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

Antimicrobial peptide A9K as a gene delivery vector in cancer cells

Designed peptides are promising biomaterials for biomedical applications. The amphiphilic cationic antimicrobial peptide (AMP), A9K, can self-assemble into nano-rod structures and has shown cancer cell selectivity and could therefore be a promising candidate for therapeutic delivery into cancer cells. In this paper, we investigate the selectivity of A9K for cancer cell models, examining its effect on two human cancer cell lines, A431 and HCT-116. Little or no activity was observed on the control, human dermal fibroblasts (HDFs). In the cancer cell lines the peptide inhibited cellular growth through changes in mitochondrial morphology and membrane potential while remaining harmless towards HDFs. In addition, the peptide can bind to and protect nucleic acids while transporting them into both 2D cultures and 3D spheroids of cancer cells. A9K showed high efficiency in delivering siRNA molecules into the centre of the spheroids. A9K was also explored in vivo, using a zebrafish (Danio rerio) development toxicity assay, showing that the peptide is safe at low doses. Finally, a high-content imaging screen, using RNA interference (RNAi) targeted towards cellular uptake, in HCT-116 cells was carried out. Our findings suggest that active cellular uptake is involved in peptide internalisation, mediated through clathrin-mediated endocytosis. These new discoveries make A9K attractive for future developments in clinical and biotechnological applications.

Effects of hydroxyl group in cyclo(Pro-Tyr)-like cyclic dipeptides on their anti-QS activity and self-assembly

We investigated the influence of hydroxyl groups on the anti-quorum-sensing (anti-QS) and anti-biofilm activity of structurally similar cyclic dipeptides, namely cyclo(L-Pro-L-Tyr), cyclo(L-Hyp-L-Tyr), and cyclo(L-Pro-L-Phe), against Pseudomonas aeruginosa PAO1. Cyclo(L-Pro-L-Phe), lacking hydroxyl groups, displayed higher virulence factor inhibition and cytotoxicity, but showed less inhibitory ability in biofilm formation. Cyclo(L-Pro-L-Tyr) and cyclo(L-Hyp-L-Tyr) suppressed genes in both the las and rhl systems, whereas cyclo(L-Pro-L-Phe) mainly downregulated rhlI and pqsR expression. These cyclic dipeptides interacted with the QS-related protein LasR, with similar binding efficiency to the autoinducer 3OC12-HSL, except for cyclo(L-Pro-L-Phe) which had lower affinity. In addition, the introduction of hydroxyl groups significantly improved the self-assembly ability of these peptides. Both cyclo(L-Pro-L-Tyr) and cyclo(L-Hyp-L-Tyr) formed assembly particles at the highest tested concentration. The findings revealed the structure-function relationship of this kind of cyclic dipeptides and provided basis for our follow-up research in the design and modification of anti-QS compounds.

Overcoming the challenge: cell-penetrating peptides and membrane permeability

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

Peptide nano 'bead-grafting' for SDT-facilitated immune checkpoints blocking

Combination therapies based on immune checkpoint blockade (ICB) are currently the mainstay of cancer treatment, in which the synergetic delivery of multiple drugs is the essential step. Although nanoparticle drugs (NPDs) show satisfactory anticancer effects, the promotion of active co-delivery of NPDs is premature, since the processes are usually difficult to predict and control. Targeting peptide self-assemblies have been widely used as carriers for small-molecular drugs, but remain elusive for NPDs. We describe here peptide-based nano 'bead-grafting' for the active delivery of quantum-dot NPDs through a co-assembly method. Based on a 'de novo' design, we used a 'one-bead-one-compound (OBOC)' combinatorial chemical screening method to select a peptide RT with high affinity for the immune checkpoint CD47, which could also form biocompatible nanofibers and efficiently trap Ag2S quantum dots along the self-assembly path. This system can combine ICB therapy and sonodynamic therapy (SDT) to effectively inhibit tumor growth. Moreover, the tumor antigen produced by SDT can activate the adaptive immune system, which enhances the anti-tumor immune response of the ICB and shows efficient inhibition of both primary and distant tumors. This study provides a new strategy for the active control and delivery of NPDs and a new option for ICB therapy with immune checkpoints that are highly susceptible to systemic side effects.

