Rational design of alpha-helical antimicrobial peptides with enhanced activities and specificity/therapeutic index

Evolving and assembling to pierce through: Evolutionary and structural aspects of antimicrobial peptides

The burgeoning menace of antimicrobial resistance across the globe has necessitated investigations into other chemotherapeutic strategies to combat infections. Antimicrobial peptides, or host defense peptides, are a set of promising therapeutic candidates in this regard. Most of them cause membrane permeabilization and are a key component of the innate immune response to pathogenic invasion. It has also been reported that peptide self-assembly is a driving factor governing the microbicidal activity of these peptide candidates. While efforts have been made to develop novel synthetic peptides against various microbes, many clinical trials of such peptides have failed due to toxicity and hemolytic activity to the host. A function-guided rational peptide engineering, based on evolutionary principles, physicochemical properties and activity determinants of AMP activity, is expected to help in targeting specific microbes. Furthermore, it is important to develop a unified understanding of the evolution of AMPs in order to fully appreciate their importance in host defense. This review seeks to explore the evolution of AMPs and the physicochemical determinants of AMP activity. The specific interactions driving AMP self-assembly have also been reviewed, emphasizing implications of this self-assembly on microbicidal and immunomodulatory activity.

Anticancer activity of chicken cathelicidin peptides against different types of cancer

BACKGROUND

This study served as the pioneer in studying the anti-cancer role of chicken cathelicidin peptides.

METHODS AND RESULTS

Chicken cathelicidins were used as anticancer agent against the breast cancer cell line (MCF-7) and human colon cancer cell line (HCT116). In addition, the mechanism of action of the interaction of cationic peptides with breast cancer cell line MCF-7 was also investigated. An in vivo investigation was also achieved to evaluate the role of chicken cathelicidin in Ehrlich ascites cell (EAC) suppression as a tumor model after subcutaneous implantation in mice. It was found during the study that exposure of cell lines to 40 µg/ml of chicken cathelicidin for 72 h reduced cell lines growth rate by 90-95%. These peptides demonstrated down-regulation of (cyclin A1 and cyclin D genes) of MCF-7 cells. The study showed that two- and three-fold expression of both of caspase-3 and - 7 genes in untreated MCF-7 cells compared to treated MCF-7 cells with chicken cathelicidin peptides. Our data showed that chicken (CATH-1) enhance releasing of TNFα, INF-γ and upregulation of granzyme K in treated mice groups, in parallel, the tumor size and volume was reduced in the treated EAC-bearing groups. Tumor of mice groups treated with chicken cathelicidin displayed high area of necrosis compared to untreated EAC-bearing mice. Based on histological analysis and immunohistochemical staining revealed that the tumor section in Ehrlich solid tumor exhibited a strong Bcl2 expression in untreated control compared to mice treated with 10 & 20 µg of cathelicidin. Interestingly, low expression of Bcl2 were observed in mice taken 40 µg/mL of CATH-1.

CONCLUSIONS

This study drive intention in treatment of cancer through the efficacy of anticancer efficacy of chicken cathelicidin peptides.

Synthetic molecular evolution of antimicrobial peptides

As we learn more about how peptide structure and activity are related, we anticipate that antimicrobial peptides will be engineered to have strong potency and distinct functions and that synthetic peptides will have new biomedical applications, such as treatments for emerging infectious diseases. As a result of the enormous number of possible amino acid sequences and the low-throughput nature of antimicrobial peptide assays, computational tools for peptide design and optimization are needed for direct experimentation toward obtaining functional sequences. Recent developments in computational tools have improved peptide design, saving labor, reagents, costs, and time. At the same time, improvements in peptide synthesis and experimental platforms continue to reduce the cost and increase the throughput of peptide-drug screening. In this review, we discuss the current methods of peptide design and engineering, including in silico methods and peptide synthesis and screening, and highlight areas of potential improvement.

Kassporin-KS1: A Novel Pentadecapeptide from the Skin Secretion of Kassina senegalensis: Studies on the Structure-Activity Relationships of Site-Specific “Glycine-Lysine” Motif Insertions

Due to the abuse of traditional antibiotics and the continuous mutation of microbial resistance genes, microbial infections have become serious problems for human health. Therefore, novel antibacterial agents are urgently required, and amphibian antimicrobial peptides (AMP) are among the most interesting potential antibacterial leads. In this research, a novel peptide, named kassporin-KS1 (generically QUB-1641), with moderate antibacterial activity against Gram-positive bacteria, was discovered in the skin secretion of the Senegal running frog, Kassina senegalensis. Using site-specific sequence enrichment with a motif “glycine-lysine” that frequently occurs in ranid frog temporin peptides, a series of QUB-1641 analogues were synthesized, and effects on selected bioactivities were studied. The greatest activity enhancement was obtained when the “glycine-lysine” motif was located at the eighth and ninth position as in QUB-1570.QUB-1570 had a broader antibacterial spectrum than QUB-1641, and was eight-fold more potent. Moreover, QUB-1570 inhibited S. aureus biofilm most effectively, and significantly enhanced the viability of insect larvae infected with S. aureus. When the “glycine-lysine” motif of QUB-1570 was substituted to reduce the helix ratio and positive charge, the antibacterial activities of these synthetic analogues decreased. These data revealed that the “glycine-lysine” motif at positions 8 and 9 had the greatest enhancing effect on the antibacterial properties of QUB-1570 through increasing positive charge and helix content. This research may provide strategies for the site’s selective amino acid modification of some natural peptides to achieve the desired enhancement of activity.

Prevention, inhibition, and degradation effects of melittin alone and in combination with vancomycin and rifampin against strong biofilm producer strains of methicillin-resistant Staphylococcus epidermidis

Methicillin-resistant Staphylococcus epidermidis (MRSE) bacteria are being recognized as true pathogens as they are able to resist methicillin and commonly form biofilms. Recent studies have shown that antimicrobial peptides (AMPs) are promising agents against biofilm-associated bacterial infections. In this study, we aimed to explore the antibiofilm activity of melittin, either alone or in combination with vancomycin and rifampin, against biofilm-producing MRSE strains. Minimum biofilm preventive concentration (MBPC), minimum biofilm inhibition concentration (MBIC), and minimum biofilm eradication concentration (MBEC), as well as fractional biofilm preventive-, inhibitory-, and eradication concentrations (FBPCi, FBICi, and FBECi), were determined for the antimicrobial agents tested. Cytotoxicity and hemolytic activity of melittin at its synergistic concentration were examined on human embryonic kidney cells (HEK-293) and Red Blood Cells (RBCs), respectively. The effect of melittin on the downregulation of biofilm-associated genes was explored using Real-Time PCR. MBPC, MBIC, and MBEC values for melittin were in the range of 0.625-20, 0.625-20, and 10-40 μg/μL, respectively. Melittin showed high synergy (FBPCi, FBICi and FBECi < 0.5). The synergism resulted in a 64-512-fold, 2-16 and 2-8-fold reduction in melittin, rifampicin and vancomycin concentrations, respectively. The synergistic melittin concentration found to be effective did not manifest either cytotoxicity on HEK-293 or hemolytic activity on RBCs. Results showed that melittin downregulated the expression of biofilm-associated icaA, aap, and psm genes in all isolates tested, ranging from 0.04-folds to 2.11-folds for icaA and from 0.05 to 3.76-folds for aap and psm. The preventive and therapeutic indexes of melittin were improved 8-fold when combined with vancomycin and rifampin. Based on these findings, the combination of melittin with conventional antibiotics could be proposed for treating or preventing biofilm-associated MRSE infections.

