PNC-28, a p53-derived peptide that is cytotoxic to cancer cells, blocks pancreatic cancer cell growthin vivo

Targeting androgen receptor (AR) with a synthetic peptide increases apoptosis in triple negative breast cancer and AR-expressing prostate cancer cell lines

BACKGROUND

The androgen receptor (AR) has been studied as an approach to cancer therapy.

AIMS

We used human breast cancer-derived cells with high, low, and very low expression levels of AR, in addition to prostate cancer-derived LNCaP and DU-145 cells as a positive and negative controls to examine apoptosis caused by a synthetic peptide that targets ARs.

METHODS AND RESULTS

The peptide was produced to inhibit AR transactivation in breast cancer cell lines. We then measured cell viability, caspase-3 activity, and the ratio of Bax/Bcl-2. The findings indicated that the peptide (100-500 nM) in the presence of dihydrotestosterone (DHT) reduced cell growth in cells with high and low expression level of AR (p < .001), but not in cells with very low levels of AR. Treatment with 100-500 nM of peptide activated caspase-3 and increased the ratio of Bax/Bcl-2 in cells with high and low expression levels of AR. Also, increasing concentrations of the peptide (100-500 nM) reduced BrdU incorporation in the presence of DHT and promoted apoptosis in cells with high and low expression levels of AR (p < .001).

CONCLUSION

The findings indicate the peptide significantly increased apoptosis in cancer cells.

Recent Advances of Cell-Penetrating Peptides and Their Application as Vectors for Delivery of Peptide and Protein-Based Cargo Molecules

Peptides and proteins, two important classes of biomacromolecules, play important roles in the biopharmaceuticals field. As compared with traditional drugs based on small molecules, peptide- and protein-based drugs offer several advantages, although most cannot traverse the cell membrane, a natural barrier that prevents biomacromolecules from directly entering cells. However, drug delivery via cell-penetrating peptides (CPPs) is increasingly replacing traditional approaches that mediate biomacromolecular cellular uptake, due to CPPs' superior safety and efficiency as drug delivery vehicles. In this review, we describe the discovery of CPPs, recent developments in CPP design, and recent advances in CPP applications for enhanced cellular delivery of peptide- and protein-based drugs. First, we discuss the discovery of natural CPPs in snake, bee, and spider venom. Second, we describe several synthetic types of CPPs, such as cyclic CPPs, glycosylated CPPs, and D-form CPPs. Finally, we summarize and discuss cell membrane permeability characteristics and therapeutic applications of different CPPs when used as vehicles to deliver peptides and proteins to cells, as assessed using various preclinical disease models. Ultimately, this review provides an overview of recent advances in CPP development with relevance to applications related to the therapeutic delivery of biomacromolecular drugs to alleviate diverse diseases.

PNC-27, a Chimeric p53-Penetratin Peptide Binds to HDM-2 in a p53 Peptide-like Structure, Induces Selective Membrane-Pore Formation and Leads to Cancer Cell Lysis

PNC-27, a 32-residue peptide that contains an HDM-2 binding domain and a cell-penetrating peptide (CPP) leader sequence kills cancer, but not normal, cells by binding to HDM-2 associated with the plasma membrane and induces the formation of pores causing tumor cell lysis and necrosis. Conformational energy calculations on the structure of PNC-27 bound to HDM-2 suggest that 1:1 complexes form between PNC-27 and HDM-2 with the leader sequence pointing away from the complex. Immuno-scanning electron microscopy was carried out with cancer cells treated with PNC-27 and decorated with an anti-PNC-27 antibody coupled to 6 nm gold particles and an anti-HDM-2 antibody linked to 15 nm gold particles. We found multiple 6 nm- and 15 nm-labeled gold particles in approximately 1:1 ratios in layered ring-shaped structures in the pores near the cell surface suggesting that these complexes are important to the pore structure. No pores formed in the control, PNC-27-treated untransformed fibroblasts. Based on the theoretical and immuno-EM studies, we propose that the pores are lined by PNC-27 bound to HDM-2 at the membrane surface with the PNC-27 leader sequence lining the pores or by PNC-27 bound to HDM-2.

