Cytosolic Protein Delivery for Intracellular Antigen Targeting Using Supercharged Polypeptide Delivery Platform

Rational design of diblock copolymer enables efficient cytosolic protein delivery

Polymer-mediated cytosolic protein delivery demonstrates a promising strategy for the development of protein therapeutics. Here, we propose a new designed diblock copolymer which realizes efficient cytosolic protein delivery both in vitro and in vivo. The polymer contains one protein-binding block composed of phenylboronic acid (PBA) and N-(3-dimethylaminopropyl) (DMAP) pendant units for protein binding and endosomal escape, respectively, followed by the response to ATP enriched in the cytosol which triggers the protein release. The other block is PEG designed to improve particle size control and circulation in vivo. By optimizing the block composition, sequence and length of the copolymer, the optimal one (BP20) was identified with the binding block containing 20 units of both PBA and DMAP, randomly distributed along the chain. When mixed with proteins, the BP20 forms stable nanoparticles and mediates efficient cytosolic delivery of a wide range of proteins including enzymes, toxic proteins and CRISPR/Cas9 ribonucleoproteins (RNP), to various cell lines. The PEG block, especially when further modified with folic acid (FA), enables tumor-targeted delivery of Saporin in vivo, which significantly suppresses the tumor growth. Our results shall inspire the design of novel polymeric vehicles with robust capability for cytosolic protein delivery, which holds great potential for both biological research and therapeutic applications.

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.

Reversible Assembly of Proteins and Phenolic Polymers for Intracellular Protein Delivery with Serum Stability

The design of intracellular delivery systems for protein drugs remains a challenge due to limited delivery efficacy and serum stability. Herein, we propose a reversible assembly strategy to assemble cargo proteins and phenolic polymers into stable nanoparticles for this purpose using a heterobifunctional adaptor (2-formylbenzeneboronic acid). The adaptor is easily decorated on cargo proteins via iminoboronate chemistry and further conjugates with catechol-bearing polymers to form nanoparticles via boronate diester linkages. The nanoparticles exhibit excellent serum stability in culture media but rapidly release the cargo proteins triggered by lysosomal acidity and GSH after endocytosis. In a proof-of-concept animal model, the strategy successfully transports superoxide dismutase to retina via intravitreal injection and efficiently ameliorates the oxidative stress and cellular damage in the retina induced by ischemia-reperfusion (I/R) with minimal adverse effects. The reversible assembly strategy represents a robust and efficient method to develop serum-stable systems for the intracellular delivery of biomacromolecules.

Genetically light-enhanced immunotherapy mediated by a fluorinated reduction-sensitive delivery system

The lack of safe and efficient therapeutic agent delivery platforms restricts combined therapy's effect, and combined cancer therapy's multi-component delivery effect needs improvement. The novel gene delivery system SS-HPT-F/pMIP-3β-KR was proposed to construct fluorine-containing degradable cationic polymers SS-HPT-F by a mild and simple amino-epoxy ring-opening reaction. By modifying the fluorinated alkyl chain, the delivery efficiency of the plasmid was greatly improved, and the cytoplasmic transport of biomolecules was completed. At the same time, a combination plasmid (MIP-3β-KillerRed) was innovatively designed for the independent expression of immune and photodynamic proteins. Which was efficiently transported to the tumor site by SS-HPT-F. The MIP-3β is expressed as an immune chemokine realize the immune mobilization behavior. The photosensitive protein KillerRed expressed in the tumor killed cancer cells under irradiation and released the exocrine immune factor MIP-3β. The immunogenic cell death (ICD) produced by photodynamic therapy (PDT) also induced the immune response of the organism. The synergistic effect of PDT and MIP-3β mobilized the immune properties of the organism, providing light-enhanced immune combination therapy against malignant tumors. Therefore, in subcutaneous tumor-bearing and metastatic animal models, the carrier tumor growth and mobilize organism produce an immune response without systemic toxicity. This work reports the first efficient gene delivery system that achieves light-enhanced immunotherapy.

