Cell-Penetrating Peptides: Design Strategies beyond Primary Structure and Amphipathicity

Intracellular delivery strategies using membrane-interacting peptides and proteins

While the cellular cytosol and organelles contain attractive targets for disease treatments, it remains a challenge to deliver therapeutic biomacromolecules to these sites. This is due to the selective permeability of the plasma and endosomal membranes, especially for large and hydrophilic therapeutic cargos such as proteins and nucleic acids. In response, many different delivery systems and molecules have been devised to help therapeutics cross these barriers to reach cytosolic targets. Among them are peptide and protein-based systems, which have several advantages over other natural and synthetic materials including their ability to interact with cell membranes. In this review, we will describe recent advances and current challenges of peptide and protein strategies that leverage cell membrane association and modulation to enable cytosolic delivery of biomacromolecule cargo. The approaches covered here include peptides and proteins derived from or inspired by natural sequences as well as those designed de novo for delivery function.

The intracellular visualization of exogenous DNA in fluorescence microscopy

In the development of non-viral gene delivery vectors, it is essential to reliably localize and quantify transfected DNA inside the cell. To track DNA, fluorescence microscopy methods are commonly applied. These mostly rely on fluorescently labeled DNA, DNA binding proteins fused to a fluorescent protein, or fluorescence in situ hybridization (FISH). In addition, co-stainings are often used to determine the colocalization of the DNA in specific cellular compartments, such as the endolysosomes or the nucleus. We provide an overview of these DNA tracking methods, advice on how they should be combined, and indicate which co-stainings or additional methods are required to draw precise conclusions from a DNA tracking experiment. Some emphasis is given to the localization of exogenous DNA inside the nucleus, which is the last step of DNA delivery. We argue that suitable tools which allow for the nuclear detection of faint signals are still missing, hampering the rational development of more efficient non-viral transfection systems.

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.

Self-assembling short peptide amphiphiles as versatile delivery agents: a new frontier in antibacterial research

Self-assembling short peptide amphiphiles, crafted through a minimalistic approach, spontaneously generate well-ordered nanostructures, facilitating the creation of precise nanostructured biomaterials for diverse biomedical applications. The seamless integration of bioactive metal ions and nanoparticles endows them with the potential to serve as pioneering materials in combating bacterial infections. Nanomanipulation of these molecules' binary structures enables effective penetration of membranes, forming structured nanoarchitectures with antibacterial properties. Through a comprehensive exploration, we attempt to reveal the innovative potential of short peptide amphiphiles, particularly in conjugation with metal cations and nanoparticles, offering insights for future research trajectories.

Unlocking the potential of protein-derived peptides to target G-quadruplex DNA: from recognition to anticancer activity

Noncanonical nucleic acid structures, particularly G-quadruplexes, have garnered significant attention as potential therapeutic targets in cancer treatment. Here, the recognition of G-quadruplex DNA by peptides derived from the Rap1 protein is explored, with the aim of developing novel peptide-based G-quadruplex ligands with enhanced selectivity and anticancer activity. Biophysical techniques were employed to assess the interaction of a peptide derived from the G-quadruplex-binding domain of the protein with various biologically relevant G-quadruplex structures. Through alanine scanning mutagenesis, key amino acids crucial for G-quadruplex recognition were identified, leading to the discovery of two peptides with improved G-quadruplex-binding properties. However, despite their in vitro efficacy, these peptides showed limited cell penetration and anticancer activity. To overcome this challenge, cell-penetrating peptide (CPP)-conjugated derivatives were designed, some of which exhibited significant cytotoxic effects on cancer cells. Interestingly, selected CPP-conjugated peptides exerted potent anticancer activity across various tumour types via a G-quadruplex-dependent mechanism. These findings underscore the potential of peptide-based G-quadruplex ligands in cancer therapy and pave the way for the development of novel therapeutic strategies targeting these DNA structures.

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.

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.

Sacha Inchi (Plukenetia volubilis L.) Protein Hydrolysate as a New Ingredient of Functional Foods

Sacha inchi (Plukenetia volubilis L.) is an under-exploited crop with great potential due to its nutritional and medicinal characteristics. A Sacha inchi protein isolate (SII), obtained from defatted Sacha inchi flour (SIF), was hydrolyzed by Bioprotease LA 660 under specific conditions. The hydrolysates were characterized chemically, and their digestibility and antioxidant capacity were evaluated by in vitro cell-free experiments to select the hydrolysate with major antioxidant activity. Sacha inchi protein hydrolysate at 20 min (SIH20B) was selected, and the anti-inflammatory capacity was evaluated by RT-qPCR and ELISA techniques, using two different doses in monocytes THP-1 stimulated with lipopolysaccharide (LPS). The results obtained showed that the in vitro administration of SIH20B down-regulated the TNF-α gene and reduced the release of this cytokine, whereas the anti-inflammatory cytokines IL-10 and IL-4 were up-regulated in LPS-stimulated monocytes and co-administrated with SIH20B. The peptides contained in SIH20B were identified, and the 20 more relatively abundant peptides with a mass by 1 kDa were subjected to in silico analysis to hypothesize those that could be responsible for the bioactivity reported in the hydrolysate. From the identified peptides, the peptides AAGALKKFL and LGVKFKGGL, among others, are proposed as the most biologically actives. In conclusion, SIH20B is a novel, natural source of high-value-added biopeptides that could be used as an ingredient in formulations of food or nutraceutical compounds.

Investigating molecular descriptors in cell-penetrating peptides prediction with deep learning: Employing N, O, and hydrophobicity according to the Eisenberg scale

Cell-penetrating peptides comprise a group of molecules that can naturally cross the lipid bilayer membrane that protects cells, sharing physicochemical and structural properties, and having several pharmaceutical applications, particularly in drug delivery. Investigations of molecular descriptors have provided not only an improvement in the performance of classifiers but also less computational complexity and an enhanced understanding of membrane permeability. Furthermore, the employment of new technologies, such as the construction of deep learning models using overfitting treatment, promotes advantages in tackling this problem. In this study, the descriptors nitrogen, oxygen, and hydrophobicity on the Eisenberg scale were investigated, using the proposed ConvBoost-CPP composed of an improved convolutional neural network with overfitting treatment and an XGBoost model with adjusted hyperparameters. The results revealed favorable to the use of ConvBoost-CPP, having as input nitrogen, oxygen, and hydrophobicity together with ten other descriptors previously investigated in this research line, showing an increase in accuracy from 88% to 91.2% in cross-validation and 82.6% to 91.3% in independent test.

