Cryptococcus neoformans (Cn) is the leading cause of fungal meningitis, a deadly disease with limited therapeutic options. Dissemination to the central nervous system hinges on the ability of Cn to breach the blood-brain barrier (BBB) and is considered an attribute of Cn virulence. Targeting virulence instead of growth for antifungal drug development has not been fully exploited despite the benefits of this approach. Mpr1 is a secreted fungal metalloprotease not required for fungal growth, but rather, it functions as a virulence factor by facilitating Cn migration across the BBB. This central role for Mpr1, its extracellular location, and lack of expression in mammalian cells make Mpr1 a high-value target for an antivirulence approach aimed at developing therapeutics for cryptococcal meningitis. To test this notion, we devised a large-scale screen to identify compounds that prohibited Cn from crossing the BBB by selectively blocking Mpr1 proteolytic activity, without inhibiting the growth of Cn A phytochemical natural product-derived library was screened to identify new molecular scaffolds of prototypes unique to a Cn microecosystem. Of the 240 pure natural products examined, 3 lead compounds, abietic acid, diosgenin, and lupinine inhibited Mpr1 proteolytic activity with 50% inhibitory concentration (IC50) values of <10 μM, displayed little to no mammalian cell toxicity, and did not affect Cn growth. Notably, the lead compounds blocked Cn from crossing the BBB, without damaging the barrier integrity, suggesting the bioactive molecules had no off-target effects. We propose that these new drug scaffolds are promising candidates for the development of antivirulence therapy against cryptococcal meningitis.IMPORTANCE Fungal infections like cryptococcal meningitis are difficult to resolve because of the limited therapies available. The small arsenal of antifungal drugs reflect the difficulty in finding available targets in fungi because like mammalian cells, fungi are eukaryotes. The limited efficacy, toxicity, and rising resistance of antifungals contribute to the high morbidity and mortality of fungal infections and further underscore the dire but unmet need for new antifungal drugs. The traditional approach in antifungal drug development has been to target fungal growth, but an attractive alternative is to target mechanisms of pathogenesis. An important attribute of Cryptococcus neoformans (Cn) pathogenesis is its ability to enter the central nervous system. Here, we describe a large-scale screen that identified three natural products that prevented Cn from crossing the blood-brain barrier by inhibiting the virulence factor Mpr1 without affecting the growth of Cn We propose that compounds identified here could be further developed as antivirulence therapy that would be administered preemptively or serve as a prophylactic in patients at high risk for developing cryptococcal meningitis.

译文

新型隐球菌 (Cn) 是真菌性脑膜炎的主要原因,真菌性脑膜炎是一种致命的疾病,治疗选择有限。传播到中枢神经系统取决于Cn突破血脑屏障 (BBB) 的能力,被认为是Cn毒力的属性。尽管这种方法的好处,但尚未充分利用针对抗真菌药物开发的毒力而不是生长。Mpr1是真菌生长不需要的分泌性真菌金属蛋白酶,而是通过促进Cn在BBB上的迁移而充当毒力因子。Mpr1的核心作用,其细胞外位置以及在哺乳动物细胞中缺乏表达,使Mpr1成为旨在开发隐球菌性脑膜炎治疗药物的抗病毒方法的高价值靶标。为了验证这一概念,我们设计了一种大规模筛选,通过选择性阻断Mpr1蛋白水解活性来鉴定禁止Cn穿越BBB的化合物,而不抑制Cn的生长。筛选了植物化学天然产物衍生的文库,以鉴定Cn微生态系统特有的新分子支架。在所检查的240种纯天然产物中,3种铅化合物,松香酸,diosgenin和lupine抑制Mpr1蛋白水解活性,50% 抑制浓度 (IC50) 值为   <10μm,几乎没有哺乳动物细胞毒性,并且不影响Cn生长。值得注意的是,铅化合物阻止Cn穿过BBB,而不损害屏障的完整性,表明生物活性分子没有脱靶作用。我们建议这些新的药物支架是开发抗隐球菌性脑膜炎的抗病毒治疗的有希望的候选者。重要的是真菌感染,如隐球菌性脑膜炎很难解决,因为可用的治疗有限。抗真菌药物的小武库反映了在真菌中寻找可用靶标的困难,因为像哺乳动物细胞一样,真菌是真核生物。抗真菌药物的有限功效,毒性和不断上升的耐药性导致了真菌感染的高发病率和死亡率,并进一步强调了对新抗真菌药物的迫切但未得到满足的需求。抗真菌药物开发的传统方法是靶向真菌生长,但有吸引力的替代方法是靶向发病机制。新型隐球菌 (Cn) 发病的一个重要属性是其进入中枢神经系统的能力。在这里,我们描述了一个大规模的筛选,该筛选确定了三种天然产物,它们通过抑制毒力因子Mpr1而不影响Cn的生长而阻止Cn穿过血脑屏障。发生隐球菌性脑膜炎的高风险。

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