How do terminal modifications of short designed IIKK peptide amphiphiles affect their antifungal activity and biocompatibility?

HYPOTHESIS

The widespread and prolonged use of antifungal antibiotics has led to the rapid emergence of multidrug resistant Candida species that compromise current treatments. Natural and synthetic antimicrobial peptides (AMPs) offer potential alternatives but require further development to overcome some of their current drawbacks. AMPs kill pathogenic fungi by permeabilising their membranes but it remains unclear how AMPs can be designed to maximise their antifungal potency whilst minimising their toxicity to host cells.

EXPERIMENTS

We have designed a group of short (IIKK)₃ AMPs via selective terminal modifications ending up with different amphiphilicities. Their antifungal performance was assessed by minimum inhibition concentration (MICs) and dynamic killing to 4 Candida strains and Cryptococcus neoformans, and the minimum biofilm-eradicating concentrations to kill 95% of the C. albicans biofilms (BEC₉₅). Different antifungal actions were interpreted on the basis of structural disruptions of the AMPs to small unilamellar vesicles from fluorescence leakage, Zeta potential, small angle neutron scattering (SANS) and molecular dynamics simulations (MD).

FINDING

AMPs possess high antifungal activities against the Candida species and Cryptococcus neoformans; some of them displayed faster dynamic killing than antibiotics like amphotericin B. G(IIKK)₃I-NH₂ and (IIKK)₃II-NH₂ were particularly potent against not only planktonic microbes but also fungal biofilms with low cytotoxicity to host cells. It was found that their high selectivity and fast action were well correlated to their fast membrane lysis, evident from data measured from Zeta potential measurements, SANS and MD, and also consistent with the previously observed antibacterial and anticancer performance. These studies demonstrate the important role of colloid and interface science in further developing short, potent and biocompatible AMPs towards clinical treatments via structure design and optimization.

Design of Polymeric Carriers for Intracellular Peptide Delivery in Oncology Applications

In recent decades, peptides, which can possess high potency, excellent selectivity, and low toxicity, have emerged as promising therapeutics for cancer applications. Combined with an improved understanding of tumor biology and immuno-oncology, peptides have demonstrated robust antitumor efficacy in preclinical tumor models. However, the translation of peptides with intracellular targets into clinical therapies has been severely hindered by limitations in their intrinsic structure, such as low systemic stability, rapid clearance, and poor membrane permeability, that impede intracellular delivery. In this Review, we summarize recent advances in polymer-mediated intracellular delivery of peptides for cancer therapy, including both therapeutic peptides and peptide antigens. We highlight strategies to engineer polymeric materials to increase peptide delivery efficiency, especially cytosolic delivery, which plays a crucial role in potentiating peptide-based therapies. Finally, we discuss future opportunities for peptides in cancer treatment, with an emphasis on the design of polymer nanocarriers for optimized peptide delivery.

Dual antimicrobial and anticancer activity of a novel synthetic α-helical antimicrobial peptide

Antimicrobial peptides (AMPs) are increasingly sought-after and researched antimicrobial agents due to its desired pharmacological properties and the continuous diminishing efficacy of antibiotics. In addition to this line of research, the aim of the present study is to determine the antimicrobial and anticancer activity of a de novo designed α-helical peptide. Circular dichroism showed 100% helical nature of the peptide in 10 mM SDS. Notably, the peptide exerted significant antimicrobial activity against the reference and antibiotic-resistant clinical isolates belonging to Pseudomonas sp. at a MIC and MBC of 2 and 8 μM, respectively. The progressive disruption and disturbance of cell membrane in the overall topography was observed in the scanning electron microscopy (SEM) micrographs of Pseudomonas aeruginosa ATCC 27853 treated with the peptide as compared to untreated control. The results of time-kill kinetics showed complete lysis at 3x MIC after 50 min of incubation of the microbe with the peptide. Moreover, the peptide did not lyse human RBCs even at the highest concentration of the peptide (10 mM) and retained its activity upon treatment at 0.5 mg/ml trypsin. Cancer cell lines, viz. A549 and MCF-7 were also found to be sensitive to peptide activity showing 50% reduction in survivability at 4 and 2 μM, respectively; however, L929 cells were unaffected. Drastic membrane permeability and necrotic mode of lysis of peptide-treated-A549 cells were affirmed by propidium iodide and live/dead cell staining. The results showed that the designed peptide could be an efficient drug molecule for clinical studies subjected to successful experiments on animal models.

