In vitro and in vivo activity of an antibacterial peptide analog against uropathogens

Combinatory Use of hLF(1-11), a Synthetic Peptide Derived from Human Lactoferrin, and Fluconazole/Amphotericin B against Malassezia furfur Reveals a Synergistic/Additive Antifungal Effect

OBJECTIVE

The increasing resistance of Malassezia yeasts against commonly used antifungal drugs dictates the need for novel antifungal compounds. Human lactoferrin-based peptides show a broad spectrum of antimicrobial activities. Various assays were performed to find the optimal growth conditions of the yeasts and to assess cell viability, using media with low lipid content to avoid peptide binding to medium components.

METHODS

In the current study, we tested the antimicrobial susceptibility of 30 strains of M. furfur that cover the known IGS1 genotypic variation.

RESULTS

hLF(1-11) inhibited the growth of all species tested, resulting in minimum inhibitory concentrations (MIC) values ranging from 12.5 to 100 μg/mL. In the combinatory tests, the majority of fractional inhibitory concentration indexes (FIC) for the tested strains of M. furfur were up to 1.0, showing that there is a synergistic or additive effect on the efficacy of the antifungal drugs when used in combination with hLF(1-11).

CONCLUSION

Results showed that hLF(1-11) could be combined with fluconazole or amphotericin for the antimicrobial treatment of resistant strains, enhancing the potency of these antifungal drugs, resulting in an improved outcome for the patient.

Antimicrobial and Immunoregulatory Activities of TS40, a Derived Peptide of a TFPI-2 Homologue from Black Rockfish (Sebastes schlegelii)

Tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type serine protease inhibitor. Previous reports have shown that TFPI-2 plays an important role in innate immunity, and the C-terminal region of TFPI-2 proved to be active against a broad-spectrum of microorganisms. In this study, the TFPI-2 homologue (SsTFPI-2) of black rockfish (Sebastods schegelii) was analyzed and characterized, and the biological functions of its C-terminal derived peptide TS40 (FVSRQSCMDVCAKGAKQHTSRGNVRRARRNRKNRITYLQA, corresponding to the amino acid sequence of 187-226) was investigated. The qRT-PCR (quantitative real-time reverse transcription-PCR) analysis showed that the expression of SsTFPI-2 was higher in the spleen and liver. The expression of SsTFPI-2 increased significantly under the stimulation of Listonella anguillarum. TS40 had a strong bactericidal effect on L. anguillarum and Staphylococcus aureus. Further studies found that TS40 can destroy the cell structure and enter the cytoplasm to interact with nucleic acids to exert its antibacterial activity. The in vivo study showed that TS40 treatment could significantly reduce the transmission of L. anguillarum and the viral evasion in fish. Finally, TS40 enhanced the respiratory burst ability, reactive oxygen species production and the expression of immune-related genes in macrophages, as well as promoted the proliferation of peripheral blood leukocytes. These results provide new insights into the role of teleost TFPI-2.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

TC26, a teleost TFPI-1 derived antibacterial peptide that induces degradation of bacterial nucleic acids and inhibits bacterial infection in vivo

At present, several reports have indicated that the C-terminal peptides of tissue factor pathway inhibitor 1 (TFPI-1) were active antibacterial peptides. However, the functions of TFPI-1 C-terminal peptides in teleost are still very limited. In this study, a C-terminal peptide, TC26 (with 26 amino acids), derived from common carp (Cyprinus carpio) TFPI-1, was synthesized and investigated for its antibacterial spectrum, action mechanism, as well as the in vivo effects on bacterial invasion. Our results showed that TC26 was active against Gram-positive bacteria Micrococcus luteus and Staphylococcus aureus, as well as Gram-negative bacterium Vibrio vulnificus. TC26 treatment facilitated the bactericidal process of erythromycin by enhancing the out-membrane permeability of V. vulnificus. During the bactericidal process, TC26 killed the target bacterial cells Vibrio vulnificus, by destroying cell membrane integrity, penetrating into the cytoplasm and inducing degradation of genomic DNA and total RNA. In vivo study showed that administration of turbot with TC26 before bacterial infection significantly reduced pathogen dissemination and replication in tissues. These results indicated that TC26 is a novel and active antibacterial peptide and may play a vital role in fighting pathogenic infection in aquaculture.

