Biological and structural characterization of new linear gomesin analogues with improved therapeutic indices

Natural Gomesin-like Peptides with More Selective Antifungal Activities

Background: Antimicrobial peptides are generally considered promising drug candidates for combating resistant bacterial infections. However, the selectivity of their action may vary significantly. Natural gomesin, isolated from haemocytes of the tarantula Acanthoscurria gomesiana, demonstrates a broad spectrum of antimicrobial activities, being the most effective against pathogenic fungi. Methods: Here, we searched for variants of natural gomesin-like peptides and produced their recombinant analogs in the bacterial expression system. The antimicrobial activities of the obtained peptides were tested against a panel of bacterial and yeast strains, and their toxicity towards human cells was examined. Results: Most of the new analogs of gomesin have primary structures homologous to that of the natural gomesin; however, they have fewer amino acid residues and post-translational modifications. One of the discovered analogs, the His-rich shorter peptide from the spider Dysdera sylvatica, designated as DsGom, displays antifungal activity comparable with that of natural gomesin. In the process of the structural-functional study of DsGom, it was shown that this analog retains a basic mechanism of action similar to that of natural gomesin. The DsGom analog has a significantly better toxicity profile as compared to gomesin. At the same time, the loss of the first Arg residue reduces, but does not annul, the antifungal activity of DsGom. Moreover, the acidification of the growth medium reduces the loss of the antifungal activity of this analog. Conclusions: The discovered natural gomesin-like peptides display more selective antifungal activities as compared to gomesin. The low cytotoxicity of DsGom, combined with its high antifungal activity and stability, allows us to consider it a promising drug candidate for the treatment of fungal infections, especially those caused by fungi of the Candida genus.

Overcoming the challenge: cell-penetrating peptides and membrane permeability

<p>Cell-penetrating peptides (CPPs) have emerged as a promising strategy for enhancing the membrane permeability of bioactive molecules, particularly in the treatment of central nervous system diseases. CPPs possess the ability to deliver a diverse array of bioactive molecules into cells using either covalent or non-covalent approaches, with a preference for non-covalent methods to preserve the biological activity of the transported molecules. By effectively traversing various physiological barriers, CPPs have exhibited significant potential in preclinical and clinical drug development. The discovery of CPPs represents a valuable solution to the challenge of limited membrane permeability of bioactive molecules and will continue to exert a crucial influence on the field of biomedical science.</p>

Native and Engineered Cyclic Disulfide-Rich Peptides as Drug Leads

Bioactive peptides are a highly abundant and diverse group of molecules that exhibit a wide range of structural and functional variation. Despite their immense therapeutic potential, bioactive peptides have been traditionally perceived as poor drug candidates, largely due to intrinsic shortcomings that reflect their endogenous heritage, i.e., short biological half-lives and poor cell permeability. In this review, we examine the utility of molecular engineering to insert bioactive sequences into constrained scaffolds with desired pharmaceutical properties. Applying lessons learnt from nature, we focus on molecular grafting of cyclic disulfide-rich scaffolds (naturally derived or engineered), shown to be intrinsically stable and amenable to sequence modifications, and their utility as privileged frameworks in drug design.

Unlocking the Potential of the Antimicrobial Peptide Gomesin: From Discovery and Structure-Activity Relationships to Therapeutic Applications

Gomesin is a cationic antimicrobial peptide which is isolated from the haemocytes of the Brazilian tarantula Acanthoscurria gomesiana and can be produced chemically by Fmoc solid-phase peptide synthesis. Gomesin exhibits a range of biological activities, as demonstrated by its toxicity against therapeutically relevant pathogens such as Gram-positive or Gram-negative bacteria, fungi, cancer cells, and parasites. In recent years, a cyclic version of gomesin has been used for drug design and development as it is more stable than native gomesin in human serum and can penetrate and enter cancer cells. It can therefore interact with intracellular targets and has the potential to be developed as a drug lead for to treat cancer, infectious diseases, and other human diseases. This review provides a perspective on the discovery, structure-activity relationships, mechanism of action, biological activity, and potential clinical applications of gomesin.

Antimicrobial Peptides with Anti-Candida Activity

Mycoses are accountable for millions of infections yearly worldwide. Invasive candidiasis is the most usual, presenting a high morbidity and mortality. Candida albicans remains the prevalent etiologic agent, but the incidence of other species such as Candida parapsilosis, Candida glabrata and Candida auris keeps increasing. These pathogens frequently show a reduced susceptibility to commonly used antifungal drugs, including polyenes, triazoles and echinocandins, and the incidence of emerging multi-drug-resistant strains of these species continues to increase. Therefore, the need to search for new molecules that target these pathogenic species in a different manner is now more urgent than ever. Nature is an almost endless source of interesting new molecules that could meet this need. Among these molecules, antimicrobial peptides, present in different sources in nature, possess some advantages over conventional antifungal agents, even with their own drawbacks, and are considered as a promising pharmacological option against a wide range of microbial infections. In this review, we describe 20 antimicrobial peptides from different origins that possess an activity against Candida.

Two Tachykinin-Related Peptides with Antimicrobial Activity Isolated from Triatoma infestans Hemolymph

Antimicrobial peptides and proteins (AMPs) are molecules that can interact with microbial cells and lead to membrane disruption or intracellular molecule interactions and death. Several molecules with antimicrobial effects also present other biological activities. One such protein group representing the duplicity of activities is the tachykinin family. Tachykinins (TKs) form a family of neuropeptides in vertebrates with a consensus C-terminal region (F-X-G-Y-R-NH2). Invertebrate TKs and TK-related peptides (TKRPs) are subfamilies found in invertebrates that present high homology with TKs and have similar biological effects. Several of these molecules have already been described but reports of TKRP in Hemiptera species are limited. By analyzing the Triatoma infestans hemolymph by reversed-phase high-performance liquid chromatography, biological assays, and mass spectrometry, two antimicrobial molecules were isolated and identified as TKRPs, which we named as TRP1-TINF and TRP2-TINF (tachykinin-related peptides I and II from T. infestans). TRP1-TINF is a random secondary structure peptide with 9 amino acid residues. It is susceptible to aminopeptidases degradation and is active mainly against Micrococcus luteus (32 μM). TRP2-TINF is a 10-amino acid peptide with a 310 helix secondary structure and is susceptible to carboxypeptidases degradation. It has major antimicrobial activity against both Pseudomonas aeruginosa and Escherichia coli (45 μM). Neither molecule is toxic to human erythrocytes and both present minor toxicity toward Vero cells at a concentration of 1000 μM. As the first description of TKRPs with antimicrobial activity in T. infestans, this work contributes to the wider comprehension of the insects’ physiology and describes pharmacological relevant molecules.

