Bacterial Resistance to Leucyl-tRNA Synthetase Inhibitor GSK2251052 Develops during Treatment of Complicated Urinary Tract Infections

Abstract

e GSK2251052, a novel leucyl-tRNA synthetase (LeuRS) inhibitor, was in development for the treatment of infections caused by multidrug-resistant Gram-negative pathogens. In a phase II study (study LRS114688) evaluating the efficacy of GSK2251052 in complicated urinary tract infections, resistance developed very rapidly in 3 of 14 subjects enrolled, with >32-fold increases in the GSK2251052 MIC of the infecting pathogen being detected. A fourth subject did not exhibit the development of resistance in the baseline pathogen but posttherapy did present with a different pathogen resistant to GSK2251052. Whole-genome DNA sequencing of Escherichia coli isolates collected longitudinally from two study LRS114688 subjects confirmed that GSK2251052 resistance was due to specific mutations, selected on the first day of therapy, in the LeuRS editing domain. Phylogenetic analysis strongly suggested that resistant Escherichia coli isolates resulted from clonal expansion of baseline susceptible strains. This resistance development likely resulted from the confluence of multiple factors, of which only some can be assessed preclinically. Our study shows the challenges of developing antibiotics and the importance of clinical studies to evaluate their effect on disease pathogenesis. (These studies have been registered at ClinicalTrials.gov under registration no. NCT01381549 for the study of complicated urinary tract infections and registration no. NCT01381562 for the study of complicated intra-abdominal infections.) A pproximately 5% of patients admitted to hospitals in the United States develop nosocomial infections that increase not only patient mortality (1) but also hospitalization time and cost of treatment (2, 3). In the United States, Gram-negative bacterial pathogens, such as Escherichia coli, Klebsiella pneumoniae/Klebsiella oxytoca, Pseudomonas aeruginosa, and Acinetobacter baumannii, are responsible for 35% of the most common hospitalacquired infections (HAIs) or conditions, including urinary tract infections (UTIs), pneumonia, and surgical site and bloodstream infections. Furthermore, Ͼ70% of the bacteria causing HAIs are resistant to at least one of the most commonly used antibiotics (4-6). The continuing emergence of resistance has compromised treatment options for Gram-negative bacterial pathogens and forced the use of polymyxins (7), an old antibiotic class with nephrotoxicity issues. Despite the clear need for alternatives to treat these multidrug-resistant life-threatening pathogens, a review of the antibacterial pipeline reveals a scarcity of new antibiotic candidates (8).Aminoacyl-tRNA synthetases (AaRSs) play an essential role in protein synthesis (9) and have been clinically validated to be antibacterial targets of mupirocin (10), an inhibitor of isoleucyltRNA synthetase that has been successfully used since 1985 in the topical treatment of Gram-positive bacterial skin infections (11). Their ubiquitous nature, high degree of conservation within a broad spectrum of bacterial species, and considerable divergence...

Novel Antibacterial Targets and Compounds Revealed by a High-Throughput Cell Wall Reporter Assay

“…In addition, it has been argued that because of preexisting mutations in bacterial populations, single-gene targets are susceptible to single-step, high-level resistance and will need to be paired with agents that target other functions (6,48). The results for the two targets presented here support these ideas, as do the recently published results on clinical resistance to the Anacor/GlaxoSmithKline oxaborole compound, which targets the leucyl tRNA synthetase editing site (49). Multiple-therapeutic-compound strategies for single-gene targets are employed as a matter of course in tuberculosis therapy (50).…”

A Polymorphism in leuS Confers Reduced Susceptibility to GSK2251052 in a Clinical Isolate of Staphylococcus aureus

“…GSK'052 exhibited a MIC of 2 to 4 mg/liter against all isolates, with the exception of one (strain 1372), for which the MIC was 16 mg/liter. This degree of reduced susceptibility to GSK'052 is equivalent to that exhibited by a resistant Escherichia coli strain selected in a patient upon administration of GSK'052 in the phase II clinical trial, and which was associated with microbiological failure (2).…”

“…Although this compound appears to possess many of the requisite properties of an antibacterial drug for treating infection in humans, it also has the undesirable feature of rapidly selecting resistance in bacteria; in phase II clinical trials involving adult subjects suffering from complicated urinary tract infections, resistance to GSK'052 developed within 2 days of administration in three of 14 patients (1,2). Here, we report that in addition to arising rapidly in bacteria under selection, reduced susceptibility to GSK'052 is preexisting among clinical isolates of Staphylococcus aureus that have not been exposed to the drug, a phenomenon that is the result of polymorphism in the drug target.…”

“…To evaluate the susceptibility of staphylococcal strains to this compound, a small panel of S. aureus blood culture isolates (n ϭ 52) was tested using the microbroth dilution method, according to CLSI guidelines (4). These isolates were recovered from patients at the Erasmus MC University Medical Center Rotterdam (The Netherlands) between November 2009 and May 2010 and therefore originate from a country in which GSK'052 has never been trialed, and during a period that predates the clinical evaluation of GSK'052 (2). Consequently, it may be stated with some confidence that these isolates have never been exposed to this compound in the clinic.…”

Synthesis and Antimicrobial Evaluation of Amixicile-Based Inhibitors of the Pyruvate-Ferredoxin Oxidoreductases of Anaerobic Bacteria and Epsilonproteobacteria

“…For most antibiotics that are derivatives of natural products, resistance mechanisms often precede clinical usage, and these resistance genes over time tend to accumulate in pathogens via lateral transfer of genetic elements (1)(2)(3). In contrast, synthetic antimicrobials developed against new drug targets where no natural-product inhibitor exists are prone to mutation-based drug resistance (4,5). Strategies employing empirical approaches to target identification and high-throughput screening of chemical libraries have also failed to deliver new therapeutics to the clinic (1,2,6,7).…”