Advantage of a Narrow Spectrum Host Defense (Antimicrobial) Peptide Over a Broad Spectrum Analog in Preclinical Drug Development

The APO-type proline-arginine-rich host defense peptides exhibit potent in vitro killing parameters against Enterobacteriaceae but not to other bacteria. Because of the excellent in vivo properties against systemic and local infections, attempts are regularly made to further improve the activity spectrum. A C-terminal hydrazide analog of the Chex1-Arg20 amide (ARV-1502) shows somewhat improved minimal inhibitory concentration against Moraxellaceae. Here we compared the activity of the two peptides as well as an inactive dimeric reverse amide analog in a systemic Acinetobacter baumannii infection. Only the narrow spectrum amide derivative reduced the 6-h blood bacterial burden by >2 log₁₀ units reaching statistical significance (p = 0.03 at 5 mg/kg and 0.031 at 2 mg/kg administered intramuscularly). The hydrazide derivative, probably due to stronger activity on cell membranes, lysed erythrocytes at lower concentrations, and caused toxic effects at lower doses (10 mg/kg vs. 25 mg/kg). In a limited study, the amide induced a >5-fold production of the anti-inflammatory cytokine IL-10 over untreated naïve mice and minor increases in the anti-inflammatory IL-4 and pro-inflammatory cytokines TNF-α and IL-6, in blood. The blood of hydrazide-treated mice exhibited significantly lowered levels of IL-10 and slightly decreased IL-4 and TNF-α. These results suggest that the improved efficacy of the narrow-spectrum amide analog is likely associated with increased anti-inflammatory cytokine production and better stimulation of the immune system. Although blood IL-6 and TNF-α levels are frequently used as markers of potential toxicity in drug development, we did not observe any notable increase in mice receiving the toxic polyamide antibiotic colistin.

TO17: A teleost antimicrobial peptide that induces degradation of bacterial nucleic acids and inhibits bacterial infection in red drum, Sciaenops ocellatus

Tissue factor pathway inhibitor (TFPI)-1 is well known for its role as an inhibitor of blood coagulation. Several studies have demonstrated that the C-terminal peptides of TFPI-1 are active against a broad spectrum of microorganisms. In a previous study, we found that TO17 (with 17 amino acids), a TFPI-1 C-terminal peptide from red drum (Sciaenops ocellatus), was active against Edwardsiella tarda. In the present study, we investigated further the antimicrobial spectrum, action mode, as well as the immunostimulatory property of TO17. Our results showed that TO17 displayed antimicrobial activity against Staphylococcus aureus, Micrococcus luteus, Vibrio vulnificus, and infectious spleen and kidney necrosis virus, independent of host serum. Furthermore, the activity of TO17 was influenced by the length or type of amino acids at the N and C termini. During its interaction with V. vulnificus, TO17 exerted its antibacterial activity by destroying cell membrane integrity, penetrating the cytoplasm and inducing degradation of genomic DNA and total RNA. In addition, TO17 had no hemolytic activity against red drum blood cells. In vitro, TO17 enhanced production of nitric oxide and bactericidal activity of red drum macrophages. In vivo, administration of red drum with TO17 before bacterial infection significantly reduced pathogen dissemination and replication in tissues. These results indicate that TO17 is a broad-spectrum antimicrobial peptide with immunostimulatory properties and it has the potential to be used as an antimicrobial agent in aquaculture.

TC38, a teleost TFPI-2 peptide that kills bacteria via penetration of the cell membrane and interaction with nucleic acids

Tissue factor pathway inhibitor 2 (TFPI-2) is an analog of TFPI-1 and a potent endogenous inhibitor of tissue factor (TF)-mediated blood coagulation. Recent reports have proven that the C-terminal of TFPI-2 peptides in humans and several other vertebrates possesses antibacterial activity against Gram-positive and Gram-negative bacteria. In our previous study, we reported that the TFPI-2 peptide, TC38 in tongue sole (Cynoglossus semilaevis) was active against Micrococcus luteus. In this study, we further examine the antimicrobial spectrum, mechanism of action, and function of TC38 in tongue sole. Our results indicate that TC38 is active against the Gram-negative bacteria Vibrio ichthyoenteri, Vibrio litoralis, Vibrio parahaemolyticus, and Vibrio vulnificus, as well as the fish Megalocytivirus, infectious spleen and kidney necrosis virus (ISKNV). The mechanism of action of TC38 against V. vulnificus was explored. The results showed that TC38 killed V. vulnificus cells without lysis of the cell membrane. FITC-labeled TC38 was able to penetrate the cell membrane and bind to DNA and RNA, then disrupt cellular function, eventually leading to cell death. Administration of TC38 to tongue sole significantly improved its defense against V. vulnificus infection. Overall, these results indicate that TC38 is a novel peptide with a broad antimicrobial spectrum. Furthermore, the unique action of TC38 against V. vulnificus adds new insights to the mechanism of action of vertebrate TFPI peptides. Moreover, TC38 is an interesting antimicrobial agent that could be useful in the fight against pathogenic invasion in aquaculture.

