Cytotoxicity and apoptosis mediated by two peptides of innate immunity

MA-PEP: A novel anticancer peptide prediction framework with multimodal feature fusion based on attention mechanism

AntiCancer Peptides (ACPs) have emerged as promising therapeutic agents for cancer treatment. The time-consuming and costly nature of wet-lab discriminatory methods has spurred the development of various machine learning and deep learning-based ACP classification methods. Nonetheless, current methods encountered challenges in efficiently integrating features from various peptide modalities, thereby limiting a more comprehensive understanding of ACPs and further restricting the improvement of prediction model performance. In this study, we introduce a novel ACP prediction method, MA-PEP, which leverages multiple attention mechanisms for feature enhancement and fusion to improve ACP prediction. By integrating the enhanced molecular-level chemical features and sequence information of peptides, MA-PEP demonstrates superior prediction performance across several benchmark datasets, highlighting its efficacy in ACP prediction. Moreover, the visual analysis and case studies further demonstrate MA-PEP's reliable feature extraction capability and its promise in the realm of ACP exploration. The code and datasets for MA-PEP are available at https://github.com/liangxiaodata/MA-PEP.

Capillary electrophoresis in the analysis of therapeutic peptides-A review

Therapeutic peptides are a growing class of innovative drugs with high efficiency and a low risk of adverse effects. These biomolecules fall within the molecular mass range between that of small molecules and proteins. However, their inherent instability and potential for degradation underscore the importance of reliable and effective analytical methods for pharmaceutical quality control, therapeutic drug monitoring, and compliance testing. Liquid chromatography-mass spectrometry (LC-MS) has long time been the "gold standard" conventional method for peptide analysis, but capillary electrophoresis (CE) is increasingly being recognized as a complementary and, in some cases, superior, highly efficient, green, and cost-effective alternative technique. CE can separate peptides composed of different amino acids owing to differences in their net charge and size, determining their migration behavior in an electric field. This review provides a comprehensive overview of therapeutic peptides that have been used in the clinical environment for the last 25 years. It describes the properties, classification, current trends in development, and clinical use of therapeutic peptides. From the analytical point of view, it discusses the challenges associated with the analysis of therapeutic peptides in pharmaceutical and biological matrices, as well as the evaluation of CE as a whole and the comparison with LC methods. The article also highlights the use of microchip electrophoresis, nonaqueous CE, and nonconventional hydrodynamically closed CE systems and their applications. Overall, the article emphasizes the importance of developing new CE-based analytical methods to ensure the high quality, safety, and efficacy of therapeutic peptides in clinical practice.

A Peptide-Conjugated Probe with Cleavage-Induced Morphological Change for Treatment on Tumor Cell Membrane

Despite the promising advancements of in situ forming nanoassembly for the inhibition of tumor growth and metastasis, the lack of sufficient triggering sites and hardly controlling the forming position restrict their further developments. Herein, a smart transformable peptide-conjugated probe (DMFA) with enzyme cleavage-induced morphological change is designed for treatment on the tumor cell membrane. Specifically, after self-assembling into nanoparticles and anchoring on the cell membrane with sufficient interaction sites rapidly and stably, DMFA will be efficiently cleaved into α-helix forming part (DP) and β-sheet forming part (LFA) by overexpressed matrix metalloproteinase-2. Thus, the promoted Ca2+ influx by DP-induced cell membrane breakage and decreased Na+ /K+ -ATPase activity by LFA-assembled nanofibers wrapping the cells can inhibit PI3K-Akt signaling pathway, leading to the inhibition of tumor cell growth and metastasis. This peptide-conjugated probe undergoes in situ morphological transformation on the cell membrane, exhibiting great potential in tumor therapy.

Anti-Cancer Peptides: Status and Future Prospects

The dramatic rise in cancer incidence, alongside treatment deficiencies, has elevated cancer to the second-leading cause of death globally. The increasing morbidity and mortality of this disease can be traced back to a number of causes, including treatment-related side effects, drug resistance, inadequate curative treatment and tumor relapse. Recently, anti-cancer bioactive peptides (ACPs) have emerged as a potential therapeutic choice within the pharmaceutical arsenal due to their high penetration, specificity and fewer side effects. In this contribution, we present a general overview of the literature concerning the conformational structures, modes of action and membrane interaction mechanisms of ACPs, as well as provide recent examples of their successful employment as targeting ligands in cancer treatment. The use of ACPs as a diagnostic tool is summarized, and their advantages in these applications are highlighted. This review expounds on the main approaches for peptide synthesis along with their reconstruction and modification needed to enhance their therapeutic effect. Computational approaches that could predict therapeutic efficacy and suggest ACP candidates for experimental studies are discussed. Future research prospects in this rapidly expanding area are also offered.

Functional and toxicological evaluation of the MAA-41: a novel rationally designed antimicrobial peptide using hybridization and modification methods from LL-37 and BMAP-28

Background:

Managing bacterial infections caused by multidrug-resistant (MDR) and biofilm-forming bacteria is a global health concern. Therefore, enormous efforts were directed toward finding potential alternative antimicrobial agents such as antimicrobial peptides (AMPs).

Aim:

We aimed to synthesize a novel modified hybrid peptide designed from natural parents’ peptides with enhanced activity and reduced toxicity profile.

Method:

Rational design was used to hybridize the two antimicrobial peptides, in which the alpha-helical parts of BMAP-28 and LL-37 were combined. Then, several amino acid modifications were applied to generate a modified hybrid peptide named MAA-41. The physicochemical properties were checked using in silico methods. The MAA-41 was evaluated for its antimicrobial and anti-biofilm activities. Synergistic studies were performed with five conventional antibiotics. Finally, the cytotoxicity on mammalian cells and the hemolytic activity were assessed.

Results:

The MAA-41 revealed a broad-spectrum activity against both Gram-positive and Gram-negative bacteria including standard and MDR bacterial strains. The concentration against planktonic cells ranged between 10 and 20 μM with higher potency against Gram-negative bacteria. Additionally, the MAA-41 displayed potent activity in eradicating biofilm-forming cells, and the reported MBECs were equal to the MIC values reported for planktonic cells. This new peptide exhibited reduced toxicity profiles against erythrocyte cells but not against Vero cells. Combining MAA-41 peptides with conventional antibiotics improved the antimicrobial activity of the combined agents. Either synergistic or additive effects were shown as a significant decrease in MIC to 0.25 μM.

Conclusion:

This study proposes the validity of a novel peptide (MAA-41) with enhanced antimicrobial activity and reduced toxicity, especially when used as conventional antibiotic combinations.