Molecular determinants for brain targeting by peptides: a meta-analysis approach with experimental validation

Blood-brain barrier (BBB) peptide-shuttles (BBBpS) are able to translocate the BBB and reach the brain. Despite the importance of brain targeting in pharmacology, BBBpS are poorly characterized. Currently, their development relies on the empiric assumption that cell-penetrating peptides (CPPs), with proven ability to traverse lipid membranes, will likewise behave as a BBBpS. The relationship between CPPs/BBBpS remains elusive and, to the best of our knowledge, has not hitherto been subject to thorough experimental scrutiny. In this work, we have identified/quantified the main physicochemical properties of BBBpS and then searched for CPPs with these properties, hence potential BBBpS. The specific features found for BBBpS are: (i) small size, (ii) none or few aromatic residues, (iii) hydrophobic, and (iv) slight cationic nature. Then, we selected the 10 scoring best in an ordinary least squares analysis, and tested them in vitro and in vivo. Overall, we identified the molecular determinants for brain targeting by peptides, devised a methodology that can be used to assist in the design of peptides with potential brain penetration from amino acid residue sequences, and found four new BBBpS within the CPP library.

A comparative analysis of peptide-delivered antisense antibiotics using diverse nucleotide mimics

Antisense oligomer (ASO)-based antibiotics that target mRNAs of essential bacterial genes have great potential for counteracting antimicrobial resistance and for precision microbiome editing. To date, the development of such antisense antibiotics has primarily focused on using phosphorodiamidate morpholino (PMO) and peptide nucleic acid (PNA) backbones, largely ignoring the growing number of chemical modalities that have spurred the success of ASO-based human therapy. Here, we directly compare the activities of seven chemically distinct 10mer ASOs, all designed to target the essential gene acpP upon delivery with a KFF-peptide carrier into Salmonella. Our systematic analysis of PNA, PMO, phosphorothioate (PTO)-modified DNA, 2'-methylated RNA (RNA-OMe), 2'-methoxyethylated RNA (RNA-MOE), 2'-fluorinated RNA (RNA-F), and 2'-4'-locked RNA (LNA) is based on a variety of in vitro and in vivo methods to evaluate ASO uptake, target pairing and inhibition of bacterial growth. Our data show that only PNA and PMO are efficiently delivered by the KFF peptide into Salmonella to inhibit bacterial growth. Nevertheless, the strong target binding affinity and in vitro translational repression activity of LNA and RNA-MOE make them promising modalities for antisense antibiotics that will require the identification of an effective carrier.

Therapeutic Potential of Nanocarrier Mediated Delivery of Peptides for Wound Healing: Current Status, Challenges and Future Prospective

Wound healing presents a complex physiological process that involves a sequence of events orchestrated by various cellular and molecular mechanisms. In recent years, there has been growing interest in leveraging nanomaterials and peptides to enhance wound healing outcomes. Nanocarriers offer unique properties such as high surface area-to-volume ratio, tunable physicochemical characteristics, and the ability to deliver therapeutic agents in a controlled manner. Similarly, peptides, with their diverse biological activities and low immunogenicity, hold great promise as therapeutics in wound healing applications. In this review, authors explore the potential of peptides as bioactive components in wound healing formulations, focusing on their antimicrobial, anti-inflammatory, and pro-regenerative properties. Despite the significant progress made in this field, several challenges remain, including the need for standardized characterization methods, optimization of biocompatibility and safety profiles, and translation from bench to bedside. Furthermore, developing multifunctional nanomaterial-peptide hybrid systems represents promising avenues for future research. Overall, the integration of nanomaterials made up of natural or synthetic polymers with peptide-based formulations holds tremendous therapeutic potential in advancing the field of wound healing and improving clinical outcomes for patients with acute and chronic wounds.

De novo design of potential peptide analogs against the main protease of Omicron variant using in silico studies

SARS-CoV-2 and its variants are crossing the immunity barrier induced through vaccination. Recent Omicron sub-variants are highly transmissible and have a low mortality rate. Despite the low severity of Omicron variants, these new variants are known to cause acute post-infectious syndromes. Nowadays, novel strategies to develop new potential inhibitors for SARS-CoV-2 and other Omicron variants have gained prominence. For viral replication and survival the main protease of SARS-CoV-2 plays a vital role. Peptide-like inhibitors that mimic the substrate peptide have already proved to be effective in inhibiting the Mpro of SARS-CoV-2 variants. Our systematic canonical amino acid point mutation analysis on the native peptide has revealed various ways to improve the native peptide of the main protease. Multi mutation analysis has led us to identify and design potent peptide-analog inhibitors that act against the Mpro of the Omicron sub-variants. Our in-depth analysis of all-atom molecular dynamics studies has paved the way to characterize the atomistic behavior of Mpro in Omicron variants. Our goal is to develop potent peptide-analogs that could be therapeutically effective against Omicron and its sub-variants.

Hydrophobicity: The door to drug delivery

The engineering of intracellular delivery systems with the goal of achieving personalized medicine has been encouraged by advances in nanomaterial science as well as a greater understanding of diseases and of the biochemical pathways implicated in many disorders. The development of vectors able to transport the drug to a target location and release it only on demand is undoubtedly the primary issue. From a molecular perspective, the topography of drug carrier surfaces is directly related to the design of an effective drug carrier because it provides a physical hint to modifying its interactions with biological systems. For instance, the initial ratio of hydrophilic to hydrophobic surfaces and the changes brought about by external factors enable the release or encapsulation of a therapeutic molecule and the ability of the nanosystem to cross biological barriers and reach its target without causing systemic toxicity. The first step in creating new materials with enhanced functionality is to comprehend and characterize the interplay between hydrophilic and hydrophobic molecules at the molecular level. Therefore, the focus of this review is on the function of hydrophobicity, which is essential for matching the complexity of biological environments with the intended functionality.

Combating bone marrow failure with polymer materials

Bone marrow failure (BMF) has become one of the most studied autoimmune disorders, particularly due to its prevalence both as an inherited disease, but also as a result of chemotherapies. BMF is associated with severe symptoms such as bleeding episodes and susceptibility to infections, and often has underlying characteristics, such as anemia, thrombocytopenia, and neutropenia. The current treatment landscape for BMF requires stem cell transplantation or chemotherapies to induce immune suppression. However, there is limited donor cell availability or dose related toxicity associated with these treatments. Optimizing these treatments has become a necessity. Polymer-based materials have become increasingly popular, as current research efforts are focused on synthesizing novel cell matrices for stem cell expansion to solve limited donor cell availability, as well as applying polymer delivery vehicles to intracellularly deliver cargo that can aid in immunosuppression. Here, we discuss the importance and impact of polymer materials to enhance therapeutics in the context of BMF.

