Intracellular delivery of immunoglobulin G at nanomolar concentrations with domain Z-fused multimeric α-helical cell penetrating peptides

Polysaccharide-Based Coacervate Microgel Bearing Cationic Peptides That Achieve Dynamic Cell-Membrane Structure Alteration and Facile Cytosolic Infusion of IgGs

Conjugates of the biocompatible polysaccharide pullulan with a cell membrane permeabilizing peptide L17E (PL-L17Es) were prepared with the aim of producing complex coacervates with pronounced intracellular antibody (IgG) delivery activity and stable structures. Coacervates with diameters of a few μm were formed simply by mixing PL-L17Es with IgG labeled with negatively charged fluorescent moieties of Alexa Fluor 488 [IgG(AF488)]. The coacervate resulted in a pronounced cytosolic infusion of IgG(AF488) and IgG binding to the target proteins inside the cell. The droplet structures were maintained even under high salt conditions, and the fluorescence in the droplet was not recovered after photobleaching, suggesting the formation of complex coacervate microgels. Dynamic changes in cell membrane structure to entrap the coacervate microgels were captured by confocal and electron microscopy, resulting in cytosolic IgG infusion. The use of M-lycotoxin instead of L17E resulted in a coacervate microgel with marked IgG delivery activity even in the presence of serum. Successful IgG delivery to primary hepatocytes, undifferentiated induced pluripotent stem (iPS) cells, and iPS cell-derived intestinal epithelial cells was also achieved. The construction of complex coacervate microgels with design flexibility and the validity of intracellular IgG delivery with high salt stability were thus demonstrated.

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.

Enhanced Delivery of Biomolecules into Caco2 Cells Based on the Cell-Penetrating Ability of Keratin Peptides

Keratin, as a promising bioresource, possesses significant potential for diverse biological applications due to its favorable biocompatibility, low toxicity, biodegradability, and cell adhesion ability. However, there are few studies on the cell-penetrating ability of keratin peptides (KEPs) for biomolecule delivery. Therefore, this study explored the cell-penetrating ability of KEPs with different molecular weights (Mw) on Caco2 cells using fluorescein-labeled insulin (FITC-INS) as the target intracellular biomolecule. The potential cell-penetrating mechanism was elaborated by combining cellular investigation with the physicochemical characterization of KEPs. The result shows that the KEPs <3 kDa (KEP1) exhibited the highest cell-penetrating ability at 2 mg/mL, allowing efficient delivery of FITC-INS into Caco2 cells without covalent bonding. The cellular uptake mechanism was energy-dependent, mainly involving macropinocytosis. The further fractionation of KEP1 reveals that the most effective components consisted of 8-19 amino acids, including specific hydrophobic peptides (e.g., RVVIEPSPVVV and IIIQPSPVVV), PPII amphipathic peptides (e.g., PPPVVVTFP and FIQPPPVVV), and Cys-rich peptides (e.g., LCAPTPCGPTPL and CLPCRPCGPTPL). Additionally, analysis of the secondary and tertiary structure and amino acid composition illustrated that KEP1 exhibited rich hydrophobic residues and disulfide bonds, which probably contributed to its cell-penetrating ability, as opposed to its small particle size and electrostatic interactions. This study reveals the cell-penetrating ability of KEPs, thus highlighting their potential as biomaterials for noncovalently delivering biomolecules.

Charge-guided masking of a membrane-destabilizing peptide enables efficient endosomal escape for targeted intracellular delivery of proteins

Intracellular delivery of biologicals such as peptides, proteins, and nucleic acids presents a great opportunity for innovative therapeutics. However, the endosome entrapment remains a major bottleneck in the intracellular delivery of biomacromolecules, largely limiting their therapeutic potential. Here, we converted a cell-penetrating peptide (CPP), low molecular weight protamine (LMWP), to endosomal escape peptides (EEPs) by masking LMWP with a pH-responsive counter-ionic peptide. The resulting masked CPPs (mLMWP and mLMWP2) effectively promoted the escape of peptide/protein cargoes from endosomes into the cytoplasm. Consequential lysosome repair and lysophagy were initiated upon the endolysosomal leakage. Minimal reactive oxygen species (ROS) elevation or cell death was observed. Based on mLMWP2, we constructed an intracellular protein delivery system containing an antibody as a targeting module, mLMWP2 as an endosomal escape module, and the desired protein cargo. With the HER2-targeting delivery system, we efficiently translocated cyclization recombination enzyme (Cre) and BH3-interacting domain death agonist (BID) into the cytosol of HER2+ cells to exert their biological activity. Thereby, the modular delivery system shows its potential as a promising tool for scientific studies and therapeutic applications.

