Antimicrobial resistance (AMR) represents a global health issue threatening our social lifestyle and the world economy. Efflux pumps are widely involved in AMR by playing a primary role in the development of specific mechanisms of resistance. In addition, they seem to be involved in the process of biofilm formation and maintenance, contributing to enhance the risk of creating superbugs difficult to treat. Accordingly, the identification of non-antibiotic molecules able to block efflux pumps, namely efflux pump inhibitors (EPIs), could be a promising strategy to counteract AMR and restore the antimicrobial activity of ineffective antibiotics. Herein, we enlarge the knowledge about the structure-activity relationship of 2-phenylquinoline Staphylococcus aureus NorA EPIs by reporting a new series of very potent C-6 functionalized derivatives. Best compounds significantly inhibited ethidium bromide efflux in a NorA-overexpressing S. aureus strain (SA-1199B) and strongly synergized at very low concentrations (0.20–0.78 μg/mL) with ciprofloxacin (CPX) against CPX-resistant S. aureus strains (SA-1199B and SA-K2378), as proved by checkerboard and time-kill experiments. In addition, some of these EPIs (9b and 10a) produced a post-antibiotic effect of 1.2 h and strongly enhanced antibiofilm activity of CPX against SA-1199B strain. Interestingly, at the concentrations used to reach synergy with CPX against resistant S. aureus strains, most of the EPI compounds did not show any human cell toxicity. Finally, by exploiting the recent released crystal structure of NorA, we observed that best EPI 9b highlighted a favourable docking pose, establishing some interesting interactions with key residues.

抗菌素耐药性 (AMR) 是威胁我们社会生活方式和世界经济的全球健康问题。外排泵通过在特定耐药机制的发展中发挥主要作用而广泛参与 AMR。此外，它们似乎参与了生物膜的形成和维持过程，有助于增加产生难以治疗的超级细菌的风险。因此，鉴定能够阻断外排泵的非抗生素分子，即外排泵抑制剂（EPI），可能是对抗 AMR 和恢复无效抗生素的抗菌活性的有前景的策略。在此，我们扩大了对2-苯基喹啉金黄色葡萄球菌构效关系的认识。NorA EPI 报告了一系列新的非常有效的 C-6 官能化衍生物。最好的化合物显着抑制过表达 NorA 的金黄色葡萄球菌菌株 (SA-1199B)中的溴化乙锭流出，并在极低浓度 (0.20–0.78 μg/mL) 下与环丙沙星 (CPX) 对 CPX 抗性金黄色葡萄球菌菌株产生强烈协同作用 ( SA-1199B 和 SA-K2378），如棋盘格和计时实验所证明的那样。此外，其中一些 EPI（9b和10a）产生了 1.2 小时的抗生素后效应，并强烈增强了 CPX 对 SA-1199B 菌株的抗生物膜活性。有趣的是，在用于与 CPX 协同对抗耐药金黄色葡萄球菌的浓度下在菌株中，大多数 EPI 化合物没有表现出任何人体细胞毒性。最后，通过利用最近发布的 NorA 晶体结构，我们观察到最佳 EPI 9b突出了有利的对接姿势，与关键残基建立了一些有趣的相互作用。