Discovery and Characterization of a Peptide That Enhances Endosomal Escape of Delivered Proteins in Vitro and in Vivo

Advances in Cytosolic Delivery of Proteins: Approaches, Challenges, and Emerging Technologies

Although therapeutic proteins have achieved recognized clinical success, they are inherently membrane impermeable, which limits them to acting only on extracellular or membrane-associated targets. Developing an efficient protein delivery method will provide a unique opportunity for intracellular target-related therapeutic proteins. In this review article, we summarize the different pathways by which cells take up proteins. These pathways fall into two main categories: One in which proteins are transported directly across the cell membrane and the other through endocytosis. At the same time, important features to ensure successful delivery through these pathways are highlighted. We then provide a comprehensive overview of the latest developments in the transduction of covalent protein modifications, such as coupling cell-penetrating motifs and supercharging, as well as the use of nanocarriers to mediate protein transport, such as liposomes, polymers, and inorganic nanoparticles. Finally, we emphasize the existing challenges of cytoplasmic protein delivery and provide an outlook for future progress.

Enhanced glucose regulation potential of C-peptide mimics

The connecting peptide (C-peptide), once relegated as an epiphenomenon in insulin biosynthesis, has now been recognized for its capacity to instigate molecular effects along with important physiological functions. These findings suggest that C-peptide is a hormonally active molecule responsible for controlling a number of diabetes-related complications, in addition to proinsulin processing. Notably, it demonstrates cellular responsiveness and acts as a robust biomarker for beta cell functions, with a half-life longer than that of insulin. Herein, we investigated the effect of some synthetic C-peptide mimics on glucose homeostasis, specifically focusing on glucose uptake, GLUT4 translocation and associated membrane trafficking processes. The glucose utilization potential of some of the C-peptide mimics in L6 muscle myotubes was significantly better than that of the human C-peptide. One of the synthesized C-peptide mimics, CP8, showed glucose metabolism akin to insulin, including potential for Akt phosphorylation and IRβ autophosphorylation. Also, it showed the ability to mitigate intramolecular reactive oxygen species production. The results obtained here highlight the potential of C-peptide mimics on glucose metabolism, as well as interaction with Akt and IRβ, positioning them as promising candidates for future diabetes research.

Histidine-rich enantiomeric peptide coacervates enhance antigen sequestration and presentation to T cells

Peptides and peptidomimetics that self-assemble through LLPS have recently emerged as vital building blocks for creating functional biomaterials, thanks to their unique physicochemical properties and dynamic nature. One of life's most distinctive features is its selectivity for chiral molecules. To date, coacervates comprised of d-amino acids have not been reported. Here, we demonstrate that histidine-rich repeats of (GHGXY)4 (X = L/V/P) and their enantiomers undergo LLPS, paving the way for improved coacervate stability. Through a series of biophysical studies, we found that the droplet size can be tuned based on L, V, or P substitution, and molecular cargo between 600 and 150 000 Da is efficiently recruited in a bioactivity-preserving aqueous environment during phase separation. Mechanistic studies reveal that the droplets enter cells via energy-dependent endocytic pathways, exhibit composition-selective fusion properties, and effectively deliver molecular therapeutics across various cell types. Finally, we demonstrate that the coacervates enhance antigen presentation to CD4+ and CD8+ T cells, resulting in robust proliferation and the production of functional cytokines. Our study outlines the development and characterization of enantiomeric peptide coacervates as promising vaccine delivery vehicles with tunable physicochemical properties.

A method for the detection and enrichment of endogenous cereblon substrates

C-Terminal cyclic imides are posttranslational modifications on proteins that are recognized and removed by the E3 ligase substrate adapter cereblon (CRBN). Despite the observation of these modifications across the proteome by mass spectrometry-based proteomics, an orthogonal and generalizable method to visualize the C-terminal cyclic imide would enhance detection, sensitivity, and throughput of endogenous CRBN substrate characterization. Here we develop an antibody-like reagent, termed "cerebody," for visualizing and enriching C-terminal cyclic imide-modified proteins. We describe the engineering of CRBN derivatives to produce cerebody and use it to identify CRBN substrates by Western blot and enrichment from whole cell and tissue lysates. CRBN substrates identified by cerebody enrichment are mapped, validated, and further characterized for dependence on the C-terminal cyclic imide modification. These methods will accelerate the characterization of endogenous CRBN substrates and their regulation.

Green synthesis of highly fluorescent carbon quantum dots from almond resin for advanced theranostics in biomedical applications

Fluorescent Carbon Quantum Dots (CQDs) are being used in medical applications, particularly in theranostics. These Carbon Quantum Dots have been gaining more attention lately due to their potential as an effective replacement for hazardous synthetic organic dyes in a variety of biomedical applications, including live cell imaging and diagnostics. In this study, highly fluorescent Carbon Quantum Dots by one pot microwave based green route with a size of less than 10 nm, was prepared from commercially available almond resin, Prunus dulcis and conjugated with honey as additional reagent for surface functionalization. They exhibit a deep blue emission on excitation at 350 nm with an elevated quantum yield at 61%. They possess atomic nature and basic features such as high photo-stability, varying fluorescence, greater biocompatibility, and better water solubility. These fluorescent labels exhibit faster cellular invagination without disturbing the cell stability. The CQDs present cell imaging capacity with multi-coloration for visualizing the fine architecture of the nucleus naming, the nuclear membrane and nucleolus, which is linked with their varied, surface structures such as amphiphilic property and higher positive charges. These characteristics with minimal invasion have made carbon quantum dots to become the spotlight in theranostics. They can be used as alternatives to synthetic dyes for fluorescence- related cell-imaging. The intriguing fact about this approach is that it opens the possibility of combining therapy and diagnostics into one unit, which can alter how some diseases are handled and, in turn, transform the field of healthcare.