Intracellular Protein Delivery: Approaches, Challenges, and Clinical Applications

Protein biologics are powerful therapeutic agents with diverse inhibitory and enzymatic functions. However, their clinical use has been limited to extracellular applications due to their inability to cross plasma membranes. Overcoming this physiological barrier would unlock the potential of protein drugs for the treatment of many intractable diseases. In this review, we highlight progress made toward achieving cytosolic delivery of recombinant proteins. We start by first considering intracellular protein delivery as a drug modality compared to existing Food and Drug Administration-approved drug modalities. Then, we summarize strategies that have been reported to achieve protein internalization. These techniques can be broadly classified into 3 categories: physical methods, direct protein engineering, and nanocarrier-mediated delivery. Finally, we highlight existing challenges for cytosolic protein delivery and offer an outlook for future advances.

Protein-based delivery systems for RNA delivery

RNA-based therapeutics have emerged as promising approaches to modulate gene expression and generate therapeutic proteins or antigens capable of inducing immune responses to treat a variety of diseases, such as infectious diseases, cancers, immunologic disorders, and genetic disorders. However, the efficient delivery of RNA molecules into cells poses significant challenges due to their large molecular weight, negative charge, and susceptibility to degradation by RNase enzymes. To overcome these obstacles, viral and non-viral vectors have been developed, including lipid nanoparticles, viral vectors, proteins, dendritic macromolecules, among others. Among these carriers, protein-based delivery systems have garnered considerable attention due to their potential to address specific issues associated with nanoparticle-based systems, such as liver accumulation and immunogenicity. This review provides an overview of currently marketed RNA drugs, underscores the significance of RNA delivery vector development, delineates the essential characteristics of an ideal RNA delivery vector, and introduces existing protein carriers for RNA delivery. By offering valuable insights, this review aims to serve as a reference for the future development of protein-based delivery vectors for RNA therapeutics.

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.

A Smart DNA-Based Nanosystem Containing Ribosome-Regulating siRNA for Enhanced mRNA Transfection

Messenger RNA (mRNA) transfection is the prerequisite for the application of mRNA-based therapeutics. In hard-to-transfect cells, such as macrophages, the effective transfection of mRNA remains a long-standing challenge. Herein, a smart DNA-based nanosystem is reported containing ribosome biogenesis-promoting siRNA, realizing efficient mRNA transfection in macrophages. Four monomers are copolymerized to form a nanoframework (NF), including N-isopropylacrylamide (NIPAM) as the skeleton and acrydite-DNA as the initiator to trigger the cascade assembly of DNA hairpins (H1-polyT and H2-siRNA). By virtue of the phase transition characteristic of polymeric NIPAM, below the lower critical solution temperature (LCST, ≈34 °C), the NF swells to expose polyT sequences to hybridize with the polyA tail of mRNA. Above the LCST, the NF deswells to encapsulate mRNA. The disulfide bond in the NF responds to glutathione, triggering the disassembly of the nanosystem; the siRNA and mRNA are released in response to triphosadenine and RNase H. The siRNA down-regulates the expression of heat shock protein 27, which up-regulates the expression of phosphorylated ribosomal protein S6. The nanosystem shows satisfactory mRNA transfection and translation efficiency in a mouse model. It is envisioned that the DNA-based nanosystem will provide a promising carrier to deliver mRNA in hard-to-transfect cells and promote the development of mRNA-based therapeutics.

Direct Cytosolic Delivery of Proteins and CRISPR-Cas9 Genome Editing by Gemini Amphiphiles via Non-Endocytic Translocation Pathways

