Pharmacokinetics and in vivo efficacy of optimized oncocin derivatives

The proline-rich antimicrobial peptide Api137 disrupts large ribosomal subunit assembly and induces misfolding

The proline-rich antimicrobial designer peptide Api137 inhibits protein expression in bacteria by binding simultaneously to the ribosomal polypeptide exit tunnel and the release factor (RF), depleting the cellular RF pool and leading to ribosomal arrest at stop codons. This study investigates the additional effect of Api137 on the assembly of ribosomes using an Escherichia coli reporter strain expressing one ribosomal protein per 30S and 50S subunit tagged with mCherry and EGFP, respectively. Separation of cellular extracts derived from cells exposed to Api137 in a sucrose gradient reveals elevated levels of partially assembled and not fully matured precursors of the 50S subunit (pre-50S). High-resolution structures obtained by cryogenic electron microscopy demonstrate that a large proportion of pre-50S states are missing up to five proteins (uL22, bL32, uL29, bL23, and uL16) and have misfolded helices in 23S rRNA domain IV. These data suggest a second mechanism for Api137, wherein it disrupts 50S subunit assembly by inducing the formation of misfolded precursor particles potentially incapable of evolving into active ribosomes, suggesting a bactericidal mechanism.

Proline-Rich Antimicrobial Peptides from Invertebrates

Antimicrobial peptides (AMPs) constitute a large and diverse group of molecules with antibacterial, antifungal, antiviral, antiprotozoan, and anticancer activity. In animals, they are key components of innate immunity involved in fighting against various pathogens. Proline-rich (Pr) AMPs are characterized by a high content of proline (and arginine) residues that can be organized into Pro-Arg-Pro motifs. Such peptides have been described in many invertebrates (annelids, crustaceans, insects, mollusks) and some vertebrates (mammals). The main objective of this review is to present the diversity of invertebrate PrAMPs, which are associated with the presence of cysteine-rich domains or whey acidic protein domains in the molecular structure, in addition to the presence of characteristic proline-rich regions. Moreover, PrAMPs can target intracellular structures in bacteria, e.g., 70S ribosomes and/or heat shock protein DnaK, leading to the inhibition of protein synthesis and accumulation of misfolded polypeptides in the cell. This unique mechanism of action makes it difficult for pathogens to acquire resistance to this type of molecule. Invertebrate PrAMPs have become the basis for the development of new synthetic analogues effective in combating pathogens. Due to their great diversity, new highly active molecules are still being searched for among PrAMPs from invertebrates.

Antimicrobial peptide-based strategies to overcome antimicrobial resistance

Antibiotic resistance has emerged as a global threat, rendering the existing conventional treatment strategies ineffective. In view of this, antimicrobial peptides (AMPs) have proven to be potent alternative therapeutic interventions with a wide range of applications in clinical health. AMPs are small peptides produced naturally as a part of the innate immune responses against a broad range of bacterial, fungal and viral pathogens. AMPs present a myriad of advantages over traditional antibiotics, including their ability to target multiple sites, reduced susceptibility to resistance development, and high efficacy at low doses. These peptides have demonstrated notable potential in inhibiting microbes resistant to traditional antibiotics, including the notorious ESKAPE pathogens, recognized as the primary culprits behind nosocomial infections. AMPs, with their multifaceted benefits, emerge as promising candidates in the ongoing efforts to combat the escalating challenges posed by antibiotic resistance. This in-depth review provides a detailed discussion on AMPs, encompassing their classification, mechanism of action, and diverse clinical applications. Focus has been laid on combating newly emerging drug-resistant organisms, emphasizing the significance of AMPs in mitigating this pressing challenge. The review also illuminates potential future strategies that may be implemented to improve AMP efficacy, such as structural modifications and using AMPs in combination with antibiotics and matrix-inhibiting compounds.

Biodistribution of the cationic host defense peptide LL-37 using SPECT/CT

Human cathelicidin LL-37, a cationic host defense peptide (CHDP), has several important physiological roles, including antimicrobial activity, immune modulation, and wound healing, and is a being investigated as a therapeutic candidate for several indications. While the effects of endogenously produced LL-37 are well studied, the biodistribution of exogenously administered LL-37 are less known. Here we assess the biodistribution of a gallium-67 labeled variant of LL-37 using nuclear imaging techniques over a 48 h period in healthy mice. When administered as an intravenous bolus just over 20 µg, the LL-37-based radiotracer was rapidly cleared from the blood, largely by the liver, while an appreciable fraction of the dose temporarily distributed to the lungs. When administered subcutaneously at the same dose level, the radiotracer was absorbed systemically following a two-phase kinetic model and was predominately cleared renally. Uptake into sites rich in immune cells, such as the lymph nodes and the spleen, was observed for both routes of administration. Scans of free gallium-67 were also performed as controls. Important preclinical insights into the biodistribution of exogenously administered LL-37 were gained from this study, which can aid in the understanding of this and related cationic host-defense peptides.