Peptide-coated DNA nanostructures as a platform for control of lysosomal function in cells

DNA nanotechnology is a rapidly growing field that provides exciting tools for biomedical applications. Targeting lysosomal functions with nanomaterials, such as DNA nanostructures (DNs), represents a rational and systematic way to control cell functionality. Here we present a versatile DNA nanostructure-based platform that can modulate a number of cellular functions depending on the concentration and surface decoration of the nanostructure. Utilizing different peptides for surface functionalization of DNs, we were able to rationally modulate lysosomal activity, which in turn translated into the control of cellular function, ranging from changes in cell morphology to modulation of immune signaling and cell death. Low concentrations of decalysine peptide-coated DNs induced lysosomal acidification, altering the metabolic activity of susceptible cells. In contrast, DNs coated with an aurein-bearing peptide promoted lysosomal alkalization, triggering STING activation. High concentrations of decalysine peptide-coated DNs caused lysosomal swelling, loss of cell-cell contacts, and morphological changes without inducing cell death. Conversely, high concentrations of aurein-coated DNs led to lysosomal rupture and mitochondrial damage, resulting in significant cytotoxicity. Our study holds promise for the rational design of a new generation of versatile DNA-based nanoplatforms that can be used in various biomedical applications, like the development of combinatorial anti-cancer platforms, efficient systems for endolysosomal escape, and nanoplatforms modulating lysosomal pH.

New targets and designed inhibitors of ASAP Arf-GAPs derived from structural characterization of the ASAP1/440-kD ankyrin-B interaction

ASAP1 and its paralog ASAP2 belong to a PI4,5P2-dependent Arf GTPase-activating protein (Arf-GAP) family capable of modulating membrane and cytoskeletal dynamics. ASAPs regulate cell adhesive structures such as invadosomes and focal adhesions during cell attachment and migration. Malfunctioning of ASAP1 has been implicated in the malignant phenotypes of various cancers. Here, we discovered that the SH3 domain of ASAP1 or ASAP2 specifically binds to a 12-residue, positively charged peptide fragment from the 440 kDa giant ankyrin-B, a neuronal axon specific scaffold protein. The high-resolution structure of the ASAP1-SH3 domain in complex with the gAnkB peptide revealed a noncanonical SH3-ligand binding mode with high affinity and specificity. Structural analysis of the complex readily uncovered a consensus ASAP1-SH3 binding motif, which allowed the discovery of a number of previously unknown binding partners of ASAP1-SH3 including Clasp1/Clasp2, ALS2, β-Pix, DAPK3, PHIP, and Limk1. Fittingly, these newly identified ASAP1 binding partners are primarily key modulators of the cytoskeletons. Finally, we designed a cell-penetrating, highly potent ASAP1 SH3 domain binding peptide with a Kd ∼7 nM as a tool for studying the roles of ASAPs in different cellular processes.

Emerging Landscape of Supercharged Proteins and Peptides for Drug Delivery

Although groundbreaking biotechnological techniques such as gene editing have significantly progressed, the effective and targeted transport of therapeutic agents into host cells remains a major obstacle to the development of biotherapeutics. Confronting the unique challenge posed by large macromolecules such as proteins, peptides, and nucleic acids adds complexity to this issue. Recent findings reveal that the supercharging of proteins and peptides not only enables control over critical properties, such as temperature resistance and catalytic activity, but also holds promise as a viable strategy for their use in drug delivery. This review provides a concise summary of the attributes of supercharged proteins and peptides, encompassing both their natural occurrence and engineered variants. Furthermore, it sheds light on the present status and future possibilities of supercharged proteins and peptides as carriers for significant biomolecules in the realms of medical research and therapeutic applications.

Mechanism study of cross presentation of exogenous antigen induced by cholera toxin-like chimeric protein

Tumor subunit vaccines have great potential in personalized cancer immunotherapy. They are usually administered with adjuvant owing to their low immunogenicity. Cholera toxin (CT) is a biological adjuvant with diverse biological functions and a long history of use. Our earlier study revealed that a CT-like chimeric protein co-delivered with murine granulocyte-macrophage colony stimulating factor (mGM-CSF) and prostate cancer antigen epitope could co-stimulate dendritic cells (DCs) and enhance cross presentation of tumor epitope. To further study the molecular mechanism of CT-like chimeric protein in cross presentation, major histocompatibility complex class I (MHC I)-restricted epitope 257-264 of ovalbumin (OVAT) was used as a model antigen peptide in this study. Recombinant A subunit and pentameric B subunit of CT protein were respectively genetically constructed and purified. Then both assembled into AB5 chimeric protein in vitro. Three different chimeric biomacromolecules containing mGM-CSF and OVAT were constructed according to the different fusion sites and whether the endoplasmic reticulum (ER) retention sequence was included. It was found that A2 domain and B subunit of CT were both available for loading epitopes and retaining GM1 affinity. The binding activity of GM1 was positively correlated with antigen endocytosis. Once internalized, DCs became mature and cross-presented antigen. KDEL helped the whole molecule to be retained in the ER, and this improved the cross presentation of antigen on MHC I molecules. In conclusion, hexameric CT-like chimeric protein with dual effects of GM1 affinity and ER retention sequence were potential in improvement of cross presentation. The results laid a foundation for designing personalized tumor vaccine based on CT-like chimeric protein molecular structure.

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.

Extracellular vesicles for developing targeted hearing loss therapy

Substantial efforts have been made for local administration of small molecules or biologics in treating hearing loss diseases caused by either trauma, genetic mutations, or drug ototoxicity. Recently, extracellular vesicles (EVs) naturally secreted from cells have drawn increasing attention on attenuating hearing impairment from both preclinical studies and clinical studies. Highly emerging field utilizing diverse bioengineering technologies for developing EVs as the bioderived therapeutic materials, along with artificial intelligence (AI)-based targeting toolkits, shed the light on the unique properties of EVs specific to inner ear delivery. This review will illuminate such exciting research field from fundamentals of hearing protective functions of EVs to biotechnology advancement and potential clinical translation of functionalized EVs. Specifically, the advancements in assessing targeting ligands using AI algorithms are systematically discussed. The overall translational potential of EVs is reviewed in the context of auditory sensing system for developing next generation gene therapy.

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.

