Glycopeptide Antibiotics

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

Urinary Tract Infection and Associated Factors among Pregnant Women Receiving Antenatal Care at a Primary Health Care Facility in the Northern Region of Ghana

Urinary tract infection (UTI) is frequently encountered during pregnancy and is associated with adverse maternal, fetal, and neonatal effects. However, very little information is available on the prevalence of UTI among pregnant women in the northern part of Ghana, a region with a high birth rate. This study employed a cross-sectional analysis of the prevalence, antimicrobial profile, and risk factors associated with UTI in 560 pregnant women attending primary care for antenatal check-ups. Sociodemographic obstetrical history and personal hygiene information were obtained using a well-structured questionnaire. Afterward, clean catch mid-stream urine samples were collected from all participants and subjected to routine microscopy examination and culture. Of 560 pregnant women, 223 cases (39.8%) were positive for UTI. There was a statistically significant association between sociodemographic, obstetric, and personal hygiene variables and UTI (p < 0.0001). Escherichia coli (27.8%) was the commonest bacterial isolate followed by CoNS (13.5%) and Proteus species (12.6%). These isolates exhibited greater resistance to ampicillin (70.1-97.3%) and cotrimoxazole (48.1-89.7%) but were fairly susceptible to gentamycin and ciprofloxacin. Gram-negative resistance to meropenem was up to 25.0%, and Gram positives resistance to cefoxitin and vancomycin was up to 33.3% and 71.4% respectively. The current findings extend our knowledge of the high frequency of UTIs and associated risk factors in pregnant women with E. Coli being the predominant and usual isolate. Variation existed in the resistance pattern of isolates to various drugs, underscoring the need to perform urine culture and susceptibility before treatment.

Systemic Antibiotic Therapy in Hidradenitis Suppurativa: A Review on Treatment Landscape and Current Issues

Hidradenitis suppurativa (HS) is a chronic, recurrent, and inflammatory skin disease characterized by painful, deep-seated, nodules, abscesses, and sinus tracts in sensitive areas of the body, including axillary, inguinal, and anogenital regions. Antibiotics represent the first-line pharmacological treatment of HS because of their anti-inflammatory properties and antimicrobial effects. This narrative review summarizes the most significant current issues on the role of systemic antibiotics in the management of HS, critically analyzing the main limits of their use (antibiotic resistance and toxicity). Although, in the last decades, several cytokines have been implicated in the pathomechanism of HS and the research on the use of novel biologic agents in HS has been intensified, antibiotics remain a valid therapeutic approach. Future challenges regarding antibiotic therapy in HS comprise their use in association with biologics in the management of acute flare or as a bridge therapy to surgery.

Palladium-catalyzed enantioselective three-component synthesis of α-arylglycine derivatives from glyoxylic acid, sulfonamides and aryltrifluoroborates

A palladium-catalyzed enantioselective three-component reaction of glyoxylic acid, sulfonamides and aryltrifluoroborates is described. This process provides modular access to the important α-arylglycine motif in moderate to good yields and enantioselectivies. The formed α-arylglycine products constitute useful building blocks for the synthesis of peptides or arylglycine-containing natural products.

Design, synthesis and glycosidase inhibition of DAB derivatives with C-4 peptide and dipeptide branches

A series of DAB-peptide and DAB-dipeptide derivatives were synthesized from D-tartrate-derived nitrone 18. The DAB peptides 16 are derivatives of trans,trans-3,4-dihydroxy-L-proline. Glycosidase inhibition assay found four of them to be weak and selective bovine liver β-galactosidase inhibitors, and the C-2' methyl substituted compound 23b showed the most potent β-galactosidase inhibition (IC₅₀ = 0.66 μM). Molecular docking studies revealed different docking modes of compound 23b compared to those of other DAB-peptides, and partial similarity of compound 23b to DGJ.

Palladium-catalyzed asymmetric three-component reaction between glyoxylic acid, sulfonamides and arylboronic acids for the synthesis of α-arylglycine derivatives

A palladium-catalyzed asymmetric three-component synthesis of α-arylglycine derivatives starting from glyoxylic acid, sulfonamides and arylboronic acids is reported. This novel, operationally simple method offers access to the α-arylglycine scaffold in good yields and enantioselectivities. The utilization of α tailored catalyst system enables the enantioselective synthesis of the desired α-arylglycines despite a fast racemic background reaction. The obtained products can be directly employed as building blocks in peptide synthesis.

Improved preparative enzymatic glycosylation of vancomycin aglycon and analogues

Modifications to the enzymatic glycosylation of vancomycin and its residue 4 thioamide analogue are detailed that significantly reduce the enzyme loading and amount of glycosyl donor needed for each glycosylation reaction, provide a streamlined synthesis and replacement for the synthetic UDP-vancosamine glycosyl donor to improve both access and storage stability, and permit a single-pot, two-step conversion of the aglycons to the fully glycosylated synthetic glycopeptides now conducted at higher concentrations. The improvements are exemplified with the two-step, one-pot glycosylation of [Ψ[C(=S)NH]Tpg4]vancomycin aglycon (92%) conducted on a 400 mg scale (2 mg to 1 g scales) and vancomycin aglycon itself (5 mg scale, 84%).

