Mechanism of Quinolone Resistance

氟喹诺酮类药物，如环丙沙星，是最有效和广谱的口服抗菌药物之一 在临床上使用。世界卫生组织将其列为五个“最高优先级的至关重要的抗- 这些药物是退伍军人管理局医院最常用的抗菌药物。 氟喹诺酮类药物的细胞靶点是细菌II型拓扑异构酶、促旋酶和拓扑异构酶IV。 这些必需的酶调节DNA的欠缠绕和过缠绕，并从基因组中去除结和缠结 通过在遗传物质中产生短暂的双链断裂。氟喹诺酮类药物通过增加 由促旋酶和拓扑异构酶IV产生的双链DNA断裂，将这些酶转化为 分裂基因组的细胞毒素促旋酶和拓扑异构酶IV都是荧光素酶的生理靶点。 喹诺酮类，但它们对药物作用的相对重要性似乎是种属和药物依赖性的。 抗菌药物耐药危机日益严重，氟喹诺酮类药物耐药现象日益普遍。这 耐药性正在威胁氟喹诺酮类药物的临床疗效及其治疗美国退伍军人的用途。比如说， 氟喹诺酮类药物通常用于治疗淋病（由淋病奈瑟菌引起）， 从1993年开始，这种传染病在军队中流行，在退伍军人中上升。 然而，由于耐药性发生率高，2006年停止了将其用作一线治疗。 最初的氟喹诺酮类耐药最常与促旋酶和/或 拓扑异构酶IV，其存在于丝氨酸残基（最初描述为大肠杆菌GyrA亚基中的Ser 83 大肠杆菌促旋酶）和下游4个氨基酸的谷氨酸/天冬氨酸残基。基于已发布的结构 根据Osheroff实验室的功能研究，这些残留物被提议用于锚水金属离子 作为氟喹诺酮类和促旋酶/拓扑异构酶IV之间的主要通道的桥梁。通过 以氟喹诺酮-酶相互作用为特征，PI设计了克服耐药性的新药， 结核分枝杆菌促旋酶和炭疽杆菌促旋酶以及拓扑异构酶IV的突变。 鉴定和表征的新的代理人，对这些行之有效的拓扑异构酶 目标和克服氟喹诺酮耐药性可能对退伍军人的健康产生重要影响。 最近，已经描述了两类新的促旋酶/拓扑异构酶IV靶向剂，它们似乎 新的细菌拓扑异构酶抑制剂（NBTI）和螺嘧啶三酮（SPT）。 这些类别的成员，吉泊替辛（NBTI）和zoliflodacin（SPT），已进入3期临床试验。 NBTI是独特的，因为它们诱导单链而不是双链酶产生的DNA断裂。但是，在这方面， 关于NBTI和SPT对促旋酶/拓扑异构酶IV的作用或它们的抗性基础知之甚少。 目前迫切需要开发出更有效的药物，显示对氟喹诺酮类耐药的活性 细菌这项研究的前提是，了解药物如何与它们之间的相互作用。 酶靶点使我们处于更有利的地位来开发克服耐药性的药物。因此，具体 该建议的目的是1）确定氟喹诺酮作用和耐药性的机制基础， 跨物种的促旋酶和拓扑异构酶IV;以及2）确定NBTI作用的机制基础 以及针对不同物种的促旋酶和拓扑异构酶IV的SPT。拟议的实验将建立在以前的基础上 Osheroff实验室的研究和细菌II型拓扑异构酶机制的初步数据 以及它们与氟喹诺酮、NBTI和SPT的相互作用。研究将大大受益于广泛的图书馆 Osheroff实验室已经建立的野生型和抗药性促旋酶/拓扑异构酶IV。此库 包括来自B的酶。anthracis、E.大肠杆菌、金黄色葡萄球菌、M.结核病，淋病奈瑟菌， 土拉热弗朗西斯菌和鲍曼不动杆菌。这些病原体中的许多经常影响美国人的健康， 老兵初步研究将集中在N。gonorrhoeae、M. tuberculosis和E. coli作为模型系统。

Fluoroquinolones, such as ciprofloxacin, are among the most efficacious and broad-spectrum oral antibacterials in clinical use. The World Health Organization lists them in their five “Highest Priority Critically Important Anti- microbials,” and these drugs are the most heavily prescribed antibacterials at Veterans Administration hospitals. The cellular targets of fluoroquinolones are the bacterial type II topoisomerases, gyrase and topoisomerase IV. These essential enzymes regulate DNA under- and overwinding and remove knots and tangles from the genome by generating transient double-stranded breaks in the genetic material. Fluoroquinolones act by increasing levels of double-stranded DNA breaks generated by gyrase and topoisomerase IV, which converts these enzymes into cellular toxins that fragment the genome. Both gyrase and topoisomerase IV are physiological targets for fluoro- quinolones, but their relative importance to drug action appears to be species- and drug-dependent. There is a growing crisis in antibacterial resistance and fluoroquinolone resistance is becoming prevalent. This resistance is threatening the clinical efficacy of fluoroquinolones and their use to treat US Veterans. For example, fluoroquinolones were used routinely to treat gonorrhea (which is caused by Neisseria gonorrhoeae), a sexually transmitted disease that is prevalent in the military and elevated in Veteran populations, starting in 1993. However, their use as front-line therapy was