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

An approach for the intracellular delivery of IgG via enzymatic ligation with a cell-permeable attenuated cationic amphiphilic lytic peptide

Achieving effective intracellular delivery of therapeutic molecules such as antibodies (IgG) is a challenge in biomedical research and pharmaceutical development. Conjugation of IgG with a cell-penetrating peptide is a rational approach. Here, not only the efficacy of the conjugates in internalizing into cells, but also the physicochemical property of the conjugates allowing their solubilized states in solution without forming aggregates are critical. In this study, we have shown that the first requirement can be addressed using a cell-permeable attenuated cationic amphiphilic lytic (CP-ACAL) peptide, L17ER4. The second requirement can be addressed by ligation of IgG to L17ER4 using sortase A, where the use of a linker of appropriate chain length is also important. For evaluation, the intracellular delivery efficacy was studied using conjugate structures with different orientations and conjugation modes of L17ER4 in ligation to a model protein, green fluorescent protein fused to a nuclear localization signal (NLS-EGFP). The effect of tetraarginine positioning in the L17ER4 sequence was also investigated. Following these studies, an optimized peptide sequence containing L17ER4 was ligated to an anti-green fluorescent protein (GFP) IgG bearing a sortase A recognition sequence. Treatment of the cells with the conjugate of anti-GFP IgG and L17ER4 resulted in a high efficiency of cytosolic translocation of the conjugate and the binding to the target protein in the cell without significant aggregate formation. The feasibility of the d-form of L17ER4 as a CP-ACAL was also confirmed.

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.

Weakly acidic pH-responsive liposomal content release induced by histidine-modified agents

Internal stimuli-responsive controlled release from liposomal vesicles is an innovative approach for site-specific delivery of therapeutic drugs. In this study, to enhance the endosomal pH control of drug release from liposomes, a series of histidine-modified pH-sensitive Cn-His (n = 8, 12, 18) agents were designed and utilized as triggers for liposomal content release. The pH-dependent properties of Cn-His-incorporated liposomes were characterized using dynamic light scattering, ζ-potential, and fluorescence spectroscopy. The liposomes maintained a relatively uniform size across all pH conditions. However, the ζ-potential exhibited positive values at endosomal acidic pH levels and neutral or negative values at physiological pH levels. Furthermore, acidic pH-dependent release of both polar content (carboxyfluorescein) and nonpolar content (Nile red) was observed from the Cn-His-incorporated liposomes. Notably, with C12-His as the pH sensitizer, the pH dependence of liposomal content release was significantly evident. This work establishes endosomal pH-controllable liposome platforms, laying the groundwork for developing clinically applicable triggered release formulations.

Liquid Droplet-Mediated Formulation of Lipid Nanoparticles Encapsulating Immunoglobulin G for Cytosolic Delivery

Antibodies are promising biopharmaceuticals that offer new therapeutic options for diseases. Since antibodies are membrane impermeable, approaches that allow immunoglobulin Gs (IgGs) to access intracellular therapeutic targets would open new horizons in antibody therapies. Lipid nanoparticles (LNPs) are among the classes of vectors that deliver biopharmaceuticals into cells. Using liquid droplets formed by IgG and polyglutamate, we report here a unique approach to forming LNPs containing IgG via liquid droplets formed in the presence of polyglutamic acid (polyE). The addition of polyE promoted the formation of smaller LNPs with cationic lipids than in its absence, and the formed LNPs were much more efficient in cytosolic IgG delivery and targeting of cellular proteins. This approach also allows for the encapsulation of intact IgG without the need for chemical or sequence modification. The intracellularly delivered IgG retained its target binding ability, as demonstrated by labeling of nuclear pore complex and HRas-GFP and inhibition of antiapoptotic cell death by phosphorylated Akt protein in live cells.

