Activity of a novel cyclic lipopeptide, CB-183,315, against resistant Clostridium difficile and other Gram-positive aerobic and anaerobic intestinal pathogens

Pathogenicity and virulence of Clostridioides difficile

Clostridioides difficile is the most common cause of nosocomial antibiotic-associated diarrhea, and is responsible for a spectrum of diseases characterized by high levels of recurrence, morbidity, and mortality. Treatment is complex, since antibiotics constitute both the main treatment and the major risk factor for infection. Worryingly, resistance to multiple antibiotics is becoming increasingly widespread, leading to the classification of this pathogen as an urgent threat to global health. As a consummate opportunist, C. difficile is well equipped for promoting disease, owing to its arsenal of virulence factors: transmission of this anaerobe is highly efficient due to the formation of robust endospores, and an array of adhesins promote gut colonization. C. difficile produces multiple toxins acting upon gut epithelia, resulting in manifestations typical of diarrheal disease, and severe inflammation in a subset of patients. This review focuses on such virulence factors, as well as the importance of antimicrobial resistance and genome plasticity in enabling pathogenesis and persistence of this important pathogen.

Mechanism of Antibacterial Activity of Bacillus amyloliquefaciens C-1 Lipopeptide toward Anaerobic Clostridium difficile

Probiotics may offer an attractive alternative for standard antibiotic therapy to treat Clostridium difficile infections (CDI). In this study, the antibacterial mechanism in vitro of newly isolated B. amyloliquefaciens C-1 against C. difficile was investigated. The lipopeptides surfactin, iturin, and fengycin produced by C-1 strongly inhibited C. difficile growth and viability. Systematic research of the bacteriostatic mechanism showed that the C-1 lipopeptides damage the integrity of the C. difficile cell wall and cell membrane. In addition, the lipopeptide binds to C. difficile genomic DNA, leading to cell death. Genome resequencing revealed many important antimicrobial compound-encoding clusters, including six nonribosomal peptides (surfactins (srfABCD), iturins (ituABCD), fengycins (fenABCDE), bacillibactin (bmyABC), teichuronic, and bacilysin) and three polyketides (bacillaene (baeEDLMNJRS), difficidin (difABCDEFGHIJ), and macrolactin (mlnABCDEFGHI)). In addition, there were other beneficial genes, such as phospholipase and seven siderophore biosynthesis gene clusters, which may contribute synergistically to the antibacterial activity of B. amyloliquefaciens C-1. We suggest that proper application of antimicrobial peptides may be effective in C. difficile control.

The Quest for Novel Antimicrobial Compounds: Emerging Trends in Research, Development, and Technologies

Pathogenic antibiotic resistant bacteria pose one of the most important health challenges of the 21st century. The overuse and abuse of antibiotics coupled with the natural evolutionary processes of bacteria has led to this crisis. Only incremental advances in antibiotic development have occurred over the last 30 years. Novel classes of molecules, such as engineered antibodies, antibiotic enhancers, siderophore conjugates, engineered phages, photo-switchable antibiotics, and genome editing facilitated by the CRISPR/Cas system, are providing new avenues to facilitate the development of antimicrobial therapies. The informatics revolution is transforming research and development efforts to discover novel antibiotics. The explosion of nanotechnology and micro-engineering is driving the invention of antimicrobial materials, enabling the cultivation of "uncultivable" microbes and creating specific and rapid diagnostic technologies. Finally, a revival in the ecological aspects of microbial disease management, the growth of prebiotics, and integrated management based on the "One Health" model, provide additional avenues to manage this health crisis. These, and future scientific and technological developments, must be coupled and aligned with sound policy and public awareness to address the risks posed by rising antibiotic resistance.

Current developments in lantibiotic discovery for treating Clostridium difficile infection

INTRODUCTION

Clostridium difficile is a major cause of healthcare-associated diarrhea linked to the misuse of antimicrobials and the corresponding deleterious impact they have on the protective microbiota of the gut. Resistance to agents used to treat C. difficile including metronizadole and vancomycin has been reported highlighting the need for novel agents. Lantibiotics represent a novel class of agents that many studies have highlighted as effective against C. difficile. Areas covered: In this review lantibiotics including nisin, actagardine, mersacidin, NAI-107 and MU-1140 that exhibit good activity against C.difficile, all of which are currently in the preclinical phase of investigation are discussed. The lantibiotic NVB302, which has completed phase I clinical trials for the treatment of C. difficile, is also described. Expert opinion: Lantibiotics represent promising candidates for the treatment of C. difficile infections due to their novel mode of action, which is thought to decrease the potential of resistance developing and the fact they often possess a less deleterious effect on the protective gut microbiota when compared to traditional agents. They are also extremely amenable to bioengineering approaches and the incorporation of synthetic biology to produce more potent variants.

Sub-lethal doses of surotomycin and vancomycin have similar effects on Clostridium difficile virulence factor production in vitro

PURPOSE

Clostridium difficile is an anaerobic spore-forming bacterial pathogen that causes a spectrum of illness severity ranging from mild diarrhoea to severe life-threatening pseudomembranous colitis. C. difficile infection (CDI) is antibiotic-associated and primarily mediated by two exotoxins, Toxins A and B. We and others have shown that some antibiotics stimulate Toxin A and B production by C. difficile in a strain-specific manner. Still, the effects of newer anti-C. difficile antibiotics on this process and spore formation remain to be investigated.

METHODOLOGY

Surotomycin (formally CB-183,315) is a novel, minimally absorbed, narrow-spectrum antibiotic. We determined the effects of surotomycin on C. difficile growth, toxin production and sporulation in historical and BI/NAP1/027 epidemic strains of C. difficile.Results/Key findings. While antibiotic free controls showed toxin production during the stationary phase growth, all strains exposed to sub-inhibitory concentrations of surotomycin and vancomycin demonstrated increased TcdA and TcdB production during early (log phase) growth by all strains. However, this effect was not observed at 24 or 48 h post-treatment by any of the C. difficile strains exposed to either antibiotic. Additionally, all doses of surotomycin and vancomycin suppressed spore formation in all tested strains.

CONCLUSION

In summary, these findings demonstrate that surotomycin and vancomycin have similar effects on exotoxin production and sporulation by C. difficile in vitro. Furthermore, since spores contribute to recurrent infection, the ability of surotomycin to suppress spore formation may explain its ability to disrupt the reinfection cycle in the clinical setting.