The unusual conformation of cross-strand disulfide bonds is critical to the stability of β-hairpin peptides

The cross-strand disulfides (CSDs) found in β-hairpin antimicrobial peptides (β-AMPs) show a unique disulfide geometry that is characterized by unusual torsion angles and a short Cα-Cα distance. While the sequence and disulfide bond connectivity of disulfide-rich peptides is well studied, much less is known about the disulfide geometry found in CSDs and their role in the stability of β-AMPs. To address this, we solved the nuclear magnetic resonance (NMR) structure of the β-AMP gomesin (Gm) at 278, 298, and 310 K, examined the disulfide bond geometry of over 800 disulfide-rich peptides, and carried out extensive molecular dynamics (MD) simulation of the peptides Gm and protegrin. The NMR data suggests Cα-Cα distances characteristic for CSDs are independent of temperature. Analysis of disulfide-rich peptides from the Protein Data Bank revealed that right-handed and left-handed rotamers are equally likely in CSDs. The previously reported preference for right-handed rotamers was likely biased by restricting the analysis to peptides and proteins solved using X-ray crystallography. Furthermore, data from MD simulations showed that the short Cα-Cα distance is critical for the stability of these peptides. The unique disulfide geometry of CSDs poses a challenge to biomolecular force fields and to retain the stability of β-hairpin fold over long simulation times, restraints on the torsion angles might be required.

The Biological and Biophysical Properties of the Spider Peptide Gomesin

This review summarises the current knowledge of Gomesin (Gm), an 18-residue long, cationic anti-microbial peptide originally isolated from the haemocytes of the Brazilian tarantula Acanthoscurria gomesiana. The peptide shows potent cytotoxic activity against clinically relevant microbes including Gram-positive and Gram-negative bacteria, fungi, and parasites. In addition, Gm shows in-vitro and in-vivo anti-cancer activities against several human and murine cancers. The peptide exerts its cytotoxic activity by permeabilising cell membranes, but the underlying molecular mechanism of action is still unclear. Due to its potential as a therapeutic agent, the structure and membrane-binding properties, as well as the leakage and cytotoxic activities of Gm have been studied using a range of techniques. This review provides a summary of these studies, with a particular focus on biophysical characterisation studies of peptide variants that have attempted to establish a structure-activity relationship. Future studies are still needed to rationalise the binding affinity and cell-type-specific selectivity of Gm and its variants, while more pre-clinical studies are required to develop Gm into a therapeutically useful peptide.

Insights into Antimicrobial Peptides from Spiders and Scorpions

The venoms of spiders and scorpions contain a variety of chemical compounds. Antimicrobial peptides (AMPs) from these organisms were first discovered in the 1990s. As of May 2015, there were 42 spider's and 63 scorpion's AMPs in the Antimicrobial Peptide Database (http://aps.unmc.edu/AP). These peptides have demonstrated broad or narrow-spectrum activities against bacteria, fungi, viruses, and parasites. In addition, they can be toxic to cancer cells, insects and erythrocytes. To provide insight into such an activity spectrum, this article discusses the discovery, classification, structure and activity relationships, bioinformatics analysis, and potential applications of spider and scorpion AMPs. Our analysis reveals that, in the case of linear peptides, spiders use both glycine-rich and helical peptide models for defense, whereas scorpions use two distinct helical peptide models with different amino acid compositions to exert the observed antimicrobial activities and hemolytic toxicity. Our structural bioinformatics study improves the knowledge in the field and can be used to design more selective peptides to combat tumors, parasites, and viruses.

LL-37-derived membrane-active FK-13 analogs possessing cell selectivity, anti-biofilm activity and synergy with chloramphenicol and anti-inflammatory activity

Although the human-derived antimicrobial peptide (AMP) LL-37 has potent antimicrobial and anti-inflammatory activities, its therapeutic application is limited by its low cell selectivity and high production cost due to its large size. To overcome these problems, we tried to develop novel LL-37-derived short α-helical AMPs with improved cell selectivity and without a significant loss of anti-inflammatory activity relative to that of parental LL-37. Using amino acid substitution, we designed and synthesized a series of FK13 analogs based on the sequence of the 13-meric short FK13 peptide (residues 17-29 of LL-37) that has been identified as the region responsible for the antimicrobial activity of LL-37. Among the designed FK13 analogs, FK-13-a1 and FK-13-a7 showed high cell selectivity and retained the anti-inflammatory activity. The therapeutic index (a measure of cell selectivity) of FK-13-a1 and FK-13-a7 was 6.3- and 2.3-fold that of parental LL-37, respectively. Furthermore, FK-13-a1 and FK-13-a7 displayed more potent antimicrobial activity against antibiotic-resistant bacteria including MRSA, MDRPA, and VREF, than did LL-37. In addition, FK-13-a1 and FK-13-a7 exhibited greater synergistic effects with chloramphenicol against MRSA and MDRPA and were more effective anti-biofilm agents against MDRPA than LL-37 was. Moreover, FK-13-a1 and FK-13-a7 maintained their activities in the presence of physiological salts and human serum. SYTOX green uptake, membrane depolarization and killing kinetics revealed that FK13-a1 and FK13-a7 kills microbial cells by permeabilizing the cell membrane and damaging membrane integrity. Taken together, our results suggest that FK13-a1 and FK13-a7 can be developed as novel antimicrobial/anti-inflammatory agents.

Gomesin acts in the immune system and promotes myeloid differentiation and monocyte/macrophage activation in mouse

Due to the cytotoxic effect of antimicrobial peptides (AMP) against several microorganism and tumor cells has been proposed their association with the immune system. However, just a few reports have shown this relationship. In this study, mice were treated with gomesin, a β-hairpin AMP that exhibit high cytotoxicity against bacterial and tumor cells. Different effects in the immune system were observed, such as, decrease of CD3⁺ in T lymphocytes (Control: 17.7±1.4%; Gomesin: 7.67±1.2%) and in hematopoietic progenitors and increase of hematopoietic stem cell (Control: 0.046±0.004%; Gomesin: 0.067±0.003%), B220⁺ B lymphocytes (Control: 38.63±1.5%; Gomesin: 47.83±0.48%), and Mac-1⁺F4/80⁺ macrophages (Control: 11.76±3.4%; Gomesin: 27.13±4.0%). Additionally, macrophage increase was accompanied by an increase of macrophage phagocytosis (Control 20.85±1.53; Gomesin 31.32±1 Geometric mean), interleukin 6 (Control: 47.24±1.9ng/mL; Gomesin: 138.68±33.68ng/mL) and monocyte chemoattractant protein-1 (Control: 0.872±0.093ng/mL; Gomesin: 1.83±0.067ng/mL). Thus, this report showed immunomodulatory activity of gomesin in the immune system of mice.