An Integrative Sialomic Analysis Reveals Molecules From Triatoma sordida (Hemiptera: Reduviidae)

Triatomines have evolved salivary glands that produce versatile molecules with various biological functions, including those leading their interactions with vertebrate hosts’ hemostatic and immunological systems. Here, using high-throughput transcriptomics and proteomics, we report the first sialome study on the synanthropic triatomine Triatoma sordida. As a result, 57,645,372 reads were assembled into 26,670 coding sequences (CDS). From these, a total of 16,683 were successfully annotated. The sialotranscriptomic profile shows Lipocalin as the most abundant protein family within putative secreted transcripts. Trialysins and Kazal-type protease inhibitors have high transcript levels followed by ubiquitous protein families and enzyme classes. Interestingly, abundant trialysin and Kazal-type members are highlighted in this triatomine sialotranscriptome. Furthermore, we identified 132 proteins in T. sordida salivary gland soluble extract through LC-MS/MS spectrometry. Lipocalins, Hemiptera specific families, CRISP/Antigen-5 and Kazal-type protein inhibitors proteins were identified. Our study provides a comprehensive description of the transcript and protein compositions of the salivary glands of T. sordida. It significantly enhances the information in the Triatominae sialome databanks reported so far, improving the understanding of the vector’s biology, the hematophagous behaviour, and the Triatominae subfamily’s evolution.

Antimicrobial, Insecticidal and Cytotoxic Activity of Linear Venom Peptides from the Pseudoscorpion Chelifer cancroides

Linear cationic venom peptides are antimicrobial peptides (AMPs) that exert their effects by damaging cell membranes. These peptides can be highly specific, and for some, a significant therapeutic value was proposed, in particular for treatment of bacterial infections. A prolific source of novel AMPs are arthropod venoms, especially those of hitherto neglected groups such as pseudoscorpions. In this study, we describe for the first time pharmacological effects of AMPs discovered in pseudoscorpion venom. We examined the antimicrobial, cytotoxic, and insecticidal activity of full-length Checacin1, a major component of the Chelifer cancroides venom, and three truncated forms of this peptide. The antimicrobial tests revealed a potent inhibitory activity of Checacin1 against several bacteria and fungi, including methicillin resistant Staphylococcus aureus (MRSA) and even Gram-negative pathogens. All peptides reduced survival rates of aphids, with Checacin1 and the C-terminally truncated Checacin11-21 exhibiting effects comparable to Spinosad, a commercially used pesticide. Cytotoxic effects on mammalian cells were observed mainly for the full-length Checacin1. All tested peptides might be potential candidates for developing lead structures for aphid pest treatment. However, as these peptides were not yet tested on other insects, aphid specificity has not been proven. The N- and C-terminal fragments of Checacin1 are less potent against aphids but exhibit no cytotoxicity on mammalian cells at the tested concentration of 100 µM.

The Potential of Modified and Multimeric Antimicrobial Peptide Materials as Superbug Killers

Antimicrobial peptides (AMPs) are found in nearly all living organisms, show broad spectrum antibacterial activity, and can modulate the immune system. Furthermore, they have a very low level of resistance induction in bacteria, which makes them an ideal target for drug development and for targeting multi-drug resistant bacteria 'Superbugs'. Despite this promise, AMP therapeutic use is hampered as typically they are toxic to mammalian cells, less active under physiological conditions and are susceptible to proteolytic degradation. Research has focused on addressing these limitations by modifying natural AMP sequences by including e.g., d-amino acids and N-terminal and amino acid side chain modifications to alter structure, hydrophobicity, amphipathicity, and charge of the AMP to improve antimicrobial activity and specificity and at the same time reduce mammalian cell toxicity. Recently, multimerisation (dimers, oligomer conjugates, dendrimers, polymers and self-assembly) of natural and modified AMPs has further been used to address these limitations and has created compounds that have improved activity and biocompatibility compared to their linear counterparts. This review investigates how modifying and multimerising AMPs impacts their activity against bacteria in planktonic and biofilm states of growth.

Lysine Stapling Screening Provides Stable and Low Toxic Cationic Antimicrobial Peptides Combating Multidrug-Resistant Bacteria In Vitro and In Vivo

Cationic antimicrobial peptides (CAMPs) are promising for treatment of multidrug-resistant (MDR) bacteria-caused infections. However, clinical application of CAMPs has been hampered mostly due to their poor proteolytic stability and hemolytic toxicity. Recently, lysine-stapled CAMPs developed by us had been proved to increase peptide stability in vitro without induction of hemolysis. Herein, the applicability of the lysine stapling strategy was further explored by using five natural or artificial CAMPs as model peptides. Lysine stapling screening was implemented to provide 13 cyclic analogues in total. Biological screening of these cyclic analogues showed that CAMPs with a better amphiphilic structure were inclined to exhibit improved antimicrobial activity, protease stability, and biocompatibility after lysine-stapling. One of the stapled analogues of BF15-a1 was found to have extended half-life in plasma, enhanced antimicrobial activity against clinically isolated MDR ESKAPE pathogens, and remained highly effective in combating MRSA infection in a mouse model.

Chemical modifications to increase the therapeutic potential of antimicrobial peptides

The continued use of antibiotics has been accompanied by the rapid emergence and spread of antibiotic-resistant strains of bacteria. Antimicrobial peptides (AMPs), also known as host defense peptides, show multiple features as an ideal antimicrobial agent, including potent, rapid, and broad-spectrum antimicrobial activity, low promotion of antimicrobial resistance, potent anti-biofilm activity, and lethality against metabolically inactive microorganisms. However, several crucial drawbacks constrain the use of AMPs as clinical drugs, e.g., liability in vivo, toxicity when used systemically, and high production costs. Based on recent findings and our own experiences, here we summarize some chemical modifications and key design strategies to increase the therapeutic potential of AMPs, including 1) enhancing antimicrobial activities, 2) improving in vivo effectiveness, and 3) reduction in toxicity, which may facilitate the design and optimization of AMPs for the development of drug candidates. We also discuss the present challenges in the optimization of AMPs and future concerns about the resistance and cross-resistance to AMPs in the development of AMPs as therapeutic drugs.

Tandem Repeat of a Short Human Chemerin-Derived Peptide and Its Nontoxic d-Lysine-Containing Enantiomer Display Broad-Spectrum Antimicrobial and Antitubercular Activities

To design novel antimicrobial peptides by utilizing the sequence of the human host defense protein, chemerin, a seven-residue amphipathic stretch located in the amino acid region, 109-115, was identified, which possesses the highest density of hydrophobic and positively charged residues. Although this 7-mer peptide was inactive toward microorganisms, its 14-mer tandem repeat (Chem-KVL) was highly active against different bacteria including methicillin-resistant Staphylococcus aureus, a multidrug-resistant Staphylococcus aureus strain, and slow- and fast-growing mycobacterial species. The selective enantiomeric substitutions of its two l-lysine residues were attempted to confer cell selectivity and proteolytic stability to Chem-KVL. Chem-8dK with a d-lysine replacement in its middle (eighth position) showed the lowest hemolytic activity against human red blood cells among Chem-KVL analogues and maintained high antimicrobial properties. Chem-8dK showed in vivo efficacy against Pseudomonas aeruginosa infection in BALB/c mice and inhibited the development of resistance in this microorganism up to 30 serial passages and growth of intracellular mycobacteria in THP-1 cells.

