Oncocin Onc72 is efficacious against antibiotic-susceptible Klebsiella pneumoniae ATCC 43816 in a murine thigh infection model

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 (t_1/2 ) 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 t_1/2 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 t_1/2 and a constant release of Onc72 in mice, potentially limiting adverse effects and increasing efficacy.

Antimicrobial Mechanisms and Clinical Application Prospects of Antimicrobial Peptides

Antimicrobial peptides are a type of small-molecule peptide that widely exist in nature and are components of the innate immunity of almost all living things. They play an important role in resisting foreign invading microorganisms. Antimicrobial peptides have a wide range of antibacterial activities against bacteria, fungi, viruses and other microorganisms. They are active against traditional antibiotic-resistant strains and do not easily induce the development of drug resistance. Therefore, they have become a hot spot of medical research and are expected to become a new substitute for fighting microbial infection and represent a new method for treating drug-resistant bacteria. This review briefly introduces the source and structural characteristics of antimicrobial peptides and describes those that have been used against common clinical microorganisms (bacteria, fungi, viruses, and especially coronaviruses), focusing on their antimicrobial mechanism of action and clinical application prospects.

Effects of Lipidation on a Proline-Rich Antibacterial Peptide

The emergence of multidrug-resistant bacteria is a worldwide health problem. Antimicrobial peptides have been recognized as potential alternatives to conventional antibiotics, but still require optimization. The proline-rich antimicrobial peptide Bac7(1-16) is active against only a limited number of Gram-negative bacteria. It kills bacteria by inhibiting protein synthesis after its internalization, which is mainly supported by the bacterial transporter SbmA. In this study, we tested two different lipidated forms of Bac7(1-16) with the aim of extending its activity against those bacterial species that lack SbmA. We linked a C12-alkyl chain or an ultrashort cationic lipopeptide Lp-I to the C-terminus of Bac7(1-16). Both the lipidated Bac-C12 and Bac-Lp-I forms acquired activity at low micromolar MIC values against several Gram-positive and Gram-negative bacteria. Moreover, unlike Bac7(1-16), Bac-C12, and Bac-Lp-I did not select resistant mutants in E. coli after 14 times of exposure to sub-MIC concentrations of the respective peptide. We demonstrated that the extended spectrum of activity and absence of de novo resistance are likely related to the acquired capability of the peptides to permeabilize cell membranes. These results indicate that C-terminal lipidation of a short proline-rich peptide profoundly alters its function and mode of action and provides useful insights into the design of novel broad-spectrum antibacterial agents.

Comparison of a Short Linear Antimicrobial Peptide with Its Disulfide-Cyclized and Cyclotide-Grafted Variants against Clinically Relevant Pathogens

According to the World Health Organization (WHO) the development of resistance against antibiotics by microbes is one of the most pressing health concerns. The situation will intensify since only a few pharmacological companies are currently developing novel antimicrobial compounds. Discovery and development of novel antimicrobial compounds with new modes of action are urgently needed. Antimicrobial peptides (AMPs) are known to be able to kill multidrug-resistant bacteria and, therefore, of interest to be developed into antimicrobial drugs. Proteolytic stability and toxicities of these peptides are challenges to overcome, and one strategy frequently used to address stability is cyclization. Here we introduced a disulfide-bond to cyclize a potent and nontoxic 9mer peptide and, in addition, as a proof-of-concept study, grafted this peptide into loop 6 of the cyclotide MCoTI-II. This is the first time an antimicrobial peptide has been successfully grafted onto the cyclotide scaffold. The disulfide-cyclized and grafted cyclotide showed moderate activity in broth and strong activity in 1/5 broth against clinically relevant resistant pathogens. The linear peptide showed superior activity in both conditions. The half-life time in 100% human serum was determined, for the linear peptide, to be 13 min, for the simple disulfide-cyclized peptide, 9 min, and, for the grafted cyclotide 7 h 15 min. The addition of 10% human serum led to a loss of antimicrobial activity for the different organisms, ranging from 1 to >8-fold for the cyclotide. For the disulfide-cyclized version and the linear version, activity also dropped to different degrees, 2 to 18-fold, and 1 to 30-fold respectively. Despite the massive difference in stability, the linear peptide still showed superior antimicrobial activity. The cyclotide and the disulfide-cyclized version demonstrated a slower bactericidal effect than the linear version. All three peptides were stable at high and low pH, and had very low hemolytic and cytotoxic activity.