Natural and synthetic peptides with antifungal activity

In recent years, the increase of invasive fungal infections and the emergence of antifungal resistance stressed the need for new antifungal drugs. Peptides have shown to be good candidates for the development of alternative antimicrobial agents through high-throughput screening, and subsequent optimization according to a rational approach. This review presents a brief overview on antifungal natural peptides of different sources (animals, plants, micro-organisms), peptide fragments derived by proteolytic cleavage of precursor physiological proteins (cryptides), synthetic unnatural peptides and peptide derivatives. Antifungal peptides are schematically reported based on their structure, antifungal spectrum and reported effects. Natural or synthetic peptides and their modified derivatives may represent the basis for new compounds active against fungal infections.

Contribution of Amphipathicity and Hydrophobicity to the Antimicrobial Activity and Cytotoxicity of β-Hairpin Peptides

Bacteria have acquired extensive resistance mechanisms to protect themselves against antibiotic action. Today the bacterial membrane has become one of the “final frontiers” in the search for new compounds acting on novel targets to address the threat of multi-drug resistant (MDR) and XDR bacterial pathogens. β-Hairpin antimicrobial peptides are amphipathic, membrane-binding antibiotics that exhibit a broad range of activities against Gram-positive, Gram-negative, and fungal pathogens. However, most members of the class also possess adverse cytotoxicity and hemolytic activity that preclude their development as candidate antimicrobials. We examined peptide hydrophobicity, amphipathicity, and structure to better dissect and understand the correlation between antimicrobial activity and toxicity, membrane binding, and membrane permeability. The hydrophobicity, pI, net charge at physiological pH, and amphipathic moment for the β-hairpin antimicrobial peptides tachyplesin-1, polyphemusin-1, protegrin-1, gomesin, arenicin-3, and thanatin were determined and correlated with key antimicrobial activity and toxicity data. These included antimicrobial activity against five key bacterial pathogens and two fungi, cytotoxicity against human cell lines, and hemolytic activity in human erythrocytes. Observed antimicrobial activity trends correlated with compound amphipathicity and, to a lesser extent, with overall hydrophobicity. Antimicrobial activity increased with amphipathicity, but unfortunately so did toxicity. Of note, tachyplesin-1 was found to be 8-fold more amphipathic than gomesin. These analyses identify tachyplesin-1 as a promising scaffold for rational design and synthetic optimization toward an antibiotic candidate.

Biochemical and biophysical combined study of bicarinalin, an ant venom antimicrobial peptide

We have recently characterized bicarinalin as the most abundant peptide from the venom of the ant Tetramorium bicarinatum. This antimicrobial peptide is active against Staphylococcus and Enterobacteriaceae. To further investigate the antimicrobial properties of this cationic and cysteine-free peptide, we have studied its antibacterial, antifungal and antiparasitic activities on a large array of microorganisms. Bicarinalin was active against fifteen microorganisms with minimal inhibitory concentrations ranging from 2 and 25μmolL(-1). Cronobacter sakazakii, Salmonella enterica, Candida albicans, Aspergilus niger and Saccharomyces cerevisiae were particularly susceptible to this novel antimicrobial peptide. Resistant strains of Staphylococcus aureus, Pseudomonas aeruginosa and C. albicans were as susceptible as the canonical strains. Interestingly, bicarinalin was also active against the parasite Leishmania infantum with a minimal inhibitory concentrations of 2μmolL(-1). The bicarinalin pre-propeptide cDNA sequence has been determined using a combination of degenerated primers with RACE PCR strategy. Interestingly, the N-terminal domain of bicarinalin pre-propeptide exhibited sequence similarity with the pilosulin antimicrobial peptide family previously described in the Myrmecia venoms. Moreover, using SYTOX green uptake assay, we showed that, for all the tested microorganisms, bicarinalin acted through a membrane permeabilization mechanism. Two dimensional-NMR experiments showed that bicarinalin displayed a 10 residue-long α-helical structure flanked by two N- and C-terminal disordered regions. This partially amphipathic helix may explain the membrane permeabilization mechanism of bicarinalin observed in this study. Finally, therapeutic value of bicarinalin was highlighted by its low cytotoxicity against human lymphocytes at bactericidal concentrations and its long half-life in human serum which was around 15h.

Comparative study of the mechanism of action of the antimicrobial peptide gomesin and its linear analogue: The role of the β-hairpin structure

Gomesin (Gm) is an antimicrobial peptide first isolated from the hemolymph of a Brazilian spider. Its powerful antimicrobial activity is, however, accompanied by hemolysis. As an alternative to this issue, a linear analogue (named GmL) lacking the disulfide bonds was designed. Here, CD spectroscopy, a fluorescence-based leakage assay, isothermal titration calorimetry (ITC) and light scattering are used to study the interaction of both Gm and GmL with large unilamellar vesicles (LUVs) composed of POPC (palmitoyl oleoyl phosphatidylcholine) with 25 and 50 mol% POPG (palmitoyl oleoyl phosphatidylglycerol). The activities of Gm and GmL in respect to their binding affinity/enthalpy, ability to permeabilize membranes and to induce vesicle aggregation are correlated with peptide secondary structure. Whereas Gm displays a quite stable β-hairpin motif irrespective of the environment, GmL assumes a random conformation in aqueous solution and in the presence of 25 mol% POPG but adopts a β-like structure in the presence of 50 mol% POPG. Gm exhibited high lytic activity against both surface charge densities. Instead, the activity of GmL was found to be negligible in the presence of 25 mol% POPG LUVs, but comparable to that of the native peptide against 50 mol% POPG as a consequence of peptide structuring. We conclude that the activity of Gm and its linear analogue is intimately related to the formation of a β-turn motif, in which the hydrophobic residues form a hydrophobic face able to insert into the membrane and disrupt it.