Bioactive Peptides: A Promising Alternative to Chemical Preservatives for Food Preservation

Bioactive peptides used for food preservation can prolong the shelf life through bacteriostasis and antioxidation. On the one hand, bioactive peptides can inhibit lipid oxidation by scavenging free radicals, interacting with metal ions, and inhibiting lipid peroxidation. On the other hand, bioactive peptides can fundamentally inhibit the growth and reproduction of microorganisms by destroying their cell membranes or targeting intracellular components. Besides, bioactive peptides are biocompatible and biodegradable in vivo. Therefore, they are regarded as a promising alternative to chemical preservatives. However, bioactive peptides are easily affected by the external environment in practical application, which hinders their commercialization. Currently, the studies to overcome the weakness focus on encapsulation and chemical synthesis. Bioactive peptides have been applied to the preservation of various foods in experimental research, with good results. In the future, with the deepening understanding of their safety and structure-activity relationship, there may be more bioactive peptides as food preservatives.

Antimicrobial peptides (AMPs): A promising class of antimicrobial compounds

Antimicrobial peptides (AMPs) are compounds, which have inhibitory activity against microorganisms. In the last decades, AMPs have become powerful alternative agents that have met the need for novel anti-infectives to overcome increasing antibiotic resistance problems. Moreover, recent epidemics and pandemics are increasing the popularity of AMPs, due to the urgent necessity for effective antimicrobial agents in combating the new emergence of microbial diseases. AMPs inhibit a wide range of microorganisms through diverse and special mechanisms by targeting mainly cell membranes or specific intracellular components. In addition to extraction from natural sources, AMPs are produced in various hosts using recombinant methods. More recently, the synthetic analogues of AMPs, designed with some modifications, are predicted to overcome the limitations of stability, toxicity and activity associated with natural AMPs. AMPs have potential applications as antimicrobial agents in food, agriculture, environment, animal husbandry and pharmaceutical industries. In this review, we have provided an overview of the structure, classification and mechanism of action of AMPs, as well as discussed opportunities for their current and potential applications.

Interaction of Human β Defensin Type 3 (hBD-3) with Different PIP2-Containing Membranes, a Molecular Dynamics Simulation Study

Human β defensin type 3 (hBD-3) is a cysteine-rich small antibacterial peptide. It belongs to the human innate immune system. hBD-3 has six cysteine residues, which form three pairs of disulfide bonds, and those bonds break in the reducing condition. It is known that hBD-3 can interact with bacterial membrane, and even eukaryotic cell membrane, which has a low concentration of phosphatidylinositol 4,5-bisphosphate (PIP2) lipids. PIP2 is a vital component in cell membranes and has been found to play important roles during antimicrobial peptide (AMP) interaction with membranes. To understand the functional mechanism of hBD-3 interacting with PIP2-containing membranes, the binding structures of hBD-3 on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers mixed with 10% of PIP2 were predicted using two kinds of methods. The first one is by placing the hBD-3 monomer in different orientations above the POPC + 10%PIP2 membrane to set up five different initial simulation systems and performing long-term simulations on each to predict the most stable binding structure. It was found that hBD-3 analogue binds on the mixed lipid membrane on the two loop regions. The second method is by running long-term simulations on one or nine hBD-3 dimers binding on POPC mixed with 10%PIP2 lipid bilayer starting from the solid-state NMR (ssNMR)-suggested orientation. The dimer dissociated, and the most stable binding of hBD-3 in wild-type on the mixed membrane is also through the two loop regions, which agrees with the prediction from both the first method and the lipid self-assembly result. The PIP2 lipids can form long-lasting hydrogen bonds with positively charged residues such as Arg and Lys on hBD-3, thus forming clusters with hBD-3. As a comparison, hBD-3 dimers binding with a combined bilayer having 1,2-palmitoyl-oleoyl-sn-glycero-3-phosphoserine (POPS) on the upper and POPC on the lower leaflets and the combined POPS + POPC bilayer mixing with 10%PIP2 were also studied. The long-term simulation result shows that hBD-3 can bind with the heads of negatively charged POPS and PIP2 lipids and form hydrogen bonds. The stable binding sites of hBD-3 on PIP2 or POPS mixed bilayers are still on the two loop regions. On the combined POPS + POPC mixed with 10%PIP2 bilayer, the binding of hBD-3 with PIP2 lipids became less stable and fewer because of the competition of binding with the POPS lipids. Besides that, binding with hBD-3 can decrease the membrane thickness of the POPC + PIP2, POPS + POPC, and POPS + POPC + PIP2 bilayers and make POPS and PIP2 lipids more flexible based on the order parameter calculations. Our results supply molecular insight on AMP binding with different membranes and can help understand the functional mechanism of hBD-3 disrupting PIP2-containing membranes.

Virtual Screening for Biomimetic Anti-Cancer Peptides from Cordyceps militaris Putative Pepsinized Peptidome and Validation on Colon Cancer Cell Line

Colorectal cancer is one of the leading causes of cancer-related death in Thailand and many other countries. The standard practice for curing this cancer is surgery with an adjuvant chemotherapy treatment. However, the unfavorable side effects of chemotherapeutic drugs are undeniable. Recently, protein hydrolysates and anticancer peptides have become popular alternative options for colon cancer treatment. Therefore, we aimed to screen and select the anticancer peptide candidates from the in silico pepsin hydrolysate of a Cordyceps militaris (CM) proteome using machine-learning-based prediction servers for anticancer prediction, i.e., AntiCP, iACP, and MLACP. The selected CM-anticancer peptide candidates could be an alternative treatment or co-treatment agent for colorectal cancer, reducing the use of chemotherapeutic drugs. To ensure the anticancer properties, an in vitro assay was performed with "CM-biomimetic peptides" on the non-metastatic colon cancer cell line (HT-29). According to the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay results from peptide candidate treatments at 0-400 µM, the IC₅₀ doses of the CM-biomimetic peptide with no toxic and cancer-cell-penetrating ability, original C. militaris biomimetic peptide (C-ori), against the HT-29 cell line were 114.9 µM at 72 hours. The effects of C-ori compared to the doxorubicin, a conventional chemotherapeutic drug for colon cancer treatment, and the combination effects of both the CM-anticancer peptide and doxorubicin were observed. The results showed that C-ori increased the overall efficiency in the combination treatment with doxorubicin. According to the acridine orange/propidium iodine (AO/PI) staining assay, C-ori can induce apoptosis in HT-29 cells significantly, confirmed by chromatin condensation, membrane blebbing, apoptotic bodies, and late apoptosis which were observed under a fluorescence microscope.

PEP27-2, a Potent Antimicrobial Cell-Penetrating Peptide, Reduces Skin Abscess Formation during Staphylococcus aureus Infections in Mouse When Used in Combination with Antibiotics

PEP27, a 27-amino acid (aa) peptide secreted by Streptococcus pneumoniae, is an autolytic peptide that functions as a major virulence factor. To develop a clinically applicable antimicrobial peptide (AMP), we designed PEP27 analogs with Trp substitutions to enhance its antimicrobial activity compared to that of PEP27. Particularly, PEP27-2 showed strong antimicrobial activity against a wide variety of bacteria, including multidrug-resistant (MDR) bacteria. It was found that the antimicrobial activity of PEP27-2 was increased by substituting Trp for the aa at the middle position of PEP27. We found that PEP27-2 acts as an effective cell-penetrating peptide in bacterial and mammalian cells. Here, we proved that subcutaneous infection with MDR Staphylococcus aureus induced skin lesions such as skeletal muscle damage, deep inflammation, and necrosis of the overlaying dermis in mice. Combination treatment with antibiotics revealed synergistic effects, remarkably reducing abscess size and improving the bacteria removal rate from the infection site. Moreover, PEP27-2-antibiotic combination treatment reduced inflammation, lowering levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, inducible NO synthase (iNOS), and cyclooxygenase (COX-2) in skin abscess tissue. The results suggest that the PEP27-2 peptide is a promising therapeutic option for combating MDR bacterial strains by enhancing antibiotic penetration and protecting against MDR bacteria.

