Enhanced Membrane Pore Formation through High-Affinity Targeted Antimicrobial Peptides

Many cationic antimicrobial peptides (AMPs) target the unique lipid composition of the prokaryotic cell membrane. However, the micromolar activities common for these peptides are considered weak in comparison to nisin, which follows a targeted, pore-forming mode of action. Here we show that AMPs can be modified with a high-affinity targeting module, which enables membrane permeabilization at low concentration. Magainin 2 and a truncated peptide analog were conjugated to vancomycin using click chemistry, and could be directed towards specific membrane embedded receptors both in model membrane systems and whole cells. Compared with untargeted vesicles, a gain in permeabilization efficacy of two orders of magnitude was reached with large unilamellar vesicles that included lipid II, the target of vancomycin. The truncated vancomycin-peptide conjugate showed an increased activity against vancomycin resistant Enterococci, whereas the full-length conjugate was more active against a targeted eukaryotic cell model: lipid II containing erythrocytes. This study highlights that AMPs can be made more selective and more potent against biological membranes that contain structures that can be targeted

Prognostic significance of endogenous adhesion/growth-regulatory lectins in lung cancer

Objective: To determine the expression of endogenous adhesion/growth-regulatory lectins and their binding sites using labeled tissue lectins as well as the binding profile of hyaluronic acid as an approach to define new prognostic markers. Methods: Sections of paraffin-embedded histological material of 481 lungs from lung tumor patients following radical lung excision processed by a routine immunohistochemical method (avidin-biotin labeling, DAB chromogen). Specific antibodies against galectins-1 and - 3 and the heparin-binding lectin were tested. Staining by labeled galectins and hyaluronic acid was similarly visualized by a routine protocol. After semiquantitative assessment of staining, the results were compared with the pT and pN stages and the histological type. Survival was calculated by univariate and multivariate methods. Results: Binding of galectin-1 and its expression tended to increase, whereas the parameters for galectin-3 decreased in advanced pT and pN stages at a statistically significant level. The number of positive cases was considerably smaller among the cases with small cell lung cancer than in the group with non-small-cell lung cancer, among which adenocarcinomas figured prominently with the exception of galectin-1 expression. Kaplan-Meier computations revealed that the survival rate of patients with galectin-3-binding or galectin-1-expressing tumors was significantly poorer than that of the negative cases. In the multivariate calculations of survival lymph node metastases ( p < 0.0001), histological type ( p = 0.003), galectin-3-binding capacity ( p = 0.01), galectin-3 expression ( p = 0.03) and pT status ( p = 0.003) proved to be independent prognostic factors, not correlated with the pN stage. Conclusion: The expression and the capacity to bind the adhesion/growth regulatory galectin-3 is defined as an unfavorable prognostic factor not correlated with the pTN stage. Copyright (C) 2005 S. Karger AG, Basel

In vitro Activities of Nisin Alone or in Combination with Vancomycin and Ciprofloxacin against Methicillin-Resistant and Methicillin-Susceptible <i>Staphylococcus aureus</i> Strains

Background: We investigated the in vitro activities of nisin alone or in combination with vancomycin and ciprofloxacin against methicillin-resistant (MRSA) and -susceptible Staphylococcus aureus (MSSA) strains. Methods: The minimum inhibitory concentrations were determined by microbroth dilution technique. Antibiotic combinations were assessed using the checkerboard technique. The time-kill curve method was used for determining the bactericidal activity of nisin alone and in combination. Results: For both MSSA and MRSA strains, the minimum inhibitory concentrations of nisin ranged between 4 and 16 mg/l. With a fractional inhibitory concentration of >= 0.5 as borderline, synergistic interactions were seen in three of five isolates with nisin-ciprofloxacin compared to two of five isolates with nisin-vancomycin combinations against both MSSA and MRSA. No antagonism was observed. The results of time-kill curve analysis demonstrated concentration-dependent rapid bactericidal activity of nisin and synergism almost in all strains when nisin was used in combination with ciprofloxacin, and early synergistic interactions in some of the strains when it was used in combination with vancomycin. Conclusion: Nisin seems to be a good candidate for further investigations in the treatment of Gram-positive bacteria, alone or in combination with antibiotics. Copyright (C) 2012 S. Karger AG, Base

