Extracellular Microvesicles Modified with Arginine-Rich Peptides for Active Macropinocytosis Induction and Delivery of Therapeutic Molecules

Extracellular vesicles (EVs), including exosomes and microvesicles (MVs), transfer bioactive molecules from donor to recipient cells in various pathophysiological settings, thereby mediating intercellular communication. Despite their significant roles in extracellular signaling, the cellular uptake mechanisms of different EV subpopulations remain unknown. In particular, plasma membrane-derived MVs are larger vesicles (100 nm to 1 μm in diameter) and may serve as efficient molecular delivery systems due to their large capacity; however, because of size limitations, receptor-mediated endocytosis is considered an inefficient means for cellular MV uptake. This study demonstrated that macropinocytosis (lamellipodia formation and plasma membrane ruffling, causing the engulfment of large fluid volumes outside cells) can enhance cellular MV uptake. We developed experimental techniques to induce macropinocytosis-mediated MV uptake by modifying MV membranes with arginine-rich cell-penetrating peptides for the intracellular delivery of therapeutic molecules.

Regulatory network of ferroptosis and autophagy by targeting oxidative stress defense using sulfasalazine in triple-negative breast cancer

AIMS

The cellular defense system against oxidative stress is important for the survival ability and sensitization in chemotherapy; however, the regulatory mechanisms remain unknown in triple-negative breast cancer (TNBC) cells. This study aimed to investigate the relationship between ferroptosis and autophagy by targeting the defense of oxidative stress through the cystine transporter (xCT) using sulfasalazine (SASP), which is a widely employed xCT inhibitor.

MAIN METHODS

We analyzed the cell death process of SASP in human TNBC cells, and examined the effects of SASP on tumor progression by using xenograft mouse model.

KEY FINDINGS

TNBC cells demonstrated a high defense capacity against reactive oxidative species through xCT. SASP significantly attenuated oxidative stress resistance in MDA-MB-231, which is a generally used model cell as TNBC, through decreased glutathione levels, causing a marked iron-dependent ferroptotic cell death induction. Moreover, autophagy was required to trigger efficient SASP-induced ferroptosis at the early stage of cell death. Tamoxifen, which is currently in clinical use as the gold standard for endocrine therapy of estrogen receptor-positive breast cancer, was a beneficial tool as an autophagy regulator under ferroptotic cell death by SASP. Additionally, SASP suppressed tumor growth and metastasis progression through total glutathione reduction in the primary tumor, indicating high anticancer activity against TNBC without liver injury in vivo.

SIGNIFICANCE

We revealed that SASP can efficiently induce ferroptosis associated with autophagy and that an understanding of the mechanism of cell death regulation by SASP is a promising new strategy for TNBC therapy and drug repositioning.

Effective design of PEGylated polyion complex (PIC) nanoparticles for enhancing PIC internalisation in cells utilising block copolymer combinations with mismatched ionic chain lengths

In nanomedicine, PEGylation of nanomaterials poses a dilemma since it inhibits their interaction with target cells and enables their retention in target tissues despite its biocompatibility and nonspecific internalisation suppression. PEGylated polypeptide-based polyion complexes (PICs) are fabricated via the self-assembly of PEGylated aniomers and homocatiomers based on electrostatic interactions. We propose that various parameters like block copolymer design and PIC domain characteristics can enhance the cell-PEGylated PIC interactions. Remarkably, the properties of the PIC domain were tuned by the matched/mismatched ionomer chain lengths, PIC domain crosslinking degree, chemical modification of cationic species after crosslinking, PIC morphologies (vesicles/micelles) and polyethylene glycol (PEG) chain lengths. Cellular internalisation of the prepared PICs was evaluated using HeLa cells. Consequently, mismatched ionomer chain lengths and vesicle morphology enhanced cell-PIC interactions, and the states of ion pairing, particularly cationic residues, affected the internalisation behaviours of PICs via acetylation or guanidinylation of amino groups on catiomers. This treatment attenuated the cell-PIC interactions, possibly because of reduced interaction of PICs with negatively charged species on the cell-surface, glycosaminoglycans. Moreover, morphology and PEG length were correlated with PIC internalisation, in which PICs with longer and denser PEG were internalised less effectively. Cell line dependency was tested using RAW 264.7 macrophage cells; PIC recognition could be maintained after capping amino groups on catiomers, indicating that the remaining anionic groups were still effectively recognised by the scavenger receptors of macrophages. Our strategy for tuning the physicochemical properties of the PEGylated PIC nanocarriers is promising for overcoming the PEG issue.

Gene Delivery into T-Cells Using Ternary Complexes of DNA, Lipofectamine, and Carboxy-Terminal Phenylalanine-Modified Dendrimers

T-cells play critical roles in various immune reactions, and genetically engineered T-cells have attracted attention for the treatment of cancer and autoimmune diseases. Previously, it is shown that a polyamidoamine dendrimer of generation 4 (G4), modified with 1,2-cyclohexanedicarboxylic anhydride (CHex) and phenylalanine (Phe) (G4-CHex-Phe), is useful for delivery into T-cells and their subsets. In this study, an efficient non-viral gene delivery system is constructed using this dendrimer. Ternary complexes are prepared using different ratios of plasmid DNA, Lipofectamine, and G4-CHex-Phe. A carboxy-terminal dendrimer lacking Phe (G3.5) is used for comparison. These complexes are characterized using agarose gel electrophoresis, dynamic light scattering, and ζpotential measurements. In Jurkat cells, the ternary complex with G4-CHex-Phe at a P/COOH ratio of 1/5 shows higher transfection activity than other complexes, such as binary and ternary complexes with G3.5, without any significant cytotoxicity. The transfection efficiency of the G4-CHex-Phe ternary complexes decreases considerably in the presence of free G4-CHex-Phe and upon altering the complex preparation method. These results suggest that G4-CHex-Phe promotes the cellular internalization of the complexes, which is useful for gene delivery into T-cells.

