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

Screening and evaluation of hydrophobic cell-penetrating peptides for antisense oligonucleotide delivery

Antisense oligonucleotides (ASOs) are promising therapeutic agents targeting intracellular RNA, yet their clinical application is limited by poor membrane permeability. To overcome this challenge, we investigated hydrophobic cell-penetrating peptides (CPPs) as alternative delivery vectors. Ten hydrophobic CPPs were synthesized and screened for cellular uptake using live-cell fluorescence imaging. Selected CPPs were conjugated to a chemically modified ASO via click chemistry, and their intracellular delivery and antisense efficacy were evaluated using a splicing reporter assay in HeLa 705 cells. While certain CPPs, such as MPG, showed high membrane permeability, conjugation with ASOs did not always translate to enhanced antisense activity. Notably, among the evaluated CPP-ASO conjugates, SP-ASO exhibited the most potent functional activity despite moderate uptake. This finding suggests that factors beyond membrane permeability, such as endosomal escape, intracellular trafficking, or nuclear delivery efficiency, may critically influence the overall efficacy. Fluorescence microscopy confirmed lysosomal entrapment of both naked and CPP-conjugated ASOs. These findings emphasize the importance of rational design strategies that address endosomal release to maximize the therapeutic potential of CPP-ASO conjugates.

Plasmid DNA delivery using arginine-rich cell-penetrating L/D-peptides containing α-aminoisobutyric acids

The relationship between intracellular uptake efficacy and the folding behavior of arginine-rich cell-penetrating L/D-peptides with α,α-disubstituted α-amino acids in plasmid DNA (pDNA) delivery was examined. Nano-sized complexes formed from pDNA and L/D-peptides efficiently traversed the cell membrane regardless of the peptide conformation. This finding represents a significant deviation from previously reported covalent cargo delivery methods using cell penetrating peptides with L- and D-amino acids.

An insight into cell-penetrating peptides: perspectives on design, optimization, and targeting in drug delivery systems

The authors carried out a comprehensive review of the application of peptides known as cell-penetrating peptides (CPPs) in various drug delivery systems (DDS), with the prospect of achieving novel solutions and ideas to overcome the challenges of DDS, by making them more able to penetrate cells and biological membranes. A conceptual search was conducted in relevant literature databases (Scopus, PubMed, Web of Science, and Google Scholar) up to 1 April 2025 using keywords such as drug delivery systems, cell-penetrating peptides, CPPs, complexes, conjugates, nanoparticles, dendrimers, exosomes, liquid crystalline, liposomes, micelles, nanospheres and lipid nanoparticles. The studies demonstrate that the antimicrobial effect of drugs, including curcumin, gentamicin, and antifungal drugs like imidazoacridinone derivatives, can be enhanced when they are conjugated or complexed with CPPs. CPPs possess positive charges, which make them suitable for gene therapy applications by facilitating the delivery of plasmids and siRNAs with negative charges in modern delivery systems. Medicinal formulations containing CPPs in combination with liquid crystals or nanostructured lipid carriers (NLCs) increase drugs penetration to the skin. Additionally, several investigations showed that CPPs could have a positive impact on the pharmacokinetic and pharmacodynamic of chemotherapy agents, reducing their side effects. CPPs have significant potential in enhancing penetration, bioavailability, targeting, and optimization of DDS. By using computer modeling and designing CPPs with more desirable features and conducting more clinical studies, new methods for treating diseases and better formulations can be achieved.

Strategies for the optimisation of troublesome peptide nucleic acid (PNA) sequences

Through the use of a pseudo-peptidic backbone, peptide nucleic acids (PNA) mimic the functionality of native nucleic acids while enjoying improved binding affinity and metabolic stability. However, many aspects of the application of PNA to biological and medicinal settings still requires sequence specific optimisation. This review highlights key areas for refinement, including synthesis, tuning of physical properties, cell permeability and analysis, including common strategies for the pracitioner to apply in each area.

Cytoplasmic delivery of antibodies through grafting a functional single complementarity-determining region loop

The mouse 3D8 anti-DNA antibody can enter cells and localize in the cytoplasm, primarily facilitated by the complementarity-determining region 1 of the variable light chain (CDR L1) domain. In this study, we grafted the CDR L1 loop from 3D8 onto non-cell-penetrating IgG antibodies to investigate whether these IgGs could acquire cytoplasmic localization ability while retaining antigen-binding activity. One of three IgGs was successfully delivered into the cytoplasm while maintaining antigen-binding activity. In silico protein modeling suggests that this capability is linked to structural similarity between CDR L1 in the grafted Ab and that in 3D8. This study proposes a strategy to confer cell-penetrating capability by incorporating a specific CDR loop into an antibody backbone while retaining affinity.

An Intracellular Peptide Library Screening Platform Identifies Irreversible Covalent Transcription Factor Inhibitors

The development of an intracellular peptide library screening platform is described to identify covalent transcription factor (TF) antagonists. The Transcription Block Survival (TBS) assay and subsequent hit refinement previously produced potent but reversible antagonists of the oncogenic TF cJun. TBS moves beyond a target binding readout to ensure loss of TF function by blocking TF-DNA binding. Here, the TBS methodology is significantly expanded to identify covalent and highly selective inhibitors. A 131,072-member library is probed containing a Cys option at nine positions within a non-reducing cell line. This identified a single Cys residue with the appropriate geometry for disulphide bond formation with cJun C269 in its DNA binding domain. The selection of a unique Cys in the antagonist indicates both target shutdown and concomitant disulphide formation in a single step, resulting in increased potency. Substituting Cys with an electrophile generates an irreversible yet highly selective covalent cJun inhibitor capable of penetrating human melanoma cells in culture and depleting oncogenic cJun levels to inhibit cell viability, with enhanced efficacy compared to a previous cJun-targeting peptide. This enhanced covalent-TBS screening pipeline provides a robust approach to profile target protein surfaces for ligandable cysteines, producing covalent and selective antagonists with appropriately positioned warheads.

Peptide-Drug Conjugates as Next-Generation Therapeutics: Exploring the Potential and Clinical Progress

Peptide-drug conjugates (PDCs) have emerged as a next-generation therapeutic platform, combining the target specificity of peptides with the pharmacological potency of small-molecule drugs. As an evolution beyond antibody-drug conjugates (ADCs), PDCs offer distinct advantages, including enhanced cellular permeability, improved drug selectivity, and versatile design flexibility. This review provides a comprehensive analysis of the fundamental components of PDCs, including homing peptide selection, linker engineering, and payload optimization, alongside strategies to address their inherent challenges, such as stability, bioactivity, and clinical translation barriers. Therapeutic applications of PDCs span oncology, infectious diseases, metabolic disorders, and emerging areas like COVID-19, with several conjugates advancing in clinical trials and achieving regulatory milestones. Innovations, including bicyclic peptides, supramolecular architectures, and novel linker technologies, are explored as promising avenues to enhance PDC design. Additionally, this review examines the clinical trajectory of PDCs, emphasizing their therapeutic potential and highlighting ongoing trials that exemplify their efficacy. By addressing limitations and leveraging emerging advancements, PDCs hold immense promise as targeted therapeutics capable of addressing complex disease states and driving progress in precision medicine.