Intracellular delivery of therapeutic biomacromolecules is often challenged by the poor transmembrane and limited endosomal escape. Here, we establish a combinatorial library composed of 150 molecular weight-defined gemini amphiphiles (GAs) to identify the vehicles that facilitate robust cytosolic delivery of proteins in vitro and in vivo. These GAs display similar skeletal structures but differential amphiphilicity by adjusting the length of alkyl tails, type of ionizable cationic heads, and hydrophobicity or hydrophilicity of a spacer. The top candidate is highly efficient in translocating a broad spectrum of proteins with various molecular weights and isoelectric points into the cytosol. Particularly, we notice that the entry mechanism is predominantly mediated via the lipid raft-dependent membrane fusion, bypassing the classical endocytic pathway that limits the cytosolic delivery efficiency of many presently available carriers. Remarkably, the top GA candidate is capable of delivering hard-to-deliver Cas9 ribonucleoprotein in vivo, disrupting KRAS mutation in the tumor-bearing mice to inhibit tumor growth and extend their survival. Our study reveals a GA-based small-molecule carrier platform for the direct cytosolic delivery of various types of proteins for therapeutic purposes.

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.

Unstructured Polypeptides as a Versatile Drug Delivery Technology

Although polyethylene glycol (PEG), or "PEGylation" has become a widely applied approach for improving the efficiency of drug delivery, the immunogenicity and non-biodegradability of this synthetic polymer have prompted an evident need for alternatives. To overcome these caveats and to mimic PEG -or other natural or synthetic polymers- for the purpose of drug half-life extension, unstructured polypeptides are designed. Due to their tunable length, biodegradability, low immunogenicity and easy production, unstructured polypeptides have the potential to replace PEG as the preferred technology for therapeutic protein/peptide delivery. This review provides an overview of the evolution of unstructured polypeptides, starting from natural polypeptides to engineered polypeptides and discusses their characteristics. Then, it is described that unstructured polypeptides have been successfully applied to numerous drugs, including peptides, proteins, antibody fragments, and nanocarriers, for half-life extension. Innovative applications of unstructured peptides as releasable masks, multimolecular adaptors and intracellular delivery carriers are also discussed. Finally, challenges and future perspectives of this promising field are briefly presented. STATEMENT OF SIGNIFICANCE: : Polypeptide fusion technology simulating PEGylation has become an important topic for the development of long-circulating peptide or protein drugs without reduced activity, complex processes, and kidney injury caused by PEG modification. Here we provide a detailed and in-depth review of the recent advances in unstructured polypeptides. In addition to the application of enhanced pharmacokinetic performance, emphasis is placed on polypeptides as scaffolders for the delivery of multiple drugs, and on the preparation of reasonably designed polypeptides to manipulate the performance of proteins and peptides. This review will provide insight into future application of polypeptides in peptide or protein drug development and the design of novel functional polypeptides.

Protein Delivery to Insect Epithelial Cells In Vivo: Potential Application to Functional Molecular Analysis of Proteins in Butterfly Wing Development

Protein delivery to cells in vivo has great potential for the functional analysis of proteins in nonmodel organisms. In this study, using the butterfly wing system, we investigated a method of protein delivery to insect epithelial cells that allows for easy access, treatment, and observation in real time in vivo. Topical and systemic applications (called the sandwich and injection methods, respectively) were tested. In both methods, green/orange fluorescent proteins (GFP/OFP) were naturally incorporated into intracellular vesicles and occasionally into the cytosol from the apical surface without any delivery reagent. However, the antibodies were not delivered by the sandwich method at all, and were delivered only into vesicles by the injection method. A membrane-lytic peptide, L17E, appeared to slightly improve the delivery of GFP/OFP and antibodies. A novel peptide reagent, ProteoCarry, successfully promoted the delivery of both GFP/OFP and antibodies into the cytosol via both the sandwich and injection methods. These protein delivery results will provide opportunities for the functional molecular analysis of proteins in butterfly wing development, and may offer a new way to deliver proteins into target cells in vivo in nonmodel organisms.

Phenylboronic Acid-Functionalized Polyplexes Tailored to Oral CRISPR Delivery

Effective delivery of the CRISPR-Cas9 components is crucial to realizing the therapeutic potential. Although many delivery approaches have been developed for this application, oral delivery has not been explored due to the degradative nature of the gastrointestinal tract. For this issue, we developed a series of novel phenylboronic acid (PBA)-functionalized chitosan-polyethylenimine (CS-PEI) polymers for oral CRISPR delivery. PBA functionalization equipped the polyplex with higher stability, smooth transport across the mucus, and efficient endosomal escape and cytosolic unpackaging in the cells. From a library of 12 PBA-functionalized CS-PEI polyplexes, we identified a formulation that showed the most effective penetration in the intestinal mucosa after oral gavage to mice. The optimized formulation performed feasible CRISPR-mediated downregulation of the target protein and reduction in the downstream cholesterol. As the first oral CRISPR carrier, this study suggests the potential of addressing the needs of both local and systemic editing in a patient-compliant manner.