Inkjet-Based Intracellular Delivery System that Effectively Utilizes Cell-Penetrating Peptides for Cytosolic Introduction of Biomacromolecules through the Cell Membrane

In the drug delivery system, the cytosolic delivery of biofunctional molecules such as enzymes and genes must achieve sophisticated activities in cells, and microinjection and electroporation systems are typically used as experimental techniques. These methods are highly reliable, and they have high intracellular transduction efficacy. However, a high degree of proficiency is necessary, and induced cytotoxicity is considered as a technical problem. In this research, a new intracellular introduction technology was developed through the cell membrane using an inkjet device and cell-penetrating peptides (CPPs). Using the inkjet system, the droplet volume, droplet velocity, and dropping position can be accurately controlled, and minute samples (up to 30 pL/shot) can be carried out by direct administration. In addition, CPPs, which have excellent cell membrane penetration functions, can deliver high-molecular-weight drugs and nanoparticles that are difficult to penetrate through the cell membrane. By using the inkjet system, the CPPs with biofunctional cargo, including peptides, proteins such as antibodies, and exosomes, could be accurately delivered to cells, and efficient cytosolic transduction was confirmed.

Ultrafast sensitivity-controlled and specific detection of extracellular vesicles using optical force with antibody-modified microparticles in a microflow system

Extracellular vesicles (EVs), including nanoscale exosomes and ectosomes, hold promise as biomarkers that provide information about the cell of origin through their cargo of nucleic acids and proteins, both on their surface and within. Here, we develop a detection method of EVs based on light-induced acceleration of specific binding between their surface and antibody-modified microparticles, using a controlled microflow with three-dimensional analysis by confocal microscopy. Our method successfully detected 10³-10⁴ nanoscale EVs in liquid samples as small as a 500 nanoliters within 5 minutes, with the ability to distinguish multiple membrane proteins. Remarkably, we achieved the specific detection of EVs secreted from living cancer cell lines with high linearity, without the need for a time-consuming ultracentrifugation process that can take several hours. Furthermore, the detection range can be controlled by adjusting the action range of optical force using a defocused laser, consistent with the theoretical calculations. These findings demonstrate an ultrafast, sensitive, and quantitative approach for measuring biological nanoparticles, enabling innovative analyses of cell-to-cell communication and early diagnosis of various diseases, including cancer.

A universal method to analyze cellular internalization mechanisms via endocytosis without non-specific cross-effects

Endocytosis is an essential biological process for nutrient absorption and intercellular communication; it can also be used to accelerate the cellular internalization of drug delivery carriers. Clarifying the cellular uptake mechanisms of unidentified endogenous and exogenous molecules and designing new effective drug delivery systems require an accurate, specific endocytosis analysis methodology. Therefore, we developed a method to specifically evaluate cellular internalization via three main endocytic pathways: clathrin- and caveolae-mediated endocytosis, and macropinocytosis. We first revealed that most known endocytosis inhibitors had no specific inhibitory effect or were cytotoxic. Second, we successfully established an alternative method using small interfering RNA to knock down dynamin-2 and caveolin-1, which are necessary for clathrin- and caveolae-mediated endocytosis, in HeLa cells. Third, we established another method to specifically analyze macropinocytosis using rottlerin on A431 cells. Finally, we validated the proposed methods by testing the cellular internalization of a biological molecule (insulin) and carriers (nanoparticles and cell-penetrating peptides). Through this study, we established versatile methods to precisely and specifically evaluate endocytosis of newly developed biopharmaceuticals or drug delivery systems.

Light-Induced Condensation of Biofunctional Molecules around Targeted Living Cells to Accelerate Cytosolic Delivery

The light-induced force and convection can be enhanced by the collective effect of electrons (superradiance and red shift) in high-density metallic nanoparticles, leading to macroscopic assembly of target molecules. We here demonstrate application of the light-induced assembly for drug delivery system with enhancement of cell membrane accumulation and penetration of biofunctional molecules including cell-penetrating peptides (CPPs) with superradiance-mediated photothermal convection. For induction of photothermal assembly around targeted living cells in cell culture medium, infrared continuous-wave laser light was focused onto high-density gold-particle-bound glass bottom dishes exhibiting plasmonic superradiance or thin gold-film-coated glass bottom dishes. In this system, the biofunctional molecules can be concentrated around the targeted living cells and internalized into them only by 100 s laser irradiation. Using this simple approach, we successfully achieved enhanced cytosolic release of the CPPs and apoptosis induction using a pro-apoptotic domain with a very low peptide concentration (nM level) by light-induced condensation.

Controlled release of canine MSC-derived extracellular vesicles by cationized gelatin hydrogels

Introduction

Canine mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) have emerged as a promising form of regenerative therapy. Therapeutic application of EVs remains difficult due to the short half-life of EVs in vivo and their rapid clearance from the body. We have developed cationized gelatin hydrogels that prolong the retention of EVs to overcome this problem.

Methods

Canine MSCs were isolated from bone marrow. MSC-derived EVs were isolated from the culture supernatant by ultracentrifugation. Gelatin was mixed with ethylene diamine anhydrate to cationized. Distinct cross-linked cationized gelatin hydrogels were created by thermal dehydration. Hydrogels were implanted into the back subcutis of mice in order to evaluate the degradation profiles. Hydrogels with collagenase were incubated at 37 °C in vitro to quantize the release of EVs from hydrogels. Lipopolysaccharide (LPS)-stimulated BV-2 cells were used to evaluate the immunomodulatory effect of EVs after release from the hydrogels.

Results

The cationized gelatin hydrogels suppressed EV release in PBS. More than 60% of immobilized EVs are not released from the hydrogels. The cationized hydrogels released EVs in a sustainable manner and prolonged the retention time of EVs depending on the intensity of cross-linking after degradation by collagenase. The expression of IL-1β in LPS-stimulated BV-2 cells was lower in EVs released from the hydrogels than in controls.

Conclusions

Our results indicate that the controlled release of EVs can be achieved by cationized gelatin hydrogels. The released EVs experimentally confirmed to be effective in reducing proinflammatory response. The cationized gelatin hydrogels appear to be useful biomaterials for releasing canine MSC-derived EVs for regenerative therapy.