A TFPI-1 peptide that induces degradation of bacterial nucleic acids, and inhibits bacterial and viral infection in half-smooth tongue sole, Cynoglossus semilaevis

Tissue factor pathway inhibitor 1 (TFPI-1) is a serine protease inhibitor that inhibits tissue factor (TF)-mediated coagulation. The C-terminal region of TFPI-1 could be cleaved off and proved to be antimicrobial against a broad-spectrum of microorganism. In a previous study, a C-terminal peptide, TC24 (with 24 amino acids), derived from tongue sole (Cynoglossus semilaevis) TFPI-1, was synthesized and found antibacterial against Micrococcus luteus. In the present study, the antibacterial spectrum and the action mode of TC24 was further examined, and its in vivo function was analyzed. Our results showed that TC24 also possesses bactericidal activity against Staphylococcus aureus and Vibrio vulnificus. During its interaction with the target bacterial cells, TC24 destroyed cell membrane integrity, penetrated into the cytoplasm, and induced degradation of genomic DNA and total RNA. In vivo study showed that administration of tongue sole with TC24 before bacterial and viral infection significantly reduced pathogen dissemination and replication in tissues. These results indicated that TC24 is a novel antimicrobial peptide against bacterial and viral pathogens, and that the observed effect of TC24 on bacterial RNA adds new insights to the action mechanism of fish antimicrobial peptides. Moreover, TC24 may play an important role in fighting pathogenic infection in aquaculture.

Breaking the Spell: Combating Multidrug Resistant 'Superbugs'

Multidrug-resistant (MDR) bacteria have become a severe threat to community wellbeing. Conventional antibiotics are getting progressively more ineffective as a consequence of resistance, making it imperative to realize improved antimicrobial options. In this review we emphasized the microorganisms primarily reported of being resistance, referred as ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, and Enterobacteriaceae) accentuating their capacity to "escape" from routine antimicrobial regimes. The upcoming antimicrobial agents showing great potential and can serve as alternative therapeutic options are discussed. We also provided succinct overview of two evolving technologies; specifically network pharmacology and functional genomics profiling. Furthermore, In vivo imaging techniques can provide novel targets and a real time tool for potential lead molecule assessment. The employment of such approaches at prelude of a drug development process, will enables more informed decisions on candidate drug selection and will maximize or predict therapeutic potential before clinical testing.

Pharmacokinetics and in vivo efficacy of optimized oncocin derivatives

OBJECTIVES

To evaluate the efficacy of antimicrobial peptide Onc112 in a lethal Escherichia coli infection model and the pharmacokinetics of Onc72 and Onc112 administered intravenously or intraperitoneally in mice.

METHODS

Onc72, Onc112 and their major metabolites in blood, kidneys, liver, brain and urine were quantified by MS using multiple reaction monitoring (MRM) and isotope-labelled peptides.

RESULTS

Onc112 rescued all animals when administered intraperitoneally at a dose of 2.5 mg/kg and was thus slightly more efficient than Onc72. The MRM method provided limits of quantification in plasma, urine and kidney, liver and brain homogenates of 7-80 μg/L, well below the MICs of 2-4 mg/L. Onc72 and Onc112 reached all organs within 10 min when administered intraperitoneally (5 mg/kg). Their initial concentrations in plasma were 11.9 and 22.6 mg/L, respectively, with elimination t1/2 values of ∼14 and 21 min. The peptide concentrations in blood remained above their MICs for 20 min for Onc72 and 80 min for Onc112. The highest peptide concentrations were detected in kidney homogenates, which also contained the highest content of metabolites, indicating, together with the results from analysis of urine samples, that both peptides are cleared through the kidneys.

CONCLUSIONS

Onc72 and Onc112 reach organs, including the brain, within 10 min after intravenous and intraperitoneal administration. Onc112 remained in blood at concentrations above its MIC for 80 min. The pharmacokinetic profiles explain the high in vivo efficacies in models of systemic infection and indicate the potential use of these agents for the treatment of urinary tract infections.