Biologics-based degraders - an expanding toolkit for targeted-protein degradation

Targeted protein degradation (TPD) is a broadly useful proteome editing tool for biological research and therapeutic development. TPD offers several advantages over functional inhibition alone, including the ability to target previously undruggable proteins and the substantial and sustained knockout of protein activity. A variety of small molecule approaches hijack endogenous protein degradation machinery, but are limited to proteins with a cytosolic domain and suitable binding pocket. Recently, biologics-based methods have expanded the TPD toolbox by allowing access to extracellular and surface-exposed proteins and increasing target specificity. Here, we summarize recent advances in the use of biologics to deplete proteins through either the ubiquitin-proteasome system or the lysosomal degradation pathway, and discuss routes to their effective delivery as potential therapeutic interventions.

Dibenzocyclooctyne linked lysine-cyclodextrin for efficient intranucleus delivery of proteins

Intranuclear protein delivery shows great prospects in broadening the application scope of protein therapy and revolutionizing medicine, however, effective delivery of native proteins into the nucleus of cells remains a great challenge. Herein, we report the supramolecular nanoparticles based on the self-assembly of dibenzocyclooctyne (DIBO) linked lysine-cyclodextrin (DLC) for efficient intranucleus delivery of proteins. Coordination-driven self-assembly of DLCs in aqueous solution enables efficient encapsulation of proteins just by simple mixing, so as to maintain their biological activity in a reliable way. DLC nanoparticles ensure effective intranuclear protein delivery for therapeutic applications and gene regulation. This rationally designed DIBO containing amino acid-cyclodextrin derivative allows the development of a convenient and universal nanoplatform for intranuclear delivery of native proteins.

Robust Reversible Cross-Linking Strategy for Intracellular Protein Delivery with Excellent Serum Tolerance

Intracellular protein delivery has attracted increasing attentions in biomedical applications. However, current delivery systems usually have poor serum stability due to the competitive binding of serum proteins to the polymers during delivery. Here, we report a reversible cross-linking strategy to improve the serum stability of polymers for robust intracellular protein delivery. In the proposed delivery system, nanoparticles are assembled by cargo proteins and cationic polymers and further stabilized by a glutathione-cleavable and traceless cross-linker. The cross-linked nanoparticles show high stability and efficient cell internalization in serum containing medium and can release the cargo proteins in response to intracellular glutathione and acidic pH in a traceless manner. The generality and versatility of the proposed strategy were demonstrated on different types of cationic polymers, cargo proteins, as well as cell lines. The study provides a facile and efficient method for improving the serum tolerance of cationic polymers in intracellular protein delivery.

Endocytosis-Independent and Cancer-Selective Cytosolic Protein Delivery via Reversible Tagging with LAT1 substrate

Protein drugs targeting intracellular machineries have shown profound therapeutic potentials, but their clinical utilities are greatly hampered by the lack of efficient cytosolic delivery techniques. Existing strategies mainly rely on nanocarriers or conjugated cell-penetrating peptides (CPPs), which often have drawbacks such as materials complexity/toxicity, lack of cell specificity, and endolysosomal entrapment. Herein, a unique carrier-free approach is reported for mediating cancer-selective and endocytosis-free cytosolic protein delivery. Proteins are sequentially modified with 4-nitrophenyl 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) benzyl carbonate as the H₂ O₂ -responsive domain and 3,4-dihydroxy-l-phenylalanine as the substrate of l-type amino acid transporter 1 (LAT1). Thus, the pro-protein can be directly transported into tumor cells by overexpressed LAT1 on cell membranes, bypassing endocytosis and endolysosomal entrapment. In the cytosol, overproduced H₂ O₂ restores the protein structure and activity. Using this technique, versatile proteins are delivered into tumor cells with robust efficiency, including toxins, enzymes, CRISPR-Cas9 ribonucleoprotein, and antibodies. Furthermore, intravenously injected pro-protein of saporin shows potent anticancer efficacy in 4T1-tumor-bearing mice, without provoking systemic toxicity. Such a facile and versatile pro-protein platform may benefit the development of protein pharmaceuticals.

