Systematic screening of the cellular uptake of designed alpha-helix peptides

One New Acid-Activated Hybrid Anticancer Peptide by Coupling with a Desirable pH-Sensitive Anionic Partner Peptide

Anticancer peptides (ACPs) are promising antitumor resources, and developing acid-activated ACPs as more effective and selective antitumor drugs would represent new progress in cancer therapy. In this study, we designed a new class of acid-activated hybrid peptides LK-LE by altering the charge shielding position of the anionic binding partner LE based on the cationic ACP LK and investigated their pH response, cytotoxic activity, and serum stability, in hoping to achieve a desirable acid-activatable ACP. As expected, the obtained hybrid peptides could be activated and exhibit a remarkable antitumor activity by rapid membrane disruption at acidic pH, whereas its killing activity could be alleviated at normal pH, showing a significant pH response compared with LK. Importantly, this study found that the peptide LK-LE3 with the charge shielding in the N-terminal of LK displayed notably low cytotoxicity and more stability, demonstrating that the position of charge masking is extremely important for the improvement of peptide toxicity and stability. In short, our work opens a new avenue to design promising acid-activated ACPs as potential targeting agents for cancer treatment.

A Peptide Inhibitor of the Human Cytomegalovirus Core Nuclear Egress Complex

The replication of human cytomegalovirus (HCMV) involves a process termed nuclear egress, which enables translocation of newly formed viral capsids from the nucleus into the cytoplasm. The HCMV core nuclear egress complex (core NEC), a heterodimer of viral proteins pUL50 and pUL53, is therefore considered a promising target for new antiviral drugs. We have recently shown that a 29-mer peptide presenting an N-terminal alpha-helical hook-like segment of pUL53, through which pUL53 interacts with pUL50, binds to pUL50 with high affinity, and inhibits the pUL50–pUL53 interaction in vitro. Here, we show that this peptide is also able to interfere with HCMV infection of cells, as well as with core NEC formation in HCMV-infected cells. As the target of the peptide, i.e., the pUL50–pUL53 interaction, is localized at the inner nuclear membrane of the cell, the peptide had to be equipped with translocation moieties that facilitate peptide uptake into the cell and the nucleus, respectively. For the resulting fusion peptide (NLS-CPP-Hook), specific cellular and nuclear uptake into HFF cells, as well as inhibition of infection with HCMV, could be demonstrated, further substantiating the HCMV core NEC as a potential antiviral target.

Recent Advances and Trends in Chemical CPP-Drug Conjugation Techniques

This review summarizes recent developments in conjugation techniques for the synthesis of cell-penetrating peptide (CPP)–drug conjugates targeting cancer cells. We will focus on small organic molecules as well as metal complexes that were used as cytostatic payloads. Moreover, two principle ways of coupling chemistry will be discussed direct conjugation as well as the use of bifunctional linkers. While direct conjugation of the drug to the CPP is still popular, the use of bifunctional linkers seems to gain increasing attention as it offers more advantages related to the linker chemistry. Thus, three main categories of linkers will be highlighted, forming either disulfide acid-sensitive or stimuli-sensitive bonds. All techniques will be thoroughly discussed by their pros and cons with the aim to help the reader in the choice of the optimal conjugation technique that might be used for the synthesis of a given CPP–drug conjugate

Affinity Control of Monosaccharide Conjugated Peptides against Lectins with a Set of Amino Acid Substitutions on α-Helical Structures

Saccharides are well-known to play important roles in various biological events through specific interactions with target molecules such as carbohydrate-binding proteins (so-called lectins). Although characterization and identification of lectin molecules with saccharides are essential to understand biological events, they are still difficult due to weak interactions of saccharides, especially with monosaccharides. Herein, we demonstrate enhancement and control of monosaccharide affinity toward lectin proteins using chemical conjugation of monosaccharides with structurally regulated peptide and amino acid substitution. Thermodynamic analyses of the interactions by isothermal calorimetry measurements were performed to characterize the interactions between monosaccharide-conjugated peptide and the lectin molecules in detail. Conjugation with α-helical 16-mer short peptides drastically enhanced the affinity to lectins as compared with peptides with random coil structures, indicating that the α-helical peptide-based scaffold cooperatively interacted with lectins through additional interactions by suitable amino acids. Furthermore, suitable arrangement of the amino acids surrounding the monosaccharides on the α-helix afforded the conjugated peptides with varied affinities for two types of lectins. Our results indicate that the affinity of monosaccharide-conjugated peptides toward lectins is generally designable by appropriate conjugation of a simple monosaccharide with designed peptides, leading to the construction of a monosaccharide-modified peptide microarray toward high-throughput identification and/or screening of lectins in various biological events.