Rapid synthesis, RNA binding, and antibacterial screening of a peptidic-aminosugar (PA) library

A 215-member mono- and diamino acid peptidic-aminosugar (PA) library, with neomycin as the model aminosugar, was systematically and rapidly synthesized via solid phase synthesis. Antibacterial activities of the PA library, on 13 bacterial strains (seven Gram-positive and six Gram-negative bacterial strains), and binding affinities of the PA library for a 27-base model of the bacterial 16S ribosomal A-site RNA were evaluated using high-throughput screening. The results of the two assays were correlated using Ribosomal Binding-Bacterial Inhibition Plot (RB-BIP) analysis to provide structure-activity relationship (SAR) information. From this work, we have identified PAs that can discriminate the E. coli A-site from the human A-site by up to a 28-fold difference in binding affinity. Aminoglycoside-modifying enzyme activity studies indicate that APH(2″)-Ia showed nearly complete removal of activity with a number of PAs. The synthesis of the compound library and screening can both be performed rapidly, allowing for an iterative process of aminoglycoside synthesis and screening of PA libraries for optimal binding and antibacterial activity for lead identification.

Mechanism of Escherichia coli resistance to Pyrrhocoricin

Due to their lack of toxicity to mammalian cells and good serum stability, proline-rich antimicrobial peptides (PR-AMPs) have been proposed as promising candidates for the treatment of infections caused by antimicrobial-resistant bacterial pathogens. It has been hypothesized that these peptides act on multiple targets within bacterial cells, and therefore the likelihood of the emergence of resistance was considered to be low. Here, we show that spontaneous Escherichia coli mutants resistant to pyrrhocoricin arise at a frequency of approximately 6 × 10(-7). Multiple independently derived mutants all contained a deletion in a nonessential gene that encodes the putative peptide uptake permease SbmA. Sensitivity could be restored to the mutants by complementation with an intact copy of the sbmA gene. These findings question the viability of the development of insect PR-AMPs as antimicrobials.

Characterization of ribosomal binding and antibacterial activities using two orthogonal high-throughput screens

We report here the affinity and antibacterial activity of a structurally similar class of neomycin dimers. The affinity of the dimer library for rRNA was established by using a screen that measures the displacement of fluorescein-neomycin (F-neo) probe from RNA. A rapid growth inhibition assay using a single drug concentration was used to examine the antibacterial activity. The structure-activity relationship data were then rapidly analyzed using a two-dimensional ribosomal binding-bacterial inhibition plot analysis.

Synergistic effects between silibinin and antibiotics on methicillin-resistant Staphylococcus aureus isolated from clinical specimens

Methicillin-resistant Staphylococcus aureus (MRSA) is a dangerous microorganism, and creates serious medical problems. It causes many types of infections in humans and often acquires multi-drug resistance. In this study, silibinin was evaluated against 20 clinical isolates of MRSA, either alone or in combination with ampicillin or oxacillin, using a checkerboard assay. The silibinin exhibited good activity against isolates of MRSA, and MRSA ATCC33952 and MSSA ATCC25923, with minimum inhibitory concentrations/minimum bactericidal concentrations (MICs/MBCs) ranging between 2-8/4-16 μg/mL, for ampicillin 2-1024/2-2048 μg/mL, and for oxacillin 0.25-32/0.5-64 μg/mL. The range of MIC(50) and MIC(90) were 0.5-4 μg/mL and 2-8 μg/mL, respectively. The MICs/MBCs for the combination of silibinin plus oxacillin or ampicillin were reduced by ≥4-fold against the MRSA isolates tested, demonstrating a synergistic effect, as defined by a fractional inhibitory concentration index (FICI) of ≤0.5. Furthermore, a time-kill study evaluating the growth of the tested bacteria showed that growth was completely attenuated after 2-5 h of treatment with the 1/2 MIC of silibinin, regardless of whether it was administered alone or with oxacillin (1/2 MIC) or ampicillin (1/2 MIC). In conclusion, silibinin exerted synergistic effects when administered with oxacillin or ampicillin and the antibacterial activity and resistant regulation of silibinin against clinical isolates of MRSA might be useful in controlling MRSA infections.