A Small Molecule-Screening Pipeline to Evaluate the Therapeutic Potential of 2-Aminoimidazole Molecules Against Clostridium difficile

Antibiotics are considered to be the first line of treatment for mild to moderately severe Clostridium difficile infection (CDI) in humans. However, antibiotics are also risk factors for CDI as they decrease colonization resistance against C. difficile by altering the gut microbiota and metabolome. Finding compounds that selectively inhibit different stages of the C. difficile life cycle, while sparing the indigenous gut microbiota is important for the development of alternatives to standard antibiotic treatment. 2-aminoimidazole (2-AI) molecules are known to disrupt bacterial protection mechanisms in antibiotic resistant bacteria such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus, but are yet to be evaluated against C. difficile. A comprehensive small molecule-screening pipeline was developed to investigate how novel small molecules affect different stages of the C. difficile life cycle (growth, toxin, and sporulation) in vitro, and a library of commensal bacteria that are associated with colonization resistance against C. difficile. The initial screening tested the efficacy of eleven 2-AI molecules (compound 1 through 11) against C. difficile R20291 compared to a vancomycin (2 μg/ml) control. Molecules were selected for their ability to inhibit C. difficile growth, toxin activity, and sporulation. Further testing included growth inhibition of other C. difficile strains (CD196, M68, CF5, 630, BI9, M120) belonging to distinct PCR ribotypes, and a commensal panel (Bacteroides fragilis, B. thetaiotaomicron, C. scindens, C. hylemonae, Lactobacillus acidophilus, L. gasseri, Escherichia coli, B. longum subsp. infantis). Three molecules compound 1 and 2, and 3 were microbicidal, whereas compounds 4, 7, 9, and 11 inhibited toxin activity without affecting the growth of C. difficile strains and the commensal microbiota. The antimicrobial and anti-toxin effects of 2-AI molecules need to be further characterized for mode of action and validated in a mouse model of CDI.

New and emerging therapies in treatment of Clostridium difficile infection

Clostridium difficile infection (CDI) represents one of the most serious nosocomial infections that have grown dramatically over the past decade. Vancomycin and metronidazole are currently used as a standard therapy for CDI. Metronidazole is recommended as a first-line therapy for mild-to-moderate infections and vancomycin is mainly used for severe and/or refractory cases. However, studies have demonstrated that there are quite high CDI relapse rates with both of these medications, which represents a challenge for clinicians. Over the last decade, a number of newer and novel therapeutic options have emerged as promising alternatives to these standard CDI therapies. The following review provides the updated summaries of these newer therapeutic agents and their status in the treatment of CDI.

Novel Antimicrobials for the Treatment of Clostridium difficile Infection

The current picture of Clostridium difficile infection (CDI) is alarming with a mortality rate ranging between 3% and 15% and a CDI recurrence rate ranging from 12% to 40%. Despite the great efforts made over the past 10 years to face the CDI burden, there are still gray areas in our knowledge on CDI management. The traditional anti-CDI antimicrobials are not always adequate in addressing the current needs in CDI management. The aim of our review is to give an update on novel antimicrobials for the treatment of CDI, considering the currently available evidences on their efficacy, safety, molecular mechanism of action, and their probability to be successfully introduced into the clinical practice in the near future. We identified, through a PubMed search, 16 novel antimicrobial molecules under study for CDI treatment: cadazolid, surotomycin, ridinilazole, LFF571, ramoplanin, CRS3123, fusidic acid, nitazoxanide, rifampin, rifaximin, tigecycline, auranofin, NVB302, thuricin CD, lacticin 3147, and acyldepsipeptide antimicrobials. In comparison with the traditional anti-CDI antimicrobial treatment, some of the novel antimicrobials reviewed in this study offer several advantages, i.e., the favorable pharmacokinetic and pharmacodynamic profile, the narrow-spectrum activity against CD that implicates a low impact on the gut microbiota composition, the inhibitory activity on CD sporulation and toxins production. Among these novel antimicrobials, the most active compounds in reducing spore production are cadazolid, ridinilazole, CRS3123, ramoplanin and, potentially, the acyldepsipeptide antimicrobials. These antimicrobials may potentially reduce CD environment spread and persistence, thus reducing CDI healthcare-associated acquisition. However, some of them, i.e., surotomycin, fusidic acid, etc., will not be available due to lack of superiority versus standard of treatment. The most CD narrow-spectrum novel antimicrobials that allow to preserve microbiota integrity are cadazolid, ridinilazole, auranofin, and thuricin CD. In conclusion, the novel antimicrobial molecules under development for CDI have promising key features and advancements in comparison to the traditional anti-CDI antimicrobials. In the near future, some of these new molecules might be effective alternatives to fight CDI.

Clostridioides (Clostridium) difficile infection: current and alternative therapeutic strategies

Clostridioides difficile (C. difficile) has become a pathogen of worldwide importance considering that epidemic strains are disseminated in hospitals of several countries, where community-acquired infections act as a constant source of new C. difficile strains into hospitals. Despite the advances in the treatment of infections, more effective therapies against C. difficile are needed but, at the same time, these therapies should be less harmful to the resident gastrointestinal microbiota. The purpose of this review is to present a description of issues associated to C. difficile infection, a summary of current therapies and those in developmental stage, and a discussion of potential combinations that may lead to an increased efficacy of C. difficile infection treatment.

Actinomycetes: still a source of novel antibiotics

Covering: 2006 to 2017Actinomycetes have been, for decades, one of the most important sources for the discovery of new antibiotics with an important number of drugs and analogs successfully introduced in the market and still used today in clinical practice. The intensive antibacterial discovery effort that generated the large number of highly potent broad-spectrum antibiotics, has seen a dramatic decline in the large pharma industry in the last two decades resulting in a lack of new classes of antibiotics with novel mechanisms of action reaching the clinic. Whereas the decline in the number of new chemical scaffolds and the rediscovery problem of old known molecules has become a hurdle for industrial natural products discovery programs, new actinomycetes compounds and leads have continued to be discovered and developed to the preclinical stages. Actinomycetes are still one of the most important sources of chemical diversity and a reservoir to mine for novel structures that is requiring the integration of diverse disciplines. These can range from novel strategies to isolate species previously not cultivated, innovative whole cell screening approaches and on-site analytical detection and dereplication tools for novel compounds, to in silico biosynthetic predictions from whole gene sequences and novel engineered heterologous expression, that have inspired the isolation of new NPs and shown their potential application in the discovery of novel antibiotics. This review will address the discovery of antibiotics from actinomycetes from two different perspectives including: (1) an update of the most important antibiotics that have only reached the clinical development in the recent years despite their early discovery, and (2) an overview of the most recent classes of antibiotics described from 2006 to 2017 in the framework of the different strategies employed to untap novel compounds previously overlooked with traditional approaches.

