A survey on "Trojan Horse" peptides: opportunities, issues and controlled entry to "Troy"

Evaluating the cytotoxicity mechanism of the cell-penetrating peptide TP10 on Jurkat cells

TP10, a classic cell-penetrating peptide, shows a high degree of similarity to AMPs in structure. Although TP10 has been widely used in drug delivery, the mechanism underlying its cytotoxicity is yet to be elucidated. Herein, we explored the cell-killing mechanism of TP10 against human leukemia Jurkat cells. TP10 induced necrosis in Jurkat cells via rapid disruption of cell membranes, particularly at high concentrations. Although mitochondria in Jurkat cells were damaged by TP10, mitochondria-mediated apoptosis did not occur, possibly due to intracellular ATP depletion. Necroptosis in TP10-treated Jurkat cells became an alternative route of apoptosis. Our results demonstrate that necrosis and necroptosis rather than apoptosis are involved in the cell-killing mechanism of TP10, which contributes to the understanding of its toxicity.

Multibarrier-penetrating drug delivery systems for deep tumor therapy based on synergistic penetration strategy

Nanotherapies, valued for their high efficacy and low toxicity, frequently serve as antitumor treatments, but do not readily penetrate deep into tumor tissues and cells. Here we developed an improved tumor-penetrating peptide (TPP)-based drug delivery system. Briefly, the established TPP iNGR was modified to generate a linear NGR peptide capable of transporting nanotherapeutic drugs into tumors through a CendR pathway-dependent, neuropilin-1 receptor-mediated process. Although TPPs have been reported to reach intended tumor targets, they often fail to penetrate cell membranes to deliver tumoricidal drugs to intracellular targets. We addressed this issue by harnessing cell penetrating peptide technology to develop a liposome-based multibarrier-penetrating delivery system (mbPDS) with improved synergistic drug penetration into deep tumor tissues and cells. The system incorporated doxorubicin-loaded liposomes coated with nona-arginine (R9) CPP and cyclic iNGR (CRNGRGPDC) molecules, yielding Lip-mbPDS. Lip-mbPDS tumor-targeting, tumor cell/tissue-penetrating and antitumor capabilities were assessed using CD13-positive human fibrosarcoma-derived cell (HT1080)-based in vitro and in vivo tumor models. Lip-mbPDS evaluation included three-dimensional layer-by-layer confocal laser scanning microscopy, cell internalization/toxicity assays, three-dimensional tumor spheroid-based penetration assays and antitumor efficacy assays conducted in an animal model. Lip-mbPDS provided enhanced synergistic drug penetration of multiple biointerfaces for potentially deep tumor therapeutic outcomes.

Cell-penetrating peptides for transmucosal delivery of proteins

Enabling non-invasive delivery of proteins across the mucosal barriers promises improved patient compliance and therapeutic efficacies. Cell-penetrating peptides (CPPs) are emerging as a promising and versatile tool to enhance protein and peptide permeation across various mucosal barriers. This review examines the structural and physicochemical attributes of the nasal, buccal, sublingual, and oral mucosa that hamper macromolecular delivery. Recent development of CPPs for overcoming those mucosal barriers for protein delivery is summarized and analyzed. Perspectives regarding current challenges and future research directions towards improving non-invasive transmucosal delivery of macromolecules for ultimate clinical translation are discussed.

Cell Penetrating Peptides: Classification, Mechanisms, Methods of Study, and Applications

Cell-penetrating peptides (CPPs) encompass a class of peptides that possess the remarkable ability to cross cell membranes and deliver various types of cargoes, including drugs, nucleic acids, and proteins, into cells. For this reason, CPPs are largely investigated in drug delivery applications in the context of many diseases, such as cancer, diabetes, and genetic disorders. While sharing this functionality and some common structural features, such as a high content of positively charged amino acids, CPPs represent an extremely diverse group of elements, which can differentiate under many aspects. In this review, we summarize the most common characteristics of CPPs, introduce their main distinctive features, mechanistic aspects that drive their function, and outline the most widely used techniques for their structural and functional studies. We highlight current gaps and future perspectives in this field, which have the potential to significantly impact the future field of drug delivery and therapeutics.

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.

Orally-delivered insulin-peptide nanocomplexes enhance transcytosis from cellular depots and improve diabetic blood glucose control

Insulin regulates blood glucose levels, and is the mainstay for the treatment of type-1 diabetes and type-2 when other drugs provide inadequate control. Therefore, effective oral Insulin delivery would be a significant advance in drug delivery. Herein, we report the use of the modified cell penetrating peptide (CPP) platform, Glycosaminoglycan-(GAG)-binding-enhanced-transduction (GET), as an efficacious transepithelial delivery vector in vitro and to mediate oral Insulin activity in diabetic animals. Insulin can be conjugated with GET via electrostatic interaction to form nanocomplexes (Insulin GET-NCs). These NCs (size and charge; 140 nm, +27.10 mV) greatly enhanced Insulin transport in differentiated in vitro intestinal epithelium models (Caco2 assays; >22-fold increased translocation) with progressive and significant apical and basal release of up-taken Insulin. Delivery resulted in intracellular accumulation of NCs, enabling cells to act as depots for subsequent sustained release without affecting viability and barrier integrity. Importantly Insulin GET-NCs have enhanced proteolytic stability, and retained significant Insulin biological activity (exploiting Insulin-responsive reporter assays). Our study culminates in demonstrating oral delivery of Insulin GET-NCs which can control elevated blood-glucose levels in streptozotocin (STZ)-induced diabetic mice over several days with serial dosing. As GET promotes Insulin absorption, transcytosis and intracellular release, along with in vivo function, our simplistic complexation platform could allow effective bioavailability of other oral peptide therapeutics and help transform the treatment of diabetes.

Fabrication, characterization and evaluation of a new designed botulinum toxin-cell penetrating peptide nanoparticulate complex

BACKGROUND

To have a better and longer effect, botulinum neurotoxin (BoNT) is injected several times in a treatment course, which could increase side effects and cost. Some of the most cutting-edge strategies being investigated for proteins to their physiologic targets involve the reformulation of BoNT based on peptide-based delivery systems. For this purpose, cell-penetrating peptides (CPPs) are of particular interest because of their capacity to cross the biological membranes.

OBJECTIVES

A short and simple CPP sequence was used as a carrier to create nanocomplex particles from BoNT/A, with the purpose of increasing toxin entrapment by target cells, reducing diffusion, and increasing the duration of the effect.

METHOD

CPP-BoNT/A nanocomplexes were formed by polyelectrolyte complex (PEC) method, considering the anionic structure of botulinum toxin and the cationic CPP sequence. The cellular toxicity, and absorption profile of the complex nanoparticles were evaluated, and the digit abduction score (DAS) was used to assess the local muscle weakening efficacy of BoNT/A and CPP-BoNT/A.