Cell penetrating peptides: the potent multi-cargo intracellular carriers

Introduction: Cell penetrating peptides (CPPs) known as protein translocation domains (PTD), membrane translocating sequences (MTS), or Trojan peptides (TP) are able to cross biological membranes without clear toxicity using different mechanisms, and facilitate the intracellular delivery of a variety of bioactive cargos. CPPs could overcome some limitations of drug delivery and combat resistant strains against a broad range of diseases. Despite delivery of different therapeutic molecules by CPPs, they lack cell specificity and have a short duration of action. These limitations led to design of combined cargo delivery systems and subsequently improvement of their clinical applications. Areas covered: This review covers all our studies and other researchers in different aspects of CPPs such as classification, uptake mechanisms, and biomedical applications. Expert opinion: Due to low cytotoxicity of CPPs as compared to other carriers and final degradation to amino acids, they are suitable for preclinical and clinical studies. Generally, the efficiency of CPPs was suitable to penetrate the cell membrane and deliver different cargos to specific intracellular sites. However, no CPP-based therapeutic approach has approved by FDA, yet; because there are some disadvantages for CPPs including short half-life in blood, and nonspecific CPP-mediated delivery to normal tissue. Thus, some methods were used to develop the functions of CPPs in vitro and in vivo including the augmentation of cell specificity by activatable CPPs, specific transport into cell organelles by insertion of corresponding localization sequences, incorporation of CPPs into multifunctional dendrimeric or liposomal nanocarriers to improve selectivity and efficiency especially in tumor cells.

Targeting cell membrane HDM2: A novel therapeutic approach for acute myeloid leukemia

The E3 ligase human double minute 2 (HDM2) regulates the activity of the tumor suppressor protein p53. A p53-independent HDM2 expression has been reported on the membrane of cancer cells but not on that of normal cells. Herein, we first showed that membrane HDM2 (mHDM2) is exclusively expressed on human and mouse AML blasts, including leukemia stem cell (LSC)-enriched subpopulations, but not on normal hematopoietic stem cells (HSCs). Higher mHDM2 levels in AML blasts were associated with leukemia-initiating capacity, quiescence, and chemoresistance. We also showed that a synthetic peptide PNC-27 binds to mHDM2 and enhances the interaction of mHDM2 and E-cadherin on the cell membrane; in turn, E-cadherin ubiquitination and degradation lead to membrane damage and cell death of AML blasts by necrobiosis. PNC-27 treatment in vivo resulted in a significant killing of both AML "bulk" blasts and LSCs, as demonstrated respectively in primary and secondary transplant experiments, using both human and murine AML models. Notably, PNC-27 spares normal HSC activity, as demonstrated in primary and secondary BM transplant experiments of wild-type mice. We concluded that mHDM2 represents a novel and unique therapeutic target, and targeting mHDM2 using PNC-27 selectively kills AML cells, including LSCs, with minimal off-target hematopoietic toxicity.

Aptamer-displaying peptide amphiphile micelles as a cell-targeted delivery vehicle of peptide cargoes

Peptide amphiphile micelles (PAMs) are attractive vehicles for the delivery of a variety of therapeutic and prophylactic peptides. However, a key limitation of PAMs is their lack of preferential targeting ability. In this paper, we describe our design of a PAM system that incorporates a DNA oligonucleotide amphiphile (antitail amphiphile-AA) to form A/PAMs. A cell-targeting DNA aptamer with a 3' extension sequence (tail) complementary to the AA is annealed to the surface to form aptamer-displaying PAMs (Aptamer~A/PAMs). Aptamer~A/PAMs are small, anionic, stable nanoparticles capable of delivering a large mass percentage peptide amphiphile (PA) compared to targeting DNA components. Aptamer~A/PAMs are stable for over 4 h in the presence of biological fluids. Additionally, the aptamer retains its cell-targeting properties when annealed to the A/PAM, thus leading to enhanced delivery to a specifically-targeted B-cell leukemia cell line. This exciting modular technology can be readily used with a library of different targeting aptamers and PAs, capable of improving the bioavailability and potency of the peptide cargo.

Evaluation of the use of therapeutic peptides for cancer treatment

Cancer along with cardiovascular disease are the main causes of death in the industrialised countries around the World. Conventional cancer treatments are losing their therapeutic uses due to drug resistance, lack of tumour selectivity and solubility and as such there is a need to develop new therapeutic agents. Therapeutic peptides are a promising and a novel approach to treat many diseases including cancer. They have several advantages over proteins or antibodies: as they are (a) easy to synthesise, (b) have a high target specificity and selectivity and (c) have low toxicity. Therapeutic peptides do have some significant drawbacks related to their stability and short half-life. In this review, strategies used to overcome peptide limitations and to enhance their therapeutic effect will be compared. The use of short cell permeable peptides that interfere and inhibit protein-protein interactions will also be evaluated.

