Department of Biotechnology, Chemistry and Pharmacy - Department of Excellence 2018-2022, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy.
Department of Life Science, University of Modena and Reggio Emilia, Via Campi 103, 41125 Modena, Italy.
Acta Crystallogr D Struct Biol. 2020 Jun 1;76(Pt 6):558-564. doi: 10.1107/S2059798320004891. Epub 2020 May 29.
The protozoan parasite Trypanosoma brucei is the etiological agent of human African trypanosomiasis (HAT). HAT, together with other neglected tropical diseases, causes serious health and economic issues, especially in tropical and subtropical areas. The classical antifolates targeting dihydrofolate reductase (DHFR) are ineffective towards trypanosomatid parasites owing to a metabolic bypass by the expression of pteridine reductase 1 (PTR1). The combined inhibition of PTR1 and DHFR activities in Trypanosoma parasites represents a promising strategy for the development of new effective treatments for HAT. To date, only monocyclic and bicyclic aromatic systems have been proposed as inhibitors of T. brucei PTR1 (TbPTR1); nevertheless, the size of the catalytic cavity allows the accommodation of expanded molecular cores. Here, an innovative tricyclic-based compound has been explored as a TbPTR1-targeting molecule and its potential application for the development of a new class of PTR1 inhibitors has been evaluated. 2,4-Diaminopyrimido[4,5-b]indol-6-ol (1) was designed and synthesized, and was found to be effective in blocking TbPTR1 activity, with a K in the low-micromolar range. The binding mode of 1 was clarified through the structural characterization of its ternary complex with TbPTR1 and the cofactor NADP(H), which was determined to 1.30 Å resolution. The compound adopts a substrate-like orientation inside the cavity that maximizes the binding contributions of hydrophobic and hydrogen-bond interactions. The binding mode of 1 was compared with those of previously reported bicyclic inhibitors, providing new insights for the design of innovative tricyclic-based molecules targeting TbPTR1.
原生动物寄生虫布氏锥虫是人类非洲锥虫病（HAT）的病原体。HAT 与其他被忽视的热带病一起，给热带和亚热带地区带来了严重的健康和经济问题。经典的抗叶酸类药物针对二氢叶酸还原酶（DHFR），但由于表达蝶呤还原酶 1（PTR1）的代谢旁路，对锥虫寄生虫无效。在锥虫寄生虫中联合抑制 PTR1 和 DHFR 的活性是开发新的有效的 HAT 治疗方法的有前途的策略。迄今为止，只有单环和双环芳族系统被提议作为 T. brucei PTR1（TbPTR1）的抑制剂；然而，催化腔的大小允许容纳扩展的分子核心。在这里，探索了一种基于三环的化合物作为 TbPTR1 靶向分子，并评估了其作为开发新型 PTR1 抑制剂的潜在应用。设计并合成了 2,4-二氨基嘧啶并[4,5-b]吲哚-6-醇（1），并发现其有效阻断 TbPTR1 活性，K 值在低微摩尔范围内。通过与 TbPTR1 和辅因子 NADP（H）的三元复合物的结构表征阐明了 1 的结合模式，其分辨率为 1.30 Å。该化合物在腔内采用类似底物的取向，最大限度地提高了疏水性和氢键相互作用的结合贡献。将 1 的结合模式与先前报道的双环抑制剂进行比较，为设计针对 TbPTR1 的创新三环类分子提供了新的见解。