Broad-spectrum cytotoxicity to cancer cells of Brevilaterin C from Brevibacillus laterosporus and its specific mechanism on human epidermal cancer cells

Antimicrobial peptides (AMP) from Brevibacillus laterosporus have good prospects as clinical treatments for cancer. Nevertheless, details about their anticancer spectrum and mode of cytotoxicity remain poorly understood. A newly found AMP (named Brevilaterin C) secreted by B. laterosporus S62-9 exhibited strong inhibition on almost cancer cell lines examined at a concentration of 8 µg/ml but was relatively safe for normal cells. We further systematically examined its cytotoxicity and mechanism toward human epidermal cancer cell A431. A dosage of 3 µg/ml of Brevilaterin C could significantly increase lactate dehydrogenase release of tumor cells. Moreover, it could remarkably increase the ratio of apoptosis and reactive oxygen species generation of A431, indicating effective induction of apoptosis. Moreover, the formation of JC-1 aggregates was effectively prevented by a low concentration of Brevilaterin C, indicating its effective induction of A431's apoptosis. Brevilaterin C exhibited broad-spectrum cytotoxicity to cancer cells, indicating a good potential prospect in the medical field.

Antimicrobial Peptides and Cationic Nanoparticles: A Broad-Spectrum Weapon to Fight Multi-Drug Resistance Not Only in Bacteria

In the last few years, antibiotic resistance and, analogously, anticancer drug resistance have increased considerably, becoming one of the main public health problems. For this reason, it is crucial to find therapeutic strategies able to counteract the onset of multi-drug resistance (MDR). In this review, a critical overview of the innovative tools available today to fight MDR is reported. In this direction, the use of membrane-disruptive peptides/peptidomimetics (MDPs), such as antimicrobial peptides (AMPs), has received particular attention, due to their high selectivity and to their limited side effects. Moreover, similarities between bacteria and cancer cells are herein reported and the hypothesis of the possible use of AMPs also in anticancer therapies is discussed. However, it is important to take into account the limitations that could negatively impact clinical application and, in particular, the need for an efficient delivery system. In this regard, the use of nanoparticles (NPs) is proposed as a potential strategy to improve therapy; moreover, among polymeric NPs, cationic ones are emerging as promising tools able to fight the onset of MDR both in bacteria and in cancer cells.

Elucidating the anticancer activities of guanidinium-functionalized amphiphilic random copolymers by varying the structure and composition in the hydrophobic monomer

Rationale: Use of traditional anticancer chemotherapeutics has been hindered by the multifactorial nature of multi-drug resistance (MDR) development and metastasis. Recently, cationic polycarbonates were reported as novel unconventional anticancer agents that mitigated MDR and inhibited metastasis. The aim of this study is to explore structure-anticancer activity relationship. Specifically, a series of cationic guanidinium-based random copolymers of varying hydrophobicity was synthesized with a narrow polydispersity (Ð = 1.12-1.27) via organocatalytic ring-opening polymerization (OROP) of functional cyclic carbonate monomers, and evaluated for anticancer activity, killing kinetics, degradability and functional mechanism. Methods: Linear, branched and aromatic hydrophobic side chain units, such as ethyl, benzyl, butyl, isobutyl and hexyl moieties were explored as comonomer units for modulating anticancer activity. As hydrophobicity/hydrophilicity balance of the polymers determines their anticancer efficacy, the feed ratio between the two monomers was varied to tune their hydrophobicity. Results: Notably, incorporating the hexyl moiety greatly enhanced anticancer efficiency and killing kinetics on cancer cells. Degradation studies showed that the polymers degraded completely within 4-6 days. Flow cytometry and lactate dehydrogenase (LDH) release analyses demonstrated that anticancer mechanism of the copolymers containing a hydrophobic co-monomer was concentration dependent, apoptosis at IC50, and both apoptosis and necrosis at 2 × IC50. In contrast, the homopolymer without a hydrophobic comonomer killed cancer cells predominantly via apoptotic mechanism. Conclusion: The hydrophobicity of the polymers played an important role in anticancer efficacy, killing kinetics and anticancer mechanism. This study provides valuable insights into designing novel anticancer agents utilizing polymers.

Protein-Based Films Functionalized with a Truncated Antimicrobial Peptide Sequence Display Broad Antimicrobial Activity

The increasing bacterial resistance to antibiotics is driving strong demand for new antimicrobial biomaterials. This work describes the fabrication of free-standing films exhibiting antimicrobial properties by combining, in the same polypeptide chain, an elastin-like recombinamer comprising 200 repetitions of the pentamer VPAVG (A200) and an 18-amino-acid truncated variant of the antimicrobial peptide BMAP-28, termed BMAP-18. The fusion protein BMAP-18A200 was overexpressed and conveniently purified by a simplified and scalable nonchromatographic process. Free-standing films of BMAP-18A200 demonstrated to be stable without requiring cross-linking agents and displayed high antimicrobial activity against skin pathogens including Gram-negative and Gram-positive bacteria as well as unicellular and filamentous fungi. The antimicrobial activity of the films was mediated by direct contact of cells with the film surface, resulting in compromised structural integrity of microbial cells. Furthermore, the BMAP-18A200 films showed no cytotoxicity on normal human cell lines (skin fibroblasts and keratinocytes). All of these results highlight the potential of these biotechnological multifunctional polymers as new drug-free materials to prevent and treat microbial infections.

Antimicrobial Peptides in Farm Animals: An Updated Review on Its Diversity, Function, Modes of Action and Therapeutic Prospects

Antimicrobial peptides (AMPs) are the arsenals of the innate host defense system, exhibiting evolutionarily conserved characteristics that are present in practically all forms of life. Recent years have witnessed the emergence of antibiotic-resistant bacteria compounded with a slow discovery rate for new antibiotics that have necessitated scientific efforts to search for alternatives to antibiotics. Research on the identification of AMPs has generated very encouraging evidence that they curb infectious pathologies and are also useful as novel biologics to function as immunotherapeutic agents. Being innate, they exhibit the least cytotoxicity to the host and exerts a wide spectrum of biological activity including low resistance among microbes and increased wound healing actions. Notably, in veterinary science, the constant practice of massive doses of antibiotics with inappropriate withdrawal programs led to a high risk of livestock-associated antimicrobial resistance. Therefore, the world faces tremendous pressure for designing and devising strategies to mitigate the use of antibiotics in animals and keep it safe for posterity. In this review, we illustrate the diversity of farm animal-specific AMPs, and their biochemical foundations, mode of action, and prospective application in clinics. Subsequently, we present the data for their systematic classification under the major and minor groups, antipathogenic action, and allied bioactivities in the host. Finally, we address the limitations of their clinical implementation and envision areas for further advancement.