In vitro and in vivo delivery of therapeutic proteins using cell penetrating peptides

The failure of proteins to penetrate mammalian cells or target tumor cells restricts their value as therapeutic tools in a variety of diseases such as cancers. Recently, protein transduction domains (PTDs) or cell penetrating peptides (CPPs) have been shown to promote the delivery of therapeutic proteins or peptides into live cells. The successful delivery of proteins mainly depends on their physicochemical properties. Although, linear cell penetrating peptides are one of the most effective delivery vehicles; but currently, cyclic CPPs has been developed to potently transport bioactive full-length proteins into cells. Up to now, several small protein transduction domains from viral proteins including Tat or VP22 could be fused to other peptides or proteins to entry them in various cell types at a dose-dependent approach. A major disadvantage of PTD-fusion proteins is primary uptake into endosomal vesicles leading to inefficient release of the fusion proteins into the cytosol. Recently, non-covalent complex formation (Chariot) between proteins and CPPs has attracted a special interest to overcome some delivery limitations (e.g., toxicity). Many preclinical and clinical trials of CPP-based delivery are currently under evaluation. Generally, development of more efficient protein transduction domains would significantly increase the potency of protein therapeutics. Moreover, the synergistic or combined effects of CPPs with other delivery systems for protein/peptide drug delivery would promote their therapeutic effects in cancer and other diseases. In this review, we will describe the functions and implications of CPPs for delivering the therapeutic proteins or peptides in preclinical and clinical studies.

Single-Stranded DNA Assisted Cell Penetrating Peptide-DNA Conjugation Strategy for Intracellular Imaging of Nucleases

Cell penetrating peptides (CPPs) are very useful tools for delivery of DNA molecules into living cells without damaging the cell membranes. However, covalent conjugation of DNAs to CPPs is technically difficult, and the reactions between DNA and target nucleases are also liable to be affected by the cationic CPP molecules. In this work, we demonstrate that the electrostatic interactions between CPPs and single-stranded DNA (ssDNA) were stronger than those between CPP and double-stranded DNA (dsDNA). Taking advantage of this property, we developed an ssDNA protected CPP-DNA fluorescent probe which allowed for noninvasive and efficient cellular uptake and rapid imaging of target nucleases in living cells. The probe is highly sensitive and selective. This work represents the first example of using CPP-DNA conjugate to deliver DNA fluorescent probes for in situ imaging of nucleases within cells. The developed approach also holds great potential for the cellular delivery of other nucleic acid molecules for diagnosis or therapeutics purposes.

GFP-complementation assay to detect functional CPP and protein delivery into living cells

Efficient cargo uptake is essential for cell-penetrating peptide (CPP) therapeutics, which deliver widely diverse cargoes by exploiting natural cell processes to penetrate the cell’s membranes. Yet most current CPP activity assays are hampered by limitations in assessing uptake, including confounding effects of conjugated fluorophores or ligands, indirect read-outs requiring secondary processing, and difficulty in discriminating internalization from endosomally trapped cargo. Split-complementation Endosomal Escape (SEE) provides the first direct assay visualizing true cytoplasmic-delivery of proteins at biologically relevant concentrations. The SEE assay has minimal background, is amenable to high-throughput processes, and adaptable to different transient and stable cell lines. This split-GFP-based platform can be useful to study transduction mechanisms, cellular imaging, and characterizing novel CPPs as pharmaceutical delivery agents in the treatment of disease.

Cell-penetrating peptides: A tool for effective delivery in gene-targeted therapies

The current landscapes of novel therapeutic approaches rely mostly on gene-targeted technologies, enabling to fight rare genomic diseases, from infections to cancer and hereditary diseases. Although, reaching the action-site for this novel treatments requires to deliver nucleic acids, or other macromolecules into cells, which may pose difficult tasks to pharmaceutical companies. To overcome this technological limitation, a wide variety of vectors have been developed in the past decades and have proven to be successful in delivering various therapeutics. Cell-penetrating peptides (CPP) have been one of the technologies widely studied and have been increasingly used to transport small RNA/DNA, plasmids, antibodies, and nanoparticles into cells. Despite the already proved huge potential that these peptide-based approaches may suggest, few advances have been put to pharmacological or clinical use. This review will describe the origin, development, and usage of CPP to deliver therapeutic agents into cells, with special emphasis on their current application to gene-therapies. Specifically, we will describe the current trials being conducted to treat cancer, gene disorders, and autoimmune diseases using CPP-based therapies. © 2014 IUBMB Life, 66(3):182-194, 2014.