Recent advances in synthetic lipopeptides as anti-microbial agents: designs and synthetic approaches

Infectious diseases impose serious public health burdens and continue to be a global public health crisis. The treatment of infections caused by multidrug-resistant pathogens is challenging because only a few viable therapeutic options are clinically available. The emergence and risk of drug-resistant superbugs and the dearth of new classes of antibiotics have drawn increasing awareness that we may return to the pre-antibiotic era. To date, lipopeptides have been received considerable attention because of the following properties: They exhibit potent antimicrobial activities against a broad spectrum of pathogens, rapid bactericidal activity and have a different antimicrobial action compared with most of the conventional antibiotics used today and very slow development of drug resistance tendency. In general, lipopeptides can be structurally classified into two parts: a hydrophilic peptide moiety and a hydrophobic fatty acyl chain. To date, a significant amount of design and synthesis of lipopeptides have been done to improve the therapeutic potential of lipopeptides. This review will present the current knowledge and the recent research in design and synthesis of new lipopeptides and their derivatives in the last 5 years.

Susceptibilities of clinical Clostridium difficile isolates to antimicrobials: a systematic review and meta-analysis of studies since 1970

OBJECTIVES

Although exposure to antibiotics can cause Clostridium difficile infection, certain antibiotics are used to treat C. difficile. Measurements of antimicrobial C. difficile activity could help to identify antibiotic risk and emergent resistance. Here, we describe publication patterns relating to C. difficile susceptibilities and estimate minimum inhibitory concentrations (MIC) for antibiotic classes in the published literature between January 1970 and June 2014.

METHODS

We queried PUBMED and EMBASE for studies reporting antibiotic C. difficile MIC in English or French. We used mixed-effects models to obtain pooled estimates of antibiotic class median MIC (MIC₅₀), 90th percentile of MIC (MIC₉₀), and MIC₉₀:MIC₅₀ ratio.

RESULTS

Our search identified 182 articles that met our inclusion criteria, of which 27 were retained for meta-analysis. Aminoglycosides (MIC₅₀ 120 mg/L, 95% CI 62-250), 3rd (MIC₅₀ 75 mg/L, 95% CI 39-130) and 2nd generation cephalosporins (MIC₅₀ 64 mg/L, 95% CI 27-140) had the least C. difficile activity. Rifamycins (MIC₅₀ 0.034 mg/L, 95% CI 0.012-0.099) and tetracyclines (MIC₅₀ 0.29 mg/L, 95% CI 0.054-1.7) had the highest level of activity. The activity of 3rd generation cephalosporins was more than three times lower than that of 1st generation agents (MIC₅₀ 19 mg/L, 95% CI 7.0-54). Time-trends in MIC₅₀ were increasing for carbapenems (70% increase per 10 years) while decreasing for tetracyclines (51% decrease per 10 years).

CONCLUSIONS

We found a 3500-fold variation in antibiotic C. difficile MIC₅₀, with aminoglycosides as the least active agents and rifamycins as the most active. Further research is needed to determine how in vitro measures can help assess patient C. difficile risk and guide antimicrobial stewardship.

Orally Absorbed Cyclic Peptides

Peptides and proteins are not orally bioavailable in mammals, although a few peptides are intestinally absorbed in small amounts. Polypeptides are generally too large and polar to passively diffuse through lipid membranes, while most known active transport mechanisms facilitate cell uptake of only very small peptides. Systematic evaluations of peptides with molecular weights above 500 Da are needed to identify parameters that influence oral bioavailability. Here we describe 125 cyclic peptides containing four to thirty-seven amino acids that are orally absorbed by mammals. Cyclization minimizes degradation in the gut, blood, and tissues by removing cleavable N- and C-termini and by shielding components from metabolic enzymes. Cyclization also folds peptides into bioactive conformations that determine exposure of polar atoms to solvation by water and lipids and therefore can influence oral bioavailability. Key chemical properties thought to influence oral absorption and bioavailability are analyzed, including molecular weight, octanol-water partitioning, hydrogen bond donors/acceptors, rotatable bonds, and polar surface area. The cyclic peptides violated to different degrees all of the limits traditionally considered to be important for oral bioavailability of drug-like small molecules, although fewer hydrogen bond donors and reduced flexibility generally favored oral absorption.

Pharmacokinetics of surotomycin from phase 1 single and multiple ascending dose studies in healthy volunteers

Background

Surotomycin, a novel, orally administered, cyclic, lipopeptide antibacterial in development for the treatment of Clostridium difficile-associated diarrhea, has demonstrated minimal intestinal absorption in animal models.

Methods

Safety, tolerability, and plasma pharmacokinetics of single and multiple ascending oral doses (SAD/MAD) of surotomycin in healthy volunteers were characterized in two randomized, double-blind, placebo-controlled, phase 1 studies.

Results

Participants were sequentially enrolled into one of four SAD (500, 1000, 2000, 4000 mg surotomycin) or three MAD (250, 500, 1000 mg surotomycin twice/day for 14 days) cohorts. Ten subjects were randomized 4:1 into each cohort to receive surotomycin or placebo. Surotomycin plasma concentrations rose as dose increased (maximum plasma concentration [C_max]: 10.5, 21.5, 66.6, and 86.7 ng/mL). Systemic levels were generally low, with peak median surotomycin plasma concentrations observed 6–12 h after the first dose. In the MAD study, surotomycin plasma concentrations were higher on day 14 (C_max: 25.5, 37.6, and 93.5 ng/mL) than on day 1 (C_max: 6.8, 11.0, and 21.1 ng/mL for increasing doses), indicating accumulation. In the SAD study, <0.01% of the administered dose was recovered in urine. Mean surotomycin stool concentration from the 1000 mg MAD cohort was 6394 μg/g on day 5. Both cohorts were well tolerated with all adverse events reported as mild to moderate.