Discovery and development of a synthetic peptide derived from lactoferrin for clinical use

There is an urgent need to develop new antimicrobial drugs especially for combating the rise of infections caused by multi-resistant pathogens such as MRSA and VRSA. The problem of antibiotic resistant micro-organisms is expected to increase disproportionally and controlling of infections is becoming difficult because of the rapid spread of those micro-organisms. Primary therapy with classical antibiotics is becoming more ineffective. Combinational therapy of antibiotics with antimicrobial peptides (AMP's) has been suggested as an alternative approach to improve treatment outcome. Their unique mechanism of action and safety profile makes AMP's appealing candidates for simultaneous or sequential use in different cases of infections. In this review, for antimicrobial treatment the application of synthetic antimicrobial peptide hLF(1-11), derived from the first 11 amino acids of human lactoferrin is evaluated in both pre-clinical and clinical settings. Present information indicates that this derivate from lactoferrin is well tolerated in pre-clinical tests and clinical trials and thus hLF(1-11) is an interesting candidate for further exploration in various clinical indications of obscure infections, including meningitis. Another approach of using AMP's is their use in prevention of infections e.g. as coating for dental or bone implants or in biosensing applications or useful as infection specific radiopharmaceutical.

[Insect antimicrobial peptides: structures, properties and gene regulation]

Insect antimicrobial peptides (AMPs) are an important group of insect innate immunity effectors. Insect AMPs are cationic and contain less than 100 amino acid residues. According to structure, insect AMPs can be divided into a limited number of families. The diverse antimicrobial spectrum of insect AMPs may indicate different modes of action. Research on the model organism Drosophila indicate that insect AMPs gene regulation involves multiple signaling pathways and a large number of signaling molecules.

Synergistic effects of the membrane actions of cecropin-melittin antimicrobial hybrid peptide BP100

BP100 (KKLFKKILKYL-NH(2)) is a short cecropin A-melittin hybrid peptide, obtained through a combinatorial chemistry approach, which is highly effective in inhibiting both the in vitro and in vivo growth of economically important plant pathogenic Gram-negatives. The intrinsic Tyr fluorescence of BP100 was taken advantage of to study the peptide's binding affinity and damaging effect on phospholipid bilayers modeling the bacterial and mammalian cytoplasmic membranes. In vitro cytotoxic effects of this peptide were also studied on mammalian fibroblast cells. Results show a stronger selectivity of BP100 toward anionic bacterial membrane models as indicated by the high obtained partition constants, one order of magnitude greater than for the neutral mammalian membrane models. For the anionic systems, membrane saturation was observed at high peptide/lipid ratios and found to be related with BP100-induced vesicle permeabilization, membrane electroneutrality, and vesicle aggregation. Occurrence of BP100 translocation was unequivocally detected at both high and low peptide/lipid ratios using a novel and extremely simple method. Moreover, cytotoxicity against mammalian models was reached at a concentration considerably higher than the minimum inhibitory concentration. Our findings unravel the relationships among the closely coupled processes of charge neutralization, permeabilization, and translocation in the mechanism of action of antimicrobial peptides.

Comparative analysis of selected methods for the assessment of antimicrobial and membrane-permeabilizing activity: a case study for lactoferricin derived peptides

Background

Growing concerns about bacterial resistance to antibiotics have prompted the development of alternative therapies like those based on cationic antimicrobial peptides (APs). These compounds not only are bactericidal by themselves but also enhance the activity of antibiotics. Studies focused on the systematic characterization of APs are hampered by the lack of standard guidelines for testing these compounds. We investigated whether the information provided by methods commonly used for the biological characterization of APs is comparable, as it is often assumed. For this purpose, we determined the bacteriostatic, bactericidal, and permeability-increasing activity of synthetic peptides (n = 57; 9–13 amino acid residues in length) analogous to the lipopolysaccharide-binding region of human lactoferricin by a number of the most frequently used methods and carried out a comparative analysis.

Results

While the minimum inhibitory concentration determined by an automated turbidimetry-based system (Bioscreen) or by conventional broth microdilution methods did not differ significantly, bactericidal activity measured under static conditions in a low-ionic strength solvent resulted in a vast overestimation of antimicrobial activity. Under these conditions the degree of antagonism between the peptides and the divalent cations differed greatly depending on the bacterial strain tested. In contrast, the bioactivity of peptides was not affected by the type of plasticware (polypropylene vs. polystyrene). Susceptibility testing of APs using cation adjusted Mueller-Hinton was the most stringent screening method, although it may overlook potentially interesting peptides. Permeability assays based on sensitization to hydrophobic antibiotics provided overall information analogous – though not quantitatively comparable- to that of tests based on the uptake of hydrophobic fluorescent probes.