Unlocking the Mitochondria for Nanomedicine-based Treatments: Overcoming Biological Barriers, Improving Designs, and Selecting Verification Techniques

Enhanced targeting approaches will support the treatment of diseases associated with dysfunctional mitochondria, which play critical roles in energy generation and cell survival. Obstacles to mitochondria-specific targeting include the presence of distinct biological barriers and the need to pass through (or avoid) various cell internalization mechanisms. A range of studies have reported the design of mitochondrially-targeted nanomedicines that navigate the complex routes required to influence mitochondrial function; nonetheless, a significant journey lies ahead before mitochondrially-targeted nanomedicines become suitable for clinical use. Moving swiftly forward will require safety studies, in vivo assays confirming effectiveness, and methodologies to validate mitochondria-targeted nanomedicines' subcellular location/activity. From a nanomedicine standpoint, we describe the biological routes involved (from administration to arrival within the mitochondria), the features influencing rational design, and the techniques used to identify/validate successful targeting. Overall, rationally-designed mitochondria-targeted-based nanomedicines hold great promise for precise subcellular therapeutic delivery.

An Endosomal Escape Trojan Horse Platform to Improve Cytosolic Delivery of Nucleic Acids

Endocytosis is a major bottleneck toward cytosolic delivery of nucleic acids, as the vast majority of nucleic acid drugs remain trapped within endosomes. Current trends to overcome endosomal entrapment and subsequent degradation provide varied success; however, active delivery agents such as cell-penetrating peptides have emerged as a prominent strategy to improve cytosolic delivery. Yet, these membrane-active agents have poor selectivity for endosomal membranes, leading to toxicity. A hallmark of endosomes is their acidic environment, which aids in degradation of foreign materials. Here, we develop a pH-triggered spherical nucleic acid that provides smart antisense oligonucleotide (ASO) release upon endosomal acidification and selective membrane disruption, termed DNA EndosomaL Escape Vehicle Response (DELVR). We anchor i-Motif DNA to a nanoparticle (AuNP), where the complement strand contains both an ASO sequence and a functionalized endosomal escape peptide (EEP). By orienting the EEP toward the AuNP core, the EEP is inactive until it is released through acidification-induced i-Motif folding. In this study, we characterize a small library of i-Motif duplexes to develop a structure-switching nucleic acid sequence triggered by endosomal acidification. We evaluate antisense efficacy using HIF1a, a hypoxic indicator upregulated in many cancers, and demonstrate dose-dependent activity through RT-qPCR. We show that DELVR significantly improves ASO efficacy in vitro. Finally, we use fluorescence lifetime imaging and activity measurement to show that DELVR benefits synergistically from nuclease- and pH-driven release strategies with increased ASO endosomal escape efficiency. Overall, this study develops a modular platform that improves the cytosolic delivery of nucleic acid therapeutics and offers key insights for overcoming intracellular barriers.

Self-assembled porphyrin-peptide cages for photodynamic therapy

The development of photodynamic therapy requires access to smart photosensitizers which combine appropriate photophysical and biological properties. Interestingly, supramolecular and dynamic covalent chemistries have recently shown their ability to produce novel architectures and responsive systems through simple self-assembly approaches. Herein, we report the straightforward formation of porphyrin-peptide conjugates and cage compounds which feature on their surface chemical groups promoting cell uptake and specific organelle targeting. We show that they self-assemble, in aqueous media, into positively-charged nanoparticles which generate singlet oxygen upon green light irradiation, while also undergoing a chemically-controlled disassembly due to the presence of reversible covalent linkages. Finally, the biological evaluation in cells revealed that they act as effective photosensitizers and promote synergistic effects in combination with Doxorubicin.

Effect of animal venom toxins on the main links of the homeostasis of mammals (Review)

The human body is affected by environmental factors. The dynamic balance between the organism and its environment results from the influence of natural, anthropogenic and social aspects. The factors of exogenous origin determine development of adaptive changes. The present article summarises the mechanisms of animal venom toxins and homeostasis disruption in the body of mammals. The mechanisms underlying pathological changes are associated with shifts in biochemical reactions. Components of the immune, nervous and endocrine systems are key in the host defense and adaptation processes in response to venom by triggering signalling pathways (PI3kinase pathway, arachidonic acid cascade). Animal venom toxins initiate the development of inflammatory processes, the synthesis of pro-inflammatory mediators (cytokines), ROS, proteolytic enzymes, activate the migration of leukocytes and macrophages. Keratinocytes and endothelial cells act as protective barriers under the action of animal venom toxins on the body of mammals. In addition, the formation of pores in cell membranes, structural changes in cell ion channels are characteristic of the action of animal venom toxins.

Long-Acting Ocular Injectables: Are We Looking In The Right Direction?

The complex anatomy and physiological barriers of the eye make delivering ocular therapeutics challenging. Generally, effective drug delivery to the eye is hindered by rapid clearance and limited drug bioavailability. Biomaterial-based approaches have emerged to enhance drug delivery to ocular tissues and overcome existing limitations. In this review, some of the most promising long-acting injectables (LAIs) in ocular drug delivery are explored, focusing on novel design strategies to improve therapeutic outcomes. LAIs are designed to enable sustained therapeutic effects, thereby extending local drug residence time and facilitating controlled and targeted drug delivery. Moreover, LAIs can be engineered to enhance drug targeting and penetration across ocular physiological barriers.

Virtual Screening of Peptide Libraries: The Search for Peptide-Based Therapeutics Using Computational Tools

Over the last few decades, we have witnessed growing interest from both academic and industrial laboratories in peptides as possible therapeutics. Bioactive peptides have a high potential to treat various diseases with specificity and biological safety. Compared to small molecules, peptides represent better candidates as inhibitors (or general modulators) of key protein-protein interactions. In fact, undruggable proteins containing large and smooth surfaces can be more easily targeted with the conformational plasticity of peptides. The discovery of bioactive peptides, working against disease-relevant protein targets, generally requires the high-throughput screening of large libraries, and in silico approaches are highly exploited for their low-cost incidence and efficiency. The present review reports on the potential challenges linked to the employment of peptides as therapeutics and describes computational approaches, mainly structure-based virtual screening (SBVS), to support the identification of novel peptides for therapeutic implementations. Cutting-edge SBVS strategies are reviewed along with examples of applications focused on diverse classes of bioactive peptides (i.e., anticancer, antimicrobial/antiviral peptides, peptides blocking amyloid fiber formation).

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.

Protective effect of Tat fused HPCA protein on neuronal cell death caused by ischemic injury

Background

Bain ischemia is a disease that occurs for various reasons, induces reactive oxygen species (ROS), and causes fatal damage to the nervous system. Protective effect of HPCA on ischemic injury has not been extensively studied despite its significance in regulating calcium homeostasis and promoting neuronal survival in CA1 region of the brain.