Peptides with Dual Antimicrobial-Anticancer Activity: Strategies to Overcome Peptide Limitations and Rational Design of Anticancer Peptides

Peptides are naturally produced by all organisms and exhibit a wide range of physiological, immunomodulatory, and wound healing functions. Furthermore, they can provide with protection against microorganisms and tumor cells. Their multifaceted performance, high selectivity, and reduced toxicity have positioned them as effective therapeutic agents, representing a positive economic impact for pharmaceutical companies. Currently, efforts have been made to invest in the development of new peptides with antimicrobial and anticancer properties, but the poor stability of these molecules in physiological environments has triggered a bottleneck. Therefore, some tools, such as nanotechnology and in silico approaches can be applied as alternatives to try to overcome these obstacles. In silico studies provide a priori knowledge that can lead to the development of new anticancer peptides with enhanced biological activity and improved stability. This review focuses on the current status of research in peptides with dual antimicrobial-anticancer activity, including advances in computational biology using in silico analyses as a powerful tool for the study and rational design of these types of peptides.

Synthetic macromolecules as therapeutics that overcome resistance in cancer and microbial infection

Synthetic macromolecular antimicrobials have shown efficacy in the treatment of multidrug resistant (MDR) pathogens. These synthetic macromolecules, inspired by Nature's antimicrobial peptides (AMPs), mitigate resistance by disrupting microbial cell membrane or targeting multiple intracellular proteins or genes. Unlike AMPs, these polymers are less prone to degradation by proteases and are easier to synthesize on a large scale. Recently, various studies have revealed that cancer cell membrane, like that of microbes, is negatively charged, and AMPs can be used as anticancer agents. Nevertheless, efforts in developing polymers as anticancer agents has remained limited. This review highlights the recent advancement in the development of synthetic biodegradable antimicrobial polymers (e.g. polycarbonates, polyesters and polypeptides) and anticancer macromolecules including peptides and polymers. Additionally, strategies to improve their in vivo bioavailability and selectivity towards bacteria and cancer cells are examined. Lastly, future perspectives, including use of artificial intelligence or machine learning, in the development of antimicrobial and anticancer macromolecules are discussed.

ACPred: A Computational Tool for the Prediction and Analysis of Anticancer Peptides

Anticancer peptides (ACPs) have emerged as a new class of therapeutic agent for cancer treatment due to their lower toxicity as well as greater efficacy, selectivity and specificity when compared to conventional small molecule drugs. However, the experimental identification of ACPs still remains a time-consuming and expensive endeavor. Therefore, it is desirable to develop and improve upon existing computational models for predicting and characterizing ACPs. In this study, we present a bioinformatics tool called the ACPred, which is an interpretable tool for the prediction and characterization of the anticancer activities of peptides. ACPred was developed by utilizing powerful machine learning models (support vector machine and random forest) and various classes of peptide features. It was observed by a jackknife cross-validation test that ACPred can achieve an overall accuracy of 95.61% in identifying ACPs. In addition, analysis revealed the following distinguishing characteristics that ACPs possess: (i) hydrophobic residue enhances the cationic properties of α-helical ACPs resulting in better cell penetration; (ii) the amphipathic nature of the α-helical structure plays a crucial role in its mechanism of cytotoxicity; and (iii) the formation of disulfide bridges on β-sheets is vital for structural maintenance which correlates with its ability to kill cancer cells. Finally, for the convenience of experimental scientists, the ACPred web server was established and made freely available online.

Design and characterization of a new hybrid peptide from LL-37 and BMAP-27

Background and purpose: The world is heading to a post-antibiotic era where the treatment of bacterial infections will not be possible even with well-known last-line antibiotics. Unfortunately, the emergence of multidrug resistant bacterial strains is uncontrollable, and the humanity will face a life-threatening fate unless new antimicrobial agents with new bacterial target sites are promptly developed. Herein, we design a hybrid antimicrobial peptide (B1) from helical parts taken from the parent peptides: LL-37 and BMAP-27. The purpose of this design is to improve the potency and enhance the toxicity profile of the parent peptides. Methods: Rational design was used to hybridize two antimicrobial peptides, in which two helical parts from the bovine analog BMAP-27, and the human cathelicidin LL-37 were used to generate a novel peptide (B1). The physicochemical properties were checked using in silico methods. The antimicrobial activities were tested against nine control and resistant strains of Gram-positive and Gram-negative bacteria. On the other hand, the antibiofilm activities were tested against four resistant strains. The cytotoxicity on mammalian cells was tested using HEK293, and the hemolysis activity was also investigated on human blood. Finally, synergistic studies were performed with four conventional antibiotics against four resistant strains of Gram-positive and Gram-negative bacteria. Results: The new peptide B1 exhibited broad-spectrum activities against all tested strains. The concentration against planktonic cells ranged between 10 and 20 µM. However, 40-60 µM were needed to eradicate the biofilms. B1 showed reduced toxicity toward mammalian cells with minimal hemolysis risk. On the other hand, the synergistic studies showed improved activities for the combined conventional antibiotics with a huge reduction in their minimum inhibitory concentration values. The concentrations of B1 peptide combined with the tested antibiotics were also decreased markedly down to 0.5 µM in some cases. Conclusion: B1 is a hybrid peptide from two cathelicidin peptides. It showed an improved activity compared to parent peptides. The hybridization was successful in this study. It generated a new potent broad-spectrum antimicrobial. The toxicity profile was improved, and the synergism with the convention antibiotics showed promising results.

Anticancer Activity of the Goat Antimicrobial Peptide ChMAP-28

Cytotoxic effect of the antimicrobial peptide ChMAP-28 from leucocytes of the goat Capra hircus was examined against five cancer and two normal human cell lines. ChMAP-28 has the amino acid sequence GRFKRFRKKLKRLWHKVGPFVGPILHY and is homologous to other α-helical mammalian antimicrobial peptides. ChMAP-28 shows considerably higher cytotoxicity against cultured tumor cells than toward normal cells at concentrations of <10 μM. Our findings suggest that ChMAP-28 can initiate necrotic death of cancer cells. Its cytotoxic effect is accomplished due to disruption of the plasma membrane integrity and is not abrogated by the addition of the caspase inhibitor Z-VAD-FMK. ChMAP-28 causes permeabilization of cytoplasmic membrane of human leukemia cells HL-60 already after 15 min of incubation. Here, we show that ChMAP-28 has one of the highest antitumor activity in vitro among all known antimicrobial peptides. We speculate that the observed specificity of ChMAP-28 cytotoxic effect against tumor cells is due to its relatively low hydrophobicity and high cationicity. In the meantime, this peptide has low hemolytic activity, which generates a potential for its use as a therapeutic agent.

