A new target for malaria drug development

描述（由申请人提供）：疟疾是一种媒介传播的疾病，全世界每年有2 -3亿人感染。该病由四种疟原虫属单细胞寄生虫中的任何一种感染红细胞引起。当由恶性疟原虫引起时，疟疾会危及生命，导致1至200万人死亡，主要是幼儿。目前的治疗方法受到寄生虫耐药性日益增强的影响，而且开发疫苗的努力受到疟原虫生命周期的严重限制；因此，需要新的治疗方法。最近对最致命的疟原虫恶性疟原虫的基因组测序发现，哺乳动物和蓝藻中的两个腺苷酸环化酶基因（PfACs）与碳酸氢盐反应性可溶性腺苷酸环化酶（sAC）相关。它们的序列预测了pfac对碳酸氢盐的反应，我们假设至少有一个是疟原虫对高水平二氧化碳/碳酸氢盐生存的绝对依赖的原因。因此，pfac可能是抗疟药物的新靶点。我们用我们开发的一种小分子（KH7）治疗恶性疟原虫，这种小分子可以抑制迄今为止测试过的所有sac样环化酶，包括在哺乳动物、单细胞真核生物和细菌中发现的sac样环化酶。在红细胞中培养的寄生虫被KH7在单个细胞周期内以剂量依赖的方式杀死。一种结构相关的化合物（KH7.15）对sac样环化酶具有惰性，对寄生虫的生长没有影响。在本次拨款申请中，我们拟克隆并表征这两种PfAC环化酶，并确认它们是否是KH7致死的目标。如果pfac被证实为新的抗疟疾药物的靶点，我们建议使用纯化的疟原虫环化酶筛选化学文库，以确定相对于人类sAC的疟原虫环化酶选择性化合物。

DESCRIPTION (provided by applicant): Malaria is vector-borne disease infecting 200-300 million people per year worldwide. It is caused by infection of red blood cells by any one of four unicellular parasites from the genus Plasmodium. When caused by Plasmodium falciparum, malaria is life threatening, resulting in 1-2 million deaths, primarily in young children. Current treatments suffer from increasing resistance among parasites and efforts to develop a vaccine are severely limited by the Plasmodium life cycle; therefore, new treatments are needed. The recently sequenced genome of the most lethal malarial parasite, Plasmodium falciparum, revealed two adenylyl cyclase genes (PfACs) related to the bicarbonate responsive soluble adenylyl cyclases (sAC) in mammals and cyanobacteria. Their sequences predict the PfACs to be bicarbonate responsive, and we hypothesized that at least one is responsible for Plasmodium's absolute dependence on high levels of carbon dioxide/bicarbonate for viability. Therefore, the PfACs may represent new targets for an antimalarial drug. We treated P. falciparum with a small molecule (KH7) we developed which inhibits all sAC-like cyclases tested thus far, including sAC-like cyclases found in mammals, unicellular eukaryotes and bacteria. Parasites cultured in red blood cells were killed by KH7 in a dose dependent manner within a single cell cycle. A structurally related compound (KH7.15) which is inert towards sAC-like cyclases had no effect on parasite growth. In this grant application, we propose to clone and characterized the two PfAC cyclases and confirm whether they are the target of KH7 lethality. If the PfACs are validated as targets for new antimalarial drugs, we propose to use purified Plasmodium cyclases to screen a chemical library to identify compounds selective for Plasmodium cyclases relative to human sAC.