Cell-Penetrating Peptides for Antiviral Drug Development

Uptake pathways of cell-penetrating peptides in the context of drug delivery, gene therapy, and vaccine development

Cell-penetrating peptides have been extensively utilized for the purpose of facilitating the intracellular delivery of cargo that is impermeable to the cell membrane. The researchers have exhibited proficient delivery capabilities for oligonucleotides, thereby establishing cell-penetrating peptides as a potent instrument in the field of gene therapy. Furthermore, they have demonstrated a high level of efficiency in delivering several additional payloads. Cell penetrating peptides (CPPs) possess the capability to efficiently transport therapeutic molecules to specific cells, hence offering potential remedies for many illnesses. Hence, their utilization is imperative for the improvement of therapeutic vaccines. In contemporary studies, a plethora of cell-penetrating peptides have been unveiled, each characterized by its own distinct structural attributes and associated mechanisms. Although it is widely acknowledged that there are multiple pathways through which particles might be internalized, a comprehensive understanding of the specific mechanisms by which these particles enter cells has to be fully elucidated. The absorption of cell-penetrating peptides can occur through either direct translocation or endocytosis. However, it is worth noting that categories of cell-penetrating peptides are not commonly linked to specific entrance mechanisms. Furthermore, research has demonstrated that cell-penetrating peptides (CPPs) possess the capacity to enhance antigen uptake by cells and facilitate the traversal of various biological barriers. The primary objective of this work is to examine the mechanisms by which cell-penetrating peptides are internalized by cells and their significance in facilitating the administration of drugs, particularly in the context of gene therapy and vaccine development. The current study investigates the immunostimulatory properties of numerous vaccine components administered using different cell-penetrating peptides (CPPs). This study encompassed a comprehensive discussion on various topics, including the uptake pathways and mechanisms of cell-penetrating peptides (CPPs), the utilization of CPPs as innovative vectors for gene therapy, the role of CPPs in vaccine development, and the potential of CPPs for antigen delivery in the context of vaccine development.

A molecular dynamics study of cell-penetrating peptide transportan-10 (TP10): Binding, folding and insertion to transmembrane state in zwitterionic membrane

Transportan 10 (TP10) is a 21-residue, cationic, α-helical cell-penetrating peptide that can be used as a delivery vector for various bioactive molecules. Based on recent confocal microscopy studies, it is believed that TP10 can translocate across neutral lipid membrane passively, possibly as a monomer, without the formation of permanent pore. Here, we performed extensive molecular dynamics (MD) simulations of TP10W (Y3W variant of TP10) to find the microscopic details of binding, folding and insertion of TP10W to transmembrane state in POPC bilayer. Binding study with CHARMM36 force field showed that TP10W initially binds to the membrane surface in unstructured configuration, but it spontaneously folds into α-helical conformation under the lipid head groups. Further insertion of TP10W, changing from a surface bound state to a vertically oriented transmembrane state, was investigated via umbrella simulations. The resulting free energy profile shows a relatively small barrier between two states, suggesting a possible translocation pathway as a monomer. In fact, unbiased simulation of transmembrane TP10W revealed how a charged Lys side chain can move from one leaflet to the other without a significant free energy cost. Finally, we compared the results of TP10W simulations with those of point mutated variants (TP10W-K12A18 and TP10W-K19L) to understand the effect of charge distribution on the peptide. It was observed that such a conservative mutation can cause noticeable changes in the conformations of both surface bound and transmembrane states. The results of present study will be discussed in relation to the experimentally observed activities of TP10W against neutral membrane.

