Targeted antitoxin delivery platforms as post-exposure therapies for botulism

描述(申请人提供)：为梭状芽胞杆菌神经毒素引起的肉毒杆菌中毒开发暴露后治疗方法的最大挑战之一是传统的基于抗体的抗毒素中和循环中的游离神经毒素并阻止毒素与细胞受体结合的短暂治疗窗口。正因为如此，患者通常是无症状的，直到毒素已经内化，不再能进行抗体中和。在毒素内化并表现出症状后，目前的抗毒素都不起作用。我们建议的暴露后抗毒素将满足这一关键需求。我们建议开发一种暴露后的治疗性抗肉毒杆菌神经毒素(BONT)试剂，它建立在抗体/抑制物-毒素嵌合体的概念上，该嵌合体可以针对特定的递送到神经细胞，并且在进入细胞时将递送和释放一种抑制剂到胞浆中，该抑制剂将中和BONT的催化活性，从而使细胞能够更快地恢复。在这种嵌合的抗毒素中，高亲和力的单链抗体、基于多肽的抑制剂或基于小分子的抑制剂将被连接到BONT的重链(BONT-HC)上，从而使其在特定的受体结合、转位(即递送)和释放到神经细胞的胞浆中后，能够特异性地抑制BONT-LC的金属蛋白酶活性。使用该系统的优点是中和抗毒素将被定向到发生毒素作用的相同位置-不仅是相同类型的细胞，而且是目标底物所在的相同的细胞内隔室。重要的是，我们提出的抗毒素策略有可能逆转和/或缩短中毒(即瘫痪)的临床效果持续时间。为了达到获得这种新的暴露后抗毒素疗法的目的，我们提出了以下目标：1.重组BONT重链融合蛋白作为载体的构建和优化。2.优化药物释放机制，有效地将抑制剂输送到神经细胞的胞浆。3.优化底物-单链抗体抑制剂作为中和BONT活性的支架。4.构建和优化用于递送多肽和小分子抑制剂的替代BONT/A-HC接头。

DESCRIPTION (provided by applicant): One of the greatest challenges of developing post-exposure treatments for botulism caused by clostridial neurotoxins is the brief therapeutic window for conventional antibody-based antitoxins to neutralize the free neurotoxin in the circulation and to block binding of the toxin to cellular receptors. Because of this, the patient is most often asymptomatic until after the toxin has already been internalized and is no longer accessible to antibody neutralization. No current antitoxin is effective after toxin has been internalized and symptoms manifested. Our proposed post-exposure antitoxin will address this critical need. We propose to develop a post-exposure therapeutic anti-botulinum neurotoxin (BoNT) reagent, which builds on the concept of an antibody/inhibitor-toxin chimera that can be targeted for specific delivery into neuronal cells and that upon entry into the cells will deliver and release an inhibitor into the cytosol that will neutralize the catalytic activity of BoNT, such that the cells can more rapidly recover. In this chimeric antitoxin, high affinity scFv antibodies, peptide-based inhibitors, or small molecule-based inhibitors will be attached to the heavy chain of BoNT (BoNT-HC), such that it could specifically inhibit the metalloprotease activity of BoNT-LC after specific receptor binding, translocation (i.e. delivery), and release into the cytosol of neuronal cells. The advantage of using this system is that the neutralizing antitoxin will be directed to the same location where toxin action is occurring - not only the same type of cells, but also the same intracellular compartments where the target substrates are located. Importantly, our proposed antitoxin strategy has the potential to reverse and/or shorten the duration of the clinical effects of intoxication (i.e. paralysis). To achieve the goal of obtaining this new post-exposure antitoxin therapeutic, we propose the following aims: 1. Construction and optimization of recombinant BoNT heavy chain fusion proteins as delivery vehicles. 2. Optimization of the cargo release mechanism for efficient delivery of inhibitor to the cytosol of neuronal cells. 3. Optimization of the substrate-scFv inhibitor as a scaffold for neutralization of BoNT activity. 4. Construction and optimization of alternative BoNT/A-HC adaptors for delivering peptide-based and small-molecule-based inhibitors.