HelR is a helicase-like protein that protects RNA polymerase from rifamycin antibiotics

Rifamycin antibiotics such as rifampin are potent inhibitors of prokaryotic RNA polymerase (RNAP) used to treat tuberculosis and other bacterial infections. Although resistance arises in the clinic principally through mutations in RNAP, many bacteria possess highly specific enzyme-mediated resistance mechanisms that modify and inactivate rifamycins. The expression of these enzymes is controlled by a 19-bp cis-acting rifamycin-associated element (RAE). Guided by the presence of RAE sequences, we identify a helicase-like protein, HelR, in Streptomyces venezuelae that confers broad-spectrum rifamycin resistance. We show that HelR also promotes tolerance to rifamycins, enabling bacterial evasion of the toxic properties of these antibiotics. HelR forms a complex with RNAP and rescues transcription inhibition by displacing rifamycins from RNAP, thereby providing resistance by target protection . Furthermore, HelRs are broadly distributed in Actinobacteria, including several opportunistic Mycobacterial pathogens, offering yet another challenge for developing new rifamycin antibiotics.

Complex peptide natural products: Biosynthetic principles, challenges and opportunities for pathway engineering

Complex peptide natural products exhibit diverse biological functions and a wide range of physico-chemical properties. As a result, many peptides have entered the clinics for various applications. Two main routes for the biosynthesis of complex peptides have evolved in nature: ribosomally synthesized and post-translationally modified peptide (RiPP) biosynthetic pathways and non-ribosomal peptide synthetases (NRPSs). Insights into both bioorthogonal peptide biosynthetic strategies led to the establishment of universal principles for each of the two routes. These universal rules can be leveraged for the targeted identification of novel peptide biosynthetic blueprints in genome sequences and used for the rational engineering of biosynthetic pathways to produce non-natural peptides. In this review, we contrast the key principles of both biosynthetic routes and compare the different biochemical strategies to install the most frequently encountered peptide modifications. In addition, the influence of the fundamentally different biosynthetic principles on past, current and future engineering approaches is illustrated. Despite the different biosynthetic principles of both peptide biosynthetic routes, the arsenal of characterized peptide modifications encountered in RiPP and NRPS systems is largely overlapping. The continuous expansion of the biocatalytic toolbox of peptide modifying enzymes for both routes paves the way towards the production of complex tailor-made peptides and opens up the possibility to produce NRPS-derived peptides using the ribosomal route and vice versa.

Glycopeptide antibiotic drug stability in aqueous solution

Glycopeptide antimicrobials are a class of naturally occurring or semi-synthetic glycosylated products that have shown antibacterial activity against gram-positive organisms by inhibiting cell-wall synthesis. In most cases, these drugs are prepared in dry powder (lyophilized) form due to chemical and physical instability in aqueous solution; however, from an economic and practical point of view, liquid formulations are preferred. Researchers have recently found ways to formulate some glycopeptide antibiotic therapeutic drugs in aqueous solution at refrigerated or room temperature. Chemical degradation can be significantly slowed by formulating them at a defined pH with specific buffers, avoiding oxygen reactive species, and minimizing solvent exposure. Sugars, amino acids, polyols, and surfactants can reduce physical degradation by restricting glycopeptide mobility and reducing solvent interaction. This review focuses on recent studies on glycopeptide antibiotic drug stability in aqueous solution. It is organized into three sections: (i) glycopeptide antibiotic instability due to chemical and physical degradation, (ii) strategies to improve glycopeptide antibiotic stability in aqueous solution, and (iii) a survey of glycopeptide antibiotic drugs currently available in the market and their stability based on published literature and patents. Antimicrobial resistance deaths are expected to increase by 2050, making heat-stable glycopeptides in aqueous solution an important treatment option for multidrug-resistant and extensively drug-resistant pathogens. In conclusion, it should be possible to formulate heat stable glycopeptide drugs in aqueous solution by understanding the degradation mechanisms of this class of therapeutic drugs in greater detail, making them easily accessible to developing countries with a lack of cold chains.

