Identification and characterization of novel protein-derived arginine-rich cell-penetrating peptides

Development and evaluation of a radiolabelling agent for white blood cell scans

Radiolabelled autologous leukocytes have been used for the clinical diagnosis of inflammation and infection. To develop a stable and efficient radiopharmaceutical for labelling leukocytes, we prepared a novel radioiodinated cell-penetrating peptide, 125I-TAT, using a bi-functional linker. 125I-TAT was stable for two days under three different temperature conditions of -20 °C, 4 °C, and 40 °C, with its radiochemical purity remaining over 99%. Iodinated TAT was non-toxic to leukocytes with an IC50 value of over 100 μM. The labelling efficiency of 125I-TAT using 1ｘ107 cells ranged from 27% to 53% when the three leukocyte cell lines were pre-treated with DMSO. This is comparable to the labelling efficiency recommended by the guideline for conventional labelling agents using 2ｘ108 cells. Radioiodinated cell-penetrating peptide may be an improved radiopharmaceutical for white blood cell scans by further optimization.

Cell-Penetrating and Enzyme-Responsive Peptides for Targeted Cancer Therapy: Role of Arginine Residue Length on Cell Penetration and In Vivo Systemic Toxicity

For the improved delivery of cancer therapeutics and imaging agents, the conjugation of cell-penetrating peptides (CPPs) increases the cellular uptake and water solubility of agents. Among the various CPPs, arginine-rich peptides have been the most widely used. Combining CPPs with enzyme-responsive peptides presents an innovative strategy to target specific intracellular enzymes in cancer cells and when combined with the appropriate click chemistry can enhance theranostic drug delivery through the formation of intracellular self-assembled nanostructures. However, one drawback of CPPs is their high positive charge which can cause nonspecific binding, leading to off-target accumulation and potential toxicity. Hence, balancing cell-specific penetration, toxicity, and biocompatibility is essential for future clinical efficacy. We synthesized six cancer-specific, legumain-responsive RnAANCK peptides containing one to six arginine residues, with legumain being an asparaginyl endopeptidase that is overexpressed in aggressive prostate tumors. When conjugated to Alexa Fluor 488, R1-R6AANCK peptides exhibited a concentration- and time-dependent cell penetration in prostate cancer cells, which was higher for peptides with higher R values, reaching a plateau after approximately 120 min. Highly aggressive DU145 prostate tumor cells, but not less aggressive LNCaP cells, self-assembled nanoparticles in the cytosol after the cleavage of the legumain-specific peptide. The in vivo biocompatibility was assessed in mice after the intravenous injection of R1-R6AANCK peptides, with concentrations ranging from 0.0125 to 0.4 mmol/kg. The higher arginine content in R4-6 peptides showed blood and urine indicators for the impairment of bone marrow, liver, and kidney function in a dose-dependent manner, with instant hemolysis and morbidity in extreme cases. These findings underscore the importance of designing peptides with the optimal arginine residue length for a proper balance of cell-specific penetration, toxicity, and in vivo biocompatibility.

Transdermal Properties of Cell-Penetrating Peptides: Applications and Skin Penetration Mechanisms

Cell-penetrating peptides (CPPs) consist of 5-30 amino acids with intracellular transduction abilities and diverse physicochemical properties, origins, and sequences. Although recent developments in bioinformatics have facilitated the prediction of CPP candidates with the potential for transduction into cells, the mechanisms by which CPPs penetrate cells and various tissues have not yet been elucidated at the molecular interaction level. Recently, the skin-penetrating ability of CPPs has gained wide attention and emerged as a simple and effective strategy for the delivery of macromolecules into the skin. Studies on the skin structure have suggested that the penetration potential of CPPs is based on the molecular interactions and characteristics of the lipid lamellar structure between corneocytes in the stratum corneum. This review provides a brief overview of the general properties, transduction mechanisms, applications, and safety issues of CPPs, focusing on CPPs with transdermal properties, that are currently being used to develop therapeutics and cosmetics.

