EFFICACY AND SAFETY IN MAMMALIAN SYSTEMS

在全世界范围内，疟疾是发病率和死亡率的主要原因;感染的发生率和流行率正在上升;抗药性寄生虫已变得司空见惯。人们普遍认为，迫切需要安全的新型抗疟药物。抗叶酸胸苷酸合成酶抑制剂是一类新的治疗药物，它们在体外具有有效的抗疟活性。与胸苷联合给药可增强选择性毒性。该项目将评估抗叶酸胸苷酸合成酶抑制剂在哺乳动物系统中的活性。测试化合物将包括那些已经上市或在临床试验中的化合物，以及新的化合物。本项目的目的1是评价胸苷酸合成酶抑制剂在有和没有伴随胸苷的情况下对小鼠或人细胞系的体外细胞毒性。这些研究的结果，结合抗疟效力，将为选择用于动物试验的化合物提供基础。还将分析处理细胞的细胞内核苷酸，作为胸苷酸合酶阻断程度和胸苷保护有效性的指示。在目标2中，选择的胸苷酸合成酶抑制剂， 单独或与胸苷组合，将在小鼠中测试抗伯氏疟原虫和约氏疟原虫。具有最大效力和选择性毒性的那些将是进一步临床前测试的候选者。目标3致力于人体胸苷的研究。胸苷是饮食中的非必需营养素，在血液中以亚微摩尔水平循环，并且已经在肠胃外使用超过60年来治疗各种临床疾病。值得注意的是，尽管如此，还没有人口服胸苷的正式研究。作为在疟疾患者中使用联合治疗的必要预备，将在口服胸苷治疗的健康志愿者中评价生物利用度、血浆水平和循环淋巴细胞中的核苷酸浓度。

On a worldwide basis, malaria is a leading cause of morbidity and mortality; the infection is increasing in incidence and prevalence; and drug-resistant parasites have become commonplace. The need for safe new antimalarials is widely acknowledged to be urgent. Antifolate thymidylate synthase inhibitors are a new class of therapeutic agents, and they have potent antimalarial activity in vitro. Selective toxicity is enhanced by coadministration with thymidine. This project will evaluate the activity of antifolate thymidylate synthase inhibitors in mammalian systems. Test compounds will include those already marketed or in clinical trials, as well as novel compounds. Aim 1 of this project is to evaluate the cytotoxicity of thymidylate synthase inhibitors, with and without concomitant thymidine, against mouse or human cell lines in vitro. Results of these studies, in conjunction with antimalarial potency, will provide a basis for selecting compounds for testing in animals. Treated cells will also be analyzed for intracellular nucleotides, as an indication of the extent of thymidylate synthase blockade and the effectiveness of thymidine protection. In Aim 2, selected thymidylate synthase inhibitors, alone or in combination with thymidine, will be tested against Plasmodium berghei and P. yoelii in mice. Those with greatest potency and selective toxicity will be candidates for further preclinical testing. Aim 3 is devoted to studies of thymidine in humans. Thymidine is a nonessential nutrient in the diet, circulates in submicromolar levels in the blood, and has been used parenterally for over 60 years to treat assorted clinical disorders. Remarkably, despite all this there has been no formal study of orally administered thymidine in humans. As a necessary preliminary to the use of combination therapy in patients with malaria, the bioavailability, plasma levels, and nucleotide concentrations in circulating lymphocytes, will be evaluated in healthy volunteers treated with orally administered thymidine.