RESULTS

The provided optimized polyelectrolyte complex nanoparticles had a 244 ± 20 nm particle size and 0.28 ± 0.04 PdI. In cellular toxicity, CPP-BoNT/A nanocomplexes as extended-release formulations of BoNT/A showed that nanocomplexes had a more toxic effect than BoNT/A. Furthermore, the comparison of weakening effectiveness on muscle was done among nanoparticles and free toxin on mice based on the digit abduction score (DAS) method, and nanocomplexes had a slower onset effect and a longer duration of action than toxin.

CONCLUSION

Using PEC method allowed us to form nanocomplex from proteins, and peptides without a covalent bond and harsh conditions. The muscle-weakening effect of toxin in CPP-BoNT/A nanocomplexes showed acceptable efficacy and extended-release pattern.

Advances and Challenges of Stimuli-Responsive Nucleic Acids Delivery System in Gene Therapy

Gene therapy has emerged as a powerful tool to treat various diseases, such as cardiovascular diseases, neurological diseases, ocular diseases and cancer diseases. In 2018, the FDA approved Patisiran (the siRNA therapeutic) for treating amyloidosis. Compared with traditional drugs, gene therapy can directly correct the disease-related genes at the genetic level, which guarantees a sustained effect. However, nucleic acids are unstable in circulation and have short half-lives. They cannot pass through biological membranes due to their high molecular weight and massive negative charges. To facilitate the delivery of nucleic acids, it is crucial to develop a suitable delivery strategy. The rapid development of delivery systems has brought light to the gene delivery field, which can overcome multiple extracellular and intracellular barriers that prevent the efficient delivery of nucleic acids. Moreover, the emergence of stimuli-responsive delivery systems has made it possible to control the release of nucleic acids in an intelligent manner and to precisely guide the therapeutic nucleic acids to the target site. Considering the unique properties of stimuli-responsive delivery systems, various stimuli-responsive nanocarriers have been developed. For example, taking advantage of the physiological variations of a tumor (pH, redox and enzymes), various biostimuli- or endogenous stimuli-responsive delivery systems have been fabricated to control the gene delivery processes in an intelligent manner. In addition, other external stimuli, such as light, magnetic fields and ultrasound, have also been employed to construct stimuli-responsive nanocarriers. Nevertheless, most stimuli-responsive delivery systems are in the preclinical stage, and some critical issues remain to be solved for advancing the clinical translation of these nanocarriers, such as the unsatisfactory transfection efficiency, safety issues, complexity of manufacturing and off-target effects. The purpose of this review is to elaborate the principles of stimuli-responsive nanocarriers and to emphasize the most influential advances of stimuli-responsive gene delivery systems. Current challenges of their clinical translation and corresponding solutions will also be highlighted, which will accelerate the translation of stimuli-responsive nanocarriers and advance the development of gene therapy.

Recent advances in peptide-based therapeutic strategies for breast cancer treatment

Breast cancer is the leading cause of cancer-related fatalities in female worldwide. Effective therapies with low side effects for breast cancer treatment and prevention are, accordingly, urgently required. Targeting anticancer materials, breast cancer vaccines and anticancer drugs have been studied for many years to decrease side effects, prevent breast cancer and suppress tumors, respectively. There are abundant evidences to demonstrate that peptide-based therapeutic strategies, coupling of good safety and adaptive functionalities are promising for breast cancer therapy. In recent years, peptide-based vectors have been paid attention in targeting breast cancer due to their specific binding to corresponding receptors overexpressed in cell. To overcome the low internalization, cell penetrating peptides (CPPs) could be selected to increase the penetration due to the electrostatic and hydrophobic interactions between CPPs and cell membranes. Peptide-based vaccines are at the forefront of medical development and presently, 13 types of main peptide vaccines for breast cancer are being studied on phase III, phase II, phase I/II and phase I clinical trials. In addition, peptide-based vaccines including delivery vectors and adjuvants have been implemented. Many peptides have recently been used in clinical treatments for breast cancer. These peptides show different anticancer mechanisms and some novel peptides could reverse the resistance of breast cancer to susceptibility. In this review, we will focus on current studies of peptide-based targeting vectors, CPPs, peptide-based vaccines and anticancer peptides for breast cancer therapy and prevention.

Cell penetrating peptide: A potent delivery system in vaccine development

One of the main obstacles to most medication administrations (such as the vaccine constructs) is the cellular membrane's inadequate permeability, which reduces their efficiency. Cell-penetrating peptides (CPPs) or protein transduction domains (PTDs) are well-known as potent biological nanocarriers to overcome this natural barrier, and to deliver membrane-impermeable substances into cells. The physicochemical properties of CPPs, the attached cargo, concentration, and cell type substantially influence the internalization mechanism. Although the exact mechanism of cellular uptake and the following processing of CPPs are still uncertain; but however, they can facilitate intracellular transfer through both endocytic and non-endocytic pathways. Improved endosomal escape efficiency, selective cell targeting, and improved uptake, processing, and presentation of antigen by antigen-presenting cells (APCs) have been reported by CPPs. Different in vitro and in vivo investigations using CPP conjugates show their potential as therapeutic agents in various medical areas such as infectious and non-infectious disorders. Effective treatments for a variety of diseases may be provided by vaccines that can cooperatively stimulate T cell-mediated immunity (T helper cell activity or cytotoxic T cell function), and immunologic memory. Delivery of antigen epitopes to APCs, and generation of a potent immune response is essential for an efficacious vaccine that can be facilitated by CPPs. The current review describes the delivery of numerous vaccine components by various CPPs and their immunostimulatory properties.

Cell-penetrating peptide-mediated delivery of therapeutic peptides/proteins to manage the diseases involving oxidative stress, inflammatory response and apoptosis

OBJECTIVES

Peptides and proteins represent great potential for modulating various cellular processes including oxidative stress, inflammatory response, apoptosis and consequently the treatment of related diseases. However, their therapeutic effects are limited by their inability to cross cellular barriers. Cell-penetrating peptides (CPPs), which can transport cargoes into the cell, could resolve this issue, as would be discussed in this review.

KEY FINDINGS

CPPs have been successfully exploited in vitro and in vivo for peptide/protein delivery to treat a wide range of diseases involving oxidative stress, inflammatory processes and apoptosis. Their in vivo applications are still limited due to some fundamental issues of CPPs, including nonspecificity, proteolytic instability, potential toxicity and immunogenicity.

SUMMARY

Totally, CPPs could potentially help to manage the diseases involving oxidative stress, inflammatory response and apoptosis by delivering peptides/proteins that could selectively reach proper intracellular targets. More studies to overcome related CPP limitations and confirm the efficacy and safety of this strategy are needed before their clinical usage.