Modified horseshoe crab peptides target and kill bacteria inside host cells

Bacteria that occupy an intracellular niche can evade extracellular host immune responses and antimicrobial molecules. In addition to classic intracellular pathogens, other bacteria including uropathogenic Escherichia coli (UPEC) can adopt both extracellular and intracellular lifestyles. UPEC intracellular survival and replication complicates treatment, as many therapeutic molecules do not effectively reach all components of the infection cycle. In this study, we explored cell-penetrating antimicrobial peptides from distinct structural classes as alternative molecules for targeting bacteria. We identified two β-hairpin peptides from the horseshoe crab, tachyplesin I and polyphemusin I, with broad antimicrobial activity toward a panel of pathogenic and non-pathogenic bacteria in planktonic form. Peptide analogs [I11A]tachyplesin I and [I11S]tachyplesin I maintained activity toward bacteria, but were less toxic to mammalian cells than native tachyplesin I. This important increase in therapeutic window allowed treatment with higher concentrations of [I11A]tachyplesin I and [I11S]tachyplesin I, to significantly reduce intramacrophage survival of UPEC in an in vitro infection model. Mechanistic studies using bacterial cells, model membranes and cell membrane extracts, suggest that tachyplesin I and polyphemusin I peptides kill UPEC by selectively binding and disrupting bacterial cell membranes. Moreover, treatment of UPEC with sublethal peptide concentrations increased zinc toxicity and enhanced innate macrophage antimicrobial pathways. In summary, our combined data show that cell-penetrating peptides are attractive alternatives to traditional small molecule antibiotics for treating UPEC infection, and that optimization of native peptide sequences can deliver effective antimicrobials for targeting bacteria in extracellular and intracellular environments.

Anticancer drugs in the aquatic ecosystem: Environmental occurrence, ecotoxicological effect and risk assessment

Anticancer drugs are a group of therapeutic agents used to enhance cell death in targeted cell types of neoplasia. Because of frequent use and eventual discharge, they have been often detected in wastewater from pharmaceutical factories and hospitals, domestic wastewater, and surface waters. The occurrence of these drugs in aquatic ecosystems and their effects on aquatic organisms have been poorly characterized. This review focuses on the global occurrence of major classes of anticancer drugs in water and sediments of freshwater ecosystems and their ecotoxicological effects at different biological levels. While the availability of data is fairly limited, concentrations of most anticancer drugs range from < 2 ng/L to 762 µg/L in receiving water, while levels in sediments and sludge vary from 0.25 to 42.5 µg/kg. Their detection frequencies were 58%, 52% (78%) and 59% in hospital wastewater, wastewater treatment plant effluents (influents) and surface water, respectively. Predicted log K_ow values of vincristine, imatinib mesylate and tamoxifen are higher than 3 and have estimated half-lives>60 d in waters using quantitative structure-activity relationship models, indicating high potential for persistence and bioaccumulation. Based on a species sensitivity distribution evaluation of 9 compounds, crustaceans are most sensitive to anticancer drugs. The most hazardous compound is cisplatin which has a hazard concentration at the 5th percentile. For Daphnia magna, the acute toxicities of major classes of anticancer drugs are ranked as platinum complexes > endocrine therapy agents > antibiotics > antimetabolite agents > alkylating agents. Using hazard quotient analysis based primarily on the lowest observed effect concentrations (LOECs), cyclophosphamide, cisplatin, 5-fluorouracil, imatinib mesylate, bicalutamide, etoposide and paclitaxel have the highest hazard for aquatic organisms. Further research is needed to identify appropriate chronic endpoints for risk assessment thresholds as well as to better understand the mechanisms of action and the potential multigenerational toxicity, and trophic transfer in ecosystems.

A batch study on the adsorption/desorption behavior of vancomycin on bentonite nanoparticles in aqueous solutions

In this study, adsorption/desorption of vancomycin (VAN) on bentonite nanoparticles was investigated in a batch system. Adsorption experiments were carried out as a function of several influential parameters such as adsorbent dosage, pH, contact time and ionic strength. Bentonite nanoparticles were characterized by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller, and Fourier transform infrared (FTIR) analyses and the mesoporous structure was revealed. Langmuir, Freundlich, and Temkin isotherm models were applied for the examination of equilibrium data, and Langmuir was found to be the best fit. With the increase in pH and ionic strength, the adsorption capacity decreases, which suggests the adsorption process may be dominated by the cation exchange mechanism. Moreover, VAN desorption from bentonite nanoparticles in two initial VAN loadings was investigated under different concentrations of metallic cations of various valences (Na⁺, Ca²⁺, Al³⁺), and pHs 3-10. Desorption was strongly pH-dependent and the amount of VAN desorbed increased with increasing cations concentrations. The FTIR analysis before and after VAN desorption suggests that the formation of Al-VAN and Ca-VAN complexes on the solid surface and then their detachment from the solid surface may contribute to the higher VAN desorption by Al³⁺ and Ca²⁺.