Host defense cathelicidins in cattle: types, production, bioactive functions and potential therapeutic and diagnostic applications

Cathelicidins are a primitive class of host defense peptides and are known for their broad-spectrum antimicrobial activity against bacteria, fungi, and enveloped viruses. These small, cationic, proteolytically-activated peptides are diverse in structure, encompassing a wide range of activities on host immune and inflammatory cell responses. The dual capacity of cathelicidins to directly control infection and regulate host defenses highlights the potential use of these peptides as alternatives to antibiotics and immunomodulators. Cathelicidins are found in many mammalian species; this review focuses on bovine cathelicidins. Eight naturally and two synthetically occurring bovine cathelicidins are described in detail, with a focus on recent advances in their expression, location and biological roles. This review also presents an overview of the bioactive functions of cathelicidins in bovine mastitis, a disease causing economic losses in cattle dairy production. Comparison of the structural, antimicrobial, cytotoxic and mechanistic properties of bovine cathelicidins advances the knowledge needed for the development of these peptides as potential identifiers of infectious diseases (e.g., bovine mastitis) and as novel therapeutic alternatives to antibiotics.

Tumor cell membrane-targeting cationic antimicrobial peptides: novel insights into mechanisms of action and therapeutic prospects

There is an ongoing need for effective and targeted cancer treatments that can overcome the detrimental side effects presented by current treatment options. One class of novel anticancer molecules with therapeutic potential currently under investigation are cationic antimicrobial peptides (CAPs). CAPs are small innate immunity peptides found ubiquitously throughout nature that are typically membrane-active against a wide range of pathogenic microbes. A number of CAPs can also target mammalian cells and often display selective activity towards tumor cells, making them attractive candidates as novel anticancer agents warranting further investigation. This current and comprehensive review describes key examples of naturally occurring membrane-targeting CAPs and their modified derivatives that have demonstrated anticancer activity, across multiple species of origin and structural subfamilies. In addition, we address recent advances made in the field and the ongoing challenges faced in translating experimental findings into clinically relevant treatments.

Marsupial and monotreme cathelicidins display antimicrobial activity, including against methicillin-resistant Staphylococcus aureus

With the growing demand for new antibiotics to combat increasing multi-drug resistance, a family of antimicrobial peptides known as cathelicidins has emerged as potential candidates. Expansions in cathelicidin-encoding genes in marsupials and monotremes are of specific interest as the peptides they encode have evolved to protect immunologically naive young in the harsh conditions of the pouch and burrow. Our previous work demonstrated that some marsupial and monotreme cathelicidins have broad-spectrum antibacterial activity and kill resistant bacteria, but the activity of many cathelicidins is unknown. To investigate associations between peptide antimicrobial activity and physiochemical properties, we tested 15 cathelicidin mature peptides from tammar wallaby, grey short-tailed opossum, platypus and echidna for antimicrobial activity against a range of bacterial and fungal clinical isolates. One opossum cathelicidin ModoCath4, tammar wallaby MaeuCath7 and echidna Taac-CATH1 had broad-spectrum antibacterial activity and killed methicillin-resistant Staphylococcus aureus. However, antimicrobial activity was reduced in the presence of serum or whole blood, and non-specific toxicity was observed at high concentrations. The active peptides were highly charged, potentially increasing binding to microbial surfaces, and contained amphipathic helical structures, which may facilitate membrane permeabilisation. Peptide sequence homology, net charge, amphipathicity and alpha helical content did not correlate with antimicrobial activity. However active peptides contained a significantly higher percentage of cationic residues than inactive ones, which may be used to predict active peptides in future work. Along with previous studies, our results indicate that marsupial and monotreme cathelicidins show potential for development as novel therapeutics to combat increasing antimicrobial resistance.

Mechanistic and structural basis of bioengineered bovine Cathelicidin-5 with optimized therapeutic activity

Peptide-drug discovery using host-defense peptides becomes promising against antibiotic-resistant pathogens and cancer cells. Here, we customized the therapeutic activity of bovine cathelicidin-5 targeting to bacteria, protozoa, and tumor cells. The membrane dependent conformational adaptability and plasticity of cathelicidin-5 is revealed by biophysical analysis and atomistic simulations over 200 μs in thymocytes, leukemia, and E. coli cell-membranes. Our understanding of energy-dependent cathelicidin-5 intrusion in heterogeneous membranes aided in designing novel loss/gain-of-function analogues. In vitro findings identified leucine-zipper to phenylalanine substitution in cathelicidin-5 (1-18) significantly enhance the antimicrobial and anticancer activity with trivial hemolytic activity. Targeted mutants of cathelicidin-5 at kink region and N-terminal truncation revealed loss-of-function. We ensured the existence of a bimodal mechanism of peptide action (membranolytic and non-membranolytic) in vitro. The melanoma mouse model in vivo study further supports the in vitro findings. This is the first structural report on cathelicidin-5 and our findings revealed potent therapeutic application of designed cathelicidin-5 analogues.

Breast Cancer Targeting Peptide Binds Keratin 1: A New Molecular Marker for Targeted Drug Delivery to Breast Cancer

The biomarkers or receptors expressed on cancer cells and the targeting ligands with high binding affinity for biomarkers play a key role in early detection and treatment of breast cancer. The breast cancer targeting peptide p160 (12-mer) and its enzymatically stable analogue 18-4 (10-mer) showed marked potential for breast cancer drug delivery using cell studies and animal models. Herein, we used affinity purification, liquid chromatography-tandem mass spectrometry, and proteomics to identify keratin 1 (KRT1) as the target receptor highly expressed on breast cancer cells for p160 peptide(s). Western blot and immunocytochemistry in MCF-7 breast cancer cells confirmed the identity of KRT1. We demonstrate that the p160 or 18-4 binding to MCF-7 breast cancer cells is dependent on the expression of KRT1, and we confirm peptide-KRT1 binding specificity using SPR experiments (K_d ∼ 1.1 μM and 0.98 μM for p160 and 18-4, respectively). Furthermore, we assessed the ability of peptide 18-4 to improve the cellular uptake and anticancer activity of a pro-apoptotic antimicrobial peptide, microcin J25 (MccJ25), in breast cancer cells. A covalent conjugate of peptide 18-4 with MccJ25 showed preferential cytotoxicity toward breast cancer cells with minimal cytotoxicity against normal HUVEC cells. The conjugate inhibited the growth of MDA-MB-435 MDR multidrug-resistant cells with an IC₅₀ comparable to that of nonresistant cells. Conjugation improved selective cellular uptake of MccJ25, and the conjugate triggered cancer cell death by apoptosis. Our findings establish KRT1 as a new marker for breast cancer targeting. Additionally, it pinpoints the potential use of antimicrobial lasso peptides as a novel class of anticancer therapeutics.