Engineered Histidine-Rich Peptides Enhance Endosomal Escape for Antibody-Targeted Intracellular Delivery of Functional Proteins

Currently, the clinical application of protein/peptide therapeutics is mainly limited to the modulation of diseases in extracellular spaces. Intracellular targets are hardly accessed, owing largely to the endosomal entrapment of internalized proteins/peptides. Here, we report a strategy to design and construct peptides that enable endosome-to-cytosol delivery based on an extension of the "histidine switch" principle. By substituting the Arg/Lys residues in cationic cell-penetrating peptides (CPPs) with histidine, we obtained peptides with pH-dependent membrane-perturbation activity. These peptides do not randomly penetrate cells like CPPs, but imitate the endosomal escape of CPPs following cellular uptake. Working with one such 16-residue peptide (hsLMWP) with high endosomal escape capacity, we engineered modular fusion proteins and achieved antibody-targeted delivery of diverse protein cargoes-including the pro-apoptotic protein BID (BH3-interacting domain death agonist) and Cre recombinase-into the cytosol of multiple cancer cell types. After extensive in vitro testing, an in vivo analysis with xenograft mice ultimately demonstrated that a trastuzumab-hsLMWP-BID fusion conferred strong anti-tumor efficacy without apparent side effects. Notably, our fusion protein features a modular design, allowing flexible applications for any antibody/cargo combination of choice. Therefore, the potential applications extend throughout life science and biomedicine, including gene editing, cancer treatment, and immunotherapy.

Targeting Ras with protein engineering

Ras proteins are small GTPases that regulate cell growth and division. Mutations in Ras genes are associated with many types of cancer, making them attractive targets for cancer therapy. Despite extensive efforts, targeting Ras proteins with small molecules has been extremely challenging due to Ras's mostly flat surface and lack of small molecule-binding cavities. These challenges were recently overcome by the development of the first covalent small-molecule anti-Ras drug, sotorasib, highlighting the efficacy of Ras inhibition as a therapeutic strategy. However, this drug exclusively inhibits the Ras G12C mutant, which is not a prevalent mutation in most cancer types. Unlike the G12C variant, other Ras oncogenic mutants lack reactive cysteines, rendering them unsuitable for targeting via the same strategy. Protein engineering has emerged as a promising method to target Ras, as engineered proteins have the ability to recognize various surfaces with high affinity and specificity. Over the past few years, scientists have engineered antibodies, natural Ras effectors, and novel binding domains to bind to Ras and counteract its carcinogenic activities via a variety of strategies. These include inhibiting Ras-effector interactions, disrupting Ras dimerization, interrupting Ras nucleotide exchange, stimulating Ras interaction with tumor suppressor genes, and promoting Ras degradation. In parallel, significant advancements have been made in intracellular protein delivery, enabling the delivery of the engineered anti-Ras agents into the cellular cytoplasm. These advances offer a promising path for targeting Ras proteins and other challenging drug targets, opening up new opportunities for drug discovery and development.

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.

DNA Nanomaterials-Based Platforms for Cancer Immunotherapy

The past few decades have witnessed the evolving paradigm for cancer therapy from nonspecific cytotoxic agents to selective, mechanism-based therapeutics, especially immunotherapy. In particular, the integration of nanomaterials with immunotherapy is proven to improve the therapeutic outcome and minimize off-target toxicity in the treatment. As a novel nanomaterial, DNA-based self-assemblies featuring uniform geometries, feasible modifications, programmability, surface addressability, versatility, and intrinsic biocompatibility, are extensively exploited for innovative and effective cancer immunotherapy. In this review, the successful employment of DNA nanoplatforms for cancer immunotherapy, including the delivery of immunogenic cell death inducers, adjuvants and vaccines, immune checkpoint blockers as well as the application in immune cell engineering and adoptive cell therapy is summarized. The remaining challenges and future perspectives regarding the pharmacokinetics/pharmacodynamics, in vivo fate and immunogenicity of DNA materials, and the design of intelligent DNA nanomedicine for individualized cancer immunotherapy are also discussed.

Extracellular epimorphin impairs expression and processing of profilaggrin in HaCaT keratinocytes

The expression and processing of filaggrin, a filament-associated protein in the skin epidermis, is closely associated with keratinocyte cornification. The large precursor profilaggrin (Pro-FLG) is initially detected at the granular layer in keratohyalin granules, subsequently processed into 10 to 12 filaggrin monomers (mFLGs) for keratin assembly, and ultimately degraded into smaller peptides that behave as natural moisturizing factor (NMF) at the outermost epidermis. We previously reported that epimorphin (EPM) extruded upon external stimuli severely perturbs epidermal terminal differentiation. Using HaCaT keratinocytes with inducible expression and recombinant EPM and FLG, we investigated the effect of extracellular EPM on the expression profile of filaggrin. As expression and processing of Pro-FLG in primary keratinocytes are accompanied with apoptotic cell death, we employed HaCaT keratinocytes that grow and express filaggrin mRNA in standard culture medium. In response to ectopic stimulation with extracellular EPM, Pro-FLG expression decreased with elimination of keratohyalin granules in the cells, with filaggrin mRNA remained constant and profilaggrin processing was not accelerated. Additionally, using a recombinant form of mFLG engineered for intracellular localization, we found that extracellular EPM hindered proteolytic cleavage of mFLG for production of NMF. Taken together, extracellularly extruded EPM, an epidermal cornification blocker, not only decreases Pro-FLG expression but also reduces the production of NMF in HaCaT keratinocytes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00566-8.

Programming the Cellular Uptake of Protein-Based Viromimetic Nanoparticles for Enhanced Delivery

Viral mimetics is a noteworthy strategy to design efficient delivery systems without the safety drawbacks and engineering difficulties of modifying viral vectors. The triblock polypeptide CSB was previously designed de novo to self-assemble with DNA into nanocomplexes called artificial virus-like particles (AVLPs) due to their similarities to viral particles. Here, we show how we can incorporate new blocks into the CSB polypeptide to enhance its transfection without altering its self-assembly capabilities and the stability and morphology of the AVLPs. The addition of a short peptide (aurein) and/or a large protein (transferrin) to the AVLPs improved their internalization and specific targeting to cells by up to 11 times. Overall, these results show how we can further program the cellular uptake of the AVLPs with a wide range of bioactive blocks. This can pave the way to develop programmable and efficient gene delivery systems.