Stearylated Macropinocytosis-Inducing Peptides Facilitating the Cellular Uptake of Small Extracellular Vesicles

Macropinocytosis is a form of endocytosis that allows massive uptake of extracellular materials and is a promising route for intracellular delivery of biofunctional macromolecules and nanoparticles. Our laboratory developed a potent macropinocytosis-inducing peptide named P4A. However, the ability of this peptide is not apparent in the presence of serum. This study aims to endow P4A and related peptides with the ability to induce macropinocytosis in the presence of serum by N-terminal acylation with long-chain fatty acids (i.e., decanoic, myristic, and stearic acids). Stearylated P4A (stearyl-P4A) had the highest effect on stimulating macropinocytotic uptake. Moreover, the intramolecularly disulfide-bridged analogue, stearyl-oxP4A, showed an even higher ability. The effect of stearyl-oxP4A to facilitate the intracellular delivery of small extracellular vesicles (sEVs) was evaluated in terms of (i) cellular uptake using sEVs labeled with an enhanced green fluorescent protein (EGFP) and (ii) cytosolic liberation and expression of sEV-encapsulated luciferase mRNA in recipient cells. The two- to threefold uptake of both sEVs in the presence of stearyl-oxP4A suggests the potential of the peptide for sEV delivery in the presence of serum.

Dodecaborate-Encapsulated Extracellular Vesicles with Modification of Cell-Penetrating Peptides for Enhancing Macropinocytotic Cellular Uptake and Biological Activity in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a radiation therapy for cancer. In BNCT, the internalization of boron-10 atoms by cancer cells induces cell death through the generation of α particles and recoiling lithium-7 nuclei when irradiated with low-energy thermal neutrons. In this study, we aimed to construct exosomes [extracellular vesicles (EVs)]-based drug delivery technology in BNCT. Because of their pharmaceutical advantages, such as controlled immune responses and effective usage of cell-to-cell communication, EVs are potential next-generation drug delivery carriers. In this study, we successfully developed polyhedral borane anion-encapsulated EVs with modification of hexadeca oligoarginine, which is a cell-penetrating peptide, on the EV membrane to induce the actin-dependent endocytosis pathway, macropinocytosis, which leads to efficient cellular uptake and remarkable cancer cell-killing BNCT activity. The simple and innovative technology of the EV-based delivery system with "cassette" modification of functional peptides will be applicable not only for BNCT but also for a wide variety of therapeutic methodologies.

Hypoxia enhances motility and EMT through the Na+/H+ exchanger NHE-1 in MDA-MB-231 breast cancer cells

Breast cancer metastasis is the leading cause of cancer-related deaths. Hypoxia in the tumor mass is believed to trigger cell migration, which is involved in a crucial process of breast cancer metastasis. However, the molecular mechanisms underlying aggressive behavior under hypoxic conditions have not been fully elucidated. Here, we demonstrate the significant motility of MDA-MB-231 cells cultured under hypoxic conditions compared to that of cells cultured under normoxic conditions. MDA-MB-231 cells under hypoxic conditions showed a significant increase in Na⁺/H⁺ exchanger isoform 1 (NHE1) expression level, which was observed to co-locate in lamellipodia formation. Inhibition of NHE1 significantly suppressed the intracellular pH and the expression of mesenchymal markers, thereby blocking the high migration activity in hypoxia. Moreover, treatment with ciglitazone, a potent and selective peroxisome proliferator-activated receptor γ (PPARγ) agonist, modulated hypoxia-enhanced motion in cells via the repression of NHE1. These findings highlight that NHE1 is required for migratory activity through the enhancement of epithelial-mesenchymal transition (EMT) in MDA-MB-231 cells under hypoxic conditions, and we propose new drug repurposing strategies targeting hypoxia based on NHE1 suppression by effective usage of PPARγ agonists.

Carboxy-terminal dendrimers with phenylalanine for a pH-sensitive delivery system into immune cells including T cells

Although T cells play important roles in various immune reactions, there are only a few reports on delivery systems into T cells. Our previous study showed that carboxy-terminal phenylalanine (Phe)-modified polyamidoamine (PAMAM) dendrimers have both temperature- and pH-sensitive properties, which are affected by the chemical structure. The self-assembled structures of Phe, observed in phenylketonuria, enhance the protein aggregation, the association with the cell membrane and the membrane permeability. In this study, we applied the Phe-modified dendrimers to a pH-sensitive drug delivery system into T cells. Dendrimers with different amino acids and acid anhydrides were synthesized, and their pH-responsive association with T cells and their subsets was investigated. The dendrimers modified with Phe and cyclohexanedicarboxylic acid (CHex) showed higher uptake into various cells, including Jurkat cells, CD3+ T cells, CD3 + CD4+ helper T cells and CD3 + CD8+ killer T cells. These dendrimers were internalized into T cells via endocytosis, and their cellular uptake was enhanced under weak acidic conditions (pH 6.5). Our results showed that Phe- and CHex-modified dendrimers have a delivery potential to T cells and their subsets, which may be useful for cancer immunotherapy.

Exosomes: Breast cancer-derived extracellular vesicles; recent key findings and technologies in disease progression, diagnostics, and cancer targeting

Breast cancer is one of the most frequently diagnosed types of cancer in women. Metastasis, particularly to the lungs and brain, increases mortality in breast cancer patients. Recently, breast cancer-related exosomes have received significant attention because of their key role in breast cancer progression. As a result, numerous exosome-based therapeutic tools for diagnosis and treatment have been developed, and their biological and chemical mechanisms have been explored. This review summarizes up-to-date advanced key findings and technologies in breast cancer progression, diagnostics, and targeting. We focused on recent research on the basic biology of exosomes and disease-related exosomal genes and proteins, as well as their signal transduction in cell-to-cell communications, diagnostic markers, and exosome-based antibreast cancer technologies. We also paid special attention to technologies employing exosomes modified with functional peptides for the targeted delivery of therapeutic and diagnostic agents.

Macropinocytosis-Inducible Extracellular Vesicles Modified with Antimicrobial Protein CAP18-Derived Cell-Penetrating Peptides for Efficient Intracellular Delivery

The antimicrobial protein CAP18 (approximate molecular weight: 18 000), which was first isolated from rabbit granulocytes, comprises a C-terminal fragment that has negatively charged lipopolysaccharide binding activity. In this study, we found that CAP18 (106-121)-derived (sC18)₂ peptides have macropinocytosis-inducible biological functions. In addition, we found that these peptides are highly applicable for use as extracellular vesicle (exosomes, EV)-based intracellular delivery, which is expected to be a next-generation drug delivery carrier. Here, we demonstrate that dimerized (sC18)₂ peptides can be easily introduced on EV membranes when modified with a hydrophobic moiety, and that they show high potential for enhanced cellular uptake of EVs. By glycosaminoglycan-dependent induction of macropinocytosis, cellular EV uptake in targeted cells was strongly increased by the peptide modification made to EVs, and intriguingly, our herein presented technique is efficiently applicable for the cytosolic delivery of the biologically cell-killing functional toxin protein, saporin, which was artificially encapsulated in the EVs by electroporation, suggesting a useful technique for EV-based intracellular delivery of biofunctional molecules.

