Toward Repurposing Ciclopirox as an Antibiotic against Drug-Resistant Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae

Abstract

Antibiotic-resistant infections caused by gram-negative bacteria are a major healthcare concern. Repurposing drugs circumvents the time and money limitations associated with developing new antimicrobial agents needed to combat these antibiotic-resistant infections. Here we identified the off-patent antifungal agent, ciclopirox, as a candidate to repurpose for antibiotic use. To test the efficacy of ciclopirox against antibiotic-resistant pathogens, we used a curated collection of Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae clinical isolates that are representative of known antibiotic resistance phenotypes. We found that ciclopirox, at 5–15 µg/ml concentrations, inhibited bacterial growth regardless of the antibiotic resistance status. At these same concentrations, ciclopirox reduced growth of Pseudomonas aeruginosa clinical isolates, but some of these pathogens required higher ciclopirox concentrations to completely block growth. To determine how ciclopirox inhibits bacterial growth, we performed an overexpression screen in E. coli. This screen revealed that galE, which encodes UDP-glucose 4-epimerase, rescued bacterial growth at otherwise restrictive ciclopirox concentrations. We found that ciclopirox does not inhibit epimerization of UDP-galactose by purified E. coli GalE; however, ΔgalU, ΔgalE, ΔrfaI, or ΔrfaB mutant strains all have lower ciclopirox minimum inhibitory concentrations than the parent strain. The galU, galE, rfaI, and rfaB genes all encode enzymes that use UDP-galactose or UDP-glucose for galactose metabolism and lipopolysaccharide (LPS) biosynthesis. Indeed, we found that ciclopirox altered LPS composition of an E. coli clinical isolate. Taken together, our data demonstrate that ciclopirox affects galactose metabolism and LPS biosynthesis, two pathways important for bacterial growth and virulence. The lack of any reported fungal resistance to ciclopirox in over twenty years of use in the clinic, its excellent safety profiles, novel target(s), and efficacy, make ciclopirox a promising potential antimicrobial agent to use against multidrug-resistant problematic gram-negative pathogens.

In vitro evaluation of ciclopirox as an adjuvant for polymyxin B against gram-negative bacteria

“…10 Very recently, ciclopirox was also suggested as a repurposed bacteriostatic antibiotic for gram-negative bacteria. 11 Ciclopirox affects galactose metabolism and alters the composition of lipopolysaccharide (LPS), 11 a target of polymyxin B. 12 Thus, ciclopirox may activate polymyxin B function, possibly allowing the reduced use of polymyxin B in treating infections by gram-negative pathogens.…”

“…Ciclopirox ⩾ 12.5 μg ml − 1 severely delayed or completely inhibited the growth, but did not result in cell death, thus confirming ciclopirox as a bacteriostatic. 11 However, the addition of ciclopirox to low-dose polymyxin B conferred bactericidal activity. Thus, ciclopirox may potentiate the bactericidal nature of polymyxin B.…”

Escherichia coli Free Radical-Based Killing Mechanism Driven by a Unique Combination of Iron Restriction and Certain Antibiotics

“…The VAN-DFP combination could technically be defined as synergy (see Materials and Methods). In fact, when we assessed the effects of VAN plus DFP on six ExPEC isolates from the blood of patients at Texas Children's Hospital (all of which demonstrated diverse antibiotic resistance profiles [21]), in each case, the combination treatment was more effective than each compound given alone (see Fig. S3 in the supplemental material; P Ͻ 0.01).…”

“…A chloramphenicol (CHL) resistance gene was inserted into CP9 for selection (20). Clinical E. coli isolates (ELZ4013, ELZ4045, ELZ4046, ELZ4234, ELZ4251, and ELZ4486) (21) were generously provided by Lynn Zechiedrich (Baylor College of Medicine, Houston, TX). All experiments were performed with brain heart infusion (BHI) medium or cation-adjusted Mueller-Hinton broth (CAMHB; both from Teknova).…”

A New Natural Product Analog of Blasticidin S Reveals Cellular Uptake Facilitated by the NorA Multidrug Transporter

“…Although blasticidin S, due to its eukaryotic toxicity, is not a clinically used antibiotic, the resolved crystal structure of blasticidin S bound to the ribosome has been used as the basis for rational design of novel analogs with improved drug-like properties (10). The refinement and repurposing of old antibiotic compounds that have fallen out of clinical use due to unfavorable properties are becoming increasingly common and represent promising strategies to counteract the spread of resistance to the range of drugs in modern usage (11,12).…”