School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia; Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia; Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia.
Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia.
Bioorg Med Chem. 2018 Nov 1;26(20):5408-5419. doi: 10.1016/j.bmc.2018.09.004. Epub 2018 Sep 5.
Fungi cause serious life-threatening infections in immunocompromised individuals and current treatments are now complicated by toxicity issues and the emergence of drug resistant strains. Consequently, there is a need for development of new antifungal drugs. Inosine monophosphate dehydrogenase (IMPDH), a key component of the de novo purine biosynthetic pathway, is essential for growth and virulence of fungi and is a potential drug target. In this study, a high-throughput screen of 114,000 drug-like compounds against Cryptococcus neoformans IMPDH was performed. We identified three 3-((5-substituted)-1,3,4-oxadiazol-2-yl)thio benzo[b]thiophene 1,1-dioxides that inhibited Cryptococcus IMPDH and also possessed whole cell antifungal activity. Analogs were synthesized to explore the SAR of these hits. Modification of the fifth substituent on the 1,3,4-oxadiazole ring yielded compounds with nanomolar in vitro activity, but with associated cytotoxicity. In contrast, two analogs generated by substituting the 1,3,4-oxadiazole ring with imidazole and 1,2,4-triazole gave reduced IMPDH inhibition in vitro, but were not cytotoxic. During enzyme kinetic studies in the presence of DTT, nucleophilic attack of a free thiol occurred with the benzo[b]thiophene 1,1-dioxide. Two representative compounds with substitution at the 5 position of the 1,3,4-oxadiazole ring, showed mixed inhibition in the absence of DTT. Incubation of these compounds with Cryptococcus IMPDH followed by mass spectrometry analysis showed non-specific and covalent binding with IMPDH at multiple cysteine residues. These results support recent reports that the benzo[b]thiophene 1,1-dioxides moiety as PAINS (pan-assay interference compounds) contributor.
真菌在免疫功能低下的个体中引起严重的危及生命的感染，而目前的治疗方法现在因毒性问题和耐药菌株的出现而变得复杂。因此，需要开发新的抗真菌药物。肌苷单磷酸脱氢酶（IMPDH）是从头嘌呤生物合成途径的关键组成部分，对真菌的生长和毒力至关重要，是一个潜在的药物靶点。在这项研究中，对 114000 种类似药物的化合物对新型隐球菌 IMPDH 进行了高通量筛选。我们鉴定了三种 3-（（5-取代）-1,3,4-噁二唑-2-基）硫代苯并[b]噻吩 1,1-二氧化物，它们抑制新型隐球菌 IMPDH 并具有全细胞抗真菌活性。合成了类似物来探索这些命中化合物的 SAR。对 1,3,4-噁二唑环上的第五个取代基进行修饰，得到了具有纳摩尔体外活性的化合物，但具有相关的细胞毒性。相比之下，用咪唑和 1,2,4-三唑取代 1,3,4-噁二唑环生成的两种类似物，体外 IMPDH 抑制作用降低，但无细胞毒性。在 DTT 存在下进行酶动力学研究时，发生了亲核攻击游离硫醇，与苯并[b]噻吩 1,1-二氧化物发生反应。两个在 1,3,4-噁二唑环的 5 位具有取代基的代表性化合物在没有 DTT 的情况下表现出混合抑制作用。将这些化合物与新型隐球菌 IMPDH 孵育后进行质谱分析表明，在多个半胱氨酸残基处与 IMPDH 发生非特异性和共价结合。这些结果支持最近的报道，即苯并[b]噻吩 1,1-二氧化物部分作为 PAINS（泛分析干扰化合物）的贡献者。
