NTD Highlight Notice: Defining and leveraging the mechanism of action of suramin for treatment of trypanosomiasis.

锥虫是高度分化的原生动物；许多原生动物，包括本申请的主题布氏锥虫，寄生于人类及其家畜，而其他物种对植物和整个生物圈有巨大影响。由于与人类的进化距离很远，它们的许多生物学特性与我们的不同，经常被认为是进行治疗干预的潜在机会。药物治疗是有限的，大多数是剧毒的，并且出现了耐药性。由于表面结构复杂，接种疫苗不太可能是一种治疗选择。在现有的药物中，大约70年前首次推出的苏拉明仍然是早期疾病治疗的首选药物。然而，苏拉明被带入寄生虫或发挥杀胰酶活性的机制(S)仍不清楚。布氏毛滴虫在其许多哺乳动物宿主体内能长期存活，这得益于抗原的变异。单变型表面糖蛋白(VSG)在寄生虫表面表达密度极高。这种皮毛的定期更换是为了防止整个种群的免疫消除。免疫逃避系统的第二个方面是高效的内体转运，负责清除表面结合的免疫球蛋白。此外，一些丰富的非变异表面蛋白也是已知的；这些不变的表面糖蛋白(ISGs)也非常有效地内化。ISG家族中的两个，ISG65和ISG75通过泛素依赖的机制相对较快地被翻转。因此，内吞作用可能是一种有吸引力的将化合物输送到寄生虫内部的方法，如果有一种机制可以针对锥虫体内的特异杀锥虫药物。最近，我们使用RNA干扰进行了全基因组筛选，以确定与锥体对苏拉明敏感有关的基因产物。其中许多参与内吞作用，包括ISG75家族，但相当多的没有已知的功能。这项申请旨在更详细地探索这些蛋白质，并发现可能在苏拉明摄取和杀胰酶作用中发挥作用的其他因素。我们将研究ISG75是否代表苏拉明的真实受体，将更多的基因产物与内吞作用联系起来，并探索利用ISG75作为一种手段，将杀锥虫化合物特异性地运送到锥虫体内，以获得治疗收益。该工作计划将进一步提高我们对苏拉明作用模式的了解，更详细地描绘与寄生虫相互作用的途径，并提供更精确定义的治疗见解和靶点。此外，该计划将探索一种潜在的新方法来传递从这项工作中出现的杀锥虫化合物，这可能具有广泛的适用性。

Trypanosomatids are highly divergent protozoa; many, including the subject of this application, Trypanosoma brucei, are parasitic to humans and their livestock, while other species have huge impact on plants and the biosphere in general. Due to great evolutionary distance from humans, much of their biology is distinct from ours, and frequently cited as a potential opportunity for therapeutic intervention. Drug therapies are limited, with most being highly toxic and with emerging resistance. Due to complex surface architecture, vaccination is an unlikely therapeutic option. Of the available drugs, suramin, first introduced some 70 years ago, remains a drug of choice for early stage disease treatment. However, the mechanism(s) by which suramin is taken into the parasite or exerts trypanocidal activity have remained unknown. T. brucei survives for long periods within many of its mammalian hosts, facilitated by antigenic variation. A single variant surface glycoprotein (VSG) is expressed to extremely high density on the parasite surface. Periodic switching of this coat serves to prevent immunological elimination of the entire population. A second aspect of the immune evasion system is highly efficient endosomal trafficking, responsible for removing surface-bound immunoglobulin. Further, several abundant non-variant surface proteins are also known; these 'invariant' surface glycoproteins (ISGs) are also internalized extremely efficiently. Two of the ISG families, ISG65 and ISG75 are turned over comparatively rapidly, via a ubiquitin-dependent mechanism. Endocytosis then may represent an attractive means to deliver compounds to the parasite interior, if a mechanism were available to target trypanocidal agents specifically to the trypanosome. Most recently, we performed a genome wide screen using RNA interference to identify the gene products that are involved in the sensitization of trypanosomes to suramin. Many of these are involved in endocytosis, including the ISG75 family, but a substantial number have no known function. This application seeks to explore these proteins in more detail, and also to uncover additional factors that may play roles in suramin uptake and trypanocidal action. We shall examine if ISG75 represents the true receptor for suramin, link additional gene products with endocytosis, and explore the possibility of exploiting ISG75 as a means to specifically deliver trypanocidal compounds to the interior of the trypanosome, for therapeutic gain. The program of work will further improve our understanding of the mode of action of suramin, delineating pathways of interaction with the parasite in even greater detail, and offering more precisely defined therapeutic insights and targets. Further, the program will explore a potentially novel approach to delivery of trypanocidal compounds emerging from this work, which may have broad applicability.