Maxamycins: Durable Antibiotics Derived by Rational Redesign of Vancomycin

Since its discovery, vancomycin has been used in the clinic for >60 years. Because of their durability, vancomycin and related glycopeptides serve as the antibiotics of last resort for the treatment of protracted bacterial infections of resistant Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant (MDR) Streptococcus pneumoniae. After 30 years of use, vancomycin resistance was first observed and is now widespread in enterococci and more recently in S. aureus. The widespread prevalence of vancomycin-resistant enterococci (VRE) and the emergence of vancomycin-resistant S. aureus (VRSA) represent a call to focus on the challenge of resistance, highlight the need for new therapeutics, and provide the inspiration for the design of more durable antibiotics less prone to bacterial resistance than even vancomycin.Herein we summarize progress on efforts to overcome vancomycin resistance, first addressing recovery of its original durable mechanism of action and then introducing additional independent mechanisms of action intended to increase the potency and durability beyond that of vancomycin itself. The knowledge of the origin of vancomycin resistance and an understanding of the molecular basis of the loss of binding affinity between vancomycin and the altered target ligand d-Ala-d-Lac provided the basis for the subtle and rational redesign of the vancomycin binding pocket to remove the destabilizing lone-pair repulsion or reintroduce a lost H-bond while not impeding binding to the unaltered ligand d-Ala-d-Ala. Preparation of the modified glycopeptide core structure was conducted by total synthesis, providing binding pocket-modified vancomycin aglycons with dual d-Ala-d-Ala/d-Lac binding properties that directly address the intrinsic mechanism of resistance to vancomycin. Fully glycosylated pocket-modified vancomycin analogues were generated through a subsequent two-step enzymatic glycosylation, providing a starting point for peripheral modifications used to introduce additional mechanisms of action. A well-established vancosamine N-(4-chlorobiphenyl)methyl (CBP) modification as well as newly discovered C-terminal trimethylammonium cation (C1) or guanidine modifications were introduced, providing two additional synergistic mechanisms of action independent of d-Ala-d-Ala/d-Lac binding. The CBP modification provides an additional stage for inhibition of cell wall synthesis that results from direct competitive inhibition of transglycosylase, whereas the C1/guanidine modification induces bacteria cell permeablization. The synergistic behavior of the three independent mechanisms of action combined in a single molecule provides ultrapotent antibiotics (MIC = 0.01-0.005 μg/mL against VanA VRE). Beyond the remarkable antimicrobial activity, the multiple mechanisms of action suppress the rate at which resistance may be selected, where any single mechanism of action is protected by the action of others. The results detailed herein show that rational targeting of durable vancomycin-derived antibiotics has generated compounds with a "resistance against resistance", provided new candidate antibiotics, and may serve as a generalizable strategy to combat antibacterial resistance.

Proximate and ultimate causes of the bactericidal action of antibiotics

During the past 85 years of antibiotic use, we have learned a great deal about how these ‘miracle’ drugs work. We know the molecular structures and interactions of these drugs and their targets and the effects on the structure, physiology and replication of bacteria. Collectively, we know a great deal about these proximate mechanisms of action for virtually all antibiotics in current use. What we do not know is the ultimate mechanism of action; that is, how these drugs irreversibly terminate the ‘individuality’ of bacterial cells by removing barriers to the external world (cell envelopes) or by destroying their genetic identity (DNA). Antibiotics have many different ‘mechanisms of action’ that converge to irreversible lethal effects. In this Perspective, we consider what our knowledge of the proximate mechanisms of action of antibiotics and the pharmacodynamics of their interaction with bacteria tell us about the ultimate mechanisms by which these antibiotics kill bacteria.

We know a lot about antibiotics and their targets; however, how antibiotics actually kill bacteria is not entirely clear and is up for debate. In this Perspective, Baquero and Levin reflect on this ultimate action of antibiotics and consider different mechanisms and modulating factors.

Vancomycin C-Terminus Guanidine Modifications and Further Insights into an Added Mechanism of Action Imparted by a Peripheral Structural Modification

A series of vancomycin C-terminus guanidine modifications is disclosed that improves antimicrobial activity, enhances the durability of antimicrobial action against selection or induction of resistance, and introduces a synergistic mechanism of action independent of d-Ala-d-Ala binding and inhibition of cell wall biosynthesis. The added mechanism of action results in induced bacterial cell permeability, which we show may involve interaction with cell envelope teichoic acid. Significantly, the compounds examined that contain two combined peripheral modifications, a (4-chlorobiphenyl)methyl (CBP) and C-terminus guanidinium modification, offer opportunities for new treatments against not only vancomycin-sensitive but especially vancomycin-resistant bacteria where they act by two synergistic and now durable mechanisms of action independent of d-Ala-d-Ala/d-Lac binding and display superb antimicrobial potencies (MIC 0.6-0.15 μg/mL, VanA VRE). For the first time, we demonstrate that the synergistic behavior of the peripheral modifications examined requires the presence of both the CBP and guanidine modifications in a single molecule versus their combined use as an equimolar mixture of singly modified compounds. Finally, we show that a prototypical member of the series, G3-CBP-vancomycin (15), exhibits no hemolytic activity, displays no mammalian cell growth inhibition, possesses improved and especially attractive in vivo pharmacokinetic (PK) properties, and displays excellent in vivo efficacy and potency against an especially challenging multidrug-resistant (MRSA) and VanA vancomycin-resistant (VRSA) Staphylococcus aureus bacterial strain.

