Ramoplanin: a topical lipoglycodepsipeptide antibacterial agent

Ramoplanin, a novel antibiotic with activity against aerobic and anaerobic gram-positive bacteria, acts to prevent cell wall peptidoglycan formation by binding to a key intermediate moiety, lipid II. It has been fast-tracked by the US FDA for the prevention of enterococcal infections and the treatment of Clostridium difficile. The minimum inhibitory concentration(90s) have been < or = 1.0 microg/ml against gram-positive organisms examined. In carriers of vancomycin-resistant enterococci, a double-blind, placebo-controlled Phase II trial of two doses of ramoplanin versus placebo showed proof of concept. A second Phase II trial also demonstrated the equivalence of ramoplanin compared with vancomycin for the treatment of C. difficile colitis. The clinical value and place in therapy of ramoplanin is dependent upon the results of Phase III trials addressing its utility in suppressing carriage of target organisms in the gastrointestinal tract or in the nares.     

Ramoplanin at Bactericidal Concentrations Induces Bacterial Membrane Depolarization in Staphylococcus aureus

Ramoplanin is an actinomycetes-derived antibiotic with broad-spectrum activity against Gram-positive bacteria that has been evaluated in clinical trials for the treatment of gastrointestinal vancomycin-resistant enterococci (VRE) and Clostridium difficile infections. Recent studies have proposed that ramoplanin binds to bacterial membranes as a C₂ symmetrical dimer that can sequester Lipid II, which causes inhibition of cell wall peptidoglycan biosynthesis and cell death. In this study, ramoplanin was shown to bind to anionic and zwitterionic membrane mimetics with a higher affinity for anionic membranes and to induce membrane depolarization of methicillin-susceptible Staphylococcus aureus (MSSA) ATCC 25923 at concentrations at or above the minimal bactericidal concentration (MBC). The ultrastructural effects of ramoplanin on S. aureus were also examined by transmission electron microscopy (TEM), and this showed dramatic changes to bacterial cell morphology. The correlation observed between membrane depolarization and bacterial cell viability suggests that this mechanism may contribute to the bactericidal activity of ramoplanin.     

Ambush of Clostridium difficile Spores by Ramoplanin: Activity in an In Vitro Model

Clostridium difficile infection (CDI) is a gastrointestinal disease caused by C. difficile, a spore-forming bacterium that in its spore form is tolerant to standard antimicrobials. Ramoplanin is a glycolipodepsipeptide antibiotic that is active against C. difficile with MICs ranging from 0.25 to 0.50 μg/ml. The activity of ramoplanin against the spores of C. difficile has not been well characterized; such activity, however, may hold promise, since posttreatment residual intraluminal spores are likely elements of disease relapse, which can impact more than 20% of patients who are successfully treated. C. difficile spores were found to be stable in deionized water for 6 days. In vitro spore counts were consistently below the level of detection for 28 days after even brief (30-min) exposure to ramoplanin at concentrations found in feces (300 μg/ml). In contrast, suppression of spore counts was not observed for metronidazole or vancomycin at human fecal concentrations during treatment (10 μg/ml and 500 μg/ml, respectively). Removal of the C. difficile exosporium resulted in an increase in spore counts after exposure to 300 μg/ml of ramoplanin. Therefore, we propose that rather than being directly sporicidal, ramoplanin adheres to the exosporium for a prolonged period, during which time it is available to attack germinating cells. This action, in conjunction with its already established bactericidal activity against vegetative C. difficile forms, supports further evaluation of ramoplanin for the prevention of relapse after C. difficile infection in patients.     