Engineered phage with cell-penetrating peptides for intracellular bacterial infections

IMPORTANCE

Salmonella infection is a significant threat to global public health, and the increasing prevalence of antibiotic resistance exacerbates the situation. Therefore, finding new and effective ways to combat this pathogen is essential. Phages are natural predators of bacteria and can be used as an alternative to antibiotics to kill specific bacteria, including drug-resistant strains. One significant limitation of using phages as antimicrobial agents is their low cellular uptake, which limits their effectiveness against intracellular bacterial infections. Therefore, finding ways to enhance phage uptake is crucial. Our study provides a straightforward strategy for displaying cell-penetrating peptides on non-model phages, offering a promising novel and effective therapeutic approach for treating intracellular and drug-resistant bacteria. This approach has the potential to address the global challenge of antibiotic resistance and improve public health outcomes.

Biotherapeutic effect of cell-penetrating peptides against microbial agents: a review

Selective permeability of biological membranes represents a significant barrier to the delivery of therapeutic substances into both microorganisms and mammalian cells, restricting the access of drugs into intracellular pathogens. Cell-penetrating peptides usually 5-30 amino acids with the characteristic ability to penetrate biological membranes have emerged as promising antimicrobial agents for treating infections as well as an effective delivery modality for biological conjugates such as nucleic acids, drugs, vaccines, nanoparticles, and therapeutic antibodies. However, several factors such as antimicrobial resistance and poor drug delivery of the existing medications justify the urgent need for developing a new class of antimicrobials. Herein, we review cell-penetrating peptides (CPPs) used to treat microbial infections. Although these peptides are biologically active for infections, effective transduction into membranes and cargo transport, serum stability, and half-life must be improved for optimum functions and development of next-generation antimicrobial agents.

B3Pred: A Random-Forest-Based Method for Predicting and Designing Blood-Brain Barrier Penetrating Peptides

The blood–brain barrier is a major obstacle in treating brain-related disorders, as it does not allow the delivery of drugs into the brain. We developed a method for predicting blood–brain barrier penetrating peptides to facilitate drug delivery into the brain. These blood–brain barrier penetrating peptides (B3PPs) can act as therapeutics, as well as drug delivery agents. We trained, tested, and evaluated our models on blood–brain barrier peptides obtained from the B3Pdb database. First, we computed a wide range of peptide features. Then, we selected relevant peptide features. Finally, we developed numerous machine-learning-based models for predicting blood–brain barrier peptides using the selected features. The random-forest-based model performed the best with respect to the top 80 selected features and achieved a maximal 85.08% accuracy with an AUROC of 0.93. We also developed a webserver, B3pred, that implements our best models. It has three major modules that allow users to predict/design B3PPs and scan B3PPs in a protein sequence.

In silico identification and experimental validation of cellular uptake by a new cell penetrating peptide P1 derived from MARCKS

Viral vectors for vaccine delivery are challenged by recently reported safety issues like immunogenicity and risk for cancer development, and thus there is a growing need for the development of non-viral vectors. Cell penetrating peptides (CPPs) are non-viral vectors that can enter plasma membranes efficiently and deliver a broad range of cargoes. Our bioinformatic prediction and wet-lab validation data suggested that peptide P1 derived from MARCKS protein phosphorylation site domain is a new potential CPP candidate. We found that peptide P1 can efficiently internalize into various cell lines in a concentration-dependent manner. Receptor-mediated endocytosis pathway is the major mechanism of P1 penetration, although P1 also directly penetrates the plasma membrane. We also found that peptide P1 has low cytotoxicity in cultured cell lines as well as mouse red blood cells. Furthermore, peptide P1 not only can enter into cultured cells itself, but it also can interact with plasmid DNA and mediate the functional delivery of plasmid DNA into cultured cells, even in hard-to-transfect cells. Combined, these findings indicate that P1 may be a promising vector for efficient intracellular delivery of bioactive cargos.