Implicit Membrane Investigation of the Stability of Antimicrobial Peptide β-Barrels and Arcs

Previous simulations showed that the β-hairpin antimicrobial peptide (AMP) protegrin-1 can form stable octameric β-barrels and tetrameric arcs (half barrels) in both implicit and explicit membranes. Here, we extend this investigation to several AMPs of similar structure: tachyplesin, androctonin, polyphemusin, gomesin, and the retrocyclin θ-defensin. These peptides form short β-hairpins stabilized by 2-3 disulfide bonds. We also examine synthetic β-sheet peptides selected from a combinatorial library for their ability or inability to form pores in lipid membranes. When heptameric, octameric, and decameric β-barrels and tetrameric arcs of these peptides were embedded in pre-formed neutral or anionic lipid pores (i.e., pores in neutral or anionic membranes, respectively), a variety of behaviors and membrane binding energies were observed. Due to the cationic charge of the peptides, more favorable transfer energies and more stable binding were observed in anionic than neutral pores. The synthetic peptides bound very strongly and formed stable barrels and arcs in both neutral and anionic pores. The natural AMPs exhibited unfavorable or marginally favorable binding energy and kinetic stability in neutral pores, consistent with the lower hemolytic activity of some of them compared with protegrin-1. Binding to anionic pores was more favorable, but significant distortions of the barrel or arc structures were sometimes noted. These results are discussed in light of the available experimental data. The diversity of behaviors obtained makes it unlikely that the barrel and arc mechanisms are valid for the entire family of β-hairpin AMPs.

An insect defensin-derived β-hairpin peptide with enhanced antibacterial activity

Insect defensins are a class of small, cysteine-rich antimicrobial peptides primarily active on Gram-positive bacteria. Their roles in maggot therapy for treating chronic wound infection have been reported recently. However, a relatively narrow antibacterial spectrum together with the lack of a cost-effective means of commercial-scale production has limited their application. To further exploit the therapeutic potential of these molecules, we engineered the carboxyl-terminal β-sheet of navidefensin2-2, an insect defensin from Nasonia vitripennis, based on its structural similarity to naturally occurring microbicidal β-hairpin peptides. The designed peptide of 14 residues, referred to as NvBH, spans the β-sheet region of the defensin with two amino acids substituted for assembly of a disulfide-bonded amphipathic β-hairpin structure. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) combined with circular dichroism (CD) analysis shows that the oxidized NvBH (oNvBH), produced from the synthetic peptide by air oxidization in an alkaline environment, folds into a typical β-hairpin structure linked by two disulfide bridges (Cys1-Cys4; Cys2-Cys3). However, such a structure appears not to be functionally necessary as synthetic NvBH with a spontaneously oxidized disulfide bridge (Cys2-Cys3) (termed poNvBH) displayed similar antibacterial potency to oNvBH. In comparison with oNvBH, poNvBH exhibited higher serum stability and more resistance on tryptic digestion. These two forms of peptides are capable of killing an array of Gram-positive (including antibiotic-resistant strains of Staphylococcus) and Gram-negative bacterial pathogens at low micromolar concentrations through a membrane disruptive mode of action. Our work indicates that the β-sheet region of insect defensins is a promising subdomain of proteins in anti-infective drug discovery.

Bacterial killing mechanism of sheep myeloid antimicrobial peptide-18 (SMAP-18) and its Trp-substituted analog with improved cell selectivity and reduced mammalian cell toxicity

To develop short antimicrobial peptide with improved cell selectivity and reduced mammalian cell toxicity compared to sheep myeloid antimicrobial peptide-29 (SMAP-29) and elucidate the possible mechanisms responsible for their antimicrobial action, we synthesized a N-terminal 18-residue peptide amide (SMAP-18) from SMAP-29 and its Trp-substituted analog (SMAP-18-W). Due to their reduced hemolytic activity and retained antimicrobial activity, SMAP-18 and SMAP-18-W showed higher cell selectivity than SMAP-29. In addition, SMAP-18 and SMAP-18-W had no cytotoxicity against three different mammalian cells such as RAW 264.7, NIH-3T3 and HeLa cells even at 100 μM. These results suggest that SMAP-18 and SMAP-18-W have potential for future development as novel therapeutic antimicrobial agent. Unlike SMAP-29, SMAP-18 and SMAP-18-W showed relatively weak ability to induce dye leakage from bacterial membrane-mimicking liposomes, N-phenyl-1-napthylamine (NPN) uptake and o-nitrophenyl-β-galactoside (ONPG) hydrolysis. Similar to SMAP-29, SMAP-18-W led to a significant membrane depolarization (> 80%) against Staphylococcus aureus at 2 × MIC. In contrast, SMAP-18 did not cause any membrane depolarization even at 4 × MIC. In confocal laser scanning microscopy, we observed translocation of SMAP-18 across the membrane in a non-membrane disruptive manner. SMAP-29 and SMAP-18-W were unable to translocate the bacterial membrane. Collectively, we propose here that SMAP-29 and SMAP-18-W kill microorganisms by disrupting/perturbing the lipid bilayer and forming pore/ion channels on bacterial cell membranes, respectively. In contrast, SMAP-18 may kill bacteria via intracellular-targeting mechanism.

Properties and mechanisms of action of naturally occurring antifungal peptides

Antimicrobial peptides are a vital component of the innate immune system of all eukaryotic organisms and many of these peptides have potent antifungal activity. They have potential application in the control of fungal pathogens that are a serious threat to both human health and food security. Development of antifungal peptides as therapeutics requires an understanding of their mechanism of action on fungal cells. To date, most research on antimicrobial peptides has focused on their activity against bacteria. Several antimicrobial peptides specifically target fungal cells and are not active against bacteria. Others with broader specificity often have different mechanisms of action against bacteria and fungi. This review focuses on the mechanism of action of naturally occurring antifungal peptides from a diverse range of sources including plants, mammals, amphibians, insects, crabs, spiders, and fungi. While antimicrobial peptides were originally proposed to act via membrane permeabilization, the mechanism of antifungal activity for these peptides is generally more complex and often involves entry of the peptide into the cell.