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.

Proline-rich antimicrobial peptide Api137 is bactericidal in porcine blood infected ex vivo with a porcine or human Klebsiella pneumoniae strain

OBJECTIVES

Klebsiella pneumoniae is an emerging invasive pathogen in humans and pigs. Resistance against multiple antibiotics in this species is a major health concern and the development of new antibiotics is urgently needed. The objective of this study was to investigate the effects of proline-rich antimicrobial peptides (PrAMPs) on the survival of K. pneumoniae strains in porcine blood.

METHODS

We established a bactericidal assay with K. pneumoniae in fresh blood drawn from 4-week-old piglets. PrAMPs, namely the apidaecins Api137 and Api802 as well as the oncocin Onc112, were added to ex vivo-infected whole blood samples in order to study their bactericidal effects and, in the case of Api137, also immune responses.

RESULTS

A porcine invasive and a human iucA+rmpA+ K. pneumoniae strain showed prominent proliferation in porcine blood. Application of Api137 resulted in a dose-dependent prominent bactericidal effect killing the invasive porcine K. pneumoniae strain. Addition of 8 μg/mL Api137 also resulted in complete killing of the human iucA+rmpA+ strain. Cytotoxicity, haemolysis and induction of the pro-inflammatory cytokine tumour necrosis factor-alpha (TNFα) in K. pneumoniae-infected porcine blood treated with Api137 was comparable with values obtained after application of 10 μg/mL cefquinome.

CONCLUSION

We describe a new non-rodent model for invasive K. pneumoniae bacteraemia and present promising data for the PrAMP Api137 for the control of infection with hypervirulent K. pneumoniae strains.

Two distinct amphipathic peptide antibiotics with systemic efficacy

Antimicrobial peptides are important candidates for developing new classes of antibiotics because of their potency against antibiotic-resistant pathogens. Current research focuses on topical applications and it is unclear how to design peptides with systemic efficacy. To address this problem, we designed two potent peptides by combining database-guided discovery with structure-based design. When bound to membranes, these two short peptides with an identical amino acid composition can adopt two distinct amphipathic structures: A classic horizontal helix (horine) and a novel vertical spiral structure (verine). Their horizontal and vertical orientations on membranes were determined by solid-state ¹⁵N NMR data. While horine was potent primarily against gram-positive pathogens, verine showed broad-spectrum antimicrobial activity. Both peptides protected greater than 80% mice from infection-caused deaths. Moreover, horine and verine also displayed significant systemic efficacy in different murine models comparable to conventional antibiotics. In addition, they could eliminate resistant pathogens and preformed biofilms. Significantly, the peptides showed no nephrotoxicity to mice after intraperitoneal or intravenous administration for 1 wk. Our study underscores the significance of horine and verine in fighting drug-resistant pathogens.

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.

Efficacy of ARV-1502, a Proline-Rich Antimicrobial Peptide, in a Murine Model of Bacteremia Caused by Multi-Drug Resistant (MDR) Acinetobacter baumannii

