Aminoglycoside antibiotics exhibit broad-spectrum antibacterial activity, good efficacy, and stability. However, due to the emergence of antibiotic resistance, their use as broad-spectrum antibiotics is restricted. Bacteria producing the bifunctional enzyme, 6′-aminoglycoside acetyltransferase 2″-aminoglycoside phosphotransferase [AAC(6′)-APH(2″)], can modify aminoglycoside antibiotics, leading to the emergence of clinical drug resistance. A method based on ultra-high performance liquid chromatography–mass spectrometry (UHPLC-MS) is reported to monitor the modification of aminoglycoside antibiotics and to screen potential inhibitors of AAC(6′)-APH(2″) from marine natural products. Instead of using purified AAC(6′)-APH(2″), Escherichia coli cells harboring AAC(6′)-APH(2″) were employed. In vivo enzyme assays, conducted in the physiological environment, compensated for the disparity between in vitro responses and those in living cells. The inhibition zone method was used to verify the reliability of the UHPLC-MS results. From a library of 63 marine natural products, Mer-C-3 and Mer-c-8e pyridine alkaloids were shown to provide inhibitory activity against AAC(6′)-APH(2″) in living bacteria. The UHPLC-MS-based approach offers improved speed, convenience, and sensitivity compared with the traditional inhibition zone assay for the screening of enzyme inhibitors.
Li Zhu,Ruonan Liu,Tangrong Liu,Xuan Zou,Zhe Xu,Huashi Guan
Resistance to aminoglycoside antibiotics occurs primarily as a result of aminoglycoside-modification enzymes (AMEs) that modify the antibiotics. In this work, a novel strategy to combat the effects of antibiotic resistance was developed by screening multiple AMEs inhibitors with ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF MS). The method screened inhibitors of three AMEs (AAC(6’)-APH(2”), AAC(6’) and APH(2”)) simultaneously through measuring the acetyltransferase activity and phosphotransferase activity of AAC(6’)-APH(2”) enzyme in a single assay. Screening inhibitors of multiple targets could greatly improve the screening efficiency at early-stages of drug discovery. In this study, enzyme reaction conditions including cosubstrate, enzyme concentration and cosubstrate concentration were optimized. The inhibition constants ( K i ) for two known inhibitors, paromomycin and quercetin, were determined to be 1.23 and 20.27 μM, respectively. The assay was further validated through the determination of a high Z' factor value of 0.73. The developed assay was applied to screen a chemical library against bifunctional AAC(6’)-APH(2’’) enzyme. Using this assay, two pyrimidinyl indole derivatives were found to be potent, and effective AAC(6’)-APH(2’’) inhibitors. The assay of exploring the selective inhibitory effect on two AAC(6’)-APH(2’’) active sites was further performed. Two pyrimidinyl indole derivatives were found to exhibit striking inhibitory activities on AAC(6’).
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