Size and surface modification of silica nanoparticles affect the severity of lung toxicity by modulating endosomal ROS generation in macrophages

Background

As the application of silica nanomaterials continues to expand, increasing chances of its exposure to the human body and potential harm are anticipated. Although the toxicity of silica nanomaterials is assumed to be affected by their physio-chemical properties, including size and surface functionalization, its molecular mechanisms remain unclear. We hypothesized that analysis of intracellular localization of the particles and subsequent intracellular signaling could reveal a novel determinant of inflammatory response against silica particles with different physico-chemical properties.

Results

We employed a murine intratracheal instillation model of amorphous silica nanoparticles (NPs) exposure to compare their in vivo toxicities in the respiratory system. Pristine silica-NPs of 50 nm diameters (50 nm-plain) induced airway-centered lung injury with marked neutrophilic infiltration. By contrast, instillation of pristine silica particles of a larger diameter (3 μm; 3 μm-plain) significantly reduced the severity of lung injury and neutrophilic infiltration, possibly through attenuated induction of neutrophil chemotactic chemokines including MIP2. Ex vivo analysis of alveolar macrophages as well as in vitro assessment using RAW264.7 cells revealed a remarkably lower cellular uptake of 3 μm-plain particles compared with 50 nm-plain, which is assumed to be the underlying mechanism of attenuated immune response. The severity of lung injury and neutrophilic infiltration was also significantly reduced after intratracheal instillation of silica NPs with an amine surface modification (50 nm-NH₂) when compared with 50 nm-plain. Despite unchanged efficacy in cellular uptake, treatment with 50 nm-NH₂ induced a significantly attenuated immune response in RAW264.7 cells. Assessment of intracellular redox signaling revealed increased reactive oxygen species (ROS) in endosomal compartments of RAW264.7 cells treated with 50 nm-plain when compared with vehicle-treated control. In contrast, augmentation of endosomal ROS signals in cells treated with 50 nm-NH₂ was significantly lower. Moreover, selective inhibition of NADPH oxidase 2 (NOX2) was sufficient to inhibit endosomal ROS bursts and induction of chemokine expressions in cells treated with silica NPs, suggesting the central role of endosomal ROS generated by NOX2 in the regulation of the inflammatory response in macrophages that endocytosed silica NPs.

Conclusions

Our murine model suggested that the pulmonary toxicity of silica NPs depended on their physico-chemical properties through distinct mechanisms. Cellular uptake of larger particles by macrophages decreased, while surface amine modification modulated endosomal ROS signaling via NOX2, both of which are assumed to be involved in mitigating immune response in macrophages and resulting lung injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00415-0.

A "ligand-targeting" peptide-drug conjugate: Targeted intracellular drug delivery by VEGF-binding helix-loop-helix peptides via receptor-mediated endocytosis

As a new alternative to antibody-drug conjugates, we generated “ligand-targeting” peptide-drug conjugates (PDCs), which utilize receptor-mediated endocytosis for targeted intracellular drug delivery. The PDC makes a complex with an extracellular ligand and then binds to the receptor on the cell surface to stimulate intracellular uptake via the endocytic pathway. A helix-loop-helix (HLH) peptide was designed as the drug carrier and randomized to give a conformationally constrained peptide library. The phage-displayed library was screened against vascular endothelial growth factor (VEGF) to yield the binding peptide M49, which exhibited strong binding affinity (K_D = 0.87 nM). The confocal fluorescence microscopy revealed that peptide M49 formed a ternary complex with VEGF and its receptor, which was then internalized into human umbilical vein endothelial cells (HUVECs) via VEGF receptor-mediated endocytosis. The backbone-cyclized peptide M49K was conjugated with a drug, monomethyl auristatin E, to afford a PDC, which inhibited VEGF-induced HUVEC proliferation. HLH peptides and their PDCs have great potential as a new modality for targeted molecular therapy.

Environmental pH stress influences cellular secretion and uptake of extracellular vesicles

Exosomes (extracellular vesicles/EVs) participate in cell–cell communication and contain bioactive molecules, such as microRNAs. However, the detailed characteristics of secreted EVs produced by cells grown under low pH conditions are still unknown. Here, we report that low pH in the cell culture medium significantly affected the secretion of EVs with increased protein content and zeta potential. The intracellular expression level and location of stably expressed GFP‐fused CD63 (an EV tetraspanin) in HeLa cells were also significantly affected by environmental pH. In addition, increased cellular uptake of EVs was observed. Moreover, the uptake rate was influenced by the presence of serum in the cell culture medium. Our findings contribute to our understanding of the effect of environmental conditions on EV‐based cell–cell communication.

Direct entry of cell-penetrating peptide can be controlled by maneuvering the membrane curvature

A biomembrane's role is to be a barrier for interior cytosol from an exterior environment to execute the cell's normal biological functions. However, a water-soluble peptide called cell-penetrating peptide (CPP) has been known for its ability to directly penetrate through the biomembranes into cells (cytolysis) without perturbating cell viability and expected to be a promising drug delivery vector. Examples of CPP include peptides with multiple arginine units with strong cationic properties, which is the key to cytolysis. Here we show the conclusive evidence to support the mechanism of CPP's cytolysis and way to control it. The mechanism we proposed is attributed to biomembrane's physicochemical nature as lamellar liquid crystal (Lα). Cytolysis occurs as the temporal and local dynamic phase transitions from Lα to an undulated lamellar with pores called Mesh1. We have shown this phase transfer of Lα composed of dioleoyl-phosphatidylcholine (DOPC) with water by adding oligo-arginine (Rx) as CPP at the equilibrium. Using giant unilamellar vesicle composed of DOPC as a single cell model, we could control the level of cytolysis of CPP (FITC-R8) by changing the curvature of the membrane through osmotic pressure modulation. The cytolysis of CPP utilizes biomembrane's inherent topological and functional flexibility corresponding to the stimuli.