Conclusion

Both SAD and MAD studies of surotomycin demonstrated minimal systemic exposure, with feces the primary route of elimination following oral administration; consistent with observations with similar compounds, such as fidaxomicin. Results of these phase 1 studies support the continued clinical development of surotomycin for the treatment of Clostridium difficile-associated diarrhea.

Trial registration

NCT02835118 and NCT02835105. Retrospectively registered, July 13 2016.

A Review of Experimental and Off-Label Therapies for Clostridium difficile Infection

In spite of increased awareness and the efforts taken to optimize Clostridium difficile infection (CDI) management, with the limited number of currently available antibiotics for C. difficile the halt of this increasing epidemic remains out of reach. There are, however, close to 80 alternative treatment methods with controversial anti-clostridial efficacy or in experimental phase today. Indeed, some of these therapies are expected to become acknowledged members of the recommended anti-CDI arsenal within the next few years. None of these alternative treatment methods can respond in itself to all the major challenges of CDI management, which are primary prophylaxis in the susceptible population, clinical cure of severe cases, prevention of recurrences, and forestallment of asymptomatic C. difficile carriage and in-hospital spread. Yet, the greater the variety of treatment choices on hand, the better combination strategies can be developed to reach these goals in the future. The aim of this article is to provide a comprehensive summary of these experimental and currently off-label therapeutic options.

Primary Outcomes From a Phase 3, Randomized, Double-Blind, Active-Controlled Trial of Surotomycin in Subjects With Clostridium difficile Infection

Background

Although the incidence of Clostridium difficile infection (CDI) is increasing, available CDI treatment options are limited in terms of sustained response after treatment. This phase 3 trial assessed the efficacy and safety of surotomycin, a novel bactericidal cyclic lipopeptide, versus oral vancomycin in subjects with CDI.

Methods

In this randomized, double-blind, active-controlled, multicenter, international trial, subjects with CDI confirmed by a positive toxin result were randomized to receive surotomycin (250 mg twice daily) or vancomycin (125 mg 4 times daily) orally for 10 days. The primary endpoints were clinical response at end of treatment and evaluation of surotomycin safety. The key secondary endpoints were clinical response over time and sustained clinical response through a 30- to 40-day follow-up period. Clostridium difficile infection recurrence during follow-up and time to diarrhea resolution were also analyzed.

Results

In total, 570 subjects were randomized and had confirmed CDI; 290 subjects received surotomycin and 280 subjects received vancomycin. Surotomycin clinical cure rates at end of treatment (surotomycin/vancomycin: 79.0%/83.6%; difference of −4.6%; 95% confidence interval, −11.0 to 1.9]), clinical response over time (stratified log-rank test, P = .832), and sustained clinical response at end of trial (Day 40–50) (60.6%/61.4%; difference of −0.8%; 95% CI, −8.8 to 7.1) in the microbiological modified intent to treat population did not meet noninferiority or superiority criteria versus vancomycin. Both treatments were generally well tolerated.

Conclusions

Surotomycin failed to meet the criteria for noninferiority versus vancomycin for the primary and key secondary endpoints in this trial.

Novel antibiotics in development to treat Clostridium difficile infection

PURPOSE OF REVIEW

Clostridium difficile infections (CDI) remain a challenge to treat clinically due primarily to limited number of antibiotics available and unacceptably high recurrence rates. Because of this, there has been significant demand for creating innovative therapeutics, which has resulted in the development of several novel antibiotics.

RECENT FINDINGS

This review updates seven different antibiotics that are currently in development to treat CDI including fidaxomicin, surotomycin, ridinilazole, ramoplanin, cadazolid, LFF571, and CRS3123. Available preclinical and clinical data are compared between these antibiotics.

SUMMARY

Many of these new antibiotics display almost ideal properties for antibiotics directed against CDI. Despite these properties, not all clinical development of these compounds has been successful. These studies have provided key insights into the pathogenesis of CDI and will continue to inform future drug development. Successful phase III clinical trials should result in several new and novel antibiotics to treat CDI.

Reprofiled anthelmintics abate hypervirulent stationary-phase Clostridium difficile

Prolonged use of broad-spectrum antibiotics disrupts the indigenous gut microbiota, which consequently enables toxigenic Clostridium difficile species to proliferate and cause infection. The burden of C. difficile infections was exacerbated with the outbreak of hypervirulent strains that produce copious amounts of enterotoxins and spores. In recent past, membrane-active agents have generated a surge of interest due to their bactericidal property with a low propensity for resistance. In this study, we capitalized on the antimicrobial property and low oral bioavailability of salicylanilide anthelmintics (closantel, rafoxanide, niclosamide, oxyclozanide) to target the gut pathogen. By broth microdilution techniques, we determined the MIC values of the anthelmintics against 16 C. difficile isolates of defined PCR-ribotype. The anthelmintics broadly inhibited C. difficile growth in vitro via a membrane depolarization mechanism. Interestingly, the salicylanilides were bactericidal against logarithmic- and stationary-phase cultures of the BI/NAP1/027 strain 4118. The salicylanilides were poorly active against select gut commensals (Bacteroides, Bifidobacterium and Lactobacillus species), and were non-hemolytic and non-toxic to mammalian cell lines HepG2 and HEK 293T/17 within the range of their in vitro MICs and MBCs. The salicylanilide anthelmintics exhibit desirable properties for repositioning as anti-C. difficile agents.

New antibiotics in clinical trials for Clostridium difficile

INTRODUCTION

There are limited number of approved therapies for C. difficile infections (CDIs) and new treatments are needed to decrease recurrence rates. Over the past 5 years, four novel antibiotics have been evaluated in clinical trials that offer distinct advantages over existing therapies for the treatment of CDI.

AREAS COVERED

This article reviews the preclinical and clinical studies of cadazolid, LFF571, ridinilazole, and surotomycin. The advantages that these antibiotics may have in the treatment of CDI is compared with current therapies metronidazole, vancomycin, and fidaxomicin. Expert commentary: The antibiotics examined have the potential to improve rates of CDI treatment without recurrence. We anticipate that one or more of these medications will be approved within five years.