Cell-Penetrating Peptides: A Powerful Tool for Targeted Drug Delivery

The cellular membrane hinders the effective delivery of therapeutics to targeted sites. Cellpenetrating peptide (CPP) is one of the best options for rapidly internalizing across the cellular membrane. CPPs have recently attracted lots of attention because of their excellent transduction efficiency and low cytotoxicity. The CPP-cargo complex is an effective and efficient method of delivering several chemotherapeutic agents used to treat various diseases. Additionally, CPP has become another strategy to overcome some of the current therapeutic agents' limitations. However, no CPP complex is approved by the US FDA because of its limitations and issues. In this review, we mainly discuss the cellpenetrating peptide as the delivery vehicle, the cellular uptake mechanism of CPPs, their design, and some strategies to synthesize the CPP complex via some linkers such as disulfide bond, oxime, etc. Here, we also discuss the recent status of CPPs in the market.

Cell-Penetrating Peptides as Vehicles for Delivery of Therapeutic Nucleic Acids. Mechanisms and Application in Medicine

Currently, nucleic acid therapeutics are actively developed for the treatment and prophylactic of metabolic disorders and oncological, inflammatory, and infectious diseases. A growing number of approved nucleic acid-based drugs evidences a high potential of gene therapy in medicine. Therapeutic nucleic acids act in the cytoplasm, which makes the plasma membrane the main barrier for the penetration of nucleic acid-based drugs into the cell and requires development of special vehicles for their intracellular delivery. The optimal carrier should not only facilitate internalization of nucleic acids, but also exhibit no toxic effects, ensure stabilization of the cargo molecules, and be suitable for a large-scale and low-cost production. Cell-penetrating peptides (CPPs), which match all these requirements, were found to be efficient and low-toxic carriers of nucleic acids. CPPs are typically basic peptides with a positive charge at physiological pH that can form nanostructures with negatively charged nucleic acids. The prospects of CPPs as vehicles for the delivery of therapeutic nucleic acids have been demonstrated in numerous preclinical studies. Some CPP-based drugs had successfully passed clinical trials and were implemented into medical practice. In this review, we described different types of therapeutic nucleic acids and summarized the data on the use of CPPs for their intracellular delivery, as well as discussed, the mechanisms of CPP uptake by the cells, as understanding of these mechanisms can significantly accelerate the development of new gene therapy approaches.

Cell-permeable peptide nucleic acid antisense oligonucleotide platform targeting human betacoronaviruses

Introduction

Antisense oligonucleotides (ASOs) with therapeutic potential have recently been reported to target the SARS-CoV-2 genome. Peptide nucleic acids (PNAs)-based ASOs have been regarded as promising drug candidates, but intracellular delivery has been a significant obstacle. Here, we present novel modified PNAs, termed OPNAs, with excellent cell permeability that disrupt the RNA genome of SARS-CoV-2 and HCoV-OC43 by introducing cationic lipid moiety onto the nucleobase of PNA oligomer backbone.

Methods

HCT-8 cells and Caco-2 cells were treated with 1 μM antisense OPNAs at the time of viral challenge and the Viral RNA levels were measured by RT-qPCR three days post infection.

Results

NSP 14 targeting OPNA 5 and 11, reduced the viral titer to a half and OPNA 530, 531 and 533 lowered viral gene expression levels to less than 50% of control by targeting the 5' UTR region. Several modifications (oligo size and position, etc.) were introduced to enhance the efficacy of selected OPNAs. Improved OPNAs exhibited a dose-dependent reduction in viral replication and nucleoprotein (NP) protein. When a mixture of oligomers was applied to infected cells, viral titer and NP levels decreased by more than eightfold.

Discussion

In this study, we have developed a modified PNA ASO platform with exceptional chemical stability, high binding affinity, and cellular permeability. These findings indicate that OPNAs are a promising platform for the development of antivirals to combat future pandemic viral infections that do not require a carrier.