Acinetobacter baumannii bacteremia represents a serious and increasing clinical problem due to the high mortality and treatment failures because of high rates of antibiotic resistance. Any additional new therapies for A. baumannii bacteremia would address a growing unmet medical need. ARV-1502 (designated as Chex1-Arg20 or A3-APO monomer in prior publications) is a designer proline-rich antimicrobial peptide chaperone protein inhibitor derived from insects and has demonstrated potent activity against multi-drug resistant (MDR) Gram-negative bacteria. In the current studies, we investigated the therapeutic efficacy of ARV-1502 administered intravenously (iv) alone and in combination with imipenem/cilastatin (IPM/CIL) in a mouse bacteremia model due to a MDR clinical A. baumannii strain, HUMC1. All ARV-1502 regimens (1.25, 2.5 and 5.0 mg/kg) significantly reduced bacterial density in the target tissues in a dose-dependent manner, as compared to the untreated control and IPM/CIL monotherapy (40 mg/kg) groups in the model. In addition, ARV-1502 treatment, even at the lowest dose, significantly improved survival vs. the control and IPM alone groups. As expected, IMP/CIL monotherapy had no therapeutic efficacy in the model, since the HUMC1 strain was resistant to IMP in vitro. However, the combination of ARV-1502 and IPM/CIL significantly enhanced the efficacy of ARV-1502, except the lowest dose of ARV-1502. The superior efficacy of ARV-1502 in the bacteremia model caused by MDR A. baumannii provides further support for studying this compound in severe infections caused by other MDR Gram-positive and -negative pathogens.

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.

Intracellular Antimicrobial Peptides Targeting the Protein Synthesis Machinery

While antimicrobial peptides (AMPs) are well-known for their disruptive effects on bacterial membranes, the mechanism of many intracellular AMPs is still being elucidated. In the recent years, it has been demonstrated that the subclass of proline-rich AMPs (PrAMPs) can pass through the bacterial membrane and kill bacteria by inhibiting protein synthesis. PrAMPs are a product of the innate immune system and are secreted in response to bacterial infection. So far PrAMPs have been identified in many arthropods, such as beetles, wasps, and flies, as well as some mammals, such as sheep, cows, and goats. PrAMPs show high potency against Gram-negative bacteria, while exhibiting low toxicity in eukaryotes, suggesting that they may represent a promising avenue for the development of future antimicrobial agents to combat the increase of multidrug-resistant bacterial pathogens. Structural and biochemical data have revealed the PrAMP binding sites on the ribosome as well as insight into their mechanisms of action. While the binding site of all so far investigated PrAMPs is situated within nascent polypeptide exit tunnel, the mechanism of action is distinct between class I and II PrAMPs. Specifically, class I PrAMPs, such as Bac7, Onc112, pyrrhocoricin, and metalnikowin, block the delivery of aa-tRNA by EF-Tu to the ribosomal A-site, whereas the class II PrAMPs, such as apidaecin 1b and Api137, act during translation termination and inhibit protein synthesis by trapping of release factors on the 70S ribosome following hydrolysis of the nascent polypeptide chain.

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).

Host defense antimicrobial peptides as antibiotics: design and application strategies

This review deals with the design and application strategies of new antibiotics based on naturally occurring antimicrobial peptides (AMPs). The initial candidate can be designed based on three-dimensional structure or selected from a library of peptides from natural or laboratory sources followed by optimization via structure-activity relationship studies. There are also advanced application strategies such as induction of AMP expression from host cells by various factors (e.g., metals, amino acids, vitamin D and sunlight), the use of engineered probiotic bacteria to deliver peptides, the design of prodrug and peptide conjugates to improve specific targeting. In addition, combined uses of newly developed AMPs with existing antimicrobial agents may provide a practical avenue for effective management of antibiotic-resistant bacteria (superbugs), including biofilms. Finally, we highlight AMPs already in use or under clinical trials.

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.