CRISPR-Cas9-Based Technology and Its Relevance to Gene Editing in Parkinson's Disease

Parkinson’s disease (PD) and other chronic and debilitating neurodegenerative diseases (NDs) impose a substantial medical, emotional, and financial burden on individuals and society. The origin of PD is unknown due to a complex combination of hereditary and environmental risk factors. However, over the last several decades, a significant amount of available data from clinical and experimental studies has implicated neuroinflammation, oxidative stress, dysregulated protein degradation, and mitochondrial dysfunction as the primary causes of PD neurodegeneration. The new gene-editing techniques hold great promise for research and therapy of NDs, such as PD, for which there are currently no effective disease-modifying treatments. As a result, gene therapy may offer new treatment options, transforming our ability to treat this disease. We present a detailed overview of novel gene-editing delivery vehicles, which is essential for their successful implementation in both cutting-edge research and prospective therapeutics. Moreover, we review the most recent advancements in CRISPR-based applications and gene therapies for a better understanding of treating PD. We explore the benefits and drawbacks of using them for a range of gene-editing applications in the brain, emphasizing some fascinating possibilities.

An update on cell-penetrating peptides with intracellular organelle targeting

INTRODUCTION

Cell-penetrating peptide (CPP) technologies represent an important strategy to address drug delivery to specific intracellular compartments by covalent conjugation to targeting sequences, potentially enabling strategies to combat most diseases.

AREAS COVERED

This updated review article provides an overview of current intracellular organelle targeting by CPP. The targeting strategies of CPP and CPP/cargo complexes to specific cells or intracellular organelles are summarized, and the review provides an update on the current data for their pharmacological and therapeutical applications.

EXPERT OPINION

Targeted drug delivery is moving from the level of tissue or specific pathogenic cell to the level of specific organelle that is the target of the drug, an important aspect in drug design and development. Organelle-targeted drug delivery results in improved efficacy, ability to control mode of action, reduction of undesired toxicities and side effects, and possibility to overcome drug resistance mechanisms.

Cell-penetrating peptides improve pharmacokinetics and pharmacodynamics of anticancer drugs

This review concentrates on the research concerning conjugates of anticancer drugs with versatile cell-penetrating peptides (CPPs). For a better insight into the relationship between the components of the constructs, it starts with the characteristic of the peptides and considers its following aspects: mechanisms of cellular internalization, interaction with cancer-modified membranes, selectivity against tumor tissue. Also, CPPs with anticancer activity have been distinguished and summarized with their mechanisms of action. With respect to the conjugates, the preclinical studies (in vitro, in vivo) indicated that they possess several merits in comparison to the parent drugs. They concerned not only better cellular internalization but also other improvements in pharmacokinetics (e.g. access to the brain tissue) and pharmacodynamics (e.g. overcoming drug resistance). The anticancer activity of the conjugates was usually superior to that of the unconjugated drug. Certain anticancer CPPs and conjugates entered clinical trials.

Cell-Penetrating Peptides as Carriers for Transepithelial Drug Delivery

This chapter describes the use of cell-penetrating peptides (CPPs) as carriers for transepithelial delivery of therapeutic peptides. Assessment of transepithelial peptide permeation and the mechanisms of action that permeability enhancing drug carriers exert on the epithelium requires subtle sample preparation and analysis by orthogonal methods. Here, the preparation and use of CPP-insulin physical mixture samples including the quantification of insulin by enzyme-linked immunosorbent assay (ELISA) is described. In addition, effects of CPPs on the epithelium and its barrier properties immediately upon exposure and after a recovery period are evaluated by epithelial cell viability, transepithelial electrical resistance, immunostaining of the tight junction associated zonula occludens (ZO-1) protein, and actin cytoskeleton staining.

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.

Traditional herbal medicine and nanomedicine: Converging disciplines to improve therapeutic efficacy and human health

Traditional herbal medicine (THM), an ancient science, is a gift from nature. For thousands of years, it has helped humans fight diseases and protect life, health, and reproduction. Nanomedicine, a newer discipline has evolved from exploitation of the unique nanoscale morphology and is widely used in diagnosis, imaging, drug delivery, and other biomedical fields. Although THM and nanomedicine differ greatly in time span and discipline dimensions, they are closely related and are even evolving toward integration and convergence. This review begins with the history and latest research progress of THM and nanomedicine, expounding their respective developmental trajectory. It then discusses the overlapping connectivity and relevance of the two fields, including nanoaggregates generated in herbal medicine decoctions, the application of nanotechnology in the delivery and treatment of natural active ingredients, and the influence of physiological regulatory capability of THM on the in vivo fate of nanoparticles. Finally, future development trends, challenges, and research directions are discussed.

Engineered synthetic cell penetrating peptide with intracellular anti-inflammatory bioactivity: An in vitro and in vivo study

Various biomaterials have been used for bone and cartilage regeneration, and inflammation associated with biomaterial implantation is also increased. A 15-mer synthetic anti-inflammatory peptide (SAP15) was designed from human β-defensin 3 to penetrate cells and induce intracellular downregulation of inflammation. The downregulation of inflammation was achieved by the binding of SAP15 to intracellular histone deacetylase (HDAC5). SAP15-mediated inhibition of inflammation was examined in vitro and in vivo using murine macrophages, human articular chondrocytes, and a collagen-induced arthritis (CIA) rat model. Surface plasmon resonance and immunoprecipitation assays indicated that SAP15 binds to HDAC5. SAP15 inhibited the lipopolysaccharide (LPS)-induced phosphorylation of intracellular HDAC5 and NF-κB p65 in murine macrophages. SAP15 treatment increased aggrecan and type II collagen expression and decreased osteocalcin expression in LPS-induced chondrocytes. Subcutaneous injection of SAP15-loaded sodium hyaluronic acid (HA) solution significantly decreased hind paw swelling, joint inflammation, and serum cytokine levels in CIA rats compared with the effects of sodium HA solution alone. The SAP15-loaded HA group exhibited preservation of cartilage and bone structure in CIA rat joints. Moreover, a more robust anti-inflammatory effect of the SAP15 loaded HA was observed than that of etanercept (an anti-tumor necrosis factor-alpha [TNF-α] antibody)-loaded HA. These findings suggest that SAP15 has an anti-inflammatory effect that is not controlled by sodium HA and is mediated by inhibiting HDAC5, unlike the anti-inflammatory mechanism of etanercept. These results demonstrate that SAP15 is useful as an inflammatory regulator of biomaterials and can be developed as a therapeutic for the treatment of inflammation.

Cell-Penetrating Peptides and Transportan

In the most recent 25–30 years, multiple novel mechanisms and applications of cell-penetrating peptides (CPP) have been demonstrated, leading to novel drug delivery systems. In this review, I present a brief introduction to the CPP area with selected recent achievements. This is followed by a nostalgic journey into the research in my own laboratories, which lead to multiple CPPs, starting from transportan and paving a way to CPP-based therapeutic developments in the delivery of bio-functional materials, such as peptides, proteins, vaccines, oligonucleotides and small molecules, etc.

