Purine biosynthesis as a therapeutic target for Helicobacter pylori infection

幽门螺杆菌是一种革兰氏阴性微需氧细菌，也是人类最常见的细菌病原体之一，慢性感染大约一半的世界人口的胃粘膜。虽然感染可能是无症状的，但幽门螺杆菌会导致慢性炎症、十二指肠和胃溃疡、胃粘膜相关淋巴组织(MALT)淋巴瘤和胃癌。作为人类癌症的诱因，幽门螺杆菌被世界卫生组织列为I类致癌物质。 除非根除幽门螺杆菌，否则幽门螺杆菌感染将持续一生。针对幽门螺杆菌的抗菌疗法是可用的，但它们需要在至少7天的过程中结合质子泵抑制剂的多种药物方案。除了患者依从性的问题外，对常用抗生素的耐药性正在成为一个重要的问题。因此，迫切需要新的抗菌药来治疗幽门螺杆菌。即便如此，通过抗菌疗法成功根除并不能预防随后的感染。对抗幽门螺杆菌的另一种方法是接种疫苗。 目前探索/发展研究基金的目标是评估参与嘌呤生物合成的肌苷5‘-单磷酸脱氢酶(IMPDH)作为幽门螺杆菌的可行药物靶点。我们已经认识到在体外可以抑制幽门螺杆菌IMPDH和幽门螺杆菌生长的化合物。在这里，我们将评估新的化合物，这些化合物在小鼠口服时没有显示出250 mg/kg的毒性，并且已经由我们的同事Lizbeth Hedstrom博士(Brandeis大学)在小鼠隐孢子虫病模型中进行了测试。我们将在体外和幽门螺杆菌感染的小鼠模型中测试这些药物对幽门螺杆菌的生长抑制作用。我们还构建了一株编码IMPDH基因(GuaB)缺失的幽门螺杆菌菌株。我们已经证明该突变体是营养缺陷型的，并且缺乏IMPDH活性。在这里，我们将测试幽门螺杆菌guaB突变体是否在小鼠感染模型中减弱。随后，它将作为一种活疫苗进行评估，以提供对幽门螺杆菌感染的保护。如果疫苗接种有效，将确定保护机制和保护性抗原。如果guaB突变体没有得到足够的减毒，将测试具有不同营养缺乏症要求的其他嘌呤生物合成突变体。这项建议中的实验是确定嘌呤生物合成是否代表幽门螺杆菌可行的治疗靶点的适当的第一步。 公共卫生相关性：幽门螺杆菌感染世界50%的人口的胃；它可导致慢性炎症、十二指肠和胃溃疡、胃粘膜相关淋巴组织(MALT)淋巴瘤和胃癌。这项探索/发展研究基金的目标是使用幽门螺杆菌感染的小鼠模型来评估我们的合作者Brandeis大学的Lizbeth Hedstrom博士提供的肌苷5‘-单磷酸脱氢酶(IMPDH)抑制剂作为抗菌剂。此外，我们将确定编码IMPDH基因突变的幽门螺杆菌菌株是否可以用作疫苗来预防幽门螺杆菌感染。

DESCRIPTION (provided by applicant Helicobacter pylori is a Gram-negative, microaerophilic bacterium and one of the most common human bacterial pathogens, chronically infecting the gastric mucosa of approximately half of the world's population. While infection can be asymptomatic, H. pylori can cause chronic inflammation, duodenal and gastric ulcers, gastric mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric cancer. As the causative agent of human cancer, H. pylori is considered a class I carcinogen by the WHO. H. pylori infection persists throughout life unless the organism is eradicated. Antimicrobial therapies against H. pylori are available, but they require multidrug regimens in combination with proton-pump inhibitors, over the course of at least 7 days. In addition to problems with patient compliance, resistance to commonly used antibiotics is becoming an important problem. Thus, there is an urgent need for new antimicrobials to treat H. pylori. Even so, successful eradication via antimicrobial therapy does not protect against subsequent infection. Another approach to combat H. pylori is vaccination. The goal of the current Exploratory/Developmental Research Grant is to evaluate the enzyme inosine 5'- monophosphate dehydrogenase (IMPDH), involved in purine biosynthesis, as a viable drug target for H. pylori. We have already recognized compounds that can inhibit H. pylori IMPDH and the growth of H. pylori in vitro. Here we will evaluate newer compounds that display no toxicity at 250 mg/kg when given orally to mice and have been already been tested by our colleague Dr. Lizbeth Hedstrom (Brandeis University) in a mouse model of cryptosporidiosis. We will test these for growth inhibition of H. pylori in vitro and in a mouse model of H. pylori infection. We have also constructed an H. pylori strain with a deletion in the gene (guaB) that encodes IMPDH. We have shown that this mutant is auxotrophic and lacks IMPDH activity. Here, we will test whether the H. pylori ¿guaB mutant is attenuated in a mouse model of infection. Subsequently, it will be evaluated as a live vaccine to provide protection against H. pylori infection. If vaccination is effective, the mechanism of protection and protective antigens will be identified. If the ¿guaB mutant is not sufficiently attenuated other purine biosynthetic mutants with different auxotrophic requirements will be tested. The experiments in this proposal are the appropriate first steps to determine whether purine biosynthesis represents a viable therapeutic target for H. pylori. PUBLIC HEALTH RELEVANCE: Helicobacter pylori infect the stomach of 50% of the world's population; it can cause chronic inflammation, duodenal and gastric ulcers, gastric mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric cancer. The goal of this Exploratory/Developmental Research Grant is to use mouse models of H. pylori infection to evaluate inhibitors of inosine 5'-monophosphate dehydrogenase (IMPDH) that are available from our collaborator Dr. Lizbeth Hedstrom (Brandeis University) as antimicrobial agents. Further, we will determine whether an H. pylori strain mutated in the gene encoding IMPDH can be used as a vaccine to protect against H. pylori infection.