Receptor Decoy Inhibitor of Anthrax Toxin

描述（由申请人提供）：孢子形成细菌炭疽杆菌引起炭疽，被列为六种A类制剂之一，被认为是生物武器的主要威胁。由于其在疾病发病机制中的关键作用，目前正在开发许多抑制炭疽毒素的策略，包括基于单克隆抗体的疗法。然而，存在对细菌可被工程化以避免疫苗保护或抗毒素治疗的容易性的显著关注，例如通过从保护性抗原（PA）毒素亚基去除抗体结合位点。解决这一限制的下一代抗毒素开发策略涉及使用可溶性受体诱饵抑制剂（RDI）;据推测，PA不能被工程化以逃避细胞受体识别，因此RDI即使对已被故意改变以抵抗抗体中和的PA形式也应该有效。我们最近开发了一种RDI，它具有广泛作用的炭疽治疗剂所需的许多特性：它与PA的受体结合位点结合，其亲和力与一些领先的治疗性抗体相当（Kd = 0.2nM）;它通过炭疽毒素的两种已知细胞受体阻断中毒;它与PA的解离速率非常慢（t1/2复合物= 15小时）;它是非免疫原性的;其生产使用细菌表达系统是容易可缩放的;它可以中和化学计量浓度的PA并保护大鼠免受毒素杀伤。这项研究计划代表了推进RDI作为炭疽候选疗法的全面战略。我们将通过破坏其与其生理配体（IV型胶原和层粘连蛋白）的相互作用，以及利用聚乙二醇化和IG融合蛋白方法来表征和优化其药代动力学特性。我们还将确定这类抑制剂是否如预期的那样有效中和PA的抗体耐药形式。此外，我们将确定这类抑制剂是否可以预防由表达野生型或抗体抗性PA的Sterne孢子引起的小鼠疾病。这些实验将为未来的研究奠定基础，旨在确定RDI在预防由B强毒株引起的疾病方面的有效性。炭疽病我们预计RDI将是一种有用的炭疽辅助疗法，可能与单克隆抗体协同作用，治疗野生型细菌菌株引起的感染，同时提供一种简单的策略来处理工程化的武器化细菌菌株。

DESCRIPTION (provided by applicant): The spore-forming bacterium Bacillus anthracis causes anthrax, and is classified as one of six Category A agents considered as major threats as a bioweapon. Because of its pivotal role in disease pathogenesis, a number of strategies to inhibit anthrax toxin are currently under development, including monoclonal antibody- based therapies. However, there is significant concern about the ease with which the bacterium may be engineered to avoid vaccine protection or antitoxin therapy, e.g. by removing antibody-binding sites from the protective antigen (PA) toxin subunit. A next-generation strategy for antitoxin development, one that addresses this limitation, involves the use of a soluble receptor decoy inhibitor (RDI); Presumably PA cannot be engineered to evade cellular receptor recognition and therefore the RDI should be effective even against forms of PA that have been deliberately altered to resist antibody neutralization. We have recently developed an RDI which has many properties desirable in a broadly acting anthrax therapeutic: it binds to the receptor-binding site of PA with an affinity that is on a par with some of the leading therapeutic antibodies (Kd = 0.2nM); it blocks intoxication via both known cellular receptors for anthrax toxin; its dissociation rate from PA is extremely slow (t1/2 complex = 15 hours); it is non-immunogenic; its production is easily scaleable using a bacterial expression system; it can neutralize PA at stoichiometric concentrations and protects rats against toxin killing. This research plan represents a comprehensive strategy for advancing the RDI as a candidate therapy for anthrax. We will characterize and optimize its pharmacokinetic properties by disrupting its interaction with its physiological ligands (collagen IV and laminin), and by exploiting PEGylation and Ig fusion protein approaches. We will also establish if this class of inhibitor is effective at neutralizing antibody-resistant forms of PA, as expected. Moreover, we will establish if this class of inhibitor can prevent disease in mice caused by Sterne spores that express either wild-type or antibody-resistant PA. These experiments will set the stage for future studies aimed at establishing the effectiveness of the RDI in preventing disease caused by highly virulent strains of B. anthracis. We anticipate that the RDI will be a useful adjunct anthrax therapy that could potentially synergize with monoclonal antibodies to treat infections caused by wild-type bacterial strains while at the same time providing a straightforward strategy for dealing with engineered, weaponized bacterial strains.