Progress in tumour-targeted drug delivery based on cell-penetrating peptides

Since the discovery of cell-penetrating peptides (CPP) in the 1980s, they have played a unique role in various fields owing to their excellent and unique cell membrane penetration function. In particular, in the treatment of tumours, CPPS have been used to deliver several types of 'cargos' to cancer cells. To address the insufficient targeting ability, non-selectivity, and blood instability, activatable cell-penetrating peptides, which can achieve targeted drug delivery in tumour treatment, enhance curative effects, and reduce toxicity have been developed. This study reviews the application of different cell-penetrating peptides in tumour-targeted delivery, overcoming multidrug resistance, organelle targeting, tumour imaging, and diagnosis, and summarises the different mechanisms of activatable cell-penetrating peptides in detail.

Integrating Biomaterials and Genome Editing Approaches to Advance Biomedical Science

The recent discovery and subsequent development of the CRISPR-Cas9 (clustered regularly interspaced short palindromic repeat-CRISPR-associated protein 9) platform as a precise genome editing tool have transformed biomedicine. As these CRISPR-based tools have matured, multiple stages of the gene editing process and the bioengineering of human cells and tissues have advanced. Here, we highlight recent intersections in the development of biomaterials and genome editing technologies. These intersections include the delivery of macromolecules, where biomaterial platforms have been harnessed to enable nonviral delivery of genome engineering tools to cells and tissues in vivo. Further, engineering native-like biomaterial platforms for cell culture facilitates complex modeling of human development and disease when combined with genome engineering tools. Deeper integration of biomaterial platforms in these fields could play a significant role in enabling new breakthroughs in the application of gene editing for the treatment of human disease.

Predicting cell-penetrating peptides using machine learning algorithms and navigating in their chemical space

Cell-penetrating peptides (CPPs) are naturally able to cross the lipid bilayer membrane that protects cells. These peptides share common structural and physicochemical properties and show different pharmaceutical applications, among which drug delivery is the most important. Due to their ability to cross the membranes by pulling high-molecular-weight polar molecules, they are termed Trojan horses. In this study, we proposed a machine learning (ML)-based framework named BChemRF-CPPred (beyond chemical rules-based framework for CPP prediction) that uses an artificial neural network, a support vector machine, and a Gaussian process classifier to differentiate CPPs from non-CPPs, using structure- and sequence-based descriptors extracted from PDB and FASTA formats. The performance of our algorithm was evaluated by tenfold cross-validation and compared with those of previously reported prediction tools using an independent dataset. The BChemRF-CPPred satisfactorily identified CPP-like structures using natural and synthetic modified peptide libraries and also obtained better performance than those of previously reported ML-based algorithms, reaching the independent test accuracy of 90.66% (AUC = 0.9365) for PDB, and an accuracy of 86.5% (AUC = 0.9216) for FASTA input. Moreover, our analyses of the CPP chemical space demonstrated that these peptides break some molecular rules related to the prediction of permeability of therapeutic molecules in cell membranes. This is the first comprehensive analysis to predict synthetic and natural CPP structures and to evaluate their chemical space using an ML-based framework. Our algorithm is freely available for academic use at http://comptools.linc.ufpa.br/BChemRF-CPPred .

Trends in peptide drug discovery

Since the introduction of insulin almost a century ago, more than 80 peptide drugs have reached the market for a wide range of diseases, including diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain. In this Perspective, we summarize key trends in peptide drug discovery and development, covering the early efforts focused on human hormones, elegant medicinal chemistry and rational design strategies, peptide drugs derived from nature, and major breakthroughs in molecular biology and peptide chemistry that continue to advance the field. We emphasize lessons from earlier approaches that are still relevant today as well as emerging strategies such as integrated venomics and peptide-display libraries that create new avenues for peptide drug discovery. We also discuss the pharmaceutical landscape in which peptide drugs could be particularly valuable and analyse the challenges that need to be addressed for them to reach their full potential.

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

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

Topical Application of Peptide-Chondroitin Sulfate Nanoparticles Allows Efficient Photoprotection in Skin

In this article, we describe a method of delivery of chondroitin sulfate to skin as nanoparticles and demonstrate its anti-inflammatory and antioxidant role using UV irradiation as a model condition. These nanoparticles, formed through electrostatic interactions of chondroitin sulfate with a skin-penetrating peptide, were found to be homogenous with positive surface charges and stable at physiological and acidic pH under certain conditions. They were able to enter into the human keratinocyte cell line (HaCaT), artificial skin membrane (mimicking the human skin), and mouse skin tissue unlike free chondroitin sulfate. The preapplication of nanoparticles also exhibited reduced levels of oxidative stress, cyclobutane pyrimidine dimer formation, TNF-α, and so on in UV-B-irradiated HaCaT cells. In an acute UV-B irradiation mouse model, their topical application resulted in reduced epidermal thickness and sunburn cells, unlike in the case of free chondroitin sulfate. Thus, a completely noninvasive method was used to deliver a bio-macromolecule into the skin without using injections or abrasive procedures.

Emerging era of microneedle array for pharmaceutical and biomedical applications: recent advances and toxicological perspectives

Background

Microneedles (MNs) are the utmost unique, efficient, and minimally invasive inventions in the pharmaceutical field. Over the past decades, many scientists around the globe have reported MNs cautious because of their superb future in distinct areas. Concerning the wise use of MNs herein, we deal in depth with the present applications of MNs in drug delivery.

Main text

The present review comprises various fabrication materials and methods used for MN synthesis. The article also noted the distinctive advantages of these MNs, which holds huge potential for pharmaceutical and biomedical applications. The role of MNs in serving as a platform to treat various ailments has been explained accompanied by unusual approaches. The review also inculcates the pharmacokinetics of MNs, which includes permeation, absorption, and bioavailability enhancement. Besides this, the in vitro/in vivo toxicity, biosafety, and marketed product of MNs have been reviewed. We have also discussed the clinical trials and patents on the pharmaceutical applications of MNs in brief.

Conclusion

To sum up, this article gives insight into the MNs and provides a recent advancement in MNs, which pave the pathway for future pharmaceutical and biomedical applications.

Graphical abstract

Pharmaceutical and biomedical applications of MNs

pH-Activatable cell penetrating peptide dimers for potent delivery of anticancer drug to triple-negative breast cancer

We developed a pH-activatable cell-penetrating peptide dimer LH₂ with histidine residues, which can penetrate cells, specifically in weak acidic conditions, even at few tens of nanomolar concentrations. LH₂ effectively delivered paclitaxel into triple-negative breast cancer cells, MDA-MB-231, via formation of non-covalent complexes (PTX-LH₂(M)) or covalent conjugates (PTX-LH₂(C)). Moreover, LH₂ showed prolonged circulation in the body and enhanced accumulation in tumors. Both PTX-LH₂(M) and PTX-LH₂(C) showed strong antitumor effects in a triple-negative breast cancer grafted mouse model at an extremely low dosage.

