Pore-forming activity of new conjugate antibiotics based on amphotericin B

A series of amides of the antifungal antibiotic amphotericin B (AmB) and its conjugates with benzoxaboroles was tested to determine whether they form pores in lipid bilayers and to compare their channel characteristics. The tested derivatives produced pores of larger amplitude and shorter lifetime than those of the parent antibiotic. The pore conductance was related to changes in the partial charge of the hydrogens of the hydroxyl groups in the lactone ring that determined the anion coordination in the channel. Neutralization of one of the polar group charges in the AmB head during chemical modification produced a pronounced effect by diminishing the dwell time of the polyene channel compared to modification of both groups. In this study, compounds that had a modification of one carboxyl or amino group were less effective in initializing phase separation in POPC-membranes compared to derivatives that had modifications of both polar groups as well as the parent antibiotic. The effects were attributed to the restriction of the aggregation process by electrical repulsion between charged derivatives in contrast to neutral compounds. The significant correlation between the ability of derivatives to increase the permeability of model membranes—causing the appearance of single channels in lipid bilayers or inducing calcein leakage from unilamellar vesicles—and the minimal inhibitory concentration indicated that the antifungal effect of the conjugates was due to pore formation in the membranes of target cells.

本研究测试了一系列抗真菌抗生素两性霉素B（amphotericin B, AmB）的酰胺类衍生物及其与苯并硼唑（benzoxaboroles）的缀合物，以探究它们是否能在脂质双分子层（lipid bilayers）中形成孔道，并比较其通道特性。相较于母本抗生素，所测试的衍生物所形成的孔道振幅更大、寿命更短。单通道电导与内酯环（lactone ring）羟基氢的部分电荷变化相关，而该电荷变化决定了孔道内的阴离子配位（anion coordination）过程。在化学修饰过程中，中和两性霉素B头部的其中一个极性基团电荷，相较于同时修饰两个极性基团的情况，会显著缩短多烯通道（polyene channel）的驻留时长。本研究中，仅修饰一个羧基或氨基的化合物，相较于同时修饰两个极性基团的衍生物以及母本抗生素，在引发POPC（1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱, POPC）膜相分离方面效果更弱。上述效应可归因于带电衍生物之间的静电排斥作用限制了聚集过程，这与中性化合物的情况形成对比。衍生物提升模型膜通透性的能力——即引发脂质双分子层中单通道出现，或诱导钙黄绿素（calcein）从单层囊泡中渗漏——与最低抑菌浓度（minimal inhibitory concentration, MIC）之间存在显著相关性，这表明该缀合物的抗真菌活性源于在靶细胞膜中形成孔道。