Pharmacokinetic and pharmacodynamic evaluation of the lantibiotic MU1140

Natural products from the human microbiome: an emergent frontier in organic synthesis and drug discovery

Often referred to as the "second genome", the human microbiome is at the epicenter of complex inter-habitat biochemical networks like the "gut-brain axis", which has emerged as a significant determinant of cognition, overall health and well-being, as well as resistance to antibiotics and susceptibility to diseases. As part of a broader understanding of the nexus between the human microbiome, diseases and microbial interactions, whether encoded secondary metabolites (natural products) play crucial signalling roles has been the subject of intense scrutiny in the recent past. A major focus of these activities involves harvesting the genomic potential of the human microbiome via bioinformatics guided genome mining and culturomics. Through these efforts, an impressive number of structurally intriguing antibiotics, with enhanced chemical diversity vis-à-vis conventional antibiotics have been isolated from human commensal bacteria, thereby generating considerable interest in their total synthesis and expanding their therapeutic space for drug discovery. These developments augur well for the discovery of new drugs and antibiotics, particularly in the context of challenges posed by mycobacterial resistance and emerging new diseases. The current landscape of various synthetic campaigns and drug discovery initiatives on antibacterial natural products from the human microbiome is captured in this review with an intent to stimulate further activities in this interdisciplinary arena among the new generation.

Evaluating the Translational Potential of Bacteriocins as an Alternative Treatment for Staphylococcus aureus Infections in Animals and Humans

Antibiotic resistance remains a global threat to human and animal health. Staphylococcus aureus is an opportunistic pathogen that causes minor to life-threatening infections. The widespread use of antibiotics in the clinical, veterinary, and agricultural setting combined with the increasing prevalence of antibiotic-resistant S. aureus strains makes it abundantly clear that alternatives to antibiotics are urgently needed. Bacteriocins represent one potential alternative therapeutic. They are antimicrobial peptides that are produced by bacteria that are generally nontoxic and have a relatively narrow target spectrum, and they leave many commensals and most mammalian cells unperturbed. Multiple studies involving bacteriocins (e.g., nisin, epidermicin, mersacidin, and lysostaphin) have demonstrated their efficacy at eliminating or treating a wide variety of S. aureus infections in animal models. This review provides a comprehensive and updated evaluation of animal studies involving bacteriocins and highlights their translational potential. The strengths and limitations associated with bacteriocin treatments compared with traditional antibiotic therapies are evaluated, and the challenges that are involved with implementing novel therapeutics are discussed.

Diversity of Bacterial Secondary Metabolite Biosynthetic Gene Clusters in Three Vietnamese Sponges

Recent reviews have reinforced sponge-associated bacteria as a valuable source of structurally diverse secondary metabolites with potent biological properties, which makes these microbial communities promising sources of new drug candidates. However, the overall diversity of secondary metabolite biosynthetic potential present in bacteria is difficult to access due to the fact that the majority of bacteria are not readily cultured in the laboratory. Thus, use of cultivation-independent approaches may allow accessing "silent" and "cryptic" secondary metabolite biosynthetic gene clusters present in bacteria that cannot yet be cultured. In the present study, we investigated the diversity of secondary metabolite biosynthetic gene clusters (BGCs) in metagenomes of bacterial communities associated with three sponge species: Clathria reinwardti, Rhabdastrella globostellata, and Spheciospongia sp. The results reveal that the three metagenomes contain a high number of predicted BGCs, ranging from 282 to 463 BGCs per metagenome. The types of BGCs were diverse and represented 12 different cluster types. Clusters predicted to encode fatty acid synthases and polyketide synthases (PKS) were the most dominant BGC types, followed by clusters encoding synthesis of terpenes and bacteriocins. Based on BGC sequence similarity analysis, 363 gene cluster families (GCFs) were identified. Interestingly, no GCFs were assigned to pathways responsible for the production of known compounds, implying that the clusters detected might be responsible for production of several novel compounds. The KS gene sequences from PKS clusters were used to predict the taxonomic origin of the clusters involved. The KS sequences were related to 12 bacterial phyla with Actinobacteria, Proteobacteria, and Firmicutes as the most predominant. At the genus level, the KSs were most related to those found in the genera Mycolicibacterium, Mycobacterium, Burkholderia, and Streptomyces. Phylogenetic analysis of KS sequences resulted in detection of two known 'sponge-specific' BGCs, i.e., SupA and SwfA, as well as a new 'sponge-specific' cluster related to fatty acid synthesis in the phylum Candidatus Poribacteria and composed only by KS sequences of the three sponge-associated bacterial communities assessed here.

Antimicrobial peptide-based materials: opportunities and challenges

The multifunctional properties of antimicrobial peptides (AMPs) make them attractive candidates for the treatment of various diseases. AMPs are considered alternatives to antibiotics due to the rising number of multidrug-resistant...

Probiotics, Prebiotics, Synbiotics and Dental Caries. New Perspectives, Suggestions, and Patient Coaching Approach for a Cavity-Free Mouth

Probiotic therapy forms a new strategy for dental caries prevention. Probiotic microorganisms possess the ability to displace cariogenic microorganisms and colonize the oral cavity. They can produce various antimicrobial substances such as bacteriocins, bacteriocin-like peptides, lactic acid, and hydrogen peroxide. Dairy products may be ideal for probiotic administration in dental patients. Many other means have been proposed, primarily for those allergic to dairy components, such as capsules, liquid form, tablets, drops, lozenges, sweetened cakes, and ice creams. The last two forms can be used in a coaching approach for children and elderly patients who find it difficult to avoid sugary beverages in their daily routine and benefit from the suggestion of easy, cheap, and common forms of delicacies. In caries prevention, the concept of the effector strain is already considered an integral part of the contemporary caries cure or prevention strategy in adults. Adults, though, seem not to be favored as much as children at early ages by using probiotics primarily due to their oral microbiome’s stability. In this non-systematic review we describe the modes of action of probiotics, their use in the cariology field, their clinical potential, and propose options to prevent caries through a patient coaching approach for the daily dental practice.