Endosomal escape for cell-targeted proteins. Going out after going in

Protein-based nanocarriers are versatile and biocompatible drug delivery systems. They are of particular interest in nanomedicine as they can recruit multiple functions in a single modular polypeptide. Many cell-targeting peptides or protein domains can promote cell uptake when included in these nanoparticles through receptor-mediated endocytosis. In that way, targeting drugs to specific cell receptors allows a selective intracellular delivery process, avoiding potential side effects of the payload. However, once internalized, the endo-lysosomal route taken by the engulfed material usually results in full degradation, preventing their adequate subcellular localization, bioavailability and subsequent therapeutic effect. Thus, entrapment into endo-lysosomes is a main bottleneck in the efficacy of protein-drug nanomedicines. Promoting endosomal escape and preventing lysosomal degradation would make this therapeutic approach clinically plausible. In this review, we discuss the mechanisms intended to evade lysosomal degradation of proteins, with the most relevant examples and associated strategies, and the methods available to measure that effect. In addition, based on the increasing catalogue of peptide domains tailored to face this challenge as components of protein nanocarriers, we emphasize how their particular mechanisms of action can potentially alter the functionality of accompanying protein materials, especially in terms of targeting and specificity in the delivery process.

Design of a self-driven probiotic-CRISPR/Cas9 nanosystem for sono-immunometabolic cancer therapy

Reprogramming the tumor immunosuppressive microenvironment is a promising strategy for improving tumor immunotherapy efficacy. The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 system can be used to knockdown tumor immunosuppression-related genes. Therefore, here, a self-driven multifunctional delivery vector is constructed to efficiently deliver the CRISPR-Cas9 nanosystem for indoleamine 2,3-dioxygenase-1 (IDO1) knockdown in order to amplify immunogenic cell death (ICD) and then reverse tumor immunosuppression. Lactobacillus rhamnosus GG (LGG) is a self-driven safety probiotic that can penetrate the hypoxia tumor center, allowing efficient delivery of the CRISPR/Cas9 system to the tumor region. While LGG efficiently colonizes the tumor area, it also stimulates the organism to activate the immune system. The CRISPR/Cas9 nanosystem can generate abundant reactive oxygen species (ROS) under the ultrasound irradiation, resulting in ICD, while the produced ROS can induce endosomal/lysosomal rupture and then releasing Cas9/sgRNA to knock down the IDO1 gene to lift immunosuppression. The system generates immune responses that effectively attack tumor cells in mice, contributing to the inhibition of tumor re-challenge in vivo. In addition, this strategy provides an immunological memory effect which offers protection against lung metastasis.

Improved transfer efficiency of supercharged 36 + GFP protein mediate nucleic acid delivery

The potential of nucleic acid therapeutics to treat diseases by targeting specific cells has resulted in its increasing number of uses in clinical settings. However, the major challenge is to deliver bio-macromolecules into target cells and/or subcellular locations of interest ahead in the development of delivery systems. Although, supercharged residues replaced protein 36 + GFP can facilitate itself and cargoes delivery, its efficiency is still limited. Therefore, we combined our recent progress to further improve 36 + GFP based delivery efficiency. We found that the penetration efficacy of 36 + GFP protein was significantly improved by fusion with CPP-Dot1l or treatment with penetration enhancer dimethyl sulfoxide (DMSO) in vitro. After safely packaged with plasmid DNA, we found that the efficacy of in vitro and in vivo transfection mediated by 36 + GFP-Dot1l fusion protein is also significantly improved than 36 + GFP itself. Our findings illustrated that fusion with CPP-Dot1l or incubation with DMSO is an alternative way to synergically promote 36 + GFP mediated plasmid DNA delivery in vitro and in vivo.

The E3 ligase adapter cereblon targets the C-terminal cyclic imide degron

The ubiquitin E3 ligase substrate adapter cereblon (CRBN) is a target of thalidomide and lenalidomide¹, therapeutic agents used in the treatment of haematopoietic malignancies^2-4 and as ligands for targeted protein degradation^5-7. These agents are proposed to mimic a naturally occurring degron; however, the structural motif recognized by the thalidomide-binding domain of CRBN remains unknown. Here we report that C-terminal cyclic imides, post-translational modifications that arise from intramolecular cyclization of glutamine or asparagine residues, are physiological degrons on substrates for CRBN. Dipeptides bearing the C-terminal cyclic imide degron substitute for thalidomide when embedded within bifunctional chemical degraders. Addition of the degron to the C terminus of proteins induces CRBN-dependent ubiquitination and degradation in vitro and in cells. C-terminal cyclic imides form adventitiously on physiologically relevant timescales throughout the human proteome to afford a degron that is endogenously recognized and removed by CRBN. The discovery of the C-terminal cyclic imide degron defines a regulatory process that may affect the physiological function and therapeutic engagement of CRBN.

The interactions between DNA nanostructures and cells: A critical overview from a cell biology perspective

DNA nanotechnology has yielded remarkable advances in  composite materials with diverse applications in biomedicine. The specificity and predictability of building 3D structures at the nanometer scale make DNA nanotechnology a promising tool for uses in biosensing, drug delivery, cell modulation, and bioimaging. However, for successful translation of DNA nanostructures to real-world applications, it is crucial to understand how they interact with living cells, and the consequences of such interactions. In this review, we summarize the current state of knowledge on the interactions of DNA nanostructures with cells. We identify key challenges, from a cell biology perspective, that influence progress towards the clinical translation of DNA nanostructures. We close by providing an outlook on what questions must be addressed to accelerate the clinical translation of DNA nanostructures. STATEMENT OF SIGNIFICANCE: Self-assembled DNA nanostructures (DNs) offers unique opportunities to overcome persistent challenges in the nanobiotechnology field. However, the interactions between engineered DNs and living cells are still not well defined. Critical systematization of current cellular models and biological responses triggered by DNs is a crucial foundation for the successful clinical translation of DNA nanostructures. Moreover, such an analysis will identify the pitfalls and challenges that are present in the field, and provide a basis for overcoming those challenges.