Glycopeptide Hypersensitivity and Adverse Reactions

Glycopeptides, such as vancomycin and teicoplanin, are primarily used in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections, such as cellulitis, endocarditis, meningitis, pneumonia, and septicemia, and are some of the most commonly prescribed parenteral antimicrobials. Parenteral glycopeptides are first-line therapy for severe MRSA infections; however, oral vancomycin is used as a first-line treatment of Clostridioides difficile infections. Also, we currently have the longer-acting lipoglycopeptides, such as dalbavancin, oritavancin, and telavancin to our armamentarium for the treatment of MRSA infections. Lastly, vancomycin is often used as an alternative treatment for patients with β-lactam hypersensitivity. Common adverse effects associated with glycopeptide use include nephrotoxicity, ototoxicity, and Redman Syndrome (RMS). The RMS is often mistaken for a true allergy; however, it is a histamine-related infusion reaction rather than a true immunoglobulin E (IgE)-mediated allergic reaction. Although hypersensitivity to glycopeptides is rare, both immune-mediated and delayed reactions have been reported in the literature. We describe the various types of glycopeptide hypersensitivity reactions associated with glycopeptides and lipoglycopeptides, including IgE-mediated reactions, RMS, and linear immunoglobulin A bullous dermatosis, as well as describe cross-reactivity with other glycopeptides.

Autism Spectrum Disorder as a Brain-Gut-Microbiome Axis Disorder

While there are numerous medical comorbidities associated with ASD, gastrointestinal (GI) issues have a significant impact on quality of life for these individuals. Recent findings continue to support the relationship between the gut microbiome and both GI symptoms and behavior, but the heterogeneity within the autism spectrum requires in-depth clinical characterization of these clinical cohorts. Large, diverse, well-controlled studies in this area of research are still needed. Although there is still much to discover about the brain-gut-microbiome axis in ASD, microbially mediated therapies, specifically probiotics and fecal microbiota transplantation have shown promise in the treatment of GI symptoms in ASD, with potential benefit to the core behavioral symptoms of ASD as well. Future research and clinical trials must increasingly consider complex phenotypes in ASD in stratification of large datasets as well as in design of inclusion criteria for individual therapeutic interventions.

Exploration of the site-specific nature and generalizability of a trimethylammonium salt modification on vancomycin: A-ring derivatives

Vancomycin analogues bearing an A-ring trimethylammonium salt modification were synthesized and their antimicrobial activity against vancomycin-resistant Enterococci (VRE) was evaluated. The modification increased antimicrobial potency and provided the capability to induce bacteria cell membrane permeabilization, but both properties were weaker than that found with our earlier reported similar C-terminus modification. The results provide further insights on the additive effect and generalizability of the structural and site-specific nature of a peripheral quaternary trimethylammonium salt modification of vancomycin.

Synthesis and Medicinal Chemistry of Muraymycins, Nucleoside Antibiotics

Muraymycins, isolated from a culture broth of Streptomyces sp., are members of a class of naturally occurring nucleoside antibiotics. They are strong inhibitors of the phospho-MurNAc-pentapeptide translocase (MraY), which is responsible for the peptidoglycan biosynthesis. Since MraY is an essential enzyme among bacteria, muraymycins are expected to be a novel antibacterial agent. In this review, our efforts to synthesize muraymycin D2, simplify the chemical structure, improve antibacterial spectrum, and solve the X-ray crystal structure of the muraymycin D2/MraY complex are described.

N-Terminus Alkylation of Vancomycin: Ligand Binding Affinity, Antimicrobial Activity, and Site-Specific Nature of Quaternary Trimethylammonium Salt Modification

A series of vancomycin derivatives alkylated at the N-terminus amine were synthesized, including those that contain quaternary trimethylammonium salts either directly at the terminal amine site or with an intervening three-carbon spacer. The examination of their properties provides important comparisons with a C-terminus trimethylammonium salt modification that we recently found to improve the antimicrobial potency of vancomycin analogues through an added mechanism of action. The N-terminus modifications disclosed herein were well-tolerated, minimally altering model ligand binding affinities (d-Ala-d-Ala) and antimicrobial activity, but did not induce membrane permeabilization that was observed with a similar C-terminus modification. The results indicate that our earlier observations with the C-terminus modification are sensitive to the site as well as structure of the trimethylammonium salt modification and are not simply the result of nonspecific effects derived from introduction of a cationic charge.

Eremomycin pyrrolidide: a novel semisynthetic glycopeptide with improved chemotherapeutic properties

PURPOSE

Development of new semisynthetic glycopeptides with improved antibacterial efficacy and reduced pseudoallergic reactions.