Objective

We investigate the role of HPCA in ischemic injury using a cell-permeable Tat peptide fused HPCA protein (Tat-HPCA).

Methods

Western blot analysis determined the penetration of Tat-HPCA into HT-22 cells and apoptotic signaling pathways. 5-CFDA, AM, DCF-DA, and TUNEL staining confirmed intracellular ROS production and DNA damage. The intracellular Ca2+ was measured in primary cultured neurons treated with H2O2. Protective effects were examined using immunohistochemistry and cognitive function tests by passive avoidance test and 8-arm radial maze test.

Results

Tat-HPCA effectively penetrated into HT-22 cells and inhibited H2O2-induced apoptosis, oxidative stress, and DNA fragmentation. It also effectively inhibited phosphorylation of JNK and regulated the activation of Caspase, Bax, Bcl-2, and PARP, leading to inhibition of apoptosis. Moreover, Ca2+ concentration decreased in cells treated with Tat-HPCA in primary cultured neurons. In an animal model of ischemia, Tat-HPCA effectively penetrated the hippocampus, inhibited cell death, and regulated activities of astrocytes and microglia. Additionally, Cognitive function tests show that Tat-HPCA improves neurobehavioral outcomes after cerebral ischemic injury.

Conclusion

These results suggest that Tat-HPCA might have potential as a therapeutic agent for treating oxidative stress-related diseases induced by ischemic injury, including ischemia.

Alcohol-containing protein transduction domain mimics

The application and design of protein transduction domains (PTDs) and protein transduction domain mimics (PTDMs) have revolutionized the field of biomacromolecule delivery. Our group has previously synthesized block copolymer PTDMs with well-defined hydrophobic and cationic blocks via ring-opening metathesis polymerization (ROMP). We have optimized the balance of hydrophobicity and cationic density to intracellularly deliver model proteins, active proteins, and antibodies. Despite the presence of serine, threonine, and tyrosine in naturally occurring PTDs, synthetic analogs have yet to be studied in PTDMs. In our present work, we introduce different alcohol groups to our PTDM structures as a new design parameter. A library of nine novel PTDMs were synthesized to incorporate alcohol groups of varying structures and evaluated based on their ability to intracellularly deliver fluorescently labeled antibodies. One PTDM in this novel library, named PTDM4, incorporates alcohol groups in both the hydrophobic and cationic blocks and was found to be the best performing PTDM with almost twice the median fluorescence intensity of the delivered antibody and half the cationic density compared to our positive control, a PTDM thoroughly studied by our group. PTDM4 was further studied by intracellularly delivering the active enzyme, TAT-Cre Recombinase. The activity of TAT-Cre Recombinase delivered by PTDM4 was comparable to that of the positive control, again with half the cationic density. This study is one of the first to examine the effects of alcohol groups on intracellular antibody and active enzyme delivery.

Marine polysaccharides, proteins, lipids, and silica for drug delivery systems: A review

Marine environments represent an incredible source of biopolymers with potential biomedical applications. Recently, drug delivery studies have received great attention for the increasing need to improve site specificity, therapeutic value, and bioavailability, reducing off-target effects. Marine polymers, such as alginate, carrageenan, collagen, chitosan, and silica, have reported unique biochemical features, allowing an efficient binding with drugs, and a controlled release to the target tissue, also obtainable through "green processes". In the present review, we i) analysed the last ten years of scientific peer-reviewed literature; ii) divided the articles based on the achieved experimental phases, tagged as chemistry, drug release, and drug delivery, and iii) compared the best performances among marine polymers extracted from micro- and macro-organisms. Many reviews describe drug carriers from marine organisms, focusing on a single biopolymer or a chemical class. Our study is a groundbreaking literature collection, representing the first thorough investigation of all marine biopolymers described. Most articles report experimental results on the chemical characterisation of marine biopolymers and their in vitro behaviour as drug carriers, although development processes and commercial applications are still in the early stages. Hence, the next efforts should be focused on the sustainable production of marine polymers and final product development.

Apoptosis/Necroptosis Inducing Thiazole-Containing Artificial Polypeptide for Immunogenic Cell Death of Cancer

Immunogenic cell death (ICD) has emerged as a promising approach to cancer immunotherapy. During ICD, cancer cell death and the release of damage-associated molecular pattern (DAMP) signals occur simultaneously. Increased production of reactive oxygen species (ROS) and severe endoplasmic reticulum stress are necessary for enhanced ICD. Furthermore, the levels of ROS and reduced glutathione (GSH) are involved in various cell death mechanisms. The thiazole ring structure has gained considerable interest as a functional moiety for anticancer agents. This study designed and synthesized a positively charged cell-penetrating polypeptide with a thiazole functional moiety (NS). The NS internalizes into the cancer cells through direct penetration and endo-lysosomal escape. The NS induces mitochondrial depolarization and ER stress in a concentration-dependent manner, leading to a significant ROS production and GSH depletion. Consequently, the ICD of cancer cells is activated, resulting in the release of DAMP signals. Furthermore, NS causes a shift in the cell death pathway from apoptosis to necroptosis as the concentration increases. In this study, we confirmed the possibility of NS as a promising ICD inducer that can be used while varying the concentration according to the cancer type.

Deciphering variations in the endocytic uptake of a cell-penetrating peptide: the crucial role of cell culture protocols

Delivery tools, including cell-penetrating peptides (CPPs), are often inefficient due to a combination of poor endocytosis and endosomal escape. Aspects that impact the delivery of CPPs are typically characterized using tissue culture models. One problem of using cell culture is that cell culture protocols have the potential to contribute to endosomal uptake and endosomal release of CPPs. Hence, a systematic study to identify which aspects of cell culturing techniques impact the endocytic uptake of a typical CPP, the TMR-TAT peptide (peptide sequence derived from HIV1-TAT with the N-terminus labeled with tetramethylrhodamine), was conducted. Aspects of cell culturing protocols previously found to generally modulate endocytosis, such as cell density, washing steps, and cell aging, did not affect TMR-TAT endocytosis. In contrast, cell dissociation methods, media, temperature, serum starvation, and media composition all contributed to changes in uptake. To establish a range of endocytosis achievable by different cell culture protocols, TMR-TAT uptake was compared among protocols. These protocols led to changes in uptake of more than 13-fold, indicating that differences in cell culturing techniques have a cumulative effect on CPP uptake. Taken together this study highlights how different protocols can influence the amount of endocytic uptake of TMR-TAT. Additionally, parameters that can be exploited to improve CPP accumulation in endosomes were identified. The protocols identified herein have the potential to be paired with other delivery enhancing strategies to improve overall delivery efficiency of CPPs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00591-1.