discontinued in 2006 due to the high incidence of resistance. Initial fluoroquinolone resistance is most often associated with specific mutations in gyrase and/or topoisomerase IV that occur at a serine residue (originally described as Ser83 in the GyrA subunit of Escherichia coli gyrase) and a glutamic/aspartic acid residue 4 amino acids downstream. Based on a published structure and functional studies from the Osheroff laboratory, these residues are proposed to anchor a water-metal ion bridge that serves as the primary conduit between fluoroquinolones and gyrase/topoisomerase IV. By characterizing fluoroquinolone-enzyme interactions, the PI has designed novel drugs that overcome resistance mutations in Mycobacterium tuberculosis gyrase and Bacillus anthracis gyrase and topoisomerase IV. The identification and characterization of novel agents that act against these well-validated topoisomerase targets and overcome fluoroquinolone resistance could have important ramifications for the health of Veterans. Recently, two new classes of gyrase/topoisomerase IV-targeted agents have been described that appear to overcome this resistance, Novel Bacterial Topoisomerase Inhibitors (NBTIs) and Spiropyrimidinetriones (SPTs). Members of these classes, gepotidacin (NBTI) and zoliflodacin (SPT), have advanced to phase 3 clinical trials. NBTIs are unique, as they induce single- rather than double-stranded enzyme-generated DNA breaks. However, little is known about the actions of NBTIs and SPTs against gyrase/topoisomerase IV or their basis of resistance. There is an urgent need to develop more effective drugs that display activity against fluoroquinolone-resistant bacteria. The premise underlying the proposed research is that understanding how drugs interact with their enzyme targets places us in a far better position to develop agents that overcome resistance. Thus, the specific aims of this proposal are to 1) determine the mechanistic basis for fluoroquinolone action and resistance with gyrase and topoisomerase IV across species; and 2) determine the mechanistic basis for the actions of NBTIs and SPTs against gyrase and topoisomerase IV across species. Proposed experiments will build upon previous studies from the Osheroff laboratory and preliminary data on the mechanism of bacterial type II topoisomerases and their interactions with fluoroquinolones, NBTI, and SPTs. Research will benefit greatly from the broad library of wild-type and drug-resistant gyrase/topoisomerase IV that the Osheroff laboratory has established. This library includes enzymes from B. anthracis, E. coli, Staphylococcus aureus, M. tuberculosis, Neisseria gonorrhoeae, Francisella tularensis, and Acinetobacter baumannii. Many of these pathogens routinely affect the health of US Veterans. Initial studies will focus on N. gonorrhoeae, M. tuberculosis, and E. coli as the model systems.