Application of Cell Penetrating Peptides as a Promising Drug Carrier to Combat Viral Infections

Novel effective drugs or therapeutic vaccines have been already developed to eradicate viral infections. Some non-viral carriers have been used for effective drug delivery to a target cell or tissue. Among them, cell penetrating peptides (CPPs) attracted a special interest to enhance drug delivery into the cells with low toxicity. They were also applied to transfer peptide/protein-based and nucleic acids-based therapeutic vaccines against viral infections. CPPs-conjugated drugs or vaccines were investigated in several viral infections including poliovirus, Ebola, coronavirus, herpes simplex virus, human immunodeficiency virus, hepatitis B virus, hepatitis C virus, Japanese encephalitis virus, and influenza A virus. Some studies showed that the uptake of CPPs or CPPs-conjugated drugs can be performed through both non-endocytic and endocytic pathways. Despite high potential of CPPs for cargo delivery, there are some serious drawbacks such as non-tissue-specificity, instability, and suboptimal pharmacokinetics features that limit their clinical applications. At present, some solutions are utilized to improve the CPPs properties such as conjugation of CPPs with targeting moieties, the use of fusogenic lipids, generation of the proton sponge effect, etc. Up to now, no CPP or composition containing CPPs has been approved by the Food and Drug Administration (FDA) due to the lack of sufficient in vivo studies on stability, immunological assays, toxicity, and endosomal escape of CPPs. In this review, we briefly describe the properties, uptake mechanisms, advantages and disadvantages, and improvement of intracellular delivery, and bioavailability of cell penetrating peptides. Moreover, we focus on their application as an effective drug carrier to combat viral infections.

Novel Nanotechnology-Based Approaches for Targeting HIV Reservoirs

Highly active anti-retroviral therapy (HAART) is prescribed for HIV infection and, to a certain extent, limits the infection’s spread. However, it cannot completely eradicate the latent virus in remote and cellular reservoir areas, and due to the complex nature of the infection, the total eradication of HIV is difficult to achieve. Furthermore, monotherapy and multiple therapies are not of much help. Hence, there is a dire need for novel drug delivery strategies that may improve efficacy, decrease side effects, reduce dosing frequency, and improve patient adherence to therapy. Such a novel strategy could help to target the reservoir sites and eradicate HIV from different biological sanctuaries. In the current review, we have described HIV pathogenesis, the mechanism of HIV replication, and different biological reservoir sites to better understand the underlying mechanisms of HIV spread. Further, the review deliberates on the challenges faced by the current conventional drug delivery systems and introduces some novel drug delivery strategies that have been explored to overcome conventional drug delivery limitations. In addition, the review also summarizes several nanotechnology-based approaches that are being explored to resolve the challenges of HIV treatment by the virtue of delivering a variety of anti-HIV agents, either as combination therapies or by actively targeting HIV reservoir sites.

Antiviral nanopharmaceuticals: Engineered surface interactions and virus-selective activity

The COVID-19 pandemic has inspired large research investments from the global scientific community in the study of viral properties and antiviral technologies (e.g., self-cleaning surfaces, virucides, antiviral drugs, and vaccines). Emerging viruses are a constant threat due to the substantial variation in viral structures, limiting the potential for expanded broad-spectrum antiviral agent development, and the complexity of targeting multiple and diverse viral species with unique characteristics involving their virulence. Multiple, more infectious variants of SARS-CoV2 (e.g., Delta, Omicron) have already appeared, necessitating research into versatile, robust control strategies in response to the looming threat of future viruses. Nanotechnology and nanomaterials have played a vital role in addressing current viral threats, from mRNA-based vaccines to nanoparticle-based drugs and nanotechnology enhanced disinfection methods. Rapid progress in the field has prompted a review of the current literature primarily focused on nanotechnology-based virucides and antivirals. In this review, a brief description of antiviral drugs is provided first as background with most of the discussion focused on key design considerations for high-efficacy antiviral nanomaterials (e.g., nanopharmaceuticals) as determined from published studies as well as related modes of biological activity. Insights into potential future research directions are also provided with a section devoted specifically to the SARS-CoV2 virus. This article is categorized under: Toxicology and Regulatory Issues in Nanomediciney > Toxicology of Nanomaterials Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Respiratory Disease.