Biodistribution of Native and Nanoformulated Innate Defense Regulator Peptide 1002

Innate defense regulator-1002 (IDR-1002) is a synthetic peptide with promising immunomodulatory and antibiofilm properties. An appreciable body of work exists around its mechanism of action at the cellular and molecular level, along with its efficacy across several infection and inflammation models. However, little is known about its absorption, distribution, and excretion in live organisms. Here, we performed a comprehensive biodistribution assessment with a gallium-67 radiolabeled derivative of IDR-1002 using nuclear tracing techniques. Various dose levels of the radiotracer (2-40 mg/kg) were administered into the blood, peritoneal cavity, and subcutaneous tissue, or instilled into the lungs. The peptide was well tolerated at all subcutaneous and intraperitoneal doses, although higher levels were associated with delayed absorption kinetics and precipitation of the peptide within the tissues. Low intratracheal doses were rapidly absorbed systemically, and small increases in the dose level were lethal. Intravenous doses were rapidly cleared from the blood at lower levels, and upon escalation, were toxic with a high proportion of the dose accumulating within the lung tissue. To improve biocompatibility and prolong its circulation within the blood, IDR-1002 was further formulated onto high molecular weight hyperbranched polyglycerol (HPG) polymers. Constructs prepared at 5:1 and 10:1 peptide-to-polymer ratios were colloidally stable, maintained the biological profile of the peptide payload and helped reduce red blood cell lysis. The 5:1 construct circulated well in the blood, but higher peptide loading was associated with rapid clearance by the reticuloendothelial system. Many peptides face pharmacokinetic and biocompatibility challenges, but formulations such as those with HPG have the potential to overcome these limitations.

Pharmacokinetics and pharmacodynamics of antibacterial peptide NZX in Staphylococcus aureus mastitis mouse model

Staphylococcus aureus is associated with dairy mastitis, which causes serious economic losses to dairy farming industry. Antibacterial peptide NZX showed good antibacterial activity against S. aureus. This study aimed to evaluate pharmacokinetics and pharmacodynamics of NZX against S. aureus-induced mouse mastitis. NZX exhibited potent in vitro antibacterial activity against the test S. aureus strains (minimal inhibitory concentration (MIC): 0.23-0.46 μM), low mutant prevention concentration (MPC: 1.18-3.68 μM), and a long post antibiotic effect (PAE: 2.20-8.84 h), which was superior to those of lincomycin and ceftiofur. Antibacterial mechanisms showed that NZX could penetrate the cell membrane, resulting in obvious cell membrane perforation and morphological changes, and bind to intracellular DNA. Furthermore, NZX had a good stability in milk environment (retention rate: 85.36%, 24 h) than that in mammary homogenate (47.90%, 24 h). In mouse mastitis model, NZX (25-400 μg/gland) could significantly reduce the bacterial load of mammary tissue in a dose-dependent manner. In addition, NZX (100 μg/gland) could relieve the inflammatory symptoms of mammary tissue, and significantly decreased its pathological scores. The concentration-time curve of NZX (100 μg/gland) in the mammary tissue was plotted and the corresponding pharmacokinetic parameters were obtained by non-compartment model calculation. Those parameters of Tmax, T1/2, Cmax and AUC were 0.5 h, 35.11 h, 32.49 μg/g and 391 μg·h/g, respectively. Therefore, these results suggest that NZX could act as a promising candidate for treating dairy mastitis disease caused by S. aureus. KEY POINTS: • NZX could kill S. aureus by dual mechanism involved in membrane and DNA disruption • NZX could relieve S. aureus-induced mouse mastitis • Pharmacokinetic parameters of NZX in mouse mammary gland were obtained.

Evaluation of proline-rich antimicrobial peptides as potential lead structures for novel antimycotics against Cryptococcus neoformans

Background

Cryptococcosis and cryptococcal meningitis, caused by Cryptococcus neoformans infections, lead to approximately 180,000 deaths per year, primarily in developing countries. Individuals with compromised immune systems, e.g., due to HIV infection (AIDS) or chemotherapy, are particularly vulnerable. Conventional treatment options are often limited and can cause severe side effects. Therefore, this study aimed to investigate the antifungal effect of insect-derived proline-rich antimicrobial peptides (PrAMPs) against C. neoformans. These peptides are known for their low toxicity and their high efficacy in murine infection models, making them a promising alternative for treatment.

Results

A preliminary screening of the minimal inhibitory concentrations (MICs) of 20 AMPs, including the well-known PrAMPs Onc112, Api137, and Chex1Arg20 as well as the cathelicidin CRAMP against the C. neoformans strains 1841, H99, and KN99α revealed promising results, with MICs as low as 1.6 μmol/L. Subsequent investigations of selected peptides, determining their influence on fungal colony-forming units, confirmed their strong activity. The antifungal activity was affected by factors such as peptide net charge and sequence, with stronger effects at higher net charges probably due to better intracellular uptake confirmed by confocal laser scanning microscopy. Inactive scrambled peptides suggest a specific intracellular target, although scanning electron microscopy showed that PrAMPs also damaged the cell exterior for a low proportion of the cells. Possible pore formation could facilitate entry into the cytosol.