From antimicrobial to anticancer peptides. A review

Antimicrobial peptides (AMPs) are part of the innate immune defense mechanism of many organisms. Although AMPs have been essentially studied and developed as potential alternatives for fighting infectious diseases, their use as anticancer peptides (ACPs) in cancer therapy either alone or in combination with other conventional drugs has been regarded as a therapeutic strategy to explore. As human cancer remains a cause of high morbidity and mortality worldwide, an urgent need of new, selective, and more efficient drugs is evident. Even though ACPs are expected to be selective toward tumor cells without impairing the normal body physiological functions, the development of a selective ACP has been a challenge. It is not yet possible to predict antitumor activity based on ACPs structures. ACPs are unique molecules when compared to the actual chemotherapeutic arsenal available for cancer treatment and display a variety of modes of action which in some types of cancer seem to co-exist. Regardless the debate surrounding the definition of structure-activity relationships for ACPs, great effort has been invested in ACP design and the challenge of improving effective killing of tumor cells remains. As detailed studies on ACPs mechanisms of action are crucial for optimizing drug development, in this review we provide an overview of the literature concerning peptides' structure, modes of action, selectivity, and efficacy and also summarize some of the many ACPs studied and/or developed for targeting different solid and hematologic malignancies with special emphasis on the first group. Strategies described for drug development and for increasing peptide selectivity toward specific cells while reducing toxicity are also discussed.

Short KR-12 analogs designed from human cathelicidin LL-37 possessing both antimicrobial and antiendotoxic activities without mammalian cell toxicity

KR-12 (residues 18-29 of LL-37) was known to be the smallest peptide of human cathelicidin LL-37 possessing antimicrobial activity. In order to optimize α-helical short antimicrobial peptides having both antimicrobial and antiendotoxic activities without mammalian cell toxicity, we designed and synthesized a series of KR-12 analogs. Highest hydrophobic analogs KR-12-a5 and KR-12-a6 displayed greater inhibition of lipopolysaccharide (LPS)-stimulated tumor necrosis factor-α production and higher LPS-binding activity. We have observed that antimicrobial activity is independent of charge, but LPS neutralization requires a balance of hydrophobicity and net positive charge. Among KR-12 analogs, KR-12-a2, KR-12-a3 and KR-12-a4 showed much higher cell specificity for bacteria over erythrocytes and retained antiendotoxic activity, relative to parental LL-37. KR-12-a5 displayed the strongest antiendotoxic activity but almost similar cell specificity as compared with LL-37. Also, these KR-12 analogs (KR-12-a2, KR-12-a3, KR-12-a4 and KR-12-a5) exhibited potent antimicrobial activity (minimal inhibitory concentration: 4 μM) against methicillin-resistant Staphylococcus aureus. Taken together, these KR-12 analogs have the potential for future development as a novel class of antimicrobial and anti-inflammatory therapeutic agents.

Interaction of the antimicrobial peptide gomesin with model membranes: a calorimetric study

Gomesin is a potent cationic antimicrobial peptide (z = +6) isolated from the Brazilian spider Acanthoscurria gomesiana . The interaction of gomesin with large unilamellar vesicles composed of a 1:1 mixture of zwitterionic (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and anionic (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) phospholipids is studied with isothermal titration calorimetry (ITC). In parallel, light scattering and optical microscopy are used to assess peptide-induced vesicle aggregation. The ability of gomesin to permeabilize the membrane is examined with fluorescence spectroscopy of the leakage of 5,6-carboxyfluorescein (CF). Vesicles coated with 3 mol % 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (PE-PEG) lipids are also investigated to assess the influence of peptide-induced vesicle aggregation in the activity of gomesin. The ITC and light scattering titrations are done in two ways: lipid into peptide and peptide into lipid injections. Although some differences arise between the two setups, the basic interaction of gomesin with anionic vesicles is preserved. A surface partition model combined with the Gouy-Chapman theory is put forward to fit the ITC results. The intrinsic binding constant of gomesin is found to be K ≈ 10(3) M(-1). The interaction of gomesin with anionic membranes is highly exothermic and enthalpy-driven. Binding of gomesin is virtually always accompanied by vesicle aggregation and changes in membrane permeability, leading to CF leakage. Addition of PE-PEG to the membrane strongly attenuates vesicle aggregation but does not significantly change the mode of action of gomesin. The results point to a strong interaction of gomesin with the membrane surface, causing membrane rupture without a deep penetration into the bilayer core.

Peptides as the next generation of anti-infectives

Synthesis and large-scale manufacturing technologies are now available for the commercial production of even the most complex peptide anti-infectives. Married with the potential of this class of molecule as the next generation of effective, resistance-free and safe antimicrobials, and a much better understanding of their biology, pharmacology and pharmacodynamics, the first regulatory approvals and introduction into clinical practice of these promising drug candidates will likely be soon. This is a key juncture in the history/life cycle of peptide anti-infectives and, perhaps, their commercial and therapeutic potential is about to be realized. This review highlights the promise of these agents as the next generation of therapeutics and summarizes the challenges faced in, and lessons learned from, the past.

Linear bactenecin analogs with cell selectivity and anti-endotoxic activity

Bactenecin (Bac) is a 12-residue disulfide-linked antimicrobial peptide isolated from the granules of bovine neutrophils. In this study, to develop novel linear Bac analogs with cell selectivity and anti-endotoxic activity, we designed and synthesized a series of linear Bac analogs with amino acid substitution in Cys3,11 and/or Val6,7 of Bac. Among Bac analogs, some analogs (Bac-W, Bac-KW, Bac-L, Bac-KL, Bac-LW, and Bac-KLW) with higher hydrophobicity showed the amalgamated property of cell selectivity and anti-endotoxic activity. Furthermore, Bac-W, Bac-KW, Bac-LW, and Bac-KLW showed serum stability comparable with that of disulfide-bonded Bac. Therefore, these Bac analogs (Bac-W, Bac-KW, Bac-LW, and Bac-KLW) can serve as promising antibiotics for the development of therapeutic agents for treatment against endotoxic shock and bacterial infection. In addition, our results suggest that a little increase in hydrophobicity may be responsible for the decreased cell selectivity of the multiple Arg-containing peptides (Bac-W, Bac-L, and Bac-LW) over the multiple Lys-containing peptides (Bac-KW, Bac-KL, and Bac-KLW).