Use of anticancer peptides as an alternative approach for targeted therapy in breast cancer: a review

Breast cancer is the most common cancer in women worldwide. Traditional therapies are expensive and cause severe side effects. Targeted therapy is a powerful method to circumvent the problems of other therapies. It also allows drugs to localize at predefined targets in a selective manner. Currently, there are several monoclonal antibodies which target breast cancer cell surface markers. However, using antibodies has some limitations. In the last two decades, many investigators have discovered peptides that may be useful to target breast cancer cells. In this article, we provide an overview on anti-breast cancer peptides, their sources and biological activities. We further discuss the pros and cons of using anticancer peptides with further emphasis on how to improve their effectiveness in cancer therapy.

A Review of Bioactive Peptides: Chemical Modification, Structural Characterization and Therapeutic Applications

In recent years, the development and applications of protein drugs have attracted extensive attention from researchers. However, the shortcomings of protein drugs also limit their further development. Therefore, bioactive peptides isolated or simulated from protein polymers have broad application prospects in food, medicine, biotechnology, and other industries. Such peptides have a molecular weight distribution between 180 and 1000 Da. As a small molecule substance, bioactive peptide is usually degraded by various enzymes in the organism and have a short half-life. At the same time, such substances have poor stability and are difficult to produce and store. Therefore, these active peptides may be modified through phosphorylation, glycosylation, and acylation. Compared with other protein drugs, the modified active peptides are more easily absorbed by the body, have longer half-life, stronger targeting, and fewer side effects in addition to higher bioavailability. In the light of their functions, bioactive peptide can be divided into antimicrobial, anti-tumour, anti-angiogenic, antioxidant, anti-fatigue, and anti-hypertensive peptides. This article mainly focuses on the introduction of several promising biologically active peptides functioning as antimicrobial, anti-tumour, antiangiogenic, and antioxidant peptides from the three aspects modification, structural characteristics and mechanism of action.

A Review for Antimicrobial Peptides with Anticancer Properties: Re-purposing of Potential Anticancer Agents

Abstract In recent years, various research on cancer treatment has achieved significant progress. However, some of these treatments remain disputable because of the emergence and development of drug resistance, and the toxic side effects that were brought about by the lack of selectivity displayed by the treatments. Hence, there is considerable interest in a new class of anticancer molecules that is currently still under investigation termed the cationic antimicrobial peptides (AMPs). AMPs are a group of pervasive components of the innate immunity which can be found throughout all classes of life. The small innate peptides cover a broad spectrum of antibacterial activities due to their electrostatic interactions with the negatively charged bacterial membrane. Compared with normal cells, cancer cells have increased proportions of negatively charged molecules, including phosphatidylserine, glycoproteins, and glycolipids, on the outer plasma membrane. This provides an opportunity for exploiting the interaction between AMPs and negatively charged cell membranes in developing unconventional anticancer strategies. Some AMPs may also be categorized into a group of potential anticancer agents called cationic anticancer peptides (ACPs) due to their relative selectivity in cell membrane penetration and lysis, which is similar to their interaction with bacterial membranes. Several examples of ACPs that are used in tumor therapy for their ability in penetrating or lysing tumor cell membrane will be reviewed in this paper, along with a discussion on the recent advances and challenges in the application of ACPs.