In Vitro Properties and Pharmacokinetics of Temporarily PEGylated Onc72 Prodrugs

The favorable properties of antimicrobial peptides (AMPs) to rapidly kill pathogens are often limited by unfavorable pharmacokinetics due to fast degradation and renal clearance rates. Here, a prodrug strategy linking proline-rich AMP Onc72 to polyethylene glycol (PEGs) with average molecular weights of 5 and 20 kDa via a peptide linker containing a protease cleavage site is tested for the first time in vivo. Onc72 is released from these 5k- and 20k-prodrugs in mouse serum with half-life times (t1/2 ) of 8 and 14 h, respectively. Importantly, PEGylation protects Onc72 from proteolytic degradation providing a prolonged release of Onc72, balancing the degradation of free Onc72, and leading to relatively stable Onc72 concentrations and high antibacterial activities. The prodrugs are not hemolytic on human erythrocytes and show only slight cytotoxic effects on human cell lines indicating promising safety margins. When administered subcutaneously to female CD-1 mice, the prodrugs elimination t1/2 are 66 min and ≈5.5 h, respectively, compared to 43 min of free Onc72. The maximal Onc72 plasma levels are obtained ≈1 and ≈8 h postadministration, respectively. In conclusion, the prodrugs provide extended elimination t1/2 and a constant release of Onc72 in mice, potentially limiting adverse effects and increasing efficacy.

Plant derived antimicrobial peptides: Mechanism of target, isolation techniques, sources and pharmaceutical applications

Antimicrobial resistance is a global health and development threat which is caused by the excess and prolonged usage of antimicrobial compounds in agriculture and pharmaceutical industries. Resistance of pathogenic microorganisms to the already existing drugs represent a serious risk to public health. Plant sources such as cereals, legumes, fruits and vegetables are potential substrates for the isolation of antimicrobial peptides (AMP) with broad spectrum antimicrobial activity against bacteria, fungi and viruses with novel immunomodulatory activities. Thus, in the quest of new antimicrobial agents, AMPs have recently gained interest. Therefore, AMP can be used in agriculture, pharmaceutical and food industries. This review focuses on various explored and unexplored plant based food sources of AMPs, their isolation techniques and antimicrobial mechanism of peptides. Therefore, the literature discussed in this review paper will prove beneficial the research purposes for agriculture, pharmaceutical and food industries. PRACTICAL APPLICATIONS: Isolation of antimicrobial peptides (AMPs) can be done on industrial scale. AMP isolated from food sources can be used in pharmaceutical and agriculture industries. AMP from natural sources mitigate the problem of antimicrobial resistance. AMP isolated from food products can be used as nutraceutical.

Biodistribution and Toxicity of Innate Defense Regulator 1018 (IDR-1018)

Innate defense regulators (IDRs) are synthetic host-defense peptides (HDPs) with broad-spectrum anti-infective properties, including immunomodulatory, anti-biofilm and direct antimicrobial activities. A lack of pharmacokinetic data about these peptides hinders their development and makes it challenging to fully understand how they work in vivo since their mechanism of action is dependent on tissue concentrations of the peptide. Here, we set out to define in detail the pharmacokinetics of a well-characterized IDR molecule, IDR-1018. To make the peptide traceable, it was radiolabeled with the long-lived gamma-emitting isotope gallium-67. After a series of bench-top characterizations, the radiotracer was administered to healthy mice intravenously (IV) or subcutaneously (SQ) at various dose levels (2.5-13 mg/kg). Nuclear imaging and ex-vivo biodistributions were used to quantify organ and tissue uptake of the radiotracer over time. When administered as an IV bolus, the distribution profile of the radiotracer changed as the dose was escalated. At 2.5 mg/kg, the peptide was well-tolerated, poorly circulated in the blood and was cleared predominately by the reticuloendothelial system. Higher doses (7 and 13 mg/kg) as an IV bolus were almost immediately lethal due to respiratory arrest; significant lung uptake of the radiotracer was observed from nuclear scans of these animals, and histological examination found extensive damage to the pulmonary vasculature and alveoli. When administered SQ at a dose of 3 mg/kg, radiolabeled IDR-1018 was rapidly absorbed from the site of injection and predominately cleared renally. Apart from the SQ injection site, no other tissue had a concentration above the minimum inhibitory concentration that would enable this peptide to exert direct antimicrobial effects against most pathogenic bacteria. Tissue concentrations were sufficient however to disrupt microbial biofilms and alter the host immune response. Overall, this study demonstrated that the administration of synthetic IDR peptide in vivo is best suited to local administration which avoids some of the issues associated with peptide toxicity that are observed when administered systemically by IV injection, an issue that will have to be addressed through formulation.

