Antimicrobial resistance poses a serious threat to human health and was associated with nearly 5 million deaths in 2019. Non-specific drug efflux pumps are predominant resistance factors and can confer resistance to multiple classes of antibiotics. Moreover, these efflux pumps are also implicated in bacterial virulence and the formation of impenetrable bacterial biofilms.
In this project, we aimed to develop inhibitors of bacterial drug efflux pumps to reverse resistance to antibiotics, inhibit virulence, and prevent biofilm formation. Putative efflux pump inhibitors were identified through in silico screening of an FDA-approved drug library. We have developed a combined structure- and ligand-based model, using OpenEye software, for the identification of inhibitors of AcrB, the inner membrane protein component of the AcrAB-TolC efflux pump in Enterobacteralis. From a database of 1391 FDA-approved drugs, 23 compounds were selected to test for efflux inhibition in E. coli using a bespoke pipeline of optimised methods. Seven compounds enhanced the activity of antimicrobials and inhibited the efflux pump-mediated removal of the substrate Nile Red from cells. Of these, ivacaftor was the most promising efflux pump inhibitor. Since ivacaftor is used as a potentiator in the treatment of cystic fibrosis, and chronic infection with Pseudomonas aeruginosa is the main cause of mortality in people suffering from cystic fibrosis, we investigated if ivacaftor could also inhibit the drug efflux pumps in P. aeruginosa isolated from cystic fibrosis patients. In the presence of sub-MIC concentrations of colistin to permeabilise the outer membrane of P. aeruginosa, ivacaftor could reduce the MIC values of multiple antibiotics by 4 – 8-fold. Ivacaftor was also able to completely inhibit drug efflux in these pathogens and to reduce virulence by inhibiting swarming and the excretion of virulence factors such as pyoverdine and pyocyanin. These results initiated a clinical study on combining ivacaftor and antibiotics to treat intractable and recurrent P. aeruginosa infections in cystic fibrosis patients who would not otherwise qualify for ivacaftor treatment.
In this study, we have identified ivacaftor as a compound for repurposing as a drug efflux pump inhibitor for the potential treatment of chronic infections in cystic fibrosis patients caused by multidrug-resistant pathogens.