Advances in cell-penetrating peptide-based nose-to-brain drug delivery systems

The incidence of brain disorders has gained worldwide attention and the presence of the blood-brain barrier prevents numerous drugs from reaching the targeted brain. The specific physiology of the nasal cavity and the brain provides the feasibility of direct nose-brain delivery, a system that bypasses the blood-brain barrier in a non-invasive manner for brain-targeted drug delivery via intracellular and extracellular mechanisms. The use of CPPs provides further feasibility for naso-brain drug delivery studies, and liposomes, nanopolymer particles, and gels modified with CPPs have demonstrated significant brain-targeting capabilities after nasal delivery. In this paper, the physiology of the nasal cavity and brain, the pathways of naso-brain delivery and the influencing factors are discussed in detail. At the same time, the introduction, classification, mechanism of action and application of CPPs in the nasal-brain delivery system are discussed in detail to provide a theoretical basis for the in-depth study of the application of CPPs in the nasal-brain delivery system.

HPMA Copolymers: A Versatile Platform for Targeted Peptide Drug Delivery

Peptide drugs have been broadly applied in cancer treatment and diagnosis due to their ability to accurately identify biomarkers with good biocompatibility. However, their clinical application is limited by protease degradation, which induces short circulation half-life, low bioavailability, and high renal clearance. In recent years, delivery systems based on nanomaterial technology have become an important strategy to break through the bottleneck of peptide drug delivery. Among them, N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers have attracted much attention due to their good biocompatibility, hydrophilicity, and low immunogenicity. The high molecular weight of HPMA copolymer-peptide can circumvent renal clearance, significantly prolong the circulation time in the body, and achieve drug accumulation and microenvironment-triggered release synergistically with EPR effects and active targeting. This review introduces the basic properties of HPMA copolymers, including solubility, biocompatibility, and tunable chemical structure. The important applications of HPMA copolymer-peptide in tumor diagnosis and treatment are discussed. This review deepens our understanding of the future development of HPMA copolymers and will provide more references for improving peptides by simple copolymers.

CPPCGM: A Highly Efficient Sequence-Based Tool for Simultaneously Identifying and Generating Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are usually short oligopeptides with 5-30 amino acid residues. CPPs have been proven as important drug delivery vehicles into cells through different mechanisms, demonstrating their potential as therapeutic candidates. However, experimental screening and synthesis of CPPs could be time-consuming and expensive. Recently, numerous attempts have been made to develop computational methods as a cost-effective way for screening a number of potential CPP candidates. Despite significant advancements, current methods exhibit limited feature representation capabilities, thereby constraining the potential for further performance enhancements. In this study, we developed a deep learning framework called CPPCGM, which uses protein language models (PLMs) to identify and generate novel CPPs. There are two separate blocks in this framework: CPPClassifier and CPPGenerator. The former utilizes three pretrained models for simple voting, thereby accurately categorizing CPPs and non-CPPs. The latter, similar to a generative adversarial network, including a discriminator and a generator, generates peptides that are not present in the training data set. Our proposed CPPCGM has achieved remarkably high Matthews correlation coefficient scores of 0.876, 0.923, and 0.664 on three data sets based on the classification results. Compared with the state-of-the-art methods, the performance of our method is significantly improved. The results also demonstrated the generating potential of CPPCGM through qualitative and quantitative evaluation of the generated samples. Significantly, using PLM-based methods can optimize peptides for biochemical functions, benefiting drug delivery and biomedical applications. Materials related are publicly available at https://github.com/QiufenChen/CPPCGM.

Metabolic Stability and Targeted Delivery of Oligonucleotides: Advancing RNA Therapeutics Beyond The Liver

Oligonucleotides have emerged as a formidable new class of nucleic acid therapeutics. Fully modified oligonucleotides exhibit enhanced metabolic stability and display successful clinical applicability for targets formerly considered "undruggable". Accumulating studies show that conjugation to targeting modalities of stabilized oligonucleotides, especially small interfering RNAs (siRNAs), has enabled robust delivery to intended cells/tissues. However, the major challenge in the field has been the stability and targeted delivery of oligonucleotides (siRNAs and antisense oligonucleotides (ASOs)) to extrahepatic tissues. In this Perspective, we review chemistry innovations and emerging delivery approaches that have revolutionized oligonucleotide drug discovery and development. We explore findings from both academia and industry that highlight the potential of oligonucleotides for indications involving different extrahepatic organs─including skeletal muscles, brain, lungs, skin, heart, adipose tissue, and eyes. In all, continued advances in chemistry coupled with conjugation-based approaches or novel administration routes will further advance the delivery of oligonucleotides to extrahepatic tissues.

Curcumin delivery system based on a chitosan-liposome encapsulated zeolitic imidazolate framework-8: a potential treatment antioxidant and antibacterial treatment after phacoemulsification

Curcumin is a natural polyphenol extracted from plants that can interact with various molecular targets, including antioxidant, antibacterial, anticancer, and anti-aging activities. Due to its variety of pharmacological activities and large margin pf safety, curcumin has been used in the prevention and treatment of various diseases, such as Alzheimer's, heart, and rheumatic immune diseases. To develop curcumin eye drops that can be used as antioxidant and antibacterial agents after phacoemulsification, we have designed a nano-based drug delivery system to improve curcumin bioavailability and duration of action. We successfully prepared zeolitic imidazolate framework-8 (ZIF-8) coated with chitosan-liposome (Cur@ZIF-8/CS-Lip) for curcumin delivery. It can release curcumin for over 20 hin vitroand exhibits excellent biosafety, antioxidant, and antibacterial activities. Therefore, we hypothesized that Cur@ZIF-8/CS-Lip could reduce the incidence of oxidative stress and infection after cataract surgery.

Dual cell-penetrating peptide-conjugated polymeric nanocarriers for miRNA-205-5p delivery in gene therapy of cutaneous squamous cell carcinoma

Despite the potential of microRNAs (miRNAs) in suppressing tumorigenesis, the main challenges are achieving tumor-specific selectivity and efficient delivery into cancer cells. In this study, miR-205-5p-loaded polymeric nanoparticles conjugated with dual cell-penetrating peptides (CPPs) were designed for targeting and treating cutaneous squamous cell carcinoma (cSCC). The CPPs, R9, and p28, demonstrated high cell-penetrating/targeting abilities and antitumor activity. The anti-cSCC effect of the nanocarriers was examined using in vitro cellular 2D and 3D models and in vivo spheroid-xenografted murine models. The average size of the dual CPP-conjugated nanocarriers was 193 nm with a zeta potential of 5.7 mV. These nanocarriers were readily internalized by A431 cells, resulting in decreased proliferation compared to naked agomiR and nanoparticles with a single CPP. The nanocarriers induced cell cycle arrest in the G0/G1 stage. By loading the miR-205-5p mimic, the dual CPP-conjugated nanoparticles enhanced cell apoptosis threefold compared to the control, activating caspases and poly(ADP-ribose) polymerase (PARP). The wound healing assay demonstrated that the nanocarriers significantly inhibited the migration and invasion of cSCC cells. Additionally, the CPP-conjugated nanocarriers penetrated cSCC 3D spheroids, reducing spheroidal size and proliferation. In vivo studies demonstrated that the intratumoral CPP-conjugated nanocarriers achieved a 30 % reduction in tumor volume than the PBS control. The number of Ki67-positive cells in the nanocarrier-treated tumor decreased fivefold than the untreated tumors. The nanoparticulate agomiR (1 μM) exhibited no cytotoxicity towards normal keratinocytes. No significant toxicity was observed in the skin and peripheral organs following subcutaneous administration of the nanoparticles in healthy mice. These findings demonstrate that miR-205-5p mimic delivery via dual CPP-conjugated nanocarriers can promote efficient and safe cSCC regression. STATEMENT OF SIGNIFICANCE: Cutaneous squamous cell carcinoma (cSCC) is a highly invasive skin malignancy with limited treatment options. This study introduces dual cell-penetrating peptide (CPP)-conjugated polymeric nanoparticles for delivering miR-205-5p, a tumor-suppressor microRNA, to cSCC cells. The nanosystem enhances cellular uptake, inhibits cell proliferation, and promotes apoptosis in both 2D and 3D tumor models. In vivo, the nanocarriers demonstrate significant antitumor efficacy with minimal toxicity, highlighting their potential as a targeted, non-invasive therapy. This research represents a promising advance in gene therapy for cSCC by combining nanotechnology and CPPs to address challenges in miRNA delivery and tumor targeting.