Antimicrobial Peptides as Potential Anti-Tubercular Leads: A Concise Review

Despite being considered a public health emergency for the last 25 years, tuberculosis (TB) is still one of the deadliest infectious diseases, responsible for over a million deaths every year. The length and toxicity of available treatments and the increasing emergence of multidrug-resistant strains of Mycobacterium tuberculosis renders standard regimens increasingly inefficient and emphasizes the urgency to develop new approaches that are not only cost- and time-effective but also less toxic. Antimicrobial peptides (AMP) are small cationic and amphipathic molecules that play a vital role in the host immune system by acting as a first barrier against invading pathogens. The broad spectrum of properties that peptides possess make them one of the best possible alternatives for a new “post-antibiotic” era. In this context, research into AMP as potential anti-tubercular agents has been driven by the increasing danger revolving around the emergence of extremely-resistant strains, the innate resistance that mycobacteria possess and the low compliance of patients towards the toxic anti-TB treatments. In this review, we will focus on AMP from various sources, such as animal, non-animal and synthetic, with reported inhibitory activity towards Mycobacterium tuberculosis.

Complete synthesis of the bicyclic ring of a mutacin analog with orthogonally protected lanthionine via solid-phase intracyclization

Mutacin 1140 (MU1140) is a naturally occurring lantibiotic derived from posttranslational modifications of a ribosomally synthesized peptide during the fermentation of a bacterium called Streptococcus mutans, the etiological agent of dental cavities. A practical approach for chemically synthesizing lantibiotics would be a valuable tool to expand the MU1140 library with additional semisynthetic analogs. In turn, an expanded library may prove useful to explore additional therapeutic indications for this pipeline of novel compounds. In this work, orthogonally protected lanthionine analogs were synthesized via an aziridine ring opening strategy. This lanthionine was utilized to synthesize a cysteamine (Cya) instead of the (S)-aminovinyl-D-cysteine (AviCys) that is naturally found in MU1140. The Cya containing bicyclic C/D ring of MU1140 was synthesized by Fmoc solid-phase peptide synthesis (SPPS). The linear peptides were synthesized using OPfp ester derivatives and using various common coupling reagents such as COMU and TCTU. The linear peptide was intracyclized with DEPBT to construct the so-called bicyclic ring C/D. This is the first report on the complete chemical synthesis of the bicyclic C/D ring of a MU1140 analog using orthogonally protected lanthionines using SPPS.

Preclinical evaluation of the maximum tolerated dose and toxicokinetics of enteric-coated lantibiotic OG253 capsules

Clostridium difficile associated disease (CDAD) is the leading infectious cause of antibiotic-associated diarrhea and colitis in the United States. Both the incidence and severity of CDAD have been increased over the past two decades. We evaluated the maximum tolerated dose (MTD) and toxicokinetics of OG253, a novel lantibiotic in development for the treatment of CDAD. OG253 was orally administered to Wistar Han rats as enteric-coated capsules in a one-day dose escalation study, followed by a seven-day repeated dose toxicokinetics study. All three doses of OG253 (6.75, 27 and 108 mg/day) were generally well-tolerated with no treatment-related clinical signs, alterations in body weight or food consumption in both one-day acute tolerability and seven-days repeated dose tolerability and toxicokinetics study. OG253 capsule administration neither significantly alter the weight of organs nor affect the hematology, coagulation, clinical biochemistry parameters and urine pH compared to placebo capsule administered rats. LC-MS/MS analysis did not detect OG253 in the plasma, indicating that OG253 is not absorbed into the blood from the rat gastrointestinal tract. Glandular atrophy of the rectal mucosa was noticed in two out of six rats administered with a high dose of OG253. Surprisingly, we found that OG253 treatment significantly lowered both serum cholesterol and triglyceride levels in both sexes of rats. Overall, there was a 29.8 and 61.38% decrease in the serum cholesterol and triglyceride levels, respectively as compared to placebo-treated rats. The well-tolerated high dose of OG253 (425.7 mg/kg/day) is recommended as the MTD for safety and efficacy studies. Further preclinical study is needed to evaluate the safety profile of OG253 under longer exposure.

Pharmacological, Toxicological, and Dose Range Assessment of OG716, a Novel Lantibiotic for the Treatment of Clostridium difficile-Associated Infection

Lantibiotics present an attractive scaffold for the development of novel antibiotics. We report here a novel lantibiotic for the treatment of Clostridium difficile infection. The lead compounds were selected from a library of over 700 single- and multiple-substitution variants of the lantibiotic mutacin 1140 (MU1140). The best performers in vitro and in vivo were further used to challenge Golden Syrian hamsters orally in a Golden Syrian hamster model of Clostridium difficile-associated disease (CDAD) in a dose-response format, resulting in the selection of OG716 as the lead compound. This lantibiotic was characterized by a 50% effective dose of 23.85 mg/kg of body weight/day (10.97 μmol/kg/day) in this model. Upon oral administration of the maximum feasible dose (≥1,918 mg/kg/day), no observable toxicities or side effects were noted, and no effect on intestinal motility was observed. Compartmentalization to the gastrointestinal tract was confirmed. MU1140-derived variants offer a large pipeline for the development of novel antibiotics for the treatment of several indications and are particularly attractive considering their novel mechanism of action. Based on the currently available data, OG716 has an acceptable profile for further development for the treatment of CDAD.