Exploring novel and potent cell penetrating peptides in the proteome of SARS-COV-2 using bioinformatics approaches

Among various delivery systems for vaccine and drug delivery, cell-penetrating peptides (CPPs) have been known as a potent delivery system because of their capability to penetrate cell membranes and deliver some types of cargoes into cells. Several CPPs were found in the proteome of viruses such as Tat originated from human immunodeficiency virus-1 (HIV-1), and VP22 derived from herpes simplex virus-1 (HSV-1). In the current study, a wide-range of CPPs was identified in the proteome of SARS-CoV-2, a new member of coronaviruses family, using in silico analyses. These CPPs may play a main role for high penetration of virus into cells and infection of host. At first, we submitted the proteome of SARS-CoV-2 to CellPPD web server that resulted in a huge number of CPPs with ten residues in length. Afterward, we submitted the predicted CPPs to C2Pred web server for evaluation of the probability of each peptide. Then, the uptake efficiency of each peptide was investigated using CPPred-RF and MLCPP web servers. Next, the physicochemical properties of the predicted CPPs including net charge, theoretical isoelectric point (pI), amphipathicity, molecular weight, and water solubility were calculated using protparam and pepcalc tools. In addition, the probability of membrane binding potential and cellular localization of each CPP were estimated by Boman index using APD3 web server, D factor, and TMHMM web server. On the other hand, the immunogenicity, toxicity, allergenicity, hemolytic potency, and half-life of CPPs were predicted using various web servers. Finally, the tertiary structure and the helical wheel projection of some CPPs were predicted by PEP-FOLD3 and Heliquest web servers, respectively. These CPPs were divided into: a) CPP containing tumor homing motif (RGD) and/or tumor penetrating motif (RXXR); b) CPP with the highest Boman index; c) CPP with high half-life (~100 hour) in mammalian cells, and d) CPP with +5.00 net charge. Based on the results, we found a large number of novel CPPs with various features. Some of these CPPs possess tumor-specific motifs which can be evaluated in cancer therapy. Furthermore, the novel and potent CPPs derived from SARS-CoV-2 may be used alone or conjugated to some sequences such as nuclear localization sequence (NLS) for vaccine and drug delivery.

Identification of a novel cell-penetrating peptide derived from the capsid protein of chicken anemia virus and its application in gene delivery

Cell membranes are a great obstacle for entrance of gene therapeutic agents. Cell-penetrating peptides (CPPs) have been proven as a promising gene delivery tool. However, the early TAT peptide derived from the HIV transcription activator protein has been proven that the sequence contains Furin protease cleaved motifs which limited the TAT application in delivery of exogenous active molecules. In the present study, through the bioinformatics and experimental approach, we have identified a novel CPP derived from the N terminus of VP1 protein of chicken anemia virus (CAV), designated as CVP1-N2, which is rich in arginine residues and contains α-helical structure. Then, the ability of CVP1-N2 cell penetrating was detected using confocal imaging and flow cytometry. FITC-labeled CVP1-N2 peptide could rapidly internalize into different types of live cells with dose dependence and without cytotoxic effects by MTT assay. Surprisingly, CVP1-N2 with a pattern of nuclear sub-location has shown the higher uptake efficiency than TAT. At 10, 1, and 0.1 μM, the mean relative internalization of CVP1-N2 was respectively 1.08-, 12-, and 75-fold higher than that of CVP1, as well as 1.6-, 56-, and 75-fold higher than that of TAT. Moreover, using endocytic inhibitors along with low-temperature stress validated that the CVP1-N2 internalization route is direct translocation pathway. Finally, the capacity of CVP1-N2 for delivery of gene into cells was determined, where it was able to carry red fluorescent protein (RFP) and apoptin genes into cells respectively and induce the apoptosis. All these data indicate that CVP1-N2 could be used as a novel gene delivery vehicle for gene therapy in the future. KEY POINTS: • 1CVP1-N2 was identified as a novel more efficient cell-penetrating peptide. • 2. CVP1-N2 localized to the nucleus through the direct transduction pathway. • 3. CVP1-N2 was able to deliver the apoptin gene into HCT116 cells and induce apoptosis.