METHODS

Semisynthetic glycopeptides 3-6 were synthesized from vancomycin (1) or eremomycin (2) by the condensation with pyrrolidine or piperidine. The minimum inhibitory concentration (MIC) for the new derivatives was measured by the broth micro-dilution method on a panel of clinical isolates of Staphylococcus and Enterococcus. Acute toxicity (50% lethal dose, maximum tolerated doses), antibacterial efficacy on model of systemic bacterial infection with S. aureus and pseudoallergic inflammatory reaction (on concanavalin A) of eremomycin pyrrolidide (5) were evaluated in mice according to standard procedures.

RESULTS

The eremomycin pyrrolidide (5) was the most active compound and showed a high activity against Gram-positive bacteria: vancomycin-susceptible staphylococci and enterococci (minimum inhibitory concentrations [MICs] 0.13-0.25 mg/L), as well as vancomycin-intermediate resistant Staphylococcus aureus (MICs 1 mg/L). Antimicrobial susceptibility tested on a panel of 676 isolates showed that 5 had similar activity for the genera Staphylococcus and Enterococcus with MIC90=0.5 mg/L, while vancomycin had MIC90=1-2 mg/L. The number of resistant strains of Enterococcus faecium (vancomycin-resistant enterococci) (MIC =64 mg/L) with this value was 7 (8%) for vancomycin (1) and 0 for the compound 5. In vivo comparative studies in a mouse model of systemic bacterial infection with S. aureus demonstrated that the efficacy of 5 was notably higher than that of the original antibiotics 1 and 2. In contrast to 1, compound 5 did not induce pseudoallergic inflammatory reaction (on concanavalin A).

CONCLUSION

The new semisynthetic derivative eremomycin pyrrolidide (5) has high activity against staphylococci and enterococci including vancomycin-resistant strains. Compound 5 has a higher efficacy in a model of staphylococcal sepsis than vancomycin (1) or eremomycin (2). In striking contrast to natural antibiotics, the novel derivative 5 does not induce a pseudoallergic inflammatory reaction to concanavalin A and therefore has no histamine release activity. These results indicate the advantages of a new semisynthetic glycopeptide antibiotic eremomycin pyrrolidide (5) which may be a prospective antimicrobial agent for further pre-clinical and clinical evaluations.

Diversity and regulation of intrinsic β-lactamases from non-fermenting and other Gram-negative opportunistic pathogens

This review deeply addresses for the first time the diversity, regulation and mechanisms leading to mutational overexpression of intrinsic β-lactamases from non-fermenting and other non-Enterobacteriaceae Gram-negative opportunistic pathogens. After a general overview of the intrinsic β-lactamases described so far in these microorganisms, including circa. 60 species and 100 different enzymes, we review the wide array of regulatory pathways of these β-lactamases. They include diverse LysR-type regulators, which control the expression of β-lactamases from relevant nosocomial pathogens such as Pseudomonas aeruginosa or Stenothrophomonas maltophilia or two-component regulators, with special relevance in Aeromonas spp., along with other pathways. Likewise, the multiple mutational mechanisms leading to β-lactamase overexpression and β-lactam resistance development, including AmpD (N-acetyl-muramyl-L-alanine amidase), DacB (PBP4), MrcA (PPBP1A) and other PBPs, BlrAB (two-component regulator) or several lytic transglycosylases among others, are also described. Moreover, we address the growing evidence of a major interplay between β-lactamase regulation, peptidoglycan metabolism and virulence. Finally, we analyse recent works showing that blocking of peptidoglycan recycling (such as inhibition of NagZ or AmpG) might be useful to prevent and revert β-lactam resistance. Altogether, the provided information and the identified gaps should be valuable for guiding future strategies for combating multidrug-resistant Gram-negative pathogens.

Antibacterial mode of action of violacein from Chromobacterium violaceum UTM5 against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA)

Violacein, violet pigment produced by Chromobacterium violaceum, has attracted much attention recently due to its pharmacological properties including antibacterial activity. The present study investigated possible antibacterial mode of action of violacein from C. violaceum UTM5 against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) strains. Violet fraction was obtained by cultivating C. violaceum UTM5 in liquid pineapple waste medium, extracted, and fractionated using ethyl acetate and vacuum liquid chromatography technique. Violacein was quantified as major compound in violet fraction using HPLC analysis. Violet fraction displayed bacteriostatic activity against S. aureus ATCC 29213 and methicillin-resistant S. aureus ATCC 43300 with minimum inhibitory concentration (MIC) of 3.9 μg/mL. Fluorescence dyes for membrane damage and scanning electron microscopic analysis confirmed the inhibitory effect by disruption on membrane integrity, morphological alternations, and rupture of the cell membranes of both strains. Transmission electron microscopic analysis showed membrane damage, mesosome formation, and leakage of intracellular constituents of both bacterial strains. Mode of action of violet fraction on the cell membrane integrity of both strains was shown by release of protein, K⁺, and extracellular adenosine 5'-triphosphate (ATP) with 110.5 μg/mL, 2.34 μg/mL, and 87.24 ng/μL, respectively, at 48 h of incubation. Violet fraction was toxic to human embryonic kidney (HEK293) and human fetal lung fibroblast (IMR90) cell lines with LC₅₀ value of 0.998 ± 0.058 and 0.387 ± 0.002 μg/mL, respectively. Thus, violet fraction showed a strong antibacterial property by disrupting the membrane integrity of S. aureus and MRSA strains. This is the first report on the possible mode of antibacterial action of violet fraction from C. violaceum UTM5 on S. aureus and MRSA strains.