Membrane Mediated Antimicrobial and Antitumor Activity of Cathelicidin 6: Structural Insights from Molecular Dynamics Simulation on Multi-Microsecond Scale

The cathelicidin derived bovine antimicrobial peptide BMAP27 exhibits an effective microbicidal activity and moderate cytotoxicity towards erythrocytes. Irrespective of its therapeutic and multidimensional potentiality, the structural studies are still elusive. Moreover, the mechanism of BMAP27 mediated pore formation in heterogeneous lipid membrane systems is poorly explored. Here, we studied the effect of BMAP27 in model cell-membrane systems such as zwitterionic, anionic, thymocytes-like (TLM) and leukemia-like membranes (LLM) by performing molecular dynamics (MD) simulation longer than 100 μs. All-atom MD studies revealed a stable helical conformation in the presence of anionic lipids, however, significant loss of helicity was identified in TLM and zwitterionic systems. A peptide tilt (~45˚) and central kink (at residue F10) was found in anionic and LLM models, respectively, with an average membrane penetration of < 0.5 nm. Coarse-grained (CG) MD analysis on a multi-μs scale shed light on the membrane-dependent peptide and lipid organization. Stable micelle and end-to-end like oligomers were formed in zwitterionic and TLM models, respectively. In contrast, unstable oligomer formation and monomeric BMAP27 penetration were observed in anionic and LLM systems with selective anionic lipid aggregation (in LLM). Peptide penetration up to ~1.5 nm was observed in CG-MD systems with the BMAP27 C-terminal oriented towards the bilayer core. Structural inspection suggested membrane penetration by micelle/end-to-end like peptide oligomers (carpet-model like) in the zwitterionic/TLM systems, and transmembrane-mode (toroidal-pore like) in the anionic/LLM systems, respectively. Structural insights and energetic interpretation in BMAP27 mutant highlighted the role of F10 and hydrophobic residues in mediating a membrane-specific peptide interaction. Free energy profiling showed a favorable (-4.58 kcal mol-1 for LLM) and unfavorable (+0.17 kcal mol-1 for TLM) peptide insertion in anionic and neutral systems, respectively. This determination can be exploited to regulate cell-specific BMAP27 cytotoxicity for the development of potential drugs and antibiotics.

A re-examination of the role of the acute phase protein response in innate cancer defence

Anti-cancer host defense mechanisms are traditionally considered to consist of tumor suppressor genes and immune surveillance by cells of the innate and adaptive immune systems. However, there is mounting evidence that components of the acute phase protein response (APPR), and, in particular, certain cationic host defense peptides (HDPs), also contribute to anti-cancer host defense. In a number of in vitro studies, certain HDPs have been shown to be cytotoxic to tumor cells either directly through cancer cell membrane destabilization and lysis or through the initiation of apoptosis in the cancer cell. In addition, many cancer cells elaborate the pro-inflammatory cytokine interleukin-6, which in turn produces an APPR that involves the release of HDPs. It is therefore possible that the release of pro-inflammatory cytokines by cancer cells initiates a poorly understood anti-tumor response by the host that involves HDP induction. We hypothesize that the APPR may form an important anti-cancer host defense response. This may be an important consideration in light of cancer treatments designed to decrease systemic inflammation. Blunting of the anti-cancer effect of the APPR may also contribute to the increased cancer rates seen in chronic immunosuppressive states.

Pronounced peptide selectivity for melanoma through tryptophan end-tagging

Effects of oligotryptophan end-tagging on the uptake of arginine-rich peptides into melanoma cells was investigated under various conditions and compared to that into non-malignant keratinocytes, fibroblasts, and erythrocytes, also monitoring resulting cell toxicity. In parallel, biophysical studies on peptide binding to, and destabilization of, model lipid membranes provided mechanistic insight into the origin of the selectivity between melanoma and non-malignant cells. Collectively, the results demonstrate that W-tagging represents a powerful way to increase selective peptide internalization in melanoma cells, resulting in toxicity against these, but not against the non-malignant cells. These effects were shown to be due to increased peptide adsorption to the outer membrane in melanoma cells, caused by the presence of anionic lipids such as phosphatidylserine and ganglioside GM1, and to peptide effects on mitochondria membranes and resulting apoptosis. In addition, the possibility of using W-tagged peptides for targeted uptake of nanoparticles/drug carriers in melanoma was demonstrated, as was the possibility to open up the outer membrane of melanoma cells in order to facilitate uptake of low Mw anticancer drugs, here demonstrated for doxorubicin.

Membranolytic anticancer peptides

Understanding the structure–activity relationships and mechanisms of action of membranolytic anticancer peptides could help them advance to therapeutic success.

Host defense peptides for treatment of colorectal carcinoma - a comparative in vitro and in vivo analysis

Host defense peptides (HDP) constitute effector molecules of the innate immune system. Besides acting against microbia and fungi, they exhibit broad and selective oncolytic activity. The underlying mechanism is at least partially attributable to elevated surface-exposed levels of phosphatidylserine (PS) on tumor targets. In this study, comprehensive analysis of NK-2-based derivatives (C7A, C7A-D21K, and C7A-Δ) was done on patient-derived ultra-low passage colorectal carcinoma (CRC) cell lines. Peptides were designed to improve antitumoral potential. Mellitin was used as positive control and a non-toxic peptide (NK11) served as negative control. Subsequently, effectiveness of local HDP application was determined in xenopatients.

Generally, CRC lines displayed a heterogeneous pattern of surface-exposed PS, which was usually below standard CRC cells. Of note, five out of seven cell lines were susceptible towards HDP-mediated lysis (lytic activity of peptides: C7A-D21K > C7A-Δ= C7A). Oncolytic activity correlated mostly with surface-exposed PS levels. Apoptosis as well as necrosis were involved in killing. In an in vivo experiment, substantial growth inhibition of HROC24 xenografts was observed after HDP therapy and, surprisingly, also after NK11 treatment.