Cell-penetrating peptides: achievements and challenges in application for cancer treatment

One of the major hurdles to cure cancer lies in the low potency of currently available drugs, which could eventually be solved by using more potent therapeutic macromolecules, such as proteins or genes. However, although these macromolecules possess greater potency inside the cancer cells, the barely permeable cell membrane remains a formidable barrier to exert their efficacy. A widely used strategy is to use cell penetrating peptides (CPPs) to improve their intracellular uptake. Since the discovery of the first CPP, numerous CPPs have been derived from natural or synthesized products. Both in vitro and in vivo studies have demonstrated that those CPPs are highly efficient in transducing cargoes into almost all cell types. Therefore, to date, CPPs have been widely used for intracellular delivery of various cargoes, including peptides, proteins, genes, and even nanoparticles. In addition, recently, based on the successes of CPPs in cellular studies, their applications in vivo have been actively pursued. This review will focus on the advanced applications of CPP-based in vivo delivery of therapeutics (e.g., small molecule drugs, proteins, and genes). In addition, we will highlight certain updated applications of CPPs for intracellular delivery of nanoparticulate drug carriers, as well as several "smart" strategies for tumor targeted delivery of CPP-cargoes.

Peptides for cancer therapy: a drug-development opportunity and a drug-delivery challenge

Therapeutic peptides (TPs) are a class of peptide-based agents capable of eliciting a therapeutic response by modulation of targets within or on the surface of cells. TPs are advantageous because they are amenable to rational design, they have high specificity for their targets and can be made to target almost any protein of interest, including proteins for which we have no small-molecule drugs. Owing to this versatility, TPs have a great potential for cancer therapy in an age of personalized medicine, in which we need novel drugs to target the many novel pathways being discovered as tumor drivers. However, in order to utilize TPs as drugs, many obstacles must be overcome. TPs have short half-lives in systemic circulation, are easily degraded by proteases in plasma and target cells, are often cleared by the reticuloendothelial system and can be immunogenic. This article will discuss ways of overcoming many of these hurdles by utilizing macromolecular peptide delivery systems and tumor-targeting agents.

Light induced drug delivery into cancer cells

Cell-penetrating peptides (CPPs) can be used for intracellular delivery of a broad variety of cargoes, including various nanoparticulate pharmaceutical carriers. However, the cationic nature of all CPP sequences, and thus lack of cell specificity, limits their in vivo use for drug delivery applications. Here, we have devised and tested a strategy for site-specific delivery of dyes and drugs into cancer cells by using polymers bearing a light activated caged CPP (cCPP). The positive charge of Lys residues on the minimum sequence of the CPP penetratin ((52)RRMKWKK(58)) was masked with photo-cleavable groups to minimize non-specific adsorption and cellular uptake. Once illuminated by UV light, these protecting groups were cleaved, the positively charged CPP regained its activity and facilitated rapid intracellular delivery of the polymer-dye or polymer-drug conjugates into cancer cells. We have found that a 10-min light illumination time was sufficient to enhance the penetration of the polymer-CPP conjugates bearing the proapoptotic peptide, (D)(KLAKLAK)(2), into 80% of the target cells, and to promote a 'switch' like cytotoxic activity resulting a shift from 100% to 10% in cell viability after 2 h. This report provides an example for tumor targeting by means of light activation of cell-penetrating peptides for intracellular drug delivery.

Chondroitin sulfate as a molecular portal that preferentially mediates the apoptotic killing of tumor cells by penetratin-directed mitochondria-disrupting peptides

The use of cell-penetrating peptides (CPPs) as drug carriers for targeted therapy is limited by the unrestricted cellular translocation of CPPs. The preferential induction of tumor cell death by penetratin (Antp)-directed peptides (PNC27 and PNC28), however, suggests that the CPP Antp may contribute to the preferential cytotoxicity of these peptides. Using PNC27 as a molecular model, we constructed three novel peptides (PT, PR9, and PD3) by replacing the leader peptide Antp with one of three distinct CPPs (TAT, R9, or DPV3), respectively. The IC(50) values of PNC27 in tumor cells were 2-3 times lower than in normal cells. However, all three engineered peptides demonstrated similar cytotoxic effects in tumor and normal cells. Another three chimeric peptides containing the leader peptide Antp with different mitochondria-disrupting peptides (KLA-Antp (KGA), B27-Antp (BA27), and B28-Antp (BA28)), preferentially induced apoptosis in tumor cells. The IC(50) values of these peptides (3-10 microM) were 3-6 times lower in tumor cells than in normal cells. In contrast, TAT-directed peptides (TAT-KLA (TK), TAT-B27 (TB27), and TAT-B28 (TB28)), were cytotoxic to both tumor and normal cells. These data demonstrate that the leader peptide Antp contributes to the preferential cytotoxicity of Antp-directed peptides. Furthermore, Antp-directed peptides bind chondroitin sulfate (CS), and the removal of endogenous CS reduces the cytotoxic effects of Antp-directed peptides in tumor cells. The overexpression of CS in tumor cells is positively correlated to the cell entry and cytotoxicity of Antp- directed peptides. These results suggest that CS overexpression in tumor cells is an important molecular portal that mediates the preferential cytotoxicity of Antp-directed peptides.