E3MPH16: An efficient endosomolytic peptide for intracellular protein delivery

To facilitate the introduction of proteins, such as antibodies, into cells, a variety of delivery peptides have been engineered. These peptides are typically highly cationic and somewhat hydrophobic, enabling cytosolic protein delivery at the cost of causing cell damage by rupturing membranes. This balance between delivery effectiveness and cytotoxicity presents obstacles for their real-world use. To tackle this problem, we designed a new endosome-disruptive cytosolic delivery peptide, E3MPH16, inspired by mastoparan X (MP). E3MPH16 was engineered to incorporate three Glu (E3) and 16 His (H16) residues at the N- and C-termini of MP, respectively. The negative charges of E3 substantially mitigate the cell-surface damage induced by MP. The H16 segment is known to enhance cell-surface adsorption and endocytic uptake of the associated molecules. With these modifications, E3MPH16 was successfully trapped within endosomes. The acidification of endosomes is expected to protonate the side chains of E3 and H16, enabling E3MPH16 to rupture endosomal membranes. As a result, nearly 100% of cells achieved cytosolic delivery of a model biomacromolecule, Alexa Fluor 488-labeled dextran (10 kDa), via endosomal escape by co-incubation with E3MPH16. The delivery process also suggested the involvement of macropinocytosis and caveolae-mediated endocytosis. With the assistance of E3MPH16, Cre recombinase and anti-Ras-IgG delivered into HEK293 cells and HT1080 cells enabled gene recombination and inhibited cell proliferation, respectively. The potential for in vivo application of this intracellular delivery method was further validated by topically injecting the green fluorescent protein fused with a nuclear localization signal (NLS-GFP) along with E3MPH16 into Colon-26 tumor xenografts in mice.

Cell-Penetrating Peptides: A Powerful Tool for Targeted Drug Delivery

The cellular membrane hinders the effective delivery of therapeutics to targeted sites. Cellpenetrating peptide (CPP) is one of the best options for rapidly internalizing across the cellular membrane. CPPs have recently attracted lots of attention because of their excellent transduction efficiency and low cytotoxicity. The CPP-cargo complex is an effective and efficient method of delivering several chemotherapeutic agents used to treat various diseases. Additionally, CPP has become another strategy to overcome some of the current therapeutic agents' limitations. However, no CPP complex is approved by the US FDA because of its limitations and issues. In this review, we mainly discuss the cellpenetrating peptide as the delivery vehicle, the cellular uptake mechanism of CPPs, their design, and some strategies to synthesize the CPP complex via some linkers such as disulfide bond, oxime, etc. Here, we also discuss the recent status of CPPs in the market.

Photo-Responsive Phase-Separating Fluorescent Molecules for Intracellular Protein Delivery

Cellular membranes, including the plasma and endosome membranes, are barriers to outside proteins. Various vehicles have been devised to deliver proteins across the plasma membrane, but in many cases, the payload gets trapped in the endosome. Here we designed a photo-responsive phase-separating fluorescent molecule (PPFM) with a molecular weight of 666.8 daltons. The PPFM compound condensates as fluorescent droplets in the aqueous solution by liquid-liquid phase separation (LLPS), which disintegrate upon photoirradiation with a 405 nm light-emitting diode (LED) lamp within 20 min or a 405 nm laser within 3 min. The PPFM coacervates recruit a wide range of peptides and proteins and deliver them into mammalian cells. Photolysis disperses the payload from condensates into the cytosolic space. Altogether, a type of small molecules that are photo-responsive and phase separating are discovered; their coacervates can serve as transmembrane vehicles for intracellular delivery of proteins, whereas photo illumination triggers the cytosolic distribution of the payload.

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 Wnt-β-Catenin Signaling Pathway for Hepatocellular Carcinoma Nanomedicine

Hepatocellular carcinoma (HCC) represents a high-fatality cancer with a 5-year survival of 22%. The Wnt/β-catenin signaling pathway presents as one of the most upregulated pathways in HCC. However, it has so far not been targetable in the clinical setting. Therefore, studying new targets of this signaling cascade from a therapeutic aspect could enable reversal, delay, or prevention of hepatocarcinogenesis. Although enormous advancement has been achieved in HCC research and its therapeutic management, since HCC often occurs in the context of other liver diseases such as cirrhosis leading to liver dysfunction and/or impaired drug metabolism, the current therapies face the challenge of safely and effectively delivering drugs to the HCC tumor site. In this review, we discuss how a targeted nano drug delivery system could help minimize the off-target toxicities of conventional HCC therapies as well as enhance treatment efficacy. We also put forward the current challenges in HCC nanomedicine along with some potential therapeutic targets from the Wnt/β-catenin signaling pathway that could be used for HCC therapy. Overall, this review will provide an insight to the current advances, limitations and how HCC nanomedicine could change the landscape of some of the undruggable targets in the Wnt/β-catenin pathway.