Efficacious Analogs of the Lantibiotic Mutacin 1140 against a Systemic Methicillin-Resistant Staphylococcus aureus Infection

Mutacin 1140, a member of the epidermin family of type AI lantibiotics, has a broad spectrum of activity against Gram-positive bacteria. It blocks cell wall synthesis by binding to lipid II. Although it has rapid bactericidal effects and potent activity against Gram-positive pathogens, its rapid clearance and short half-life in vivo limit its development in the clinic. In this study, we evaluated the effect of charged and dehydrated residues on the pharmacokinetics of mutacin 1140. The dehydrated residues were determined to contribute to the stability of mutacin 1140, while alanine substitutions for the lysine or arginine residues improved the pharmacological properties of the antibiotic. Analogs K2A and R13A had significantly lower clearances, leading to higher plasma concentrations over time. They also had improved bioactivities against several pathogenic bacteria. In a murine systemic methicillin-resistant Staphylococcus aureus (MRSA) infection model, a 10-mg/kg single intravenous bolus injection of the K2A and R13A analogs (1:1 ratio) protected 100% of the infected mice, while a 2.5-mg/kg dose resulted in 50% survival. The 10-mg/kg treatment group had a significant reduction in bacteria load in the livers and kidneys compared to that in the vehicle control group. The study provides lead compounds for the future development of antibiotics used to treat systemic Gram-positive infections.

Modifying the Lantibiotic Mutacin 1140 for Increased Yield, Activity, and Stability

Mutacin 1140 belongs to the epidermin family of type AI lantibiotics. This family has a broad spectrum of activity against Gram-positive bacteria. The binding of mutacin 1140 to lipid II leads to the inhibition of cell wall synthesis. Pharmacokinetic experiments with type AI lantibiotics are generally discouraging for clinical applications due to the short half-life of these compounds. The unprotected dehydrated and protease-susceptible residues outside the lanthionine rings may play a role in the short half-life in physiological settings. Previous mutagenesis work on mutacin 1140 has been limited to the lanthionine-forming residues, the C-terminally decarboxylated residue, and single amino acid substitutions at residues Phe1, Trp4, Dha5, and Arg13. To study the importance of the dehydrated (Dha5 and Dhb14) and protease-susceptible (Lys2 and Arg13) residues within mutacin 1140 for stability and bioactivity, each of these residues was evaluated for its impact on production and inhibitory activity. More than 15 analogs were purified, enabling direct comparison of the activities against a select panel of Gram-positive bacteria. The efficiency of the posttranslational modification (PTM) machinery of mutacin 1140 is highly restricted on its substrate. Analogs in the various intermediate stages of PTMs were observed as minor products following single point mutations at the 2nd, 5th, 13th, and 14th positions. The combination of alanine substitutions at the Dha5 and Dhb14 positions abolished mutacin 1140 production, while the production was restored by substitution of a Gly residue at one of these positions. Analogs with improved activity, productivity, and proteolytic stability were identified.IMPORTANCE Our findings show that the efficiency of mutacin 1140 PTMs is highly dependent on the core peptide sequence. Analogs in various intermediate stages of PTMs can be transported by the bacterium, which indicates that PTMs and transport are finely tuned for the native mutacin 1140 core peptide. Only certain combinations of amino acid substitutions at the Dha5 and Dhb14 dehydrated residue positions were tolerated. Observation of glutamylated core peptide analogs shows that dehydrations occur in a glutamate-dependent manner. Interestingly, mutations at positions outside rings A and B, the lipid II binding domain, would interfere with lipid II binding. Purified mutacin 1140 analogs have various activities and selectivities against different genera of bacteria, supporting the effort to generate analogs with higher specificity against pathogenic bacteria. The discovery of analogs with improved inhibitory activity against pathogenic bacteria, increased stability in the presence of protease, and higher product yields may promote the clinical development of this unique antimicrobial compound.

OG716: Designing a fit-for-purpose lantibiotic for the treatment of Clostridium difficile infections

Lantibiotics continue to offer an untapped pipeline for the development of novel antibiotics. We report here the discovery of a novel lantibiotic for the treatment of C. difficile infection (CDI). The leads were selected from a library of over 300 multiple substitution variants of the lantibiotic Mutacin 1140 (MU1140). Top performers were selected based on testing for superior potency, solubility, manufacturability, and physicochemical and/or metabolic stability in biologically-relevant systems. The best performers in vitro were further evaluated orally in the Golden Syrian hamster model of CDAD. In vivo testing ultimately identified OG716 as the lead compound, which conferred 100% survival and no relapse at 3 weeks post infection. MU1140-derived variants are particularly attractive for further clinical development considering their novel mechanism of action.