To What Extent Do Fluorophores Bias the Biological Activity of Peptides? A Practical Approach Using Membrane-Active Peptides as Models

The characterization of biologically active peptides relies heavily on the study of their efficacy, toxicity, mechanism of action, cellular uptake, or intracellular location, using both in vitro and in vivo studies. These studies frequently depend on the use of fluorescence-based techniques. Since most peptides are not intrinsically fluorescent, they are conjugated to a fluorophore. The conjugation may interfere with peptide properties, thus biasing the results. The selection of the most suitable fluorophore is highly relevant. Here, a comprehensive study with blood-brain barrier (BBB) peptide shuttles (PepH3 and PepNeg) and antimicrobial peptides (AMPs) (vCPP2319 and Ctn[15-34]), tested as anticancer peptides (ACPs), having different fluorophores, namely 5(6)-carboxyfluorescein (CF), rhodamine B (RhB), quasar 570 (Q570), or tide fluor 3 (TF3) attached is presented. The goal is the evaluation of the impact of the selected fluorophores on peptide performance, applying routinely used techniques to assess cytotoxicity/toxicity, secondary structure, BBB translocation, and cellular internalization. Our results show that some fluorophores significantly modulate peptide activity when compared with unlabeled peptides, being more noticeable in hydrophobic and charged fluorophores. This study highlights the need for a careful experimental design for fluorescently labeled molecules, such as peptides.

Multifunctional nanoparticles of paclitaxel and cyclodextrin-polypeptide conjugates with in vitro anticancer activity

In this study, the cyclodextrin polypeptide (R8-CMβCD) was successfully synthesized by the conjugation of a cell-penetrating peptide (R8) with carboxymethyl-β-cyclodextrin (CMβCD) via the carbon diamine reaction. Then, paclitaxel-loaded nanoparticles (PTX@R8-CMβCD NPs) was prepared. Results of transmission electron microscopy (TEM) showed that PTX@R8-CMβCD NPs were spherical with smooth surfaces and an average diameter about 144 nm. The amount of PTX released from NPs was less than 20% at pH7.4, but it increased significantly to 80% in the weakly acidic cytoplasm of tumors (pH5.0). Furthermore, PTX@R8-CMβCD NPs promoted the cellular uptake of PTX. Further studies on the mechanism showed that cellular uptake of PTX@R8-CMβCD NPs could rely on multiple pathways. In addition, the NPs had the ability to inhibit P-gp efflux pumps. Cytotoxicity tests showed that the NPs had no side effects. Taken together, PTX@R8-CMβCD NPs is an effective anticancer drug delivery system, and the material (R8-CMβCD) may be a promising anti-cancer drug carrier.

PRRDB 2.0: a comprehensive database of pattern-recognition receptors and their ligands

PRRDB 2.0 is an updated version of PRRDB that maintains comprehensive information about pattern-recognition receptors (PRRs) and their ligands. The current version of the database has ~2700 entries, which are nearly five times of the previous version. It contains extensive information about 467 unique PRRs and 827 pathogens-associated molecular patterns (PAMPs), manually extracted from ~600 research articles. It possesses information about PRRs and PAMPs that has been extracted manually from research articles and public databases. Each entry provides comprehensive details about PRRs and PAMPs that includes their name, sequence, origin, source, type, etc. We have provided internal and external links to various databases/resources (like Swiss-Prot, PubChem) to obtain further information about PRRs and their ligands. This database also provides links to ~4500 experimentally determined structures in the protein data bank of various PRRs and their complexes. In addition, 110 PRRs with unknown structures have also been predicted, which are important in order to understand the structure-function relationship between receptors and their ligands. Numerous web-based tools have been integrated into PRRDB 2.0 to facilitate users to perform different tasks like (i) extensive searching of the database; (ii) browsing or categorization of data based on receptors, ligands, source, etc. and (iii) similarity search using BLAST and Smith-Waterman algorithm.