The role of cell-penetrating peptides in potential anti-cancer therapy

Due to the complex physiological structure, microenvironment and multiple physiological barriers, traditional anti-cancer drugs are severely restricted from reaching the tumour site. Cell-penetrating peptides (CPPs) are typically made up of 5-30 amino acids, and can be utilised as molecular transporters to facilitate the passage of therapeutic drugs across physiological barriers. Up to now, CPPs have widely been used in many anti-cancer treatment strategies, serving as an excellent potential choice for oncology treatment. However, their drawbacks, such as the lack of cell specificity, short duration of action, poor stability in vivo, compatibility problems (i.e. immunogenicity), poor therapeutic efficacy and formation of unwanted metabolites, have limited their further application in cancer treatment. The cellular uptake mechanisms of CPPs involve mainly endocytosis and direct penetration, but still remain highly controversial in academia. The CPPs-based drug delivery strategy could be improved by clever design or chemical modifications to develop the next-generation CPPs with enhanced cell penetration capability, stability and selectivity. In addition, some recent advances in targeted cell penetration that involve CPPs provide some new ideas to optimise CPPs.

Smart pH-responsive nanomedicines for disease therapy

Background

Currently nanomedicines are the focus of attention from researchers and clinicians because of the successes of lipid-nanoparticles-based COVID-19 vaccines. Nanoparticles improve existing treatments by providing a number of advantages including protection of cargo molecules from external stresses, delivery of drugs to target tissues, and sustained drug release. To prevent premature release-related side effects, stable drug loading in nanoformulations is required, but the increased stability of the formulation could also lead to a poor drug-release profile at the target sites. Thus, researchers have exploited differences in a range of properties (e.g., enzyme levels, pH, levels of reduced glutathione, and reactive oxygen species) between non-target and target sites for site-specific release of drugs. Among these environmental stimuli, pH gradients have been widely used to design novel, responsive nanoparticles.

Area covered

In this review, we assess drug delivery based on pH-responsive nanoparticles at the levels of tissues (tumor microenvironment, pH ~ 6.5) and of intracellular compartments (endosome and lysosome, pH 4.5-6.5). Upon exposure to these pH stimuli, pH-responsive nanoparticles respond with physicochemical changes to their material structure and surface characteristics. These changes include swelling, dissociation, or surface charge switching, in a manner that favors drug release at the target site (the tumor microenvironment region and the cytosol followed by endosomal escape) rather than the surrounding tissues.

Expert opinion

Lastly, we consider the challenges involved in the development of pH-responsive nanomedicines.

Phase-separating peptides for direct cytosolic delivery and redox-activated release of macromolecular therapeutics

Biomacromolecules are highly promising therapeutic modalities to treat various diseases. However, they suffer from poor cellular membrane permeability, limiting their access to intracellular targets. Strategies to overcome this challenge often employ nanoscale carriers that can get trapped in endosomal compartments. Here we report conjugated peptides that form pH- and redox-responsive coacervate microdroplets by liquid-liquid phase separation that readily cross the cell membrane. A wide range of macromolecules can be quickly recruited within the microdroplets, including small peptides, enzymes as large as 430 kDa and messenger RNAs (mRNAs). The therapeutic-loaded coacervates bypass classical endocytic pathways to enter the cytosol, where they undergo glutathione-mediated release of payload, the bioactivity of which is retained in the cell, while mRNAs exhibit a high transfection efficiency. These peptide coacervates represent a promising platform for the intracellular delivery of a large palette of macromolecular therapeutics that have potential for treating various pathologies (for example, cancers and metabolic diseases) or as carriers for mRNA-based vaccines.

Incorporation of Endosomolytic Peptides with Varying Disruption Mechanisms into EGFR-Targeted Protein Conjugates: The Effect on Intracellular Protein Delivery and EGFR Specificity in Breast Cancer Cells

Intracellular delivery of protein therapeutics remains a significant challenge limiting the majority of clinically available protein drugs to extracellular targets. Strategies to deliver proteins to subcellular compartments have traditionally relied on cell-penetrating peptides, which can drive enhanced internalization but exhibit unreliable activity and are rarely able to target specific cells, leading to off-target effects. Moreover, few design rules exist regarding the relative efficacy of various endosomal escape strategies in proteins. Accordingly, we developed a simple fusion modification approach to incorporate endosomolytic peptides onto epidermal growth factor receptor (EGFR)-targeted protein conjugates and performed a systematic comparison of the endosomal escape efficacy, mechanism of action, and capacity to maintain EGFR-targeting specificity of conjugates modified with four different endosomolytic sequences of varying modes of action (Aurein 1.2, GALA, HA2, and L17E). Use of the recently developed Gal8-YFP assay indicated that the fusion of each endosomolytic peptide led to enhanced endosomal disruption. Additionally, the incorporation of each endosomolytic peptide increased the half-life of the internalized protein and lowered lysosomal colocalization, further supporting the membrane-disruptive capacity. Despite this, only EGFR-targeted conjugates modified with Aurein 1.2 or GALA maintained EGFR specificity. These results thus demonstrated that the choice of endosomal escape moiety can substantially affect targeting capability, cytotoxicity, and bioactivity and provided important new insights into endosomolytic peptide selection for the design of targeted protein delivery systems.

Cell-penetrating peptides in protein mimicry and cancer therapeutics

Extensive research has been undertaken in the pursuit of anticancer therapeutics. Many anticancer drugs require specificity of delivery to cancer cells, whilst sparing healthy tissue. Cell-penetrating peptides (CPPs), now well established as facilitators of intracellular delivery, have in recent years advanced to incorporate target specificity and thus possess great potential for the targeted delivery of anticancer cargoes. Though none have yet been approved for clinical use, this novel technology has already entered clinical trials. In this review we present CPPs, discuss their classification, mechanisms of cargo internalization and highlight strategies for conjugation to anticancer moieties including their incorporation into therapeutic proteins. As the mainstay of this review, strategies to build specificity into tumor targeting CPP constructs through exploitation of the tumor microenvironment and the use of tumor homing peptides are discussed, whilst acknowledging the extensive contribution made by CPP constructs to target specific protein-protein interactions integral to intracellular signaling pathways associated with tumor cell survival and progression. Finally, antibody/antigen CPP conjugates and their potential roles in cancer immunotherapy and diagnostics are considered. In summary, this review aims to harness the potential of CPP-aided drug delivery for future cancer therapies and diagnostics whilst highlighting some of the most recent achievements in selective delivery of anticancer drugs, including cytostatic drugs, to a range of tumor cells both in vitro and in vivo.