Mutacin 1140 Lantibiotic Variants Are Efficacious Against Clostridium difficile Infection

Lantibiotics offer an untapped pipeline for the development of novel antibiotics to treat serious Gram-positive (+) infections including Clostridium difficile. Mutacin 1140 (MU1140) is a lantibiotic produced by Streptococcus mutans and acts via a novel mechanism of action, which may limit the development of resistance. This study sought to identify a lead compound for the treatment of C. difficile associated diarrhea (CDAD). Compounds were selected from a saturation mutagenesis library of 418 single amino acid variants of MU1140. Compounds were produced by small scale fermentation, purified, characterized and then subjected to a panel of assays aimed at identifying the best performers. The screening assays included: in vitro susceptibility testing [MIC against Micrococcus luteus, Clostridium difficile, vancomycin-resistant enterococci (VRE), Staphylococcus aureus, Streptococcus pneumonia, Mycobacterium phlei, and Pseudomonas aeruginosa; cytotoxicity screening on HepG2 hepatocytes; in vitro pharmacological profiling with the Safety Screen 44^TM, metabolic and chemical stability in biologically relevant fluids (FaSSGF, FaSSIF and serum); and efficacy in vivo]. Several lantibiotic compounds had better MIC against C. difficile, compared to vancomycin, but not against other bacterial species tested. The Safety Screen 44^TMin vitro pharmacological profiling assay suggested that this class of compounds has relatively low overall toxicity and that compound OG253 (MU1140, Phe1Ile) is not likely to present inadvertent off-target effects, as evidenced by a low promiscuity score. The in vitro cytotoxicity assay also indicated that this class of compounds was characterized by low toxicity; the EC₅₀ of OG253 was 636 mg/mL on HepG2 cells. The half-life in simulated gastric fluid was >240 min. for all compound tested. The stability in simulated intestinal fluid ranged between a half-life of 5 min to >240 min, and paralleled the half-life in serum. OG253 ultimately emerged as the lead compound based on superior in vivo efficacy along with an apparent lack of relapse in a hamster model of infection. The lessons learned from this report are applicable to therapeutic lanthipeptides in general and may assist in the design of novel molecules with improved pharmacological, therapeutic and physicochemical profiles. The data presented also support the continued clinical development of OG253 as a novel antibiotic against CDAD that could prevent recurrence of the infection.

Improving the attrition rate of Lanthipeptide discovery for commercial applications

INTRODUCTION

Lanthipeptides are a class of ribosomally synthesized and post-translationally modified peptides. Lanthipeptides with antimicrobial activity are referred to as lantibiotics. Lantibiotics are generally active against Gram-positive bacteria. However, some modifications have expanded their activity toward Gram-negative bacteria. Furthermore, additional functions aside from antibacterial activities have been reported for lanthipeptides. Areas covered: This review provides a synopsis of current anthipeptide research for potential therapeutics. The review highlights the current tools used for identifying lanthipeptides from genomic sequencing data. It also describes the current approaches that have been used to overcome the limitations in the purification and isolation of lanthipeptides. The status of lanthipeptides in terms of potential applications and approaches that are currently being done to promote the development of lanthipeptides as novel therapeutics are also discussed. Expert opinion: Significant improvements have been made to promote the discovery of new lanthipeptides, while, simultaneously, tools have been developed to promote their production and isolation. Lanthipeptides are showing significant promise for treating bacterial infections, as well as for new applications as anticancer and antiviral agents, or as a novel treatment for pain management. At the current rate of lanthipeptide discovery and isolation of the products, it is likely several new applications will be discovered.

Host Antimicrobial Peptides: The Promise of New Treatment Strategies against Tuberculosis

Tuberculosis (TB) continues to be a devastating infectious disease and remerges as a global health emergency due to an alarming rise of antimicrobial resistance to its treatment. Despite of the serious effort that has been applied to develop effective antitubercular chemotherapies, the potential of antimicrobial peptides (AMPs) remains underexploited. A large amount of literature is now accessible on the AMP mechanisms of action against a diversity of pathogens; nevertheless, research on their activity on mycobacteria is still scarce. In particular, there is an urgent need to integrate all available interdisciplinary strategies to eradicate extensively drug-resistant Mycobacterium tuberculosis strains. In this context, we should not underestimate our endogenous antimicrobial proteins and peptides as ancient players of the human host defense system. We are confident that novel antibiotics based on human AMPs displaying a rapid and multifaceted mechanism, with reduced toxicity, should significantly contribute to reverse the tide of antimycobacterial drug resistance. In this review, we have provided an up to date perspective of the current research on AMPs to be applied in the fight against TB. A better understanding on the mechanisms of action of human endogenous peptides should ensure the basis for the best guided design of novel antitubercular chemotherapeutics.

Antimicrobial peptides as an alternative to anti-tuberculosis drugs

Tuberculosis (TB) presently accounts for high global mortality and morbidity rates, despite the introduction four decades ago of the affordable and efficient four-drugs (isoniazid, rifampicin, pyrazinamide and ethambutol). Thus, a strong need exists for new drugs with special structures and uncommon modes of action to effectively overcome M. tuberculosis. Within this scope, antimicrobial peptides (AMPs), which are small, cationic and amphipathic peptides that comprise a section of the innate immune system, are currently the leading potential agents for the treatment of TB. Many studies have recently illustrated the capability of anti-mycobacterial peptides to disrupt the normal mycobacterial cell wall function through various modes, thereby interacting with the intracellular targets, as well as encompassing nucleic acids, enzymes and organelles. This review presents a wide array of antimicrobial activities, alongside the associated properties of the AMPs that could be utilized as potential agents in therapeutic tactics for TB treatment.