Synthesis and properties of cyclic gomesin and analogues

Gomesin (Gm) was the first antimicrobial peptide (AMP) isolated from the hemocytes of a spider, the Brazilian mygalomorph Acanthoscurria gomesiana. We have been studying the properties of this interesting AMP, which also displays anticancer, antimalarial, anticryptococcal and anti-Leishmania activities. In the present study, the total syntheses of backbone-cyclized analogues of Gm (two disulfide bonds), [Cys(Acm)(2,15)]-Gm (one disulfide bond) and [Thr(2,6,11,15),(D)-Pro(9)]-Gm (no disulfide bonds) were accomplished, and the impact of cyclization on their properties was examined. The consequence of simultaneous deletion of pGlu(1) and Arg(16) -Glu-Arg(18) -NH(2) on Gm antimicrobial activity and structure was also analyzed. The results obtained showed that the synthetic route that includes peptide backbone cyclization on resin was advantageous and that a combination of 20% DMSO/NMP, EDC/HOBt, 60 °C and conventional heating appears to be particularly suitable for backbone cyclization of bioactive peptides. The biological properties of the Gm analogues clearly revealed that the N-terminal amino acid pGlu(1) and the amidated C-terminal tripeptide Arg(16) -Glu-Arg(18) -NH(2) play a major role in the interaction of Gm with the target membranes. Moreover, backbone cyclization practically did not affect the stability of the peptides in human serum; it also did not affect or enhanced hemolytic activity, but induced selectivity and, in some cases, discrete enhancements of antimicrobial activity and salt tolerance. Because of its high therapeutic index, easy synthesis and lower cost, the [Thr(2,6,11,15),(D)-Pro(9)]-Gm analogue remains the best active Gm-derived AMP developed so far; nevertheless, its elevated instability in human serum may limit its therapeutic potential.

Prokaryotic selectivity and LPS-neutralizing activity of short antimicrobial peptides designed from the human antimicrobial peptide LL-37

To develop novel antimicrobial peptides (AMPs) with shorter lengths, improved prokaryotic selectivity and retained lipolysaccharide (LPS)-neutralizing activity compared to human cathelicidin AMP, LL-37, a series of amino acid-substituted analogs based on IG-19 (residues 13-31 of LL-37) were synthesized. Among the IG-19 analogs, the analog a4 showed the highest prokaryotic selectivity, but much lower LPS-neutralizing activity compared to parental LL-37. The analogs, a5, a6, a7 and a8 with higher hydrophobicity displayed LPS-neutralizing activity comparable to that of LL-37, but much lesser prokaryotic selectivity. These results indicate that the proper hydrophobicity of the peptides is crucial to exert the amalgamated property of LPS-neutralizing activity and prokaryotic selectivity. Furthermore, to increase LPS-neutralizing activity of the analog a4 without a remarkable decrease in prokaryotic selectivity, we synthesized Trp-substituted analogs (a4-W1 and a4-W2), in which Phe(5) or Phe(15) of a4 is replaced by Trp. Despite their same prokaryotic selectivity, a4-W2 displayed much higher LPS-neutralizing activity compared to a4-W1. When compared with parental LL-37, a4-W2 showed retained LPS-neutralizing activity and 2.8-fold enhanced prokaryotic selectivity. These results suggest that the effective site for Trp-substitution when designing novel AMPs with higher LPS-neutralizing activity, without a remarkable reduction in prokaryotic selectivity, is the amphipathic interface between the end of the hydrophilic side and the start of the hydrophobic side rather than the central position of the hydrophobic side in their α-helical wheel projection. Taken together, the analog a4-W2 can serve as a promising template for the development of therapeutic agents for the treatment of endotoxic shock and bacterial infection.

Characterization of dual effects induced by antimicrobial peptides: regulated cell death or membrane disruption

BACKGROUND

Some reports describe lysis mechanisms by antimicrobial peptides (AMPs), while others describe the activation of regulated cell death. In this study, we compare the cell death-inducing activities of four β-hairpin AMPs (gomesin, protegrin, tachyplesin and polyphemusin II) along with their linear analogs in the human erythroleukemia K562 cell line to investigate the relationship between their structure and activity.

METHODS

K562 cells were exposed to AMPs. Morphological and biochemistry alterations were evaluated using light microscopy, confocal microscopy and flow cytometry.

RESULTS

Gomesin and protegrin displayed cytotoxic properties that their linear counterparts did not. Tachyplesin and polyphemusin II and also their linear analogs induced cell death. We were able to distinguish two ways in which these AMPs induced cell death. Lower concentrations of AMPs induced controlled cell death mechanisms. Gomesin, tachyplesin and linear-tachyplesin promoted apoptosis that was characterized by annexin labeling, sensitivity to Z-VAD, and caspase-3 activation, but was also inhibited by necrostatin-1. Gomesin and protegrin induced cell death was dependent on intracellular Ca2+ mechanisms and the participation of free radicals was observed in protegrin induced cell death. Polyphemusin II and its linear analog mainly induced necrosis. Conversely, treatment with higher concentrations of AMPs primarily resulted in cell membrane disruption, but with clearly different patterns of action for each AMP tested.

CONCLUSION

Different actions by β-hairpin AMPs were observed at low concentrations and at higher concentrations despite the structure similarity.

GENERAL SIGNIFICANCE

Controlled intracellular mechanism and direct membrane disruption were clearly distinguished helping to understand the real action of AMPs in mammalian cells.

Antimicrobial activity, bactericidal mechanism and LPS-neutralizing activity of the cell-penetrating peptide pVEC and its analogs

pVEC is a cell-penetrating peptide derived from the murine vascular endothelial-cadherin protein. To evaluate the potential of pVEC as antimicrobial peptide (AMP), we synthesized pVEC and its analogs with Trp and Arg/Lys substitution, and their antimicrobial and lipopolysaccharide (LPS)-neutralizing activities were investigated. pVEC and its analogs displayed a potent antimicrobial activity (minimal inhibitory concentration: 4-16 μM) against Gram-positive and Gram-negative bacteria but no or less hemolytic activity (less than 10% hemolysis) even at a concentration of 200 μM. These peptides induced a near-complete membrane depolarization (more than 80%) at 4 μM against Staphylococcus aureus and a significant dye leakage (35-70%) from bacterial membrane-mimicking liposome at a concentration as low as 1 μM. The fluorescence profiles of pVEC and its analogs in dye leakage from liposome and membrane depolarization were similar to those of a frog-derived AMP, magainin 2. These results suggest that pVEC and its analogs kill bacteria by forming a pore or ion channel in the cytoplasmic membrane. pVEC and its analogs significantly inhibited nitric oxide production or tumor necrosis factor-α release in LPS-stimulated mouse macrophage RAW264.7 cells at 10 to 50 μM, in which RAW264.7 were not damaged. Taken together, our results suggest that pVEC and its analogs with potent antimicrobial and LPS-neutralizing activities can serve as AMPs for the treatment of microbial infection and sepsis.