Host Cell Interactions Are a Significant Barrier to the Clinical Utility of Peptide Antibiotics

Despite longstanding promise and many known examples, antimicrobial peptides (AMPs) have failed, thus far, to impact human medicine. On the basis of the physical chemistry and mechanism of action of AMPs, we hypothesized that host cell interactions could contribute to a loss of activity in vivo where host cells are highly concentrated. To test this idea, we characterized AMP activity in the presence of human red blood cells (RBC). Indeed, we show that most of a representative set of natural and synthetic AMPs tested are significantly inhibited by preincubation with host cells and would be effectively inactive at physiological cell density. We studied an example broad-spectrum AMP, ARVA (RRGWALRLVLAY), in a direct, label-free binding assay. We show that weak binding to host cells, coupled with their high concentration, is sufficient to account for a loss of useful activity, for at least some AMPs, because >1 × 10⁸ peptides must be bound to each bacterial cell to achieve sterilization. The effect of host cell preincubation on AMP activity is comparable to that of serum protein binding. Feasible changes in host cell binding could lead to AMPs that do not lose activity through interaction with host cells. We suggest that the intentional identification of AMPs that are active in the presence of concentrated host cells can be achieved with a paradigm shift in the way AMPs are discovered.

Insect-derived short proline-rich and murine cathelicidin-related antimicrobial peptides act synergistically on Gram-negative bacteria in vitro

AIM

Organisms express a set of antimicrobial peptides (AMP) to protect the host against invading microbes by targeting their membranes or intracellular structures. Structurally optimized proline-rich AMPs (PrAMPs) are substantially more efficient in murine infection models than previously assumed from in vitro activities. Thus, we hypothesized that PrAMPs act synergistically with lytic AMPs intrinsically produced in hosts in response to an infection.

METHODS & RESULTS

Synergistic effects between lytic murine cathelicidin-related AMP (CRAMP) and apidaecin- and oncocin-derivatives were studied in chequerboard assays. Evaluation of fractional inhibitory concentration indices revealed synergies against Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa.

CONCLUSION

CRAMP synergistically enhances the activity of proline-rich AMPs, which will allow evaluating their therapeutic potential more precisely in vitro.

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.

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.

Optimization of oncocin for antibacterial activity using a SPOT synthesis approach: extending the pathogen spectrum to Staphylococcus aureus

The identification of lead molecules against multidrug-resistant bacteria ensuing the development of novel antimicrobial drugs is an urgent task. Proline-rich antimicrobial peptides are highly active in vitro and in vivo, but only against a few Gram-negative human pathogens, with rather weak activities against Pseudomonas aeruginosa and Staphylococcus aureus. This reduced level of efficacy could be related to inadequate uptake mechanisms or structural differences of the intracellular target proteins, i.e., the 70S ribosome or chaperone DnaK. Here we synthesized peptide arrays on cellulose membranes using cleavable linkers to release the free individual peptides for further antimicrobial tests. Thus, a library of singly substituted oncocin analogs was produced by replacing each residue by all other 19 canonical amino acids yielding a set of 361 individual peptides to be evaluated against a luminescent P. aeruginosa strain. Thirteen substitutions appeared promising and their improved antibacterial activities were confirmed for different bacteria after larger scale synthesis of these analogs. By combining two favorable substitutions into one peptide, we finally obtained an oncocin analog that was ten times more active against P. aeruginosa and even 100-fold more active against S. aureus than the original oncocin, providing minimal inhibitory concentrations of 4-8 and 0.5 µg/mL, respectively.

Immunogenicity and pharmacokinetics of short, proline-rich antimicrobial peptides

Aim: The potential of proline-rich antimicrobial peptides (PrAMPs) to treat multidrug-resistant Gram-negative pathogens has been intensively investigated. They are efficacious at low doses in infection models and well tolerated in healthy mice at high doses. Methods & results: PrAMPs Onc72 and Api88 were nonimmunogenic in mice unless conjugated to a carrier protein. Monoclonal IgG1/IgG2b antibodies produced by hybridoma cells were mapped to different Onc72 regions and combined in a sandwich-ELISA in a pharmacokinetic study. Onc72 was detected at concentrations up to 32 µg/ml in murine blood after administering 20 mg/kg and reached several organs within 10 min. Conclusion: Both PrAMPs were not immunogenic and Onc72 concentrations in blood were well above the minimal inhibitory concentrations for Enterobacteriaceae further confirming their potential as novel antibiotics.