Surotomycin versus vancomycin for Clostridium difficile infection: Phase 2, randomized, controlled, double-blind, non-inferiority, multicentre trial

OBJECTIVES

Clostridium difficile infection (CDI) is a major public health concern. Treatment with commonly prescribed antibiotics is associated with high rates of recurrence after initial cure. Here, we present the efficacy and safety of surotomycin, an orally administered, minimally absorbed, selective bactericidal cyclic lipopeptide, compared with vancomycin, in patients with CDI.

METHODS

In this Phase 2, randomized, controlled, double-blind, non-inferiority, multicentre trial, participants received surotomycin 125 mg twice daily, surotomycin 250 mg twice daily or vancomycin 125 mg four times daily for 10 days. The primary efficacy outcome was clinical response at end of treatment. The registration number of the study on clinicaltrials.gov is NCT01085591.

RESULTS

Clinical cure rates were similar among treatment groups (92.4% for surotomycin 125 mg twice daily, 86.6% for surotomycin 250 mg twice daily and 89.4% for vancomycin). Recurrence rates were 27.9% for surotomycin 125 mg twice daily, 17.2% for surotomycin 250 mg twice daily and 35.6% for vancomycin. The lower recurrence rate with surotomycin 250 mg twice daily versus vancomycin was statistically significant (P = 0.035). Recurrence rates were statistically similar between the surotomycin dose groups (P = 0.193). Rates of sustained clinical response at end of study were 66.7% for surotomycin 125 mg twice daily, 70.1% for surotomycin 250 mg twice daily and 56.1% for vancomycin. Incidence of adverse events was similar among treatment arms.

CONCLUSIONS

Recurrence rates of CDI were lower with surotomycin with higher sustained clinical response rates compared with vancomycin, both of which may offer potential clinical benefits.

Antibiotics in the clinical pipeline at the end of 2015

There is growing global recognition that the continued emergence of multidrug-resistant bacteria poses a serious threat to human health. Action plans released by the World Health Organization and governments of the UK and USA in particular recognize that discovering new antibiotics, particularly those with new modes of action, is one essential element required to avert future catastrophic pandemics. This review lists the 30 antibiotics and two β-lactamase/β-lactam combinations first launched since 2000, and analyzes in depth seven new antibiotics and two new β-lactam/β-lactamase inhibitor combinations launched since 2013. The development status, mode of action, spectra of activity and genesis (natural product, natural product-derived, synthetic or protein/mammalian peptide) of the 37 compounds and six β-lactamase/β-lactam combinations being evaluated in clinical trials between 2013 and 2015 are discussed. Compounds discontinued from clinical development since 2013 and new antibacterial pharmacophores are also reviewed.

Effect of Surotomycin, a Novel Cyclic Lipopeptide Antibiotic, on Intestinal Colonization with Vancomycin-Resistant Enterococci and Klebsiella pneumoniae in Mice

Surotomycin (formerly called CB-183,315) is a novel, orally administered cyclic lipopeptide antibacterial in development for the treatment of Clostridium difficile infection (CDI) that has potent activity against vancomycin-resistant enterococci (VRE) but limited activity against Gram-negative bacilli, including Bacteroides spp. We used a mouse model to investigate the impact of surotomycin exposure on the microbiome, and to test the consequences of the disruption on colonization by vancomycin-resistant enterococci (VRE) and extended-spectrum β-lactamase-producing Klebsiella pneumoniae (ESBL-KP), in comparison with the effects of oral vancomycin and metronidazole. Mice (8 per group) received saline, vancomycin, metronidazole, or surotomycin through an orogastric tube daily for 5 days and were challenged with 10(5) CFU of VRE or ESBL-KP administered through an orogastric tube on day 2 of treatment. The concentrations of the pathogens in stool were determined during and after treatment by plating on selective media. A second experiment was conducted to determine if the antibiotics would inhibit established VRE colonization. In comparison to controls, oral vancomycin promoted VRE and ESBL-KP overgrowth in stool (8 log10 to 10 log10 CFU/g; P < 0.001), whereas metronidazole did not (<4 log10 CFU/g; P > 0.5). Surotomycin promoted ESBL-KP overgrowth (>8 log10 CFU/g; P, <0.001 for comparison with saline controls) but not VRE overgrowth. Surotomycin suppressed preexisting VRE colonization, whereas metronidazole and vancomycin did not. These results suggest that treatment of CDI with surotomycin could reduce levels of VRE acquisition and overgrowth from those with agents such as vancomycin and metronidazole. However, surotomycin and vancomycin may promote colonization by antibiotic-resistant Gram-negative bacilli.

Impact of Surotomycin on the Gut Microbiota of Healthy Volunteers in a Phase 1 Clinical Trial

Clostridium difficile-associated diarrhea has been associated with disruption of the normal intestinal microbiota, particularly theBacteroides fragilisgroup andPrevotellaspecies. Surotomycin is a bactericidal cyclic lipopeptide in development for treatment ofClostridium difficile-associated diarrhea that has selective and potent activity againstC. difficileand other Gram-positive bacteria and a minimal impact on intestinal Gram-negative organisms. The impacts of ascending doses of surotomycin on major organism groups in the gut microbiota of healthy volunteers were evaluated during a randomized, double-blind, placebo-controlled, multiple-dose phase 1 study. Thirty volunteers were randomized into 3 cohorts, using a 4:1 ratio, to receive 250 mg, 500 mg, or 1,000 mg of surotomycin, or placebo, twice daily for 14 days. Stool samples collected at baseline (days 0 and 1) and at the end of treatment (days 13 to 15) were cultured quantitatively. TheB. fragilisgroup, theBacteroides/Prevotellagroup, andEnterobacteriaceaewere also quantified by quantitative real-time PCR. Baseline and end-of-treatment stool samples showed 1- to 2-log10CFU/g reductions in total bacterial counts for most volunteers. Various decreases in clostridial,Lactobacillus-Bifidobacteriumgroup, and enterococcus-streptococcus group counts occurred while patients were receiving surotomycin, whereas the enterobacteria and theB. fragilisgroup persisted at the end of treatment. There was no change in enterococcus MICs of surotomycin, nor was vancomycin-resistantEnterococcusdetected after exposure. Surotomycin at doses of up to 1,000 mg twice daily had only modest disruptive effects on the gut microbiota. The potential sparing of the gut microbiota by surotomycin may decrease the risk of disease recurrence.