Kibdelomycin Is a Potent and Selective Agent against Toxigenic Clostridium difficile

Clostridium difficile is the causative agent of C. difficile-associated diarrhea (CDAD), with increased risk in elderly populations. Kibdelomycin, a novel natural-product inhibitor of type II topoisomerase enzymes, was evaluated for activity against C. difficile and gastrointestinal anaerobic organisms. Toxigenic C. difficile isolates (n = 168) from U.S. hospitals and anaerobic Gram-positive and Gram-negative organisms (n = 598) from Chicago-area hospitals were tested. Kibdelomycin showed potent activity against toxigenic C. difficile (MIC₉₀ = 0.25 μg/ml) and most Gram-positive aerobic organisms but had little activity against Bacteroides species (MIC₅₀ > 32 μg/ml; n = 270). Potent anti-C. difficile activity was also observed in the hamster model of C. difficile colitis. Dosing at 1.6 mg/kg (twice-daily oral dose) resulted in protection from a lethal infection and a 2-log reduction in C. difficile cecal counts. A 6.25-mg/kg twice-daily oral dose completely eliminated detectable C. difficile counts in cecal contents. A single 6.25-mg/kg oral dose showed that cecal contents were exposed to the drug at >2 μM (eightfold higher than the MIC), with no significant plasma exposure. These findings support further exploration of kibdelomycin for development of an anti-C. difficile agent.     

Ceftobiprole: a new cephalosporin for the treatment of skin and skin structure infections

Ceftobiprole is among the first of a new generation of cephalosporins with activity against aerobic Gram-negative bacilli, which extends to cefepime-sensitive Pseudomonas aeruginosa, and activity against Gram-positive organisms, which includes methicillin-resistant Staphylococcus aureus. Ceftobiprole is currently undergoing evaluation by the US FDA for the treatment of complicated skin and skin structure infections, with a decision pending further evaluation of study site monitoring. It is also being evaluated for the treatment of community-acquired and healthcare-associated pneumonia. Two Phase III multicenter trials have demonstrated noninferiority in complicated skin and skin structure infections when tested against vancomycin in primarily Gram-positive bacterial infections, and when tested against vancomycin plus ceftazidime in Gram-positive and Gram-negative bacterial infections. It is well tolerated, with the most common side effects being nausea and dysgeusia. Ceftobiprole is likely to prove useful as an empiric as well as directed monotherapy in patients with complicated skin and skin structure infections, in which both Gram-positive pathogens including methicillin-resistant S. aureus and Gram-negative pathogens including cefepime-sensitive P. aeruginosa may be involved.     

Using a Novel Lysin To Help Control Clostridium difficile Infections

As a consequence of excessive antibiotic therapies in hospitalized patients, Clostridium difficile, a Gram-positive anaerobic spore-forming intestinal pathogen, is the leading cause of hospital-acquired diarrhea and colitis. Drug treatments for these diseases are often complicated by antibiotic-resistant strains and a high frequency of treatment failures and relapse; therefore, novel nonantibiotic approaches may prove to be more effective. In this study, we recombinantly expressed a prophage lysin identified from a C. difficile strain, CD630, which we named PlyCD. PlyCD was found to have lytic activity against specific C. difficile strains. However, the recombinantly expressed catalytic domain of this protein, PlyCD_1–174, displayed significantly greater lytic activity (>4-log kill) and a broader lytic spectrum against C. difficile strains while still retaining a high degree of specificity toward C. difficile versus commensal clostridia and other bacterial species. Our data also indicated that noneffective doses of vancomycin and PlyCD_1–174 when combined in vitro could be significantly more bactericidal against C. difficile. In an ex vivo treatment model of mouse colon infection, we found that PlyCD_1–174 functioned in the presence of intestinal contents, significantly decreasing colonizing C. difficile compared to controls. Together, these data suggest that PlyCD_1–174 has potential as a novel therapeutic for clinical application against C. difficile infection, either alone or in combination with other preexisting treatments to improve their efficacy.     