These promising data underline the high potential of HDPs for oncolytic therapies and may provide a rationale for optimizing preclinical treatment schedules based on NK-2.

Assessment of anti-plasmodial activity of non-hemolytic, non-immunogenic, non-toxic antimicrobial peptides (AMPs LR14) produced by Lactobacillus plantarum LR/14

BACKGROUND AND OBJECTIVES

Lactobacillus plantarum strains are known to exhibit an antimicrobial property against bacteria and fungi. In the present investigation, AMPs LR14, antimicrobial peptides produced by L. plantarum strain LR/14, were tested against a protozoan system, Plasmodium falciparum and its non-toxic nature was envisaged on a mammalian system.

METHODS

Human erythrocytes infected with chloroquine-sensitive and -resistant strains of P. falciparum were treated with purified AMPs LR14. The loss in cell viability was assessed by monitoring the incorporation of [(3)H]-hypoxanthine in the nucleic acid of the parasite. The hemolytic activity of AMPs LR14 was monitored at different concentrations and the investigations into the in vivo toxicity of AMPs LR14 were carried out on a mammalian system (Wistar rat). The level of toxicity in the tissues was visualized by histopathological studies conducted on the liver and kidney of the test and control rats. A study was also undertaken to see the production of antibodies in an animal (rabbit) after it was immunized with AMPs LR14.

RESULTS

A loss in cell viability was observed in both test strains of P. falciparum. However, the dose required for inhibition of the chloroquine-resistant strain was ~2 times the dose required for the chloroquine-sensitive strain. At these concentrations, no hemolysis of human erythrocytes was observed. The studies conducted on in vivo toxicity of AMPs LR14 suggest that the lethal dose (LD50) is beyond 1,000 mg/kg body weight, suggesting its safe use against microbes and protozoans. Antibodies were also not detected against these peptides, indicating a non-immunogenic nature.

CONCLUSION

The data indicate that AMPs LR14 are non-toxic, potent anti-plasmodial peptides causing growth inhibition of P. falciparum without causing hemolysis. These results pave the way for the development of bioactive peptides as therapeutics.

Osmotin: a plant sentinel and a possible agonist of mammalian adiponectin

Osmotin is a stress responsive antifungal protein belonging to the pathogenesis-related (PR)-5 family that confers tolerance to both biotic and abiotic stresses in plants. Protective efforts of osmotin in plants range from high temperature to cold and salt to drought. It lyses the plasma membrane of the pathogens. It is widely distributed in fruits and vegetables. It is a differentially expressed and developmentally regulated protein that protects the cells from osmotic stress and invading pathogens as well, by structural or metabolic alterations. During stress conditions, osmotin helps in the accumulation of the osmolyte proline, which quenches reactive oxygen species and free radicals. Osmotin expression results in the accumulation of storage reserves and increases the shelf-life of fruits. It binds to a seven-transmembrane-domain receptor-like protein and induces programmed cell death in Saccharomyces cerevisiae through RAS2/cAMP signaling pathway. Adiponectin, produced in adipose tissues of mammals, is an insulin-sensitizing hormone. Strangely, osmotin acts like the mammalian hormone adiponectin in various in vitro and in vivo models. Adiponectin and osmotin, the two receptor binding proteins do not share sequence similarity at the amino acid level, but interestingly they have a similar structural and functional properties. In experimental mice, adiponectin inhibits endothelial cell proliferation and migration, primary tumor growth, and reduces atherosclerosis. This retrospective work examines the vital role of osmotin in plant defense and as a potential targeted therapeutic drug for humans.

Novel phospholipase A2 inhibitors from python serum are potent peptide antibiotics

Antimicrobial peptides (AMPs) play a vital role in defense against resistant bacteria. In this study, eight different AMPs synthesized from Python reticulatus serum protein were tested for bactericidal activity against various Gram-positive and Gram-negative bacteria (Staphylococcus aureus, Burkholderia pseudomallei (KHW and TES strains), and Proteus vulgaris) using a disc-diffusion method (20 μg/disc). Among the tested peptides, phospholipase A2 inhibitory peptide (PIP)-18[59-76], β-Asp65-PIP[59-67], D-Ala66-PNT.II, and D60,65E-PIP[59-67] displayed the most potent bactericidal activity against all tested pathogens in a dose-dependent manner (100-6.8 μg/ml), with a remarkable activity noted against S. aureus at 6.8 μg/ml dose within 6 h of incubation. Determination of minimum inhibitory concentrations (MICs) by a micro-broth dilution method at 100-3.125 μg/ml revealed that PIP-18[59-76], β-Asp65-PIP[59-67] and D-Ala66-PNT.II peptides exerted a potent inhibitory effect against S. aureus and B. pseudomallei (KHW) (MICs 3.125 μg/ml), while a much less inhibitory potency (MICs 12.5 μg/ml) was noted for β-Asp65-PIP[59-67] and D-Ala66-PNT.II peptides against B. pseudomallei (TES). Higher doses of peptides had no effect on the other two strains (i.e., Klebsiella pneumoniae and Streptococcus pneumoniae). Overall, PIP-18[59-76] possessed higher antimicrobial activity than that of chloramphenicol (CHL), ceftazidime (CF) and streptomycin (ST) (30 μg/disc). When the two most active peptides, PIP-18[59-76] and β-Asp65-PIP[59-67], were applied topically at a 150 mg/kg dose for testing wound healing activity in a mouse model of S. aureus infection, the former accelerates faster wound healing than the latter peptide at 14 days post-treatment. The western blot data suggest that the topical application of peptides (PIP-18[59-67] and β-Asp65-PIP[59-67]) modulates NF-kB mediated wound repair in mice with relatively little haemolytic (100-1.56 μg/ml) and cytotoxic (1000-3.125 μg/ml) effects evident on human cells in vitro.

Current scenario of peptide-based drugs: the key roles of cationic antitumor and antiviral peptides

Cationic antimicrobial peptides (AMPs) and host defense peptides (HDPs) show vast potential as peptide-based drugs. Great effort has been made in order to exploit their mechanisms of action, aiming to identify their targets as well as to enhance their activity and bioavailability. In this review, we will focus on both naturally occurring and designed antiviral and antitumor cationic peptides, including those here called promiscuous, in which multiple targets are associated with a single peptide structure. Emphasis will be given to their biochemical features, selectivity against extra targets, and molecular mechanisms. Peptides which possess antitumor activity against different cancer cell lines will be discussed, as well as peptides which inhibit virus replication, focusing on their applications for human health, animal health and agriculture, and their potential as new therapeutic drugs. Moreover, the current scenario for production and the use of nanotechnology as delivery tool for both classes of cationic peptides, as well as the perspectives on improving them is considered.

