Melectin MAPs: the influence of dendrimerization on antimicrobial and hemolytic activity

The Antimicrobial Peptide Melectin Shows Both Antimicrobial and Antitumor Activity via Membrane Interference and DNA Binding

Purpose

Increasingly complex diseases require novel drugs for their treatment. Antimicrobial peptides (AMPs) are promising candidate treatments due to their broad existence and special characteristics. However, the current understanding of AMPs is not sufficient to allow them to be produced commercially for clinical use.

Materials and Methods

Melectin, from the venom of the cleptoparasitic bee Melecta albifrons, does not exhibit sequence homology with other wasp venom peptides. To investigate this more deeply, we explored the antibacterial and antitumor activities of Melectin and related mechanisms.

Results

Our results demonstrate that Melectin possesses antimicrobial properties against standard sensitive/clinical drug-resistant bacteria strains as well as antitumor activity. It has an α-helix form and exhibits moderate cytotoxicity. Its action mechanisms are involved with membrane interfering and DNA binding. The membrane interfering effect was distinct between different phospholipid compositions.

Conclusion

We found that Melectin may serve as a new potential template in the battle against multidrug resistance, and our study indicated that there are promising prospects for medically applicable drugs based on AMPs.

From Nanobiotechnology, Positively Charged Biomimetic Dendrimers as Novel Antibacterial Agents: A Review

The alarming increase in antimicrobial resistance, based on the built-in abilities of bacteria to nullify the activity of current antibiotics, leaves a growing number of bacterial infections untreatable. An appealing approach, advanced in recent decades, concerns the development of novel agents able to interact with the external layers of bacteria, causing irreparable damage. Regarding this, some natural cationic antimicrobial peptides (CAMPs) have been reconsidered, and synthetic cationic polymers, mimicking CAMPs and able to kill bacteria by non-specific detrimental interaction with the negative bacterial membranes, have been proposed as promising solutions. Lately, also dendrimers were considered suitable macromolecules for the preparation of more advanced cationic biomimetic nanoparticles, able to harmonize the typical properties of dendrimers, including nanosize, mono-dispersion, long-term stability, high functionality, and the non-specific mechanism of action of CAMPs. Although cationic dendrimers are extensively applied in nanomedicine for drug or gene delivery, their application as antimicrobial agents is still in its infancy. The state of the art of their potential applications in this important field has therefore been reviewed here, with particular attention to the innovative case studies in the literature including also amino acid-modified polyester-based dendrimers, practically unexplored as membrane-active antimicrobials and able to kill bacteria on contact.

Antibacterial Activity of Non-Cytotoxic, Amino Acid-Modified Polycationic Dendrimers against Pseudomonas aeruginosa and Other Non-Fermenting Gram-Negative Bacteria

Due to the rapid increase of antimicrobial resistance with ensuring therapeutic failures, the purpose of this study was to identify novel synthetic molecules as alternatives to conventional available, but presently ineffective antibiotics. Variously structured cationic dendrimers previously reported have provided promising outcomes. However, the problem of their cytotoxicity towards eukaryotic cells has not been completely overcome. We have now investigated the antibacterial activities of three not cytotoxic cationic dendrimers (G5Ds: G5H, G5K, and G5HK) against several multidrug-resistant (MDR) clinical strains. All G5Ds displayed remarkable activity against MDR non-fermenting Gram-negative species such as P. aeruginosa, S. maltophilia, and A. baumannii (MICs = 0.5-33.2 µM). In particular, very low MIC values (0.5-2.1 µM) were observed for G5K, which proved to be more active than the potent colistin (2.1 versus 3.19 µM) against P. aeruginosa. Concerning its mechanism of action, in time-killing and turbidimetric studies, G5K displayed a rapid non-lytic bactericidal activity. Considering the absence of cytotoxicity of these new compounds and their potency, comparable or even higher than that provided by the dendrimers previously reported, G5Ds may be proposed as promising novel antibacterial agents capable of overcoming the alarming resistance rates of several nosocomial non-fermenting Gram-negative pathogens.

Isolation and Characterization of Antimicrobial Peptides with Unusual Disulfide Connectivity from the Colonial Ascidian Synoicum turgens

This study reports the isolation of two novel cysteine-rich antibacterial peptides, turgencin A and turgencin B, along with their oxidized derivatives, from the Arctic marine colonial ascidian Synoicum turgens. The peptides are post-translationally modified, containing six cysteines with an unusual disulfide connectivity of Cys¹-Cys⁶, Cys²-Cys⁵, and Cys³-Cys⁴ and an amidated C-terminus. Furthermore, the peptides contain methionine residues resulting in the isolation of peptides with different degrees of oxidation. The most potent peptide, turgencin A_Mox1 with one oxidized methionine, displayed antimicrobial activity against both Gram-negative and Gram-positive bacteria with a minimum inhibitory concentration (MIC) as low as 0.4 µM against selected bacterial strains. In addition, the peptide inhibited the growth of the melanoma cancer cell line A2058 (IC₅₀ = 1.4 µM) and the human fibroblast cell line MRC-5 (IC₅₀ = 4.8 µM). The results from this study show that natural peptides isolated from marine tunicates have the potential to be promising drug leads.