pH-Responsive PEG-Shedding and Targeting Peptide-Modified Nanoparticles for Dual-Delivery of Irinotecan and microRNA to Enhance Tumor-Specific Therapy

Irinotecan is one of the main chemotherapeutic agents for colorectal cancer (CRC). MicroRNA-200 (miR-200) has been reported to inhibit metastasis in cancer cells. Herein, pH-sensitive and peptide-modified liposomes and solid lipid nanoparticles (SLN) are designed for encapsulation of irinotecan and miR-200, respectively. These peptides include one cell-penetrating peptide, one ligand targeted to tumor neovasculature undergoing angiogenesis, and one mitochondria-targeting peptide. The peptide-modified nanoparticles are further coated with a pH-sensitive PEG-lipid derivative with an imine bond. These specially-designed nanoparticles exhibit pH-responsive release, internalization, and intracellular distribution in acidic pH of colon cancer HCT116 cells. These nanoparticles display low toxicity to blood and noncancerous intestinal cells. Delivery of miR-200 by SLN further increases the cytotoxicity of irinotecan-loaded liposomes against CRC cells by triggering apoptosis and suppressing RAS/β-catenin/ZEB/multiple drug resistance (MDR) pathways. Using CRC-bearing mice, the in vivo results further indicate that irinotecan and miR-200 in pH-responsive targeting nanoparticles exhibit positive therapeutic outcomes by inhibiting colorectal tumor growth and reducing systemic toxicity. Overall, successful delivery of miR and chemotherapy by multifunctional nanoparticles may modulate β-catenin/MDR/apoptosis/metastasis signaling pathways and induce programmed cancer cell death. Thus, these pH-responsive targeting nanoparticles may provide a potential regimen for effective treatment of colorectal cancer.

Design of a new pH-activatable cell-penetrating peptide for drug delivery into tumor cells

Cell-penetrating peptides (CPPs) have been considered as potential drug delivery vectors due to their remarkable membrane translocation capacity. However, lack of specificity and extreme systemic toxicity hamper their successful application for drug delivery. Here, we designed a new pH-activatable CPP, LHHLLHHLHHLLHH-NH₂ (LH), by substitution of all lysines and two leucines of LKKLLKLLKKLLKL-NH₂ (LK) with histidines. As expected, histidine-rich LH could be activated and penetrate into cells at pH 6.0, whereas its membrane transduction activity could be shielded at pH 7.4. In contrast, LK showed no obviously different cellular uptake at both pH conditions. Importantly, LH was significantly less cytotoxicity compared with LK at both pH values, suggesting a better safety for further application. In addition, after conjugation of camptothecin (CPT) with LH, this conjugate displayed remarkably pH-dependent antitumor activity than free CPT and LK-CPT. This study provides a new tumor pH-responsive CPP with low toxicity for selective anticancer drug delivery.

Channel current analysis estimates the pore-formation and the penetration of transmembrane peptides

We measured the current signal of the transmembrane model peptides using the barrel-stave, toroidal pore, and penetration models in order to establish a precise assignment of the channel signals.

Enhancing Anticancer Effect of Gefitinib across the Blood-Brain Barrier Model Using Liposomes Modified with One α-Helical Cell-Penetrating Peptide or Glutathione and Tween 80