Role of glycosylation in the anticancer activity of antibacterial peptides against breast cancer cells

Antibacterial peptides (ABPs) with cancer-selective toxicity have received much more attention as alternative chemotherapeutic agents in recent years. However, the basis of their anticancer activity remains unclear. The modification of cell surface glycosylation is a characteristic of cancer cells. The present study investigated the effect of glycosylation, in particular sialic acid, on the anticancer activity of ABPs. We showed that aurein 1.2, buforin IIb and BMAP-28m exhibited selective cytotoxicity toward MX-1 and MCF-7 breast cancer cells. The binding activity, cytotoxicity and apoptotic activity of ABPs were enhanced by the presence of O-, N-glycoproteins, gangliosides and sialic acid on the surface of breast cancer cells. Among N-, O-glycoproteins and ganglioside, O-glycoproteins almost had the strongest effect on the binding and cytotoxicity of the three peptides. Further, up-regulation of hST6Gal1 in CHO-K1 cells enhanced the susceptibility of cells to these peptides. Finally, the growth of MX-1 xenograft tumors in mice was significantly suppressed by buforin IIb treatment, which was associated with induction of apoptosis and inhibition of vascularization. These data demonstrate that the three peptides bind to breast cancer cells via an interaction with surface O-, N-glycoproteins and gangliosides. Sialic acids act as key glycan binding sites for cationic ABP binding to glycoproteins and gangliosides. Therefore, glycosylation in breast cancer cells plays an important role in the anticancer activity of ABPs, which may partly explain their cancer-selective toxicity. Anticancer ABPs with cancer-selective cytotoxicity will be promising candidates for anticancer therapy in the future.

Cathelicidin-like helminth defence molecules (HDMs): absence of cytotoxic, anti-microbial and anti-protozoan activities imply a specific adaptation to immune modulation

Host defence peptides (HDPs) are expressed throughout the animal and plant kingdoms. They have multifunctional roles in the defence against infectious agents of mammals, possessing both bactericidal and immune-modulatory activities. We have identified a novel family of molecules secreted by helminth parasites (helminth defence molecules; HDMs) that exhibit similar structural and biochemical characteristics to the HDPs. Here, we have analyzed the functional activities of four HDMs derived from Schistosoma mansoni and Fasciola hepatica and compared them to human, mouse, bovine and sheep HDPs. Unlike the mammalian HDPs the helminth-derived HDMs show no antimicrobial activity and are non-cytotoxic to mammalian cells (macrophages and red blood cells). However, both the mammalian- and helminth-derived peptides suppress the activation of macrophages by microbial stimuli and alter the response of B cells to cytokine stimulation. Therefore, we hypothesise that HDMs represent a novel family of HDPs that evolved to regulate the immune responses of their mammalian hosts by retaining potent immune modulatory properties without causing deleterious cytotoxic effects.

In mammals, secreted host defence peptides (HDPs) protect against a wide range of infectious pathogens. They also perform a range of immune modulatory functions which regulate the immune response to pathogens, ensuring that the protective inflammatory response is not exacerbated and that post-infection repair mechanisms are initiated. We identified a novel family of molecules secreted by medically-important helminth pathogens (termed helminth defence molecules; HDMs) that exhibit striking structural and biochemical similarities to the HDPs. To further investigate the extent of this similarity, we have performed a comparative functional study between several well characterized, anti-microbial, mammalian HDPs and a series of parasite-derived peptides. The parasite HDMs displayed immune modulatory properties that were similar to their HDP homologs in mammals, but possessed no antimicrobial or cytotoxic activity. We propose that HDMs of these helminth pathogens underwent specific adaptation, losing their anti-microbial activity but retaining their ability to regulate the immune responses of their mammalian hosts. This absence of cytotoxicity and retention of immune-modulatory activity offers an opportunity to design novel immunotherapeutics derived from the HDMs which could be used to combat destructive inflammatory responses associated with microbial infection and immune-related disorders.

Antimicrobial peptides: versatile biological properties

Antimicrobial peptides are diverse group of biologically active molecules with multidimensional properties. In recent past, a wide variety of AMPs with diverse structures have been reported from different sources such as plants, animals, mammals, and microorganisms. The presence of unusual amino acids and structural motifs in AMPs confers unique structural properties to the peptide that attribute for their specific mode of action. The ability of these active AMPs to act as multifunctional effector molecules such as signalling molecule, immune modulators, mitogen, antitumor, and contraceptive agent makes it an interesting candidate to study every aspect of their structural and biological properties for prophylactic and therapeutic applications. In addition, easy cloning and recombinant expression of AMPs in heterologous plant host systems provided a pipeline for production of disease resistant transgenic plants. Besides these properties, AMPs were also used as drug delivery vectors to deliver cell impermeable drugs to cell interior. The present review focuses on the diversity and broad spectrum antimicrobial activity of AMPs along with its multidimensional properties that could be exploited for the application of these bioactive peptides as a potential and promising drug candidate in pharmaceutical industries.

Polymyxins as novel and safe mucosal adjuvants to induce humoral immune responses in mice

There is currently an urgent need to develop safe and effective adjuvants for enhancing vaccine-induced antigen-specific immune responses. We demonstrate here that intranasal immunization with clinically used polypeptide antibiotics, polymyxin B (PMB) and colistin (CL), along with ovalbumin (OVA), increases OVA-specific humoral immune responses in a dose-dependently manner at both mucosal and systemic compartments. Enhanced immunity by boosting was found to persist during 8 months of observation. Moreover, mice intranasally immunized with OVA plus various doses of PMB or CL showed neither inflammatory responses in the nasal cavity and olfactory bulbs nor renal damages, compared to those given OVA alone. These data suggest that polymyxins may serve as novel and safe mucosal adjuvants to induce humoral immune responses. The polymyxin adjuvanticity was found to be independent of endotoxins liberated by its bactericidal activity, as indicated by similar enhancing effects of PMB in lipopolysaccharide (LPS)-hyporesponsive and LPS-susceptible mice. However, despite the presence of preexisting anti-PMB antibodies, we observed no reduction in the adjuvant function of polymyxins when they were given intranasally. Furthermore, the titers of OVA-specific Abs in mice intranasally immunized with OVA plus PMB or CL were significantly higher than those in mice administered with polymyxin analogues, such as polymyxin B nonapeptide and colistin methanesulfonate. The levels of released β-hexosaminidase and histamine in mast cell culture supernatants stimulated by PMB or CL were also significantly higher than those stimulated by their analogues. These results suggest that both the hydrophobic carbon chain and hydrophilic cationic cyclic peptide contribute to the mucosal adjuvanticity of PMB and CL.

