The BET family of bromodomain-containing proteins (BRDs) is believed to be a promising drug target for therapeutic intervention in a number of diseases including cancer, inflammation and cardiovascular diseases. Hence, there is a great demand for novel chemotypes of BET inhibitors. The drug repurposing strategy offers great benefits to find inhibitors with known safety and pharmacokinetic profiles, thus increasing medicinal chemists’ interest in recent years. Using the drug repurposing strategy, a BRD4-specific score based virtual screening campaign on an in-house drug library was conducted followed by the ALPHA screen assay test. Nitroxoline, an FDA-approved antibiotic, was identified to effectively disrupt the interaction between the first bromodomain of BRD4 (bromodomain-containing protein 4) and acetylated H4 peptide with IC₅₀ of 0.98 μM. Nitroxoline inhibited all BET family members with good selectivity against non-BET bromodomain-containing proteins, thus it is defined as a selective BET inhibitor. Based on the crystal structure of the nitroxoline-BRD4_BD1 complex, the mechanism of action as well as BET specificity of nitroxoline were determined. Since the anticancer activity of nitroxoline against MLL leukemia, one of the BET related diseases, has not been studied before, we tested whether nitroxoline might serve as a potential repurposing drug candidate for MLL leukemia. Nitroxoline effectively inhibited the proliferation of MLL leukemia cells by inducing cell cycle arrest and apoptosis. The profound efficacy is, at least in part, due to the inhibition of BET and downregulation of target gene transcription. Our discovery of nitroxoline as a BET inhibitor suggests potential application of nitroxoline and its derivatives for clinical translation in BET family related diseases.

中文翻译：

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通过药物重用硝氧嘧啶及其类似物发现新的BET抑制剂

含溴结构域的蛋白质（BRD）的BET家族被认为是治疗多种疾病（包括癌症，炎症和心血管疾病）的有前途的药物靶标。因此，非常需要新的BET抑制剂的化学型。重新利用药物的策略为寻找具有已知安全性和药代动力学特征的抑制剂提供了极大的好处，因此近年来增加了化学药剂师的兴趣。使用药物重用策略，在内部药物库上进行了基于BRD4特异性评分的虚拟筛选活动，然后进行了ALPHA筛选测定测试。已确定使用FDA批准的抗生素Nitroxoline可有效破坏BRD4的第一个溴结构域（含溴结构域的蛋白质4）与乙酰化H4肽之间的相互作用（使用IC）₅₀为0.98μM。硝基氧可抑制所有BET家族成员对非BET含溴结构域的蛋白质具有良好的选择性，因此被定义为选择性BET抑制剂。根据硝氧代林-BRD4_BD1配合物的晶体结构，确定了硝氧代林的作用机理以及BET特异性。由于之前尚未研究硝唑啉对与BET相关的疾病之一的MLL白血病的抗癌活性，因此我们测试了硝恶唑啉是否可能作为MLL白血病的潜在替代药物。硝基氧可通过诱导细胞周期停滞和凋亡来有效抑制MLL白血病细胞的增殖。深刻的功效至少部分是由于BET的抑制和靶基因转录的下调。