Dynamic signature of ligand binding over a protein surface

We study the motion of Zn^{2+} in the presence of ubiquitin by all-atom molecular-dynamics simulations. We observe that unlike normal diffusive liquid, metal ions show an exponential tail in the self-van Hove function (self-vHf). Moreover, the metal ions are trapped strongly by acidic residues which form a binding pocket over the protein surface. The exponential tail disappears by mutation of trapping residues, suggesting that the tail appears due to trapped motion of the ions. The mean-squared displacements, however, in all the cases show linear dependence on time. Our model establishes that ligand binding generically results in an exponential tail of self-vHf. The self-vHf may give an approach to find binding pockets over a protein surface.

DNA/Lysozyme-binding affinity study of novel peptides from TAT (47-57) and BRCA1 (782-786) in vitro by spectroscopic analysis

SISLL-TAT and TAT-SISLL were synthesized by modifying the N- or C-termini of cell-penetrating peptides as transacting activator of transcription TAT (47-57) by attaching BRCA1 (782-786) (SISLL). The novel peptides were synthesized through Fmoc solid-phase synthesis procedures and characterized by LCQ Fleet MS, ¹H NMR and ¹³C NMR. SISLL-TAT and TAT-SISLL displayed forceful antibacterial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella typhimurium with low hemolysis. SISLL-TAT showed better antibacterial activity than TAT-SISLL, with the minimum inhibitory concentration (MIC) values of 10-33 μg·mL^-1. The results of the DNA-binding activities showed that both SISLL-TAT and TAT-SISLL could interact with DNA via the minor groove mode, and the binding constants were 4.97 × 10⁵ L·mol^-1 and 4.42 × 10⁵ L·mol^-1 at 310 K, respectively. Circular dichroism analysis showed slight transformation of the lysozyme secondary structure caused by SISLL-TAT and TAT-SISLL. We also found that the novel peptides SISLL-TAT and TAT-SISLL targeted bacterial DNA resulting in cell death. This explains the antibacterial mechanism of SISLL-TAT and TAT-SISLL, and is a solid theoretical basis for further designing novel and highly effective antibiotics for clinical application.

Protein moiety in oligochitosan modified vector regulates internalization mechanism and gene delivery: Polyplex characterization, intracellular trafficking and transfection

Oligochitosan-modified proteins have gained attention as efficient non-viral vectors for gene delivery. However, little information exists if protein moieties can serve as an important role for internalization and endosome escape ability of the genetic material. To explore this issue, we designed two cationic oligochitosan-modified vectors that consist of different proteins, namely a hydrophobic plant protein (zein) and a hydrophilic animal protein (ovalbumin (OVA)) to deliver pDNA to epithelial cell line CHO-K1 and HEK 293 T. These cationic vectors were systematically characterized by molecular weight, infrared (IR) structural analysis, transmission electron microscopy (TEM) morphology, and surface charge. A remarkable impact of protein moieties was observed on physiochemical properties of the developed vectors. Oligochitosan-modified zein containing hydrophobic protein exhibited high buffering capacity and excellent DNA binding ability compared to the oligochitosan-modified OVA. The data on transfection in the presence of endocytic inhibitors indicated that the caveolae-mediated pathway (CvME) played a key role in the internalization of the zein-based polyplex. However, the OVA-based polyplex was internalized in CHO-K1 cells via CvME and in HEK 293 T cells via the lipid-mediated pathway. Moreover, oligochitosan-modified zein exhibited lower cytotoxicity, greater lysosomal escape ability, better plasmid stability, and better transfection efficiency than the oligochitosan-modified OVA. This study offers a facile procedure for the synthesis of cationic vectors and elucidates the relationship that exists between protein moieties and transfection activity, thus providing an alternative, non-viral platform for the gene delivery.

In Silico Tools and Databases for Designing Peptide-Based Vaccine and Drugs

The prolonged conventional approaches of drug screening and vaccine designing prerequisite patience, vigorous effort, outrageous cost as well as additional manpower. Screening and experimentally validating thousands of molecules for a specific therapeutic property never proved to be an easy task. Similarly, traditional way of vaccination includes administration of either whole or attenuated pathogen, which raises toxicity and safety issues. Emergence of sequencing and recombinant DNA technology led to the epitope-based advanced vaccination concept, i.e., small peptides (epitope) can stimulate specific immune response. Advent of bioinformatics proved to be an adjunct in vaccine and drug designing. Genomic study of pathogens aid to identify and analyze the protective epitope. A number of in silico tools have been developed to design immunotherapy as well as peptide-based drugs in the last two decades. These tools proved to be a catalyst in drug and vaccine designing. This review solicits therapeutic peptide databases as well as in silico tools developed for designing peptide-based vaccine and drugs.