Biophysical Measurement Strategies for Antiviral Drug Development: Recent Progress in Virus-Mimetic Platforms Down to the Single Particle Level

The rapid growth in the global human population has increased the prevalence of emerging infectious diseases, which poses a major risk to public health. In search of effective clinical solutions, the acquisition of knowledge and understanding of biomolecular processes associated with viral pathogens represents a prerequisite. In this context, biophysical engineering approaches are particularly promising since they can resolve biomolecular interactions systematically by circumventing the complexities associated with experiments involving natural biological systems. The engineering approaches encompass the design and construction of biomimetic platforms that simulate the physiological system. This approach enables us to characterize, measure, and quantitatively analyze biomolecular interactions.In this Account, we summarize biophysical measurements that our group has successfully adopted to develop broad-spectrum antiviral drugs based on the lipid envelope antiviral disruption (LEAD) strategy, targeting the structural integrity of the outer viral membrane to abrogate viral infectivity. We particularly focus on the engineering aspects related to the design and construction of the tethered lipid vesicle platform, which closely mimics the viral membrane. We first outline the development of the LEAD agents screening platform that integrates soft matter design components with biomaterials and surface functionalization strategies to facilitate parallel measurements tracking peptide-induced destabilization of nanoscale, virus-mimicking vesicles with tunable size and composition. Then, we describe how this platform can be effectively employed to gain insights into the membrane curvature dependency of certain peptides. The fundamental knowledge acquired through this systematic process is crucial in the identification and subsequent development of antiviral drug candidates. In particular, we highlight the development of curvature-sensitive α-helical (AH) peptides as a broad-spectrum antiviral agent that has been demonstrated as an effective therapeutic treatment against multiple enveloped viruses. Also, we introduce a tethered cluster of vesicles to mimic clusters of enveloped viruses, exhibiting higher infectivity levels in the biological system. Then, we discuss key considerations, including experimental artifacts, namely dye leakage and imaging-related photobleaching, and corresponding corrective measures to improve the accuracy of quantitative interpretation. With the ongoing development and application of the tethered lipid vesicle platform, there is a compelling opportunity to explore fundamental biointerfacial science and develop a new class of broad-spectrum antiviral agents to prepare for the future membrane-enveloped viral pandemics.

The multifaceted nature of antimicrobial peptides: current synthetic chemistry approaches and future directions

Bacterial infections caused by 'superbugs' are increasing globally, and conventional antibiotics are becoming less effective against these bacteria, such that we risk entering a post-antibiotic era. In recent years, antimicrobial peptides (AMPs) have gained significant attention for their clinical potential as a new class of antibiotics to combat antimicrobial resistance. In this review, we discuss several facets of AMPs including their diversity, physicochemical properties, mechanisms of action, and effects of environmental factors on these features. This review outlines various chemical synthetic strategies that have been applied to develop novel AMPs, including chemical modifications of existing peptides, semi-synthesis, and computer-aided design. We will also highlight novel AMP structures, including hybrids, antimicrobial dendrimers and polypeptides, peptidomimetics, and AMP-drug conjugates and consider recent developments in their chemical synthesis.

Switching Cytolytic Nanopores into Antimicrobial Fractal Ruptures by a Single Side Chain Mutation

Disruption of cell membranes is a fundamental host defense response found in virtually all forms of life. The molecular mechanisms vary but generally lead to energetically favored circular nanopores. Here, we report an elaborate fractal rupture pattern induced by a single side-chain mutation in ultrashort (8-11-mers) helical peptides, which otherwise form transmembrane pores. In contrast to known mechanisms, this mode of membrane disruption is restricted to the upper leaflet of the bilayer where it exhibits propagating fronts of peptide-lipid interfaces that are strikingly similar to viscous instabilities in fluid flow. The two distinct disruption modes, pores and fractal patterns, are both strongly antimicrobial, but only the fractal rupture is nonhemolytic. The results offer wide implications for elucidating differential membrane targeting phenomena defined at the nanoscale.

Synthetic Antimicrobial Peptides: III—Effect of Cationic Groups of Lysine, Arginine, and Histidine on Antimicrobial Activity of Peptides with a Linear Type of Amphipathicity

Abstract

We have studied the antimicrobial and hemolytic activity of synthetic antimicrobial peptides (SAMPs), i.e., Arg9Phe2 (P1-Arg), Lys9Phe2 (P2-Lys), and His9Phe2 (P3-His), which have a “linear” type of amphipathicity and contain the cationic amino acid residues of arginine, lysine, or histidine. In this study, we have used various pathogenic microorganism strains of gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, and Salmonella enterica), gram-positive bacteria (Staphylococcus aureus), and the conditionally pathogenic yeast fungus (Candida albicans). It has been shown that the replacement of the arginine residues by lysine or histidine residues in the tested SAMPs significantly degrades their antibacterial properties in the series: P1-Arg > P2-Lys $$ \gg $$P3-His. The cationic analog of SAMP, P1-Arg, has the highest antibacterial activity (MIC50 = 43–76 μM), while peptide P3-His does not exhibit this activity (MIC50 > 100 μM). The P1-Arg and P2-Lys peptides were 6–10 times more active against the opportunistic fungus C. albicans (MIC50 6.7 and 10.9 μM, respectively) and the P3-His peptide has 100-times increased antimycotic activity (MIC50 0.6 μM) compared with their effect on bacterial cells. All of the tested peptides with the linear type of amphipathicity and low hydrophobicity, i.e., P1-Arg, P2-Lys, and P3-His, that contain only two Phe residues regardless of the presence of cationic amino acids (Arg, Lys, or His) exhibit a relatively low hemolytic activity (not more than 4% hemolysis at 1000 μM peptide concentration). Thus, considering the same synthesis efficiency (56–63%) and approximately the same low toxicity of the tested SAMPs with a linear type of amphipathicity, it is recommended to use those that contain the cationic arginine or histidine residues to create antibacterial or antifungal peptide agents, respectively.

Carbon-Based Nanomaterials: Promising Antiviral Agents to Combat COVID-19 in the Microbial-Resistant Era

Therapeutic options for the highly pathogenic human severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing the current pandemic coronavirus disease (COVID-19) are urgently needed. COVID-19 is associated with viral pneumonia and acute respiratory distress syndrome causing significant morbidity and mortality. The proposed treatments for COVID-19 have shown little or no effect in the clinic so far. Additionally, bacterial and fungal pathogens contribute to the SARS-CoV-2-mediated pneumonia disease complex. The antibiotic resistance in pneumonia treatment is increasing at an alarming rate. Therefore, carbon-based nanomaterials (CBNs), such as fullerene, carbon dots, graphene, and their derivatives constitute a promising alternative due to their wide-spectrum antimicrobial activity, biocompatibility, biodegradability, and capacity to induce tissue regeneration. Furthermore, the antimicrobial mode of action is mainly physical (e.g., membrane distortion), characterized by a low risk of antimicrobial resistance. In this Review, we evaluated the literature on the antiviral activity and broad-spectrum antimicrobial properties of CBNs. CBNs had antiviral activity against 13 enveloped positive-sense single-stranded RNA viruses, including SARS-CoV-2. CBNs with low or no toxicity to humans are promising therapeutics against the COVID-19 pneumonia complex with other viruses, bacteria, and fungi, including those that are multidrug-resistant.