Anticancer mechanisms of temporin-1CEa, an amphipathic α-helical antimicrobial peptide, in Bcap-37 human breast cancer cells

AIMS

Temporin-1CEa, a 17-residue antimicrobial peptide, is known to exert broad-spectrum anticancer activity that acts preferentially on cancer cells instead of normal cells. However, the mechanism of cancer cell death induced by temporin-1CEa is weakly understood.

MAIN METHODS

Here, we investigated the cytotoxic and membrane-disrupting effects of temporin-1CEa on human breast cancer cell line Bcap-37, using MTT assay, electronic microscope observation, fluorescence imaging and flow cytometry analysis.

KEY FINDINGS

The MTT assay indicated that one-hour temporin-1CEa treatment led to rapid cell death in either caspase-dependent or -independent manner. The electronic microscope observation suggested that temporin-1CEa exposure resulted in profound morphological changes in Bcap-37 cells. The fluorescence imaging and flow cytometry analysis demonstrated that temporin-1CEa exhibited membrane-disrupting property characterized by induction of cell-surface phosphatidylserine exposure, elevation of plasma membrane permeability, and rapid transmembrane potential depolarization. Moreover, temporin-1CEa might also induce rapid cell death through mitochondria-involved mechanisms, including rapid intracellular Ca(2+) leakage, collapse of mitochondrial membrane potential (Δφm) and over-generation of reactive oxygen species (ROS).

SIGNIFICANCE

In summary, the present study indicates that temporin-1CEa triggers a rapid cytotoxicity in Bcap-37 cells through membrane-destruction and intracellular mechanisms involving mitochondria. These intracellular mechanisms and direct membrane-destruction effect were evaluated helping to understand the detail action of antimicrobial peptides in mammalian cancer cells.

Dual modes of antitumor action of an amphiphilic peptide A(9)K

Following our recent report of attractive antibacterial properties of a designed amphiphilic peptide, A(9)K, we have investigated its antitumor activities by examining the modes of its action against different mammalian cell types. The peptide strongly inhibited the growth of cancerous HeLa cells and human promyelocytic leukemia HL60 cells whilst remaining benign to the host cells, including Cos 7 cells, mouse fibroblast NIH3T3 cells and human red blood cells. Images from SEM and fluorescence microscopy showed that A(9)K penetrated HeLa cell membranes and disrupted membrane structures, a feature broadly similar to that observed from its bactericidal actions. Further interactions of A(9)K with inner cellular membranes caused mitochondrial dysfunction associated with the F-actin reorganization and the decreased transcription of bcl-2 and c-myc genes, resulting in HeLa cell apoptosis in a mitochondria-induced apoptosis pathway. Thus A(9)K has high selectivity against cancerous cells and kills them by dual modes of action: membrane disruption and cell apoptosis. In addition, the peptide does not induce non-specific immunological effects and is not degraded by proteases. These features are crucial for developing their applications in future research.

Cathelicidins: family of antimicrobial peptides. A review

Cathelicidins are small, cationic, antimicrobial peptides found in humans and other species, including farm animals (cattle, horses, pigs, sheep, goats, chickens, rabbits and in some species of fish). These proteolytically activated peptides are part of the innate immune system of many vertebrates. These peptides show a broad spectrum of antimicrobial activity against bacteria, enveloped viruses and fungi. Apart from exerting direct antimicrobial effects, cathelicidins can also trigger specific defense responses in the host. Their roles in various pathophysiological conditions have been studied in mice and humans, but there are limited information about their expression sites and activities in livestock. The aim of the present review is to summarize current information about these antimicrobial peptides in farm animals, highlighting peptide expression sites, activities, and future applications for human and veterinary medicine.

Anti-proliferative effect of an analogue of the LL-37 peptide in the colon cancer derived cell line HCT116 p53+/+ and p53-/-

Antimicrobial peptides of the cathelicidin family are found in many mammalian species, and are focused on various effects other than antimicrobial action. In this study, we evaluated the anti-proliferative effect of an analogue peptide, FF/CAP18, derived from an endogenous cathelicidin family member against the colon cancer cell line HCT116. FF/CAP18 significantly decreased the proliferation of HCT116 cells in a dose-dependent fashion. Furthermore, the treatment of HCT116 with FF/CAP18 caused loss of mitochondrial membrane potential, and resulted in the immunoreactivity to the single-strand DNA antibody, suggesting the early stage of apoptosis. Interestingly, the anti-proliferative effect of FF/CAP18 was constant regardless of the genotype of p53 (wild-type and p53 mutant type HCT116 cells). Therefore, the signaling pathway of p53 is not involved in the growth suppression effect of the cathelicidin analogue peptide. These results indicate that the treatment of certain types of cancer cells with FF/CAP18 may increase the sensitivity of the chemotherapeutic reagents, which might relate to the reduction of the side effects.

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.

Oncolytic activities of host defense peptides

Cancer continues to be a leading source of morbidity and mortality worldwide in spite of progress in oncolytic therapies. In addition, the incidence of cancers affecting the breast, kidney, prostate and skin among others continue to rise. Chemotherapeutic drugs are widely used in cancer treatment but have the serious drawback of nonspecific toxicity because these agents target any rapidly dividing cell without discriminating between healthy and malignant cells. In addition, many neoplasms eventually become resistant to conventional chemotherapy due to selection for multidrug-resistant variants. The limitations associated with existing chemotherapeutic drugs have stimulated the search for new oncolytic therapies. Host defense peptides (HDPs) may represent a novel family of oncolytic agents that can avoid the shortcomings of conventional chemotherapy because they exhibit selective cytotoxicity against a broad spectrum of malignant human cells, including multi-drug-resistant neoplastic cells. Oncolytic activity by HDPs is usually via necrosis due to cell membrane lysis, but some HDPs can trigger apoptosis in cancer cells via mitochondrial membrane disruption. In addition, certain HDPs are anti-angiogenic which may inhibit cancer progression. This paper reviews oncolytic HDP studies in order to address the suitability of selected HDPs as oncolytic therapies.