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

Test parameter variations were evaluated for their effects on surotomycin MICs. Calcium concentration was the only variable that influenced MICs; therefore, 50 μg/ml (standard for lipopeptide testing) is recommended. Quality control ranges for Clostridium difficile (0.12 to 1 μg/ml) and Eggerthella lenta (broth, 1 to 4 μg/ml; agar, 1 to 8 μg/ml) were approved by the Clinical and Laboratory Standards Institute based on these data.

Discovery and development of surotomycin for the treatment of Clostridium difficile

The primary challenge for treating Clostridium difficile infections (CDI) is maintenance of clinical response after the end of treatment (sustained clinical response). Disease recurrence following a positive clinical response occurs in approximately 6-25 % of patients after the first episode and in up to 65 % for subsequent recurrences. Surotomycin, a novel cyclic lipopeptide antibiotic with a core derived by Streptomyces roseosporus fermentation, disrupts C. difficile cellular membrane activity in both logarithmic and stationary phases and minimally disturbs normal gastrointestinal microbiota because of its lack of activity against Gram-negative anaerobes and facultative anaerobes. Preclinical and clinical evidence indicate that surotomycin has low oral bioavailability, allowing gastrointestinal tract concentrations to greatly exceed its minimum inhibitory concentration for C. difficile. Surotomycin is well tolerated and effective in hamster models of CDI. Phase 2 clinical evidence suggests that surotomycin (250 mg twice daily) is an effective CDI treatment, with statistically lower recurrence rates than vancomycin.

Recurrent Clostridium difficile infection: From colonization to cure

Clostridium difficile infection (CDI) is increasingly prevalent, dangerous and challenging to prevent and manage. Despite intense national and international attention the incidence of primary and of recurrent CDI (PCDI and RCDI, respectively) have risen rapidly throughout the past decade. Of major concern is the increase in cases of RCDI resulting in substantial morbidity, morality and economic burden. RCDI management remains challenging as there is no uniformly effective therapy, no firm consensus on optimal treatment, and reliable data regarding RCDI-specific treatment options is scant. Novel therapeutic strategies are critically needed to rapidly, accurately, and effectively identify and treat patients with, or at-risk for, RCDI. In this review we consider the factors implicated in the epidemiology, pathogenesis and clinical presentation of RCDI, evaluate current management options for RCDI and explore novel and emerging therapies.

Novel riboswitch-binding flavin analog that protects mice against Clostridium difficile infection without inhibiting cecal flora

Novel mechanisms of action and new chemical scaffolds are needed to rejuvenate antibacterial drug discovery, and riboswitch regulators of bacterial gene expression are a promising class of targets for the discovery of new leads. Herein, we report the characterization of 5-(3-(4-fluorophenyl)butyl)-7,8-dimethylpyrido[3,4-b]quinoxaline-1,3(2H,5H)-dione (5FDQD)-an analog of riboflavin that was designed to bind riboswitches that naturally recognize the essential coenzyme flavin mononucleotide (FMN) and regulate FMN and riboflavin homeostasis. In vitro, 5FDQD and FMN bind to and trigger the function of an FMN riboswitch with equipotent activity. MIC and time-kill studies demonstrated that 5FDQD has potent and rapidly bactericidal activity against Clostridium difficile. In C57BL/6 mice, 5FDQD completely prevented the onset of lethal antibiotic-induced C. difficile infection (CDI). Against a panel of bacteria representative of healthy bowel flora, the antibacterial selectivity of 5FDQD was superior to currently marketed CDI therapeutics, with very little activity against representative strains from the Bacteroides, Lactobacillus, Bifidobacterium, Actinomyces, and Prevotella genera. Accordingly, a single oral dose of 5FDQD caused less alteration of culturable cecal flora in mice than the comparators. Collectively, these data suggest that 5FDQD or closely related analogs could potentially provide a high rate of CDI cure with a low likelihood of infection recurrence. Future studies will seek to assess the role of FMN riboswitch binding to the mechanism of 5FDQD antibacterial action. In aggregate, our results indicate that riboswitch-binding antibacterial compounds can be discovered and optimized to exhibit activity profiles that merit preclinical and clinical development as potential antibacterial therapeutic agents.

Clostridium difficile drug pipeline: challenges in discovery and development of new agents

In the past decade Clostridium difficile has become a bacterial pathogen of global significance. Epidemic strains have spread throughout hospitals, while community acquired infections and other sources ensure a constant inoculation of spores into hospitals. In response to the increasing medical burden, a new C. difficile antibiotic, fidaxomicin, was approved in 2011 for the treatment of C. difficile-associated diarrhea. Rudimentary fecal transplants are also being trialed as effective treatments. Despite these advances, therapies that are more effective against C. difficile spores and less damaging to the resident gastrointestinal microbiome and that reduce recurrent disease are still desperately needed. However, bringing a new treatment for C. difficile infection to market involves particular challenges. This review covers the current drug discovery pipeline, including both small molecule and biologic therapies, and highlights the challenges associated with in vitro and in vivo models of C. difficile infection for drug screening and lead optimization.

Mutations associated with reduced surotomycin susceptibility in Clostridium difficile and Enterococcus species

Clostridium difficile infection (CDI) is an urgent public health concern causing considerable clinical and economic burdens. CDI can be treated with antibiotics, but recurrence of the disease following successful treatment of the initial episode often occurs. Surotomycin is a rapidly bactericidal cyclic lipopeptide antibiotic that is in clinical trials for CDI treatment and that has demonstrated superiority over vancomycin in preventing CDI relapse. Surotomycin is a structural analogue of the membrane-active antibiotic daptomycin. Previously, we utilized in vitro serial passage experiments to derive C. difficile strains with reduced surotomycin susceptibilities. The parent strains used included ATCC 700057 and clinical isolates from the restriction endonuclease analysis (REA) groups BI and K. Serial passage experiments were also performed with vancomycin-resistant and vancomycin-susceptible Enterococcus faecium and Enterococcus faecalis. The goal of this study is to identify mutations associated with reduced surotomycin susceptibility in C. difficile and enterococci. Illumina sequence data generated for the parent strains and serial passage isolates were compared. We identified nonsynonymous mutations in genes coding for cardiolipin synthase in C. difficile ATCC 700057, enoyl-(acyl carrier protein) reductase II (FabK) and cell division protein FtsH2 in C. difficile REA type BI, and a PadR family transcriptional regulator in C. difficile REA type K. Among the 4 enterococcal strain pairs, 20 mutations were identified, and those mutations overlap those associated with daptomycin resistance. These data give insight into the mechanism of action of surotomycin against C. difficile, possible mechanisms for resistance emergence during clinical use, and the potential impacts of surotomycin therapy on intestinal enterococci.