An alternatingly amphiphilic, resistance-resistant antimicrobial oligoguanidine with dual mechanisms of action

The increasing number of infections caused by multi-drug resistance (MDR) bacteria is an omen of a new global challenge. As one of the countermeasures under development, antimicrobial peptides (AMPs) and AMP mimics have emerged as a new family of antimicrobial agents with high potential, due to their low resistance generation rate and effectiveness against MDR bacterial strains resulted from their membrane-disrupting mechanism of action. However, most reported AMPs and AMP mimics have facially amphiphilic structures, which may lead to undesired self-aggregation and non-specific binding, as well as increased cytotoxicity toward mammalian cells, all of which put significant limits on their applications. Here, we report an oligomer with the size of short AMPs, with both hydrophobic carbon chain and cationic groups placed on its backbone, giving an alternatingly amphiphilic structure that brings better selectivity between mammalian and bacterial cell membranes. In addition, the oligomer shows affinity toward DNA, thus it can utilize bacterial DNA located in the vulnerable nucleoid as the second drug target. Benefiting from these designs, the oligomer shows higher therapeutic index and synergistic effect with other antibiotics, while its low resistance generation rate and effectiveness on multi-drug resistant bacterial strains can be maintained. We demonstrate that this alternatingly amphiphilic, DNA-binding oligomer is not only resistance-resistant, but is also able to selectively eliminate bacteria at the presence of mammalian cells. Importantly, the oligomer exhibits good in vivo activity: it cleans all bacteria on Caenorhabditis elegans without causing apparent toxicity, and significantly improves the survival rate of mice with severely infected wounds in a mice excision wound model study.

A teleost bactericidal permeability-increasing protein-derived peptide that possesses a broad antibacterial spectrum and inhibits bacterial infection as well as human colon cancer cells growth

The bactericidal permeability-increasing protein (BPI) is a multifunctional cationic protein produced by neutrophils with antibacterial, antitumor, and LPS-neutralizing properties. In teleost, a number of BPIs have been reported, but their functions are very limited. In this study, an N-terminal peptide, BO18 (with 18 amino acids), derived from rock bream (Oplegnathus fasciatus) BPI, was synthesized and investigated for its antibacterial spectrum, action mechanism, immunoregulatory property as well as the inhibition effects on bacterial invasion and human colon cancer cells growth. The results showed that BO18 was active against Gram-positive bacteria Bscillus subiilis, Micrococcus luteus, and Staphylococcus aureus, as well as Gram-negative bacteria Vibrio alginolyticus, Vibrio litoralis, Vibrio parahaemolyticus and Vibrio vulnificus. BO18 treatment facilitated the bactericidal process of erythromycin and rifampicin by enhancing the permeability of the outer membrane. During its interaction with V. alginolyticus, BO18 exerted its antibacterial activity by destroying cell membrane integrity, penetrating into the cytoplasm and binding to genomic DNA and total RNA. In vitro analysis indicated BO18 could enhance the respiratory burst ability and regulate the expression of immune related genes of macrophages. In vivo detection showed the administration of fish with BO18 before bacterial infection significantly reduced pathogen dissemination and replication in tissues. In addition, BO18 exerted a cytotoxic effect on the growth of human colon cancer cells HT-29. Together, these results add new insights into the function of teleost BPIs, and support that BO18 is a novel and broad-spectrum antibacterial peptide with potential to apply in fighting pathogenic infection in aquaculture.

The effect of acidic pH on the adsorption and lytic activity of the peptides Polybia-MP1 and its histidine-containing analog in anionic lipid membrane: a biophysical study by molecular dynamics and spectroscopy

Antimicrobial peptides (AMPs) are part of the innate immune system of many species. AMPs are short sequences rich in charged and non-polar residues. They act on the lipid phase of the plasma membrane without requiring membrane receptors. Polybia-MP1 (MP1), extracted from a native wasp, is a broad-spectrum bactericide, an inhibitor of cancer cell proliferation being non-hemolytic and non-cytotoxic. MP1 mechanism of action and its adsorption mode is not yet completely known. Its adsorption to lipid bilayer and lytic activity is most likely dependent on the ionization state of its two acidic and three basic residues and consequently on the bulk pH. Here we investigated the effect of bulk acidic (pH 5.5) and neutral pH (7.4) solution on the adsorption, insertion, and lytic activity of MP1 and its analog H-MP1 to anionic (7POPC:3POPG) model membrane. H-MP1 is a synthetic analog of MP1 with lysines replaced by histidines. Bulk pH changes could modulate this peptide efficiency. The combination of different experimental techniques and molecular dynamics (MD) simulations showed that the adsorption, insertion, and lytic activity of H-MP1 are highly sensitive to bulk pH in opposition to MP1. The atomistic details, provided by MD simulations, showed peptides contact their N-termini to the bilayer before the insertion and then lay parallel to the bilayer. Their hydrophobic faces inserted into the acyl chain phase disturb the lipid-packing.

Modulatory Effects of Acidic pH and Membrane Potential on the Adsorption of pH-Sensitive Peptides to Anionic Lipid Membrane

Anionic lipid membrane electrostatic potential and solution pH can influence cationic peptide adsorption to these bilayers, especially those containing simultaneously acid and basic residues. Here, we investigate the effects of the pH solution on MP1 (IDWKKLLDAAKQIL-NH2) adsorption to anionic (7POPC:3POPG) lipid vesicles in comparison to its analog H-MP1, with histidines substituting lysines. We used the association of adsorption isotherms and constant pH molecular dynamic simulations (CpHMD) to explore the effects of membrane potential and pH on peptides' adsorption on this lipid membrane. We analyzed the fluorescence and zeta potential adsorption isotherms using the Gouy-Chapman theory. In CpHMD simulations for the peptides in solution and adsorbed on the lipid bilayer, we used the conformations obtained by conventional MD simulations at a μs timescale. Non-equilibrium Monte Carlo simulations provided the protonation states of acidic and basic residues. CpHMD showed average pKa shifts of two to three units, resulting in a higher net charge for the analog than for MP1, strongly modulating the peptide adsorption. The fractions of the protonation of acidic and basic residues and the peptides' net charges obtained from the analysis of the adsorption isotherms were in reasonable agreement with those from CpHMD. MP1 adsorption was almost insensitive to solution pH. H-MP1 was much more sensitive to partitioning, at acidic pH, with an affinity ten times higher than in neutral ones.

Rational design of antimicrobial peptides targeting Gram-negative bacteria

Membrane-targeting host antimicrobial peptides (AMPs) can kill or inhibit the growth of Gram-negative bacteria. However, the evolution of resistance among microbes poses a substantial barrier to the long-term utility of the host AMPs. Combining experiment and molecular dynamics simulations, we show that terminal carboxyl capping enhances both membrane insertion and antibacterial activity of an AMP called P1. Furthermore, we show that a bacterial strain with evolved resistance to this peptide becomes susceptible to P1 variants with either backbone capping or lysine-to-arginine substitutions. Our results suggest that cocktails of closely related AMPs may be useful in overcoming evolved resistance.

Deep Learning for Novel Antimicrobial Peptide Design

Antimicrobial resistance is an increasing issue in healthcare as the overuse of antibacterial agents rises during the COVID-19 pandemic. The need for new antibiotics is high, while the arsenal of available agents is decreasing, especially for the treatment of infections by Gram-negative bacteria like Escherichia coli. Antimicrobial peptides (AMPs) are offering a promising route for novel antibiotic development and deep learning techniques can be utilised for successful AMP design. In this study, a long short-term memory (LSTM) generative model and a bidirectional LSTM classification model were constructed to design short novel AMP sequences with potential antibacterial activity against E. coli. Two versions of the generative model and six versions of the classification model were trained and optimised using Bayesian hyperparameter optimisation. These models were used to generate sets of short novel sequences that were classified as antimicrobial or non-antimicrobial. The validation accuracies of the classification models were 81.6–88.9% and the novel AMPs were classified as antimicrobial with accuracies of 70.6–91.7%. Predicted three-dimensional conformations of selected short AMPs exhibited the alpha-helical structure with amphipathic surfaces. This demonstrates that LSTMs are effective tools for generating novel AMPs against targeted bacteria and could be utilised in the search for new antibiotics leads.