Antibody-Based Receptor Targeting Using an Fc-Binding Peptide-Dodecaborate Conjugate and Macropinocytosis Induction for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a radiation method used for cancer therapy. Cellular uptake of boron-10 (¹⁰B) atoms induces cancer cell death by the generation of alpha particles and recoiling lithium-7 (⁷Li) nuclei when the cells are irradiated with low-energy thermal neutrons. Current BNCT technology shows effective therapeutic benefits in refractory cancers such as brain tumors and head and neck cancers. However, improvements to cancer targeting and the cellular uptake efficacy of the boron compounds and the expansion of the diseases treatable by BNCT are highly desirable. In this research, we aimed to develop an antibody-based drug delivery method for BNCT through the use of the Z33 peptide, which shows specific recognition of and interaction with the Fc domain of human IgG, for on-demand receptor targeting. In addition, we determined with an in vitro assay that macropinocytosis induction during antibody-based drug delivery is crucial for the biological activity of BNCT.

Key Process and Factors Controlling the Direct Translocation of Cell-Penetrating Peptide through Bio-Membrane

Cell-penetrating peptide (CPP) can directly penetrate the cytosol (cytolysis) and is expected to be a potent vector for a drug delivery system (DDS). Although there is general agreement that CPP cytolysis is related to dynamic membrane deformation, a distinctive process has yet to be established. Here, we report the key process and factors controlling CPP cytolysis. To elucidate the task, we have introduced trypsin digestion of adsorbed CPP onto giant unilamellar vesicle (GUV) to quantify the adsorption and internalization (cytolysis) separately. Also, the time-course analysis was introduced for the geometric calculation of adsorption and internalization amount per lipid molecule consisting of GUV. As a result, we found that adsorption and internalization assumed to occur successively by CPP molecule come into contact with membrane lipid. Adsorption is quick to saturate within 10 min, while cytolysis of each CPP on the membrane follows successively. After adsorption is saturated, cytolysis proceeds further linearly by time with a different rate constant that is dependent on the osmotic pressure. We also found that temperature and lipid composition influence cytolysis by modulating lipid mobility. The electrolyte in the outer media is also affected as a chemical mediator to control CPP cytolysis by following the Hoffmeister effect for membrane hydration. These results confirmed the mechanism of cytolysis as temporal and local phase transfer of membrane lipid from Lα to Mesh1, which has punctured bilayer morphologies.

Association of Hydrophobic Carboxyl-Terminal Dendrimers with Lymph Node-Resident Lymphocytes

Delivery systems to lymph node-resident T cells around tumor tissues are essential for cancer immunotherapy, in order to boost the immune responses. We previously reported that anionic dendrimers, such as carboxyl-, sulfonyl-, and phosphate-terminal dendrimers, were efficiently accumulated in lymph nodes via the intradermal injection. Depending on the terminal structure, their cell association properties were different, and the carboxyl-terminal dendrimers did not associate with any immune cells majorly. In this study, we investigated the delivery of carboxyl-terminal dendrimers with different hydrophobicity to lymph node-resident lymphocytes. Four types of carboxyl-terminal dendrimers-succinylated (C) and 2-carboxy-cyclohexanoylated (Chex) dendrimers with and without phenylalanine (Phe)-were synthesized and named C-den, C-Phe-den, Chex-den, and Chex-Phe-den, respectively. Chex-Phe-den was well associated with lymphocytes, but others were not. Chex-Phe-den, intradermally injected at the footpads of mice, was accumulated in the lymph node, and was highly associated with the lymphocytes, including T cells. Our results suggest that Chex-Phe-den has the potential for delivery to the lymph node-resident T cells, without any specific T cell-targeted ligands.

Intracellular target delivery of cell-penetrating peptide-conjugated dodecaborate for boron neutron capture therapy (BNCT)

In this study, we designed and synthesized organelle-targeted cell-penetrating peptide (CPP)-conjugated boron compounds to increase their cellular uptake and to control the intracellular locations for the induction of sophisticated anticancer biological activity in boron neutron capture therapy (BNCT), leading to anticancer effects with ATP reduction and apoptosis when irradiated with neutrons in an in vitro BNCT assay.

Abstract A106: A peptide based on transmembrane domain of S1PR4 as a tumor cell growth inhibitor

Background: Many anti-tumor agents are used in chemotherapy for cancers. However, they also have serious side effects because they express similar growth inhibitory activity in normal cells. Meanwhile, the development of molecular target drugs inhibiting biomolecules relating to tumor growth, invasion, and metastasis has been proceeding with the goal of selectively attacking cancer cells. It has been revealed that the proliferation of cancer stem cells involved in redevelopment, invasion, and metastasis is promoted by sphingosine-1-phosphate (S1P). We focused on the transmembrane domains of sphingosine 1 phosphate receptor 4 (S1PR4), and hypothesized that peptides which utilized these domains would exhibit a selective anti-tumor effect in cancer cells. We designed peptides based on the transmembrane domains of S1PR4 and evaluated whether the peptides showed tumor cell growth inhibitory activity against various kinds of human tumor cells. Material and methods: We chemically synthesized conjugation peptides of the human S1PR4 transmembrane domain sequences and a cell-penetrating peptide HIV TAT. The peptides were evaluated for growth inhibitory activity against human melanoma, non-small cell lung cancer (NSCLC),kidney cancer by WST assay. Results: The peptide based on the S1PR4 transmembrane domain 2 exhibited the strongest anti-tumor activity in the synthesized peptides based on the domain from 1 to 7. The result was that more than 95% of the tumor cells were inhibited in cells treated with a concentration of 25μM for 48 hours. Conclusions: We demonstrated a novel strategy for discovering an anti-tumor molecule by focusing on transmembrane domains of proteins involved in the proliferation of cancer cells. In particular, the peptide based on the transmembrane domain 2 of S1PR4 exhibits remarkable anti-tumor activity against human melanoma, NSCLC, kidney cancer which suggests that the peptide could be a candidate for a new anti-tumor agent. COI: I/we (in case of co-authors) have no potential conflict of interest to disclose

Citation Format: Tetsuhiko Yoshida, Kenichi Tanaka, Shuichi Asakawa, Makoto Sawada, Yoshinori Hasegawa, Ikuhiko Nakase, Nahoko Bailey Kobayashi. A peptide based on transmembrane domain of S1PR4 as a tumor cell growth inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A106. doi:10.1158/1535-7163.TARG-19-A106