In vitro activity of surotomycin against contemporary clinical isolates of toxigenic Clostridium difficile strains obtained in Spain

OBJECTIVES

Clostridium difficile infection (CDI) is the leading cause of hospital-acquired diarrhoea in developed countries. Metronidazole and vancomycin are the mainstay of treatment, although they are associated with treatment failure and recurrence. Novel agents have emerged to address these shortcomings. We investigated the in vitro activity of a novel agent, surotomycin (formerly CB-183,315), and seven other antimicrobial agents against clinical C. difficile isolates.

METHODS

Antimicrobial susceptibility to surotomycin, fidaxomicin, metronidazole, vancomycin, clindamycin, rifaximin, moxifloxacin and tigecycline was determined for 100 contemporary clinical isolates of C. difficile collected in 2013. MICs were determined by agar dilution according to CLSI procedures. In addition, 10 strains with reduced susceptibility to metronidazole (n = 6) and vancomycin (n = 4) were also tested. Strains were PCR ribotyped.

RESULTS

The MICs of surotomycin for the 100 isolates ranged from ≤0.06 to 2 mg/L, with a geometric mean (GM) of 0.31 mg/L and an MIC50/90 of 0.25/0.5 mg/L. The MIC range of surotomycin was 0.25-1 mg/L (GM = 0.45 mg/L) for isolates with reduced metronidazole susceptibility and 0.125-0.5 mg/L (GM = 0.25 mg/L) for isolates with reduced vancomycin susceptibility. The three most common ribotypes were 001 (31.0%), 014/020 (17.0%) and 078/126 (17.0%). Ribotype 014/020 exhibited the lowest MICs of surotomycin (GM = 0.22 mg/L); the highest MICs were for ribotype 078/126 (GM = 0.72 mg/L).

CONCLUSIONS

Surotomycin exhibited potent in vitro activity against all the isolates tested, including those with elevated metronidazole and vancomycin MICs. The potential role of this agent in the treatment of CDI requires further clinical evaluation.

Surotomycin demonstrates low in vitro frequency of resistance and rapid bactericidal activity in Clostridium difficile, Enterococcus faecalis, and Enterococcus faecium

Surotomycin (CB-183,315) is an orally administered, minimally absorbed, selective bactericidal cyclic lipopeptide in phase 3 development for the treatment of Clostridium difficile-associated diarrhea. The aim of this study was to evaluate the emergence of resistance in C. difficile (ATCC 700057 and three recent clinical isolates from the restriction endonuclease analysis groups BI, BK, and K), vancomycin-susceptible (VS) Enterococcus faecalis (ATCC 49452), vancomycin-resistant (VR) E. faecalis (ATCC 700802), VS Enterococcus faecium (ATCC 6569), and VR E. faecium (ATCC 51559) under anaerobic conditions. The rate of spontaneous resistance was below the limit of detection (<10(-8) to <10(-9)) for surotomycin at 16 and 32× the MIC for all isolates tested. Under selective pressure by serial passage, C. difficile grew in a maximum of 4 μg/ml surotomycin (final MICs of 2 to 8 μg/ml [4- to 16-fold higher than those of the naive control]) at day 15, with the exception of the C. difficile BK strain, which grew in 16 to 32 μg/ml (final MICs of 8 to 32 μg/ml [16- to 64-fold higher than those of the naive control]). Enterococci remained relatively unchanged over 15 days, growing in a maximum of 8 μg/ml surotomycin (final MICs of 2 to 16 μg/ml [8- to 64-fold higher than those of the naive control]). Of the isolates tested, no cross-resistance to vancomycin, rifampin, ampicillin, metronidazole, or moxifloxacin was observed. Surotomycin at 20× MIC demonstrated equally rapid bactericidal activity (≥ 3-log-unit reduction in CFU/ml in ≤ 8 h) against naive and reduced-susceptibility isolates of C. difficile, VS Enterococcus (VSE), and VR Enterococcus (VRE), except for C. difficile BK (2.6-log-unit reductions for both). These results suggest that emergence of resistance to surotomycin against C. difficile, E. faecalis, and E. faecium is likely to be rare.

New developments in chemotherapeutic options for Clostridium difficile colitis

PURPOSE OF REVIEW

Clostridium difficile infections (CDIs) are of increasing concern in healthcare due to increasing incidence as well as suboptimal response to standard therapies. This review focuses on current updates in chemotherapeutic treatment options for primary CDI as well as for relapse.

RECENT FINDINGS

Metronidazole and vancomycin remain the standard therapy for mild and severe CDI, respectively. Fidaxomicin was approved for use in CDI by the US Food and Drug Administration in 2011 and new studies have shown a decreased rate of recurrence as compared with vancomycin as well as potential promise for use as a chaser. Rifaximin may be useful in salvage therapy for recurrent CDI as well as for a chaser. Tigecycline, teicoplanin, doxycycline, linezolid, nitazoxanide, amixicile, LFF571, and CB-183 315 have in-vitro activity and are under different stages of study. Monoclonal antitoxin antibodies for prevention of relapse of CDI are currently under evaluation in a phase 3 clinical trial.

SUMMARY

A variety of promising new treatment options for Clostridium difficile are under development, although further studies are necessary to determine the efficacy of these newer treatments for cure and preventing disease relapse.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.