Synthetic Biology and Computer-Based Frameworks for Antimicrobial Peptide Discovery

Antibiotic resistance is one of the greatest challenges of our time. This global health problem originated from a paucity of truly effective antibiotic classes and an increased incidence of multi-drug-resistant bacterial isolates in hospitals worldwide. Indeed, it has been recently estimated that 10 million people will die annually from drug-resistant infections by the year 2050. Therefore, the need to develop out-of-the-box strategies to combat antibiotic resistance is urgent. The biological world has provided natural templates, called antimicrobial peptides (AMPs), which exhibit multiple intrinsic medical properties including the targeting of bacteria. AMPs can be used as scaffolds and, via engineering, can be reconfigured for optimized potency and targetability toward drug-resistant pathogens. Here, we review the recent development of tools for the discovery, design, and production of AMPs and propose that the future of peptide drug discovery will involve the convergence of computational and synthetic biology principles.

Outer-membrane-acting peptides and lipid II-targeting antibiotics cooperatively kill Gram-negative pathogens

The development and dissemination of antibiotic-resistant bacterial pathogens is a growing global threat to public health. Novel compounds and/or therapeutic strategies are required to face the challenge posed, in particular, by Gram-negative bacteria. Here we assess the combined effect of potent cell-wall synthesis inhibitors with either natural or synthetic peptides that can act on the outer-membrane. Thus, several linear peptides, either alone or combined with vancomycin or nisin, were tested against selected Gram-negative pathogens, and the best one was improved by further engineering. Finally, peptide D-11 and vancomycin displayed a potent antimicrobial activity at low μM concentrations against a panel of relevant Gram-negative pathogens. This combination was highly active in biological fluids like blood, but was non-hemolytic and non-toxic against cell lines. We conclude that vancomycin and D-11 are safe at >50-fold their MICs. Based on the results obtained, and as a proof of concept for the newly observed synergy, a Pseudomonas aeruginosa mouse infection model experiment was also performed, showing a 4 log₁₀ reduction of the pathogen after treatment with the combination. This approach offers a potent alternative strategy to fight (drug-resistant) Gram-negative pathogens in humans and mammals.

Antimicrobial Contribution of Chitosan Surface-Modified Nanoliposomes Combined with Colistin against Sensitive and Colistin-Resistant Clinical Pseudomonas aeruginosa

Colistin is a re-emergent antibiotic peptide used as a last resort in clinical practice to overcome multi-drug resistant (MDR) Gram-negative bacterial infections. Unfortunately, the dissemination of colistin-resistant strains has increased in recent years and is considered a public health problem worldwide. Strategies to reduce resistance to antibiotics such as nanotechnology have been applied successfully. In this work, colistin was characterized physicochemically by surface tension measurements. Subsequently, nanoliposomes coated with highly deacetylated chitosan were prepared with and without colistin. The nanoliposomes were characterized using dynamic light scattering and zeta potential measurements. Both physicochemical parameters fluctuated relatively to the addition of colistin and/or polymer. The antimicrobial activity of formulations increased by four-fold against clinical isolates of susceptible Pseudomona aeruginosa but did not have antimicrobial activity against multidrug-resistant (MDR) bacteria. Interestingly, the free coated nanoliposomes exhibited the same antibacterial activity in both sensitive and MDR strains. Finally, the interaction of colistin with phospholipids was characterized using molecular dynamics (MD) simulations and determined that colistin is weakly associated with micelles constituted by zwitterionic phospholipids.

Multiple action mechanism and in vivo antimicrobial efficacy of antimicrobial peptide Jelleine-I

With the extensive use of antibiotics in medicine, agriculture and food chemistry, the emergence of multi-drug resistant bacteria become more and more frequent and posed great threats to human health and life. So novel antimicrobial agents were urgently needed to defend the resistant bacteria. Jelleine-I was a small antimicrobial peptide (AMP) with eight amino acids in its sequence. It was believed to be an ideal template for developing antimicrobial agents. In the present study, the possible action mode against both gram-negative bacteria and gram-positive bacteria and in vivo antimicrobial activity was explored. Our results showed that Jelleine-I exhibits its antimicrobial activity mainly by disrupting the integrity of the cell membrane, which would not be affected by the conventional resistant mechanism. It also aims at some intracellular targets such as genomic DNA to inhibit the growth of microbes. In addition, the result of in vivo antimicrobial activity experiment showed that Jelleine-I performed a good therapeutic effect toward the mice with Escherichia coli infected peritonitis. Notably, Jelleine-I has negligible cytotoxicity toward the tested mammalian cells, indicating excellent cell selectivity between prokaryotic cells and eurkayotic cells. In summary, our results showed that Jelleine-I would be a potential candidate to be developed as a novel antimicrobial agent.

Temporin-Like Peptides Show Antimicrobial and Anti-Biofilm Activities against Streptococcus mutans with Reduced Hemolysis

In our previous study, temporin-GHaR (GHaR) showed potent antimicrobial activity with strong hemolytic toxicity. To overcome its weakness, we designed GHaR6R, GHaR7R, GHaR8R, GHaR9R, and GHaR9W by changing the number of positive charges and the hydrophobic surface of GHaR. With the exception of GHaR7R, the hemolytic toxicity of the derived peptides had been reduced, and the antimicrobial activities remained close to the parent peptide (except for GHaR9R). GHaR6R, GHaR7R, GHaR8R, and GHaR9W exhibited a great bactericidal effect on Streptococcus mutans (S. mutans), which is one of the main pathogens causing dental caries. According to the membrane permeation and scanning electron microscope (SEM) analysis, these derived peptides targeted to the cell membranes of planktonic bacteria, contributing to the disruption of the membrane integrity and leakage of the intracellular contents. Moreover, they inhibited the formation of biofilms and eradicated the mature biofilms of S. mutans. Compared with GHaR7R, the derived peptides showed less cytotoxicity to human oral epithelial cells (HOECs). The derived peptides are expected to be the molecular templates for designing antibacterial agents to prevent dental caries.

Effects of Rationally Designed Physico-Chemical Variants of the Peptide PuroA on Biocidal Activity towards Bacterial and Mammalian Cells

Antimicrobial peptides (AMPs) often exhibit wide-spectrum activities and are considered ideal candidates for effectively controlling persistent and multidrug-resistant wound infections. PuroA, a synthetic peptide based on the tryptophan (Trp)-rich domain of the wheat protein puroindoline A, displays strong antimicrobial activities. In this work, a number of peptides were designed based on PuroA, varying in physico-chemical parameters of length, number of Trp residues, net charge, hydrophobicity or amphipathicity, D-versus L-isomers of amino acids, cyclization or dimerization, and were tested for antimicrobial potency and salt and protease tolerance. Selected peptides were assessed for effects on biofilms of methicillin-resistant Staphylococcus aureus (MRSA) and selected mammalian cells. Peptide P1, with the highest amphipathicity, six Trp and a net charge of +7, showed strong antimicrobial activity and salt stability. Peptides W7, W8 and WW (seven to eight residues) were generally more active than PuroA and all diastereomers were protease-resistant. PuroA and certain variants significantly inhibited initial biomass attachment and eradicated preformed biofilms of MRSA. Further, P1 and dimeric PuroA were cytotoxic to HeLa cells. The work has led to peptides with biocidal effects on common human pathogens and/or anticancer potential, also offering great insights into the relationship between physico-chemical parameters and bioactivities, accelerating progress towards rational design of AMPs for therapeutics.

