Development of B8C1ad as an Orphan Drug for Iatrogenic Botulism

摘要 A1型肉毒神经毒素(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强的蛋白质。虽然严重不良事件(AEs)很少见，但他们的 FDA批准的所有BONT/A1的标签中包含的黑盒警告认识到了重要性 产品。在最近3年的时间里，FDA收到了13,087份被具体描述为“过量”的AE报告， 主要与治疗适应症有关。涉及大肌肉群的治疗(如中风后) 痉挛、脑瘫和颈肌张力障碍)。与BONT/A1相关的医源性疾病尚无治疗方法 而不是支持性护理。唯一可用的肉毒杆菌中毒治疗方法是马源性抗毒素(BAT， 紧急生物溶液)，不能接触到导致医源性症状的神经细胞内毒素蛋白酶， 因此，在治疗与BONT/A1过量和靶外行为相关的不良反应方面用处不大。我们有 开发了一种针对BONT/A1中毒的症状后解毒剂，具有神经内作用机制， 指定为B8C1ad。B8C1ad是通过基因融合单域抗体(sdAb，B8)而产生的 重组BONT/C1的无毒衍生物(C1ad为无毒衍生物)，可作为分子载体传递 针对BONT/A1有毒蛋白酶所在的神经细胞质的B8抗体。B8抗体是 选自骆驼VHH文库，因其对BONT/A1蛋白水解酶具有有效抑制作用。B8C1ad已经被 证明可以在中毒后有效地抢救全身BONT/A1中毒的动物 常规抗体是无效的，因为它们不能访问神经元内的BONT/A1 LC蛋白酶。 B8C1ad逆转BONT/A1中毒症状和拯救动物的安全性和有效性 已经发表在三个物种上，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而过量服用BONT/A1，并将B8C1ad发展为 治疗与临床使用BONT/A1药物相关的非靶点医源性AEs的孤儿药物 产品。成功完成拟议的研究将支持组装目标产品配置文件 B8C1ad，将与FDA共享，以请求召开C类会议，以指导 B8C1ad被批准为孤儿药物，用于治疗与BONT/A1药物相关的医源性过量。

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.