Review of pyridylpiperazine-based inhibitors for multi-drug resistance via efflux pump inhibition

Multi-drug resistance (MDR) bacteria pose a significant global health challenge, primarily driven by the activity of multi-drug efflux pumps and their intimate coupling to bacterial membrane bioenergetics. Among these systems, proton-motive force (PMF) dependent Resistance, Nodulation–Division (RND) efflux pumps, such as AcrAB-TolC, play a central role in both intrinsic and acquired antibiotic resistance by expelling structurally diverse antimicrobial agents. Recent evidence indicates that efflux pumps are not merely drug extrusion devices but also key regulators of bacterial physiology, influencing membrane potential, redox balance, metabolic state, stress adaptation, and growth-phase transitions. Structural and mechanistic advances have uncovered conserved allosteric sites within RND pumps that are distinct from substrate-binding pockets, enabling the development of allosteric efflux pump inhibitors (EPIs) that disrupt conformational cycling and proton relay without competing with antibiotics. Pyridylpiperazine-based inhibitors, including BDM-series compounds, have demonstrated potent efflux inhibition, antibiotic potentiation, and in-vivo efficacy in preclinical models. This review integrates current knowledge on efflux pump architecture, PMF-driven transport mechanisms, membrane potential dynamics, and allosteric inhibition, emphasizing the therapeutic potential of dual-targeting strategies that combine efflux inhibition with bioenergetics disruption. This study also focused on translational challenges, including drug penetration, resistance evolution, and pharmacokinetic constraints, and future directions for incorporating efflux–bioenergetic targeting into next-generation antimicrobial discovery pipelines to restore antibiotic efficacy against MDR Gram-negative pathogens.