In vitro evaluation of ramoplanin (A16686 or MDL62198). A new depsipeptide complex for potential topical use

Ramoplanin, a new depsipeptide complex, was found to be 4- to 8-fold more active than vancomycin against all Gram-positive species (500 strains). Similarly, ramoplanin was both more active and had an additional spectrum compared to mupirocin (formerly pseudomonic acid) against Bacillus spp., Corynebacterium jeikeium, enterococci and Listeria monocytogenes. Mupirocin-resistant Staphylococcus spp. strains (less than 1%) were identified in these organisms collected from over 40 medical centers in the United States. These strains (S. capitis and S. saprophyticus) were susceptible to ramoplanin at 0.25 micrograms/ml or less. The three tested antimicrobial agents were not effective against Gram-negative organisms (20 species tested). Ramoplanin was bactericidal and MICs were not adversely influenced by high (greater than or equal to 10(7) CFU/ml) inoculum concentrations. Because ramoplanin has previously shown promise as a topical drug, these in vitro results further substantiate its wide spectrum, potency, and potential clinical usefulness as mupirocin-resistant staphylococci and other Gram-positive species become more prevalent.     

Clostridium difficile infection: molecular pathogenesis and novel therapeutics

The Gram-positive anaerobic bacterium Clostridium difficile produces toxins A and B, which can cause a spectrum of diseases from pseudomembranous colitis to C. difficile-associated diarrhea. A limited number of C. difficile strains also produce a binary toxin that exhibits ADP ribosyltransferase activity. Here, the structure and the mechanism of action of these toxins as well as their role in disease are reviewed. Nosocomial C. difficile infection is often contracted in hospital when patients treated with antibiotics suffer a disturbance in normal gut microflora. C. difficile spores can persist on dry, inanimate surface for months. Metronidazole and oral vancomycin are clinically used for treatment of C. difficile infection but clinical failure and concern about promotion of resistance are motivating the search for novel non-antibiotic therapeutics. Methods for controlling both toxins and spores, replacing gut microflora by probiotics or fecal transplant, and killing bacteria in the anaerobic gut by photodynamic therapy are discussed.     

Ceftaroline fosamil for treatment of communityacquired pneumonia: findings from FOCUS 1 and 2 and potential role in therapy

Cephalosporins have been widely used over the last few decades (often as first-line antibiotic therapy) for numerous infections, owing primarily to their broad spectrum of microbiologic activity and favorable safety profile. Current Infectious Diseases Society of America guidelines identify a third-generation cephalosporin in combination with a macrolide antibiotic as an option for treatment of hospitalized adult patients with community-acquired pneumonia (CAP) outside the intensive care unit setting. Although ceftriaxone is a frequently used agent for CAP, increasing incidence of multidrug-resistant Streptococcus pneumoniae and concerns regarding poor outcomes associated with ineffective therapy have prompted the search for a well-tolerated treatment alternative that is effective against bacteria that can cause CAP. Ceftaroline fosamil, the prodrug of ceftaroline, is a new extended-spectrum cephalosporin that exhibits time-dependant bactericidal activity against numerous Gram-negative and Gram-positive organisms, including methicillin-resistant Staphylococcus aureus and penicillin-resistant S. pneumoniae. Notable exceptions include Pseudomonas spp. and Gram-negative organisms that produce extended-spectrum β-lactamases or carbapenemases. Two large Phase III clinical trials (FOCUS 1 and 2) reported that ceftaroline fosamil was well tolerated, with a clinical cure rate of CAP that was noninferior to that with ceftriaxone in nonintensive care unit adult inpatients with moderately severe (Pneumonia Outcomes Research Team score of III or IV) community-acquired pneumonia.     