Circumsporozoite Protein of Plasmodium berghei- and George Baker Virus A-Derived Peptides Trigger Efficient Cell Internalization of Bioconjugates and Functionalized Poly(ethylene glycol)-b-poly(benzyl malate)-Based Nanoparticles in Human Hepatoma Cells

In order to identify the peptides, selected from the literature, that exhibit the strongest tropism towards human hepatoma cells, cell uptake assays were performed using biotinylated synthetic peptides bound to fluorescent streptavidin or engrafted onto nanoparticles (NPs), prepared from biotin-poly(ethylene glycol)-block-poly(benzyl malate) (Biot-PEG-b-PMLABe) via streptavidin bridging. Two peptides, derived from the circumsporozoite protein of Plasmodium berghei- (CPB) and George Baker (GB) Virus A (GBVA10-9), strongly enhanced the endocytosis of both streptavidin conjugates and NPs in hepatoma cells, compared to primary human hepatocytes and non-hepatic cells. Unexpectedly, the uptake of CPB- and GBVA10-9 functionalized PEG-b-PMLABe-based NPs by hepatoma cells involved, at least in part, the peptide binding to apolipoproteins, which would promote NP’s interactions with cell membrane receptors of HDL particles. In addition, CPB and GBVA10-9 peptide–streptavidin conjugates favored the uptake by hepatoma cells over that of the human macrophages, known to strongly internalize nanoparticles by phagocytosis. These two peptides are promising candidate ligands for targeting hepatocellular carcinomas.

Targeting Zika Virus with New Brain- and Placenta-Crossing Peptide–Porphyrin Conjugates

Viral disease outbreaks affect hundreds of millions of people worldwide and remain a serious threat to global health. The current SARS-CoV-2 pandemic and other recent geographically- confined viral outbreaks (severe acute respiratory syndrome (SARS), Ebola, dengue, zika and ever-recurring seasonal influenza), also with devastating tolls at sanitary and socio-economic levels, are sobering reminders in this respect. Among the respective pathogenic agents, Zika virus (ZIKV), transmitted by Aedes mosquito vectors and causing the eponymous fever, is particularly insidious in that infection during pregnancy results in complications such as foetal loss, preterm birth or irreversible brain abnormalities, including microcephaly. So far, there is no effective remedy for ZIKV infection, mainly due to the limited ability of antiviral drugs to cross blood–placental and/or blood–brain barriers (BPB and BBB, respectively). Despite its restricted permeability, the BBB is penetrable by a variety of molecules, mainly peptide-based, and named BBB peptide shuttles (BBBpS), able to ferry various payloads (e.g., drugs, antibodies, etc.) into the brain. Recently, we have described peptide–porphyrin conjugates (PPCs) as successful BBBpS-associated drug leads for HIV, an enveloped virus in which group ZIKV also belongs. Herein, we report on several brain-directed, low-toxicity PPCs capable of targeting ZIKV. One of the conjugates, PP-P1, crossing both BPB and BBB, has shown to be effective against ZIKV (IC₅₀ 1.08 µM) and has high serum stability (t_1/2 ca. 22 h) without altering cell viability at all tested concentrations. Peptide–porphyrin conjugation stands out as a promising strategy to fill the ZIKV treatment gap.