Activation of cell-penetrating peptide fragments by disulfide formation

Three cell-penetrating peptides (CPPs), Tat, Pep-3 and penetratin, were split into two parts and each fragment was terminated with a cysteine residue, to allow disulfide bridge formation, as well as a fluorescent label, for visualization and quantitative analysis. After disulfide formation between two complementary CPP fragments, cellular uptake of the resulting conjugates was observed. As confirmed by in vitro experiments, the conjugated peptides showed uptake activity comparable to the native CPP sequences, while the truncated peptides were hardly active. Until now, this split CPP strategy has only been demonstrated for oligo-arginine CPPs, but here we demonstrate that it is also applicable to other cell-penetrating peptides. This wider applicability may help in the design of new activatable cell-penetrating peptides for, e.g., targeted drug delivery.

A Selective Carborane-Functionalized Gastrin-Releasing Peptide Receptor Agonist as Boron Delivery Agent for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) allows the selective elimination of malignant tumor cells without affecting healthy tissue. Although this binary radiotherapy approach has been known for decades, BNCT failed to reach the daily clinics to date. One of the reasons is the lack of selective boron delivery agents. Using boron loaded peptide conjugates, which address G protein-coupled receptors overexpressed on tumor cells allow the intracellular accumulation of boron. The gastrin-releasing peptide receptor (GRPR) is a well-known target in cancer diagnosis and can potentially be used for BNCT. Here, we present the successful introduction of multiple bis-deoxygalactosyl-carborane building blocks to the GRPR-selective ligand [d-Phe⁶, β-Ala¹¹, Ala¹³, Nle¹⁴]Bn(6-14) (sBB2L) generating peptide conjugates with up to 80 boron atoms per molecule. Receptor activation was retained, metabolic stability was increased, and uptake into PC3 cells was proven without showing any intrinsic cytotoxicity. Furthermore, undesired uptake into liver cells was suppressed by using l-deoxygalactosyl modified carborane building blocks. Due to its high boron loading and excellent GRPR selectivity, this conjugate can be considered as a promising boron delivery agent for BNCT.

Selective Neuropeptide Y Conjugates with Maximized Carborane Loading as Promising Boron Delivery Agents for Boron Neutron Capture Therapy

G-protein-coupled receptors like the human Y₁ receptor (hY₁R) are promising targets in cancer therapy due to their high overexpression on cancer cells and their ability to internalize together with the bound ligand. This mechanism was exploited to shuttle boron atoms into cancer cells for the application of boron neutron capture therapy (BNCT), a noninvasive approach to eliminate cancer cells. A maximized number of carboranes was introduced to the hY₁R-preferring ligand [F⁷,P³⁴]-NPY by solid phase peptide synthesis. Branched conjugates loaded with up to 80 boron atoms per peptide molecule exhibited a maintained receptor activation profile, and the selective uptake into hY₁R-expressing cells was demonstrated by internalization studies. In order to ensure appropriate solubility in aqueous solution, we proved the need for eight hydroxyl groups per carborane. Thus, we suggest the utilization of bis-deoxygalactosyl-carborane building blocks in solid phase peptide synthesis to produce selective boron delivery agents for BNCT.

Stimuli-Sensitive Cell Penetrating Peptide-Modified Nanocarriers

The integration of drugs into nanocarriers favorably altered their pharmacodynamics and pharmacokinetics compared to free drugs, and increased their therapeutic index. However, selective cellular internalization in diseased tissues rather than normal tissues still presents a formidable challenge. In this chapter I will cover solutions involving environment-responsive cell-penetrating peptides (CPPs). I will discuss properties of CPPs as universal cellular uptake enhancers, and the modifications imparted to CPP-modified nanocarriers to confine CPP activation to diseased tissues.

Strategies to facilitate or block nose-to-brain drug delivery

Nose-to-brain delivery has gained significant interest over the past several decades. This has resulted in numerous strategies described to improve the delivery of drugs to the brain directly through the olfactory epithelium of the nasal cavity. In some cases, intranasal administration may be more effective than other routes of administration in treating central nervous system and related disorders. Here, we briefly review the strategies that have been used to facilitate nose-to-brain delivery as well as approaches to block the delivery of drugs from the nose to the brain. Even though numerous strategies have already been used to increase nose-to-brain delivery, the research for strategies inhibitory of nose-to-brain delivery seems to be scarce.

Editing the Central Nervous System Through CRISPR/Cas9 Systems

The translational gap to treatments based on gene therapy has been reduced in recent years because of improvements in gene editing tools, such as the CRISPR/Cas9 system and its variations. This has allowed the development of more precise therapies for neurodegenerative diseases, where access is privileged. As a result, engineering of complexes that can access the central nervous system (CNS) with the least potential inconvenience is fundamental. In this review article, we describe current alternatives to generate systems based on CRISPR/Cas9 that can cross the blood-brain barrier (BBB) and may be used further clinically to improve treatment for neurodegeneration in Parkinson's and Alzheimer's disease (AD).

Tumor gene therapy by systemic delivery of plasmid DNA with cell-penetrating peptides

Gene therapy is a prospective strategy for treating cancer. However, finding efficient and tumor-specific gene delivery vectors remains an issue. Tumor responsive cell-penetrating peptide (CPP) PepFect144 (PF144) has previously been shown to deliver reporter gene encoding plasmid DNA specifically into tumors upon systemic administration, but its capability to reduce tumor growth has not yet been evaluated. Here, we study the potential of PF144-based anti-angiogenic gene delivery to inhibit tumor growth by silencing vascular endothelial growth factor (VEGF) expression in tumors. This approach led to the inhibition of tumor growth in both the HT1080 fibrosarcoma model and orthotopic 4T1 breast tumor model. We additionally saw that the addition of αvβ3 integrin targeting did not further improve the tumor sensitive CPPs. Our results suggest that activatable cell-penetrating peptide PF144 is a promising nonviral plasmid DNA delivery vector for cancer treatment.

1988-2018: Thirty years of drug smuggling at the nano scale. Challenges and opportunities of cell-penetrating peptides in biomedical research

In 1988, two unrelated papers reported the discovery of peptide vectors with innate cell translocation properties, setting the ground for a new area of research that over the years has grown into considerable therapeutic potential. The vectors, named cell-penetrating peptides (CPPs), constitute a now large and diversified family, sharing the extraordinary ability to diffuse unaltered across cell membranes while ferrying diverse associated cargos. Such properties have made CPPs ideal tools for delivery of nucleic acids, proteins and other therapeutic/diagnostic molecules to cells and tissues via covalent conjugation or complexation. This year 2018 marks the 30^th anniversary of a peptide research landmark opening new perspectives in drug delivery. Given its vastness, exhaustive coverage of the main features and accomplishments in the CPP field is virtually impossible. Hence this manuscript, after saluting the above 30^th jubilee, focuses by necessity on the most recent contributions, providing a comprehensive list of recognized CPPs and their latest-reported applications over the last two years. In addition, it thoroughly reviews three areas of peptide vector research of particular interest to us, namely (i) efficient transport of low-bioavailability drugs into the brain; (ii) CPP-delivered disruptors of G protein-coupled receptor (GPCRs) heteromers related to several disorders, and (iii) CPP-mediated delivery of useful but poorly internalized drugs into parasites.