Biodegradable silica nanocapsules enable efficient nuclear-targeted delivery of native proteins for cancer therapy

Cell nucleus is the desired subcellular organelle of many therapeutic drugs. Although numerous nanomaterial-based methods have been developed which could facilitate nuclear-targeted delivery of small-molecule drugs, few are known to be capable of delivering exogenous native proteins. Herein, we report a convenient and highly robust approach for effective nuclear-targeted delivery of native proteins/antibodies by using biodegradable silica nanocapsules (BSNPs) that were surface-modified with different nuclear localization signals (NLS) peptides. We found that, upon gaining entry to mammalian cells via endocytosis, such nanocapsules (protein@BSNP-NLS) could effectively escape from endolysosomal vesicles with the assistance of an endosomolytic peptide (i.e., L17E), accumulate in cell nuclei and release the encapsulated protein cargo with biological activities. Cloaked with HeLa cell membrane, DNase@BSNP-NLS/L17E-M (with L17E encapsulated) homologously delivered functional proteins to cancer cell nuclei in tumor-xenografted mice. In vitro and in vivo anti-tumor properties, such as long blood circulation time and effective tumor growth inhibition, indicate that the nuclear-targeted cell-membrane-cloaked BSNPs (DNase@BSNP-NLS/L17E-M) platform is a promising therapeutic approach to nuclear related diseases.

Recent Advances in Imaging Agents Anchored with pH (Low) Insertion Peptides for Cancer Theranostics

The acidic extracellular microenvironment has become an effective target for diagnosing and treating tumors. A pH (low) insertion peptide (pHLIP) is a kind of peptide that can spontaneously fold into a transmembrane helix in an acidic microenvironment, and then insert into and cross the cell membrane for material transfer. The characteristics of the acidic tumor microenvironment provide a new method for pH-targeted molecular imaging and tumor-targeted therapy. As research has increased, the role of pHLIP as an imaging agent carrier in the field of tumor theranostics has become increasingly prominent. In this paper, we describe the current applications of pHLIP-anchored imaging agents for tumor diagnosis and treatment in terms of different molecular imaging methods, including magnetic resonance T1 imaging, magnetic resonance T2 imaging, SPECT/PET, fluorescence imaging, and photoacoustic imaging. Additionally, we discuss relevant challenges and future development prospects.

Discovery of endosomalytic cell-penetrating peptides based on bacterial membrane-targeting sequences

Cell-penetrating peptides (CPPs) are prominent scaffolds for drug developments and related research, particularly the endocytic delivery of biomacromolecules. Effective cargo release from endosomes prior to lysosomal degradation is a crucial step, where the rational design and selection of CPPs remains a challenge and calls for deeper mechanistic understandings. Here, we have investigated a strategy of designing CPPs that selectively disrupt endosomal membranes based on bacterial membrane targeting sequences (MTSs). Six synthesized MTS peptides all exhibit cell-penetrating abilities, among which two d-peptides (d-EcMTS and d-TpMTS) are able to escape from endosomes and localize at ER after entering the cell. The utility of this strategy has been demonstrated by the intracellular delivery of green fluorescent protein (GFP). Together, these results suggest that the large pool of bacterial MTSs may be a rich source for the development of novel CPPs.

Self-healing cyclic peptide hydrogels

Hydrogels are soft materials of great interest in different areas such as chemistry, biology, and therapy. Gels made by the self-assembly of small molecules are known as supramolecular gels. The modulation of their properties by monomer molecular design is still difficult to predict due to the potential impact of subtle structural modifications in the self-assembly process. Herein, we introduce the design principles of a new family of self-assembling cyclic octapeptides of alternating chirality that can be used as scaffolds for the development of self-healing hydrogelator libraries with tunable properties. The strategy was used in the preparation of an amphiphilic cyclic peptide monomer bearing an alkoxyamine connector, which allowed the insertion of different aromatic aldehyde pendants to modulate the hydrophobic/hydrophilic balance and fine-tune the properties of the resulting gel. The resulting amphiphiles were able to form self-healable hydrogels with viscoelastic properties (loss tangent, storage modulus), which were strongly dependent on the nature and number of aromatic moieties anchored to the hydrophilic peptide. Structural studies by SEM, STEM and AFM indicated that the structure of the hydrogels was based on a dense network of peptide nanotubes. Excellent agreement was established between the peptide primary structure, nanotube length distributions and viscoelastic behaviour.