DNA T-shaped crossover tiles for 2D tessellation and nanoring reconfiguration

DNA tiles serve as the fundamental building blocks for DNA self-assembled nanostructures such as DNA arrays, origami, and designer crystals. Introducing additional binding arms to DNA crossover tiles holds the promise of unlocking diverse nano-assemblies and potential applications. Here, we present one-, two-, and three-layer T-shaped crossover tiles, by integrating T junction with antiparallel crossover tiles. These tiles carry over the orthogonal binding directions from T junction and retain the rigidity from antiparallel crossover tiles, enabling the assembly of various 2D tessellations. To demonstrate the versatility of the design rules, we create 2-state reconfigurable nanorings from both single-stranded tiles and single-unit assemblies. Moreover, four sets of 4-state reconfiguration systems are constructed, showing effective transformations between ladders and/or rings with pore sizes spanning ~20 nm to ~168 nm. These DNA tiles enrich the design tools in nucleic acid nanotechnology, offering exciting opportunities for the creation of artificial dynamic DNA nanopores.

Carrier peptide interactions with liposome membranes induce reversible clustering by surface adsorption and shape deformation

The cell-penetrating peptide penetratin and its analogues shuffle and penetramax have been used as carrier peptides for oral delivery of therapeutic peptides such as insulin. Their mechanism of action for this purpose is not fully understood but is believed to depend on the interactions of the peptide with the cell membrane. In the present study, peptide-liposome interactions were investigated using advanced biophysical techniques including small-angle neutron scattering and fluorescence lifetime imaging microscopy. Liposomes were used as a model system for the cell membrane. All the investigated carrier peptides induced liposome clustering at a specific peptide/lipid ratio. However, distinctively different types of membrane interactions were observed, as the liposome clustering was irreversible for penetratin, but fully or partly reversible for shuffle and penetramax, respectively. All three peptides were found to adsorb to the surface of the lipid bilayers, while only shuffle and penetramax led to shape deformation of the liposomes. Importantly, the peptide interactions did not disrupt the liposomes under any of the investigated conditions, which is advantageous for their application in drug delivery. This detailed insight on peptide-membrane interactions is important for understanding the mechanism of peptide-based excipients and the influence of peptide sequence modifications.

Structural flexibility of apolipoprotein E-derived arginine-rich peptides improves their cell penetration capability

Amphipathic arginine-rich peptide, A2-17, exhibits moderate perturbation of lipid membranes and the highest cell penetration among its structural isomers. We investigated the direct cell-membrane penetration mechanism of the A2-17 peptide while focusing on structural flexibility. We designed conformationally constrained versions of A2-17, stapled (StpA2-17) and stitched (StchA2-17), whose α-helical conformations were stabilized by chemical crosslinking. Circular dichroism confirmed that StpA2-17 and StchA2-17 had higher α-helix content than A2-17 in aqueous solution. Upon liposome binding, only A2-17 exhibited a coil-to-helix transition. Confocal microscopy revealed that A2-17 had higher cell penetration efficiency than StpA2-17, whereas StchA2-17 remained on the cell membrane without cell penetration. Although the tryptophan fluorescence analysis suggested that A2-17 and its analogs had similar membrane-insertion positions between the interface and hydrophobic core, StchA2-17 exhibited a higher membrane affinity than A2-17 or StpA2-17. Atomic force microscopy demonstrated that A2-17 reduced the mechanical rigidity of liposomes to a greater extent than StpA2-17 and StchA2-17. Finally, electrophysiological analysis showed that A2-17 induced a higher charge influx through transient pores in a planer lipid bilayer than StpA2-17 and StchA2-17. These findings indicate that structural flexibility, which enables diverse conformations of A2-17, leads to a membrane perturbation mode that contributes to cell membrane penetration.

In situ transient transfection of 3D cell cultures and tissues, a promising tool for tissue engineering and gene therapy

Various research fields use the transfection of mammalian cells with genetic material to induce the expression of a target transgene or gene silencing. It is a tool widely used in biological research, bioproduction, and therapy. Current transfection protocols are usually performed on 2D adherent cells or suspension cultures. The important rise of new gene therapies and regenerative medicine in the last decade raises the need for new tools to empower the in situ transfection of tissues and 3D cell cultures. This review will present novel in situ transfection methods based on a chemical or physical non-viral transfection of cells in tissues and 3D cultures, discuss the advantages and remaining gaps, and propose future developments and applications.

A cell-penetrating peptide derived from SARS-CoV-2 protein Orf9b allosterically inhibits MARK4 activity and mitigates tau toxicity

Abnormal activation of microtubule affinity-regulating kinase 4 (MARK4) and its phosphorylation of the microtubule-associated protein tau are believed to play a role in the pathogenesis of Alzheimer's disease, and MARK4 inhibition can be a strategy to develop disease-modifying therapy. Here we report the development of a membrane-permeable peptide that inhibits MARK4 activity in an allosteric manner. The SARS-CoV-2-derived protein Orf9b inhibited MARK4-mediated tau phosphorylation in primary neurons and Drosophila. Orf9b inhibited MARK4 activity in an allosteric manner and did not inhibit the activity of MARK2, which is another MARK family member and is closely related to MARK4. Co-expression of Orf9b in the fly retina expressing human tau and MARK4 suppressed phosphorylation of tau at the microtubule-binding repeats and tau-induced neurodegeneration. We identified the minimal sequence of Orf9b required to suppress MARK4 activity and fused it to a cell-permeable sequence (TAT-Orf9b10-18_78-95). Extracellular supplementation of TAT-Orf9b10-18_78-95 inhibited MARK4 activity in primary neurons, and feeding TAT-Orf9b10-18_78-95 to a fly model of tauopathy lowered phospho-tau levels and suppressed neurodegeneration. These results suggest that TAT-Orf9b10-18_78-95 is a unique class of MARK4 inhibitor and can be used to modify tau toxicity.

A novel cell-permeable peptide prevents protein SUMOylation and supports the mislocalization and aggregation of TDP-43

SUMOylation is a post-translational modification (PTM) that exerts a regulatory role in different cellular processes, including protein localization, aggregation, and biological activities. It consists of the dynamic formation of covalent isopeptide bonds between a family member of the Small Ubiquitin Like Modifiers (SUMOs) and the target proteins. Interestingly, it is a cellular mechanism implicated in several neurodegenerative pathologies and potentially it could become a new therapeutic target; however, there are very few pharmacological tools to modulate the SUMOylation process. In this study, we have designed and tested the activity of a novel small cell-permeable peptide, COV-1, in a neuroblastoma cell line that specifically prevents protein SUMOylation. COV-1 inhibits UBC9-protein target interaction and efficiently decreases global SUMO-1ylation. Moreover, it can perturb RanGAP-1 perinuclear localization by inducing the downregulation of UBC9. In parallel, we found that COV-1 causes an increase in the ubiquitin degradation system up to its engulfment while enhancing the autophagic flux. Surprisingly, COV-1 modifies protein aggregation, and specifically it mislocalizes TDP-43 within cells, inducing its aggregation and co-localization with SUMO-1. These data suggest that COV-1 could be taken into future consideration as an interesting pharmacological tool to study the cellular cascade effects of SUMOylation prevention.

