善了 ARS的多种动物模型，包括小鼠、大鼠、狗和非人灵长类动物（NHP）。TPO也是 显示促进血管内皮祖细胞向血管损伤部位的移动。因此， 假设除了治疗辐射诱导的血小板减少症外，TPOm还可以促进 SEC在多个组织干细胞龛中的再生，包括骨髓和肠，从而， 加速辐射后的组织再生 该提案需要一个逐步的计划，以确定TPOm在血管损伤中的放射性疗效， 在特定目标1下，使用急性放射损伤模型在外周和组织水平下进行。这些研究将侧重于 外周血管损伤，造血和血管周围生态位的内皮损伤（H-ARS模型）， 以及腺窝和绒毛中的血管内皮损伤（GI-ARS模型）。我们还将验证TPOm的有效性 在小鼠中，确定其剂量修饰因子及其在特定条件下对炎性细胞因子谱的影响， 目标2.最后，我们将确定其对肺和肾的DEARE的影响，确定早期生物标志物， 在全身和组织水平的内皮损伤，并开发成像技术，以评估损伤使用高 对比显微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.