A VEGFR targeting peptide-drug conjugate (PDC) suppresses tumor angiogenesis in a TACE model for hepatocellular carcinoma therapy

Transcatheter arterial chemoembolization (TACE) has become the preferred therapy for unresectable advanced hepatocellular carcinoma (HCC). However, the embolization of tumor-feeding arteries by TACE always leads to hypoxia-related tumor angiogenesis, which limited the therapeutic effect for HCC. In this paper, we used a VEGFR targeting peptide VEGF125 − 136 (QKRKRKKSRYKS) to conjugate with a lytic peptide (KLUKLUKKLUKLUK) to form a peptide-drug conjugate (PDC). We used cell affinity assay to detect the peptide binding ability to VEGFR highly expressed cell lines, and CCK8, cell apoptosis to confirm the cellular toxicity for different cell lines. Meanwhile, we created a VX2 tumor-bearing rabbit model to assess the in vivo anti-tumor effect of the peptide conjugate in combination with TAE. HE staining was used to verify the in vivo safety of the peptide conjugate. IHC was used to assess the anti-angiogenesis and cell toxicity of the peptide conjugate in tumor tissues. The peptide conjugate could not only target VEGFR in cell surface and inhibit VEGFR function, but also have potent anti-cancer effect. We luckily found the peptide conjugate showed potent cytotoxicity for liver cancer cell Huh7 (IC50 7.3 ± 0.74 μM) and endothelial cell HUVEC (IC50 10.7 ± 0.292 μM) and induced cell apoptosis of these two cell lines. We also found the peptide conjugate inhibited cell migration of HUVEC through wound healing assay. Besides, these peptides also showed better in vivo anti-tumor effect than traditional drug DOX through TACE in VX2 rabbit tumor model, and efficiently inhibit angiogenesis in tumor tissues with good safety. In conclusion, our work may provide an alternative option for clinical HCC therapy via TACE combination.

Schematic presentation of the design of VEGFR targeting peptide conjugate (QR-KLU) and the antineoplastic efficacy of peptide QR-KLU in vitro and in vivo.

Fluorous-Tagged Peptide Nanoparticles Ameliorate Acute Lung Injury via Lysosomal Stabilization and Inflammation Inhibition in Pulmonary Macrophages

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a common respiratory critical syndrome that currently has no effective therapeutic interventions. Pulmonary macrophages play a principal role in the initiation and progression of the overwhelming inflammation in ALI/ARDS. Here, a type of fluorous-tagged bioactive peptide nanoparticle termed CFF13F is developed, which can be efficiently internalized by macrophages and suppress the excessive expression of cytokines and the overproduction of reactive oxygen species (ROS) triggered by lipopolysaccharide (LPS). The cytoprotective effect of CFF13F may be attributed to the lysosomal-stabilization property and regulation of the antioxidative system. Moreover, intratracheal pretreatment with CFF13F can effectively reduce local and systematic inflammation, and ameliorate pulmonary damage in an LPS-induced ALI murine model. The therapeutic efficacy of CFF13F is affected by the administration routes, and the local intratracheal injection is found to be the optimal choice for ALI treatment, with preferred biodistribution profiles. The present study provides solid evidence of the potent immunomodulatory bioactivity of the fluorous-tagged peptide nanoparticles CFF13F in vitro and in vivo, and sheds light on the development of novel efficient nanodrugs for ALI/ARDS.

Mechanism of endosomal escape by pH-responsive nucleic-acid vectors

Successful intracellular delivery of nucleic acids (NAs) hinges on many factors, one of them being NAs' efficacious escape from endosomes. As competent NA vectors, pH-responsive gemini surfactants (GSs) might achieve high efficacy by facilitating endosomal escape. However, how the GSs assist the escape remains debated as many proposed mechanisms still lack experimental support, which hinders replication and further improvement of the efficient delivery. Here, via UV, fluorescence spectroscopy, and small-angle neutron scattering (SANS), we examined a pH-responsive GS's and a pH-unresponsive GS's capabilities to compact DNA and withstand binding competition, and their interactions with model endosomal and lysosomal membranes, at varied pHs. Acidification-driven enhancement of DNA-compaction capability and of stability against binding competition were found specific to the pH-responsive GS. Alongside the pH-responsive GS's structural perturbation to the membranes as observed with SANS, the features suggest that pH-responsive GSs facilitate endosomal escape by releasing excess GS molecules from DNA-GS complexes upon acidification in endosome maturation, with the released GS molecules disrupting endosomal and lysosomal membranes and thereby assisting the escape. A general design principle for NA vectors is proposed on the basis of this experimental finding.