Plant antimicrobial peptides: An overview about classification, toxicity and clinical applications

Antimicrobial peptides, also known as AMPs, are cationic and amphipathic molecules found in all living organisms, composing part of the defense mechanisms against various pathogens, including fungi, viruses, bacteria, and nematodes. AMPs derived from plants are the focus of this review because they have gained attention as alternative molecules to overcome pathogen resistance as well as new drugs to combat cancer. Plant AMPs are generally classified based on their sequences and structures, as thionins, defensins, hevein-like peptides, knottins, stable-like peptides, lipid transfer proteins, snakins, and cyclotides. Although there are studies reporting the toxicity of plant AMPs to nontarget cells or limitations of oral administration, synthetic AMPs with reduced toxicity or allergenicity, or greater resistance to peptidases can be designed by using different bioinformatics tools. Thus, this review provides information about the classification of plant AMPs, their characteristics, mechanisms of action, hemolytic and cytotoxic potential, possible applications in the medical field, and finally, the use of bioinformatics to help design synthetic AMPs with improved features.

Methods for the design and characterization of peptide antibiotics

Multi-drug resistant infections cause the death of millions of people worldwide. Today, there is an urgent need to identify innovative and sustainable alternatives to conventional antibiotics and to develop outside the box strategies to counter drug resistance. Versatile molecules such as antimicrobial peptides (AMPs), which display multiple mechanisms of action, have been explored as templates constituting a new generation of antibiotics. Here, we review recent methodological advances for the design, structural and functional characterization of AMPs. The methodologies outlined here have been validated and well established and may be used as a guide for the discovery, design, development, and reprogramming of peptide antibiotics.

Antimicrobial Peptides: A New Hope in Biomedical and Pharmaceutical Fields

Antibiotics are essential drugs used to treat pathogenic bacteria, but their prolonged use contributes to the development and spread of drug-resistant microorganisms. Antibiotic resistance is a serious challenge and has led to the need for new alternative molecules less prone to bacterial resistance. Antimicrobial peptides (AMPs) have aroused great interest as potential next-generation antibiotics, since they are bioactive small proteins, naturally produced by all living organisms, and representing the first line of defense against fungi, viruses and bacteria. AMPs are commonly classified according to their sources, which are represented by microorganisms, plants and animals, as well as to their secondary structure, their biosynthesis and their mechanism of action. They find application in different fields such as agriculture, food industry and medicine, on which we focused our attention in this review. Particularly, we examined AMP potential applicability in wound healing, skin infections and metabolic syndrome, considering their ability to act as potential Angiotensin-Converting Enzyme I and pancreatic lipase inhibitory peptides as well as antioxidant peptides. Moreover, we argued about the pharmacokinetic and pharmacodynamic approaches to develop new antibiotics, the drug development strategies and the formulation approaches which need to be taken into account in developing clinically suitable AMP applications.

Emerging peptide antibiotics with therapeutic potential

This review covers some of the recent progress in the field of peptide antibiotics with a focus on compounds with novel or established mode of action and with demonstrated efficacy in animal infection models. Novel drug discovery approaches, linear and macrocyclic peptide antibiotics, lipopeptides like the polymyxins as well as peptides addressing targets located in the plasma membrane or in the outer membrane of bacterial cells are discussed.

Caprine Bactenecins as Promising Tools for Developing New Antimicrobial and Antitumor Drugs

Proline-rich antimicrobial peptides (PR-AMPs) having a potent antimicrobial activity predominantly toward Gram-negative bacteria and negligible toxicity toward host cells, are attracting attention as new templates for developing antibiotic drugs. We have previously isolated and characterized several bactenecins that are promising in this respect, from the leukocytes of the domestic goat Capra hircus: ChBac5, miniChBac7.5N-α, and -β, as well as ChBac3.4. Unlike the others, ChBac3.4 shows a somewhat unusual pattern of activities for a mammalian PR-AMP: it is more active against bacterial membranes as well as tumor and, to the lesser extent, normal cells. Here we describe a SAR study of ChBac3.4 (RFRLPFRRPPIRIHPPPFYPPFRRFL-NH2) which elucidates its peculiarities and evaluates its potential as a lead for antimicrobial or anticancer drugs based on this peptide. A set of designed structural analogues of ChBac3.4 was explored for antibacterial activity toward drug-resistant clinical isolates and antitumor properties. The N-terminal region was found to be important for the antimicrobial action, but not responsible for the toxicity toward mammalian cells. A shortened variant with the best selectivity index toward bacteria demonstrated a pronounced synergy in combination with antibiotics against Gram-negative strains, albeit with a somewhat reduced ability to inhibit biofilm formation compared to native peptide. C-terminal amidation was examined for some analogues, which did not affect antimicrobial activity, but somewhat altered the cytotoxicity toward host cells. Interestingly, non-amidated peptides showed a slight delay in their impact on bacterial membrane integrity. Peptides with enhanced hydrophobicity showed increased toxicity, but in most cases their selectivity toward tumor cells also improved. While most analogues lacked hemolytic properties, a ChBac3.4 variant with two additional tryptophan residues demonstrated an appreciable activity toward human erythrocytes. The variant demonstrating the best tumor/nontumor cell selectivity was found to more actively initiate apoptosis in target cells, though its action was slower than that of the native ChBac3.4. Its antitumor effectiveness was successfully verified in vivo in a murine Ehrlich ascites carcinoma model. The obtained results demonstrate the potential of structural modification to manage caprine bactenecins’ selectivity and activity spectrum and confirm that they are promising prototypes for antimicrobial and anticancer drugs design.