Conclusion

We demonstrate that subtle changes in methods for testing cationic peptides bring about marked differences in activity. Our results show that careful selection of the test strains for susceptibility testing and for screenings of antibiotic-sensitizing activity is of critical importance. A number of peptides proved to have potent permeability-increasing activity at subinhibitory concentrations and efficiently sensitized Pseudomonas aeruginosa both to hydrophilic and hydrophobic antibiotics.

Scope and limitations of the designer proline-rich antibacterial peptide dimer, A3-APO, alone or in synergy with conventional antibiotics

The proline-rich antimicrobial peptide dimer, A3-APO, was designed based on a statistical analysis of native antibacterial peptide and protein sequences. Analysis of a series of structural analogs failed to identify any single or multiple amino acid modification or architectural changes that would significantly improve its potential as a clinical therapeutic. However, a single chain Chex1-Arg20 version, a natural in vivo metabolite, showed a 2 to 8-fold increase in activity against test Enterobacteriaceae strains. In addition to bacterial species close to Escherichia coli in phylogeny, A3-APO analogs were able to effectively kill Pseudomonas aeruginosa and Staphylococcus saprophyticus. Antibacterial efficacy analysis together with biochemical experiments provided further evidence for a multiple mode of action of A3-APO that includes binding and inhibition of the bacterial heat shock protein DnaK. Through inactivating of resistance enzymes, A3-APO was able to recover the lost activity of conventional antibiotics including chloramphenicol, beta-lactams, sulfonamides or trimethoprim against multidrug resistant strains with partial or full synergy. However, the synergy appeared to be individual strain and small molecule drug combination-dependent.

Broth microdilution antibacterial assay of peptides

Native peptides exhibit various biological activities from which the antimicrobial property is one of the most frequently studied. A convenient way of telling whether peptides influence the life cycle of bacteria is the broth microdilution assay. In this measure, growing bacteria are incubated with peptides and growth inhibition is detected with colorimetric methods. Highly charged and protease-sensitive peptides need special considerations in assay design and readout interpretation to reveal the true antimicrobial efficacy and potential utility as human or veterinary therapeutics. The broth microdilution assay is suitable for first assessment of antimicrobial resistance induction.

Alternative stabilities of a proline-rich antibacterial peptide in vitro and in vivo

The proline-rich designer antibacterial peptide dimer A3-APO is currently under preclinical development for the treatment of systemic infections caused by antibiotic-resistant Gram-negative bacteria. The peptide showed remarkable stability in 25% mouse serum in vitro, exhibiting a half-life of approximately 100 min as documented by reversed-phase chromatography. Indeed, after a 30-min incubation period in undiluted mouse serum ex vivo, mass spectrometry failed to identify any degradation product. The peptide was still a major peak in full blood ex vivo, however, with degradation products present corresponding to amino-terminal cleavage. When injected into mice intravenously, very little, if any unmodified peptide could be detected after 30 min. Nevertheless, the major early metabolite, a full single-chain fragment, was detectable until 90 min, and this fragment exhibited equal or slightly better activity in the broth microdilution antimicrobial assay against a panel of resistant Enterobactericeae strains. The Chex1-Arg20 metabolite, when administered three times at 20 mg/kg to mice infected with a sublethal dose (over LD(50)) of an extended spectrum beta-lactamase-producing Escherichia coli strain, completely sterilized the mouse blood, similar to imipenem added at a higher dose. The longer and presumably more immunogenic prodrug A3-APO, injected subcutaneously twice over a 3-wk period, did not induce any antibody production, indicating the suitability of this peptide or its active metabolite for clinical development.

Pyrrhocoricin as a potential drug delivery vehicle for Cryptosporidium parvum

This study analysed the intracellular delivery capacity of insect derived pyrrhocoricin with a peptide cargo in Cryptosporidium parvum in vitro using fluorescence microscopy. Results revealed that pyrrhocoricin was capable of acting as a delivery vehicle in transducing peptides across the parasite cell membrane for multiple life-cycle stages. The successful transduction may aid in target validation and the delivery of future peptide-based drugs against this important human pathogen.

Serum stability of peptides

Hospitals worldwide have lately reported a worrying increase in the number of isolated drug-resistant pathogenic microbes. This has to some extent fueled at least academic interest in design and development of new lead components for novel drug design. Much of this interest has been focused on antimicrobial peptides and peptides in general, primarily due to their natural occurrence and low toxicity. However, issues have been raised regarding the stability of peptide therapeutics for systemic use. The focus of this chapter is assays for measuring peptide stability in the presence of serum, both in vitro and in vivo.