Peptide classification landscape: An in-depth systematic literature review on peptide types, databases, datasets, predictors architectures and performance

Peptides are gaining significant attention in diverse fields such as the pharmaceutical market has seen a steady rise in peptide-based therapeutics over the past six decades. Peptides have been utilized in the development of distinct applications including inhibitors of SARS-COV-2 and treatments for conditions like cancer and diabetes. Distinct types of peptides possess unique characteristics, and development of peptide-specific applications require the discrimination of one peptide type from others. To the best of our knowledge, approximately 230 Artificial Intelligence (AI) driven applications have been developed for 22 distinct types of peptides, yet there remains significant room for development of new predictors. A Comprehensive review addresses the critical gap by providing a consolidated platform for the development of AI-driven peptide classification applications. This paper offers several key contributions, including presenting the biological foundations of 22 unique peptide types and categorizes them into four main classes: Regulatory, Therapeutic, Nutritional, and Delivery Peptides. It offers an in-depth overview of 47 databases that have been used to develop peptide classification benchmark datasets. It summarizes details of 288 benchmark datasets that are used in development of diverse types AI-driven peptide classification applications. It provides a detailed summary of 197 sequence representation learning methods and 94 classifiers that have been used to develop 230 distinct AI-driven peptide classification applications. Across 22 distinct types peptide classification tasks related to 288 benchmark datasets, it demonstrates performance values of 230 AI-driven peptide classification applications. It summarizes experimental settings and various evaluation measures that have been employed to assess the performance of AI-driven peptide classification applications. The primary focus of this manuscript is to consolidate scattered information into a single comprehensive platform. This resource will greatly assist researchers who are interested in developing new AI-driven peptide classification applications.

Computational investigation of antiviral peptide interactions with Mpox DNA polymerase

The Mpox DNA polymerase (DNA pol) plays a crucial role in the viral replication process, making it an ideal target for antiviral therapies. It facilitates the synthetic process of viral DNA, which is an integral stage in the life of a virus. The inhibition of the operation of Mpox DNA pol would interfere with the multiplication of the virus and help manage the disease. Peptides have emerged as a possible therapeutic alternative against viruses due to their distinct characteristics. Peptides have broad-spectrum antiviral activity, being effective against a variety of viruses. Using computational techniques, we attempted to explore the molecular details of the interaction between antiviral peptides and Mpox DNA pol. Two databases of antiviral peptides were screened in this study. This study used molecular docking, followed by molecular dynamics (MD) simulation and post-simulation binding energy predictions. From the 19 selected peptides with activity against DNA polymerases, two peptides-DRAVPe01393 and DRAVPe01399-were identified as particularly promising candidates. These peptides exhibited stable interactions with Mpox DNA pol and demonstrated good cell penetration potential as evident from the MD simulation studies. Notably, the peptides DRAVPe01399 and DRAVPe01393 have a better binding affinity of - 60.86 kcal/mol and - 47.92 kcal/mol respectively than the control ligand Cidofovir diphosphate (- 10.79 kcal/mol). These findings could lead to the development of innovative antiviral treatments to prevent monkeypox, helping global efforts to battle this emerging infectious disease.

Skin-penetrating peptides (SKPs): Enhancing skin permeation for transdermal delivery of pharmaceuticals and cosmetic compounds

Skin-penetrating peptides (SKPs) are emerging as a promising class of permeation enhancers that can facilitate macromolecule delivery across the skin. Although their pharmaceutical applications are under extensive study, SKPs are crucial for enhancing skin permeability, enabling larger molecules to penetrate the stratum corneum. This review explores the transformative role of SKPs in non-invasive transdermal drug delivery. Drawing from an extensive collection of literature, it provides insights into the current usage and application of SKPs as tools to enhance skin permeability and facilitate the delivery of larger molecules. Additionally, it highlights the opportunities, challenges, and future directions for SKP applications in transdermal drug delivery.

An immunoregulatory amphipathic peptide derived from Fasciola hepatica helminth defense molecule (FhHDM-1.C2) exhibits potent biotherapeutic activity in a murine model of multiple sclerosis

The helminth defense molecules (HDM) are a family of immune regulatory peptides exclusively expressed by trematode worms. We have previously demonstrated that in vivo FhHDM-1, the archetypal member of the HDMs, regulated macrophage responses to inflammatory ligands, thereby ameliorating the progression of immune-mediated tissue damage in several murine models of inflammatory disease. Accordingly, we postulated that an understanding of the structure-function relationship of the HDMs would facilitate the identification of the minimal bioactive peptide, which would represent a more synthesizable, cost-effective, potent biotherapeutic. Thus, using a combination of bioinformatics, structural analyses, and cellular assays we discovered a 40 amino acid peptide derivative termed FhHDM-1.C2. This peptide contains a 12 amino acid motif at its N-terminus, which facilitates cellular interaction and uptake, and an amphipathic α-helix within the C-terminus, which is necessary for lysosomal vATPase inhibitory activity, with both regions linked by a short unstructured segment. The FhHDM-1.C2 peptide exhibits enhanced regulation of macrophage function, compared with the full-length FhHDM-1, and potent prevention of the progression of relapsing-remitting-experimental autoimmune encephalomyelitis (EAE) when administered prophylactically or therapeutically. The protective effect of FhHDM-1.C2 is not associated with global immune suppression, which places the HDMs peptides as an improved class of biotherapeutics for the treatment of inflammatory diseases. Comparing the HDMs from several zoonotic trematodes revealed a similar capacity for immune regulation. These important new advances into the structure-function relationship of the lead HDM peptide, FhHDM-1, encourage further prospecting and screening of the broader trematode family of peptides for the discovery of novel and potent immune-biotherapeutics.

Prodrug Approach as a Strategy to Enhance Drug Permeability

Absorption and permeability are critical physicochemical parameters that must be balanced to achieve optimal drug uptake. These key factors are closely linked to the maximum absorbable dose required to provide appropriate plasma levels of drugs. Among the various strategies employed to enhance drug solubility and permeability, prodrug design stands out as a highly effective and versatile approach for improving physicochemical properties and enabling the optimization of biopharmaceutical and pharmacokinetic parameters while mitigating adverse effects. Prodrugs are compounds with reduced or no activity that, through bio-reversible chemical or enzymatic processes, release an active parental drug. The application of this technology has led to significant advancements in drug optimization during the design phase, and it offers broad potential for further development. Notably, approximately 13% of the drugs approved by the U.S. Food and Drug Administration (FDA) between 2012 and 2022 were prodrugs. In this review article, we will explore the application of prodrug strategies to enhance permeability, describing examples of market drugs. We also describe the use of the prodrug approach to optimize PROteolysis TArgeting Chimeras (PROTACs) permeability by using conjugation technologies. We will highlight some new technologies in prodrugs to enrich permeability properties, contributing to developing new effective and safe prodrugs.