Progress in the discovery of treatments for C. difficile infection: A clinical and medicinal chemistry review

Clostridium difficile is an anaerobic, Gram-positive pathogen that causes C. difficile infection, which results in significant morbidity and mortality. The incidence of C. difficile infection in developed countries has become increasingly high due to the emergence of newer epidemic strains, a growing elderly population, extensive use of broad spectrum antibiotics, and limited therapies for this diarrheal disease. Because treatment options currently available for C. difficile infection have some drawbacks, including cost, promotion of resistance, and selectivity problems, new agents are urgently needed to address these challenges. This review article focuses on two parts: the first part summarizes current clinical treatment strategies and agents under clinical development for C. difficile infection; the second part reviews newly reported anti-difficile agents that have been evaluated or reevaluated in the last five years and are in the early stages of drug discovery and development. Antibiotics are divided into natural product inspired and synthetic small molecule compounds that may have the potential to be more efficacious than currently approved treatments. This includes potency, selectivity, reduced cytotoxicity, and novel modes of action to prevent resistance.

Investigational antimicrobial agents of 2013

New antimicrobial agents are always needed to counteract the resistant pathogens that continue to be selected by current therapeutic regimens. This review provides a survey of known antimicrobial agents that were currently in clinical development in the fall of 2012 and spring of 2013. Data were collected from published literature primarily from 2010 to 2012, meeting abstracts (2011 to 2012), government websites, and company websites when appropriate. Compared to what was reported in previous surveys, a surprising number of new agents are currently in company pipelines, particularly in phase 3 clinical development. Familiar antibacterial classes of the quinolones, tetracyclines, oxazolidinones, glycopeptides, and cephalosporins are represented by entities with enhanced antimicrobial or pharmacological properties. More importantly, compounds of novel chemical structures targeting bacterial pathways not previously exploited are under development. Some of the most promising compounds include novel β-lactamase inhibitor combinations that target many multidrug-resistant Gram-negative bacteria, a critical medical need. Although new antimicrobial agents will continue to be needed to address increasing antibiotic resistance, there are novel agents in development to tackle at least some of the more worrisome pathogens in the current nosocomial setting.

Antibiotics in the clinical pipeline in 2013

The continued emergence of multi-drug-resistant bacteria is a major public health concern. The identification and development of new antibiotics, especially those with new modes of action, is imperative to help treat these infections. This review lists the 22 new antibiotics launched since 2000 and details the two first-in-class antibiotics, fidaxomicin (1) and bedaquiline (2), launched in 2011 and 2012, respectively. The development status, mode of action, spectra of activity, historical discovery and origin of the drug pharmacophore (natural product, natural product derived, synthetic or protein/mammalian peptide) of the 49 compounds and 6 β-lactamase/β-lactam combinations in active clinical development are discussed, as well as compounds that have been discontinued from clinical development since 2011. New antibacterial pharmacophore templates are also reviewed and analyzed.

Advances in MRSA drug discovery: where are we and where do we need to be?

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) have been on the increase during the past decade, due to the steady growth of the elderly and immunocompromised patients, and the emergence of multidrug-resistant (MDR) bacterial strains. Although there are a limited number of anti-MRSA drugs available, a number of different combination antimicrobial drug regimens have been used to treat serious MRSA infections. Thus, the addition of several new antistaphylococcal drugs into clinical practice should broaden clinician's therapeutic options. As MRSA is one of the most common and problematic bacteria associated with increasing antimicrobial resistance, continuous efforts for the discovery of lead compounds as well as development of alternative therapies and faster diagnostics are required.

AREAS COVERED

This article summarizes the FDA-approved drugs to treat MRSA infections, the drugs in clinical trials, and the drug leads for MRSA and related Gram-positive bacterial infections. In addition, the article discusses the mode of action of antistaphylococcal molecules and the resistant mechanisms of some molecules.

EXPERT OPINION

The number of pipeline drugs presently undergoing clinical trials is not particularly encouraging. There are limited and rather expensive therapeutic options for MRSA infections in the critically ill. Further research efforts are required for effective phage therapy on MRSA infections in clinical use, which seem to be attractive therapeutic options for the future.

Emerging therapies for Clostridium difficile infection - focus on fidaxomicin

The epidemiology of Clostridium difficile infections (CDI) has evolved during the last decades, with an increase in the reported incidence, severity of cases, and rate of mortality and relapses. These increases have primarily affected some special populations including the elderly, patients requiring concomitant antibiotic therapy, patients with renal failure, and patients with cancer. Until recently, the treatment of CDI was limited to either metronidazole or vancomycin. New therapeutic options have emerged to address the shortcomings of current antibiotic therapy. Fidaxomicin stands out as the first-in-class oral macrocyclic antibiotic with targeted activity against C. difficile and minimal collateral damage on the normal colonic flora. Fidaxomicin has demonstrated performance not inferior to what is considered the "gold standard" available therapy for CDI, vancomycin, in two separate Phase III clinical trials, but with significant advantages, including fewer recurrences and higher rates of sustained clinical cures. Fidaxomicin constitutes an important development in targeted antibiotic therapy for CDI and must be considered as a first-line agent for patients with risk factors known to portend relapse and severe infection.

In vitro and in vivo characterization of CB-183,315, a novel lipopeptide antibiotic for treatment of Clostridium difficile

CB-183,315 is a novel lipopeptide antibiotic structurally related to daptomycin currently in phase 3 clinical development for Clostridium difficile-associated diarrhea (CDAD). We report here the in vitro mechanism of action, spontaneous resistance incidence, resistance by serial passage, time-kill kinetics, postantibiotic effect, and efficacy of CB-183,315 in a hamster model of lethal infection. In vitro data showed that CB-183,315 dissipated the membrane potential of Staphylococcus aureus without inducing changes in membrane permeability to small molecules. The rate of spontaneous resistance to CB-183,315 at 8× the MIC was below the limit of detection in C. difficile. Under selective pressure by serial passage with CB-183,315 against C. difficile, the susceptibility of the bacteria changed no more than 2-fold during 15 days of serial passages. At 16× the MIC, CB-183,315 produced a ≥3-log reduction of C. difficile in the time-kill assay. The postantibiotic effect of CB-183,315 at 8× the MIC was 0.9 h. At 80× the MIC the postantibiotic effect was more than 6 h. In the hamster model of CDAD, CB-183,315 and vancomycin both demonstrated potent efficacy in resolving initial disease onset, even at very low doses. After the conclusion of dosing, CB-183,315 and vancomycin showed a similar dose- and time-dependent pattern with respect to rates of CDAD recurrence.