Anticancer peptide PNC-27 adopts an HDM-2-binding conformation and kills cancer cells by binding to HDM-2 in their membranes

The anticancer peptide PNC-27, which contains an HDM-2-binding domain corresponding to residues 12-26 of p53 and a transmembrane-penetrating domain, has been found to kill cancer cells (but not normal cells) by inducing membranolysis. We find that our previously determined 3D structure of the p53 residues of PNC-27 is directly superimposable on the structure for the same residues bound to HDM-2, suggesting that the peptide may target HDM-2 in the membranes of cancer cells. We now find significant levels of HDM-2 in the membranes of a variety of cancer cells but not in the membranes of several untransformed cell lines. In colocalization experiments, we find that PNC-27 binds to cell membrane-bound HDM-2. We further transfected a plasmid expressing full-length HDM-2 with a membrane-localization signal into untransformed MCF-10-2A cells not susceptible to PNC-27 and found that these cells expressing full-length HDM-2 on their cell surface became susceptible to PNC-27. We conclude that PNC-27 targets HDM-2 in the membranes of cancer cells, allowing it to induce membranolysis of these cells selectively.

Twenty years of cell-penetrating peptides: from molecular mechanisms to therapeutics

The recent discovery of new potent therapeutic molecules that do not reach the clinic due to poor delivery and low bioavailability have made of delivery a key stone in therapeutic development. Several technologies have been designed to improve cellular uptake of therapeutic molecules, including cell-penetrating peptides (CPPs). CPPs were first discovered based on the potency of several proteins to enter cells. Numerous CPPs have been described so far, which can be grouped into two major classes, the first requiring chemical linkage with the drug for cellular internalization and the second involving formation of stable, non-covalent complexes with drugs. Nowadays, CPPs constitute very promising tools for non-invasive cellular import of cargo and have been successfully applied for in vitro and in vivo delivery of therapeutic molecules varying from small chemical molecule, nucleic acids, proteins, peptides, liposomes and particles. This review will focus on the structure/function and cellular uptake mechanism of CPPs in the general context of drug delivery. We will also highlight the application of peptide carriers for the delivery of therapeutic molecules and provide an update of their clinical evaluation.

This article is part of a themed section on Vector Design and Drug Delivery. For a list of all articles in this section see the end of this paper, or visit: http://www3.interscience.wiley.com/journal/121548564/issueyear?year=2009

Electronic Structure and Physicochemical Properties Characterization of the Amino Acids 12−26 of TP53: A Theoretical Study

PNC-27, a synthetic peptide, is derived from the TP53-HDM2 binding domain that include TP53 amino acids 12-26 linked with 17 amino acids from the antennapedia protein transference domain. This peptide induces membrane rupture in tumor cells through toroidal pores formation and has motivated several experimental studies; nonetheless, its mechanism of biological action remains unknown to date. Herein, we present a theoretical study at the Hartree-Fock and density functional theory (B3LYP) levels of theory of TP53 protein residues 12-26 (PPLSQETFSDLWKLL) in order to characterize its electronic structure and physicochemical properties. Our results for atomic and group charges, fitted to the electrostatic potential (ESP) show important reactive sites (L14, S15, T18, S20, L25, and L26), suggesting that these amino acids are exposed to nucleophilic and electrophilic attacks. Analysis of bond orders, intramolecular interactions and of several global reactivity descriptors, such as ionization potentials, hardness, electrophilicity index, dipole moments, total energies, frontier molecular orbitals (HOMO-LUMO), and electrostatic potential, led us to characterize active sites and the electronic structure and physiochemical features that taken together may be important in understanding the specific selectivity for this peptides type's cancer-cell membrane lysis properties.