Pharmacogenomics influence on MDR1-associated cancer resistance and innovative drug delivery approaches: advancing precision oncology

Currently, there is a growing concern surrounding the treatment of cancer, a formidable disease. Pharmacogenomics and personalized medicine have emerged as significant areas of interest in cancer management. The efficacy of many cancer drugs is hindered by resistance mechanisms, particularly P-glycoprotein (P-gp) efflux, leading to reduced therapeutic outcomes. Efforts have intensified to inhibit P-gp efflux, thereby enhancing the effectiveness of resistant drugs. P-gp, a member of the ATP-binding cassette (ABC) superfamily, specifically the multidrug resistance (MDR)/transporter associated with antigen processing (TAP) sub-family B, member 1, utilizes energy derived from ATP hydrolysis to drive efflux. This review focuses on genetic polymorphisms associated with P-gp efflux and explores various novel pharmaceutical strategies to address this challenge. These strategies encompass SEDDS/SNEDDS, liposomes, immunoliposomes, solid lipid nanoparticles, lipid core nanocapsules, microemulsions, dendrimers, hydrogels, polymer-drug conjugates, and polymeric nanoparticles. The article aims to elucidate the interplay between pharmacogenomics, P-gp-mediated drug resistance in cancer, and formulation strategies to improve cancer therapy by tailoring formulations to genetically susceptible patients.

Overview of Peptides and Their Potential Roles in Skin Health and Beauty

Peptides are molecules that consist of at least two amino acids linked by peptide bonds. The difference between peptides and proteins is primarily based on size and structure. Typically, oligopeptides consist of fewer than about 10-20 amino acids, and polypeptides consist of more than 20 amino acids, whereas proteins usually are made up more than 50 amino acids and often contain multiple peptide subunits as stated in the International Union of Pure and Applied Chemistry rules. Beyond the nutritional properties, peptides are also structural components of hormones, enzymes, toxins, and antibiotics and play several fundamental physiological roles in the body. Since the introduction of the first commercial peptide drug, insulin, peptide-based drugs have gained increased interest. So far, more than 80 peptide-based drugs have reached the market for a wide range of conditions, such as diabetes, cardiovascular diseases, and urological disorders. Meanwhile, peptides have also gained significant attention in the cosmetic industry because of their potential in boosting skin health. In this review, peptides were comprehensively summarized in the aspects of sources, function, the use of peptides in cosmetics and skin care, and indications for the delivery of cosmetic peptides.

Temporal Microenvironment Mapping (μMap) of Intracellular Trafficking Pathways of Cell-Penetrating Peptides Across the Blood-Brain Barrier

Peptides play critical roles in cellular functions such as signaling and immune regulation, and peptide-based biotherapeutics show great promise for treating various diseases. Among these, cell-penetrating peptides (CPPs) are particularly valuable for drug delivery due to their ability to cross cell membranes. However, the mechanisms underlying CPP-mediated transport, especially across the blood-brain barrier (BBB), remain poorly understood. Mapping intracellular CPP pathways is essential for advancing drug delivery systems, particularly for neurological disorders, as understanding how CPPs navigate the complex environment of the BBB could enable the development of more effective brain-targeted therapies. Here, we leverage a nanoscale proximity labeling technique, termed μMap, to precisely probe the peptide-receptor interactions and intracellular trafficking mechanisms of photocatalyst-tagged CPPs. The unique advantage of the μMap platform lies in the ability to control the timing of light exposure, which enables the collection of time-gated data, depending on when the blue light is applied to the cells. By harnessing this spatiotemporal precision, we can uncover key peptide-receptor interactions and cellular processes, setting the stage for new innovations in drug design and brain-targeted therapies.

Targeting Tetraspanins at Cell Interfaces: Functional Modulation and Exosome-Based Drug Delivery for Precise Disease Treatment

Tetraspanins are key players in various physiological and pathological processes, including malignancy, immune response, fertilization, and infectious disease. Affinity ligands targeting the interactions between tetraspanins and partner proteins are promising for modulating downstream signaling pathways, thus emerging as attractive candidates for interfering related biological functions. Due to the involvement in vesicle biogenesis and cargo trafficking, tetraspanins are also regarded as exosome markers, and become molecular targets for drug loading and delivery. Given the rapid development in these areas, this minireview focuses on recent advances in design and engineering of affinity binders toward tetraspanins including CD63, CD81, and CD9. Their mechanism of actions in modulating protein interactions at cell interfaces and treatment of malignant diseases are discussed. Strategies for constructing exosome-based drug delivery platforms are also reviewed, with emphasis on the important roles of tetraspanins and the affinity ligands. Finally, challenges and future development of tetraspanin-targeting therapy and exosomal drug delivery platforms are also discussed.

Exploring the Utility of Cell-Penetrating Peptides as Vehicles for the Delivery of Distinct Antimalarial Drug Cargoes

The devastating impact of malaria includes significant mortality and illness worldwide. Increasing resistance of the causative parasite, Plasmodium, to existing antimalarial drugs underscores a need for additional compounds with distinct modes of action in the therapeutic development pipeline. Here we showcase peptide-drug conjugates (PDCs) as an attractive compound class, in which therapeutic or lead antimalarials are chemically conjugated to cell-penetrating peptides. This approach aims to enhance selective uptake into Plasmodium-infected red blood cells and impart additional cytotoxic actions on the intraerythrocytic parasite, thereby enabling targeted drug delivery and dual modes of action. We describe the development of PDCs featuring four compounds with antimalarial activity-primaquine, artesunate, tafenoquine and methotrexate-conjugated to three cell-penetrating peptide scaffolds with varied antiplasmodial activity, including active and inactive analogues of platelet factor 4 derived internalization peptide (PDIP), and a cyclic polyarginine peptide. Development of this diverse set of PDCs featured distinct and adaptable conjugation strategies, to produce conjugates with in vitro antiplasmodial activities ranging from low nanomolar to low micromolar potencies according to the drug cargo and bioactivity of the partner peptide. Overall, this study establishes a strategic and methodological framework for the further development of dual mode of action peptide-drug antimalarial therapeutics.

A bird's-eye view of the biological mechanism and machine learning prediction approaches for cell-penetrating peptides

Cell-penetrating peptides (CPPs) are highly effective at passing through eukaryotic membranes with various cargo molecules, like drugs, proteins, nucleic acids, and nanoparticles, without causing significant harm. Creating drug delivery systems with CPP is associated with cancer, genetic disorders, and diabetes due to their unique chemical properties. Wet lab experiments in drug discovery methodologies are time-consuming and expensive. Machine learning (ML) techniques can enhance and accelerate the drug discovery process with accurate and intricate data quality. ML classifiers, such as support vector machine (SVM), random forest (RF), gradient-boosted decision trees (GBDT), and different types of artificial neural networks (ANN), are commonly used for CPP prediction with cross-validation performance evaluation. Functional CPP prediction is improved by using these ML strategies by using CPP datasets produced by high-throughput sequencing and computational methods. This review focuses on several ML-based CPP prediction tools. We discussed the CPP mechanism to understand the basic functioning of CPPs through cells. A comparative analysis of diverse CPP prediction methods was conducted based on their algorithms, dataset size, feature encoding, software utilities, assessment metrics, and prediction scores. The performance of the CPP prediction was evaluated based on accuracy, sensitivity, specificity, and Matthews correlation coefficient (MCC) on independent datasets. In conclusion, this review will encourage the use of ML algorithms for finding effective CPPs, which will have a positive impact on future research on drug delivery and therapeutics.