L17ER4: A cell-permeable attenuated cationic amphiphilic lytic peptide

We have developed a series of attenuated cationic amphiphilic lytic (ACAL) peptides that can efficiently bring immunoglobulin G (IgG) and other functional proteins into cells. Delivery is generally achieved through the coadministration of ACAL peptides with cargo proteins. However, conjugation of ACAL peptides with cargos may be a promising approach for in vivo application to link in vivo outcomes of ACAL peptides and cargos. This study describes the creation of a new cell-permeable ACAL peptide, L17ER4. L17E is an optimized prototype of ACAL peptides previously developed in our laboratory for efficient delivery of IgGs into cells. Delivery was improved by functionalizing L17E with a tetra-arginine (R4) tag. Compared to the use of R8, a representative cell-penetrating peptide with high intracellular delivery efficacy, conjugation with L17ER4 afforded approximately four-fold higher cellular uptake of model small-molecule cargos (fluorescein isothiocyanate and HiBiT peptide). L17ER4 was also able to deliver proteins to cells. Fused with L17ER4, Cre recombinase was delivered into cells. Intracerebroventricular injection of Cre-L17ER4 into green red reporter mice, R26GRR, led to significant in vivo gene recombination in ependymal cells, suggesting that L17ER4 may be used as a cell-penetrating peptide for delivering protein therapeutics into cells in vivo.

Artificial Nanocage Formed via Self-Assembly of β-Annulus Peptide for Delivering Biofunctional Proteins into Cell Interiors

Nanocarriers that deliver functional proteins to cell interiors are an attractive platform for the intracellular delivery of intact proteins without further modification, with in vivo compatibility. Development of efficient methods for cargo protein encapsulation and release in recipient cell cytosol is needed. Herein, we assess the feasibility of the abovementioned requirements using a protein nanocage (artificial nanocage) without compromising the structure and functions of the original protein and allowing for design flexibility of the surfaces and interiors. The protein nanocage formed via the self-assembly of the β-annulus peptide (24-amino acid peptide) in water was used as a model framework. The nitrilotriacetic acid moiety was displayed on the nanocage lumen for effective encapsulation of hexahistidine-tagged proteins in the presence of Ni²⁺, and the amphiphilic cationic lytic peptide HAad was displayed on a nanocage surface to attain cell permeability. Successful intracellular delivery of cargo proteins and targeting of cytosolic proteins by a nanobody were achieved, indicating the validity of the approach employed in this study.

Rational Design of Self-Assembled Mitochondria-Targeting Lytic Peptide Conjugates with Enhanced Tumor Selectivity

Membrane lytic peptides (MLP) are widely explored as cellular delivery vehicles or antitumor/antibacterial agents. However, the poor selectivity between cancer and normal cells slims their prospects as potential anti-tumor drugs. Herein, we have developed a rationally designed self-assembly strategy to enhance tumor selectivity of MLP-based conjugates, incorporating a hydrophobic triphenylphosphonium (TPP) group for mitochondria targeting, and a hydrophilic arginine-glycine-aspartic acid (RGD) sequence targeting integrins. The self-assembly nanoparticles can enhance the stability of the peptides in vitro plasma and be endocytosed selectively into the cancer cells. The histidine-rich lytic peptide component assists the disruption of endosomal/lysosomal membranes and subsequent the mitochondria membrane, which leads to apoptosis. This rational design of MLP-based conjugates provides a practical strategy to increase the application prospects of lytic peptides in cancer treatment.

Functional Peptides That Target Biomembranes: Design and Modes of Action

Biomembranes are important targets in molecular design. Our laboratory has been exploring the design of functional peptides that modulate membrane barrier function, lipid packing, and structure. Evaluation of the results obtained and analyses of cellular mechanisms have yielded peptides with more refined designs and functions. This review highlights the progress made in our laboratory towards the development of unique peptides that modulate membrane properties.

Liquid Droplet Formation and Facile Cytosolic Translocation of IgG in the Presence of Attenuated Cationic Amphiphilic Lytic Peptides

Fc region binding peptide conjugated with attenuated cationic amphiphilic lytic peptide L17E trimer [FcB(L17E)₃ ] was designed for immunoglobulin G (IgG) delivery into cells. Particle-like liquid droplets were generated by mixing Alexa Fluor 488 labeled IgG (Alexa488-IgG) with FcB(L17E)₃ . Droplet contact with the cellular membrane led to spontaneous influx and distribution of Alexa488-IgG throughout cells in serum containing medium. Involvement of cellular machinery accompanied by actin polymerization and membrane ruffling was suggested for the translocation. Alexa488-IgG negative charges were crucial in liquid droplet formation with positively charged FcB(L17E)₃ . Binding of IgG to FcB(L17E)₃ may not be necessary. Successful intracellular delivery of Alexa Fluor 594-labeled anti-nuclear pore complex antibody and anti-mCherry-nanobody tagged with supernegatively charged green fluorescence protein allowed binding to cellular targets in the presence of FcB(L17E)₃ .