CancerGram: An Effective Classifier for Differentiating Anticancer from Antimicrobial Peptides

Antimicrobial peptides (AMPs) constitute a diverse group of bioactive molecules that provide multicellular organisms with protection against microorganisms, and microorganisms with weaponry for competition. Some AMPs can target cancer cells; thus, they are called anticancer peptides (ACPs). Due to their small size, positive charge, hydrophobicity and amphipathicity, AMPs and ACPs interact with negatively charged components of biological membranes. AMPs preferentially permeabilize microbial membranes, but ACPs additionally target mitochondrial and plasma membranes of cancer cells. The preference towards mitochondrial membranes is explained by their membrane potential, membrane composition resulting from α-proteobacterial origin and the fact that mitochondrial targeting signals could have evolved from AMPs. Taking into account the therapeutic potential of ACPs and millions of deaths due to cancer annually, it is of vital importance to find new cationic peptides that selectively destroy cancer cells. Therefore, to reduce the costs of experimental research, we have created a robust computational tool, CancerGram, that uses n-grams and random forests for predicting ACPs. Compared to other ACP classifiers, CancerGram is the first three-class model that effectively classifies peptides into: ACPs, AMPs and non-ACPs/non-AMPs, with AU1U amounting to 0.89 and a Kappa statistic of 0.65. CancerGram is available as a web server and R package on GitHub.

Mechanistic Investigation of a Self-Assembling Peptide against Escherichia coli

Because of their distinctive mode of action in targeting bacterial cell membranes, antimicrobial peptides (AMPs) are increasingly regarded as a potential candidate for the development of novel antibiotics to combat the wide spread of bacterial resistance. To date, understanding of the exact molecular process by which AMPs act on the real bacterial envelope remains challenging. Simultaneously, the aggregated state of AMPs upon interaction with bacterial envelopes is still elusive. Previously, we have demonstrated that the potent antibacterial activity of a designed surfactant-like peptide Ac-A₉K-NH₂ benefited greatly from its high self-assembling ability and appropriate self-assembled morphologies and sizes. By using high-resolution atomic force microscopy, we here not only follow the variations of the Escherichia coli cell envelope in the presence of Ac-A₉K-NH₂ but also characterize the peptide aggregates on the bacterial surface as well as on the substrate surface. The results, together with those from fluorescence, zeta potential, circular dichroism, and scanning electron microscopy measurements, indicate that both the positively charged peptide monomers and self-assembled nanostructures can directly act on the negatively charged bacterial surface, followed by their insertion into the bacterial membrane, the formation of surface nanopores, and membrane lysis. The mechanism of Ac-A₉K-NH₂ against E. coli is thus consistent with the detergent-like mode of action. This work enhances our mechanistic understanding of the antibacterial behaviors of self-assembling peptides that will be valuable in exploring their biomedical applications.

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.

pH-triggered morphological change in a self-assembling amphiphilic peptide used as an antitumor drug carrier

The geometry of nanoparticles plays an important role in the process of drug encapsulation and release. In this study, an acid-responsive amphiphilic polypeptide consisting of lysine and leucine was prepared. In neutral media, the amphiphilic peptide L₆K₄ self-assembled to form spherical nanoparticles and encapsulated fat-soluble antitumor drugs. The intratumoral accumulation of the drug-loaded nanoparticles was improved in HeLa cells compared with normal cells. Compared to a neutral environment, increasingly acidic solutions changed the secondary structure of the peptide. In addition, the drug-loaded nanoparticles expanded and decomposed, rapidly releasing the poorly soluble antitumor drug doxorubicin (DOX). In addition, the amphiphilic peptide L₆K₄ had antitumor properties, and the antitumor performance of the combination of L₆K₄ and DOX was better than that of free DOX. Our results indicate that the use of acid responsiveness to induce geometric changes in drug-loaded peptide nanoparticles could be a promising strategy for antitumor drug delivery.

Double-edged effects and mechanisms of Zn2+ microenvironments on osteogenic activity of BMSCs: osteogenic differentiation or apoptosis