The role of solithromycin in the management of bacterial community-acquired pneumonia

The fluoroketolide solithromycin is 2-fold more potent in vitro than telithromycin against pneumococci (including macrolide-resistant strains) and Haemophilus influenzae and very active on pathogens causing atypical pneumonia. In contrast, it is a 30-fold less potent inhibitor of nicotinic receptors incriminated in telithromycin toxicity. In Phase II/III trials, oral solithromycin once-daily (800 mg on day 1; 400 mg on days 2-5) proved effective and safe when compared to respiratory fluoroquinolones for the treatment of community-acquired bacterial pneumonia (CABP). A Phase III intravenous trial vs. moxifloxacin has been recently completed for the same indication. Solithromycin may restore interest in ketolides as a first-line therapy for CAPB. Solithromycin safety should nevertheless be confirmed in larger populations allowing for detection of rare adverse events.     

Efficacy of telavancin,a lipoglycopeptide antibiotic,in experimental models of Gram-positive infection

Telavancin is a parenteral lipoglycopeptide antibiotic with a dual mechanism of action contributing to bactericidal activity against multidrug-resistant Gram-positive pathogens. It has been approved for the treatment of complicated skin and skin structure infections due to susceptible Gram-positive bacteria and hospital-acquired/ventilator-associated bacterial pneumonia due to Staphylococcus aureus when other alternatives are unsuitable. Telavancin has been demonstrated to be efficacious in multiple animal models of soft tissue, cardiac, systemic, lung, bone, brain and device-associated infections involving clinically relevant Gram-positive pathogens, including methicillin-resistant S. aureus, glycopeptide-intermediate S. aureus, heterogeneous vancomycin-intermediate S. aureus and daptomycin non-susceptible methicillin-resistant S. aureus. The AUC_0–24h/MIC ratio is the primary pharmacodynamically-linked pharmacokinetic parameter. The preclinical data for telavancin supports further investigative clinical evaluation of its efficacy in additional serious infections caused by susceptible Gram-positive pathogens.     

Emerging monoclonal antibodies against Clostridium difficile infection

Introduction: Clostridium difficile infections are characterized by a high recurrence rate despite antibiotic treatments and there is an urgent need to develop new treatments such as fecal transplantation and immonotherapy. Besides active immunotherapy with vaccines, passive immunotherapy has shown promise, especially with monoclonal antibodies.

Areas covered: Herein, the authors review the different assays performed with monoclonal antibodies against C. difficile toxins and surface proteins to treat or prevent primary or recurrent episodes of C. difficile infection in animal models and in clinical trials as well. Notably, the authors lay emphasis on the phase III clinical trial (MODIFY II), which allowed bezlotoxumab to be approved by the Food and Drug Administration and the European Medicines Agency. They also review new strategies for producing single domain antibodies and nanobodies against C. difficile and new approaches to deliver them in the digestive tract.

Expert opinion: Only two human Mabs against TcdA and TcdB have been tested alone or in combination in clinical trials. However, many animal model studies have provided rationale for the use of Mabs and nanobodies in C. difficile infection and pave the way for further clinical investigation.     

Fidaxomicin: a minimally absorbed macrocyclic antibiotic for the treatment of Clostridium difficile infections

Fidaxomicin was approved for the treatment of Clostridium difficile infections in 2011. It has a novel mechanism of action and narrow spectrum of activity that makes it unique among the currently used therapies for this disease. Phase III clinical studies demonstrated a benefit of fidaxomicin over vancomycin for the outcomes of recurrence and global cure or sustained clinical response. This observation was confirmed within specific populations, including those of older age, immunocompromised due to active cancers, and patients taking concomitant antibiotics. Additionally, fidaxomicin significantly reduced recurrence rates compared to vancomycin among patients receiving treatment for recurrent C. difficile episodes. Fidaxomicin represents an advance in therapy for the treatment of C. difficile infections.     