Cell selectivity, mechanism of action and LPS-neutralizing activity of bovine myeloid antimicrobial peptide-18 (BMAP-18) and its analogs

To develop novel antimicrobial peptides (AMPs) with improved cell selectivity and potent LPS-neutralizing activity, we synthesized an 18 N-terminal residues peptide (BAMP-18) of bovine myeloid antimicrobial peptide-27 (BMAP-27) and its analogs (BMAP-18-W, BMAP-18-L, BMAP-18-I and BMAP-18-f). BMAP-18 and its analogs displayed much higher cell selectivity (about 4-97-fold increased) as compared to parental BMAP-27 because of their decreased hemolytic activity and retained antimicrobial activity. BMAP-27 caused near-complete dye leakage from bacterial-membrane-mimicking vesicles even at very low concentration of 0.5μM, whereas BMAP-18 and its analogs induced very little dye leakage (less than 40%) even at 16μM. These peptides induced near-complete membrane depolarization of Staphylococcus aureus cells under their MIC (4μM). These results suggests that BMAP-18 and its analogs exhibit lethality toward microbes due to their ability to form small channels that permit the transit of ions or protons, but not molecules as large as calcein, and not by the membrane-disruption/perturbation mode. BMAP-18 and its analogs significantly inhibited nitric oxide (NO) production or tumor necrosis factor-α (TNF-α) release in LPS-stimulated mouse macrophage RAW264.7 cells at 10μM. In particular, BMAP-18-W showed LPS-neutralizing activity comparable to that of BMAP-27. There was a significant linear correlation between the increase in the hydrophobicity of peptides and LPS-neutralizing activity. Although BMAP-18-W has lower hydrophobicity than BMAP-18-L, it showed higher LPS-neutralizing activity as compared to BMAP-18-L. This result suggests other important parameters of AMPs may be involved in their LPS-neutralizing activity, as well as positive charge and hydrophobicity.

Revealing the lytic mechanism of the antimicrobial peptide gomesin by observing giant unilamellar vesicles

Gomesin (Gm) is a potent cationic antimicrobial peptide from a Brazilian spider. Here we use optical and fluorescence microscopy to study the interaction of Gm, its low active linear analogue, [Ser(2,6,11,15)]-Gm (GmL), and a fluorescent labeled analogue, Gm-Rh, with giant unilamellar vesicles (GUVs) composed of mixtures of the neutral lipid palmitoyloleoyl phosphatidylcholine (POPC) with the negatively charged lipid palmitoyloleoyl phosphatidylglycerol (POPG) or cholesterol, so as to mimic bacterial and mammalian cell membranes, respectively. We observed the effect of injecting a peptide solution with a micropipet close to GUVs. As a result of peptide-lipid interaction, GUVs burst suddenly. Stable pores, which result in leaky vesicles, were not observed. Fluorescence microscopy of Gm-Rh injected on GUVs confirmed the high peptide/lipid affinity. These facts lead us to suggest that Gm and GmL disrupt the membrane via the carpet model. In order to quantify the lytic activity of both peptides against different membrane composition, a solution of GUVs was diluted in increasing concentration of peptides and the fraction of burst GUVs was measured as a function of time. The lytic activity of both peptides was enhanced by the presence of POPG and decreased upon addition of cholesterol. GmL exhibited lower lytic activity as compared to Gm, but this difference vanished at high POPG molar fraction.

Cell selectivity and anti-inflammatory activity of a Leu/Lys-rich alpha-helical model antimicrobial peptide and its diastereomeric peptides

To investigate the effect of the number and distribution of d-amino acids introduced into non-cell-selective alpha-helical antimicrobial peptides on the cell selectivity, protease stability and anti-inflammatory activity, we synthesized an 18-meric Leu/Lys-rich alpha-helical model peptide (K(9)L(8)W) and d-amino acid-containing diastereomeric peptides. Increasing in cell selectivity of the peptides was increased in parallel with increasing in the number of d-amino acids introduced. Despite having the same number of d-amino acids, D(9)-K(9)L(8)W-1 had better cell selectivity than D(9)-K(9)L(8)W-2, indicating that a dispersed distribution of d-amino acids in diastereomeric peptides is more effective for cell selectivity than their segregated distribution. D(3)-K(9)L(8)W-2, D(6)-K(9)L(8)W, D(9)-K(9)L(8)W-1 and D(9)-K(9)L(8)W-2 showed complete resistance to tryptic digestion. Furthermore, K(9)L(8)W and all of its diastereomeric peptides significantly inhibited nitric oxide (NO) production, inducible nitric oxide synthase (iNOS) mRNA expression and tumor necrosis factor-alpha (TNF-alpha) release in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophage cells at a lower concentration than bactericidal concentration. The order of anti-inflammatory activity for the peptides was K(9)L(8)W approximately D(3)-K(9)L(8)W-1 approximately D(3)-K(9)L(8)W-2 approximately D(6)-K(9)L(8)W approximately D(9)-K(9)L(8)W-2>D(4)-K(9)L(8)W>D(9)-K(9)L(8)W-1. Increasing in hydrophobicity or alpha-helicity of the peptides was more closely correlated with increasing in hemolytic activity and anti-inflammatory activity than antimicrobial and LPS-disaggregation activities. Collectively, we successfully developed several d-amino acid-containing antimicrobial peptides (D(4)-K(9)L(8)W, D(6)-K(9)L(8)W and D(9)-K(9)L(8)W-1) with good cell selectivity, protease stability and potent anti-inflammatory activity. These antimicrobial peptides could serve as templates for the development of peptide antibiotics for the treatment of sepsis, as well as microbial infection.

Divorcing folding from function: how acylation affects the membrane-perturbing properties of an antimicrobial peptide

Many small cationic peptides, which are unstructured in aqueous solution, have antimicrobial properties. These properties are assumed to be linked to their ability to permeabilize bacterial membranes, accompanied by the transition to an alpha-helical folding state. Here we show that there is no direct link between folding of the antimicrobial peptide Novicidin (Nc) and its membrane permeabilization. N-terminal acylation with C8-C16 alkyl chains and the inclusion of anionic lipids both increase Nc's ability to form alpha-helical structure in the presence of vesicles. Nevertheless, both acylation and anionic lipids reduce the extent of permeabilization of these vesicles and lead to slower permeabilization kinetics. Furthermore, acylation significantly decreases antimicrobial activity. Although acyl chains of increasing length also increase the tendency of the peptides to aggregate in solution, this cannot rationalize our results since permeabilization and antimicrobial activities are observed well below concentrations where aggregation occurs. This suggests that significant induction of alpha-helical structure is not a prerequisite for membrane perturbation in this class of antimicrobial peptides. Our data suggests that for Nc, induction of alpha-helical structure may inhibit rather than facilitate membrane disruption, and that a more peripheral interaction may be the most efficient permeabilization mechanism. Furthermore, acylation leads to a deeper embedding in the membrane, which could lead to an anti-permeabilizing "plugging" effect.