Cell-Penetrating Peptides

In this introductory chapter, we first define cell-penetrating peptides (CPPs), give short overview of CPP history and discuss several aspects of CPP classification. Next section is devoted to the mechanism of CPP penetration into the cells, where direct and endocytic internalization of CPP is explained. Kinetics of internalization is discussed more extensively, since this topic is not discussed in other chapters of this book. At the end of this section some features of the thermodynamics of CPP interaction with the membrane is also presented. Finally, we present different cargoes that can be transferred into the cells by CPPs and briefly discuss the effect of cargo on the rate and efficiency of penetration into the cells.

Current and future treatment approaches for Barth syndrome

Barth Syndrome is an X-linked disorder of mitochondrial cardiolipin metabolism caused by pathogenic variants in TAFAZZIN with pleiotropic effects including cardiomyopathy, neutropenia, growth delay, and skeletal myopathy. Management requires a multidisciplinary approach to the organ-specific manifestations including specialists from cardiology, hematology, nutrition, physical therapy, genetics, and metabolism. Currently, treatment is centered on management of specific clinical features, and is not targeted toward remediating the underlying biochemical defect. However, two clinical trials have been recently undertaken which target the mitochondrial pathology of this disease: a study to examine the effects of elamipretide, a cardiolipin targeted agent, and a study to examine the effects of bezafibrate, a peroxisome proliferator-activated receptor (PPAR) agonist. Treatments to directly target the defective TAFAZZIN pathway are under development, including enzyme and gene therapies.

Cellular uptake of 2-aminopyridine-modified peptide nucleic acids conjugated with cell-penetrating peptides

Cell-penetrating peptides (CPPs) have been extensively used to deliver peptide nucleic acid (PNA) in cells. We have previously found that replacement of cytosine in triplex-forming PNAs with 2-aminopyridine (M) not only enhanced RNA binding, but also improved cellular uptake of PNAs. In this study, we used confocal fluorescence microscopy to evaluate the ability of CPPs to further improve cellular uptake of M-modified PNAs. We found that PNAs conjugated with Tat and octa-arginine peptides were effectively taken up in MCF7 cells when supplied in cell media at 1 μM. Remarkably, M-modified PNA without any CPP conjugation also showed strong uptake when the concentration was increased to 5 μM. Majority of PNA conjugates remained localized in distinct cytoplasmic vesicles, as judged by dot-like fluorescence patterns. However, M-modified PNAs conjugated with Tat, octa-arginine, and even a simple tri-lysine peptide also showed dispersed fluorescence in cytoplasm and were taken up in nuclei where they localized in larger vesicles, most likely nucleoli. Endosomolytic peptides or chemicals (chloroquine and CaCl₂ ) did not release the conjugates from cytosolic vesicles, which suggested that the PNAs were not entrapped in endosomes. We hypothesize that M-modified PNAs escape endosomes and accumulate in cellular compartments rich in RNA, such as nucleoli, stress granules, and P-bodies.

Genetic and Covalent Protein Modification Strategies to Facilitate Intracellular Delivery

Protein-based therapeutics represent a rapidly growing segment of approved disease treatments. Successful intracellular delivery of proteins is an important precondition for expanded in vivo and in vitro applications of protein therapeutics. Direct modification of proteins and peptides for improved cytosolic translocation are a promising method of increasing delivery efficiency and expanding the viability of intracellular protein therapeutics. In this Review, we present recent advances in both synthetic and genetic protein modifications for intracellular delivery. Active endocytosis-based and passive internalization pathways are discussed, followed by a review of modification methods for improved cytosolic delivery. After establishing how proteins can be modified, general strategies for facilitating intracellular delivery, such as chemical supercharging or inclusion of cell-penetrating motifs, are covered. We then outline protein modifications that promote endosomal escape. We finally examine the delivery of two potential classes of therapeutic proteins, antibodies and associated antibody fragments, and gene editing proteins, such as cas9.

Improving the knock-in efficiency of the MOF-encapsulated CRISPR/Cas9 system through controllable embedding structures

Appropriate tuning of robust artificial coatings can not only enhance intracellular delivery but also preserve the biological functions of genetic molecules in gene based therapies. Here, we report a strategy to synthesize controllable nanostructures in situ by encapsulating CRISPR/Cas9 plasmids into metal-organic frameworks (MOFs) via biomimetic mineralization. The structure-functionality relationship studies indicate that MOF-coated nanostructures dramatically impact the biological features of the contained plasmids through different embedding structures. The plasmids are homogeneously distributed within the heterogeneous nanoarchitecture and protected from enzymatic degradation. In addition, the plasmid-MOF structure exhibits excellent loading capability, pH-responsive release, and affinity for plasmid binding. Through in vitro assays it was found that the superior MOF vector can greatly enhance cellular endocytosis and endo/lysosomal escape of sheltered plasmids, resulting in successful knock-in of GFP-tagged paxillin genomic sequences in cancer cell lines with high transfection potency compared to our previous studies. Thus, the development of new cost-effective approaches for MOF-based intracellular delivery systems offers an attractive option for overcoming the physiological barriers to CRISPR/Cas9 delivery, which shows great potential for investigating paxillin-associated focal adhesions and signal regulation.

Protein Corona Inhibits Endosomal Escape of Functionalized DNA Nanostructures in Living Cells

DNA nanostructures (DNs) can be designed in a controlled and programmable manner, and these structures are increasingly used in a variety of biomedical applications, such as the delivery of therapeutic agents. When exposed to biological liquids, most nanomaterials become covered by a protein corona, which in turn modulates their cellular uptake and the biological response they elicit. However, the interplay between living cells and designed DNs are still not well established. Namely, there are very limited studies that assess protein corona impact on DN biological activity. Here, we analyzed the uptake of functionalized DNs in three distinct hepatic cell lines. Our analysis indicates that cellular uptake is linearly dependent on the cell size. Further, we show that the protein corona determines the endolysosomal vesicle escape efficiency of DNs coated with an endosome escape peptide. Our study offers an important basis for future optimization of DNs as delivery systems for various biomedical applications.