Zinc-incorporated biomaterials show promoting effects on osteogenesis; however, excessive zinc ions lead to cytotoxic reactions and also have other adverse effects. Therefore, the double-edged effects of Zn2+ microenvironments on osteogenesis may become critical issues for new material development. This study systematically investigated the bidirectional influences of diverse Zn2+ microenvironments on the cell adhesion, proliferation, osteogenic differentiation and apoptosis of rBMSCs. Furthermore, the mechanisms of zinc-induced osteogenic differentiation of rBMSCs and of cell apoptosis induced by high concentration of Zn2+ were both discussed in detail. The results indicated that the Zn2+ microenvironments of 2 μg mL-1 and 5 μg mL-1 effectively improved the initial adhesion and proliferation of rBMSCs, while that of 15 μg mL-1 had exactly the opposite effect. More importantly, the suitable Zn2+ microenvironments (2 μg mL-1 and 5 μg mL-1) moderately increased the intracellular Zn2+ concentration by regulating zinc transportation, and then activated the MAPK/ERK signaling pathway to induce the osteogenic differentiation of rBMSCs. In contrast, the high Zn2+ concentration (15 μg mL-1) not only inhibited the osteogenic differentiation of rBMSCs by damaging intracellular zinc homeostasis, but also induced rBMSC apoptosis by enhancing intracellular ROS generation. The current study clarified the double-edged effects of Zn2+ microenvironments on the osteogenic properties of rBMSCs and the related mechanisms, and may provide valuable guidance for optimizing the design of zinc-doped biomaterials and zinc-based alloys.

pH-Triggered geometrical shape switching of a cationic peptide nanoparticle for cellular uptake and drug delivery

The geometry of nanoparticles plays an important role in their performance as drug carriers. However, the pH-triggered geometrical shape switching of a cationic peptide consisting of isoleucine and lysine is seldom reported. In this work, we designed a cationic peptide with acid reactivity that can be loaded with the poorly soluble antitumor drug (doxorubicin (DOX)) to enhance tumor cell uptake and drug delivery. In a weakly acidic environment, a large portion of random coil structures formed, which subsequently led to nanoparticle destruction and rapid DOX release. In vitro studies demonstrated that this cationic peptide exhibits low toxicity to normal cells. The amount of DOX-encapsulating peptide nanoparticles taken up by tumor cells was greater than that taken up by normal cells. Our results indicated that the use of a weakly acidic microenvironment to induce geometric shape switching in drug-loaded peptide nanoparticles should be a promising strategy for antitumor drug delivery.

In Vitro and MD Simulation Study to Explore Physicochemical Parameters for Antibacterial Peptide to Become Potent Anticancer Peptide

Although the physicochemical properties of antimicrobial peptides (AMPs) and anticancer peptides (ACPs) are very similar, it remains unclear which specific parameter(s) of ACPs confer the major anticancer activity. By answering how to construct a short AMP/ACP that could easily be synthesized in the most cost effective way plus conferring a maximum anticancer effect is a very important scientific breakthrough in the development of protein/peptide drugs. In this study, an 18-amino-acids antimicrobial peptide, AcrAP1 (named AP1-Z1), was used as a template. Bioinformatics algorithms were then performed to design its six mutants (AP1-Z3a, AP1-Z3b, AP1-Z5a, AP1-Z5b, AP1-Z7, and AP1-Z9). After a series of in vitro experiments plus intensive computational analysis, the data demonstrated that AP1-Z5a and AP1-Z5b induced both apoptosis and anti-angiogenic effects to achieve the maximum anticancer activity. Specifically, the most effective mutant, AP1-Z5b, exhibited high selectivity for the charged membrane in molecular dynamics simulations. These findings clearly demonstrated that both charge and hydrophobicity play an important role and are necessary to reach an optimum equilibrium for optimizing the anticancer activity of AMPs. Overall, the present study provides a very crucial theoretical basis and important scientific evidence on the key physicochemical parameters of ACP drugs development.

Proliferation of Cells with Severe Nuclear Deformation on a Micropillar Array

Cellular responses on a topographic surface are fundamental topics about interfaces and biology. Herein, a poly(lactide- co-glycolide) (PLGA) micropillar array was prepared and found to trigger significant self-deformation of cell nuclei. The time-dependent cell viability and thus cell proliferation was investigated. Despite significant nuclear deformation, all of the examined cell types (Hela, HepG2, MC3T3-E1, and NIH3T3) could survive and proliferate on the micropillar array yet exhibited different proliferation abilities. Compared to the corresponding groups on the smooth surface, the cell proliferation abilities on the micropillar array were decreased for Hela and MC3T3-E1 cells and did not change significantly for HepG2 and NIH3T3 cells. We also found that whether the proliferation ability changed was related to whether the nuclear sizes decreased in the micropillar array, and thus the size deformation of cell nuclei should, besides shape deformation, be taken into consideration in studies of cells on topological surfaces.