Antimicrobial specificity and mechanism of action of disulfide-removed linear analogs of the plant-derived Cys-rich antimicrobial peptide Ib-AMP1

Ib-AMP1 is a 20-residue disulfide-linked beta-sheet antimicrobial peptide found in the seeds of Impatiens balsamina. In order to investigate the effects of the 2 disulfide bonds on the antimicrobial specificity, to determine the mechanism of antimicrobial action of Ib-AMP1 and to develop novel cell-selective antimicrobial peptides with improved antimicrobial specificity as compared to wild-type Ib-AMP1, we synthesized a disulfide-removed linear analog of Ib-AMP1 with L-Pro, D-Pro or peptoid residues (Nala and Nlys) at the central position of the molecule. All linear analogs displayed a 3.7-4.8-fold higher antimicrobial specificity than wild-type Ib-AMP1, indicating that the disulfide bonds of Ib-AMP1 analogs are not essential for its antimicrobial specificity. Circular dichroism spectra revealed that the peptoid residues, as well as the proline at the central position of disulfide bond-removed Ib-AMP1 analogs, induce a beta-turn structure in a negatively charged bacterial membrane-mimicking environment. Ib-AMP1 was not effective in depolarizing the cytoplasmic membranes of Staphylococcus aureus and showed almost no leakage of calcein from negatively charged bacterial membranes mimicking lipid vesicles. In contrast, all linear analogs caused very weak dye leakage from negatively charged vesicles, but they almost completely depolarized the membrane potential of S. aureus cells. Collectively, our results suggest that the target of Ib-AMP1 may not be the cytoplasmic membranes of bacteria but their intracellular components. All linear analogs exhibit lethality due to their ability to form small channels that permit the transit of ions or protons and not molecules as large as calcein, and not by disrupting membranes.

Structure and mode of action of microplusin, a copper II-chelating antimicrobial peptide from the cattle tick Rhipicephalus (Boophilus) microplus

Microplusin, a Rhipicephalus (Boophilus) microplus antimicrobial peptide (AMP) is the first fully characterized member of a new family of cysteine-rich AMPs with histidine-rich regions at the N and C termini. In the tick, microplusin belongs to the arsenal of innate defense molecules active against bacteria and fungi. Here we describe the NMR solution structure of microplusin and demonstrate that the protein binds copper II and iron II. Structured as a single alpha-helical globular domain, microplusin consists of five alpha-helices: alpha1 (residues Gly-9 to Arg-21), alpha2 (residues Glu-27 to Asn-40), alpha3 (residues Arg-44 to Thr-54), alpha4 (residues Leu-57 to Tyr-64), and alpha5 (residues Asn-67 to Cys-80). The N and C termini are disordered. This structure is unlike any other AMP structures described to date. We also used NMR spectroscopy to map the copper binding region on microplusin. Finally, using the Gram-positive bacteria Micrococcus luteus as a model, we studied of mode of action of microplusin. Microplusin has a bacteriostatic effect and does not permeabilize the bacterial membrane. Because microplusin binds metals, we tested whether this was related to its antimicrobial activity. We found that the bacteriostatic effect of microplusin was fully reversed by supplementation of culture media with copper II but not iron II. We also demonstrated that microplusin affects M. luteus respiration, a copper-dependent process. Thus, we conclude that the antibacterial effect of microplusin is due to its ability to bind and sequester copper II.

Design of novel indolicidin-derived antimicrobial peptides with enhanced cell specificity and potent anti-inflammatory activity

Indolicidin (IN) is a 13-residue Trp-rich antimicrobial peptide isolated from bovine neutrophils. To develop novel IN-derived antimicrobial peptides with enhanced cell specificity (therapeutic index) and potent anti-inflammatory activity, several IN analogs were synthesized by Pro-->Lys substitution. All IN analogs displayed an increase in therapeutic index by 3- to 15-fold relative to parental IN. IN and its analogs induced a significant membrane depolarization against intact Staphylococcus aureus in a dose-dependent manner and depolarized membrane potential at 5 microg/ml (MIC for S. aureus) almost completely. However, these peptides caused less than 40% calcein leakage from negatively charged EYPG/EYPE liposomes mimicking bacterial membranes at 10 microg/ml. Based on these results, we hypothesize that IN and its analogs kill microorganisms via the formation of small ion channels that permit transit of ions or protons, but not molecules as large as calcein. Furthermore, IN and its analogs induced a remarkable suppression in nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) mRNA expression in LPS-stimulated mouse macrophage RAW264.7 cells. All IN analogs showed LPS-binding activity comparable to that of IN. Taken together, their potent antimicrobial, anti-inflammatory and LPS-neutralizing activities similar to those of IN, coupled with their no cytotoxicity, our designed IN analogs make excellent candidates for novel antimicrobial and anti-sepsis agents.

Effective topical treatment of subcutaneous murine B16F10-Nex2 melanoma by the antimicrobial peptide gomesin

Gomesin is a potent antimicrobial peptide (AMP) isolated from hemocytes of the spider Acanthoscurria gomesiana. The present study aimed at determining whether gomesin exerted antitumor activity in vitro and in vivo. Topical treatment of subcutaneous murine melanoma with gomesin incorporated in a cream base significantly delayed tumor growth. A direct cytotoxicity of gomesin in murine melanoma B16F10-Nex2 cells and several human tumor cell lineages was observed in vitro, with IC(50) values below 5 microM. The beta-hairpin structure of gomesin with disulfide bridges seemed essential for optimal activity. d-Gomesin was equally active. A membrane-permeabilizing activity was suggested, as gomesin bound to the cell membrane and cytoplasmic lactate dehydrogenase was detected extracellularly. At doses causing partial growth of tumor cells, gomesin allowed internalization of macromolecules (immunoglobulins), which increased the cytotoxic effect. The in vivo antitumor effect of gomesin might also involve a cytotoxic effect on endothelial cells because cultured human endothelial cells were killed in vitro at a similar concentration range. This effect represents a novel and potential use for gomesin as a topical agent against unsuccessfully treated intradermal and epithelial skin cancers. To our knowledge, this is the first report on the successful topical use of AMPs in cancer treatment.