Redox Balance & Drug Development in Schistosoma mansoni

描述(申请人提供)：血吸虫病是一种重要的热带寄生虫病。虽然一种有效的抗血吸虫病药物正在使用中，但据估计，仍有2亿人感染，2000万人出现严重的疾病症状，每年有28万人死于血吸虫病。此外，传播率随着药物的使用而略有变化，有证据表明抗药性寄生虫的发展。由于目前没有合适的替代疗法可用，因此迫切需要开发新的抗血吸虫药物。在这一应用中，我们建议重点研究寄生虫的生化氧化还原机制，作为抗血吸虫药物开发的新靶点。血吸虫在其最终宿主和中间宿主中必须能够在免疫和自身产生的活性氧化合物存在的情况下生存，并为许多关键的酶途径提供二硫化物还原当量。在大多数生物体中，存在两个平行的系统来提供氧化防御和还原能力，一个基于谷胱甘肽，另一个基于硫氧还蛋白。我们最近的研究结果表明，曼氏血吸虫具有与哺乳动物宿主完全不同的氧化还原机制。蠕虫中完全没有两种关键的氧化还原酶，谷胱甘肽还原酶和硫氧还蛋白还原酶。相反，这些活性共同存在于一种单一的硫氧还蛋白-谷胱甘肽还原酶(TGR)中。我们已经证明TGR是一种重要的寄生虫蛋白，抑制TGR会导致寄生虫死亡。在研究方案中，我们将：(1)基于我们已经确定的先导化合物合成潜在的TGR抑制剂，并测定它们对寄生虫和宿主酶的相对抑制活性以及它们对培养的蠕虫和哺乳动物细胞的毒性；(2)建立TGR催化机理的假说，这将进一步开发TGR抑制剂；(3)定义适合TGR结晶的条件，并确定其用于药物精制的三维结构。由于血吸虫体内的二硫键氧化还原平衡以单一的关键氧化还原酶为中心，与宿主机制有根本的不同，因此我们建议利用这一寄生虫途径作为合理药物设计的一个有希望的靶点。

DESCRIPTION (provided by applicant): Schistosomiasis is an important tropical parasitic human disease. Although an effective anti-schistosome drug is in use, it is estimated that 200 million people remain infected, 20 million individuals suffer severe disease symptoms, and 280,000 people die annually from schistosomiasis. Furthermore, transmission rates have changed a little with the use of the drug and there is evidence for the development of drug resistant parasites. Because there is currently no suitable alternative therapy available there is an urgent need for the development of novel antischistosomal agents. In this application we propose to focus on parasite biochemical redox mechanisms as novel targets for antischistosomal drug development. Schistosomes in their definitive and intermediate hosts must be able to survive in the presence of both immune and self generated reactive oxygen compounds and provide disulfide reducing equivalents for a number of critical enzymatic pathways. Two parallel systems to provide oxidative defense and reducing power occur in most organisms, one based on glutathione and the other based on thioredoxin. Our recent results indicate that Schistosoma mansoni has fundamentally different redox mechanisms from their mammalian host. Entirely absent from worms are two key redox enzymes, glutathione reductase and thioredoxin reductase. Instead, these activities are found together in a single protein thioredoxin-glutathione reductase (TGR). We have shown that TGR is an essential parasite protein and that inhibition of the TGR leads to parasite death. In the research proposal we will: (1) synthesize potential TGR inhibitors based on lead compounds we have already identified and determine their relative inhibitory activity against parasite and host enzymes and their toxicity to cultured worms and mammalian cells, (2) develop an hypothesis for the catalytic mechanism of TGR, which will further the development of TGR inhibitors and, (3) define conditions suitable for the crystallization of TGR and determine its 3D structure for drug refinement. Because disulfide redox balance in schistosomes is centered on a single key redox enzyme and is fundamentally different from host mechanisms we propose in exploit this parasite pathway as a promising target for rational drug design.