Efficient therapeutic delivery by a novel cell-permeant peptide derived from KDM4A protein for antitumor and antifibrosis

Cell-penetrating peptide (CPP) based delivery have provided immense potential for the therapeutic applications, however, most of nonhuman originated CPPs carry the risk of possible cytotoxicity and immunogenicity, thus may restricting to be used. Here, we describe a novel human-derived CPP, denoted hPP10, and hPP10 has cell-penetrating properties evaluated by CellPPD web server, as well as In-Vitro and In-Vivo analysis. In vitro studies showed that hPP10-FITC was able to penetrate into various cells including primary cultured cells, likely through an endocytosis pathway. And functionalized macromolecules, such as green fluorescent protein (GFP), tumor-specific apoptosis inducer Apoptin as well as biological active enzyme GCLC (Glutamate-cysteine ligase, catalytic subunit) can be delivered by hPP10 in vitro and in vivo. Collectively, our results suggest that hPP10 provide a novel and versatile tool to deliver exogenous proteins or drugs for clinical applications as well as reprogrammed cell-based therapy.

Contiguous hydrophobic and charged surface patches in short helix-constrained peptides drive cell permeability

Different ways to get peptides into cells.

Towards topical microRNA-directed therapy for epidermal disorders

There remains an unmet dermatological need for innovative topical agents that achieve better longterm outcomes with fewer side effects. Modulation of the expression and activity of microRNA (miRNAs) represents an emerging translational framework for the development of such innovative therapies because changes in the expression of one miRNA can have wide-ranging effects on diverse cellular processes associated with disease. In this short review, the roles of miRNA in epidermal development, psoriasis, cutaneous squamous cell carcinoma and re-epithelisation are highlighted. Consideration is given to the delivery of oligonucleotides that mimic or inhibit miRNA function using vehicles such as cell penetrating peptides, spherical nucleic acids, deformable liposomes and liquid crystalline nanodispersions. Formulation of miRNA-directed oligonucleotides with such skin-penetrating epidermal agents will drive the development of RNA-based cutaneous therapeutics for deployment as primary or adjuvant therapies for epidermal disorders.

Surface density of polyarginine influence the size, zeta potential, cellular uptake and tissue distribution of the nanostructured lipid carrier

Poly-arginines are strong tools to elevate the cellular uptake of nanopreparations. To learn the influence of poly-arginine (RRRRRRRR, R8) density on a series of properties of nanostructured lipid carrier (NLC), we build six R8 modified NLCs with different R8 densities (nR-NLC, where n represents the R8 ratio) by fusion–emulsion method with the aid of stearyl-R8. The pharmaceutical characteristics like size, zeta potential and in vitro drug release, cellular uptake, cytotoxicity to A549 cells and tissue distribution in S180 tumor-bearing mice of the six nR-NLCs are all investigated. It turns out that with as little as 2% weight ratio of stearyl-R8 modified on NLC, its pharmaceutical properties, especially zeta potential changes astonishingly; however, the stearyl-R8 ratio should be higher than 4% to upgrade the cellular uptake and cytotoxicity evidently; in the ex vivo tissue distribution assessment, the nR-NLC with less than 8% R8 showed similar tissue accumulation, while NLC with 10% R8 shows obvious acute toxicity to mice. Our study pays attention to the effect of the R8 ratio on the changes of cargo properties, and the results indicate that this topic is essential and worth to be further developed.