Performant Composite Materials Based on Oxide Semiconductors and Metallic Nanoparticles Generated from Cloves and Mandarin Peel Extracts

In this work, the metal and semiconducting nanoparticles (AgNPs, ZnONPs and AgZnONPs) were phyto-synthesized using aqueous vegetal extracts from: Caryophyllus aromaticus L. (cloves) and Citrus reticulata L. (mandarin) peels. The morphological, structural, compositional, optical and biological properties (antibacterial activity, and cytotoxicity) of the prepared composites were investigated. The most effective sample proved to be AgZnONPs, derived from cloves, with a minimum inhibitory concentration (MIC) value of 0.11 mg/mL and a minimum bactericidal concentration (MBC) value of 2.68 mg/mL. All the other three composites inhibited bacterial growth at a concentration between 0.25 mg/mL and 0.37 mg/mL, with a bactericidal concentration between 3 mg/mL and 4 mg/mL. The obtained composites presented biocidal activity against Staphylococcus aureus, and biocompatibility (on human fibroblast BJ cells) and did not damage the human red blood cells. Additionally, an important result is that the presence of silver in composite materials improved the bactericidal action of these nanomaterials against the most common nosocomial pathogen, Staphylococcus aureus.

Effect of Secondary Structure and Side Chain Length of Hydrophobic Amino Acid Residues on the Antimicrobial Activity and Toxicity of 14-Residue-Long de novo AMPs

Herein we report the efficacy and toxicity of three de novo designed cationic antimicrobial peptides (AMPs) LL-14, VV-14 and ββ-14, where side chains of the hydrophobic amino acids were reduced gradually. The AMPs showed broad-spectrum antimicrobial activity against three pathogens from the ESKAPE group and two fungal strains. This study showed that side chains which are either too long or too short increase toxicity and lower antimicrobial activity, respectively. VV-14 was found to be non-cytotoxic and highly potent under physiological salt concentrations against several pathogens, especially Salmonella typhi TY2. These AMPs acted via membrane deformation, depolarization, and lysis. The activity of the AMPs is related to their ability to take on amphipathic helical conformations in the presence of microbial membrane mimics. Among AMPs with the same charge, hydrophobic interactions between the side chains of the residues with cell membrane lipids determine their antimicrobial potency and cytotoxicity. Strikingly, an optimum hydrophobic interaction is the crux of generating highly potent non-cytotoxic AMPs.

Design, Synthesis and Biological Evaluation of Biphenylglyoxamide-Based Small Molecular Antimicrobial Peptide Mimics as Antibacterial Agents

There has been an increasing interest in the development of antimicrobial peptides (AMPs) and their synthetic mimics as a novel class of antibiotics to overcome the rapid emergence of antibiotic resistance. Recently, phenylglyoxamide-based small molecular AMP mimics have been identified as potential leads to treat bacterial infections. In this study, a new series of biphenylglyoxamide-based small molecular AMP mimics were synthesised from the ring-opening reaction of N-sulfonylisatin bearing a biphenyl backbone with a diamine, followed by the conversion into tertiary ammonium chloride, quaternary ammonium iodide and guanidinium hydrochloride salts. Structure-activity relationship studies of the analogues identified the octanesulfonyl group as being essential for both Gram-positive and Gram-negative antibacterial activity, while the biphenyl backbone was important for Gram-negative antibacterial activity. The most potent analogue was identified to be chloro-substituted quaternary ammonium iodide salt 15c, which possesses antibacterial activity against both Gram-positive (MIC against Staphylococcus aureus = 8 μM) and Gram-negative bacteria (MIC against Escherichia coli = 16 μM, Pseudomonas aeruginosa = 63 μM) and disrupted 35% of pre-established S. aureus biofilms at 32 μM. Cytoplasmic membrane permeability and tethered bilayer lipid membranes (tBLMs) studies suggested that 15c acts as a bacterial membrane disruptor. In addition, in vitro toxicity studies showed that the potent compounds are non-toxic against human cells at therapeutic dosages.

Design of a Sea Snake Antimicrobial Peptide Derivative with Therapeutic Potential against Drug-Resistant Bacterial Infection

Infections caused by drug-resistant pathogens are a worldwide challenge for public health. Antimicrobial peptides (AMPs) are regarded as promising antibiotic alternatives for the treatment of drug-resistant infections. In the present study, a series of small peptides were designed based on our previously reported sea snake AMP Hc-CATH. From them, the lead peptide HC1-D2, a truncated peptide entirely substituted by d-amino acids, was selected. HC1-D2 exhibited significantly improved stability and antibiofilm and anti-inflammatory activities. Meanwhile, HC1-D2 retained potent, broad-spectrum, and rapid antimicrobial properties against bacteria and fungi, especially drug-resistant bacteria. Moreover, HC1-D2 showed low propensity to induce bacterial resistance and low cytotoxicity and hemolytic activity. Notably, HC1-D2 showed potent in vivo anti-infective ability in mouse peritonitis models infected by both standard and drug-resistant bacteria. It significantly decreased the bacterial counts in the abdominal cavity and spleen of mice and apparently increased the survival rates of the mice. Acting through the MAPKs inflammatory pathway, HC1-D2 selectively induced the production of chemokine and the subsequent immune cell recruitment to the infection site, while inhibiting the production of pro-inflammatory cytokines with undesirable toxicities. These much improved properties make HC1-D2 a promising candidate for the development of novel peptide anti-infective agents against drug-resistant infections.

A Noncytotoxic Temporin L Analogue with In Vivo Antibacterial and Antiendotoxin Activities and a Nonmembrane-Lytic Mode of Action

Cytotoxic frog antimicrobial peptide Temporin L (TempL) is an attractive molecule for the design of lead antimicrobial agents due to its short size and versatile biological activities. However, noncytotoxic TempL variants with desirable biological activities have rarely been reported. TempL analogue Q3K,TempL is water-soluble and possesses a significant antiendotoxin property along with comparable cytotoxicity to TempL. A phenylalanine residue, located at the hydrophobic face of Q3K,TempL and the "d" position of its phenylalanine zipper sequence, was replaced with a cationic lysine residue. This analogue, Q3K,F8K,TempL, showed reduced hydrophobic moment and was noncytotoxic with lower antimicrobial activity. Interestingly, swapping between tryptophan at the fourth and serine at the sixth positions turned Q3K,F8K,TempL totally amphipathic as reflected by its helical wheel projection with clusters of hydrophobic and hydrophilic residues and the highest hydrophobic moment among these peptides. Surprisingly, this analogue, SW,Q3K,F8K,TempL, was as noncytotoxic as Q3K,F8K,TempL but showed augmented antimicrobial and antiendotoxin properties, comparable to that of TempL and Q3K,TempL. SW,Q3K,F8K,TempL exhibited appreciable survival of mice against P. aeruginosa infection and a lipopolysaccharide (LPS) challenge. Unlike TempL and Q3K,TempL, SW,Q3K,F8K,TempL adopted an unordered secondary structure in bacterial membrane mimetic lipid vesicles and did not permeabilize them or depolarize the bacterial membrane. Overall, the results demonstrate the design of a nontoxic TempL analogue that possesses clusters of hydrophobic and hydrophilic residues with impaired secondary structure and shows a nonmembrane-lytic mechanism and in vivo antiendotoxin and antimicrobial activities. This paradigm of design of antimicrobial peptide with clusters of hydrophobic and hydrophilic residues and high hydrophobic moment but low secondary structure could be attempted further.