Peptide-based drug design: here and now

After many years of stagnation, peptide therapeutics once again became the focus of innovative drug development efforts backed up by venture funds and biotechnology companies. Designer peptide drugs overcome the unattractive pharmacological properties of native peptides and protein fragments and frequently feature nonnatural amino acid or backbone replacements, cyclic or multimeric structures, or peptidic or nonpeptidic delivery modules. With their high specificity and low toxicity profile, biologicals offer viable alternatives to small molecule therapeutics. The development of peptide drugs requires specific considerations of this family of biopolymers. Historically, peptide vaccines to viral infections and antibacterial peptides led the way in clinical development, but recently many other diseases have been targeted, including the big sellers AIDS, cancer, and Alzheimer's disease. This book gives practical advice to the most important steps in peptide-based drug development such as isolation, purification, characterization, interaction with targets, structural analysis, stability studies, assessment of biodistribution and pharmacological parameters, sequence modifications, and high throughput screening. This brief overview provides historical background for each of the listed techniques and diseases.

Dual mode of action of Bac7, a proline-rich antibacterial peptide

Proline-rich peptides are a unique group of antimicrobial peptides that exert their activity selectively against Gram-negative bacteria through an apparently non-membranolytic mode of action that is not yet well understood. We have investigated the mechanism underlying the antibacterial activity of the proline-rich cathelicidin Bac7 against Salmonella enterica and Escherichia coli. The killing and membrane permeabilization kinetics as well as the cellular localization were assessed for the fully active N-terminal fragment Bac7(1-35), its all-D enantiomer and for differentially active shortened fragments. At sub-micromolar concentrations, Bac7(1-35) rapidly killed bacteria by a non-lytic, energy-dependent mechanism, whereas its D-enantiomer was inactive. Furthermore, while the L-enantiomer was rapidly internalized into bacterial cells, the D-enantiomer was virtually excluded. At higher concentrations (>or=64 microM), both L- and D-Bac7(1-35) were instead able to kill bacteria also via a lytic mechanism. Overall, these results suggest that Bac7 may inactivate bacteria via two different modes of action depending on its concentration: (i) at near-MIC concentrations via a mechanism based on a stereospecificity-dependent uptake that is likely followed by its binding to an intracellular target, and (ii) at concentrations several times the MIC value, via a non-stereoselective, membranolytic mechanism.

Prior antibacterial peptide-mediated inhibition of protein folding in bacteria mutes resistance enzymes

The antimicrobial activity of amoxicillin against TEM-1-expressing strains could be fully recovered when bacteria were preincubated with sublethal doses of an antibacterial peptide derivative. Assays with the simultaneous administration of antibiotics or synergy assays with kanamycin or ciprofloxacin, where resistance development does not involve properly folded proteins, failed to yield similar results.

Screening for peptide drugs from the natural repertoire of biodiverse protein folds

Although monoclonal antibody (mAb) drugs targeting protein interactions exist, these therapeutics cannot access intracellular proteins involved in disease complexes. Moreover, mAbs are more difficult to deliver and are frequently associated with a prohibitive 'royalty stack.' Outlined here is an alternative approach based on libraries of natural, highly structured peptides that offers new opportunities for identifying effective, specific inhibitors of protein-protein interactions. Libraries of such peptides (referred to hereafter as phylomers) comprise both random and structured peptides encoded by natural genes of diverse bacterial genomes. Because the number of protein subdomain structures found in nature is limited, diverse libraries containing millions of phylomers constitute virtually all of the available classes of protein fold structures, providing a rich source of peptides that interact specifically and with high affinity to human proteins. This approach may help not only in understanding the implications of each interaction identified within the interactome but also in the development of effective drugs targeted to particular protein functions. Although phylomers are active in animal models, the challenge remains to demonstrate efficacy and safety in a clinical setting.

Antibacterial peptides and proteins with multiple cellular targets

Native antimicrobial peptides and proteins represent bridges between innate and adaptive immunity in mammals. On the one hand they possess direct bacterial killing properties, partly by disintegrating bacterial membranes, and some also by inhibiting functions of intracellular biopolymers. On the other, native antimicrobial peptides and proteins upregulate the host defense as chemoattractants or by various additional immunostimulatory effects. Structure-activity relationship studies indicate that residues responsible for the activities on bacterial membranes or for the secondary functions do not perfectly overlap. In reality, in spite of the relatively short size (18-20 amino acid residues) of some of these molecules, the functional domains can frequently be separated, with the cell-penetrating fragments located at the C-termini and the protein binding domains found upstream. As a cumulative effect, multifunctional and target-specific (agonist or antagonist) antimicrobial peptides and proteins interfere with more than one bacterial function at low concentrations, eliminating toxicity concerns of the earlier generations of antibacterial peptides observed in the clinical setting.