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI), such as gefitinib, have been demonstrated to effectively treat the patients of extracranial non-small cell lung cancer (NSCLC). However, these patients often develop brain metastasis (BM) during their disease course. The major obstacle to treat BM is the limited penetration of anticancer drugs across the blood-brain barrier (BBB). In the present study, we utilized gefitinib-loaded liposomes with different modifications to improve gefitinib delivery across the in vitro BBB model of bEnd.3 cells. Gefitinib was encapsulated in small unilamellar liposomes modified with glutathione (GSH) and Tween 80 (SUV-G+T; one ligand plus one surfactant) or RF (SUV-RF; one α-helical cell-penetrating peptide). GSH, Tween 80, and RF were tested by the sulforhodamine B (SRB) assay to find their non-cytotoxic concentrations on bEnd.3 cells. The enhancement on gefitinib across the BBB was evaluated by cytotoxicity assay on human lung adenocarcinoma PC9 cells under the bEnd.3 cells grown on the transwell inserts. Our findings showed that gefitinib incorporated in SUV-G+T or SUV-RF across the bEnd.3 cells significantly reduced the viability of PC9 cells more than that of free gefitinib. Furthermore, SUV-RF showed no cytotoxicity on bEnd.3 cells and did not affect the transendothelial electrical resistance (TEER) and transendothelial permeability of sodium fluorescein across the BBB model. Moreover, flow cytometry and confocal laser scanning microscopy were employed to evaluate the endocytosis pathways of SUV-RF. The results indicated that the uptake into bEnd.3 cells was mainly through adsorptive-mediated mechanism via electrostatic interaction and partially through clathrin-mediated endocytosis. In conclusion, cell penetrating peptide-conjugated SUV-RF shed light on improving drug transport across the BBB via modulating the transcytosis pathway(s).

A Cell Microarray Format: A Peptide Release System Using a Photo-Cleavable Linker for Cell Toxicity and Cell Uptake Analysis

There has been increasing interest in the potential use of microarray technologies to perform systematic and high-throughput cell-based assays. We are currently focused on developing more practical array formats and detection methods that will enable researchers to conduct more detailed analyses in cell microarray studies. In this chapter, we describe the construction of a novel peptide-array format system for analyzing cellular toxicity and cellular uptake. In this system, a peptide is immobilized at the bottom of a conventional 96-well plate using a photo-cleavable linker. The peptide can then be released from the bottom by irradiating the desired wells with UV light, thus allowing the cytotoxicity or cellular uptake of the peptide to be monitored. This system will facilitate the realization of high-throughput cell arrays for cellomics analyses and cell-based phenotypic drug screens.

Interaction of amphiphilic α-helical cell-penetrating peptides with heparan sulfate

Cell-penetrating peptides (CPPs) are able to be taken up by cells and can deliver macromolecular cargos. However, the mechanism of this internalization is not yet fully understood. Recent theories suggest that the binding of cationic CPPs to negatively charged extracellular glycosaminoglycans, such as heparan sulfate (HS), is a possible mechanism of cellular uptake (CU). Our group has screened the CU activities of 54 systematically designed amphiphilic α-helical peptides in HeLa cells. Notably, a mutation in even a single residue significantly alters the CU ability of a peptide. To determine the structure-CU activity relationship of CPPs, four peptides, which contain a difference in one or two amino acids (i.e., Arg/Glu and Ala/Phe), were chosen from our CPP library to examine their interactions with HS. Fluorescence spectroscopy, isothermal titration calorimetry (ITC) and dynamic light scattering analysis indicated that the HS-binding affinities and HS-clustering abilities of the four CPPs correlated well with their CU activities in HeLa and A549 cells. The heat capacities of the CPPs, determined using ITC and binding free energy decomposition analyses in molecular dynamics simulations, revealed that electrostatic interactions were more dominant in the HS-binding processes of Arg-containing peptides in comparison to Glu-containing peptides, whereas hydrophobic contributions were the primary mode of interaction of Phe-containing peptides in comparison to Ala-containing peptides. Furthermore, it was implied that hydrophobic interactions may be more favourable than electrostatic interactions during the CU process.

Superior cell penetration by a rigid and anisotropic synthetic protein

Molecules with structural anisotropy and rigidity, such as asbestos, demonstrate high cell-penetrating activity but also high toxicity. Here we synthesize a biodegradable, rigid, and fibrous artificial protein, CCPC 140, as a potential vehicle for cellular delivery. CCPC 140 penetrated 100% of cells tested in vitro, even at a concentration of 3.1 nM-superior to previously reported cell-penetrating peptides. The effects of cell-strain-dependency and aspect ratio on the cell-penetrating activity of CCPC 140 were also investigated.

Cellular differentiation assessments by measuring the degree of cellular internalization and membrane adsorption using designed peptides

We demonstrate examples of cellular differentiation assessments, including cellular neurite outgrowth and fat cell maturation, by measuring the degree of membrane adsorption or cellular internalization using designed peptides. Because changes in the cellular membrane and cytosol during differentiation were shown to influence membrane adsorption and cellular internalization, we could successfully evaluate the extent of differentiation simply like stain indicators.