With roughly 2 billion people infected, the neurotropic protozoan Toxoplasma gondii remains one of the most pervasive and infectious parasites. Toxoplasma infection is the second leading cause of death due to foodborne illness in the United States, causes severe disease in immunocompromised patients, and is correlated with several cognitive and neurological disorders. Currently, no therapies exist that are capable of eliminating the persistent infection in the central nervous system (CNS). In this study we report the identification of triazine nitrile inhibitors of Toxoplasma cathepsin L (TgCPL) from a high throughput screen and their subsequent optimization. Through rational design, we improved inhibitor potency to as low as 5 nM, identified pharmacophore features that can be exploited for isoform selectivity (up to 7-fold for TgCPL versus human isoform), and improved metabolic stability (t_1/2 > 60 min in mouse liver microsomes) guided by a metabolite ID study. We demonstrated that this class of compounds is capable of crossing the blood-brain barrier in mice (1:1 brain/plasma at 2 h). Importantly, we also show for the first time that treatment of T. gondii bradyzoite cysts in vitro with triazine nitrile inhibitors reduces parasite viability with efficacy equivalent to a TgCPL genetic knockout.

中文翻译：

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弓形虫组织蛋白酶 L 的三嗪腈抑制剂的发现和优化，用于潜在治疗中枢神经系统慢性弓形虫病。

大约有 20 亿人被感染，嗜神经性原生动物弓形虫仍然是最普遍和传染性最强的寄生虫之一。弓形虫感染是美国食源性疾病导致死亡的第二大原因，在免疫功能低下的患者中引起严重疾病，并与几种认知和神经系统疾病相关。目前，不存在能够消除中枢神经系统 (CNS) 持续感染的疗法。在这项研究中，我们报告了弓形虫组织蛋白酶 L ( Tg ) 的三嗪腈抑制剂的鉴定。CPL) 来自高通量筛选及其后续优化。通过合理的设计，我们将抑制剂效力提高到低至 5 nM，确定了可用于异构体选择性的药效团特征（Tg CPL 与人类异构体相比高达 7 倍），并提高了代谢稳定性 ( t _1/2 > 60在代谢物 ID 研究的指导下，小鼠肝微粒体中的 min）。我们证明了这类化合物能够穿过小鼠的血脑屏障（2 小时时脑/血浆 1:1）。重要的是，我们还首次证明用三嗪腈抑制剂在体外治疗刚地弓形虫缓殖子囊肿可降低寄生虫的存活率，其功效相当于Tg CPL 基因敲除。