Carboxyl Analogue of Mutacin 1140, a Scaffold for Lead Antibacterial Discovery

Mutacin 1140 belongs to the epidermin group of lantibiotics. Epidermin class lantibiotics are ribosomally synthesized and posttranslationally modified antibiotics with potent activity against Gram-positive bacteria. In particular, this class is effective at targeting drug-resistant Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus (MRSA), Mycobacterium tuberculosis, and Clostridium difficile A C-terminal S-[(Z)-2-aminovinyl]-d-cysteine (AviCys) residue is derived from a decarboxylation of a terminal cysteine that is involved in lanthionine ring formation. Studies on mutacin 1140 have revealed new insight into the structural importance of the C-terminal AviCys residue. A C-terminal carboxyl analogue of mutacin 1140 was engineered. Capping the C-terminal carboxyl group with a primary amine restores bioactivity and affords a novel opportunity to synthesize new analogues. A C-terminal fluorescein-labeled mutacin 1140 analogue traps lipid II into a large lipid II lantibiotic complex, similar to that observed in vivo for the lantibiotic nisin. A C-terminal carboxyl analogue of mutacin 1140 competitively inhibits the activity of native mutacin 1140 and nisin. The presence of a C-terminal carboxyl group prevents the formation of the large lipid II lantibiotic complexes but does not prevent the binding of the lantibiotic to lipid II.IMPORTANCE This study addressed the importance of the C-terminal S-[(Z)-2-aminovinyl]-d-cysteine (AviCys) residue for antibacterial activity. We have learned that the posttranslational modification for making the AviCys residue is presumably important for the lateral assembly mechanism of activity that traps lipid II into a large complex. The C-terminal carboxyl analogue of this class of lantibiotics is agreeable to the addition of a wide variety of substrates. The addition of fluorescein enabled in vivo visualization of the epidermin class of lantibiotics in action. These results are significant because, as we demonstrate, the presence of the AviCys residue is not essential for bioactivity, but, more importantly, the removal of the carboxyl group is essential. The ability to make a C-terminal carboxyl analogue that is modifiable will facilitate the synthesis of novel analogues of the epidermin class of lantibiotics that can be developed for new applications.

Bacteriocin-Antimicrobial Synergy: A Medical and Food Perspective

The continuing emergence of multi-drug resistant pathogens has sparked an interest in seeking alternative therapeutic options. Antimicrobial combinatorial therapy is one such avenue. A number of studies have been conducted, involving combinations of bacteriocins with other antimicrobials, to circumvent the development of antimicrobial resistance and/or increase antimicrobial potency. Such bacteriocin-antimicrobial combinations could have tremendous value, in terms of reducing the likelihood of resistance development due to the involvement of two distinct mechanisms of antimicrobial action. Furthermore, antimicrobial synergistic interactions may also have potential financial implications in terms of decreasing the costs of treatment by reducing the concentration of an expensive antimicrobial and utilizing it in combination with an inexpensive one. In addition, combinatorial therapies with bacteriocins can broaden antimicrobial spectra and/or result in a reduction in the concentration of an antibiotic required for effective treatments to the extent that potentially toxic or adverse side effects can be reduced or eliminated. Here, we review studies in which bacteriocins were found to be effective in combination with other antimicrobials, with a view to targeting clinical and/or food-borne pathogens. Furthermore, we discuss some of the bottlenecks which are currently hindering the development of bacteriocins as viable therapeutic options, as well as addressing the need to exercise caution when attempting to predict clinical outcomes of bacteriocin-antimicrobial combinations.

Bacteriocins: antibiotics in the age of the microbiome

Antibiotics have revolutionised the treatment of infectious disease and improved the lives of billions of people worldwide over many decades. With the rise in antimicrobial resistance (AMR) and corresponding lack of antibiotic development, we find ourselves in dire need of alternative treatments. Bacteriocins are a class of bacterially produced, ribosomally synthesised, antimicrobial peptides that may be narrow or broad in their spectra of activity. Animal models have demonstrated the safety and efficacy of bacteriocins in treating a broad range of infections; however, one of the principal drawbacks has been their relatively narrow spectra when compared with small-molecule antibiotics. In an era where we are beginning to appreciate the role of the microbiota in human and animal health, the fact that bacteriocins cause much less collateral damage to the host microbiome makes them a highly desirable therapeutic. This review makes a case for the implementation of bacteriocins as therapeutic antimicrobials, either alone or in combination with existing antibiotics to alleviate the AMR crisis and to lessen the impact of antibiotics on the host microbiome.

Genome database mining for the discovery of novel lantibiotics

INTRODUCTION

The effectiveness of lantibiotics against MDR pathogens and the progression of agents MU1140, NAI-107, NVB302 and duramycin into pre-clinical and clinical trials have highlighted their potential in the fight against bacterial resistance. The number of known lantibiotics and knowledge of their biosynthetic pathways has increased in recent years due to higher quality genomic data being delivered by next generation sequencing technologies combined with the development of specific genome mining tools, enabling the prediction of lantibiotic clusters. Areas covered: In this review, the author describes how the increase of high quality genomic data has increased the discovery of novel lantibiotics. Expert opinion: Novel apparatus such as the iChip enabling the isolation of uncultable bacteria will undoubtedly increase the identification rate of novel antimicrobial peptides including lantibiotics. The ability to then assess the lantibiotic clusters via recombinant production or synthesis using a high throughput method is one of the next challenges for developing these agents into the clinical environment.