Finding ways into the cytosol: Peptide-mediated approaches for delivering proteins into cells

The delivery of functional proteins, including antibodies, into cells opens up many opportunities to regulate cellular events, with significant implications for studies in chemical biology and therapeutics. The inside of cells is isolated from the outside by the cell membrane. The hydrophilic nature of proteins prevents direct permeation of proteins through the cell membrane by passive diffusion. Therefore, delivery routes using endocytic uptake followed by endosomal escape have been explored. Alternatively, delivery concepts using transient permeabilization of cell membranes or effective promotion of endocytic uptake and endosomal escape using modified membrane-lytic peptides have been reported in recent years. Non-canonical protein delivery concepts, such as the use of liquid droplets or coacervates, have also been proposed. This review highlights some of the topics in peptide-mediated intracellular protein delivery.

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

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

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.

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.

IgG Fc Affinity Ligands and Their Applications in Antibody-Involved Drug Delivery: A Brief Review

Antibodies are not only an important class of biotherapeutic drugs, but also are targeting moieties for achieving active targeting drug delivery. Meanwhile, the rapidly increasing application of antibodies and Fc-fusion proteins has inspired the emerging development of downstream processing technologies. Thus, IgG Fc affinity ligands have come into being and have been widely exploited in antibody purification strategies. Given the high binding affinity and specificity to IgGs, binding stability in physiological medium conditions, and favorable toxicity and immunogenicity profiles, Fc affinity ligands are gradually applied to antibody delivery, non-covalent antibody-drug conjugates or antibody-mediated active-targeted drug delivery systems. In this review, we will briefly introduce IgG affinity ligands that are widely used at present and summarize their diverse applications in the field of antibody-involved drug delivery. The challenges and outlook of these systems are also discussed.

The complex of miRNA2861 and cell-penetrating, dimeric α-helical peptide accelerates the osteogenesis of mesenchymal stem cells

BACKGROUND

The restoration of the functional ability of mesenchymal stem cells (MSCs) using epigenetic modification is very promising for patients with weak osteogenesis ability. This study focused on the acceleration of osteogenesis from MSCs using microRNA (miRNA)2861 and a cell-penetrating peptide (CPP), LK.

METHODS

We performed MSCs penetration test of complex between the LK peptides and miRNA 2861. Three different experiments were performed to investigate the effects of miRNA 2861 on osteogenic differentiation in MSCs: 1) intensity of alizarin red staining, which reflects the status of mineralization by osteoblasts; 2) gene expression related to osteoblast differentiation; and 3) confirmation of corresponding protein translation for comparison with RNA expression levels.

RESULTS

We found that cLK effectively delivered miRNA 2861 into the cytoplasm of human MSCs and accelerated osteogenic differentiation from MSCs, as well as mineralization.

CONCLUSION

The complex of miRNA 2861 with LK may have a positive effect on the osteogenic differentiation from MSCs and mineralization. Therapies using miRNAs combined with LK may be good candidates for the augmentation of osteogenesis in patients.

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.

Studies of cell-penetrating peptides by biophysical methods

Biophysical studies have a very high impact on the understanding of internalization, molecular mechanisms, interactions, and localization of CPPs and CPP/cargo conjugates in live cells or in vivo. Biophysical studies are often first carried out in test-tube set-ups or in vitro, leading to the complicated in vivo systems. This review describes recent studies of CPP internalization, mechanisms, and localization. The multiple methods in these studies reveal different novel and important aspects and define the rules for CPP mechanisms, hopefully leading to their improved applicability to novel and safe therapies.

A dimeric α-helical cell penetrating peptide mounted with an HER2-selective affibody

We have developed a cell penetrating peptide (CPP) system with high selectivity and penetrability at nanomolar concentrations with a combination of an HER2-selective affibody, Z_HER2:342 (Z_HER2), and a dimeric α-helical leucine- and lysine-rich peptide, LK-2. Z_HER2 and LK-2 are linearly fused together and expressed in a prokaryotic system to create the LK-2-Z_HER2 protein, which can successfully distinguish and penetrate HER2-overexpressing cancer cells at nanomolar concentrations. LK-2-Z_HER2 has the ability to intracellularly deliver doxorubicin as a conjugate form to enhance its anti-cancer effect on HER2-overexpressing breast cancer cells with a great selectivity. The selective penetrability was confirmed in vitro, in 3D spheroids, and in in vivo models. LK-2-Z_HER2 has the capability to overcome the weak points of current CPPs, such as poor penetrability at low concentrations and a lack of selectivity, by combining powerful CPP and affibody sequences.