Role of sequence length and functionalization in interactions of bioconjugated peptides with mitomembranes

Cell-penetrating peptides are efficient tools for intracellular delivery of a variety of cargoes. In this study, we explored the effect of chain length, side chain chemistry, and the locations of conjugated molecules on the interaction between iron-chelating peptides and a mitochondrial-mimicking membrane. We report that a longer chain length enhanced peptide/membrane interactions, and conjugation at the N-terminus lowered the free-energy barrier for peptide translocation across the membrane. Peptides containing Phe side chains and those containing modified Phe (cyclohexane) side chains showed comparable peptide/membrane energetics and translocation energy barriers. Using steered molecular dynamics (SMD) simulations, we further probed the mechanistic details of translocation of each N-terminated peptide across the membrane and compared their metastable states. At a higher steering velocity, the peptide adopted a compact structure due to frequent π-π interactions among conjugated molecules, but at lower steering velocities, each N-terminated peptide adopted an extended structure. This structure allowed cationic residues to maximize their interactions with phosphate headgroups in the mitomembrane. The hydrophobic residues also formed interactions with the lipid acyl tails, facilitating the passage of peptides across the membrane with decreased free energy barriers. Our results highlight the significance of peptide chain length and conjugation in facilitating peptide transport across the membrane.

Simple Cytosolic and Nuclear Introduction of Boron Compounds Using Cationic Lipids to Enhance Cancer Cell-Killing Activity in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT), a type of nuclear capture-based radiotherapy, has received extensive attention because of its strong anticancer effects, especially in head and neck cancers. This therapy was approved for clinical use in 2020 in Japan. This study demonstrated a technique that effectively uses the electrostatic interactions of negatively charged borane cage (polyhedral borane anion) of disodium mercaptoundecahydro-closo-dodecaborate (BSH) and positively charged cationic lipids or arginine-rich cell-penetrating peptides as carriers to enhance the efficiency of cellular uptake. Mixing of fluorescein isothiocyanate (FITC)-labeled BSH (FITC-BSH) with the cationic lipids led to increased cytosolic release and nuclear accumulation of FITC-BSH, resulting in superior cancer cell-killing activity following thermal neutron irradiation. This simple technique and our experimental results provide essential insights for the further development of BNCT.

Nanostructured lipid carriers decorated with polyphosphate coated linear and loop cell-penetrating peptides

AIM

This study aimed to evaluate the cellular uptake of nanostructured lipid carriers (NLCs) decorated with polyphosphate coated linear and loop cell-penetrating peptides (CPPs).

METHODS

Linear-CPPs and loop-CPPs were synthesized via ring-opening polymerization and anchored on the surface NLCs, followed by coating with polyphosphate (PP). These nanocarriers (NCs) were characterized in terms of particle size, polydispersity index (PDI), and zeta potential. Cell viability and hemolysis, as well as enzyme-induced charge conversion via phosphate cleavage by free and membrane-bound intestinal alkaline phosphatase (IAP) were investigated. Cellular uptake studies by Caco-2 and HEK cells were quantitatively analyzed by flow cytometry and visualized by confocal microscopy.

RESULTS

A shift in charge from positive to negative was obtained for both linear- and loop-CPPs-NLCs by coating with PP. PP-linear-CPPs-NLCs and PP-loop-CPPs-NLCs exhibited a particle size < 270 nm and a PDI of approximately 0.3. They had a minor effect on cell viability and caused in a concentration of 0.1 % (m/v) around 10 % hemolysis within 24 h. IAP triggered the cleavage and release of monophosphate from the surface of NLCs causing charge conversion from -22.2 mV to + 5.3 mV (Δ27.5 mV) for PP-linear-CPPs-NLCs and from -19.2 mV to + 11.9 mV (Δ31.1 mV) for PP-loop-CPPs-NLCs. Inhibition of alkaline phosphatase activity on Caco-2 and HEK cells confirmed the involvement of this enzyme in charge conversion. PP-linear-CPPs-NLCs showed on Caco-2 cells a higher uptake than PP-loop-CPPs-NLCs, whereas on HEK cells uptake of both types of NLCs was on the same level. The results of cellular uptake were confirmed visually by confocal microscopy.

CONCLUSION

CPPs-NLCs coated with polyphosphate are a promising approach to overcome the polycationic dilemma and to enhance cellular uptake.

Cancer-Targeting Applications of Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) offer a unique and efficient mechanism for delivering therapeutic agents directly into cancer cells. These peptides can traverse cellular membranes, overcoming one of the critical barriers in drug delivery systems. In this review, we explore recent advancements in the application of CPPs for cancer treatment, focusing on mechanisms, delivery strategies, and clinical potential. The review highlights the use of CPP-drug conjugates, CPP-based vaccines, and their role in targeting and inhibiting tumor growth.

Development of bioconjugate-based delivery systems for nucleic acids

Nucleic acids are a class of drugs that can modulate gene and protein expression by various mechanisms, namely, RNAi, mRNA degradation by RNase H cleavage, splice modulation, and steric blocking of protein binding or mRNA translation, thus exhibiting immense potential to treat various genetic and rare diseases. Unlike protein-targeted therapeutics, the clinical use of nucleic acids relies on Watson-Crick sequence recognition to regulate aberrant gene expression and impede protein translation. Though promising, targeted delivery remains a bottleneck for the clinical adoption of nucleic acid-based therapeutics. To overcome the delivery challenges associated with nucleic acids, various chemical modifications and bioconjugation-based delivery strategies have been explored. Currently, liver targeting by N-acetyl galactosamine (GalNAc) conjugation has been at the forefront for the treatment of rare and various metabolic diseases, which has led to FDA approval of four nucleic acid drugs. In addition, various other bioconjugation strategies have been explored to facilitate active organ and cell-enriched targeting. This review briefly covers the different classes of nucleic acids, their mechanisms of action, and their challenges. We also elaborate on recent advances in bioconjugation strategies in developing a diverse set of ligands for targeted delivery of nucleic acid drugs.

Peptides as innovative strategies to combat drug resistance in cancer therapy

Drug resistance is the leading cause of treatment failure in patients with cancer. Thus, innovative therapeutic strategies are required to overcome this critical challenge and improve patient outcomes. In this review, we examine the potential of peptide-based therapies to combat drug resistance in cancer. We highlight the unique strategies and mechanisms that can be explored by using peptides, including their ability to selectively target tumours, facilitate drug delivery into cancer cells, and inhibit key intracellular proteins that drive cancer progression and resistance. Peptides offer a promising approach to overcoming both intrinsic and adaptative cancer resistance against chemotherapy, targeted therapies, and biologics.

A high hydrophobic moment arginine-rich peptide screened by a machine learning algorithm enhanced ADC antitumor activity

Cell-penetrating peptides (CPPs) with better biomolecule delivery properties will expand their clinical applications. Using the MLCPP2.0 machine algorithm, we screened multiple candidate sequences with potential cellular uptake ability from the nuclear localization signal/nuclear export signal database and verified them through cell-penetrating fluorescent tracing experiments. A peptide (NCR) derived from the Rev protein of the caprine arthritis-encephalitis virus exhibited efficient cell-penetrating activity, delivering over four times more EGFP than the classical CPP TAT, allowing it to accumulate in lysosomes. Structural and property analysis revealed that a high hydrophobic moment and an appropriate hydrophobic region contribute to the high delivery activity of NCR. Trastuzumab emtansine (T-DM1), a HER2-targeted antibody-drug conjugate, could improve its anti-tumor activity by enhancing targeted delivery efficiency and increasing lysosomal drug delivery. This study designed a new NCR vector to non-covalently bind T-DM1 by fusing domain Z, which can specifically bind to the Fc region of immunoglobulin G and effectively deliver T-DM1 to lysosomes. MTT results showed that the domain Z-NCR vector significantly enhanced the cytotoxicity of T-DM1 against HER2-positive tumor cells while maintaining drug specificity. Our results make a useful attempt to explore the potential application of CPP as a lysosome-targeted delivery tool.