Mechanistic Understanding of Lanthipeptide Biosynthetic Enzymes

Lanthipeptides are ribosomally synthesized and post-translationally modified peptides (RiPPs) that display a wide variety of biological activities, from antimicrobial to antiallodynic. Lanthipeptides that display antimicrobial activity are called lantibiotics. The post-translational modification reactions of lanthipeptides include dehydration of Ser and Thr residues to dehydroalanine and dehydrobutyrine, a transformation that is carried out in three unique ways in different classes of lanthipeptides. In a cyclization process, Cys residues then attack the dehydrated residues to generate the lanthionine and methyllanthionine thioether cross-linked amino acids from which lanthipeptides derive their name. The resulting polycyclic peptides have constrained conformations that confer their biological activities. After installation of the characteristic thioether cross-links, tailoring enzymes introduce additional post-translational modifications that are unique to each lanthipeptide and that fine-tune their activities and/or stability. This review focuses on studies published over the past decade that have provided much insight into the mechanisms of the enzymes that carry out the post-translational modifications.

Pharmacological and pharmacokinetic properties of lanthipeptides undergoing clinical studies

The intrinsic qualities of lanthipeptides for their use as therapeutic drugs present several challenges because of their properties, which include stability, solubility and bioavailability, which, under physiological conditions, are very low. Researches have encouraged clinical evaluation of a few compounds, such as mutacin 1140, microbisporicin, actagardine and duramycin, with pharmacokinetic profiles showing rapid distribution and elimination rates, good bioavailability and fecal excretion, as well as high protein binding. Local and parenteral administration are currently suitable to minimize environmental influences on lanthipeptides and ensure efficient activity. Nevertheless, valuable improvements on pharmacodynamic and pharmacokinetic properties may also permit systemic applications via enteral routes. Understanding how rational modifications influence the desired pharmacological and pharmacokinetic properties of these biomolecules would help to answer some specific questions about their susceptibility to environmental changes, mechanism of action and how to engineer other peptides of the same group to improve their clinical relevance.

Targeting bactoprenol-coupled cell envelope precursors

Targeting the bactoprenol-coupled cell wall precursor lipid II is a validated antibacterial strategy. In this review, selected prototype lipid II-binding antibiotics of different chemical classes are discussed. Although these compounds attack the same molecular target, they trigger nuanced and diverse cellular effects. Consequently, the mechanisms of antibacterial resistance and the likelihood of resistance development may vary substantially.

Lanthipeptides: chemical synthesis versus in vivo biosynthesis as tools for pharmaceutical production

Lanthipeptides (also called lantibiotics for those with antibacterial activities) are ribosomally synthesized post-translationally modified peptides having thioether cross-linked amino acids, lanthionines, as a structural element. Lanthipeptides have conceivable potentials to be used as therapeutics, however, the lack of stable, high-yield, well-characterized processes for their sustainable production limit their availability for clinical studies and further pharmaceutical commercialization. Though many reviews have discussed the various techniques that are currently employed to produce lanthipeptides, a direct comparison between these methods to assess industrial applicability has not yet been described. In this review we provide a synoptic comparison of research efforts on total synthesis and in vivo biosynthesis aimed at fostering lanthipeptides production. We further examine current applications and propose measures to enhance product yields. Owing to their elaborate chemical structures, chemical synthesis of these biomolecules is economically less feasible for large-scale applications, and hence biological production seems to be the only realistic alternative.

Antimicrobial peptides as novel anti-tuberculosis therapeutics

Tuberculosis (TB), a disease caused by the human pathogen Mycobacterium tuberculosis, has recently joined HIV/AIDS as the world's deadliest infectious disease, affecting around 9.6 million people worldwide in 2014. Of those, about 1.2 million died from the disease. Resistance acquisition to existing antibiotics, with the subsequent emergence of Multi-Drug Resistant mycobacteria strains, together with an increasing economic burden, has urged the development of new anti-TB drugs. In this scope, antimicrobial peptides (AMPs), which are small, cationic and amphipathic peptides that make part of the innate immune system, now arise as promising candidates for TB treatment. In this review, we analyze the potential of AMPs for this application. We address the mechanisms of action, advantages and disadvantages over conventional antibiotics and how problems associated with its use may be overcome to boost their therapeutic potential. Additionally, we address the challenges of translational development from benchside to bedside, evaluate the current development pipeline and analyze the expected global impact from a socio-economic standpoint. The quest for more efficient and more compliant anti-TB drugs, associated with the great therapeutic potential of emerging AMPs and the rising peptide market, provide an optimal environment for the emergence of AMPs as promising therapies. Still, their pharmacological properties need to be enhanced and manufacturing-associated issues need to be addressed.

Antibacterial activity of the novel semisynthetic lantibiotic NVB333 in vitro and in experimental infection models

NVB333 is a novel semisynthetic lantibiotic derived from the amide coupling of 3,5-dichlorobenzylamine to the C-terminal of deoxyactagardine B. The in vitro activity of NVB333 includes efficacy against clinically relevant pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus spp. NVB333 shows no cross-resistance with other antibiotics tested and a very low propensity for resistance development. After intravenous dosing NVB333 has high exposure in mouse plasma and shows generally improved in vivo activity compared with vancomycin in mouse infection models despite modest MIC values. In thigh infection models, promising efficacy was demonstrated against several strains of S. aureus including methicillin-resistant S. aureus (MRSA) and vancomycin-intermediate S. aureus (VISA) strains, and against Enterococcus faecalis UNT126-3. Area under the concentration curve (AUC)/MIC was shown to be the best predictor of efficacy against S. aureus UNT103-3 with an AUC/MIC of 138 (uncorrected for protein binding) achieving a static effect. NVB333 was also effective in a disseminated infection model where it conferred complete survival from the MRSA strain ATCC 33591. NVB333 showed rather modest lung penetration after intravenous dosing (AUC in lung 2-3% of plasma AUC), but because of very high plasma exposure, therapeutic levels of compound were achieved in the lung. Efficacy at least equal to vancomycin was demonstrated against an MRSA strain (UNT084-3) in a bronchoalveolar infection model. The impressive in vivo efficacy of NVB333 and strong resistance prognosis makes this compound an interesting candidate for development for treating systemic Gram-positive infections.

