Controlling Radiation Injury by TLR5 Agonists

描述（由申请方提供）：电离辐射（IR）对哺乳动物的毒性主要是由于对大多数辐射敏感组织、胃肠道（GI）和造血（HP）系统的损伤。已经开发了许多方法和化合物来保护或恢复IR暴露后的HP功能，包括免疫功能。相比之下，胃肠道放射综合征仍然难以治疗，导致显著的死亡率和生存者生活质量下降。在初步研究中，它被证明是细菌鞭毛蛋白，作为NF-？B是Toll样受体5（TLR 5）的激活激动剂，是一种强大的辐射防护剂和辐射阻断剂，当分别在致死性IR之前或之后给予时，能够改善存活率。值得注意的是，鞭毛蛋白的抗辐射作用与保护胃肠道以及HP系统有关。通过缺失对TLR 5活化非必需的鞭毛蛋白的部分来产生具有降低的免疫原性的优化的TLR 5激动剂（CBLB 502）。CBLB 502在小鼠和非人类灵长类动物中有效且无毒，正在开发成为一种稳定的、可自我施用的辐射解毒剂，用于生物防御应用。该提案的重点是破译CBLB 502作用的分子和细胞机制。目的1：研究CBLB 502对受照小鼠小肠损伤的保护和修复作用的细胞介质，特别是骨髓源性细胞的作用。目的二是分析CBLB 502诱导的分子信号通路，这些通路对CBLB 502的辐射防护和辐射拮抗特性至关重要。假设驱动和无偏功能筛选方法的组合将用于确定CBLB 502分子靶点。最后，目标3将集中于评估CBLB 502对其他放射敏感组织（包括肝、肾和肺）中IR的短期和长期病理后果的影响。将在小鼠模型中评估纤维化和癌症发展的频率和严重程度。该计划的完成将提供关于一类新兴的辐射解毒剂的关键信息，这将使人们更好地了解它们作为针对急性辐射综合征的人类治疗剂的潜力。当今世界核事故和恐怖袭击的潜在情景意味着大规模辐射伤害，即系统性暴露于放射性材料造成的伤亡。全身照射（TBI）的毒性与急性放射综合征（ARS）的诱导有关，主要涉及对高放射敏感性胃肠道（GI）和造血（HP）系统的损伤。虽然已经开发了许多方法和化合物来保护或恢复TBI后的HP功能，但GI放射综合征仍然难以治疗，导致存活者的显著死亡率和生活质量降低。一个理想的辐射对策将保护胃肠道和HP系统，并将能够既辐射防护（预防）和减轻辐射损伤。此外，生物防御应用需要一种易于自我施用、具有长保质期且不需要特殊处理或储存条件的药物。我们最近发现了一类新的药物，满足所有上述要求，最显着的是对胃肠道辐射综合征以及HP综合征有效。我们的先导化合物CBLB 502是一种强大的辐射防护剂和辐射损伤缓解剂，适用于肌肉注射。它是一种源自细菌蛋白质鞭毛蛋白的多肽，充当Toll样受体5（TLR 5）的激动剂，TLR 5在肠和骨髓祖细胞的放射敏感细胞中表达，与配体结合后，激活几种促生存途径，由NF-？介导。B信令。在这里，我们提出了一个计划，全面表征CBLB 502的抗辐射活性的分子和细胞机制，特别是集中在GI辐射综合征。我们还将研究CBLB 502对其他组织中IR的病理后果的影响，包括辐射致癌性。拟议的实验将提供基本的机理洞察到以前观察到的辐射防护和缓解CBLB 502的效果。

DESCRIPTION (provided by applicant): The toxicity of ionizing radiation (IR) in mammals is largely due to damage to the most radiosensitive tissues, the gastrointestinal (GI) tract and the hematopoietic (HP) system. A number of approaches and compounds have been developed to protect or restore HP, including immune, function following IR exposure. In contrast, GI radiation syndrome remains poorly treatable resulting in significant mortality and reduced quality of life for survivors. In preliminary studies it was demonstrated that the bacterial flagellin protein, acting as an NF-?B activating agonist of Toll-like receptor 5 (TLR5), is a powerful radioprotectant and radiomitigator capable of improving survival when given either before or after lethal IR, respectively. Notably, the anti-radiation effects of flagellin are associated with protection of the GI tract as well as the HP system. A pharmacologically optimized TLR5 agonist with reduced immunogenicity (CBLB502) was generated by deleting portions of flagellin that are non-essential for TLR5 activation. CBLB502 is effective and non-toxic in mice and non-human primates and is being developed into a stable, self-administrable radiation antidote projected for biodefense applications. This proposal is focused on deciphering the molecular and cellular mechanisms of action of CBLB502. Aim 1 will involve identification of cellular mediators of CBLB502's effect on protection and healing of small intestine in irradiated mice with particular attention on the role of bone marrow-derived cells. Aim 2 will be devoted to analysis of molecular signaling pathways induced by CBLB502 that are critical for its radioprotection and radiomitigation properties. A combination of hypothesis-driven and unbiased functional screening approaches will be used to determine CBLB502 molecular targets. Finally, Aim 3 will concentrate on assessing the effects of CBLB502 on the short- and long-term pathological consequences of IR in other radiosensitive tissues, including liver, kidney and lung. The frequency and severity of fibrosis and cancer development will be assessed in a mouse model. Completion of this program will provide critical information about an emerging class of radiation antidotes that will allow improved understanding of their potential as human therapeutics targeting acute radiation syndrome. The potential scenarios for nuclear accidents and terrorist attacks in today's world imply mass radiation injury casualties affected by systemic exposure to radioactive materials. The toxicity of total body irradiation (TBI) is associated with induction of acute radiation syndrome (ARS) primarily involving damage to the highly radiosensitive gastrointestinal (GI) tract and hematopoietic (HP) system. While a number of approaches and compounds have been developed to protect or restore HP function following TBI, GI radiation syndrome remains poorly treatable, resulting in significant mortality and reduced quality of life for survivors. An ideal radiation countermeasure would protect both the GI and HP systems and would be capable of both radioprotection (prophylaxis) and mitigation of radiation injury. Moreover, biodefense applications require a drug that is easily self-administered, has a long shelf life and does not require special handling or storage conditions. We have recently discovered a new class of agents that satisfy all of the above requirements, most notably being effective against GI radiation syndrome as well as HP syndrome. Our lead compound, named CBLB502, is a powerful radioprotectant and mitigator of radiation injury suitable for intramuscular injections. It is a polypeptide derived from bacterial protein flagellin that acts as an agonist of Toll-like receptor 5 (TLR5), which is expressed in radiosensitive cells of the intestine and bone marrow progenitors and, upon binding with the ligand, activates several pro-survival pathways, mediated by NF-?B signaling. Here we propose a program to comprehensively characterize the molecular and cellular mechanisms underlying the anti-radiation activity of CBLB502, particularly focusing on GI radiation syndrome. We will also investigate the effect of CBLB502 on the pathological consequences of IR in other tissues, including radiation carcinogenicity. The proposed experiments will provide essential mechanistic insight into the previously observed radio-protective and -mitigative effects of CBLB502.