Photoactivated In Situ Generation of Near Infrared Cyanines for Spatiotemporally Controlled Fluorescence Imaging in Living Cells

Photoactivated trimerization of 2,3,3-trimethyl-3H-indole derivatives created near infrared fluorophore Cy5. The synthetic method is air-tolerant, photosensitizer free, metal free, and condensation agent free. Living cells make Cy5 on a time scale of minutes under white light irradiation at a low power intensity, with the monomer as the only exogenous agent. The new method is promising to find applications in cell studies for in situ spatiotemporally controlled fluorescence imaging in living cells.

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.

Use of homoarginine to obtain attenuated cationic membrane lytic peptides

Our research group has been studying the design of intracellular delivery peptides based on cationic lytic peptides. By placing negatively charged amino acids on potentially hydrophobic faces of the peptides, membrane lytic activity is attenuated on the cell surface, whereas it recovers in endosomes, enabling cytosolic delivery of proteins including antibodies. These lytic peptides generally contain multiple lysines, facilitating cell surface interaction and membrane perturbation. This study evaluated the effect of lysine-to-homoarginine substitution using HAad as a model delivery peptide. The resulting peptide had a comparable or better delivery efficacy for Cre recombinase, antibodies, and the Cas9/sgRNA complex with one-quarter of the concentration of HAad, implying that a subtle structural difference can affect delivery activity.

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.

Intracellular Delivery of Active Proteins by Polyphosphazene Polymers

Achieving intracellular delivery of protein therapeutics within cells remains a significant challenge. Although custom formulations are available for some protein therapeutics, the development of non-toxic delivery systems that can incorporate a variety of active protein cargo and maintain their stability, is a topic of great relevance. This study utilized ionic polyphosphazenes (PZ) that can assemble into supramolecular complexes through non-covalent interactions with different types of protein cargo. We tested a PEGylated graft copolymer (PZ-PEG) and a pyrrolidone containing linear derivative (PZ-PYR) for their ability to intracellularly deliver FITC-avidin, a model protein. In endothelial cells, PZ-PYR/protein exhibited both faster internalization and higher uptake levels than PZ-PEG/protein, while in cancer cells both polymers achieved similar uptake levels over time, although the internalization rate was slower for PZ-PYR/protein. Uptake was mediated by endocytosis through multiple mechanisms, PZ-PEG/avidin colocalized more profusely with endo-lysosomes, and PZ-PYR/avidin achieved greater cytosolic delivery. Consequently, a PZ-PYR-delivered anti-F-actin antibody was able to bind to cytosolic actin filaments without needing cell permeabilization. Similarly, a cell-impermeable Bax-BH3 peptide known to induce apoptosis, decreased cell viability when complexed with PZ-PYR, demonstrating endo-lysosomal escape. These biodegradable PZs were non-toxic to cells and represent a promising platform for drug delivery of protein therapeutics.

Design and Construction of pH-Selective Self-Lytic Liposome System

Liposomes are well-investigated drug or gene delivery vehicles for chemotherapy, used by taking advantage of their biocompatibility and biodegradability. A central question on the construction of intracellular liposomal delivery systems is to entrap the liposomes of interest in the highly acidic and proteolytic endosomal environment. In the other words, it is essential that the liposomes release a therapeutic drug into the cytosol before they are degraded in the endosome. As a strategy to enhance the endosome escape, the self-lytic liposomes with acidic pH-selective membrane active polypeptide are considered highly effective. Here, an acidic pH-selective membrane-lytic polypeptide (LPE) and its retro isomer (rLPE) were designed, and then their membrane-lytic activities against EggPC liposomes were determined. It was noticed that the rLPE polypeptide showed an increase in activity compared with the LPE polypeptide. Furthermore, the rLPE polypeptide was conjugated to liposomes via a flexible Gly-Gly-Gly-Gly linker to facilitate the pH-selective content release. The rLPE anchoring liposomes exhibited distinctly different contents release behavior at physiological and endosomal pHs, namely typical contents release from liposomes was positively observed at acidic pH range. The overarching goal of this paper is to develop efficient pH-selective therapeutic delivery systems by using our findings.