Control of cell penetration enhancer shielding and endosomal escape-kinetics crucial for efficient and biocompatible siRNA delivery

Although cationic liposomes are efficient carriers for nucleic acid delivery, their toxicity often hampers the clinical translation. Polyethylene glycol (PEG) coating has been largely used to improve their stability and reduce toxicity. Nevertheless, it has been found to decrease the transfection process. In order to exploit the advantages of cationic liposomes and PEG decoration for nucleic acid delivery, liposomes decorated with tetraArg-[G-1]-distearoyl glycerol (Arg4-DAG) dendronic oligo-cationic lipid enhancer (OCE) and PEG-lipid have been investigated. Non decorated or OCE-decorated lipoplexes (OCEfree-LPX and OCE-LPX, respectively) were obtained by lipid film hydration using oligonucleotide (ON) solutions. PEG and OCE/PEG decorated lipoplexes (PEG-OCEfree-LPX and PEG-OCE-LPX, respectively) were obtained by post-insertion of 2 or 5 kDa PEG-DSPE on preformed lipoplexes. The OCE decoration yielded lipoplexes with size of about 240 nm, 84% loading efficiency at 10 N/P ratio, ten times higher than OCEfree-LPX, and prevented the ON release when incubated with physiological heparin concentration or with plasma. The PEG decoration reduced the zeta potential, enhanced the lipoplex stability in serum and decreased both hemolysis and cytotoxicity, while it did not affect the lipoplex size and ON loading. With respect to OCEfree-LPX, the OCE-LPX remarkably associated with cells and were taken up by different cancer cell lines (HeLa and MDA-MB-231). Interestingly, 2 or 5 kDa PEG decoration did not reduce either the cell interaction or the cell up-take of the cationic lipoplexes. With siRNA as a payload, OCE enabled efficient internalization, but endosomal release was hampered. Post-transfection treatment with the lysosomotropic drug chloroquine allowed to identify the optimal time point for endosomal escape. Chloroquine treatment after 12 to 20 h of LPX pre-incubation enabled siRNA mediated target knockdown indicating that this is the time window of endo-lysosomal processing. This indicates that OCE can protect siRNA from lysosomal degradation for up to 20 h, as shown by these rescue experiments.

Topoisomeric Membrane-Active Peptides: A Review of the Last Two Decades

In recent decades, bioactive peptides have been gaining recognition in various biomedical areas, such as intracellular drug delivery (cell-penetrating peptides, CPPs) or anti-infective action (antimicrobial peptides, AMPs), closely associated to their distinct mode of interaction with biological membranes. Exploiting the interaction of membrane-active peptides with diverse targets (healthy, tumoral, bacterial or parasitic cell membranes) is opening encouraging prospects for peptides in therapeutics. However, ordinary peptides formed by L-amino acids are easily decomposed by proteases in biological fluids. One way to sidestep this limitation is to use topoisomers, namely versions of the peptide made up of D-amino acids in either canonic (enantio) or inverted (retroenantio) sequence. Rearranging peptide sequences in this fashion provides a certain degree of native structure mimicry that, in appropriate contexts, may deliver desirable biological activity while avoiding protease degradation. In this review, we will focus on recent accounts of membrane-active topoisomeric peptides with therapeutic applications as CPP drug delivery vectors, or as antimicrobial and anticancer candidates. We will also discuss the most common modes of interaction of these peptides with their membrane targets.

Computational Study of Complex Formation between Hyaluronan Polymers and Polyarginine Peptides at Various Ratios

Hyaluronic acid, a naturally occurring carbohydrate biopolymer in human tissues, finds wide application in cosmetics, medicine, and material science. Its anionic properties play a crucial role in its interaction with positively charged macromolecules and ions. Among these macromolecules, positively charged arginine molecules or polyarginine peptides demonstrate potential in drug delivery when complexed with hyaluronan. This study aimed to compare and elucidate the results of both experimental and computational investigations on the interactions between hyaluronic acid polymers and polyarginine peptides. Experimental findings revealed that by varying the length of polyarginine peptides and the molar ratio, it is possible to modulate the size, solubility, and stability of hyaluronan-arginine particles. To further explore these interactions, molecular dynamics simulations were conducted to model the complexes formed between hyaluronic acid polymers and arginine peptides. The simulations are considered in different molar ratios and lengths of polyarginine peptides. By analysis of the data, we successfully determined the shape and size of the resulting complexes. Additionally, we identified the primary driving forces behind complex formation and explained the observed variations in peptide interactions with hyaluronan.

Engineering Proteins for Cell Entry

Proteins are essential for life, as they participate in all vital processes in the body. In the past decade, delivery of active proteins to specific cells and organs has attracted increasing interest. However, most proteins cannot enter the cytoplasm due to the cell membrane acting as a natural barrier. To overcome this challenge, various proteins have been engineered to acquire cell-penetrating capacity by mimicking or modifying natural shuttling proteins. In this review, we provide an overview of the different types of engineered cell-penetrating proteins such as cell-penetrating peptides, supercharged proteins, receptor-binding proteins, and bacterial toxins. We also discuss some strategies for improving endosomal escape such as pore formation, the proton sponge effect, and hijacking intracellular trafficking pathways. Finally, we introduce some novel methods and technologies for designing and detecting engineered cell-penetrating proteins.

Intracellular protein delivery: New insights into the therapeutic applications and emerging technologies

The inability to cross the plasma membranes traditionally limited the therapeutic use of recombinant proteins. However, in the last two decades, novel technologies made delivering proteins inside the cells possible. This allowed researchers to unlock intracellular targets, once considered 'undruggable', bringing a new research area to emerge. Protein transfection systems display a large potential in a plethora of applications. However, their modality of action is often unclear, and cytotoxic effects are elevated, whereas experimental conditions to increase transfection efficacy and cell viability still need to be identified. Furthermore, technical complexity often limits in vivo experimentation, while challenging industrial and clinical translation. This review highlights the applications of protein transfection technologies, and then critically discuss the current methodologies and their limitations. Physical membrane perforation systems are compared to systems exploiting cellular endocytosis. Research evidence of the existence of either extracellular vesicles (EVs) or cell-penetrating peptides (CPPs)- based systems, that circumvent the endosomal systems is critically analysed. Commercial systems, novel solid-phase reverse protein transfection systems, and engineered living intracellular bacteria-based mechanisms are finally described. This review ultimately aims at finding new methodologies and possible applications of protein transfection systems, while helping the development of an evidence-based research approach.

