Author(s): Catherine Stevens
Mentor(s): Eric Cheung
Institution U of U
According to the National Library of Medicine, approximately 60% of women and 12% of men will experience at least one urinary tract infection (UTI) in their lifetime. Of these, 70% are caused by the gram-negative bacterium Escherichia coli (E. coli), which is commonly treated with nitrofurantoin or ciprofloxacin. Recurrent UTIs (rUTIs) are also prevalent, particularly in patients with indwelling catheters or anatomical/functional urinary tract defects. rUTIs often require continuous treatment, which can lead to antibiotic resistance and render current antibiotics ineffective. Developing new antibiotics is costly and challenging; therefore, we aim to utilize an alternative approach known as combination therapy. Combination therapy leverages synergistic interactions between an antibiotic and a small molecule, with the small molecule enhancing the antibiotic's efficacy, effectively creating a novel therapeutic option. Our goal is to identify small molecules from an FDA-approved drug library that exhibit synergistic interactions with nitrofurantoin (NIT) and ciprofloxacin (CIP) for improved rUTI treatments. For simplicity, this abstract focuses on results for nitrofurantoin. To identify potential combinations, we developed a drug screening protocol by combining small molecules from the FDA-approved drug library with nitrofurantoin. The screen identified 21 small molecules with possible synergy with nitrofurantoin, and these combinations were further validated using checkerboard assays with E. coli MG1655 and five susceptible E. coli clinical isolates. Combinations exhibiting ≥50% synergy were then tested against resistant clinical isolates. Given E. coli's estimated nitrofurantoin resistance rate of 5%, we also tested combinations on Klebsiella pneumoniae, another gram-negative UTI pathogen with a ~50% nitrofurantoin resistance rate. Our validation process identified six drugs with ≥50% synergy with nitrofurantoin. The combination of nitrofurantoin and dequalinium (NIT+DEQ) showed the highest synergy, with 68% efficacy against susceptible strains and 94% against resistant strains. To investigate the molecular mechanism behind NIT+DEQ, we examined the actions of each component. NIT is known to inhibit enzymes in the citric acid cycle, although the precise mechanisms remain under investigation. Dequalinium inhibits F1-ATPase, preventing ATP hydrolysis and thereby limiting energy production. We propose that the synergistic effect of NIT+DEQ arises from the combined inhibition of energy precursors from the citric acid cycle and the impaired ability to hydrolyze ATP. Further studies are underway to elucidate these interactions. The effectiveness of NIT+DEQ against resistant strains suggests a promising new treatment combination for rUTIs.