In two previous studies, we identified compound 1 as a moderate GroEL/ES inhibitor with weak to moderate antibacterial activity against Gram-positive and Gram-negative bacteria including Bacillus subtilis, methicillin-resistant Staphylococcus aureus, Klebsiella pneumonia, Acinetobacter baumannii, and SM101 Escherichia coli (which has a compromised lipopolysaccharide biosynthetic pathway making bacteria more permeable to drugs). Extending from those studies, we developed two series of analogs with key substructures resembling those of known antibacterials, nitroxoline (hydroxyquinoline moiety) and nifuroxazide/nitrofurantoin (bis-cyclic-N-acylhydrazone scaffolds). Through biochemical and cell-based assays, we identified potent GroEL/ES inhibitors that selectively blocked E. faecium, S. aureus, and E. coli proliferation with low cytotoxicity to human colon and intestine cells in vitro. Initially, only the hydroxyquinoline-bearing analogs were found to be potent inhibitors in our GroEL/ES-mediated substrate refolding assays; however, subsequent testing in the presence of an E. coli nitroreductase (NfsB) in situ indicated that metabolites of the nitrofuran-bearing analogs were potent GroEL/ES inhibitor pro-drugs. Consequently, this study has identified a new target of nitrofuran-containing drugs, and is the first reported instance of such a unique class of GroEL/ES chaperonin inhibitors. The intriguing results presented herein provide impetus for expanded studies to validate inhibitor mechanisms and optimize this antibacterial class using the respective GroEL/ES chaperonin systems and nitroreductases from E. coli and the ESKAPE bacteria.

在之前的两项研究中，我们将化合物1鉴定为中度 GroEL/ES 抑制剂，对革兰氏阳性菌和革兰氏阴性菌具有弱至中度抗菌活性，包括枯草芽孢杆菌、耐甲氧西林金黄色葡萄球菌、肺炎克雷伯菌、鲍曼不动杆菌和 SM101埃希氏菌大肠杆菌（其脂多糖生物合成途径受损，使细菌对药物更具渗透性）。从这些研究中延伸，我们开发了两个系列与主要子结构类似于那些已知抗菌剂，nitroxoline（羟基喹啉结构部分）和nifuroxazide /呋喃妥因（类似物的双-cyclic- Ñ-酰基腙支架）。通过生化和基于细胞的检测，我们确定了有效的 GroEL/ES 抑制剂，可选择性地阻断粪肠球菌、金黄色葡萄球菌和大肠杆菌的增殖，并且对体外人结肠和肠道细胞的细胞毒性较低。最初，在我们的 GroEL/ES 介导的底物重折叠试验中，只有含羟基喹啉的类似物被发现是有效的抑制剂；然而，随后在存在大肠杆菌硝基还原酶 (NfsB) 的情况下进行原位测试表明含硝基呋喃类似物的代谢物是有效的 GroEL/ES 抑制剂前药。因此，这项研究确定了含硝基呋喃药物的新靶点，并且是此类独特类型的 GroEL/ES 伴侣蛋白抑制剂的首次报道实例。本文呈现的有趣结果为扩展研究提供了动力，以验证抑制剂机制并使用各自的 GroEL/ES 伴侣蛋白系统和来自大肠杆菌和ESKAPE细菌的硝基还原酶优化这种抗菌类别。