Deepened cellular/subcellular interface penetration and enhanced antitumor efficacy of cyclic peptidic ligand-decorated accelerating active targeted nanomedicines

Introduction

Acceleration and improvement of penetration across cell-membrane interfaces of active targeted nanotherapeutics into tumor cells would improve tumor-therapy efficacy by overcoming the issue of poor drug penetration. Cell-penetrating peptides, especially synthetic polyarginine, have shown promise in facilitating cargo delivery. However, it is unknown whether polyarginine can work to overcome the membrane interface in an inserted pattern for cyclic peptide ligand-mediated active targeting drug delivery. Here, we conducted a study to test the hypothesis that tandem-insert nona-arginine (tiR₉) can act as an accelerating component for intracellular internalization, enhance cellular penetration, and promote antitumor efficacy of active targeted cyclic asparagine–glycine–arginine (cNGR)-decorated nanoliposomes.

Methods

Polyarginine was coupled with the polyethylene glycol (PEG) chain and the cNGR moiety, yielding a cNGR–tiR₉–PEG_2,000–distearoylphosphatidylethanolamine conjugate.

Results

The accelerating active targeted liposome (Lip) nanocarrier (cNGR-tiR₉-Lip–doxorubicin [Dox]) constructed in this study held suitable physiochemical features, such as appropriate particle size of ~150 nm and sustained-release profiles. Subsequently, tiR₉ was shown to enhance cellular drug delivery of Dox-loaded active targeted systems (cNGR-Lip-Dox) significantly. Layer-by-layer confocal microscopy indicated that the tandem-insert polyarginine accelerated active targeted system entry into deeper intracellular regions based on observations at marginal and center locations. tiR₉ enhanced the penetration depth of cNGR-Lip–coumarin 6 through subcellular membrane barriers and caused its specific accumulation in mitochondria, endoplasmic reticulum, and Golgi apparatus. It was also obvious that cNGR-tiR₉-Lip-Dox induced enhanced apoptosis and activated caspase 3/7. Moreover, compared with cNGR-Lip-Dox, cNGR-tiR₉-Lip-Dox induced a significantly higher antiproliferative effect and markedly suppressed tumor growth in HT1080-bearing nude mice.

Conclusion

This active tumor-targeting nanocarrier incorporating a tandem-insert polyarginine (tiR₉) as an accelerating motif shows promise as an effective drug-delivery system to accelerate translocation of drugs across tumor-cell/subcellular membrane barriers to achieve improved specific tumor therapy.

Membrane Active Peptides and Their Biophysical Characterization

In the last 20 years, an increasing number of studies have been reported on membrane active peptides. These peptides exert their biological activity by interacting with the cell membrane, either to disrupt it and lead to cell lysis or to translocate through it to deliver cargos into the cell and reach their target. Membrane active peptides are attractive alternatives to currently used pharmaceuticals and the number of antimicrobial peptides (AMPs) and peptides designed for drug and gene delivery in the drug pipeline is increasing. Here, we focus on two most prominent classes of membrane active peptides; AMPs and cell-penetrating peptides (CPPs). Antimicrobial peptides are a group of membrane active peptides that disrupt the membrane integrity or inhibit the cellular functions of bacteria, virus, and fungi. Cell penetrating peptides are another group of membrane active peptides that mainly function as cargo-carriers even though they may also show antimicrobial activity. Biophysical techniques shed light on peptide–membrane interactions at higher resolution due to the advances in optics, image processing, and computational resources. Structural investigation of membrane active peptides in the presence of the membrane provides important clues on the effect of the membrane environment on peptide conformations. Live imaging techniques allow examination of peptide action at a single cell or single molecule level. In addition to these experimental biophysical techniques, molecular dynamics simulations provide clues on the peptide–lipid interactions and dynamics of the cell entry process at atomic detail. In this review, we summarize the recent advances in experimental and computational investigation of membrane active peptides with particular emphasis on two amphipathic membrane active peptides, the AMP melittin and the CPP pVEC.

Smart Cell-Penetrating Peptide-Based Techniques for Intracellular Delivery of Therapeutic Macromolecules

Many therapeutic macromolecules must enter cells to take their action. However, their treatment outcomes are often hampered by their poor transportation into target cells. Therefore, efficient intracellular delivery of these macromolecules is critical for improving their therapeutic efficacy. Cell-penetrating peptide (CPP)-based approaches are one of the most efficient methods for intracellular delivery of macromolecular therapeutics. Nevertheless, poor specificity is a significant concern for systemic administrated CPP-based delivery systems. This chapter will review recent advances in CPP-mediated macromolecule delivery with a focus on various smart strategies which not only enhance the intracellular delivery but also improve the targeting specificity.

(Some) current concepts in antibacterial drug discovery

The rise of multidrug resistance in bacteria rendering pathogens unresponsive to many clinical drugs is widely acknowledged and considered a critical global healthcare issue. There is broad consensus that novel antibacterial chemotherapeutic options are extremely urgently needed. However, the development pipeline of new antibacterial drug lead structures is poorly filled and not commensurate with the scale of the problem since the pharmaceutical industry has shown reduced interest in antibiotic development in the past decades due to high economic risks and low profit expectations. Therefore, academic research institutions have a special responsibility in finding novel treatment options for the future. In this mini review, we want to provide a broad overview of the different approaches and concepts that are currently pursued in this research field.

Hyperosmotic treatment synergistically boost efficiency of cell-permeable peptides

Therapeutics delivery into cells has been hurdled due to the barrier of cytoplasmic membrane. Although cell penetrating peptide (CPP) can potentially serve as an intracellular drug delivery vehicle, the application of CPP-based delivery is limited because the unsatisfactory delivery efficiency of CPP conjugated potent cargos is challenging their applications in present. Thus, the development of strategies for enhancing the penetrating efficiency of CPP would therefore urgent need to be explored to increase the scope of potential applications. We report here the effects of glucose, sucrose and manntiol (abbreviated as GSM) combination facilitating the penetration efficiency of CPP peptide alone or CPP-GFP (green fluorescence protein) conjugation in cultured cell lines or primary cells. Moreover, osmoprotectants glycerol and glycine supplementation help cells cope with the stress from GSM combination. Thus, our present study suggests that GSM combination in the presence of osmoprotectant can work as a new strategy for CPP penetration enhancement.