Evaluation of crotamine based probes as intracellular targeted contrast agents for magnetic resonance imaging

Crotamine is a lysine and cysteine rich 42 amino acids long bio-active polypeptide, isolated from the venom of a South American rattlesnake, that can also be used as cell penetrating peptide. A facile synthetic scheme for coupling cargo molecules like fluorophores (carboxyfluorescein) or MRI probes (Gd-DO3A-based macrocycle) is presented. The toxicity, cellular internalization and steady-state accumulation after long-term incubation for 18 h, as well as magnetic resonance relaxivities and cellular relaxation rates of crotamine based probes were evaluated and compared to its shorter synthetic fragment CyLoP-1. The longitudinal relaxivity (r₁) of the conjugates of CyLoP-1 and crotamine is significantly lower in medium than in water indicating to the lower contrast enhancement efficacy of DO3A-based probes in biological samples. Carboxyfluorescein labeled crotamine did not exhibit toxicity up to a concentration of 2.5 µM. CyLoP-1 accumulated about four times better within the cells compared to crotamine. Fluorescence microscopy suggests different predominant uptake mechanisms for crotamine and CyLoP-1 in 3T3 cells. While crotamine is predominantly localized in vesicular structures (most likely endosomes and lysosomes) within the cell, CyLoP-1 is mainly homogeneously distributed in the cytosol. The cellular relaxation rate (R_{1, cell}) of the crotamine based probe was not significantly increased whereas the corresponding CyLoP-1-derivative showed a slightly elevated R_{1, cell}. This study indicates the potential of crotamine and in particular the shorter fragment CyLoP-1 to be useful for an efficient transmembrane delivery of agents directed to intracellular (cytosolic) targets. However, the applicability of the conjugates synthesized here as contrast agents in MR imaging is limited. Further improvement is needed to prepare more efficient probes for MRI applications, i.e., by replacing the DO3A- with a DOTA-based chelate.

Tailoring Hyperbranched Poly(β-amino ester) as a Robust and Universal Platform for Cytosolic Protein Delivery

Cytosolic protein delivery is a prerequisite for protein-based biotechnologies and therapeutics on intracellular targets. Polymers that can complex with proteins to form nano-assemblies represent one of the most important categories of materials, because of the ease of nano-fabrication, high protein loading efficiency, no need for purification, and maintenance of protein bioactivity. Stable protein encapsulation and efficient intracellular liberation are two critical yet opposite processes toward cytosolic delivery, and polymers that can resolve these two conflicting challenges are still lacking. Herein, hyperbranched poly(β-amino ester) (HPAE) with backbone-embedded phenylboronic acid (PBA) is developed to synchronize these two processes, wherein PBA enhanced protein encapsulation via nitrogen-boronate (N-B) coordination while triggered polymer degradation and protein release upon oxidation by H₂ O₂ in cancer cells. Upon optimization of the branching degree, charge density, and PBA distribution, the best-performing A2-B3-C2-S₂ -P₂ is identified, which mediates robust delivery of various native proteins/peptides with distinct molecular weights (1.6-430 kDa) and isoelectric points (4.1-10.3) into cancer cells, including enzymes, toxins, antibodies, and CRISPR-Cas9 ribonucleoproteins (RNPs). Moreover, A2-B3-C2-S₂ -P₂ mediates effective cytosolic delivery of saporin both in vitro and in vivo to provoke remarkable anti-tumor efficacy. Such a potent and universal platform holds transformative potentials for protein pharmaceuticals.