Queen Mary Pre-Clinical Drug Discovery Group, School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom.
Antimicrob Agents Chemother. 2013 Apr;57(4):1638-47. doi: 10.1128/AAC.02046-12. Epub 2013 Jan 18.
The nitroheterocycle nifurtimox, as part of a nifurtimox-eflornithine combination therapy, represents one of a limited number of treatments targeting Trypanosoma brucei, the causative agent of human African trypanosomiasis. The mode of action of this prodrug involves an initial activation reaction catalyzed by a type I nitroreductase (NTR), an enzyme found predominantly in prokaryotes, leading to the formation of a cytotoxic unsaturated open-chain nitrile metabolite. Here, we evaluate the trypanocidal activities of a library of other 5-nitrofurans against the bloodstream form of T. brucei as a preliminary step in the identification of additional nitroaromatic compounds that can potentially partner with eflornithine. Biochemical screening against the purified enzyme revealed that all 5-nitrofurans were effective substrates for T. brucei NTR (TbNTR), with the preferred compounds having apparent kcat/Km values approximately 50-fold greater than those of nifurtimox. For several compounds, in vitro reduction by this nitroreductase yielded products characterized by mass spectrometry as either unsaturated or saturated open-chain nitriles. When tested against the bloodstream form of T. brucei, many of the derivatives displayed significant growth-inhibitory properties, with the most potent compounds generating 50% inhibitory concentrations (IC50s) around 200 nM. The antiparasitic activities of the most potent agents were demonstrated to be NTR dependent, as parasites having reduced levels of the enzyme displayed resistance to the compounds, while parasites overexpressing TbNTR showed hypersensitivity. We conclude that other members of the 5-nitrofuran class of nitroheterocycles have the potential to treat human African trypanosomiasis, perhaps as an alternative partner prodrug to nifurtimox, in the next generation of eflornithine-based combinational therapies.
硝呋替莫，作为硝呋替莫-依氟鸟氨酸联合疗法的一部分，是针对引起人类非洲锥虫病的布氏锥虫的少数几种治疗方法之一。这种前药的作用模式涉及由 I 型硝基还原酶（NTR）催化的初始激活反应，该酶主要存在于原核生物中，导致形成细胞毒性不饱和开链腈代谢物。在这里，我们评估了针对布氏锥虫血液形式的其他 5-硝基呋喃类化合物文库的杀锥虫活性，作为鉴定可能与依氟鸟氨酸结合的其他硝基芳烃化合物的初步步骤。针对纯化酶的生化筛选表明，所有 5-硝基呋喃类化合物都是 T. brucei NTR（TbNTR）的有效底物，首选化合物的表观 kcat/Km 值比硝呋替莫大约高 50 倍。对于几种化合物，该硝基还原酶的体外还原生成的产物通过质谱鉴定为不饱和或饱和开链腈。当针对布氏锥虫的血液形式进行测试时，许多衍生物表现出显著的生长抑制特性，最有效的化合物产生 50%抑制浓度（IC50）约为 200 nM。最有效的制剂的抗寄生虫活性被证明是 NTR 依赖性的，因为酶水平降低的寄生虫对化合物表现出抗性，而过度表达 TbNTR 的寄生虫则表现出敏感性。我们得出结论，5-硝基呋喃类硝基杂环的其他成员有可能治疗人类非洲锥虫病，也许可以作为依氟鸟氨酸为基础的联合治疗方案的下一代硝呋替莫替代前药。