Ribosomal Target-Binding Sites of Antimicrobial Peptides Api137 and Onc112 Are Conserved among Pathogens Indicating New Lead Structures To Develop Novel Broad-Spectrum Antibiotics

Proline-rich antimicrobial peptides expressed in insects are primarily active against Enterobacteriaceae. Mechanistically, they target the bacterial (70S) ribosome after partially transporter-based cellular uptake, as revealed for Api137 and Onc112 on Escherichia coli. Following molecular modeling indicating that the Onc112 contact site is conserved among the ribosomes of high-priority pathogens, the ribosome binding of Api137 and Onc112 was studied. The dissociation constants (Kd ) of Onc112 were ∼75 nmol/L for Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii, 36 nmol/L for Pseudomonas aeruginosa, and 102 nmol/L for Staphylococcus aureus, thus indicating a very promising lead structure for developing broad-spectrum antibiotics. Api137 bound weaker with Kd values ranging from 155 nmol/L to 13 μmol/L. For most bacteria, the antibacterial activities were lower than predicted from the Kd values, which was only partially explained by their ability to enter bacterial cells. Other factors limiting the activity expected from the ribosome binding might be off-target binding.

Antibacterial activity of a dual peptide targeting the Escherichia coli sliding clamp and the ribosome

The bacterial processivity factor, or sliding clamp (SC), is a target of choice for new antibacterial drugs development. We have previously developed peptides that target Escherichia coli SC and block its interaction with DNA polymerases in vitro. Here, one such SC binding peptide was fused to a Proline-rich AntiMicrobial Peptide (PrAMP) to allow its internalization into E. coli cells. Co-immunoprecipitation assays with a N-terminally modified bifunctional peptide that still enters the bacteria but fails to interact with the bacterial ribosome, the major target of PrAMPs, demonstrate that it actually interacts with the bacterial SC. Moreover, when compared to SC non-binding controls, this peptide induces a ten-fold higher antibacterial activity against E. coli, showing that the observed antimicrobial activity is linked to SC binding. Finally, an unmodified bifunctional compound significantly increases the survival of Drosophila melanogaster flies challenged by an E. coli infection. Our study demonstrates the potential of PrAMPs to transport antibiotics into the bacterial cytoplasm and validates the development of drugs targeting the bacterial processivity factor of Gram-negative bacteria as a promising new class of antibiotics.

Bifunctional peptides targeting both the translation and the replication machineries have been developed and shown to act as new antimicrobials.

Quantitation of a Novel Engineered Anti-infective Host Defense Peptide, ARV-1502: Pharmacokinetic Study of Different Doses in Rats and Dogs

The designer proline-rich antimicrobial peptide (PrAMP) Chex1-Arg20 amide (ARV-1502) is active against Gram-negative and Gram-positive pathogens in different murine infection models when administered parenterally and possesses a wide therapeutic index. Here we studied the pharmacokinetics of ARV-1502 for the first time when administered intramuscularly or intravenously (IV) in Sprague Dawley rats and Beagle dogs. First, a specific and robust quantitation method relying on parallel reaction monitoring (PRM) using a high-resolution hybrid quadrupole-Orbitrap mass spectrometer coupled on-line to reversed-phase uHPLC was established and validated. The limit of detection was 2 ng/mL and the limit of quantitation was 4 ng/mL when spiked to pooled rat and dog plasma. When ARV-1502 was administered IV at doses of 75 and 250 μg/kg in dogs and rats, the plasma concentrations were 0.7 and 3.4 μg/mL 2 min post-administration, respectively. ARV-1502 plasma concentrations declined exponentially reaching levels between 2 and 4 ng/mL after 2 h. Intramuscular administration of 0.75 mg/kg in dogs and 2.5 mg/kg in rats resulted in a different pharmacokinetics profile. The plasma concentrations peaked at 15 min post-injection at 1 μg/mL (dogs) and 12 μg/mL (rats) and decreased exponentially within 3 h to 4 and 16 ng/mL, respectively. The initial plasma concentrations of ARV-1502 and the decay timing afterwards indicated that the peptide circulated in the blood stream for several hours, at some point above the minimal inhibitory concentration against multidrug-resistant Enterobacteriaceae, with blood concentrations sufficient to suppress bacterial growth and to modulate the immune system.

Continuous Subcutaneous Delivery of Proline-Rich Antimicrobial Peptide Api137 Provides Superior Efficacy to Intravenous Administration in a Mouse Infection Model