Surveillance and management of multidrug-resistant microorganisms

Multidrug-resistant organisms are an established and growing worldwide public health problem and few therapeutic options remain available. The traditional antimicrobials (glycopeptides) for multidrug-resistant Gram-positive infections are declining in efficacy. New drugs that are presently available are linezolid, daptomicin and tigecycline, which have well-defined indications for severe infections, and talavancin, which is under Phase III trial for hospital-acquired pneumonia. Unfortunately the therapies available for multidrug-resistant Gram-negatives, including carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii and Enterobacteriaceae, are limited to only colistin and tigecycline. Both of these drugs are still not registered for severe infections, such as hospital acquired pneumonia. Consequently, as confirmed by scientific evidence, a multidisciplinary approach is needed. Surveillance, infection control procedures, isolation and antimicrobial stewardship should be implemented to reduce multidrug-resistant organism diffusion.     

Kinoid of human tumor necrosis factor-alpha for rheumatoid arthritis

Introduction: Anti-TNF-α drugs have dramatically changed treatment of rheumatoid arthritis (RA) in terms of both clinical control and articular damage prevention. Despite this, they hold some important drawbacks, such as frequent therapeutic failures and high costs. Anti-TNF-α active immunization, with a therapeutic vaccine against TNF-α, is a promising alternative anti-TNF-α targeting strategy, potentially devoid of treatment limitations of some of current anti-TNF blocking agents.

Areas covered: This review covers the preclinical proof-of-concept of anti-TNF-α vaccination with the kinoid of human TNF-α (TNFK) and analyzes the body of evidence forming the rationale for the application of this strategy in RA and other TNF-α-dependent diseases. We describe the theoretical bases of anti-TNF-α active immunization and of experimental data supporting the applicability of TNFK to human disease in terms of both safety and efficacy.

Expert opinion: Based on preclinical efficacy and safety data supporting its feasibility in a Phase I – II trial in Crohn's disease, anti-TNF-α vaccination with TNFK has entered the phase of clinical development and promises to be a valuable anti-TNF-α targeting strategy in human disease. The focus is made in the first clinical trial in RA (Phase II) on the efficacy in active RA patients having developed antibodies against anti-TNF mAbs.     

Fidaxomicin: first-in-class macrocyclic antibiotic

The incidence of Clostridium difficile has doubled over the past 15 years, and rising mortality rates associated with this infection have followed in its wake. C. difficile infection (CDI) has supplanted methicillin-resistant Staphylococcus aureus as the major cause of nosocomial infection. An insufficient response rate to currently available CDI therapies has prompted the search for new and alternative treatment modalities for this disease. The investigational pipeline includes evaluation of new antimicrobial agents that exhibit good activity against C. difficile without altering normal gut flora, C. difficile toxin-absorbing compounds, and preformed antibodies and vaccines against C. difficile toxin. In two robust clinical trials comparing fidaxomicin to vancomycin in the treatment of CDI, treatment with fidaxomicin demonstrated a superior global cure (cure without recurrence) rate compared with the current gold standard, vancomycin. Fidaxomicin, the first of a new class of macrocyclic antimicrobial agents, represents an advance in the management of CDI.     

Tedizolid for treatment of acute bacterial skin and skin structure infections

Tedizolid is a newly approved drug of the oxazolidinone class. It has high in vitro activity against Gram-positive bacteria, including multidrug-resistant strains. Peak plasma concentration of tedizolid is obtained within 3 h of oral dosing (PO), with high bioavailability. Tedizolid is mostly metabolized via the liver, and is excreted in feces in the form of a sulfate conjugate. Tedizolid 200 mg taken once daily demonstrated non-inferior efficacy and a good safety profile in patients with acute bacterial skin and skin structure infections. Results of two pivotal Phase III clinical trials showed that 6 days of 200 mg tedizolid PO or sequential intravenous (IV)/PO once-daily treatment was non-inferior to 10 days of 600 mg linezolid PO or sequential IV/PO twice-daily treatment at 48–72 h (primary end point) and at the test-of-cure in patients with acute bacterial skin and skin structure infections. The Phase II and Phase III trials also demonstrated that tedizolid was well tolerated.     

