Mode of Action and Bactericidal Properties of Surotomycin against Growing and Nongrowing Clostridium difficile

Abstract

d Surotomycin (CB-183,315), a cyclic lipopeptide, is in phase 3 clinical development for the treatment of Clostridium difficile infection. We report here the further characterization of the in vitro mode of action of surotomycin, including its activity against growing and nongrowing C. difficile. This was assessed through time-kill kinetics, allowing a determination of the effects on the membrane potential and permeability and macromolecular synthesis in C. difficile. Against representative strains of C. difficile, surotomycin displayed concentration-dependent killing of both logarithmic-phase and stationary-phase cultures at a concentration that was <16؋ the MIC. Exposure resulted in the inhibition of macromolecular synthesis (in DNA, RNA, proteins, and cell wall). At bactericidal concentrations, surotomycin dissipated the membrane potential of C. difficile without changes to the permeability of propidium iodide. These observations are consistent with surotomycin acting as a membrane-active antibiotic, exhibiting rapid bactericidal activities against growing and nongrowing C. difficile. The Gram-positive spore-forming anaerobic bacterium Clostridium difficile is the leading cause of hospital-acquired diarrhea in North America and Europe (1, 2). Elderly hospitalized patients on broad-spectrum antibiotics are the main target population, but recent observations indicate there is an increase in the incidence of C. difficile infection (CDI) in the community without known risk factors (3, 4). In the United States in 2011, there were an estimated 500,000 cases of CDI resulting in 29,300 deaths (5), which reflects the devastating impact of CDI since the turn of the last century. Furthermore, the number of cases of severe CDI has escalated, coinciding with the emergence of epidemic ribotypes, such as BI/NAP1/027 (2, 6). BI/NAP1/027 is now responsible for a significant number of cases of hospital-acquired CDI in North America (5, 6).For Ͼ30 years, vancomycin and metronidazole have been the first-line treatment choices for CDI (7). Metronidazole is prescribed for mild to moderate CDI, while vancomycin is recommended for severe CDI (6,8). However, rates of recurrence of 20 to Ն25% in severe CDI are common following treatment with metronidazole or vancomycin (6, 9, 10). The mode of action of vancomycin is well established, involving inhibition of the later stages of peptidoglycan biosynthesis, which primarily kill rapidly growing C. difficile (11). Metronidazole undergoes biochemical reduction to form reactive species that target DNA and is potent in vitro, but only low concentrations reside in the gastrointestinal tract (12-16). Fidaxomicin, which targets the bacterial RNA polymerase inhibitor, has a narrower spectrum of activity than that of metronidazole and vancomycin and is superior in the prevention of CDI recurrence (17, 18). However, additional novel therapeutics are required to effectively treat CDI and reduce the rates of recurrence following initial therapy.Surotomycin is a minimally absorbed narrow-spectrum cycl...

Evaluating the Effects of Surotomycin Treatment on Clostridium difficile Toxin A and B Production, Immune Response, and Morphological Changes

“…In this study, surotomycin exhibited potent and rapid bactericidal activity against exponentially growing cells without effect on spores, confirming previous observations (6,(10)(11)(12).…”

“…In our study, this killing effect and associated decreased toxin production led to a reduced immune activation measured using IL-8. Alam et al recently investigated the mode of action of surotomycin against growing and nongrowing C. difficile (6). In that study, surotomycin inhibited macromolecular synthesis of DNA, RNA, and protein simultaneously and dissipated the membrane potential of the bacterial cell wall.…”

“…Surotomycin (formerly CB-183,315) is a novel narrow-spectrum, minimally absorbed antibiotic that is currently being evaluated for the treatment of CDI (5). Surotomycin affects the cell wall integrity of C. difficile by dissipating the membrane potential, thereby killing the bacteria (6). Other studies have demonstrated killing activity against C. difficile; however, the effects on cell morphology, toxin A and B secretion, and associated changes in the immune response have not been examined.…”

Impact of Variations in Test Method Parameters on In Vitro Activity of Surotomycin against Clostridium difficile and Surotomycin Quality Control Limits for Broth Microdilution and Agar Dilution Susceptibility Testing

“…It previously demonstrated selective potent bactericidal activity against various C. difficile strains and other Gram-positive bacteria in vitro, with minimal impact on the Gram-negative organisms of the intestinal microbiota in vitro and in CDAD patients (15)(16)(17)(18)(19)(20). In a phase 2 trial, surotomycin was more sparing of gut microbes (primarily Bacteroides and Prevotella species) than vancomycin, with evidence for reduction in the risk of recurrence (20).…”

Mutations Associated with Reduced Surotomycin Susceptibility in Clostridium difficile and Enterococcus Species

“…Surotomycin is dosed orally, not absorbed, and rapidly bactericidal against C. difficile (5,6). Surotomycin is likely to have a mechanism of action similar to that of daptomycin, as treatment with either antibiotic leads to membrane depolarization but not increased membrane permeability in Staphylococcus aureus and C. difficile (6,7). Importantly, the MIC values of surotomycin for normal GI tract microbiota such as Bacteroides species and enterobacteria are higher than surotomycin concentrations recorded in situ during clinical trials (8).…”