Alternatives to antibiotics-a pipeline portfolio review

Antibiotics have saved countless lives and enabled the development of modern medicine over the past 70 years. However, it is clear that the success of antibiotics might only have been temporary and we now expect a long-term and perhaps never-ending challenge to find new therapies to combat antibiotic-resistant bacteria. A broader approach to address bacterial infection is needed. In this Review, we discuss alternatives to antibiotics, which we defined as non-compound approaches (products other than classic antibacterial agents) that target bacteria or any approaches that target the host. The most advanced approaches are antibodies, probiotics, and vaccines in phase 2 and phase 3 trials. This first wave of alternatives to antibiotics will probably best serve as adjunctive or preventive therapies, which suggests that conventional antibiotics are still needed. Funding of more than £1·5 billion is needed over 10 years to test and develop these alternatives to antibiotics. Investment needs to be partnered with translational expertise and targeted to support the validation of these approaches in phase 2 trials, which would be a catalyst for active engagement and investment by the pharmaceutical and biotechnology industry. Only a sustained, concerted, and coordinated international effort will provide the solutions needed for the future.

Multipronged approach for engineering novel peptide analogues of existing lantibiotics

INTRODUCTION

Lantibiotics are a class of ribosomally and post-translationally modified peptide antibiotics that are active against a broad spectrum of Gram-positive bacteria. Great efforts have been made to promote the production of these antibiotics, so that they can one day be used in our antimicrobial arsenal to combat multidrug-resistant bacterial infections.

AREAS COVERED

This review provides a synopsis of lantibiotic research aimed at furthering our understanding of the structural limitation of lantibiotics as well as identifying structural regions that can be modified to improve the bioactivity. In vivo, in vitro and chemical synthesis of lantibiotics has been useful for engineering novel variants with enhanced activities. These approaches have provided novel ways to further our understanding of lantibiotic function and have advanced the objective to develop lantibiotics for the treatment of infectious diseases.

EXPERT OPINION

Synthesis of lantibiotics with enhanced activities will lead to the discovery of new promising drug candidates that will have a long lasting impact on the treatment of Gram-positive infections. The current body of literature for producing structural variants of lantibiotics has been more of a 'proof-of-principle' approach and the application of these methods has not yet been fully utilized.

Perspectives on lantibiotic discovery - where have we failed and what improvements are required?

The increasing resistance of bacteria to conventional antimicrobial therapy within both the nosocomial and community environment has enforced the urgent requirement for the discovery of novel agents. This has stimulated increased research efforts within the field of lantibiotic discovery. Lantibiotics are ribosomally synthesised, post-translationally modified antimicrobial peptides that exhibit antimicrobial activity against a range of multi-drug-resistant (MDR) bacteria. The success of these agents as a novel treatment of MDR infections is exemplified by: the clinical development of MU1140 (mutacin 1140) and NAI-107 (microbisporicin), which are in late pre-clinical trials against gram-positive bacteria; NVB302 that has completed Phase I clinical trials for the treatment of Clostridium difficile infections and; duramycin that has completed Phase II clinical trials in the treatment of cystic fibrosis. Despite these potential successes, the traditional method of lantibiotic discovery involving the induction, production and identification is often an inefficient, time-consuming process creating a barrier to the efficient discovery of novel lantibiotics. The introduction of novel and innovative identification methods, including the application of probes and the ability to improve the stability and activity of agents via mutagenesis offer encouraging new areas to explore. The rapid expansion of available genome sequences of a wide variety of bacteria has revealed multiple interesting lantibiotic clusters that have the potential to be effective antimicrobials. However, due to the inefficient expression, screening and production methods currently employed, they are being assessed inefficiently and not rapidly enough to keep up with the ever-increasing demand for new agents.

The leader peptide of mutacin 1140 has distinct structural components compared to related class I lantibiotics

Lantibiotics are ribosomally synthesized peptide antibiotics composed of an N-terminal leader peptide that promotes the core peptide's interaction with the post translational modification (PTM) enzymes. Following PTMs, mutacin 1140 is transported out of the cell and the leader peptide is cleaved to yield the antibacterial peptide. Mutacin 1140 leader peptide is structurally unique compared to other class I lantibiotic leader peptides. Herein, we further our understanding of the structural differences of mutacin 1140 leader peptide with regard to other class I leader peptides. We have determined that the length of the leader peptide is important for the biosynthesis of mutacin 1140. We have also determined that mutacin 1140 leader peptide contains a novel four amino acid motif compared to related lantibiotics. PTM enzyme recognition of the leader peptide appears to be evolutionarily distinct from related class I lantibiotics. Our study on mutacin 1140 leader peptide provides a basis for future studies aimed at understanding its interaction with the PTM enzymes.

Advances in the arsenal of tools available enabling the discovery of novel lantibiotics with therapeutic potential

INTRODUCTION

Lantibiotics are ribosomally synthesised peptides, which undergo extensive post-translational modification. Their mode of action and effectiveness against multi-drug-resistant pathogens, and relatively low toxicity, makes them attractive therapeutic options.