A pH-Responsive Phase-Transition Polymer with High Serum Stability in Cytosolic Protein Delivery

Polymer-mediated intracellular protein delivery systems are important for the development of protein-based biotechnologies and therapeutics. However, intracellular delivery of cargo proteins in the presence of serum remains challenging due to competitive binding of serum proteins with the polymers. Here, we reported a dendrimer engineered with a high density of 4-diethylaminophenyl groups on the surface to address this issue. The dendrimer showed a pH-responsive phase-transition behavior and could assemble with cargo proteins into stable nanoparticles in serum solutions. It efficiently delivered cargo proteins into living cells, and exhibited a pH-responsive disassembly behavior after cell internalization. As a result, various cargo proteins were delivered into the cytosol of living cells with maintained bioactivity. This study provided a convenient and efficient strategy to design polymers with high serum-tolerance in cytosolic protein delivery.

Potentiating the Membrane Interaction of an Attenuated Cationic Amphiphilic Lytic Peptide for Intracellular Protein Delivery by Anchoring with Pyrene Moiety

We previously reported an approach for intracellular protein delivery by attenuating membrane-lytic activity of cationic amphiphilic peptides on cell surfaces. HAad is one such peptides that cytosolically delivers proteins of interest, including antibodies, by stimulating their endosomal escape. Additionally, HAad elicits ruffling of cell membrane, accompanied by transient membrane permeabilization, allowing for the efficient cytosolic translocation of proteins. In this study, we prepared a conjugate of HAad with pyrenebutyric acid as a membrane-anchoring unit (pBu-HAad). pBu-HAad demonstrated protein delivery into cells with only 1/20 concentration of HAad. However, the conjugates with cholesteryl hemisuccinate and aliphatic fatty acids (C = 3, 6, and 10) did not yield such marked effects. The results of time-course and inhibitor studies suggest that the membrane anchoring of HAad by a pyrene moiety leads to enhanced peptide-membrane interaction and to loosen lipid packing, thus facilitating cytosolic translocation through membranes.

Advances in peptide-mediated cytosolic delivery of proteins

The number of protein-based drugs is exponentially increasing. However, development of protein therapeutics against intracellular targets is hampered by the lack of efficient cytosolic delivery strategies. In recent years, the use of cell-penetrating peptides has been proposed as a strategy to promote protein internalization. In this article, we provide the reader with a succinct update on the strategies exploited to enable peptide-mediated cytosolic delivery of proteins. First, we analyse the various methods available for delivery. We then describe the most popular and the in vitro assays designed to assess the intracellular distribution of protein cargo.

Nanoscale Zeolitic Imidazolate Framework-8 Activator of Canonical MAPK Signaling for Bone Repair

Zeolitic imidazolate framework-8 (ZIF-8) is an important type of metal organic framework and has found numerous applications in the biomedical field. Our previous studies have demonstrated that nano ZIF-8-based titanium implants could promote osseointegration; however, its osteogenic capacity and the related mechanisms in bone regeneration have not been fully clarified. Presented here is a nanoscale ZIF-8 that could drive rat bone mesenchymal stem cell (rBMSC) differentiation into osteoblasts both in vitro and in vivo, and interestingly, nano ZIF-8 exhibited a better osteogenic effect compared with ionic conditions of Zn at the same concentration of Zn2+. Moreover, the cellular uptake mechanisms of the nanoparticles were thoroughly clarified. Specifically, nano ZIF-8 could enter the rBMSC cytoplasm probably via caveolae-mediated endocytosis and macropinocytosis. The intracellular and extracellular Zn2+ released from nano ZIF-8 and the receptors involved in the endocytosis may play a role in inducing activation of key osteogenic pathways. Furthermore, through transcriptome sequencing, multiple osteogenic pathways were found to be upregulated, among which nano ZIF-8 primarily phosphorylated ERK, thus activating the canonical mitogen-activated protein kinase pathway and promoting the osteogenesis of rBMSCs. Taken together, this study helps to elucidate the mechanism by which nano ZIF-8 regulates osteogenesis and suggests it to be a potential biomaterial for constructing multifunctional composites in bone tissue engineering.

Non-viral strategies for delivering genome editing enzymes

Genome-editing tools such as Cre recombinase (Cre), zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and most recently the clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein system have revolutionized biomedical research, agriculture, microbial engineering, and therapeutic development. Direct delivery of genome editing enzymes, as opposed to their corresponding DNA and mRNA precursors, is advantageous since they do not require transcription and/or translation. In addition, prolonged overexpression is a problem when delivering viral vector or plasmid DNA which is bypassed when delivering whole proteins. This lowers the risk of insertional mutagenesis and makes for relatively easier manufacturing. However, a major limitation of utilizing genome editing proteins in vivo is their low delivery efficiency, and currently the most successful strategy involves using potentially immunogenic viral vectors. This lack of safe and effective non-viral delivery systems is still a big hurdle for the clinical translation of such enzymes. This review discusses the challenges of non-viral delivery strategies of widely used genome editing enzymes, including Cre recombinase, ZFNs and TALENs, CRISPR/Cas9, and Cas12a (Cpf1) in their protein format and highlights recent innovations of non-viral delivery strategies which have the potential to overcome current delivery limitations and advance the clinical translation of genome editing.

A frog-derived bionic peptide with discriminative inhibition of tumors based on integrin αvβ3 identification

Aureins, natural active peptides extracted from skin secretions of Australian bell frogs, have become a research focus due to the antitumor effects caused by lysing cell membranes. However, clinical translation of Aureins is still limited by non-selective toxicity between normal and cancer cells. Herein, by structure-activity relationship analysis and rational linker design, a dual-function fusion peptide RA3 is designed by tactically fusing Aurein peptide A1 with strong anticancer activity, with a tri-peptide with integrin αvβ3-binding ability which was screened in our previous work. Rational design and selection of fusion linkers ensures α-helical conformation and active functions of this novel fusion peptide, inducing effective membrane rupture and selective apoptosis of cancer cells. The integrin binding and tumor recognition ability of the fusion peptide is further validated by fluorescence imaging in cell and mouse models, in comparison with the non-selective A1 peptide. Meanwhile, increased stability and superior therapeutic efficacy are achieved in vivo for the RA3 fusion peptide. Our study highlights that aided by computational simulation technologies, the biomimetic fusion RA3 peptide has been successfully designed, surmounting the poor tumor-selectivity of the natural defensive peptide, serving as a promising therapeutic agent for cancer treatment.