Effects of gefitinib treatment on cellular uptake of extracellular vesicles in EGFR-mutant non-small cell lung cancer cells

Extracellular vesicles (exosomes, EVs) are cell membrane particles (30-200 nm) secreted by virtually all cells. During intercellular communication in the body, secreted EVs play crucial roles by carrying functional biomolecules (e.g., microRNAs and enzymes) into other cells to affect cellular function, including disease progression. We previously reported that the macropinocytosis pathway contributes greatly to the efficient cellular uptake of EVs. The activation of growth factor receptors, such as epidermal growth factor receptor (EGFR), induces macropinocytosis. In this study, we demonstrated the effects of gefitinib, a tyrosine kinase inhibitor of EGFR, on the cellular uptake of EVs. In EGFR-mutant HCC827 non-small cell lung cancer (NSCLC) cells, which are sensitive to gefitinib, macropinocytosis was suppressed by gefitinib treatment. However, the cellular uptake of EVs was increased by gefitinib treatment, whereas that of liposomes was reduced. In accordance with the results of the cellular uptake studies, the anti-cancer activity of doxorubicin (DOX)-loaded EVs in HCC827 cells was significantly increased in the presence of gefitinib, whereas the activity of DOX-loaded liposomes was reduced. The digestion of EV proteins by trypsin did not affect uptake, suggesting that the cellular uptake of EVs might not be mediated by EV proteins. These results suggest that gefitinib can enhance cell-to-cell communication via EVs within the tumor microenvironment. In addition, EVs show potential as drug delivery vehicles in combination with gefitinib for the treatment of patients harboring EGFR-mutant NSCLC tumors.

Optimization of the method for analyzing endocytosis of fluorescently tagged molecules: Impact of incubation in the cell culture medium and cell surface wash with glycine-hydrochloric acid buffer

To obtain the therapeutic effect of biological medicines, such as proteins and nucleic acids, these medicines must achieve their intracellular target, such as the cytoplasm, and pass through biological membrane barriers. Endocytosis is an attractive route for the intracellular delivery of such drugs, and various endocytosis inhibitors have been used as tools to study the involvement of endocytosis in the cell internalization of delivery carriers. However, the specificity of these inhibitors has been insufficiently studied, and our preliminary tests could not detect the expected effect of the well-known endocytosis inhibitors. Therefore, the present study aimed to optimize the experimental conditions to precisely analyze cellular internalization via endocytosis. We first found that incubation of model molecules, such as transferrin (Tf) and cholera toxin subunit B (CTB), in cell culture medium (DMEM) could efficiently induce their internalization to HeLa cells compared to that in transport buffer (HBSS). Moreover, we clarified that cell surface wash with glycine-hydrochloric acid buffer before confocal microscopy and flow cytometry strengthened the intracellular fluorescence of Tf, CTB, and dextran tagged with fluorescent probes possibly via the neutralization of endosomal pH. Even under the optimized condition, however, the specificity of endocytosis inhibitors was disputable. The present study suggested the importance of the optimization of the study design with endocytosis inhibitors in analyzing cellular internalization.

Oligoarginine-Bearing Tandem Repeat Penetration-Accelerating Sequence Delivers Protein to Cytosol via Caveolae-Mediated Endocytosis

To facilitate the cytosolic delivery of larger molecules such as proteins, we developed a new cell-penetrating peptide sequence, named Pas2r12, consisting of a repeated Pas sequence (FFLIG-FFLIG) and d-dodeca-arginine (r12). This peptide significantly enhanced the cellular uptake and cytosolic release of enhanced green fluorescent protein and immunoglobulin G as cargos. We found that simply mixing Pas2r12 with cargos could generate cytosolic introducible forms. The cytosolic delivery of cargos by Pas2r12 was found to be an energy-requiring process, to rely on actin polymerization, and to be suppressed by caveolae-mediated endocytosis inhibitors (genistein and methyl-β-cyclodextrin) and small interfering RNA against caveolin-1. These results suggest that Pas2r12 enhances membrane penetration of cargos without the need for cross-linking and that caveolae-mediated endocytosis may be the route by which cytosolic delivery is enhanced.

Peptides with the multibasic cleavage site of the hemagglutinin from highly pathogenic influenza viruses act as cell-penetrating via binding to heparan sulfate and neuropilins

Cell-penetrating peptides (CPPs) show promise as an attractive delivery vehicle for therapeutic molecules-including nucleic acids, peptides, proteins, and even particulates-into several cell types. It is important to identify new CPPs and select the optimal CPP for each application, because CPPs differ in their internalized efficiency and internalization mechanisms. Here, we identified new CPPs derived from the peptides with the hemagglutinin cleavage site (pHACS) of highly pathogenic influenza viruses. We compared the potential of peptides from the pHACS of four subtypes of influenza A virus (H1, H3, H5, and H7) and an influenza B virus (H1-pHACS, H3-pHACS, H5-pHACS, H7-pHACS, and B-pHACS, respectively) to serve as CPPs. H5-pHACS and H7-pHACS, but not the other peptides, bound to mouse dendritic cells and human epithelial cells and were internalized efficiently into these cells. H5-pHACS and H7-pHACS required glycosaminoglycans, especially heparan sulfate and neuropilins, to bind to the cells. In addition, we designed a mutant H7-pHACS with superior cell-binding capability by changing a single amino acid. Furthermore, when conjugated with antigen, H5-pHACS and H7-pHACS induced antigen-specific antibody responses, demonstrating the usefulness of this antigen-delivery vehicle. Our results will improve our understanding of the mechanisms of CPPs and facilitate the development of novel drug-delivery vehicles designed to improve therapeutic efficacy.

Hydrogen sulfide donor micelles protect cardiomyocytes from ischemic cell death

Hydrogen sulfide, an important gaseous signaling molecule in the human body, is known to protect cardiomyocytes from ischemia, a condition characterized by insufficient oxygen supply to the cells. Here we show that a nanosized H₂S donor micelle releases H₂S intracellularly and prevents cardiomyocyte apoptosis in an in vitro ischemia model.

