PA-50/PA-41 antitoxin antibody therapy for C. difficile infection

描述（由申请人提供）：艰难梭菌感染（CDI）是美国医院获得性腹泻和肠道感染导致死亡的主要原因。CDI的发病率和严重程度在过去十年中急剧增加，部分原因是异常毒力和致命菌株的出现和在世界范围内的传播，这些毒株过度表达A和b两种毒素。这些强效细胞毒素是艰难梭菌的主要毒力因子，可以破坏结肠细胞，导致液体分泌和炎症。CDI通常是由抗生素的使用引起的，抗生素破坏了保护性的结肠菌群，为艰难梭菌的繁殖提供了机会。口服万古霉素或甲硝唑治疗导致许多患者症状缓解；然而，复发是经常发生的。对于多次复发的CDI或严重的危及生命的疾病，没有标准的治疗方法。制定新的治疗战略是全球卫生的当务之急。一种实验性治疗策略是用单克隆抗体（mab）中和毒素。抗毒素单克隆抗体代表了一种非抗生素治疗，旨在阻止毒素的有害影响，同时允许正常的结肠菌群反弹和结肠自然愈合。第一代抗毒素单克隆抗体在预防CDI复发方面显示出临床活性，但在治疗活动性疾病方面没有表现出活性。我们已经产生了高效的人源单克隆抗体，命名为PA-50和PA-41，分别针对毒素A和B上新的中和表位。与第一代单抗相比，PA-50和PA-41在体外中和BI/NAP1/027毒株毒素的效力提高了1000倍。在一个成熟的CDI仓鼠模型中，PA-50/PA-41治疗对致命攻击提供了长期保护（95%存活率），而第一代单克隆抗体延迟但不能预防死亡（0%存活率）。像PA-50和PA-41这样的高效单克隆抗体有可能打破多次复发CDI患者的感染循环，并治疗危及生命和其他挑战性的CDI病例。该项目的总体目标是完成我们的主要单克隆抗体的临床前研究，并获得FDA的同意启动人体试验。初步的临床前研究将描述PA-50和PA-41有效的毒素中和活性的分子和机制基础；这些研究也将为艰难梭菌中毒的生物学提供新的见解。我们还将在新建立的CDI仔猪模型中检测单克隆抗体治疗BI/NAP1/027菌株引起的活动性疾病的疗效。额外的转化活动旨在完成必要的制造、毒理学和其他开发活动，以准备和提交PA-50和PA-41的研究新药申请（INDs）。成功将为PA-50和PA-41进行人体临床试验做好准备，并将成为开发创新新药的关键里程碑，这些新药可能会解决艰难梭菌流行病的关键挑战。

DESCRIPTION (provided by applicant): Clostridium difficile infection (CDI) is the leading cause both of hospital-acquired diarrhea and of death due to intestinal infections in the US. The incidence and severity of CDI have increased sharply over the past decade due in part to the emergence and worldwide spread of unusually virulent and deadly strains that overexpress two toxins, A and B. These potent cytotoxins represent the main virulence factors of C. difficile and can damage cells that line the colon, resulting in fluid secretion and inflammation. CDI typically is precipitated by the use of antibiotics, which disrupt the protective colonic flora and provide an opportunity for C. difficile to flourish. Treatment with oral vancomycin or metronidazole leads to symptom resolution in many patients; however, relapse occurs frequently. There is no standard therapy for multiply recurrent CDI or severe, life-threatening disease. Development of new treatment strategies is a global health imperative. One experimental treatment strategy is to neutralize the toxins with monoclonal antibodies (mAbs). Antitoxin mAbs represent a non-antibiotic therapy that is designed to block the harmful effects of the toxins while allowing the normal colonic flora to rebound and the colon to heal naturally. First-generation antitoxin mAbs have shown clinical activity in preventing recurrence of CDI but not in treating active disease. We have generated highly potent humanized mAbs, designated PA-50 and PA-41 that are directed to novel neutralization epitopes on toxins A and B, respectively. Compared with first-generation mAbs, PA-50 and PA-41 are 1,000-fold more potent in neutralizing toxins from virulent BI/NAP1/027 strains in vitro. In a well-established hamster model of CDI, treatment with PA-50/PA-41 provided long-term protection (95% survival) from a lethal challenge, whereas first-generation mAbs delayed but did not prevent death (0% survival). Highly potent mAbs like PA-50 and PA-41 have the potential both to break the cycle of infection in patients with multiply recurrent CDI and to treat life-threatening and otherwise challenging cases of CDI. The overall goal of this project is to complete preclinical studies of our lead mAbs and obtain agreement from FDA to initiate human testing. Initial preclinical studies will delineate the molecular and mechanistic underpinnings of the potent toxin-neutralizing activities of PA-50 and PA-41; these studies will also provide new insights into the biology of C. difficile intoxication. We also will examine the efficacy of the mAbs in treating active disease caused by BI/NAP1/027 strains in a newly established piglet model of CDI. Additional translational activities are designed to complete essential manufacturing, toxicology and other development activities required to prepare and submit Investigational New Drug applications (INDs) for PA-50 and PA-41. Success would ready PA-50 and PA-41 for human clinical testing and would constitute a key milestone in the development of innovative new agents that may address key challenges of the C. difficile epidemic. PUBLIC HEALTH RELEVANCE: Clostridium difficile is a spore-forming bacterium that represents the leading cause of hospital-acquired diarrhea and affects approximately 500,000 individuals annually in the US. Unusually deadly strains have emerged in recent years, and new treatments are urgently needed. C. difficile infection (CDI) typically strikes individuals who are taking antibiotics, which can disrupt the protective gut microbes and provide an opportunity for C. difficile to flourish. C. difficile produces toxins that can damage the cells that line the large intestines. One experimental treatment strategy is to block with harmful effects of the toxins with monoclonal antibodies. We have developed novel antibodies that potently neutralize C. difficile toxins in preclinical models of CDI. In this project, we seek to complete studies that will ready our antitoxin antibodies for clinical testing as non- antibiotic therapies for CDI.