Potential of cell-penetrating peptides (CPPs) in delivery of antiviral therapeutics and vaccines

Viral infections are a great threat to human health. Currently, there are no effective vaccines and antiviral drugs against the majority of viral diseases, suggesting the need to develop novel and effective antiviral agents. Since the intracellular delivery of antiviral agents, particularly the impermeable molecules, such as peptides, proteins, and nucleic acids, are essential to exert their therapeutic effects, using a delivery system is highly required. Among various delivery systems, cell-penetrating peptides (CPPs), a group of short peptides with the unique ability of crossing cell membrane, offer great potential for the intracellular delivery of various biologically active cargoes. The results of numerous in vitro and in vivo studies with CPP conjugates demonstrate their promise as therapeutic agents in various medical fields including antiviral therapy. The CPP-mediated delivery of various antiviral agents including peptides, proteins, nucleic acids, and nanocarriers have been associated with therapeutic efficacy both in vitro and in vivo. This review describes various aspects of viruses including their biology, pathogenesis, and therapy and briefly discusses the concept of CPP and its potential in drug delivery. Particularly, it will highlight a variety of CPP applications in the management of viral infections.

Molecular docking studies of HIV TAT and sitagliptin nano-formula as potential therapeutic targeting SARS-CoV2 protease

The outbreak of COVID-19 pandemic regarded as a major health/economic hazard. The importance of coming up with mechanisms for preventing or treating SARS-CoV-2infection has been felt across the world. This work aimed at examining the efficiency of Sitagliptin (SIT) and human immunodeficiency virus type 1 (HIV-1) trans-activator transcription peptide (TAT) against SARS-CoV-2 virus. 3CL-protease inhibition activity and docking studies were examined. According to the results, the prepared complex's formula was as follows 1: 1 SIT: TAT molar ratio, whereas zeta potential and particle size values were at 34.17 ​mV and 97.19 ​nm, respectively. This combination did exhibit its antiviral potentiality against SARS-CoV-2 via IC50 values of 9.083 5.415, and 16.14 ​μM for TAT, SIT-TAT, and SIT, respectively. In addition, the complex SIT-TAT showed a significant (P ​< ​0.001) viral-3CL-protease inhibitory effect. This was further confirmed via in silico study. Molecular docking investigation has shown promising binding affinity of the formula components towards SARS-CoV-2 main protease (3-CL).

Evaluation and Optimization of Poly-d-Lysine as a Non-Natural Cationic Polypeptide for Gene Transfer in Neuroblastoma Cells

Cationic polypeptides and cationic polymers have cell-penetrating capacities and have been used in gene transfer studies. In this study, we investigate the capability of a polymer of d-lysine (PDL), a chiral form of α–Poly-lysine, as a possible nonviral vector for releasing genetic materials to neuroblastoma cells and evaluate its stability against proteases. We tested and compared its transfection effectiveness in vitro as a vehicle for the EGFP plasmid DNA (pDNA) reporter in the SH-SY5Y human neuroblastoma, HeLa, and 3T3 cell lines. Using fluorescent microscopy and flow cytometry, we demonstrated high transfection efficiencies based on EGFP fluorescence in SH-SY5Y cells, compared with HeLa and 3T3. Our results reveal PDL as an efficient vector for gene delivery specifically in the SH-SY5Y cell line and suggest that PDL can be used as a synthetic cell-penetrating polypeptide for gene therapy in neuroblastoma cells.

Targeting a Potential G-Quadruplex Forming Sequence Found in the West Nile Virus Genome by Complementary Gamma-Peptide Nucleic Acid Oligomers

In the United States, West Nile virus (WNV) infects approximately 2500 people per year, of which 100-200 cases are fatal. No antiviral drug or vaccine is currently available for WNV. In this study, we designed gamma-modified peptide nucleic acid (γPNA) oligomers to target a newly identified guanine-rich gene sequence in the WNV genome. The target is found in the NS5 protein-coding region and was previously predicted to fold into a G-quadruplex (GQ) structure. Biophysical techniques such as UV melting analysis, circular dichroism spectroscopy, and fluorescence spectroscopy demonstrated that the target RNA indeed folds into a moderately stable GQ structure at physiological temperature and potassium concentration. Successful invasion of the GQ by three complementary γPNAs was also characterized by the above-mentioned biophysical techniques. The γPNAs showed very strong binding to the target with low femtomolar affinity at physiological temperature. Targeting this potential guanine quadruplex forming sequence (PQS) and other related sequences with γPNA may represent a new approach for inhibiting both WNV replication and transcription, thereby representing a generally useful antiviral strategy.

