Broxyquinoline enhances antibacterial activity of colistin and attenuates LPS-induced inflammation

Colistin is considered one of the last-resort antibiotics for treating infections caused by multidrug-resistant (MDR) Gram-negative bacteria. However, the emergence and dissemination of mobile colistin resistance gene, mcr, have severely compromised the clinical utility of colistin. Combination therapy has emerged as a promising strategy to restore and enhance antibiotic efficacy against such bacterial infections. In this study, we identified broxyquinoline (BRO), an antiprotozoal compound, as a potent colistin adjuvant that significantly enhanced colistin activity against both colistin-susceptible and colistin-resistant Gram-negative bacteria by markedly reducing the minimum inhibitory concentration. Mechanistically, BRO disrupts bacterial membrane integrity, increases membrane permeability and fluidity, collapses the proton motive force, induces reactive oxygen species (ROS) accumulation, and depletes intracellular ATP, collectively disturbing bacterial homeostasis. Additionally, BRO exhibited high-affinity binding to lipopolysaccharide (LPS) and attenuated subsequent LPS-induced inflammatory responses in host cells. In murine thigh and lung infection models, the BRO-colistin combination restored colistin efficacy in vivo, evidenced by significantly reduced bacterial loads. In the lung infection model, this combination further improved survival, alleviated pulmonary pathological damage, and reduced the levels of pro-inflammatory cytokines (TNF-α, IL-1β) in bronchoalveolar lavage fluid. Collectively, these findings support the BRO-colistin combination as a promising therapeutic strategy to overcome colistin resistance and combat MDR Gram-negative infections.