Development of B8C1ad as an Orphan Drug for Iatrogenic Botulism

摘要 肉毒神经毒素血清型A1（BoNT/A1）已成为多种适应症的重要治疗工具， 尽管它是科学界已知的毒性最大的蛋白质虽然严重不良事件（AE）很罕见，但其 所有FDA批准的BoNT/A1标签中包含的黑盒警告确认了其重要性 产品.在最近3年期间，FDA收到了13，087份明确描述为“过量”的AE报告， 主要与治疗适应症相关。涉及大肌肉群的治疗（如中风后 痉挛、脑瘫和颈肌张力障碍）。BoNT/A1相关医源性损伤尚无治疗方法 支持治疗以外的AE。唯一可用的肉毒中毒治疗剂是马源性抗毒素（BAT， 紧急生物解决方案），不能访问负责医源性症状的神经元内毒素蛋白酶， 因此在治疗与BoNT/A1过量和脱靶作用相关的AE中几乎没有用处。我们有 开发了具有神经元内作用机制的BoNT/A1中毒的症状后解毒剂， 命名为B8 C1 ad。B8 C1 ad是通过将单结构域抗体（sdAb，B8）基因融合到 BoNT/C1的重组无毒衍生物（C1 ad为无毒衍生物），其作为分子载体递送 B8抗体针对BoNT/A1毒性蛋白酶所在的神经元细胞质。B8抗体是 选自骆驼科VHH文库，因为其对BoNT/A1蛋白酶的有效抑制。B8 C1 ad已经 证明在中毒后有效地挽救具有全身性BoNT/A1中毒的动物， 常规抗体是无效的，因为它们不能接近神经元内BoNT/A1 LC蛋白酶。 B8 C1 ad逆转BoNT/A1中毒症状和拯救动物的安全性和有效性， 在三个物种中发表，包括非人类灵长类动物。我们在这里建议建立一个模型， 通过肌肉注射超治疗剂量的BoNT/A1过量，并将B8 C1 ad发展为一种 治疗与BoNT/A1药物临床使用相关的脱靶医源性AE的孤儿药 产品.成功完成拟议研究将支持组装目标产品概况， B8 C1 ad，将与FDA共享，以请求召开C类会议，以指导以下方面的监管途径： B8 C1 ad获批作为孤儿药，用于治疗与BoNT/A1药物相关的医源性药物过量。

Abstract Botulinum neurotoxin serotype A1 (BoNT/A1) has become an important therapeutic tool for multiple indications, despite being the most toxic protein known to science. Although serious Adverse Events (AEs) are rare, their importance is recognized by the Black Box warning included in the labeling for all FDA-approved BoNT/A1 products. During a recent 3-year period FDA received 13,087 AE reports specifically described as “overdose”, primarily associated with therapeutic indications. involving the treatment of large muscle groups (eg post-stroke spasticity, cerebral palsy and cervical dystonia). No treatment is available for BoNT/A1-associated iatrogenic AEs other than supportive care. The only available botulism therapeutic is an equine-derived antitoxin (BAT, Emergent Biosolutions) that cannot access the intraneuronal toxin protease responsible for iatrogenic symptoms, and is therefore of little use in treating AEs associated with BoNT/A1 overdose and off-target actions. We have developed a post-symptomatic antidote to BoNT/A1 intoxication with an intraneuronal mechanism of action, designated B8C1ad. B8C1ad is produced by genetically fusing a single domain antibody (sdAb, B8) to a recombinant atoxic derivative of BoNT/C1 (C1ad for atoxic derivative) that acts as a molecular vehicle to deliver the B8 antibody to the neuronal cytoplasm where the BoNT/A1 toxic protease resides. The B8 antibody was selected from a camelid VHH library for its potent inhibition of the BoNT/A1 protease. B8C1ad has been demonstrated to effectively rescue animals with systemic BoNT/A1 intoxication at times post-intoxication when conventional antibodies are ineffective, because they cannot access the intra-neuronal BoNT/A1 LC protease. The safety and effectiveness of B8C1ad to reverse BoNT/A1 intoxication symptoms and rescue animals has been published in three species, including non-human primates. We here propose establishing a model for BoNT/A1 overdose via intramuscular administration of supratherapeutic doses, and developing B8C1ad as an Orphan Drug to treat off-target iatrogenic AEs associated with the clinical use of BoNT/A1 pharmaceutical products. Successful completion of the proposed studies will support assembly of a target product profile for B8C1ad, which will be shared with FDA to request a Type C meeting for guidance on the regulatory pathway for B8C1ad approval as an Orphan Drug to treat iatrogenic overdose associated with BoNT/A1 pharmaceuticals.