Targeting a cell wall biosynthesis hot spot

Covering: up to 2017History points to the bacterial cell wall biosynthetic network as a very effective target for antibiotic intervention, and numerous natural product inhibitors have been discovered. In addition to the inhibition of enzymes involved in the multistep synthesis of the macromolecular layer, in particular, interference with membrane-bound substrates and intermediates essential for the biosynthetic reactions has proven a valuable antibacterial strategy. A prominent target within the peptidoglycan biosynthetic pathway is lipid II, which represents a particular "Achilles' heel" for antibiotic attack, as it is readily accessible on the outside of the cytoplasmic membrane. Lipid II is a unique non-protein target that is one of the structurally most conserved molecules in bacterial cells. Notably, lipid II is more than just a target molecule, since sequestration of the cell wall precursor may be combined with additional antibiotic activities, such as the disruption of membrane integrity or disintegration of membrane-bound multi-enzyme machineries. Within the membrane bilayer lipid II is likely organized in specific anionic phospholipid patches that form a particular "landing platform" for antibiotics. Nature has invented a variety of different "lipid II binders" of at least 5 chemical classes, and their antibiotic activities can vary substantially depending on the compounds' physicochemical properties, such as amphiphilicity and charge, and thus trigger diverse cellular effects that are decisive for antibiotic activity.

Synergistic effects of vancomycin and β-lactams against vancomycin highly resistant Staphylococcus aureus

We previously reported isolating vancomycin (VAN) highly resistant Staphylococcus aureus (VRSA) strains from clinical methicillin-resistant S. aureus strains by repeating steps of in vitro mutagenesis and VAN selection. Here we describe that the in vitro susceptibility of these VRSA strains to VAN was markedly increased by combined treatment with β-lactams such as ceftriaxone and oxacillin. Furthermore, in an in vivo silkworm infection model with VRSA, a combination of VAN and ceftriaxone exhibited therapeutic effects, whereas a combination of VAN and oxacillin did not. These findings suggest that combining VAN with an appropriate β-lactam, such as ceftriaxone, is therapeutically effective against infectious diseases caused by VRSA.

Ru-Catalyzed highly diastereoselective hydrogenation of N-tert-butylsulfinyl ketimines for the synthesis of aryl glycine derivatives

A Ru-Pincer catalyst enables the diastereoselective hydrogenation of N-tert-butylsulfinyl ketimino esters, affording a promising method for the synthesis of aryl glycine derivatives.

Dalbavancin: A New Option for the Treatment of Gram-Positive Infections

Objective:

To review the pharmacology, microbiology, chemistry, in vitro susceptibility, pharmacokinetics, clinical efficacy, safety, tolerability, dosage, and administration of dalbavancin, a new semisynthetic lipoglycopeptide.

Data Sources:

A MEDLINE search, restricted to the English language, was conducted from 1966 through January 2006. Supplementary sources included program abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy, American Society of Microbiology, and the Infectious Diseases Society of America from 2000 to 2005 and information available from the manufacturer's Web site.

Study Selection and Data Extraction:

In vitro and preclinical studies, as well as Phase I, II, and III clinical trials, were evaluated to summarize the microbiology, pharmacology, clinical efficacy, and safety of dalbavancin. All published trials and abstracts citing dalbavancin were selected.

Data Synthesis:

Dalbavancin, a novel lipoglycopeptide, has a mechanism of action similar to that of other glycopeptides. It has in vitro activity against a variety of gram-positive organisms, but no activity against gram-negative or vancomycin-resistant enterococci that possess VanA gene. Due to its prolonged half-life (6–10 days), dalbavancin can be administered intravenously once weekly. In Phase II and III clinical trials, dalbavancin was effective and well tolerated for the treatment of skin and soft-tissue infections, catheter-related bloodstream infections, and skin and skin-structure infections. To date, adverse events are mild and limited; the most common include pyrexia, headache, nausea, oral candidiasis, diarrhea, and constipation.

Conclusions:

Dalbavancin appears to be a promising antimicrobial agent for the treatment of gram-positive infections. A new drug application was filed with the Food and Drug Administration (FDA) in December 2004. The FDA issued an approvable letter in 2005 for dalbavancin. If approved, dalbavancin is expected to be launched in the first quarter of 2006.