Apidaecins are cationic, proline-rich antimicrobial peptides originally isolated from honeybees and exhibit high Gram-negative activity by inhibiting bacterial protein translation. Pharmacokinetics of apidaecin derivative Api137 was studied using single and multiple intravenous or subcutaneous injections as well as continuous subcutaneous infusion and correlated to its efficacy in a lethal murine Escherichia coli infection model. Survival rates of infected CD-1 mice were monitored and Api137 and its metabolites were quantified in plasma of uninfected CD-1 mice and Sprague Dawley rats using reversed-phase chromatography coupled online to mass spectrometry. The highest Api137 plasma levels of 23 mg/L were obtained after a single intravenous injection of 20 mg/kg body weight, which declined fast over the next 120 min (half-life time < 30 min). In contrast, continuous subcutaneous infusion of a similar dose over an hour (19.2 mg/kg/h) lead to stable plasma levels of ∼6 mg/L, which was above the minimal inhibitory concentration against E. coli ATCC 25922 (4 mg/L). The increased exposure by continuous subcutaneous administration of Api137 at 19.2 mg/kg/h over 48 h improved efficacy in the murine intraperitoneal sepsis model with survival rates of 67% over 5 days compared to 33% after intravenous and subcutaneous administration in different dosing schemes. To the best of our knowledge, continuous subcutaneous infusion using osmotic pumps was successfully utilized for delivery of an antimicrobial peptide for the first time. Additionally, the potential of apidaecin analogs as novel antibiotics is demonstrated even in a scenario where the infection site is clearly separated from the route of administration.

Cecropin A Alleviates Inflammation Through Modulating the Gut Microbiota of C57BL/6 Mice With DSS-Induced IBD

The present study is undertaken to assess the alleviating effects of antimicrobial peptide cecropin A on inflammatory bowel disease (IBD) in C57BL/6 mice and changes in the gut microbiota, compared to an antibiotic gentamicin. Different doses of cecropin A were intraperitoneally injected into C57BL/6 mice for 5 days to determine the safe doses. The injection doses at ≤ 15 mg/kg showed no negative impact on the liver, heart, spleen, and kidney. The severe and moderate IBD mice model was successfully established via supplementation of 4 or 2.5% dextran sulfate sodium (DSS) in drinking water for 5 days. The severe IBD model was used to ensure the optimal therapeutic dose of cecropin A. Survival rate, body weight and disease activity index (DAI) scores were measured. Administration of 15 mg/kg, not 5 mg/kg cecropin A, for 5 days increased survival rate and decreased body weight loss of mice. The moderate IBD model was applied to investigate the mechanisms for cecropin A to alleviate inflammation in comparison to gentamicin. The mice were treated with 15 mg/kg cecropin A or 5 mg/kg gentamicin for 3 days. The levels of cytokines and related proteins in the colon were detected by ELISA and Western blotting. The microbiota in cecum contents were analyzed using 16S rRNA gene sequencing. The results showed that cecropin A and gentamicin relieved body weight loss, DAI, and gut mucosa disruption, while decreasing tumor necrosis factor-α (TNF-α), interlukin-1β (IL-1β), and interlukin-6 (IL-6) induced by DSS. In addition, cecropin A and gentamicin showed different effects on the gut microbiota structure. Both cecropin A and gentamicin decreased DSS-induced enrichment of Bacteroidaceae and Enterobacteriaceae. However, cecropin A showed a selective enrichment of Lactobacillus in contrast to gentamicin, which demonstrated a selective effect on Desulfovibrionaceae and Ruminococcaceae. Cecropin A alleviates IBD through decreasing harmful gut microflora and specifically enhancing beneficial gut microflora. The mechanism of this effect is different from gentamicin.

Proline-rich antimicrobial peptides show a long-lasting post-antibiotic effect on Enterobacteriaceae and Pseudomonas aeruginosa

Background

Proline-rich antimicrobial peptides (PrAMPs) represent a promising class of potential therapeutics to treat multiresistant infections. They inhibit bacterial protein translation at the 70S ribosome by either blocking the peptide-exit tunnel (oncocin type) or trapping release factors (apidaecin type).

Objectives

Besides direct concentration-dependent antibacterial effects, the post-antibiotic effect (PAE) is the second most important criterion of antimicrobial pharmacodynamics to be determined in vitro. Here, PAEs of 10 PrAMPs and three antibiotics against three Escherichia coli strains, Klebsiella pneumoniae ATCC 10031 and Pseudomonas aeruginosa ATCC 27853 were studied after 1 h of exposure.

Methods

A robust high-throughput screening to determine PAEs was established, i.e. liquid handling by a 96-channel pipetting system and continuous incubation and absorbance measurement in a microplate reader.

Results

Prolonged PAEs (≥4 h) were detected for all peptides at their MIC values against all strains; PAEs were even >10 h for Api88, Api137, Bac7(1-60) and A3-APO. The PAEs increased further at 4 × MIC. Aminoglycosides gentamicin and kanamycin usually showed lower PAEs (≤4 h) at MIC, but PAEs increased to > 10 h at 4 × MIC. Bacteriostatic chloramphenicol exhibited the shortest PAEs (<4 h).

Conclusions

The PAEs of PrAMPs studied against Enterobacteriaceae and P. aeruginosa for the first time were typically 4-fold stronger than for conventional antibiotics. Together with their fast and irreversible uptake by bacteria, the observed prolonged PAE of PrAMPs helps to explain their high in vivo efficacy despite unfavourable pharmacokinetics.