Cancer nanomedicine: focus on recent developments and self-assembled peptide nanocarriers

The applications of nanoparticulate drug delivery have received abundant interest in the field of cancer diagnosis and treatment.

Transportan 10 improves the anticancer activity of cisplatin

The aim of this paper was to examine whether cell-penetrating peptides (CPPs) such as transportan 10 (TP10) or protein transduction domain (PTD4) may improve the anticancer activity of cisplatin (cPt). The complexes of TP10 or PTD4 with cPt were used in the experiments. They were carried out on two non-cancer (HEK293 (human embryonic kidney) and HEL299 (human embryo lung)) and two cancer (HeLa (human cervical cancer) and OS143B (human osteosarcoma 143B)) cell lines. Both complexes were tested (MTT assay) with respect to their anticancer or cytotoxic actions. TAMRA (fluorescent dye)-stained preparations were visualized in a fluorescence microscope. The long-term effect of TP10 + cPt and its components on non-cancer and cancer cell lines was observed in inverted phase contrast microscopy. In the MTT test (cell viability assay), the complex of TP10 + cPt produced a more potent effect on the cancer cell lines (HeLa, OS143B) in comparison to that observed after separate treatment with TP10 or cPt. At the same time, the action of the complex and its components was rather small on non-cancer cell lines. On the other hand, a complex of another CPP with cPt, i.e., PTD4 + cPt, was without a significant effect on the cancer cell line (OS143B). The images of the fluorescent microscopy showed TAMRA-TP10 or TAMRA-TP10 + cPt in the interior of the HeLa cells. In the case of TAMRA-PTD4 or TAMRA-PTD4 + cPt, only the first compound was found inside the cancer cell line. In contrast, none of the tested compounds gained access to the interior of the non-cancer cells (HEK293, HEL299). Long-term incubation with the TP10 + cPt (estimated by inverted phase contrast microscopy) lead to an enhanced action of the complex on cell viability (decrease in the number of cells and change in their morphology) as compared with that produced by each single agent. With regard to the tested CPPs, only TP10 improved the anticancer activity of cisplatin if both compounds were used in the form of a complex. Additionally, the complex was relatively safe for non-cancer cells. What is more, TP10 also produced an anticancer effect on HeLa and OS143B cell lines.

Amino acid side chains affect the bioactivity of designed short peptide amphiphiles

The artificially designed amphiphilic peptide G(IIKK)₃I-NH₂ has been shown to be highly effective at killing bacteria and inhibiting the growth of tumor cells whilst remaining benign to normal mammalian cells. Herein we report how the side chain length and branching of constituent amino acids affect these bioactivities. Two peptide groups were designed by utilizing G(IIKK)₃I-NH₂ as the base template. In Group 1, hydrophobic residues were replaced from Ile to Leu, Nle (norleucine), or Val. It was found that an increase in the side chain carbon number from 3 (Val) to 4 (Leu, Ile or Nle) substantially enhanced their antibacterial and antitumor activities, but different branching in the butyl side chain showed very different cytotoxicities to host mammalian cells, with the γ-branching in Leu eliciting the highest potency. Group 2 covered those cationic Lys residues which were replaced by synthetic homologues with shorter side chains, namely, Orn, Dab and Dap containing 3, 2 and 1 methylene units, respectively. The replacement did not affect their antibacterial activities much, but their anticancer activities were maximized in Orn and Dab. On the other hand, their cytotoxicities also became higher, indicating a multi-faceted role played by the cationic residues. Thus, changes in both the side chain length and branching strongly affected the amphiphilicity of the short peptides and their interactions with different membranes. This work has revealed a strong relationship among side chain structures, amphiphilicity and selective bioactivities of the short peptide amphiphiles.