Designer antibacterial peptides kill fluoroquinolone-resistant clinical isolates

A significant number of Escherichia coli and Klebsiella pneumoniae bacterial strains in urinary tract infections are resistant to fluoroquinolones. Peptide antibiotics are viable alternatives although these are usually either toxic or insufficiently active. By applying multiple alignment and sequence optimization steps, we designed multifunctional proline-rich antibacterial peptides that maintained their DnaK-binding ability in bacteria and low toxicity in eukaryotes, but entered bacterial cells much more avidly than earlier peptide derivatives. The resulting chimeric and statistical analogues exhibited 8-32 microg/mL minimal inhibitory concentration efficacies in Muller-Hinton broth against a series of clinical pathogens. Significantly, the best peptide, compound 5, A3-APO, retained full antibacterial activity in the presence of mouse serum. Across a set of eight fluoroquinolone-resistant clinical isolates, peptide 5 was 4 times more potent than ciprofloxacin. On the basis of the in vitro efficacy, toxicity, and pharmacokinetics data, we estimate that peptide 5 will be suitable for treating infections in the 3-5 mg/kg dose range.

An insect antibacterial peptide-based drug delivery system

The ability of the short, proline-rich native antibacterial peptides to penetrate bacterial and host cells suggests the utility of these transport systems in delivering peptidic cargo into cells. We studied the uptake of pyrrhocoricin and its most potent dimeric analogue by bacteria as well as human dendritic cells and fibroblasts. Native pyrrhocoricin entered the susceptible organism Escherichia coli very efficiently and the nonsusceptible bacterium Staphylococcus aureus to a significant degree. The antibacterial peptide also penetrated human monocyte-derived dendritic cells. It failed, however, to enter fibroblasts, whereas the designer analogue Pip-pyrr-MeArg dimer penetrated all the cell types that were studied. When glucoincretin hormone Glp-1 fragment 7-36 was cosynthesized with the dimer, the antibacterial peptide derivative lost its ability to cross the bacterial membrane layer. In contrast, a chimera of the Pip-pyrr-MeArg dimer and two copies of a shorter (nine residues) class I major histocompatibility complex epitope successfully entered bacterial and mammalian cells. While the Pip-pyrr-MeArg dimer was not immunogenic when inoculated into mice, the chimera elicited a strong cytotoxic T-cell response, indicating the maintenance of the antigenic integrity of the cargo in the peptide conjugate. The chimera when tested for its immunological properties activated human dendritic cells significantly more strongly than any of the two independent fragments alone, yet lacked mammalian cell toxicity. These results confirm the utility of designed pyrrhocoricin analogues for delivery of peptidic cargo across cell membranes in general, and their potential as carriers for epitope-based vaccines in particular.

Biological evaluation of Tyr6 and Ser7 modified drosocin analogues

An array of analogues of the cationic antimicrobial peptide drosocin was synthesized containing substitutions of Tyr6 and Ser7 in order to increase the proteolytic stability. Stabilizing the N-terminus with unnatural amino acids increased the serum stability of analogues by almost a factor 30 over an 8 h period.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

Cyclization of pyrrhocoricin retains structural elements crucial for the antimicrobial activity of the native peptide

Pyrrhocoricin is a naturally occurring antimicrobial peptide from the European fire bug Pyrrhocoris apterus. It has submicromolar activity against a range of Gram-negative bacterial strains and has created recent interest as a lead for the development of novel antibiotic compounds. In this study, we have used NMR spectroscopy to determine the solution structures of pyrrhocoricin and a synthetic macrocyclic derivative that has improved in vivo pharmaceutical properties. Native pyrrhocoricin is largely disordered in solution, but there is evidence of a subpopulation with ordered turn regions over residues 2-5, 4-7, and 16-19. The macrocyclic derivative incorporates a nine amino acid linker joining the N- and C-termini, which does not adversely affect the antimicrobial potency but leads to a broader spectrum of activity. The NMR data suggest that the turn conformations in the cyclic derivative are similar to those in the native form, thus implicating them in the biological function.