Glycopeptide-Induced Neutropenia: Cross-Reactivity Between Vancomycin and Teicoplanin

Objective:

To report teicoplanin-related neutropenia that developed after an episode of neutropenia induced by vancomycin therapy.

Case Summary:

A 57-year-old female suffered from osteomyelitis of the left humerus, with a white blood cell (WBC) count of 2.8 × 103/mm3 and absolute neutrophil count (ANC) of 0.28 × 103/mm3, occurring after 24 days of vancomycin therapy. Vancomycin was changed to teicoplanin and the agranulocytosis resolved 4 days later. However, a new episode of neutropenia, with a WBC count of 2.8 × 103/mm3 and ANC of 0.448 × 103/mm3, occurred 11 days after teicoplanin initiation. Agranulocytosis resolved 4 days following withdrawal of teicoplanin.

Discussion:

Because of the close time relationship between drug administration and the development of symptoms and signs, as well as between drug withdrawal and changes in WBC count and ANC, the episodes of neutropenia were suspected to be drug related. Teicoplanin-induced agranulocytosis that followed vancomycin-induced agranulocytosis suggests a possible cross-reactivity between the 2 drugs. Both reactions were categorized as probable according to the Naranjo probability scale.

Conclusions:

For all patients with vancomycin-induced neutropenia, possible cross-reactivity of teicoplanin should be monitored.

Characterization of the Post-Assembly Line Tailoring Processes in Teicoplanin Biosynthesis

Actinoplanes teichomyceticus produces teicoplanin (Tcp), a "last resort" lipoglycopeptide antibiotic used to treat severe multidrug resistant infections such as methicillin-resistant Staphylococcus aureus (MRSA). A number of studies have addressed various steps of Tcp biosynthesis using in vitro assays, although the exact sequence of Tcp peptide core tailoring reactions remained speculative. Here, we describe the generation and analysis of a set of A. teichomyceticus mutant strains that have been used to elucidate the sequence of reactions from the Tcp aglycone to mature Tcp. By combining these results with previously published data, we propose an updated order of post-assembly line tailoring processes in Tcp biosynthesis. We also demonstrate that the acyl-CoA-synthetase Tei13* and the type II thioesterase Tei30* are dispensable for Tcp production. Five Tcp derivatives featuring hitherto undescribed combinations of glycosylation and acylation patterns are described. The generation of strains that produce novel Tcp analogues now provides a platform for the production of additional Tcp-like molecules via combinatorial biosynthesis or chemical derivatization.

Pseudomonas aeruginosa: targeting cell-wall metabolism for new antibacterial discovery and development

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections and is resistant to most antibiotics. With therapeutic options against P. aeruginosa dwindling, and the lack of new antibiotics in advanced developmental stages, strategies for preserving the effectiveness of current antibiotics are urgently required. β-Lactam antibiotics are important agents for treating P. aeruginosa infections, thus, adjuvants that potentiate the activity of these compounds are desirable for extending their lifespan while new antibiotics - or antibiotic classes - are discovered and developed. In this review, we discuss recent research that has identified exploitable targets of cell-wall metabolism for the design and development of compounds that hinder resistance and potentiate the activity of antipseudomonal β-lactams.

Total syntheses and initial evaluation of [Ψ[C(═S)NH]Tpg⁴]vancomycin, [Ψ[C(═NH)NH]Tpg⁴]vancomycin, [Ψ[CH₂NH]Tpg⁴]vancomycin, and their (4-chlorobiphenyl)methyl derivatives: synergistic binding pocket and peripheral modifications for the glycopeptide antibiotics

Full details of studies are disclosed on the total syntheses of binding pocket analogues of vancomycin bearing the peripheral L-vancosaminyl-1,2-D-glucosyl disaccharide that contain changes to a key single atom in the residue-4 amide (residue-4 carbonyl O → S, NH, H2) designed to directly address the underlying molecular basis of resistance to vancomycin. Also disclosed are studies piloting the late-stage transformations conducted on the synthetically more accessible C-terminus hydroxymethyl aglycon derivatives and full details of the peripheral chlorobiphenyl functionalization of all of the binding-pocket-modified vancomycin analogues designed for dual D-Ala-D-Ala/D-Ala-D-Lac binding. Their collective assessment indicates that combined binding pocket and chlorobiphenyl peripherally modified analogues exhibit a remarkable spectrum of antimicrobial activity (VSSA, MRSA, and VanA and VanB VRE) and impressive potencies against both vancomycin-sensitive and vancomycin-resistant bacteria (MICs = 0.06-0.005 and 0.5-0.06 μg/mL for the amidine and methylene analogues, respectively) and likely benefit from two independent and synergistic mechanisms of action, only one of which is dependent on D-Ala-D-Ala/D-Ala-D-Lac binding. Such analogues are likely to display especially durable antibiotic activity that is not prone to rapidly acquired clinical resistance.