Evaluation of Small Molecule Inhibitors of Hemoglobin Transport as Antimalarials

描述（由申请人提供）：我们开发了一种新的模型，用于红细胞内恶性疟原虫疟疾寄生虫中血红蛋白从宿主红细胞胞质溶胶内化和转运到消化空泡（DV）。通过电子显微镜检查疟疾感染的红细胞（IRBC）的连续切片显示，细胞口延伸到寄生虫消化空泡（DV）并与之融合，从而将血红蛋白输送给寄生虫。这个过程依赖于肌动蛋白动力学，因为稳定肌动蛋白丝的试剂阻止了血红蛋白向DV的递送。此外，我们证明了血红蛋白向DV的递送是一个专性过程，因为该过程的抑制抑制了寄生虫的发育并导致寄生虫死亡。最近，使用一种特定的小分子GT3抑制剂，我们破坏了细胞口形态，并阻止血红蛋白运输到DV，导致寄生虫发育的逮捕。我们的新发现表明，抑制血红蛋白递送到DV对恶性疟原虫是致命的，因此验证了该过程作为抗疟治疗的新靶点。我们试图利用我们的观察，开发一种体外测定，以监测血红蛋白转运到DV（作为读出），并使用它来筛选抑制这一过程和寄生虫发展的化合物的小分子库。在进入体内试验之前，将对来自小分子筛选的阳性命中进行体外验证实验。干扰血红蛋白转运系统是开发抗疟药的独特方法。鉴于迫切需要新的药物目标和抗疟疾药物，以及全世界数百万人受疟疾折磨，该项目的潜在影响非常大。 公共卫生相关性：消化空泡血红蛋白蛋白酶抑制剂正在被评估为抗疟药。报告表明这些蛋白酶中存在很大的功能冗余，并且似乎治疗需要抑制许多不同的蛋白酶。我们认为，上游细胞口血红蛋白运输系统可能是一个更好的目标。新的靶向发生在恶性疟原虫感染的红细胞而不是宿主细胞中的独特过程可能导致全新的抗疟化学型，其通过新的机制发挥作用，而不受对现有疗法的交叉耐药性的困扰。如果抑制剂被确定，那么我们将有一个合理的目标，通过合理的过程获得，这可以发展成为一个严重的健康问题的药物发现计划。

DESCRIPTION (provided by applicant): We've developed a new model for the internalization and transport of hemoglobin from host erythrocyte cytosol to the digestive vacuole (DV) in intraerythrocytic Plasmodium falciparum malaria parasites. The examination of serial sections by electron microscopy of malaria infected erythrocytes (IRBC) revealed that cytostomes extend to and fuse with the parasite digestive vacuole (DV), thereby delivering hemoglobin to the parasite. This process was dependent on actin dynamics, as agents that stabilize actin filaments prevented the delivery of hemoglobin to the DV. Furthermore, we demonstrated that the delivery of hemoglobin to the DV was an obligate process, as inhibition of this process inhibited parasite development and caused parasite death. More recently, using a specific small molecule GTPase inhibitor, we disrupted the cytostome morphology and prevented hemoglobin transport to the DV, resulting in the arrest of parasite development. Our new discoveries reveal that the inhibition of hemoglobin delivery to the DV is lethal to P. falciparum parasites and as a result validated this process as a new target for antimalarial therapy. We seek to capitalize on our observations to develop an in vitro assay to monitor hemoglobin transport to the DV (as a read out) and use it to screen a small molecule library for compounds that inhibit this process and parasite development. Validation experiments in vitro of positive hits from the small molecule screen will be performed prior to moving into in vivo testing down the road. Perturbing the hemoglobin transport system represents a unique approach for developing antimalarials. Given the urgent need for new drug targets and antimalarials and the millions of people worldwide afflicted by malaria, the potential impact of this project is very high. PUBLIC HEALTH RELEVANCE: Inhibitors of digestive vacuole hemoglobin proteases are being evaluated as antimalarials. Reports indicate great functional redundancy in these proteases and it appears that therapy would need to inhibit many different proteases. We believe the upstream cytostomal hemoglobin transport system may be a better target. Novel targeting of a unique process that occurs in Plasmodium falciparum infected erythrocytes and not in host cells could lead to entirely new antimalarial chemotypes that act by novel mechanisms untroubled by cross resistance to existing therapeutics. If inhibitors are identified then we will have a rational target, obtained by a rational process, which can be developed into a drug discovery program for a serious health problem.