Tumor-Targeted Cell-Penetrating Peptides Reveal That Monomethyl Auristatin E Temporally Modulates the Tumor Immune Microenvironment

Chemotherapies remain standard therapy for cancers but have limited efficacy and cause significant side effects, highlighting the need for targeted approaches. In the progression of cancer, tumors increase matrix metalloproteinase (MMP) activity. Leveraging and therapeutically redirecting tumor MMPs through activatable cell-penetrating peptide (ACPP) technology offers new approaches for tumor-selective drug delivery and for studying how drug payloads engage the tumor immune microenvironment. ACPPs are biosensing peptides consisting of a drug-conjugated polycationic cell-penetrating peptide masked by an autoinhibitory polyanionic peptide through an interlinking peptide linker. Since tumors overexpress MMPs, ACPP tumor-targeting is achieved using an MMP cleavable linker. Monomethyl auristatin E (MMAE) is a potent anti-tubulin and common drug payload in antibody drug conjugates; however there are limited pre-clinical studies on how this clinically effective drug modulates the interplay of cancer cells and the immune system. Here, we report the versatility of ACPP conjugates in syngeneic murine cancer models and interrogate how MMAE temporally alters the tumor immune microenvironment. We show that cRGD-ACPP-MMAE preferentially delivered MMAE to tumors in murine models. Targeted cRGD-ACPP-MMAE demonstrated anti-tumor kill activity that activated the innate and adaptive arms of the immune system. Understanding how targeted MMAE engages tumors can optimize MMAE tumor kill activity and inform rational combinations with other cancer therapeutics.

Chemical strategies for antisense antibiotics

Antibacterial resistance is a severe threat to modern medicine and human health. To stay ahead of constantly-evolving bacteria we need to expand our arsenal of effective antibiotics. As such, antisense therapy is an attractive approach. The programmability allows to in principle target any RNA sequence within bacteria, enabling tremendous selectivity. In this Tutorial Review we provide guidelines for devising effective antibacterial antisense agents and offer a concise perspective for future research. We will review the chemical architectures of antibacterial antisense agents with a special focus on the delivery and target selection for successful antisense design. This Tutorial Review will strive to serve as an essential guide for antibacterial antisense technology development.

Designed Cell-Penetrating Peptide Constructs for Inhibition of Pathogenic Protein Self-Assembly

Peptides possess a number of pharmacologically desirable properties, including greater chemical diversity than other biomolecule classes and the ability to selectively bind to specific targets with high potency, as well as biocompatibility, biodegradability, and ease and low cost of production. Consequently, there has been considerable interest in developing peptide-based therapeutics, including amyloid inhibitors. However, a major hindrance to the successful therapeutic application of peptides is their poor delivery to target tissues, cells or subcellular organelles. To overcome these issues, recent efforts have focused on engineering cell-penetrating peptide (CPP) antagonists of amyloidogenesis, which combine the attractive intrinsic properties of peptides with potent therapeutic effects (i.e., inhibition of amyloid formation and the associated cytotoxicity) and highly efficient delivery (to target tissue, cells, and organelles). This review highlights some promising CPP constructs designed to target amyloid aggregation associated with a diverse range of disorders, including Alzheimer's disease, transmissible spongiform encephalopathies (or prion diseases), Parkinson's disease, and cancer.

Enhancing Tumor Targeted Therapy: The Role of iRGD Peptide in Advanced Drug Delivery Systems

Chemotherapy remains the primary therapeutic approach in treating cancer. The tumor microenvironment (TME) is the complex network surrounding tumor cells, comprising various cell types, such as immune cells, fibroblasts, and endothelial cells, as well as ECM components, blood vessels, and signaling molecules. The often stiff and dense network of the TME interacts dynamically with tumor cells, influencing cancer growth, immune response, metastasis, and resistance to therapy. The effectiveness of the treatment of solid tumors is frequently reduced due to the poor penetration of the drug, which leads to attaining concentrations below the therapeutic levels at the site. Cell-penetrating peptides (CPPs) present a promising approach that improves the internalization of therapeutic agents. CPPs, which are short amino acid sequences, exhibit a high ability to pass cell membranes, enabling them to deliver drugs efficiently with minimal toxicity. Specifically, the iRGD peptide, a member of CPPs, is notable for its capacity to deeply penetrate tumor tissues by binding simultaneously integrins ανβ3/ανβ5 and neuropilin receptors. Indeed, ανβ3/ανβ5 integrins are characteristically expressed by tumor cells, which allows the iRGD peptide to home onto tumor cells. Notably, the respective dual-receptor targeting mechanism considerably increases the permeability of blood vessels in tumors, enabling an efficient delivery of co-administered drugs or nanoparticles into the tumor mass. Therefore, the iRGD peptide facilitates deeper drug penetration and improves the efficacy of co-administered therapies. Distinctively, we will focus on the iRGD mechanism of action, drug delivery systems and their application, and deliberate future perspectives in developing iRGD-conjugated therapeutics. In summary, this review discusses the potential of iRGD in overcoming barriers to drug delivery in cancer to maximize treatment efficiency while minimizing side effects.

Unlocking the Gates: Therapeutic Agents for Noninvasive Drug Delivery Across the Blood-Brain Barrier

The blood-brain barrier (BBB) is a highly selective network of various cell types that acts as a filter between the blood and the brain parenchyma. Because of this, the BBB remains a major obstacle for drug delivery to the central nervous system (CNS). In recent years, there has been a focus on developing various modifiable platforms, such as monoclonal antibodies (mAbs), nanobodies (Nbs), peptides, and nanoparticles, as both therapeutic agents and carriers for targeted drug delivery to treat brain cancers and diseases. Methods for bypassing the BBB can be invasive or noninvasive. Invasive techniques, such as transient disruption of the BBB using low pulse electrical fields and intracerebroventricular infusion, lack specificity and have numerous safety concerns. In this review, we will focus on noninvasive transport mechanisms that offer high levels of biocompatibility, personalization, specificity and are regarded as generally safer than their invasive counterparts. Modifiable platforms can be designed to noninvasively traverse the BBB through one or more of the following pathways: passive diffusion through a physio-pathologically disrupted BBB, adsorptive-mediated transcytosis, receptor-mediated transcytosis, shuttle-mediated transcytosis, and somatic gene transfer. Through understanding the noninvasive pathways, new applications, including Chimeric Antigen Receptors T-cell (CAR-T) therapy, and approaches for drug delivery across the BBB are emerging.

Spotlight on HIV-derived TAT peptide as a molecular shuttle in drug delivery

HIV-derived TAT peptide, with a high penetration rate into cells and its nonimmunogenic and minimally toxic nature, is an attractive tool for enhancing the biodistribution of drugs and their systemic administration. Despite the presence of numerous promising preclinical investigations illustrating its capability to specifically target distinct tissues and deliver a diverse range of pharmacological agents, the efficacy of various clinical trials incorporating TAT has been impeded by several considerable obstacles. Hence, there is much need for an in-depth investigation concerning the application of TAT in drug delivery mechanisms. In this review, we have elucidated the structure of TAT and its utility in the proficient delivery of various types of bioactive molecules.

