Methionyl-tRNA synthetase (MetRS) has been chemically validated as a drug target in the kinetoplastid parasite Trypanosoma brucei. In the present study, we investigate the validity of this target in the related trypanosomatid Leishmania donovani. Following development of a robust high-throughput compatible biochemical assay, a compound screen identified DDD806905 as a highly potent inhibitor of LdMetRS (K_i of 18 nM). Crystallography revealed this compound binds to the methionine pocket of MetRS with enzymatic studies confirming DDD806905 displays competitive inhibition with respect to methionine and mixed inhibition with respect to ATP binding. DDD806905 showed activity, albeit with different levels of potency, in various Leishmania cell-based viability assays, with on-target activity observed in both Leishmania promastigote cell assays and a Leishmania tarentolae in vitro translation assay. Unfortunately, this compound failed to show efficacy in an animal model of leishmaniasis. We investigated the potential causes for the discrepancies in activity observed in different Leishmania cell assays and the lack of efficacy in the animal model and found that high protein binding as well as sequestration of this dibasic compound into acidic compartments may play a role. Despite medicinal chemistry efforts to address the dibasic nature of DDD806905 and analogues, no progress could be achieved with the current chemical series. Although DDD806905 is not a developable antileishmanial compound, MetRS remains an attractive antileishmanial drug target.

中文翻译：

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甲硫氨酰-tRNA 合成酶作为多诺瓦尼利什曼原虫的药物靶标的化学验证

甲硫氨酰-tRNA 合成酶 (MetRS) 已被化学验证为动质体寄生虫布氏锥虫的药物靶标。在本研究中，我们调查了该目标在相关锥虫利什曼原虫中的有效性。随着稳健的高通量兼容生化检测方法的开发，化合物筛选将 DDD806905 鉴定为Ld MetRS ( K _i18纳米）。晶体学显示该化合物与 MetRS 的蛋氨酸袋结合，酶学研究证实 DDD806905 对蛋氨酸表现出竞争性抑制作用，对 ATP 结合表现出混合抑制作用。DDD806905 在各种基于利什曼原虫细胞的活力测定中显示出活性，尽管效力水平不同，在利什曼原虫前鞭毛体细胞测定和利什曼原虫体外翻译测定中都观察到了靶向活性。不幸的是，这种化合物未能在利什曼病动物模型中显示出功效。我们调查了在不同利什曼原虫中观察到的活动差异的潜在原因细胞测定和动物模型中缺乏功效，并发现高蛋白质结合以及这种二元化合物螯合到酸性隔室中可能起作用。尽管药物化学努力解决 DDD806905 和类似物的二元性质，但目前的化学系列没有取得任何进展。尽管 DDD806905 不是一种可开发的杀虫化合物，但 MetRS 仍然是一种有吸引力的杀虫药物靶点。