AREAS COVERED

This article provides background information on the four classes of lanthipeptides that have been described to date. Due to the clinical potential of these agents, specifically those from Class I and II, it is essential to identify organisms that harbour potentially interesting clusters encoding novel lantibiotics. Multiple emerging technologies have been applied to address this issue, including genome mining and specific bioinformatics programs designed to identify lantibiotic clusters present within the genome sequences. These clusters can then be effectively expressed using optimised heterologous expression systems, which are ideally amenable to large-scale production.

EXPERT OPINION

The continuing expansion of publicly available genomes, particularly genomes from microorganisms isolated from under-explored environments, combined with powerful bioinformatics tools able to accurately identify clusters of interest are of paramount importance in the discovery of novel lantibiotics. Detailed analysis of clusters drastically reduces dereplication time, which was often problematic when using the traditional method of isolation, purification and then identification. Allowing a more focused direction of 'wet lab' work, targeting the most promising agents, greatly increases the chance of novel lantibiotic discovery and development. High-throughput screening strategies are also required to enable the efficient analysis of these potentially clinically relevant agents.

Site-directed mutations in the lanthipeptide mutacin 1140

The oral bacterium Streptococcus mutans, strain JH1140, produces the antibiotic mutacin 1140. Mutacin 1140 belongs to a group of antibiotics called lanthipeptides. More specifically, mutacin 1140 is related to the epidermin type A(I) lanthipeptides. Mutagenesis experiments of this group of lanthipeptides have been primarily restricted to the posttranslationally modified meso-lanthionine and 3-methyllanthionine residues. Site-directed mutagenesis of the core peptide of mutacin 1140 was performed using the suicide vector pVA891. Substitutions of the N-terminal residue, the charged residue in the hinge region, and residues in ring A and intertwined rings C and D were investigated. A truncation and insertion of residues in ring A and intertwined rings C and D were also performed to determine whether or not they would alter the antimicrobial activity of the producing strain. Bioassays revealed that five of 14 mutants studied had improved antimicrobial activity against the indicator strain Micrococcus luteus ATCC 10240. MICs against Streptococcus mutans UA159, Streptococcus pneumoniae ATCC 27336, Staphylococcus aureus ATCC 25923, Clostridium difficile UK1, and Micrococcus luteus ATCC 10240 were determined for three mutacin 1140 variants that had the most significant increases in bioactivity in the M. luteus bioassay. This mutagenesis study of the epidermin group of lanthipeptides shows that antimicrobial activity can be significantly improved.

New horizons for host defense peptides and lantibiotics

Antimicrobial peptides from either microbial sources, or based on host defense peptides (HDPs) from higher organisms, show promising activity against human pathogens. Lantibiotics have been extensively engineered by either molecular biology approaches or chemistry and both natural and modified entities have been shown to have good efficacy in animal models of infection. Amongst HDPs either truncated peptides or non-peptide mimetic molecules show substantial promise both for their direct antibiotic action and also modulation of host functions. Members of both classes have reached clinical development for therapy of systemic infections and Clostridium difficile infection of the gastrointestinal tract.

Chemical synthesis and biological activity of analogues of the lantibiotic epilancin 15X

Lantibiotics are a large family of antibacterial peptide natural products containing multiple post-translational modifications, including the thioether structures lanthionine and methyllanthionine. Efforts to probe structure-activity relationships and engineer improved pharmacological properties have driven the development of new methods to produce non-natural analogues of these compounds. In this study, solid-supported chemical synthesis was used to produce analogues of the potent lantibiotic epilancin 15X, in order to assess the importance of several N-terminal post-translational modifications for biological activity. Surprisingly, substitution of these moieties, including the unusual N-terminal D-lactyl moiety, resulted in relatively small changes in the antimicrobial activity and pore-forming ability of the peptides.

Discovery, biosynthesis, and engineering of lantipeptides

Aided by genome-mining strategies, knowledge of the prevalence and diversity of ribosomally synthesized natural products (RNPs) is rapidly increasing. Among these are the lantipeptides, posttranslationally modified peptides containing characteristic thioether cross-links imperative for bioactivity and stability. Though this family was once thought to be a limited class of antimicrobial compounds produced by gram-positive bacteria, new insights have revealed a much larger diversity of activity, structure, biosynthetic machinery, and producing organisms than previously appreciated. Detailed investigation of the enzymes responsible for installing the posttranslational modifications has resulted in improved in vivo and in vitro engineering systems focusing on enhancement of the therapeutic potential of these compounds. Although dozens of new lantipeptides have been isolated in recent years, bioinformatic analyses indicate that many hundreds more await discovery owing to the widespread frequency of lantipeptide biosynthetic machinery in bacterial genomes.

Evaluating the feasibility of lantibiotics as an alternative therapy against bacterial infections in humans

Since the commercialization and ubiquitous use of antibiotics in the 20th century, there has been a steady increase in the number of reports on resistant bacteria. In recent years, this situation has become even more dramatic. The relatively slow development of new drugs, especially those with novel modes of action on target bacteria, is not paired with the rapid rate of resistance appearance. Lantibiotics form a group of antimicrobial peptides of bacterial origin with a dual mechanism of action not shared by other therapeutic compounds in use. They have a high potency to inhibit diverse (multidrug resistant) bacteria, combined with a low tendency to generate resistance. These properties make lantibiotics attractive candidates for clinical applications. This paper discusses some of the most recent results obtained in lantibiotic clinical application, paying special attention to the pharmacokinetic and pharmacodynamic properties they display. The objective of this paper is to give insight into the actual clinical applicability of lantibiotics and to point to the unexplored aspects that should be addressed in future research. The authors feel that lantibiotics could increase the number of second line antibiotics for systemic use in the future; however, further research is still needed before this is possible.