Cell-Penetrating Peptides and CRISPR-Cas9: A Combined Strategy for Human Genetic Disease Therapy

The advent of clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated nuclease 9 (Cas9) technology has revolutionized the field of genetic engineering, offering unprecedented potential for the targeted manipulation of DNA sequences. Advances in the mechanism of action of the CRISPR-Cas9 system allowed potential applicability for the treatment of genetic diseases. CRISPR-Cas9's mechanism of action involves the use of an RNA guide molecule to target-specific DNA sequences and the Cas9 enzyme to induce precise DNA cleavage. In the context of the CRISPR-Cas9 system, this review covers nonviral delivery methods for gene editing based on peptide internalization. Here, we describe critical areas of discussion such as immunogenicity, emphasizing the importance of safety, efficiency, and cost-effectiveness, particularly in the context of treating single-mutation genetic diseases using advanced editing techniques genetics as prime editor and base editor. The text discusses the versatility of cell-penetrating peptides (CPPs) in forming complexes for delivering biomolecules, particularly ribonucleoprotein for genome editing with CRISPR-Cas9 in human cells. In addition, it emphasizes the promise of combining CPPs with DNA base editing and prime editing systems. These systems, known for their simplicity and precision, hold great potential for correcting point mutations in human genetic diseases. In summary, the text provides a clear overview of the advantages of using CPPs for genome editing with CRISPR-Cas9, particularly in conjunction with advanced editing systems, highlighting their potential impact on clinical applications in the treatment of single-mutation genetic diseases. [Figure: see text].

Peptides inhibiting the assembly of monomeric human l-lactate dehydrogenase into catalytically active homotetramer decrease the synthesis of lactate in cultured cells

The energetic metabolism of cancer cells relies on a substantial commitment of pyruvate to the catalytic action of lactate-generating dehydrogenases. This coupling mainly depends on lactate dehydrogenase A (LDH-A), which is overexpressed in different types of cancers, and therefore represents an appealing therapeutic target. Taking into account that the activity of LDHs is exclusively exerted by their tetrameric forms, it was recently shown that peptides perturbing the monomers-to-tetramer assembly inhibit human LDH-A (hLDH-A). However, to identify these peptides, tetrameric hLDH-A was transiently exposed to strongly acidic conditions inducing its dissociation into monomers, which were tested as a target for peptides at low pH. Nevertheless, the availability of native monomeric hLDH-A would allow performing similar screenings under physiological conditions. Here we report on the unprecedented isolation of recombinant monomeric hLDH-A at neutral pH, and on its use to identify peptides inhibiting the assembly of the tetrameric enzyme. Remarkably, the GQNGISDL octapeptide, mimicking the 296-303 portion of hLDH-A C-terminal region, was observed to effectively inhibit the target enzyme. Moreover, by dissecting the action of this octapeptide, the cGQND cyclic tetrapeptide was found to act as the parental compound. Furthermore, we performed assays using MCF7 and BxPC3 cultured cells, exclusively expressing hLDH-A and hLDH-B, respectively. By means of these assays we detected a selective action of linear and cyclic GQND tetrapeptides, inhibiting lactate secretion in MCF7 cells only. Overall, our observations suggest that peptides mimicking the C-terminal region of hLDH-A effectively interfere with protein-protein interactions responsible for the assembly of the tetrameric enzyme.

Cell-penetrating peptides for sustainable agriculture

Cell-penetrating peptides (CPPs) are short (typically 5-30 amino acids), cationic, amphipathic, or hydrophobic peptides that facilitate the cellular uptake of diverse cargo molecules by eukaryotic cells via direct translocation or endocytosis across the plasma membrane. CPPs can deliver a variety of bioactive cargos, including proteins, peptides, nucleic acids, and small molecules into the cell. Once inside, the delivered cargo may function in the cytosol, nucleus, or other subcellular compartments. Numerous CPPs have been used for studies and drug delivery in mammalian systems. Although CPPs have many potential uses in plant research and agriculture, the application of CPPs in plants remains limited. Here we review the structures and mechanisms of CPPs and highlight their potential applications for sustainable agriculture.

Investigating the impact of thiol reactivity and disulfide formation on cellular uptake of cell-permeable peptides

Cell-penetrating peptides (CPPs) have been explored as versatile tools to transport various molecules into cells. The uptake mechanism of CPPs is still not clearly understood and most probably depends on several factors like the nature of the CPP itself, the attached cargo, the investigated cell system, and other experimental conditions, such as temperature and concentration. One of the first steps of internalization involves the interaction of CPPs with negatively charged molecules present at the outer layer of the cell membrane. Recently, thiol-mediated uptake has been found to support the effective translocation of sulfhydryl-bearing substances that would actually not be cell-permeable. Within this work, we aimed to understand the relevance of thiol reactivity for the uptake mechanism of cysteine-containing CPPs that we have developed previously in our group. Therefore, we compared the two peptides, sC18-Cys and CaaX-1, in their single reduced and dimeric disulfide versions. Cytotoxicity, intracellular accumulation, and impact on the internalization process of the disulfides were investigated in HeLa cells. Both disulfide CPPs demonstrated significantly stronger cytotoxic effects and membrane activity compared with their reduced counterparts. Notably, thiol-mediated uptake could be excluded as a main driver for translocation, showing that peptides like CaaX-1 are most likely taken up by other mechanisms.

Beyond Transduction: Anti-Inflammatory Effects of Cell Penetrating Peptides

One of the bottlenecks to bringing new therapies to the clinic has been a lack of vectors for delivering novel therapeutics in a targeted manner. Cell penetrating peptides (CPPs) have received a lot of attention and have been the subject of numerous developments since their identification nearly three decades ago. Known for their transduction abilities, they have generally been considered inert vectors. In this review, we present a schema for their classification, highlight what is known about their mechanism of transduction, and outline the existing literature as well as our own experience, vis a vis the intrinsic anti-inflammatory properties that certain CPPs exhibit. Given the inflammatory responses associated with viral vectors, CPPs represent a viable alternative to such vectors; furthermore, the anti-inflammatory properties of CPPs, mostly through inhibition of the NF-κB pathway, are encouraging. Much more work in relevant animal models, toxicity studies in large animal models, and ultimately human trials are needed before their potential is fully realized.

Identifying Cell-Penetrating Peptides for Effectively Delivering Antimicrobial Molecules into Streptococcus suis

Cell-penetrating peptides (CPPs) are promising carriers to effectively transport antisense oligonucleotides (ASOs), including peptide nucleic acids (PNAs), into bacterial cells to combat multidrug-resistant bacterial infections, demonstrating significant therapeutic potential. Streptococcus suis, a Gram-positive bacterium, is a major bacterial pathogen in pigs and an emerging zoonotic pathogen. In this study, through the combination of super-resolution structured illumination microscopy (SR-SIM), flow cytometry analysis, and toxicity analysis assays, we investigated the suitability of four CPPs for delivering PNAs into S. suis cells: HIV-1 TAT efficiently penetrated S. suis cells with low toxicity against S. suis; (RXR)4XB had high penetration efficiency with inherent toxicity against S. suis; (KFF)3K showed lower penetration efficiency than HIV-1 TAT and (RXR)4XB; K8 failed to penetrate S. suis cells. HIV-1 TAT-conjugated PNA specific for the essential gyrase A subunit gene (TAT-anti-gyrA PNA) effectively inhibited the growth of S. suis. TAT-anti-gyrA PNA exhibited a significant bactericidal effect on serotypes 2, 4, 5, 7, and 9 strains of S. suis, which are known to cause human infections. Our study demonstrates the potential of CPP-ASO conjugates as new antimicrobial compounds for combating S. suis infections. Furthermore, our findings demonstrate that applying SR-SIM and flow cytometry analysis provides a convenient, intuitive, and cost-effective approach to identifying suitable CPPs for delivering cargo molecules into bacterial cells.