Effects of Tigecycline and Vancomycin Administration on Established Clostridium difficile Infection

The glycylcycline antibiotic tigecycline was approved in 2005 for the treatment of complicated skin and soft tissue infections and complicated intra-abdominal infections. Tigecycline is broadly active against both Gram-negative and Gram-positive microorganisms, including Clostridium difficile. Tigecycline has a low MIC against C. difficile in vitro and thus may represent an alternate treatment for C. difficile infection (CDI). To assess the use of tigecycline for treatment of established CDI, 5- to 8-week-old C57BL/6 mice were colonized with C. difficile strain 630. After C. difficile colonization was established, mice (n = 10 per group) were treated with either a 5-day course of tigecycline (6.25 mg/kg every 12 h subcutaneously) or a 5-day course of vancomycin (0.4 mg/ml in drinking water) and compared to infected, untreated control mice. Mice were evaluated for clinical signs of CDI throughout treatment and at 1 week posttreatment to assess potential for disease development. Immediately following a treatment course, C. difficile was not detectable in the feces of vancomycin-treated mice but remained detectable in feces from tigecycline-treated and untreated control mice. Toxin activity and histopathological inflammation and edema were observed in the ceca and colons of untreated mice; tigecycline- and vancomycin-treated mice did not show such changes directly after treatment. One week after the conclusion of either antibiotic treatment, C. difficile load, toxin activity, and histopathology scores increased in the cecum and colon, indicating that C. difficile-associated disease occurred. In vitro growth studies confirmed that subinhibitory concentrations of tigecycline were able to suppress toxin activity and spore formation of C. difficile, whereas vancomycin did not. Taken together, these data show how tigecycline is able to alter C. difficile pathogenesis in a mouse model of CDI.     

Telavancin: a new lipoglycopeptide with multiple mechanisms of action

Antimicrobial resistance among Gram-positive organisms continues to increase and has reached epidemic proportions in numerous countries. Telavancin is a semisynthetic lipoglycopeptide with a dual mechanism of action that involves the inhibition of cell-wall synthesis and disruption of bacterial cell-membrane barrier functions. Telavancin exhibits a rapid bactericidal activity against Staphylococcus aureus. It is also active against coagulase-negative staphylococci, enterococci, streptococci and various anaerobic Gram-positive organisms. Telavancin has a prolonged postantibiotic effect and distributes well into cutaneous and pulmonary tissues. Furthermore, it has a low potential for development of resistance and is well tolerated. The overall incidence of adverse events in patients receiving telavancin was similar to that observed with standard therapy and recent data from preliminary clinical trials have demonstrated similar efficacy to standard therapy in the treatment of complicated skin and skin-structure infections. Therefore, telavancin is a promising new antimicrobial agent for the treatment of infections caused by resistant Gram-positive pathogens.     

Emepepimut-S for non-small cell lung cancer

Introduction: Immunotherapy as a possible therapeutic option for cancer has been of great importance due to the innovative development of vaccines. Various molecules have been tested and emepepimut-S (Biomira Liposomal Peptide 25 (BLP 25)) has emerged as an option, particularly in lung cancer.

Areas covered: A PubMed literature and ClinicalTrials.gov search was conducted using the terms: emepepimut, BLP25, NSCLC, cancer immunotherapy, cancer vaccine and MUC1. This review covers how emepepimut-S acts against the mucin 1 (MUC1) tumor-associated antigen producing a cellular immune response against the cells that express MUC1 and the most important clinical data available that led to the ongoing Phase III trial.

Expert opinion: The results obtained in the Phase I/II trials are promising, showing a favorable toxicity with a benefit in survival in NSCLC patients. As future trials develop, demonstration of the long-term survival benefit, understanding of the various mechanisms of immune response initiated by the drug and the selection of patients that will highly benefit from the immunotherapy will be elucidated. The safety and extension in survival makes emepepimut-S a very interesting drug and could, therefore, offer a possibility of treatment and maintenance, particularly for good performance status patients with locally advanced NSCLC.