Antisense peptide nucleic acid inhibits the growth of KPC-producing Klebsiella pneumoniae strain

Klebsiella pneumoniae causes common and severe hospital- and community-acquired infections with a high incidence of multidrug resistance (MDR) and mortality. In this study, we investigated the ability of the antisense peptide nucleic acids (PNA) conjugated to the (KFF)3K cell-penetrating peptide (CPP) to target the gyrA KPC-producing K. pneumoniae and inhibit bacterial growth in vitro. The inhibitory effect on gyrA gene was evaluated by measuring 16s gene amplification in KPC-producing K. pneumoniae treated with the antisense PNA conjugate. The hemolytic property of the antisense PNA conjugate was accessed toward mice red blood cells. Finally, molecular modeling and dynamics simulations analyses in aqueous solutions were performed to predict the PNA conformation alone in contact with DNA (gyrA gene sequence). PNA was capable of inhibiting bacterial growth at 50 μM, also reducing 16S gene amplification in 96.7%. Besides, PNA presented low hemolytic activity (21.1% hemolysis) at this same concentration. Bioinformatics analysis demonstrated that the structure of the PNA is stable in water without major changes in its secondary structure. The ability of PNA and its conjugated CPP ((KFF)3K) to inhibit bacterial growth demonstrates the potential of this new class of antibacterial agents, encouraging further in vivo studies to confirm its therapeutic efficacy.

Intramolecularly stapled amphipathic peptides via a boron–sugar interaction

The intramolecular interactions between the fructosyl moiety and phenylboronic acid incorporated into various positions of the peptide chain were investigated using mass spectrometry (MS), circular dichroism (CD), and nuclear magnetic resonance (NMR).

Ocular penetration of fluorometholone-loaded PEG-PLGA nanoparticles functionalized with cell-penetrating peptides

Aim: Development of fluorometholone-loaded PEG-PLGA nanoparticles (NPs) functionalized with cell-penetrating peptides (CPPs) for the treatment of ocular inflammatory disorders. Materials & methods: Synthesized polymers and peptides were used for elaboration of functionalized NPs, which were characterized physicochemically. Cytotoxicity and ability to modulate the expression of proinflammatory cytokines were evaluated in vitro using human corneal epithelial cells (HCE-2). NPs uptake was assayed in both in vitro and in vivo models. Results: NPs showed physicochemical characteristics suitable for ocular administration without evidence of cytotoxicity. TAT-NPs and G2-NPs were internalized and displayed anti-inflammatory activity in both HCE-2 cells and mouse eye. Conclusion: TAT-NPs and G2-NPs could be considered a novel strategy for the treatment of ocular inflammatory diseases of the anterior and posterior segment.

Antiviral compound screening, peptide designing, and protein network construction of influenza a virus (strain a/Puerto Rico/8/1934 H1N1)

Plant-based antiviral therapy is the current need for holistic health care management, which can be achieved through screening of phytochemicals and designing of antiviral peptides. There exist certain host's factors which are directly involved for rapid viral replication causing worldwide pandemic. A total of 177 phytochemicals from Ocimum sanctum (L.), Tinospora cordifolia (Thunb.) Miers, Cinnamomum camphora (L.) J. Presl., Allium sativum (L.), Curcuma longa (L.), and Aloe vera (L.) Burm. f. were evaluated for their affinity to all viral proteins of H1N1. Applying drug filters and keeping the threshold of such filters relative to the standards, 82 compounds were found suitable for further analysis. Consensus scoring system was used for screening top ligands from 82 compounds, which screened the top 12 compounds. Highly conserved regions (>80%) which were hydrophilic, flexible, antigenic, and also charged were screened out as potent antiviral peptides. The viral proteins were taken as the targets for the modeled peptides for protein-protein docking. Further, host-pathogen interacting network was constructed to unveil host factors involved in viral replication, from which unique protein clusters representing their involvement in viral reproduction were selected through mapping with pathway databases. Twelve compounds and five peptides were found to be highly effective against all the proteins of H1N1. Based on the uniqueness, 13 clusters of proteins were obtained which are engaged in cellular process, namely, viral reproduction, fructose-6-phosphate metabolism, nitrogen compound metabolism, biosynthesis, cellular process, oligodendrocyte development, localization, multiorganism process, primary metabolism, response to unfolded protein, metabolism, and response to protein and catabolism.