Conditional Cell-Penetrating Peptide Exposure as Selective Nanoparticle Uptake Signal

A major bottleneck diminishing the therapeutic efficacy of various drugs is that only small proportions of the administered dose reach the site of action. One promising approach to increase the drug amount in the target tissue is the delivery via nanoparticles (NPs) modified with ligands of cell surface receptors for the selective identification of target cells. However, since receptor binding can unintentionally trigger intracellular signaling cascades, our objective was to develop a receptor-independent way of NP uptake. Cell-penetrating peptides (CPPs) are an attractive tool since they allow efficient cell membrane crossing. So far, their applicability is severely limited as their uptake-promoting ability is nonspecific. Therefore, we aimed to achieve a conditional CPP-mediated NP internalization exclusively into target cells. We synthesized different CPP candidates and investigated their influence on nanoparticle stability, ζ-potential, and uptake characteristics in a core-shell nanoparticle system consisting of poly(lactid-co-glycolid) (PLGA) and poly(lactic acid)-poly(ethylene glycol) (PLA10kPEG2k) block copolymers with CPPs attached to the PEG part. We identified TAT47-57 (TAT) as the most promising candidate and subsequently combined the TAT-modified PLA10kPEG2k polymer with longer PLA10kPEG5k polymer chains, modified with the potent angiotensin-converting enzyme 2 (ACE2) inhibitor MLN-4760. While MLN-4760 enables selective target cell identification, the additional PEG length hides the CPP during a first unspecific cell contact. Only after the previous selective binding of MLN-4760 to ACE2, the established spatial proximity exposes the CPP, triggering cell uptake. We found an 18-fold uptake improvement in ACE2-positive cells compared to unmodified particles. In summary, our work paves the way for a conditional and thus highly selective receptor-independent nanoparticle uptake, which is beneficial in terms of avoiding side effects.

Peptide spiders are emerging as novel therapeutic interventions for nucleic acid delivery

The FDA has approved many nucleic acid (NA)-based products. The presence of charges and biological barriers however affect stability and restrict widespread use. The electrostatic complexation of peptide with polyethylene glycol-nucleic acids (PEG-NAs) via nonreducible and reducible agents lead to three parts at one platform.. The reducible linkage made detachment of siRNA from PEG easy compared with a nonreducible linkage. A peptide spider produces a small hydrodynamic particle size, which can improve drug release and pharmacokinetics. Several examples of peptide spiders that enhance stability, protection and transfection efficiency are discussed. Moreover, this review also covers the challenges, future perspectives and unmet needs of peptide-PEG-NAs conjugates for NAs delivery.

Covalent conjugation and non-covalent complexation strategies for intracellular delivery of proteins using cell-penetrating peptides

Therapeutic proteins provided new opportunities for patients and high sales volumes. However, they are formulated for extracellular targets. The lipophilic barrier of the plasma membrane renders the vast array of intracellular targets out of reach. Peptide-based delivery systems, namely cell-penetrating peptides (CPPs), have few safety concerns, and low immunogenicity, with control over administered doses. This study investigates CPP-based protein delivery systems by classifying them into CPP-protein "covalent conjugation" and CPP: protein "non-covalent complexation" categories. Covalent conjugates ensure the proximity of the CPP to the cargo, which can improve cellular uptake and endosomal escape. We will discuss various aspects of covalent conjugates through non-cleavable (stable) or cleavable bonds. Non-cleavable CPP-protein conjugates are produced by recombinant DNA technology to express the complete fusion protein in a host cell or by chemical ligation of CPP and protein, which ensures stability during the delivery process. CPP-protein cleavable bonds are classified into pH-sensitive and redox-sensitive bonds, enzyme-cleavable bonds, and physical stimuli cleavable linkers (light radiation, ultrasonic waves, and thermo-responsive). We have highlighted the key characteristics of non-covalent complexes through electrostatic and hydrophobic interactions to preserve the conformational integrity of the CPP and cargo. CPP-mediated protein delivery by non-covalent complexation, such as zippers, CPP adaptor methods, and avidin-biotin technology, are featured. Conclusively, non-covalent complexation methods are appropriate when a high number of CPP or protein samples are to be screened. In contrast, when the high biological activity of the protein is critical in the intracellular compartment, conjugation protocols are preferred.

Small Natural Cyclic Peptides from DBAASP Database

Antimicrobial peptides (AMPs) are promising tools for combating microbial resistance. However, their therapeutic potential is hindered by two intrinsic drawbacks-low target affinity and poor in vivo stability. Macrocyclization, a process that improves the pharmacological properties and bioactivity of peptides, can address these limitations. As a result, macrocyclic peptides represent attractive drug candidates. Moreover, many drugs are macrocycles that originated from natural product scaffolds, suggesting that nature offers solutions to the challenges faced by AMPs. In this review, we explore natural cyclic peptides from the DBAASP database. DBAASP is a comprehensive repository of data on antimicrobial/cytotoxic activities and structures of peptides. We analyze the data on small (≤25 AA) ribosomal and non-ribosomal cyclic peptides from DBAASP according to their amino acid composition, bonds used for cyclization, targets they act on, and mechanisms of action. This analysis will enhance our understanding of the small cyclic peptides that nature has provided to defend living organisms.

RNA therapeutics in targeting G protein-coupled receptors: Recent advances and challenges

G protein-coupled receptors (GPCRs) are the major targets of existing drugs for a plethora of human diseases and dominate the pharmaceutical market. However, over 50% of the GPCRs remain undruggable. To pursue a breakthrough and overcome this situation, there is significant clinical research for developing RNA-based drugs specifically targeting GPCRs, but none has been approved so far. RNA therapeutics represent a unique and promising approach to selectively targeting previously undruggable targets, including undruggable GPCRs. However, the development of RNA therapeutics faces significant challenges in areas of RNA stability and efficient in vivo delivery. This review presents an overview of the advances in RNA therapeutics and the diverse types of nanoparticle RNA delivery systems. It also describes the potential applications of GPCR-targeted RNA drugs for various human diseases.

Potential of Cell-Penetrating Peptide-Conjugated Antisense Oligonucleotides for the Treatment of SMA

Spinal muscular atrophy (SMA) is a severe neuromuscular disorder that is caused by mutations in the survival motor neuron 1 (SMN1) gene, hindering the production of functional survival motor neuron (SMN) proteins. Antisense oligonucleotides (ASOs), a versatile DNA-like drug, are adept at binding to target RNA to prevent translation or promote alternative splicing. Nusinersen is an FDA-approved ASO for the treatment of SMA. It effectively promotes alternative splicing in pre-mRNA transcribed from the SMN2 gene, an analog of the SMN1 gene, to produce a greater amount of full-length SMN protein, to compensate for the loss of functional protein translated from SMN1. Despite its efficacy in ameliorating SMA symptoms, the cellular uptake of these ASOs is suboptimal, and their inability to penetrate the CNS necessitates invasive lumbar punctures. Cell-penetrating peptides (CPPs), which can be conjugated to ASOs, represent a promising approach to improve the efficiency of these treatments for SMA and have the potential to transverse the blood-brain barrier to circumvent the need for intrusive intrathecal injections and their associated adverse effects. This review provides a comprehensive analysis of ASO therapies, their application for the treatment of SMA, and the encouraging potential of CPPs as delivery systems to improve ASO uptake and overall efficiency.