Potential Roles of GLUT12 for Glucose Sensing and Cellular Migration in MCF-7 Human Breast Cancer Cells Under High Glucose Conditions

BACKGROUND/AIM

Recent reports have indicated that hyperglycaemia is associated with breast cancer progression. High glucose conditions corresponding to hyperglycaemia significantly promote migration of MCF-7 human breast cancer cells, however, little is known about the mechanisms of glucose sensing for the acquisition of migratory properties by MCF-7 cells. This study investigated glucose sensing and mediation, which are responsible for the high motility of MCF-7 cells.

MATERIALS AND METHODS

We evaluated the migration of MCF-7 cells cultured in high glucose-containing medium and essential regulatory factors from the perspective of the glucose transport system.

RESULTS

We demonstrated that glucose transporter 12 (GLUT12) protein level increased in MCF-7 cells and co-localized with actin organization under high glucose conditions. Moreover, GLUT12-knockdown completely abrogated high glucose-induced migration, indicating that GLUT12 functionally participates in sensing high glucose concentrations.

CONCLUSION

GLUT12 plays a critical role in the model of breast cancer progression through high glucose concentrations.

In Situ Ligation of High- and Low-Affinity Ligands to Cell Surface Receptors Enables Highly Selective Recognition

This paper reports an entirely unexplored concept of simultaneously recognizing two receptors using high- and low-affinity ligands through ligating them in situ on the target cell surface. This de novo approach is inspired by the pretargeting strategy frequently applied in molecular imaging, and has now evolved as the basis of a new paradigm for visualizing target cells with a high imaging contrast. A distinct advantage of using a labeled low-affinity ligand such as glycan is that the excess labeled ligand can be washed away from the cells, whereas the ligand bound to the cell, even at the milli molar affinity level, can be anchored by a bioorthogonal reaction with a pretargeted high-affinity ligand on the surface. Consequently, nonspecific background is minimized, leading to improved imaging contrast. Importantly, despite previously unexplored for molecular imaging, a notoriously weak glycan/lectin interaction can now be utilized as a highly selective ligand to the targets.

Cell-Surface Interactions on Arginine-Rich Cell-Penetrating Peptides Allow for Multiplex Modes of Internalization

One of the recent hot topics in peptide-related chemical biology research is the potential of cell-penetrating peptides (CPPs). Owing to their ability to deliver exogenous molecules into cells easily and effectively, their flexible design that allows transporters to comprise various chemical structures and functions, and their potential in chemical and cell biology studies and clinical applications, CPPs have been attracting enormous interest among researchers in related fields. Consequently, publications on CPPs have increased significantly. Although there are many types of CPPs with different physicochemical properties and applications, arginine-rich CPPs, which include the human immunodeficiency virus type 1 (HIV-1) TAT peptide and oligoarginines, are among the most extensively employed and studied. Previous studies demonstrated the importance of the guanidino group in arginine, which confers flexibility in transporter design. Therefore, in addition to peptides, various transporters rich in guanidino groups, which do not necessarily share specific chemical and three-dimensional structures, have been developed. Typically, cell-penetrating transporters have 6-12 guanidino groups. Since the pK_a of the guanidino group in arginine is approximately 12.5, these molecules are highly basic and hydrophilic. Our group is interested in why these cationic molecules can penetrate cells. Understanding their mechanism of action should lead to the rational design of intracellular delivery systems that have high efficacy. Additionally, novel cellular uptake mechanisms may be elucidated during the course of these studies. Therefore, our group is trying to understand the basic aspects underlying the ability of these peptides to penetrate cells. Regarding the delivery of biopharmaceuticals including proteins and nucleic acids, achieving efficient and effective delivery to target organs and cells is one of the biggest challenges. Furthermore, when the target sites of these drug molecules are within cells, effective cell penetration becomes another obstacle. Cells are surrounded by a membrane that separates the inside of the cell from its outside. This barrier function is critical for keeping cellular contents inside cells, and without this, cells cannot function. Therefore, understanding the mechanism of action of CPPs is necessary to overcome these obstacles and will allow us not only to improve CPP-mediated delivery but also to create other types of intracellular delivery systems. In this Account, we summarize the current knowledge on the mechanisms of internalization of arginine-rich CPPs, from the viewpoints of both direct cell-membrane penetration (i.e., physicochemical aspects) and endocytic uptake (i.e., physiological aspects), and discuss the implications of this knowledge. We also discussed loosening of lipid packing as a factor to promote direct cell-membrane penetration.

Gefitinib Enhances Mitochondrial Biological Functions in NSCLCs with EGFR Mutations at a High Cell Density

BACKGROUND/AIM

Gefitinib is a tyrosine kinase inhibitor of epidermal growth factor receptor (EGFR) and has been approved for the treatment of non-small cell lung cancers (NSCLCs) with EGFR mutations. Here we demonstrated that gefitinib induced a significantly enhanced biological activity of succinate-tetrazolium reductase (STR) in mitochondria and mitochondrial membrane potential in HCC827 cells (EGFR mutation NSCLCs, sensitive to gefitinib) at a high cell density.

MATERIALS AND METHODS

We assessed the biological activity (STR, mitochondrial membrane potential, expression level of Bcl-2 family proteins) of gefitinib on NSCLCs at different cell densities.

RESULTS

The 3D cell culture experiments showed the enhanced mitochondrial biological activity in clustered cell culture treated with gefitinib. Interestingly, the expression levels of Bcl-x_L and Bax, were affected by the cellular number and gefitinib treatment. We also found that gefitinib prevented additive anticancer activity in the combinational treatment with doxorubicin, which induces mitochondria-dependent apoptotic cell death.

CONCLUSION

Our results indicate that gefitinib may work as a mitochondrial protector against combinational treatment with mitochondria-dependent anticancer agents in high-cell-density.

Receptor clustering and activation by multivalent interaction through recognition peptides presented on exosomes

We demonstrate a novel system for inducing clustering of cell surface receptors via recognition peptide segments displayed on exosomes, leading to receptor activation. With this system, targeting of receptor-expressing cells and facilitation of the endocytic uptake of exosomes, which contained the anti-cancer protein saporin, were successfully achieved, leading to cell death.