Synergy Between Proline-Rich Antimicrobial Peptides and Small Molecule Antibiotics Against Selected Gram-Negative Pathogens in vitro and in vivo

As monotherapy, modified proline-rich antimicrobial peptides (PrAMPs) protect animals from experimental bacteremia in a dose-dependent manner. We evaluated the in vitro synergy of a modified PrAMP, A3-APO, a dimer, previously shown to inhibit the 70 kDa bacterial heat shock protein DnaK, with imipenem or colistin against two antibiotic-resistant pathogens; a carbapenemase-expressing Klebsiella pneumoniae strain K97/09 and Acinetobacter baumannii (ATCC BAA-1605). Combining antimicrobials resulted in synergy for PrAMP/colistin combination against both K. pneumoniae and A. baumannii (ΣFIC = 0.08 both) and additive activity for the A3-APO/imipenem combination against K. pneumoniae (ΣFIC = 0.53). Chex1-Arg20, (designated as ARV-1502 in preclinical development), the single chain PrAMP monomer of A3-APO, showed synergy with meropenem against a carbapenem-resistant uropathogenic Escherichia coli strain (ΣFIC = 0.38). In a murine bacteremia model using K97/09, A3-APO at 1 mg/kg demonstrated improved survival when co-administered with standard (10 mg/kg) or subtherapeutic (1 mg/kg) doses of colistin at 36 h (p < 0.05). Surprisingly, the survival benefit of A3-APO was augmented when the A3-APO dose was decreased by 50% to 0.5 mg/kg (p < 0.02) in conjunction with a subtherapeutic colistin dose (1 mg/kg). ARV-1502, as monotherapy demonstrated prolonged (>24 h) activity in a mouse Escherichia coli infection assay. Co-treatment with ARV-1502 and subtherapeutic doses of ceftazidime (150 mg/kg) was studied in a mouse model of melioidosis. ARV-1502 provided a 50% improvement in long-term (62 days) survival, but only at the lowest of 3 administered doses; survival advantage was demonstrated at 2.5 mg/kg but not at 5 or 10 mg/kg. The mortality benefit of combination therapies was not routinely accompanied by a parallel decline in blood or tissue bacterial counts in surviving animals, suggesting that the anti-infective activity of the host defense peptides (HDP) is broader than simply bacterial eradication. In fact, the hormetic effect observed in either animal models suggest that low dose HDP treatment may change the dominant mode of action in experimental bacteremia.

Correlating uptake and activity of proline-rich antimicrobial peptides in Escherichia coli

Increasing death tolls accounted for by antimicrobial drug resistance demand novel antibiotic lead compounds. Among different promising candidate classes, proline-rich antimicrobial peptides (PrAMPs) are very favorable due to their intracellular mechanism, i.e., binding to the 70S ribosome and DnaK, after active uptake relying on bacterial transporters like SbmA and MdtM. Studies on peptide internalization as the first step of their complex mode of action rely typically on fluorophore or radioactive labeling and quantification using microscopy, flow cytometry, or radioactivity. Here, a liquid chromatography based assay was applied to quantify the unlabeled internalized full-length peptides and their proteolytic degradation products (metabolites) using UV absorbance and mass spectrometry. Knockout mutants lacking transporter proteins showed reduced PrAMP uptakes, explaining their reduced susceptibility against PrAMPs. Interestingly, major metabolites produced by bacterial proteases still bound to the 70S ribosome provide evidence that degradation by cytosolic proteases as a possible resistance mechanism is not very efficient. Graphical abstract The uptake of unlabeled proline-rich antimicrobial peptides (PrAMPs) is analyzed in Escherichia coli BW25113 wild-type and transporter knockout mutants ΔsbmA and BS2 (ΔsbmA yjiL::Tn10) by reversed-phase chromatography and quantified by UV detection or mass spectrometry with multi-reaction monitoring (scheme right). Internalized peptide amounts correlated to minimal inhibitory concentrations and bacterial transport activities based on the present transporter proteins (scheme left).

Transdermally administered proline-arginine-rich host defense peptides show systemic efficacy in a lethal mouse bacteremia model

Host defense peptides are preferably administered as topical therapeutic agents. We have investigated whether peptide A3-APO can enter the circulation when applied to the ear skin. Efficacy of peptide monotherapy as transdermal administration option was assessed in a systemic mouse Acinetobacter baumannii model. A3-APO reduced mortality and demonstrated a statistically significant reduction of blood bacterial counts, regardless whether it was administered prior or after bacterial challenge. The peptidic metabolite of A3-APO was efficacious when applied to the ear or tail.

Racing on the Wrong Track

The preclinical in vitro and in vivo benchmark figures of cationic antimicrobial peptides have to be revisited based on the newly discovered alternative modes of action.