Peptides as Therapeutic Agents for Dengue Virus

Dengue is an important global threat caused by dengue virus (DENV) that records an estimated 390 million infections annually. Despite the availability of CYD-TDV as a commercial vaccine, its long-term efficacy against all four dengue virus serotypes remains unsatisfactory. There is therefore an urgent need for the development of antiviral drugs for the treatment of dengue. Peptide was once a neglected choice of medical treatment but it has lately regained interest from the pharmaceutical industry following pioneering advancements in technology. In this review, the design of peptide drugs, antiviral activities and mechanisms of peptides and peptidomimetics (modified peptides) action against dengue virus are discussed. The development of peptides as inhibitors for viral entry, replication and translation is also described, with a focus on the three main targets, namely, the host cell receptors, viral structural proteins and viral non-structural proteins. The antiviral peptides designed based on these approaches may lead to the discovery of novel anti-DENV therapeutics that can treat dengue patients.

Cell-penetrating peptides: design, synthesis, and applications

The intrinsic property of cell-penetrating peptides (CPPs) to deliver therapeutic molecules (nucleic acids, drugs, imaging agents) to cells and tissues in a nontoxic manner has indicated that they may be potential components of future drugs and disease diagnostic agents. These versatile peptides are simple to synthesize, functionalize, and characterize yet are able to deliver covalently or noncovalently conjugated bioactive cargos (from small chemical drugs to large plasmid DNA) inside cells, primarily via endocytosis, in order to obtain high levels of gene expression, gene silencing, or tumor targeting. Typically, CPPs are often passive and nonselective yet must be functionalized or chemically modified to create effective delivery vectors that succeed in targeting specific cells or tissues. Furthermore, the design of clinically effective systemic delivery systems requires the same amount of attention to detail in both design of the delivered cargo and the cell-penetrating peptide used to deliver it.

Inhibition of influenza A virus infection in vitro by peptides designed in silico

Influenza A viruses are enveloped, segmented negative single-stranded RNA viruses, capable of causing severe human respiratory infections. Currently, only two types of drugs are used to treat influenza A infections, the M2 H⁺ ion channel blockers (amantadine and rimantadine) and the neuraminidase inhibitors (NAI) (oseltamivir and zanamivir). Moreover, the emergence of drug-resistant influenza A virus strains has emphasized the need to develop new antiviral agents to complement or replace the existing drugs. Influenza A virus has on the surface a glycoprotein named hemagglutinin (HA) which due to its important role in the initial stage of infection: receptor binding and fusion activities of viral and endosomal membranes, is a potential target for new antiviral drugs. In this work we designed nine peptides using several bioinformatics tools. These peptides were derived from the HA1 and HA2 subunits of influenza A HA with the aim to inhibit influenza A virus infection. The peptides were synthetized and their antiviral activity was tested in vitro against several influenza A viral strains: Puerto Rico/916/34 (H1N1), (H1N1)pdm09, swine (H1N1) and avian (H5N2). We found these peptides were able to inhibit the influenza A viral strains tested, without showing any cytotoxic effect. By docking studies we found evidence that all the peptides were capable to bind to the viral HA, principally to important regions on the viral HA stalk, thus could prevent the HA conformational changes required to carry out its membranes fusion activity.