Tuning Activity of Antimicrobial Peptides by Lipidation

Antimicrobial peptides (AMPs) are amino acid-based bioactive molecules that specifically target microbes. As such, they are a potent class of antibiotics, especially against bacterial infections. Naturally occurring AMPs are usually too long to be considered for therapeutic applications. To solve this, short sequences that mimic the activity of AMPs are designed. However, such endeavors are often accompanied with a reduction in antibacterial activity. To counter this, lipophilic molecules can be attached that function as a lipid anchor and target the short sequence to the bacterial membrane. For a range of short AMPs, this strategy has proven to lead to more active constructs. Although these lipidated short AMPs often work as complex target specific surfactants, more delicate modes of action that do not deviate too much from the nonlipidated counterparts are also known. This is readily observed by the large differences in activities that are detected when alterations in the lipid chain length and chirality of the amino acids residues are implemented. It is not uncommon to see that inactive or poorly active short AMPs can be turned into potent antibacterial agents. Importantly, selectivity of the short lipidated AMPs (lipoAMPs) for the bacterial membrane can be enhanced by alteration of the amino acid chirality. This strategy has led to lipoAMPs with submicromolar activities; in fact, activities that rival that of vancomycin have been observed for several short AMPs. Future research needs to determine (i) the effect of lipidation on the formation of lipid rafts in the bacterial membrane, (ii) if structural complications like branched lipids or chiral substituents on the lipid chain can be used to further increase the activity and selectivity of the conjugates, and (iii) if additional functionalities other than a membrane-anchoring ability can be bestowed on the lipid chain, e.g., redox activity or scavenger for small molecular components that traverse the lipid membrane. The interplay between degree of lipophilicity and the chirality of the amino acids of the AMP also needs further exploration, especially to see if more potent and selective (lipo)AMPs can be obtained that can be applied systemically. It may also be advisable to measure the most potent lipoAMPs in a centralized facility in order to obtain objective and comparable antibacterial activities

Toward a new and noninvasive diagnostic method of papillary thyroid cancer by using peptide vectorized contrast agents targeted to galectin-1

The incidence of papillary thyroid cancer has increased these last decades due to a better detection. High prevalence of nodules combined with the low incidence of thyroid cancers constitutes an important diagnostic challenge. We propose to develop an alternative diagnostic method to reduce the number of useless and painful thyroidectomies using a vectorized contrast agent for magnetic resonance imaging. Galectin-1 (gal-1), a protein overexpressed in well-differentiated thyroid cancer, has been targeted with a randomized linear 12-mer peptide library using the phage display technique. Selected peptides have been conjugated to ultrasmall superparamagnetic particles of iron oxide (USPIO). Peptides and their corresponding contrast agents have been tested in vitro for their specific binding and toxicity. Two peptides (P1 and P7) were selected according to their affinity toward gal-1. Their binding has been revealed by immunohistochemistry on human thyroid cancer biopsies, and they were co-localized with gal-1 by immunofluorescence on TPC-1 cell line. Both peptides induce a decrease in TPC-1 cells’ adhesion to gal-1 immobilized on culture plates. After coupling to USPIO, the peptides preserved their affinity toward gal-1. Their specific binding has been corroborated by co-localization with gal-1 expressed by TPC-1 cells and by their ability to compete with anti-gal-1 antibody. The peptides and their USPIO derivatives produce no toxicity in HepaRG cells as determined by MTT assay. The vectorized contrast agents are potential imaging probes for thyroid cancer diagnosis. Moreover, the two gal-1-targeted peptides prevent cancer cell adhesion by interacting with the carbohydrate-recognition domain of gal-1.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Synthetic multivalent antifungal peptides effective against fungi

10.1371/journal.pone.0087730PLoS ONE92-POLN

Antimicrobial peptides: Modes of mechanism, modulation of defense responses

Complicated schemes of classical breeding and their drawbacks, environmental risks imposed by agrochemicals, decrease of arable land, and coincident escalating damages of pests and pathogens have accentuated the necessity for highly efficient measures to improve crop protection. During co-evolution of host-microbe interactions, antimicrobial peptides (AMPs) have exhibited a brilliant history in protecting host organisms against devastation by invading pathogens. Since the 1980s, a plethora of AMPs has been isolated from and characterized in different organisms. Nevertheless the AMPs expressed in plants render them more resistant to diverse pathogens, a more orchestrated approach based on knowledge of their mechanisms of action and cellular targets, structural toxic principle, and possible impact on immune system of corresponding transgenic plants will considerably improve crop protection strategies against harmful plant diseases. This review outlines the current knowledge on different modes of action of AMPs and then argues the waves of AMPs' ectopic expression on transgenic plants' immune system