Anti-Toxoplasma isoprenoid pathway inhibitors and the host immune response

弓形虫是一种机会性病原体，在免疫功能低下的患者中会导致严重疾病。大多数人类感染是无症状的，但器官移植、癌症化疗或感染艾滋病毒引起的免疫抑制可能会导致感染重新激活。此外，怀孕期间胎儿感染会导致先天性弓形虫病。一些弓形虫菌株还会导致免疫功能正常的患者患上严重的眼病。弓形虫病的治疗面临着缺乏根除慢性感染的有效药物的挑战，多达50%的接受治疗的患者对治疗没有反应。目前使用的大多数药物在中枢神经系统的分布很差，它们会在大量患者中引发过敏反应。迫切需要安全有效的弓形虫病治疗方法。弓形虫在其宿主细胞内复制，并巧妙地操纵宿主细胞，以确保其生存和复制的有利条件。弓形虫感染导致多种宿主信号和代谢途径的不同调节。其中许多宿主的变化还不完全清楚，但很可能是宿主途径的改变对寄生虫的生长和生存是必不可少的。异戊二烯类化合物是自然界中种类最多、含量最丰富的化合物。许多类型的异戊二烯(如类固醇、胆固醇、维甲酸、类胡萝卜素、泛醌、戊二烯基蛋白)是所有生物体细胞结构的重要组成部分，因为它们在各种生物过程中扮演着重要的角色。所有的异戊二烯类化合物都来自一种常见的前体异戊烯基焦磷酸酯及其异构体二甲基烯丙基焦磷酸酯，它们是通过甲氧戊酸途径在哺乳动物细胞中合成的。甲氧丙戊酸途径是他汀类药物和双膦酸类药物的药理靶点，这两种药物分别用于治疗高胆固醇血症和骨病。我们发现，极低剂量的亲脂性双膦酸盐以及他汀类和双膦酸盐的组合，可以保护小鼠免受致死剂量的弓形虫的感染。体内的协同作用结合药物(一些用于临床)，保护小鼠免于死亡，组合指数低于体外获得的部分抑制浓度的10倍。最近使用癌症模型的研究表明，某些他汀类或双膦酸盐通过抑制抗原提呈细胞中包括Rab5在内的小GTP酶的Geranylgeranyly，导致内体成熟受阻，延长抗原保留，并增强T细胞激活，在小鼠和猴子身上具有强大的佐剂活性。此外，抑制甲氧戊酸途径可诱导Th1反应和细胞溶解T细胞反应。我们的假设是，他汀类药物和双膦酸类药物联合治疗弓形虫感染的有效性涉及免疫系统的参与，这一策略可以用于对抗其他细胞内病原体的感染。我们将表征宿主免疫反应在结合宿主和寄生虫途径的抑制剂时所获得的协同效应的参与。

Toxoplasma gondii is an opportunistic pathogen that causes serious disease in immunocompromised patients. Most human infections are asymptomatic but immunosuppression due to organ transplant, cancer chemotherapy, or infection with HIV can lead to re-­activation of the infection. In addition, infection of the fetus during pregnancy causes congenital toxoplasmosis. Some strains of T. gondii also cause severe ocular disease in immunocompetent patients. Treatment for toxoplasmosis is challenged by lack of effective drugs to eradicate the chronic infection and as many as 50% of the treated patients do not respond to the therapy. Most of the drugs currently used are poorly distributed to the central nervous system and they trigger allergic reactions in a large number of patients. There is a compelling need for safe and effective treatments for toxoplasmosis. Toxoplasma replicates inside its host cell and masterfully manipulates the host cell to insure favorable conditions for its survival and replication. T. gondii infection results in differential regulation of a variety of host signaling and metabolic pathways. Many of these host changes are not completely understood but it is quite likely that modifications of host pathways are essential for parasite growth and survival. Isoprenoids are the most diverse and abundant compounds occurring in nature. Many types of isoprenoids (e.g. steroids, cholesterol, retinoids, carotenoids, ubiquinones, prenyl proteins) are essential components of the cellular machinery of all organisms due to their roles in a variety of biological processes. All isoprenoids derive from a common precursor, isopentenyl pyrophosphate, and its isomer, dimethylallyl pyrophosphate, which are synthesized in mammalian cells via the mevalonate pathway. The human mevalonate pathway is the pharmacological target of statins and bisphosphonates, drugs used clinically to treat hypercholesterolemia and bone disorders, respectively. We found that very low doses of lipophilic bisphosphonates and combinations of statins and bisphosphonates, protected mice against a lethal dose of Toxoplasma. The synergistic interaction in vivo combining drugs (some used in the clinics), protected mice against death at a combination index 10 times lower than the fractional inhibitory concentration obtained in vitro. Recent work using cancer models revealed that certain statins or bisphosphonates have potent adjuvant activity in mice and monkeys by inhibiting geranylgeranylation of small GTPases, including Rab5, in antigen presenting cells, resulting in arrested endosomal maturation, prolonged antigen retention, and enhanced T cell activation. In addition, inhibiting the mevalonate pathway induces both a Th1 and cytolytic T cell response. Our hypothesis is that the effectiveness of the combination of statins and bisphosphonates for the treatment of T. gondii infection involves the participation of the immune system and that this strategy could be used against infection of other intracellular pathogens. We will characterize the participation of the host immune response in the synergistic effect obtained when combining inhibitors of host and parasite pathways.