Therapeutic delivery opportunities, obstacles and applications for cell-penetrating peptides

Advancements in the development of large bioactive molecules as therapeutic agents have made drug delivery an active and important field of research. Cell-penetrating peptides (CPPs) have the ability to deliver an array of molecules and even nano-size particles into cells in an efficient and non-toxic manner, both in vitro and in vivo. This review aims to give a perspective on the obstacles that CPP-mediated drug delivery is currently facing as well as the great opportunities for improvements that lie ahead. Strategies for delivery of novel gene-modulating agents and enhancing efficacy of classical drugs will be discussed, as well as methods for increasing bioavailability and tissue specificity of CPPs. The usefulness and potential of CPPs as therapeutic drug-delivery vectors will be exemplified by their use in the treatment of cancer, viral infection and muscular dystrophy.

Cell penetrating peptides in the delivery of biopharmaceuticals

The cell membrane is a highly selective barrier. This limits the cellular uptake of molecules including DNA, oligonucleotides, peptides and proteins used as therapeutic agents. Different approaches have been employed to increase the membrane permeability and intracellular delivery of these therapeutic molecules. One such approach is the use of Cell Penetrating Peptides (CPPs). CPPs represent a new and innovative concept, which bypasses the problem of bioavailability of drugs. The success of CPPs lies in their ability to unlock intracellular and even intranuclear targets for the delivery of agents ranging from peptides to antibodies and drug-loaded nanoparticles. This review highlights the development of cell penetrating peptides for cell-specific delivery strategies involving biomolecules that can be triggered spatially and temporally within a cell transport pathway by change in physiological conditions. The review also discusses conjugations of therapeutic agents to CPPs for enhanced intracellular delivery and bioavailability that are at the clinical stage of development.

Druggability assessment of protein-protein interfaces

Recent success stories concerning the targeting of protein-protein interactions (PPIs) have led to an increased focus on this challenging target class for drug discovery. This article explores various avenues to assess the druggability of PPIs and describes a druggability decision flow chart, which can be applied to any PPI target. This flow chart not only covers small molecules but also peptidomimetics, peptides and conformationally restricted peptides as potential modalities for targeting PPIs. Additionally, a retrospective analysis of PPI druggability using various computational tools is summarized. The application of a systematic approach as presented in this paper will increase confidence that modulators (e.g., small organic molecules or peptides) can ultimately be identified for a particular target before a decision is made to commit significant discovery resources.

Expression of an antiviral protein from Lonomia obliqua hemolymph in baculovirus/insect cell system

The control of viral infections, mainly those caused by influenza viruses, is of great interest in Public Health. Several studies have shown the presence of active properties in the hemolymph of arthropods, some of which are of interest for the development of new pharmacological drugs. Recently, we have demonstrated the existence of a potent antiviral property in the hemolymph of Lonomia obliqua caterpillars. The aim of this study was to produce an antiviral protein in a baculovirus/Sf9 cell system. The resulting bacmid contains the sequence coding for the antiviral protein previously described by our group. Total RNA from L. obliqua caterpillars was extracted with Trizol and used in the reverse transcription assay with oligo(d)T primer followed by polymerase chain reactions (RT-PCR) with specific primers for the cDNA coding for the antiviral protein, based on the sequence deposited in the GenBank database. Restriction sites were inserted in the cDNA for ligation in the donor plasmid pFastBac1™. The recombinant plasmid was selected in Escherichia coli DH5α and subsequently used in the transformation of E. coli DH10Bac for the construction of the recombinant bacmid. This bacmid was used for the expression of the antiviral protein in the baculovirus/Sf9 cell system. After identifying the protein by western blot, activity tests were performed, showing that the purified recombinant protein was able to significantly reduce viral replication (about 4 logs). Studies on the optimization of the expression system for the production of this antiviral protein in insect cells are in progress.