Molecular Dynamics Simulations of Drug-Conjugated Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are small peptides capable of translocating through biological membranes carrying various attached cargo into cells and even into the nucleus. They may also participate in transcellular transport. Our in silico study intends to model several peptides and their conjugates. We have selected three CPPs with a linear backbone, including penetratin, a naturally occurring oligopeptide; two of its modified sequence analogues (6,14-Phe-penetratin and dodeca-penetratin); and three natural CPPs with a cyclic backbone: Kalata B1, the Sunflower trypsin inhibitor 1 (SFT1), and Momordica cochinchinensis trypsin inhibitor II (MCoTI-II). We have also built conjugates with the small-molecule drug compounds doxorubicin, zidovudine, and rasagiline for each peptide. Molecular dynamics (MD) simulations were carried out with explicit membrane models. The analysis of the trajectories showed that the interaction of penetratin with the membrane led to spectacular rearrangements in the secondary structure of the peptide, while cyclic peptides remained unchanged due to their high conformational stability. Membrane-peptide and membrane-conjugate interactions have been identified and compared. Taking into account well-known examples from the literature, our simulations demonstrated the utility of computational methods for CPP complexes, and they may contribute to a better understanding of the mechanism of penetration, which could serve as the basis for delivering conjugated drug molecules to their intracellular targets.

Designing Fluorescent Nuclear Permeable Peptidomimetics to Target Proliferating Cell Nuclear Antigen

Human proliferating cell nuclear antigen (PCNA) is a critical mediator of DNA replication and repair, acting as a docking platform for replication proteins. Disrupting these interactions with a peptidomimetic agent presents as a promising avenue to limit proliferation of cancerous cells. Here, a p21-derived peptide was employed as a starting scaffold to design a modular peptidomimetic that interacts with PCNA and is cellular and nuclear permeable. Ultimately, a peptidomimetic was produced which met these criteria, consisting of a fluorescein tag and SV40 nuclear localization signal conjugated to the N-terminus of a p21 macrocycle derivative. Attachment of the fluorescein tag was found to directly affect cellular uptake of the peptidomimetic, with fluorescein being requisite for nuclear permeability. This work provides an important step forward in the development of PCNA targeting peptidomimetics for use as anti-cancer agents or as cancer diagnostics.

Membrane-Active Peptides and Their Potential Biomedical Application

Membrane-active peptides (MAPs) possess unique properties that make them valuable tools for studying membrane structure and function and promising candidates for therapeutic applications. This review paper provides an overview of the fundamental aspects of MAPs, focusing on their membrane interaction mechanisms and potential applications. MAPs exhibit various structural features, including amphipathic structures and specific amino acid residues, enabling selective interaction with multiple membranes. Their mechanisms of action involve disrupting lipid bilayers through different pathways, depending on peptide properties and membrane composition. The therapeutic potential of MAPs is significant. They have demonstrated antimicrobial activity against bacteria and fungi, making them promising alternatives to conventional antibiotics. MAPs can selectively target cancer cells and induce apoptosis, opening new avenues in cancer therapeutics. Additionally, MAPs serve as drug delivery vectors, facilitating the transport of therapeutic cargoes across cell membranes. They represent a fascinating class of biomolecules with significant potential in basic research and clinical applications. Understanding their mechanisms of action and designing peptides with enhanced selectivity and efficacy will further expand their utility in diverse fields. Exploring MAPs holds promise for developing novel therapeutic strategies against infections, cancer, and drug delivery challenges.

Pharmacokinetics, biodistribution and toxicology of novel cell-penetrating peptides

Cell-penetrating peptides (CPPs) have been used in basic and preclinical research in the past 30 years to facilitate drug delivery into target cells. However, translation toward the clinic has not been successful so far. Here, we studied the pharmacokinetic (PK) and biodistribution profiles of Shuttle cell-penetrating peptides (S-CPP) in rodents, combined or not with an immunoglobulin G (IgG) cargo. We compared two enantiomers of S-CPP that contain both a protein transduction domain and an endosomal escape domain, with previously shown capacity for cytoplasmic delivery. The plasma concentration versus time curve of both radiolabelled S-CPPs required a two-compartment PK analytical model, which showed a fast distribution phase (t1/2α ranging from 1.25 to 3 min) followed by a slower elimination phase (t1/2β ranging from 5 to 15 h) after intravenous injection. Cargo IgG combined to S-CPPs displayed longer elimination half-life, of up to 25 h. The fast decrease in plasma concentration of S-CPPs was associated with an accumulation in target organs assessed at 1 and 5 h post-injection, particularly in the liver. In addition, in situ cerebral perfusion (ISCP) of L-S-CPP yielded a brain uptake coefficient of 7.2 ± 1.1 µl g-1 s-1, consistent with penetration across the blood-brain barrier (BBB), without damaging its integrity in vivo. No sign of peripheral toxicity was detected either by examining hematologic and biochemical blood parameters, or by measuring cytokine levels in plasma. In conclusion, S-CPPs are promising non-toxic transport vectors for improved tissue distribution of drug cargos in vivo.

Bypassing the Need for Cell Permeabilization: Nanobody CDR3 Peptide Improves Binding on Living Bacteria

Membrane interaction constitutes to be an essential parameter in the mode of action of entities such as proteins, as well as cell-penetrating and antimicrobial peptides, resulting in noninvasive or lytic activities depending on the membrane compositions and interactions. Recently, a nanobody able to interact with the top priority, multidrug-resistant bacterial pathogen Acinetobacter baumannii was discovered, although binding took place with fixed cells only. To potentially overcome this limitation, linear peptides corresponding to the complementarity-determining regions (CDR) were synthesized and fluorescently labeled. Microscopy data indicated clear membrane interactions of the CDR3 sequence with living A. baumannii cells, indicating both the importance of the CDR3 as part of the parent nanobody paratope and the improved binding ability and thus avoiding the need for permeabilization of the cells. In addition, cyclization of the peptide with an additionally introduced rigidifying 1,2,3-triazole bridge retains its binding ability while proteolytically protecting the peptide. Overall, this study resulted in the discovery of novel peptides binding a multidrug-resistant pathogen.