Transportan 10 improves the anticancer activity of cisplatin

The aim of this paper was to examine whether cell-penetrating peptides (CPPs) such as transportan 10 (TP10) or protein transduction domain (PTD4) may improve the anticancer activity of cisplatin (cPt). The complexes of TP10 or PTD4 with cPt were used in the experiments. They were carried out on two non-cancer (HEK293 (human embryonic kidney) and HEL299 (human embryo lung)) and two cancer (HeLa (human cervical cancer) and OS143B (human osteosarcoma 143B)) cell lines. Both complexes were tested (MTT assay) with respect to their anticancer or cytotoxic actions. TAMRA (fluorescent dye)-stained preparations were visualized in a fluorescence microscope. The long-term effect of TP10 + cPt and its components on non-cancer and cancer cell lines was observed in inverted phase contrast microscopy. In the MTT test (cell viability assay), the complex of TP10 + cPt produced a more potent effect on the cancer cell lines (HeLa, OS143B) in comparison to that observed after separate treatment with TP10 or cPt. At the same time, the action of the complex and its components was rather small on non-cancer cell lines. On the other hand, a complex of another CPP with cPt, i.e., PTD4 + cPt, was without a significant effect on the cancer cell line (OS143B). The images of the fluorescent microscopy showed TAMRA-TP10 or TAMRA-TP10 + cPt in the interior of the HeLa cells. In the case of TAMRA-PTD4 or TAMRA-PTD4 + cPt, only the first compound was found inside the cancer cell line. In contrast, none of the tested compounds gained access to the interior of the non-cancer cells (HEK293, HEL299). Long-term incubation with the TP10 + cPt (estimated by inverted phase contrast microscopy) lead to an enhanced action of the complex on cell viability (decrease in the number of cells and change in their morphology) as compared with that produced by each single agent. With regard to the tested CPPs, only TP10 improved the anticancer activity of cisplatin if both compounds were used in the form of a complex. Additionally, the complex was relatively safe for non-cancer cells. What is more, TP10 also produced an anticancer effect on HeLa and OS143B cell lines.

Solvent Controlled Structural Transition of KI4K Self-Assemblies: from Nanotubes to Nanofibrils

The structural modulation of peptide and protein assemblies under well-controlled conditions is of both fundamental and practical significance. In spite of extensive studies, it remains hugely challenging to tune the self-assembled nanostructures in a controllable manner because the self-assembly processes are dictated by various noncovalent interactions and their interplay. We report here how to manipulate the self-assembly of a designed, symmetric amphiphilic peptide (KI4K) via the solvent-controlled structural transition. Structural transition processes were carefully followed by the combination of transmission electronic microscopy (TEM), atomic force microscopy (AFM), circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and small angle neutron scattering (SANS). The results show that the introduction of acetonitrile into water significantly affected the hydrophobic interactions among hydrophobic side chains while imposing little impact on the β-sheet hydrogen bonding between peptide backbones. A structural transition occurred from nanotubes to helical/twisted ribbons and then to thin fibrils with the addition of acetonitrile due to the reduced hydrophobic interactions and the consequent weakening of the lateral stacking between KI4K β-sheets. The increased intermolecular electrostatic repulsions among lysine side chain amino groups had little effect on the lateral stacking of KI4K β-sheets due to the molecular symmetry. Complementary molecular dynamic (MD) simulations also indicated the solvation of acetonitrile molecules into the hydrophobic domains weakening the coherence between the neighboring sheets.

Multidimensional Design of Anticancer Peptides

The computer-assisted design and optimization of peptides with selective cancer cell killing activity was achieved through merging the features of anticancer peptides, cell-penetrating peptides, and tumor-homing peptides. Machine-learning classifiers identified candidate peptides that possess the predicted properties. Starting from a template amino acid sequence, peptide cytotoxicity against a range of cancer cell lines was systematically optimized while minimizing the effects on primary human endothelial cells. The computer-generated sequences featured improved cancer-cell penetration, induced cancer-cell apoptosis, and were enabled a decrease in the cytotoxic concentration of co-administered chemotherapeutic agents in vitro. This study demonstrates the potential of multidimensional machine-learning methods for rapidly obtaining peptides with the desired cellular activities.