Differential stability of therapeutic peptides with different proteolytic cleavage sites in blood, plasma and serum

Proteolytic degradation of peptide-based drugs is often considered as major weakness limiting systemic therapeutic applications. Therefore, huge efforts are typically devoted to stabilize sequences against proteases present in serum or plasma, obtained as supernatants after complete blood coagulation or centrifugation of blood supplemented with anticoagulants, respectively. Plasma and serum are reproducibly obtained from animals and humans allowing consistent for clinical analyses and research applications. However, the spectrum of active or activated proteases appears to vary depending on the activation of proteases and cofactors during coagulation (serum) or inhibition of such enzymes by anticoagulants (plasma), such as EDTA (metallo- and Ca²⁺-dependent proteases) and heparin (e.g. thrombin, factor Xa). Here, we studied the presumed effects on peptide degradation by taking blood via cardiac puncture of CD-1 mice using a syringe containing a peptide solution. Due to absence of coagulation activators (e.g. glass surfaces and damaged cells), visible blood clotting was prevented allowing to study peptide degradation for one hour. The remaining peptide was quantified and the degradation products were identified using mass spectrometry. When the degradation rates (half-life times) were compared to serum derived freshly from the same animal and commercial serum and plasma samples, peptides of three different families showed indeed considerably different stabilities. Generally, peptides were faster degraded in serum than in plasma, but surprisingly all peptides were more stable in fresh blood and the order of degradation rates among the peptides varied among the six different incubation experiments. This indicates, that proteolytic degradation of peptide-based therapeutics may often be misleading stimulating efforts to stabilize peptides at degradation sites relevant only in vitro, i.e., for serum or plasma stability assays, but of lower importance in vivo.

In vivo Efficacy and Pharmacokinetics of Optimized Apidaecin Analogs

Proline-rich antimicrobial peptides (PrAMPs) represent promising alternative therapeutic options for the treatment of multidrug-resistant bacterial infections. PrAMPs are predominantly active against Gram-negative bacteria by inhibiting protein expression via at least two different modes of action, i.e., blocking the ribosomal exit tunnel of 70S ribosomes (oncocin-type binding) or inhibiting the assembly of the 50S ribosomal subunit (apidaecin-type binding). The in vivo efficacy and favorable biodistribution of oncocins confirmed the therapeutic potential of short PrAMPs for the first time, whereas the in vivo evaluation of apidaecins is still limited despite the promising efficacy of apidaecin-analog Api88 in an intraperitoneal murine infection model. Here, the in vivo efficacy of apidaecin-analog Api137 was studied, which rescued all NMRI mice from a lethal intraperitoneal infection with E. coli ATCC 25922 when administered three times intraperitoneal at doses of 0.6 mg/kg starting 1 h after infection. When Api88 and Api137 were administered intravenous or intraperitoneal at doses of 5 and 20 mg/kg, their plasma levels were similarly low (<3 μg/mL) and four-fold lower than for oncocin-analog Onc72. This contradicted earlier expectation based on the very low serum stability of Api88 with a half-life time of only ~5 min compared to ~6 and ~3 h for Api137 and Onc72, respectively. Pharmacokinetic data relying on a sensitive mass spectrometry method utilizing multiple reaction monitoring and isotope-labeled peptides revealed that Api88 and Api137 were present in blood, urine, and kidney, and liver homogenates at similar levels accompanied by the same major metabolites comprising residues 1-16 and 1-17. The pretended discrepancy was solved, when all peptides were incubated in peritoneal lavage. Api137 was rapidly degraded at the C-terminus, while Api88 was rather stable despite releasing the same degradation products. Onc72 was very stable explaining its higher plasma levels compared to Api88 and Api137 after intraperitoneal administration illuminating its good in vivo efficacy. The data indicate that the degradation of therapeutic peptides should be studied in serum and further body fluids. Moreover, the high efficacy in murine infection models and the fast clearance of Api88 and Api137 within ~60 min after intravenous and ~90 min after intraperitoneal injections indicate that their in vivo efficacy relates to the maximal peptide concentration achieved in blood.

Readily adaptable release kinetics of prodrugs using protease-dependent reversible PEGylation

Protein and peptide therapeutics with good in vitro activities often fail due to poor bioavailability, circulation lifetime, and immunogenicity. PEGylation, i.e. conjugation of polyethylene glycol (PEG), significantly improves serum stability and renal clearance besides reducing the immunogenicity and thus enhances pharmacokinetics and tolerance in vivo. Several PEGylated drugs are marketed including several top-selling blockbusters. However, PEGylation can mask the binding site, especially in peptides, and thereby reduce the activity drastically, which is only rarely compensated by the improved bioavailability. Prodrug strategies using temporary PEGylation, i.e. the authentic drug is released from a PEG-linked precursor by hydrolysis or enzymatic degradation, can overcome these weaknesses. Recently, we reported a strategy coupling PEG via a peptide linker cleaved C-terminally by trypsin-like proteases in blood to release the unmasked therapeutic peptide. Here, we designed twelve short peptide linkers (four or five residues) to tune the release-rates of oncocin Onc112, a proline-rich antimicrobial peptide. In 25% aqueous mouse serum, Onc112 was released with half-life times from 0.5 to 12h. When elongated N-terminally with 5kDa ɑ-methoxy-ω-mercapto PEG as thioether, the half-life times of the prodrugs ranged from 7 to 42h in full mouse serum. Conjugation of a 20kDa instead of the 5kDa PEG increased the half-life times more than twofold, whereas longer peptide linkers up to twelve residues increased them only slightly. In all cases, Onc112 was released continuously providing stable peptide levels for at least 16h. The kinetics will allow the specific design of PEG-linker-drug-combinations for optimizing the pharmacokinetics of promising peptide therapeutics.