Optimizing Charge Switching in Membrane Lytic Peptides for Endosomal Release of Biomacromolecules

Endocytic pathways are practical routes for the intracellular delivery of biomacromolecules. Along with this, effective strategies for endosomal cargo release into the cytosol are desired to achieve successful delivery. Focusing on compositional differences between the cell and endosomal membranes and the pH decrease within endosomes, we designed the lipid-sensitive and pH-responsive endosome-lytic peptide HAad. This peptide contains aminoadipic acid (Aad) residues, which serve as a safety catch for preferential permeabilization of endosomal membranes over cell membranes, and His-to-Ala substitutions enhance the endosomolytic activity. The ability of HAad to destabilize endosomal membranes was supported by model studies using large unilamellar vesicles (LUVs) and by increased intracellular delivery of biomacromolecules (including antibodies) into live cells. Cerebral ventricle injection of Cre recombinase with HAad led to Cre/loxP recombination in a mouse model, thus demonstrating potential applicability of HAad in vivo.

Cancer Cell-Targeted Photosensitizer and Therapeutic Protein Co-Delivery Nanoplatform Based on a Metal-Organic Framework for Enhanced Synergistic Photodynamic and Protein Therapy

Efficient and cancer cell-targeted delivery of photosensitizer (PS) and therapeutic protein has great potentiality for improving the anticancer effects. Herein, zeolitic imidazolate framework-8 (ZIF-8) nanoparticles, one of the most attractive metal-organic framework materials, were used for coencapsulating the chlorin e6 (Ce6, a potent PS) and cytochrome c (Cyt c, a protein apoptosis inducer); then the nanoparticle was subsequently decorated with the hyaluronic acid (HA) shell to form cancer cell-active targeted nanoplatform (Ce6/Cyt c@ZIF-8/HA). The in vitro and in vivo experiments show the cancer cell targeting capability and pH-responsive decomposition and the release behavior of Ce6/Cyt c@ZIF-8/HA. Upon light irradiation, the released Ce6 produced cytotoxic reactive oxygen species for photodynamic therapy. Meanwhile, the released Cyt c-induced programmed cell death for protein therapy. Furthermore, the Cyt c worked normally under hypoxia conditions and could decompose H2O2 to O2 (with peroxidase-/catalase-like activity), resulting in synergistically improved therapeutic efficiency. These small molecules and protein codelivery nanoplatforms would promote the development of complementary and synergetic modes for biomedical applications.

Direct Functional Protein Delivery with a Peptide into Neonatal and Adult Mammalian Inner Ear In Vivo

The aim of this study was to study an antimicrobial peptide (AMP), aurein 1.2, which substantially increased protein delivery directly into multiple mammalian inner-ear cell types in vivo. Different concentrations of aurein 1.2 with superpositively charged GFP (+36 GFP) protein fused with Cre recombinase were delivered to postnatal day 1-2 (P1-2) and adult cochleae of Cre reporter transgenic mice with various delivery methods. By cochleostomy at different concentrations of aurein 1.2-+36 GFP (1 μM, 5 μM, 22.5 μM, and 50 μM, respectively), the tdTomato (tdT) expression was observed in outer hair cells (OHCs; 20.77%, 23.02%, 76.36%, and 92.47%, respectively) and inner hair cells (IHCs; 14.90%, 44.50%, 89.59%, and 96.13%, respectively) in the cochlea. The optimal concentration was 22.5 μM with the highest transfection efficiency and the lowest cytotoxicity. Wide-spread tdT signals were detected in the cochlear-supporting cells, utricular-supporting cells, auditory nerve, and spiral ligament in neonatal and adult mice. Compared to cochleostomy, injection through the round window membrane (RWM) also produced highly efficient tdT+ labeled cells with less cell loss. In summary, the peptide aurein 1.2 fused with +36 GFP dramatically expanded the target cells with increased efficiency in direct protein delivery in the inner ear. Aurein 1.2-+36 GFP has the potential to be developed as protein-based therapy in regeneration and genome editing in the mammalian inner ear.

Quantification of protein delivery in live cells using fluorescence correlation spectroscopy

Fluorescence correlation spectroscopy (FCS) is a quantitative single-molecule method that measures the concentration and rate of diffusion of fluorophore-tagged molecules, both large and small, in vitro and within live cells, and even within discrete cellular compartments. FCS is exceptionally well-suited to directly quantify the efficiency of intracellular protein delivery-specifically, how well different "cell-penetrating" proteins and peptides guide proteinaceous materials into the cytosol and nuclei of live mammalian cells. This article provides an overview of the procedures necessary to execute robust FCS experiments and evaluate endosomal escape efficiencies: preparation of fluorophore-tagged proteins, incubation with mammalian cells and preparation of FCS samples, setup and execution of an FCS experiment, and a detailed discussion of and custom MATLAB® script for analyzing the resulting autocorrelation curves in the context of appropriate diffusion models.

A suitable and effective stepwise oxidative refolding procedure for highly-cationic tetrameric avidin in nucleic acid free conditions

Optimized conditions are needed to refold recombinant proteins from bacterial inclusion bodies into their biologically active conformations. In this study, we found two crucial requirements for efficient refolding of cationic tetrameric chicken avidin. The first step is to eliminate nucleic acid contaminants from the bacterial inclusion body. The electrostatic interactions between the remaining nucleic acids and proteins strongly enhanced protein aggregation during the refolding process. The cysteine specific reversible S-cationization procedure was successfully employed for large-scale preparation of nucleic acid free denatured protein without purification tag system. The second step is the intramolecular disulfide formation prior to refolding in dialysis removing denaturant. Disulfide intact monomeric avidin showed efficient formation of biologically active tetrameric conformation during the refolding process. Using this optimized refolding procedure, highly cationic avidin derivative designed as an intracellular delivery carrier of biotinylated protein was successfully prepared.