Halictine-2 antimicrobial peptide shows promising anti-parasitic activity against Leishmania spp

The protozoan parasite Leishmania spp. causes leishmaniases, a group of diseases creating serious health problems in many parts of the world with significant resistance to existing drugs. Insect derived antimicrobial peptides are promising alternatives to conventional drugs against several human disease-causing pathogens because they do not generate resistance. Halictine-2, a novel antimicrobial peptide from the venom of eusocial honeybee, Halictus sexcinctus showed significant anti-leishmanial activity in vitro, towards two life forms of the dimorphic parasite, the free-swimming infective metacyclic promastigotes and the intracellular amastigotes responsible for the systemic infection. The anti-leishmanial activity of the native peptide (P^5S) was significantly enhanced by serine to threonine substitution at position 5 (P^5T). The peptide showed a propensity to form α-helices after substitution at position-5, conferring amphipathicity. Distinct pores observed on the promastigote membrane after P^5T exposure suggested a mechanism of disruption of cellular integrity. Biochemical alterations in the promastigotes after P^5T exposure included generation of increased oxygen radicals with mitochondrial Ca²⁺ release, loss of mitochondrial membrane potential, reduction in total ATP content and increased mitochondrial mass, resulting in quick bioenergetic and chemiosmotic collapse leading to cell death characterized by DNA fragmentation. P^5T was able to reduce intracellular amastigote burden in an in vitro model of Leishmania infection but did not alter the proinflammatory cytokines like TNF-α and IL-6. The ability of the P^5T peptide to kill the Leishmania parasite with negligible haemolytic activity towards mouse macrophages and human erythrocytes respectively, demonstrates its potential to be considered as a future antileishmanial drug candidate.

Self-assembly of mitochondria-specific peptide amphiphiles amplifying lung cancer cell death through targeting the VDAC1-hexokinase-II complex

Mitochondria-targeting peptides represent an emergent tool for cancer inhibition. Here supramolecular assemblies of novel amphiphilic cell-penetrating peptides for targeting cancer cell mitochondria are reported. The employed strategy aims at amplifying the apoptotic stimuli by weakening the mitochondrial VDAC1 (voltage-dependent anion channel-1)-hexokinase-II (HK-II) interaction. Peptide engineering is performed with the N-terminus of the HK-II protein, which binds to VDAC1. First, a designed positively charged segment (pKV) is anchored to the specific 15 amino acid sequence (MIASHLLAYFFTELN) to yield a cell-penetrating peptide (pHK-pKV). Second, a lipid chain (Pal) is conjugated to the N-terminus of pHK-pKV in order to enhance the intracellular delivery of the HK-II scaffold. The self-assembly properties of these two synthetic peptides are investigated by synchrotron small-angle X-ray scattering (BioSAXS) and cryogenic transmission electron (cryo-TEM) imaging, which evidence the formation of nanoassemblies of ellipsoid-like shapes. Circular dichroism (CD) spectroscopy demonstrates the induction of partial α-helical structures in the amphiphilic peptides. Confocal microscopy reveals the specific mitochondrial location of Pal-pHK-pKV assemblies in human non-small cell lung cancer (NSCLC) A549 cells. The cytotoxicity and apoptotic studies indicate the enhanced bioactivity of Pal-pHK-pKV self-assembled reservoirs, which cause massive A549 cell death with regard to pHK-pKV. Of significance, Pal-pHK-pKV treatment of non-cancerous NCM460 cells resulted in substantially lower cytotoxicity. The results demonstrate the potential of self-assembled lipo-peptide (HK-II-derived) conjugates as a promising strategy in cancer therapy.

The Spectrum of Design Solutions for Improving the Activity-Selectivity Product of Peptide Antibiotics against Multidrug-Resistant Bacteria and Prostate Cancer PC-3 Cells

The link between the antimicrobial and anticancer activity of peptides has long been studied, and the number of peptides identified with both activities has recently increased considerably. In this work, we hypothesized that designed peptides with a wide spectrum of selective antimicrobial activity will also have anticancer activity, and tested this hypothesis with newly designed peptides. The spectrum of peptides, used as partial or full design templates, ranged from cell-penetrating peptides and putative bacteriocin to those from the simplest animals (placozoans) and the Chordata phylum (anurans). We applied custom computational tools to predict amino acid substitutions, conferring the increased product of bacteriostatic activity and selectivity. Experiments confirmed that better overall performance was achieved with respect to that of initial templates. Nine of our synthesized helical peptides had excellent bactericidal activity against both standard and multidrug-resistant bacteria. These peptides were then compared to a known anticancer peptide polybia-MP1, for their ability to kill prostate cancer cells and dermal primary fibroblasts. The therapeutic index was higher for seven of our peptides, and anticancer activity stronger for all of them. In conclusion, the peptides that we designed for selective antimicrobial activity also have promising potential for anticancer applications.

Anti-cancer peptides: classification, mechanism of action, reconstruction and modification

Anti-cancer peptides (ACPs) are a series of short peptides composed of 10-60 amino acids that can inhibit tumour cell proliferation or migration, or suppress the formation of tumour blood vessels, and are less likely to cause drug resistance. The aforementioned merits make ACPs the most promising anti-cancer candidate. However, ACPs may be degraded by proteases, or result in cytotoxicity in many cases. To overcome these drawbacks, a plethora of research has focused on reconstruction or modification of ACPs to improve their anti-cancer activity, while reducing their cytotoxicity. The modification of ACPs mainly includes main chain reconstruction and side chain modification. After summarizing the classification and mechanism of action of ACPs, this paper focuses on recent development and progress about their reconstruction and modification. The information collected here may provide some ideas for further research on ACPs, in particular their modification.

Advances in the Study of Structural Modification and Biological Activities of Anoplin

Anoplin is an amphipathic, α-helical bioactive peptide from wasp venom. In recent years, pharmaceutical and organic chemists discovered that anoplin and its derivatives showed multiple pharmacological activities in antibacterial, antitumor, antifungal, and antimalarial activities. Owing to the simple and unique structure and diverse biological activities, anoplin has attracted considerable research interests. This review highlights the advances in structural modification, biological activities, and the outlook of anoplin in order to provide a basis for new drug design and delivery.

Shorter Antibacterial Peptide Having High Selectivity for E. coli Membranes and Low Potential for Inducing Resistance

Antimicrobial peptides (AMPs) have been recognised as a significant therapeutic option for mitigating resistant microbial infections. It has been found recently that Plasmodium falciparum-derived, 20 residue long, peptide 35409 had antibacterial and haemolytic activity, making it an AMP having reduced selectivity, and suggesting that it should be studied more extensively for obtaining new AMPs having activity solely targeting the bacterial membrane. Peptide 35409 was thus used as template for producing short synthetic peptides (<20 residues long) and evaluating their biological activity and relevant physicochemical characteristics for therapeutic use. Four of the sixteen short peptides evaluated here had activity against E. coli without any associated haemolytic effects. The 35409-1 derivative (17 residues long) had the best therapeutic characteristics as it had high selectivity for bacterial cells, stability in the presence of human sera, activity against E. coli multiresistant clinical isolates and was shorter than the original sequence. It had a powerful membranolytic effect and low potential for inducing resistance in bacteria. This peptide’s characteristics highlighted its potential as an alternative for combating infection caused by E. coli multiresistant bacteria and/or for designing new AMPs.