Effect of helicity and hydrophobicity on cell-penetrating ability of arginine-rich peptides

Arginine (Arg)-rich peptides are one of the typical cell-penetrating peptides (CPPs), which can deliver membrane-impermeable compounds into intracellular compartments. Guanidino groups in Arg-rich peptides are critical for their high cell-penetrating ability, although it remains unclear whether peptide secondary structures contribute to this ability. In the current study, we designed four Arg-rich peptides containing α,α-disubstituted α-amino acids (dAAs), which prefer to adopt a helical structure. The four dAA-containing peptides adopted slightly different peptide secondary structures, from a random structure to a helical structure, with different hydrophobicities. In these peptides, dipropylglycine-containing peptide exhibited the highest helicity and hydrophobicity, and showed the best cell-penetrating ability. These findings suggested that the helicity and hydrophobicity of Arg-rich peptides contributes to their high cell-penetrating ability.

Adenovirus-Derived Nano-Capsid Platforms for Targeted Delivery and Penetration of Macromolecules into Resistant and Metastatic Tumors

Macromolecular therapeutics such as nucleic acids, peptides, and proteins have the potential to overcome treatment barriers for cancer. For example, nucleic acid or peptide biologics may offer an alternative strategy for attacking otherwise undruggable therapeutic targets such as transcription factors and similar oncologic drivers. Delivery of biological therapeutics into tumor cells requires a robust system of cell penetration to access therapeutic targets within the cell interior. A highly effective means of accomplishing this may be borrowed from cell-penetrating pathogens such as viruses. In particular, the cell entry function of the adenovirus penton base capsid protein has been effective at penetrating tumor cells for the intracellular deposition of macromolecular therapies and membrane-impermeable drugs. Here, we provide an overview describing the evolution of tumor-targeted penton-base-derived nano-capsids as a framework for discussing the requirements for overcoming key barriers to macromolecular delivery. The development and pre-clinical testing of these proteins for therapeutic delivery has begun to also uncover the elusive mechanism underlying the membrane-penetrating function of the penton base. An understanding of this mechanism may unlock the potential for macromolecular therapeutics to be effectively delivered into cancer cells and to provide a treatment option for tumors resisting current clinical therapies.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

Evolving strategies and application of proteins and peptide therapeutics in cancer treatment

Several proteins and peptides have therapeutic potential and can be used for cancer therapy. By binding to cell surface receptors and other indicators uniquely linked with or overexpressed on tumors compared to healthy tissue, protein biologics enhance the active targeting of cancer cells, as opposed to the passive targeting of cells by conventional small-molecule chemotherapeutics. This study focuses on peptide medications that exist to slow or stop tumor growth and the spread of cancer, demonstrating the therapeutic potential of peptides in cancer treatment. As an alternative to standard chemotherapy, peptides that selectively kill cancer cells while sparing healthy tissue are developing. A mountain of clinical evidence supports the efficacy of peptide-based cancer vaccines. Since a single treatment technique may not be sufficient to produce favourable results in the fight against cancer, combination therapy is emerging as an effective option to generate synergistic benefits. One example of this new area is the use of anticancer peptides in combination with nonpeptidic cytotoxic drugs or the combination of immunotherapy with conventional therapies like radiation and chemotherapy. This review focuses on the different natural and synthetic peptides obtained and researched. Discoveries, manufacture, and modifications of peptide drugs, as well as their contemporary applications, are summarized in this review. We also discuss the benefits and difficulties of potential advances in therapeutic peptides.

Antimicrobial efficacy of cyclic α- and β-peptides incorporated in polyurethane coatings

Microbial growth on surfaces poses health concerns and can accelerate the biodegradation of engineered materials and coatings. Cyclic peptides are promising agents to combat biofouling because they are more resistant to enzymatic degradation than their linear counterparts. They can also be designed to interact with extracellular targets and intracellular targets and/or self-assemble into transmembrane pores. Here, we determine the antimicrobial efficacy of two pore-forming cyclic peptides, α-K3W3 and β-K3W3, against bacterial and fungal liquid cultures and their capacity to inhibit biofilm formation on coated surfaces. These peptides display identical sequences, but the additional methylene group in the peptide backbone of β-amino acids results in a larger diameter and an enhancement in the dipole moment. In liquid cultures, β-K3W3 exhibited lower minimum inhibitory concentration values and greater microbicidal power in reducing the number of colony forming units (CFUs) when exposed to a gram-positive bacterium, Staphylococcus aureus, and two fungal strains, Naganishia albida and Papiliotrema laurentii. To evaluate the efficacy against the formation of fungal biofilms on painted surfaces, cyclic peptides were incorporated into polyester-based thermoplastic polyurethane. The formation of N. albida and P. laurentii microcolonies (105 per inoculation) for cells extracted from coatings containing either peptide could not be detected after a 7-day exposure. Moreover, very few CFUs (∼5) formed after 35 days of repeated depositions of freshly cultured P. laurentii every 7 days. In contrast, the number of CFUs for cells extracted from the coating without cyclic peptides was >8 log CFU.

Ocular Delivery of Therapeutic Agents by Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are short peptides with the ability to translocate through the cell membrane to facilitate their cellular uptake. CPPs can be used as drug-delivery systems for molecules that are difficult to uptake. Ocular drug delivery is challenging due to the structural and physiological complexity of the eye. CPPs may be tailored to overcome this challenge, facilitating cellular uptake and delivery to the targeted area. Retinal diseases occur at the posterior pole of the eye; thus, intravitreal injections are needed to deliver drugs at an effective concentration in situ. However, frequent injections have risks of causing vision-threatening complications. Recent investigations have focused on developing long-acting drugs and drug delivery systems to reduce the frequency of injections. In fact, conjugation with CPP could deliver FDA-approved drugs to the back of the eye, as seen by topical application in animal models. This review summarizes recent advances in CPPs, protein/peptide-based drugs for eye diseases, and the use of CPPs for drug delivery based on systematic searches in PubMed and clinical trials. We highlight targeted therapies and explore the potential of CPPs and peptide-based drugs for eye diseases.

Modular Diazo Compound for the Bioreversible Late-Stage Modification of Proteins

We introduce a versatile strategy for the bioreversible modification of proteins. Our strategy is based on a tricomponent molecule, synthesized in three steps, that incorporates a diazo moiety for chemoselective esterification of carboxyl groups, a pyridyl disulfide group for late-stage functionalization with thiolated ligands, and a self-immolative carbonate group for esterase-mediated cleavage. Using cytochrome c (Cyt c) and the green fluorescent protein (GFP) as models, we generated protein conjugates modified with diverse domains for cellular delivery that include a small molecule, targeting and cell-penetrating peptides (CPPs), and a large polysaccharide. As a proof of concept, we used our strategy to effect the delivery of proteins into the cytosol of live mammalian cells in the presence of serum. The cellular delivery of functional Cyt c, which induces apoptosis, highlighted the advantage of bioreversible conjugation on a carboxyl group versus irreversible conjugation on an amino group. The ease and utility of this traceless modification provide new opportunities for chemical biologists.