Passive delivery of protein drugs through transdermal route

Skin is the largest external organ in the human body but its use for therapeutic purposes has been minimal. Stratum corneum residing on the uppermost layer of the skin provides a tough barrier to transport the drugs across the skin. Very small group of drugs sharing Lipinski properties, i.e. drugs having molecular weight not larger than 500 Da, having high lipophilicity and optimum polarity are fortunate enough to be used on skin therapeutics. But, at a time where modern therapeutics is slowly shifting from use of small molecular drugs towards the use of macromolecular therapeutic agents such as peptides, proteins and nucleotides in origin, skin therapeutics need to be evolved accordingly to cater the delivery of these agents. Physical technologies like iontophoresis, laser ablation, micro-needles and ultrasound, etc. have been introduced to enhance skin permeability. But their success is limited due to their complex working mechanisms and involvement of certain irreversible skin damage in some or other way. This review therefore explores the delivery strategies for transport of mainly peptide and protein drugs that do not involve any injuries (non-invasive) to the skin termed as passive delivery techniques. Chemical enhancers, nanocarriers, certain biological peptides and miscellaneous approaches like prodrugs are also thoroughly reviewed for their applications in protein delivery.

Improved antibacterial activity of a marine peptide-N2 against intracellular Salmonella typhimurium by conjugating with cell-penetrating peptides-bLFcin6/Tat11

Salmonellae, gram-negative bacteria, are facultative intracellular pathogens that cause a number of diseases in animals and humans. The poor penetration ability of antimicrobial agents limits their use in the treatment of intracellular bacterial infections. In this study, the cell-penetrating peptides (CPPs) bLFcin₆ and Tat₁₁ were separately conjugated to the antimicrobial peptide N2, and the antibacterial activity and pharmacodynamics of the CPPs-N2 conjugates were first evaluated against Salmonellae typhimurium in vitro and in macrophage cells. The cytotoxicity, cellular uptake and mechanism of cellular internalization of the CPPs-N2 conjugates were also examined in RAW264.7 cells. Similar to N2, CPPs-N2 have two reverse β-sheets and three loops. The minimal inhibitory concentration (MIC) of CPPs-N2 was approximately 2 μM, which was higher than that of N2 (0.8 μM). The dose-time curves and cytotoxicity assay showed that both peptide conjugates were more effective than N2 alone at concentrations ranging from 0.25 to 1 × MIC, and they exhibited low cytotoxicity (9.78%-13.54%) at 100 μM. After 0.5 h incubation, the cell internalization ratio of B6N2 and T11N2 exceeded 28.3% and 93.5%, respectively, which was higher than that of N2. The uptake of B6N2 and T11N2 was reduced by low temperature (82.1%-91.7%), chlorpromazine (35.7%-75.1%), and amiloride (26.0%-52.1%), indicating that macropinocytosis and clathrin-mediated endocytosis may be involved. Approximately 98.85% and 91.35% of bacteria were killed within 3 h by T11N2 and B6N2, respectively, which was higher than the percentage killed by N2 (69.74%). Compared with the bactericidal activity of N2 alone, the bactericidal activity of T11N2 and B6N2 was increased by 53.7%-99.6% and 85.3-85.8%, respectively. Both CPPs-N2 conjugates may be excellent candidates for novel antimicrobial agents to treat infectious diseases caused by intracellular pathogens.

Peptide inhibition of the SETD6 methyltransferase catalytic activity

A large body of evidence accumulating in the past few years indicates the physiological significance of non-histone proteins lysine methylation, catalyzed by protein lysine methyl transferases (PKMTs). Dysregulation of these enzymes was shown to contribute to the development and progression of numerous diseases. SETD6 lysine methylatransferase was recently shown to participate in essential cellular processes, such as the NFkB pathway, oxidative stress and also the Wnt signaling cascade. In order to test the effect of blocking SETD6 catalytic activity, we used the peptide inhibition method, which is considered highly specific and can potentially target almost any protein. We designed a 15 amino acids peptide based on the sequence of the RelA protein (residues 302-316), containing the lysine that is methylated by SETD6. To enable cellular intake, the designed peptide was fused to a cell penetrating peptide (CPP) vp22. The vp22-RelA302-316 peptide showed direct and specific interaction with SETD6 in vitro. This interaction was shown to inhibit SETD6 methyltransferase activity. SETD6 catalytic blockage by the peptide was also observed in cells upon treatment with the vp22-RelA302-316, resulting in induced cellular migration and proliferation. This new insight into the activity of a methylation inhibitory peptide could represent a milestone in the development of therapeutic tools, which can be of use in physiological cases where administration of cell proliferation is required.

Intelligent "Peptide-Gathering Mechanical Arm" Tames Wild "Trojan-Horse" Peptides for the Controlled Delivery of Cancer Nanotherapeutics

Cell-penetrating peptides (CPPs), also called "Trojan-Horse" peptides, have been used for facilitating intracellular delivery of numerous diverse cargoes and even nanocarriers. However, the lack of targeting specificity ("wildness" or nonselectivity) of CPP-nanocarriers remains an intractable challenge for many in vivo applications. In this work, we used an intelligent "peptide-gathering mechanical arm" (Int PMA) to curb CPPs' wildness and enhance the selectivity of R₉-liposome-based cargo delivery for tumor targeting. The peptide NGR, serving as a cell-targeting peptide for anchoring, and peptide PLGLAG, serving as a substrate peptide for deanchoring, were embedded in the Int PMA motif. The Int PMA construct was designed to be sensitive to tumor microenvironmental stimuli, including aminopeptidase N (CD13) and matrix metalloproteinases (MMP-2/9). Moreover, Int PMA could be specifically recognized by tumor tissues via CD13-mediated anchoring and released for cell entry by MMP-2/9-mediated deanchoring. To test the Int PMA design, a series of experiments were conducted in vitro and in vivo. Functional conjugates Int PMA-R₉-poly(ethylene glycol) (PEG)₂₀₀₀-distearoylphosphatidyl-ethanolamine (DSPE) and R₉-PEG₂₀₀₀-DSPE were synthesized by Michael addition reaction and were characterized by thin-layer chromatography and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. The Int PMA-R₉-modified doxorubicin-loaded liposomes (Int PMA-R₉-Lip-DOX) exhibited a proper particle diameter (approximately 155 nm) with in vitro sustained release characteristics. Cleavage assay showed that Int PMA-R₉ peptide molecules could be cleaved by MMP-2/9 for completion of deanchoring. Flow cytometry and confocal microscopy studies indicated that Int PMA-R₉-Lip-DOX can respond to both endogenous and exogenous stimuli in the presence/absence of excess MMP-2/9 and MMP-2/9 inhibitor (GM6001) and effectively function under competitive receptor-binding conditions. Moreover, Int PMA-R₉-Lip-DOX generated more significant subcellular dispersions that were especially evident within endoplasmic reticulum (ER) and Golgi apparatus. Notably, Int PMA-R₉-Lip-DOX could induce enhanced apoptosis, during which caspase 3/7 might be activated. In addition, Int PMA-R₉-Lip-DOX displayed enhanced in vitro and in vivo antitumor efficacy versus "wild" R₉-Lip-DOX. On the basis of investigations at the molecular level, cellular level, and animals' level, the control of Int PMA was effective and promoted selective delivery of R₉-liposome cargo to the target site and reduced nonspecific uptake. This Int PMA-controlled strategy based on aminopeptidase-guided anchoring and protease-triggered deanchoring effectively curbed the wildness of CPPs and bolstered their effectiveness for in vivo delivery of nanotherapeutics. The specific nanocarrier delivery system used here could be adapted using a variety of intelligent designs based on combinations of multifunctional peptides that would specifically and preferentially bind to tumors versus nontumor tissues for tumor-localized accumulation in vivo. Thus, CPPs have a strong advantage for the development of intelligent nanomedicines for targeted tumor therapy.