Peptides as a therapeutic avenue for nanocarrier-aided targeting of glioma

INTRODUCTION

Very few successful interventions have been possible in glioma therapy owing to its aggressive nature as well as its hindrance of targeted therapy together with the limited access afforded by the blood-brain barrier (BBB). With the advent of nanotechnology based delivery vehicles such as micelles, dendrimers, polymer-based nanoparticles and nanogels, the breach of the BBB has been facilitated. However, there remains the issue of targeted therapy for glioma cells. Peptide-mediated surface modification of nanocarriers serves this purpose, extending the ability to target glioma further than the enhanced permeability and retention effect. Areas covered: Here we have tried to re-establish the significance of peptides that could be used in various ways for treating glioma. Peptide-embellished nanocarriers used to deliver anticancer drugs; nucleic acids (siRNA, miRNA); micelles or dendrimers grafted with immunogenic glioma-derived peptides used for stimulating active immunity in vaccine therapy, glioma targets for cell penetrating peptides and homing to specific receptors are reviewed. Expert opinion: Peptides have multifunctional potential in targeting, BBB and cell penetration, and can serve as antagonists of various ligands and agonists of particular over-expressed receptors as discussed in this review. Using peptides in targeted personalized therapy would be one step forward and may offer new avenues for glioma therapeutics.

Topical Delivery of Protein and Peptide Using Novel Cell Penetrating Peptide IMT-P8

Skin, being the largest organ of the body, is an important site for drug administration. However, most of the drugs have poor permeability and thus drug delivery through the skin is very challenging. In this study, we examined the transdermal delivery capability of IMT-P8, a novel cell-penetrating peptide. We generated IMT-P8-GFP and IMT-P8-KLA fusion constructs and evaluated their internalization into mouse skin after topical application. Our results demonstrate that IMT-P8 is capable of transporting green fluorescent protein (GFP) and proapoptotic peptide, KLA into the skin and also in different cell lines. Interestingly, uptake of IMT-P8-GFP was considerably higher than TAT-GFP in HeLa cells. After internalization, IMT-P8-KLA got localized to the mitochondria and caused significant cell death in HeLa cells signifying an intact biological activity. Further in vivo skin penetration experiments revealed that after topical application, IMT-P8 penetrated the stratum corneum, entered into the viable epidermis and accumulated inside the hair follicles. In addition, both IMT-P8-KLA and IMT-P8-GFP internalized into the hair follicles and dermal tissue of the skin following topical application. These results suggested that IMT-P8 could be a potential candidate to be used as a topical delivery vehicle for various cosmetic and skin disease applications.

SATPdb: a database of structurally annotated therapeutic peptides

SATPdb (http://crdd.osdd.net/raghava/satpdb/) is a database of structurally annotated therapeutic peptides, curated from 22 public domain peptide databases/datasets including 9 of our own. The current version holds 19192 unique experimentally validated therapeutic peptide sequences having length between 2 and 50 amino acids. It covers peptides having natural, non-natural and modified residues. These peptides were systematically grouped into 10 categories based on their major function or therapeutic property like 1099 anticancer, 10585 antimicrobial, 1642 drug delivery and 1698 antihypertensive peptides. We assigned or annotated structure of these therapeutic peptides using structural databases (Protein Data Bank) and state-of-the-art structure prediction methods like I-TASSER, HHsearch and PEPstrMOD. In addition, SATPdb facilitates users in performing various tasks that include: (i) structure and sequence similarity search, (ii) peptide browsing based on their function and properties, (iii) identification of moonlighting peptides and (iv) searching of peptides having desired structure and therapeutic activities. We hope this database will be useful for researchers working in the field of peptide-based therapeutics.

Assessment of SYBR green I dye-based fluorescence assay for screening antimalarial activity of cationic peptides and DNA intercalating agents

The SYBR green I (SG) dye-based fluorescence assay for screening antimalarial compounds is based on direct quantitation of parasite DNA. We show that DNA-interacting cationic cell-penetrating peptides (CPPs) and intercalating agents compete with SG dye to bind to DNA. Therefore, readouts of this assay, unlike those of the [(3)H]hypoxanthine incorporation assay, for the antimalarial activity of the above DNA binding agents may be erroneous. In the case of CPPs, false readouts can be improved by the removal of excess peptides.