Synergistic bactericide and antibiotic effects of dimeric, tetrameric, or palindromic peptides containing the RWQWR motif against Gram-positive and Gram-negative strains

Dimeric and tetrameric peptides derived from LfcinB (20-25): RRWQWR, LfcinB (20-30): RRWQWRMKKLG, LfcinB (17-31): FKARRWQWRMKKLGA, or the palindromic sequence LfcinB (21-25)Pal: RWQWRWQWR were obtained by means of the SPPS-Fmoc/tBu methodology. The antibacterial activity of these molecules was evaluated against Escherichia coli (ATCC 25922 and ATCC 11775), Staphylococcus aureus (ATCC 25923), Enterococcus faecalis (ATCC 29212), and Pseudomonas aeruginosa (ATCC 27853). The dimer LfcinB (20-25)2: (RRWQWR)2K-Ahx, the tetramer LfcinB (20-25)4: (RRWQWR)4K2-Ahx2-C2, and the palindromic sequence LfcinB (21-25)Pal exhibited the highest antibacterial activity against the tested bacterial strains. In all cases, the antibacterial activity was dependent on peptide concentration. The polyvalent molecules LfcinB (20-25)2 and LfcinB (20-25)4 exhibited bacteriostatic and bactericidal activity against E. coli, P. aeruginosa, and S. aureus strains; additionally, this dimer and this tetramer combined with ciprofloxacin exhibited a synergistic antibacterial effect against E. coli ATCC 25922 and P. aeruginosa, respectively. Furthermore, the peptides LfcinB (20-30)4, LfcinB (20-25)4, and LfcinB (21-25)Pal combined with vancomycin exhibited a synergistic antibacterial effect against S. aureus and E. faecalis, respectively. This study showed that polyvalent peptides derived from LfcinB exhibit significant antibacterial activity, suggesting that these peptides could have a therapeutic application. Furthermore, our results suggest that polyvalent peptide synthesis could be considered as an innovative and viable strategy for obtaining promising antimicrobial molecules.

Natural Antimicrobial Peptides as Inspiration for Design of a New Generation Antifungal Compounds

Invasive fungal infections are associated with high mortality rates, despite appropriate antifungal therapy. Limited therapeutic options, resistance development and the high mortality of invasive fungal infections brought about more concern triggering the search for new compounds capable of interfering with fungal viability and virulence. In this context, peptides gained attention as promising candidates for the antimycotics development. Variety of structural and functional characteristics identified for various natural antifungal peptides makes them excellent starting points for design novel drug candidates. Current review provides a brief overview of natural and synthetic antifungal peptides.

Large-scale synthesis and structural analysis of a synthetic glycopeptide dendrimer as an anti-cancer vaccine candidate

A complex glycopeptide was obtained in multigram as a fully synthetic anti-cancer vaccine for human use.

Next-generation nanoantibacterial tools developed from peptides

Bacteria resistant against various antimicrobial compounds have emerged in many countries, and the age of resistance has just started. Among the more promising novel antimicrobial compounds on which current research is focusing are the antimicrobial peptides (AMPs). These are often less susceptible to bacterial resistance since multiple modifications in the cellular membranes, cell wall and metabolism are required to reduce their effectiveness. Most likely, the use of pure AMPs will be insufficient for controlling pathogenic bacteria, and innovative approaches are required to employ AMPs in new antibiotic treatments. Therefore, here we review novel bionanotechnological approaches, including nanofibers, nanoparticles and magnetic particles for effectively using AMPs in fighting infectious diseases.

Synthetic multivalent antifungal peptides effective against fungi

Taking advantage of the cluster effect observed in multivalent peptides, this work describes antifungal activity and possible mechanism of action of tetravalent peptide (B4010) which carries 4 copies of the sequence RGRKVVRR through a branched lysine core. B4010 displayed better antifungal properties than natamycin and amphotericin B. The peptide retained significant activity in the presence of monovalent/divalent cations, trypsin and serum and tear fluid. Moreover, B4010 is non-haemolytic and non-toxic to mice by intraperitoneal (200 mg/kg) or intravenous (100 mg/kg) routes. S. cerevisiae mutant strains with altered membrane sterol structures and composition showed hyper senstivity to B4010. The peptide had no affinity for cell wall polysaccharides and caused rapid dissipation of membrane potential and release of vital ions and ATP when treated with C. albicans. We demonstrate that additives which alter the membrane potential or membrane rigidity protect C. albicans from B4010-induced lethality. Calcein release assay and molecular dynamics simulations showed that the peptide preferentially binds to mixed bilayer containing ergosterol over phophotidylcholine-cholesterol bilayers. The studies further suggested that the first arginine is important for mediating peptide-bilayer interactions. Replacing the first arginine led to a 2-4 fold decrease in antifungal activities and reduced membrane disruption properties. The combined in silico and in vitro approach should facilitate rational design of new tetravalent antifungal peptides.