Advances in therapeutic bacterial antisense biotechnology

Antisense therapeutics are a biotechnological form of antibiotic therapy using chemical analogues of short single-stranded nucleic acid sequences modified to form stable oligomers. These molecules are termed antisense oligonucleotides (ASOs) because their sequence is complementary, via Watson-Crick specific base pairing, to their target messenger RNA (mRNA). ASOs modify gene expression in this sequence-dependent manner by binding to its complementary mRNA and inhibiting its translation into protein through steric blockage and/or through RNase degradation of the ASO/RNA duplex. The widespread use of conventional antibiotics has led to the increasing emergence of multiple drug-resistant pathogenic bacteria. There is an urgent need to develop alternative therapeutic strategies to reduce the morbidity and mortality associated with bacterial infections, and until recently, the use of ASOs as therapeutic agents has been essentially limited to eukaryotic cells, with ASOs as antibacterials having been largely unexplored primarily due to the poor uptake efficiency of antisense molecules by bacteria. There are conceptual advantages to bacterial antisense antibiotic therapies, including a sequence-dependent approach that allows for a rational design to multiple specific molecular targets. This review summarizes the current knowledge of antisense bacterial biotechnology and highlights the recent progress and the current obstacles in their development for therapeutic applications.

TAT-modified self-assembled cationic peptide nanoparticles as an efficient antibacterial agent

The increasing emergence of drug resistant pathogenic bacteria poses a great challenge to clinical therapy and a threat to public health. Cationic peptides have received great attention for their unique antibacterial mechanism and ability to combat drug-resistant bacteria. In this study, we designed a TAT-modified cationic peptide PA-28 which self-assembled into nanoparticles of about 150 nm. These nanoparticles showed strong antimicrobial activities against both gram-positive and gram-negative bacteria, including drug-resistant bacteria. They were more potent than the unassembled counterpart peptide nonalysine (K₉). Their antibacterial mechanism of directly destructing bacterial wall/membrane reduces the possibility of developing bacterial resistance. In vivo anti-infective experiments showed that these nanoparticles were able to penetrate the blood-brain barrier to inhibit bacterial growth in infected brains of rats. In addition, these nanoparticles induced low hemolysis below the minimum inhibitory concentration. Therefore, the peptide designed in this study is a promising and efficient antibacterial agent against bacterial infections.

Dodging Endosomes: Effective Cytosolic Antibody Delivery

On the inside: New methodologies for delivering antibodies right into the cytosol of cells either directly across the plasma membrane or by allowing the antibody to escape from endosomes have been proposed recently by the Cardoso/Hackenberger and Futaki groups, respectively.

Cell-Permeable, MMP-2 Activatable, Nickel Ferrite and His-Tagged Fusion Protein Self-Assembled Fluorescent Nanoprobe for Tumor Magnetic-Targeting and Imaging

Matrix metalloproteinases (MMPs) activatable imaging probe has been explored for tumor detection. However, activation of the probe is mainly done in the extracellular space without intracellular uptake of the probe for more sensitivity. Although cell-penetrating peptides (CPPs) have been demonstrated to enable intracellular delivery of the imaging probe, they nevertheless encounter off-target delivery of the cargos to normal tissues. Herein, we have developed a dual MMP-2-activatable and tumor cell-permeable magnetic nanoprobe to simultaneously achieve selective and intracellular tumor imaging. This novel imaging probe was constructed by self-assembling a hexahistidine-tagged (His-tagged) fluorescent fusion protein chimera and nickel ferrite nanoparticles via a chelation mechanism. The His-tagged fluorescent protein chimera consisted of a red fluorescent protein mCherry that acted as the fluorophore, the low-molecular-weight protamine peptide as the CPP, and the MMP-2 cleavage sequence fused with the hexahistidine tag, whereas the nickel ferrite nanoparticles functioned as the His-tagged protein binder and also the fluorescent quencher. Both in vitro and in vivo results revealed that this imaging probe would not only remain nonpermeable to normal tissues, thereby offsetting the nonselective cellular uptake, but was also suppressed of fluorescent signals during magnetic tumor-targeting in the circulation, primarily because of the masking of the CPP activity and quenching of the fluorophore by the associated NiFe₂O₄ nanoparticles. However, these properties were recovered or "turned on" by the action of tumor-associated MMP-2 stimuli, leading to cell penetration of the nanoprobes as well as fluorescence restoration and visualization within the tumor cells. In this regard, the presented tumor-activatable and cell-permeable system deems to be an appealing platform to achieve selective tumor imaging and intracellular protein delivery. Its impact is therefore significant, far-reaching, and wide-spread.

Transporting carriers for intracellular targeting delivery via non-endocytic uptake pathways

To develop novel therapies for clinical treatments, it increasingly depends on sophisticated delivery systems that facilitate the drugs entry into targeting cells. Profound understanding of cellular uptake routes for transporting carriers promotes the optimization of performance in drug delivery systems. Although endocytic pathway is the most important part of cellular uptake routes for many delivery systems, it suffers the trouble of enzymatic degradation of transporting carriers trapped in endosomes/lysosomes. Therefore, it is desirable to develop alternative transporting methods for delivery systems via non-endocytic pathways to achieve more effective intracellular delivery. In this review, we summarize the literature exploring transporting carriers that mediate intracellular delivery via non-endocytic pathways to present the current research status in this field. Cell-penetrating peptides, pH (low) insertion peptides, and nanoparticles are categorized to exhibit their ability to directly transport various cargos into cytoplasm via non-endocytic uptake in different cell lines. It is hoped that this review can spur the interesting on development of drug delivery systems via non-endocytic uptake pathway.