Several trypanosomatid cyclic nucleotide phosphodiesterases (PDEs) possess a unique, parasite-specific cavity near the ligand-binding region that is referred to as the P-pocket. One of these enzymes, Trypanosoma brucei PDE B1 (TbrPDEB1), is considered a drug target for the treatment of African sleeping sickness. Here, we elucidate the molecular determinants of inhibitor binding and reveal that the P-pocket is amenable to directed design. By iterative cycles of design, synthesis, and pharmacological evaluation and by elucidating the structures of inhibitor-bound TbrPDEB1, hPDE4B, and hPDE4D complexes, we have developed 4a,5,8,8a-tetrahydrophthalazinones as the first selective TbrPDEB1 inhibitor series. Two of these, 8 (NPD-008) and 9 (NPD-039), were potent ( Ki = 100 nM) TbrPDEB1 inhibitors with antitrypanosomal effects (IC50 = 5.5 and 6.7 μM, respectively). Treatment of parasites with 8 caused an increase in intracellular cyclic adenosine monophosphate (cAMP) levels and severe disruption of T. brucei cellular organization, chemically validating trypanosomal PDEs as therapeutic targets in trypanosomiasis.

中文翻译：

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靶向布氏锥虫磷酸二酯酶B1（TbrPDEB1）中的亚型，可以实现具有锥虫杀虫作用的选择性抑制剂的基于结构的发现。

几种锥虫性环状核苷酸磷酸二酯酶（PDE）在配体结合区附近有一个独特的寄生虫特异性空腔，被称为P型口袋。这些酶之一是布鲁氏锥虫PDE B1（TbrPDEB1），被认为是治疗非洲昏睡病的药物靶标。在这里，我们阐明了抑制剂结合的分子决定因素，并揭示了P型口袋可用于定向设计。通过设计，合成和药理学评估的反复循环，并阐明与抑制剂结合的TbrPDEB1，hPDE4B和hPDE4D复合物的结构，我们开发了4a，5、8、8a-四氢邻苯二氮酮作为第一个选择性TbrPDEB1抑制剂系列。其中8种（NPD-008）和9种（NPD-039）是有效的（Ki = 100 nM）TbrPDEB1抑制剂，具有抗锥虫作用（IC50 = 5.5和6.7μM，分别）。用8处理寄生虫会导致细胞内环状单磷酸腺苷（cAMP）水平增加，布鲁氏菌（T. brucei）细胞组织受到严重破坏，化学验证了锥虫PDE作为锥虫病的治疗靶标。