Tuning gelation kinetics and mechanical rigidity of β-hairpin peptide hydrogels via hydrophobic amino acid substitutions

Self-assembling peptide hydrogels with faster gelation kinetics and higher mechanical rigidity are favorable for their practical applications. A design strategy to control the folding, self-assembly, and hydrogelation of β-hairpin peptides via hydrophobic amino acid substitutions has been explored in this study. Isoleucine has higher hydrophobicity and stronger propensity for β-sheet hydrogen bonding than valine. After the valine residues of MAX1 (VKVKVKVKV(D)PPTKVKVKVKV-NH2) were replaced with isoleucines, oscillatory rheometry and circular dichroism (CD) spectroscopy characterizations indicated that the variants had clearly faster self-assembly and hydrogelation rates and that the resulting gels displayed higher mechanical stiffness. Transmission electron microscopy (TEM) indicated the parent MAX1 and its variants all formed networks of long and entangled fibrils with the similar diameters of ∼3 nm, suggesting little effect of hydrophobic substitutions on the self-assembled morphology. The MAX1I8 (IKIKIKIKV(D)PPTKIKIKIKI-NH2) hydrogel showed the fastest gelation rate (within 5 min) and the highest gel rigidity with the series, supporting the homogeneous cell distribution within its 3D scaffold. In addition, the MAX1I8 hydrogel showed quick shear-thinning and rapid recovery upon cessation of shear strain, and the MTT and immunological assays indicated its low cytotoxicity and good biocompatibility. These features are highly attractive for its widespread use in 3D cell culturing and regenerative medical treatments.

Design of imperfectly amphipathic α-helical antimicrobial peptides with enhanced cell selectivity

Antimicrobial peptides (AMPs), which are produced by multicellular organisms as a defense mechanism against competing pathogenic microbes, appear to be excellent candidates for the development of novel antimicrobial agents. Amphipathicity is traditionally believed to be crucial to the de novo design or systematic optimization of AMPs. In this study, we designed a series of short α-helical AMPs with imperfect amphipathicity to augment the arsenal of strategies and to gain further insights into their antimicrobial and hemolytic activity. These imperfectly amphipathic α-helical AMPs were designed by replacing the paired charged amino acid residues on the polar face of an amphipathic peptide with tryptophan residues on the basis of α-helical protein folding principles. PRW4, an imperfectly amphipathic α-helical AMP with hydrogen bonds formed by paired tryptophan residues, was observed to be more selective towards bacterial cells than toward human red blood cells. PRW4 was also effective against Gram-negative and Gram-positive bacteria, and fluorescence spectroscopy, flow cytometry, scanning electron microscopy and transmission electron microscopy indicated that PRW4 killed microbial cells by permeabilizing the cell membrane and damaging their membrane integrity. Therefore, disruptive amphipathicity has excellent potential for the rational design and optimization of AMPs with promising antimicrobial activities.

Tuning the self-assembly of short peptides via sequence variations

Peptide self-assembly is of direct relevance to protein science and bionanotechnology, but the underlying mechanism is still poorly understood. Here, we demonstrate the distinct roles of the noncovalent interactions and their impact on nanostructural templating using carefully designed hexapeptides, I2K2I2, I4K2, and KI4K. These simple variations in sequence led to drastic changes in final self-assembled structures. β-sheet hydrogen bonding was found to favor the formation of one-dimensional nanostructures, such as nanofibrils from I4K2 and nanotubes from KI4K, but the lack of evident β-sheet hydrogen bonding in the case of I2K2I2 led to no nanostructure formed. The lateral stacking and twisting of the β-sheets were well-linked to the hydrophobic and electrostatic interactions between amino acid side chains and their interplay. For I4K2, the electrostatic repulsion acted to reduce the hydrophobic attraction between β-sheets, leading to their limited lateral stacking and more twisting, and final fibrillar structures; in contrast, the repulsive force had little influence in the case of KI4K, resulting in wide ribbons that eventually developed into nanotubes. The fibrillar and tubular features were demonstrated by a combination of cryogenic transmission electron microscopy (cryo-TEM), negative-stain transmission electron microscopy (TEM), and small-angle neutron scattering (SANS). SANS also provided structural information at shorter scale lengths. All atom molecular dynamics (MD) simulations were used to suggest possible molecular arrangements within the β-sheets at the very early stage of self-assembly.

From antimicrobial to anticancer peptides. A review

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