Vectorization of biomacromolecules into cells using extracellular vesicles with enhanced internalization induced by macropinocytosis

Extracellular vesicles (EVs, exosomes) are approximately 30- to 200-nm-long vesicles that have received increased attention due to their role in cell-to-cell communication. Although EVs are highly anticipated to be a next-generation intracellular delivery tool because of their pharmaceutical advantages, including non-immunogenicity, their cellular uptake efficacy is low because of the repulsion of EVs and negatively charged cell membranes and size limitations in endocytosis. Here, we demonstrate a methodology for achieving enhanced cellular EV uptake using arginine-rich cell-penetrating peptides (CPPs) to induce active macropinocytosis. The induction of macropinocytosis via a simple modification to the exosomal membrane using stearylated octaarginine, which is a representative CPP, significantly enhanced the cellular EV uptake efficacy. Consequently, effective EV-based intracellular delivery of an artificially encapsulated ribosome-inactivating protein, saporin, in EVs was attained.

Calmodulin EF-hand peptides as Ca2+ -switchable recognition tags

Calmodulin is a representative calcium-binding protein comprised of four Ca²⁺ -binding motifs with a helix-loop-helix structure (EF-hands). In this study, we clarified the potential of peptide segments derived from the third and fourth EF-hands (EF3 and EF4) to act as recognition tags. Through an analysis of the mode of disulfide formation among cysteines inserted at the N- or C-terminus of these peptide segments, EF3 and EF4 peptides were suggested to form a heterodimer with a topology similar to that in the wild-type protein. Heterodimer formation was shown to be a function of the Ca²⁺ concentration, suggesting that these structures may be used as Ca²⁺ -switchable recognition tags. An example of an "EF-tag" system involving the membrane fusion of liposomes decorated with EF3 and EF4 peptides is presented. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2016.

[Creation of artificial receptors activated by coiled-coil peptides and cellular regulation]

Exploiting the ability of coiled-coil peptides to induce dimer formation, we designed an artificial epidermal growth factor receptor (EGFR) in which dimerization is essential for increasing the tyrosine kinase activity of its intracellular domain. Using leucine-zipper coiled-coil peptides, the surface-exposed E3 ((EIAALEK)3) tag sequence was fused with EGFR (E3-EGFR) lacking domains I-III and a part of IV, which participate in dimerization of EGFR after binding to natural ligand (that is, epidermal growth factor). To dimerize E3-EGFR we synthesized conjugates of two K4 ((KIAALKE)4) peptides, called K4-conjugates, with linker lengths approximately 10 angstrom that mimic the distance of EGFR dimerization. Receptor phosphorylation of E3-EGFR was found to increase within 5 min in CHO cells expressing E3-EGFR after treatment with K4 conjugates. Increased lamellipodia formation and migration of the cells was also observed when treated with the artificial ligands. This receptor model can be applied to a wide variety of membrane-associated proteins to control cellular processes and to elucidate the functional mechanisms of these proteins using chemical biology.

Development of a novel nanoparticle by dual modification with the pluripotential cell-penetrating peptide PepFect6 for cellular uptake, endosomal escape, and decondensation of an siRNA core complex

Development of novel devices for effective nucleotide release from nanoparticles is required to improve the functionality of nonviral delivery systems, because decondensation of nucleotide/polycation complexes is considered as a key step for cytoplasmic delivery of nucleotides. Previously, PepFect6 (PF6) comprised chloroquine analog moieties and a stearylated cell-penetrating peptide to facilitate endosomal escape and cellular uptake, respectively, was developed as a device for efficient siRNA delivery. As PF6 contains bulky chloroquine analog moieties, the polyplexes are expected to be loose structure, which facilitates decondensation. In the present study, siRNA was electrostatically condensed by PF6, and the PF6/siRNA complexes were coated with lipid membranes. The surface of the nanoparticles encapsulating the PF6/siRNA core (PF6-NP) was modified with PF6 for endosomal escape (PF6/PF6-NP). The RNAi effect of PF6/PF6-NP was compared with those of stearylated cell-penetrating peptide octaarginine (R8)-modified PF6-NP, R8-modified nanoparticles encapsulating the R8/siRNA core (R8-NP) and PF6-modified R8-NP. Nanoparticles encapsulating the PF6 polyplex, especially PF/PF-NP, showed a significant knockdown effect on luciferase activity of B16-F1 cells stably expressing luciferase. siRNA was widely distributed within the cytoplasm after transfection of the nanoparticles encapsulating the PF6 polyplex, while siRNA encapsulated in the R8-presenting nanoparticles was localized within the nuclei. Thus, the siRNA distribution was dependent on the manner of peptide-modification. In conclusion, we have successfully developed PF6/PF6-NP exhibiting a potent RNAi effect resulting from high cellular uptake, efficient endosomal escape and decondensation of the polyplexes based on the multifunctional cell penetrating peptide PF6. PF6 is therefore a useful pluripotential device for siRNA delivery.

Syndecan-4 Is a Receptor for Clathrin-Mediated Endocytosis of Arginine-Rich Cell-Penetrating Peptides

Arginine-rich cell-penetrating peptides (CPPs) such as Tat and oligoarginine peptides have been widely used as carriers for intracellular delivery of bioactive molecules. Despite accumulating evidence for involvement of endocytosis in the cellular uptake of arginine-rich CPPs, the primary cell-surface receptors for these peptide carriers that would initiate endocytic processes leading to intracellular delivery of bioactive cargoes have remained poorly understood. Our previous attempt to identify membrane receptors for octa-arginine (R8) peptide, one of the representative arginine-rich CPPs, using the photo-cross-linking probe bearing a photoreactive diazirine was not successful due to considerable amounts of cellular proteins nonspecifically bound to the affinity beads. To address this issue, here we developed a photo-cross-linking probe in which a cleavable linker of a diazobenzene moiety was employed to allow selective elution of cross-linked proteins by reducing agent-mediated cleavage. We demonstrated that introduction of the diazobenzene moiety into the photoaffinity probe enables efficient purification of cross-linked proteins with significant reduction of nonspecific binding proteins, leading to successful identification of 17 membrane-associated proteins that would interact with R8 peptide. RNAi-mediated knockdown experiments in combination with the pharmacological inhibitors revealed that, among the proteins identified, syndecan-4, one of the heparan sulfate proteoglycans, is an endogenous membrane-associated receptor for the cellular uptake of R8 peptide via clathrin-mediated endocytosis. This syndecan-4-dependent pathway was also involved in the intracellular delivery of bioactive proteins mediated by R8 peptide. These results reveal that syndecan-4 is a primary cell-surface target for R8 peptide that allows intracellular delivery of bioactive cargo molecules via clathrin-mediated endocytosis.