Endocytic Trafficking of Nanoparticles Delivered by Cell-penetrating Peptides Comprised of Nona-arginine and a Penetration Accelerating Sequence

Multi-Functional Polymer Nanoparticles with Enhanced Adipocyte Uptake and Adipocytolytic Efficacy

Multi-functional polymer nanoparticles have been widely utilized to improve cellular uptake and enhance therapeutic efficacy. In this study, it is hypothesized that the cellular uptake of poly(D,L-lactide-co-glycolide) (PLG) nanoparticles loaded with calcium carbonate minerals into adipocytes can be improved by covalent modification with nona-arginine (R9 ) peptide. It is further hypothesized that the internalization mechanism of R9 -modified PLG nanoparticles by adipocytes may be contingent on the concentration of R9 peptide present in the nanoparticles. R9 -modified PLG nanoparticles followed the direct penetration mechanism when the concentration of R9 peptide in the nanoparticles reached 38 µM. Notably, macropinocytosis is the major endocytic mechanism when the R9 peptide concentration is ≤ 26 µM. The endocytic uptake of the nanoparticles effectively generated carbon dioxide gas at an endosomal pH, resulting in significant adipocytolytic effects in vitro, which are further supported by the findings in an obese mouse model induced by high-fat diet. Gas-generating PLG nanoparticles, modified with R9 peptide, demonstrated localized reduction of adipose tissue (reduction of 13.1%) after subcutaneous injection without significant side effects. These findings highlight the potential of multi-functional polymer nanoparticles for the development of effective and targeted fat reduction techniques, addressing both health and cosmetic considerations.

PepFect14 mediates the delivery of mRNA into human primary keratinocytes and in vivo

mRNA-based vaccines and candidate therapeutics have great potential in various medical fields. For the delivery of mRNA into target cells and tissues, lipid formulations are often employed. However, this approach could cause the activation of immune responses, making it unsuitable for the treatment of inflammatory conditions. Therefore, alternative delivery systems are highly demanded. In this study, we evaluated the transport efficiency and characteristics of cell-penetrating peptide PepFect14 (PF14) and mRNA nanoparticles in the presence of different additives. Our results show that all PF14-mRNA formulations entered cultured cells, while calcium chloride enhanced the transport and production of the encoded protein in HeLa and HaCaT cell lines, and polysorbate 80 did so in primary human keratinocytes. All formulations had similar physical properties and did not remarkably affect cell viability. By selectively blocking endocytosis pathways, we show that PF14-mRNA nanoparticles primarily entered HeLa cells via macropinocytosis and HaCaT cells via both macropinocytosis and clathrin-mediated endocytosis, while none of the blockers significantly affected the delivery into primary keratinocytes. Finally, subcutaneous injection of PF14-mRNA nanoparticles before inducing mouse irritant contact dermatitis resulted in the expression of a reporter protein without provoking harmful immune responses in the skin. Together, our findings suggest that PF14-mRNA nanoparticles have the potential for developing mRNA-based therapeutics for treating inflammatory skin conditions.

Intracellular lipophilic network transformation induced by protease-specific endocytosis of fluorescent Au nanoclusters

The understanding of the endocytosis process of internalized nanomedicines through membrane biomarker is essential for the development of molecular-specific nanomedicines. In various recent reports, the metalloproteases have been identified as important markers during the metastasis of cancer cells. In particular, MT1-MMP has provoked concern due to its protease activity in the degradation of the extracellular matrix adjacent to tumors. Thus, in the current work, we have applied fluorescent Au nanoclusters which present strong resistance to chemical quenching to the investigation of MT1-MMP-mediated endocytosis. We synthesized protein-based Au nanocluster (PAuNC) and MT1-MMP-specific peptide was conjugated with PAuNC (pPAuNC) for monitoring protease-mediated endocytosis. The fluorescence capacity of pPAuNC was investigated and MT1-MMP-mediated intracellular uptake of pPAuNC was subsequently confirmed by a co-localization analysis using confocal microscopy and molecular competition test. Furthermore, we confirmed a change in the intracellular lipophilic network after an endocytosis event of pPAuNC. The identical lipophilic network change did not occur with the endocytosis of bare PAuNC. By classification of the branched network between the lipophilic organelles at the nanoscale, the image-based analysis of cell organelle networking allowed the evaluation of nanoparticle internalization and impaired cellular components after intracellular accumulation at a single-cell level. Our analyses suggest a methodology to achieve a better understanding of the mechanism by which nanoparticles enter cells.

Cell-Penetrating Peptides for Use in Development of Transgenic Plants

Genetically modified plants and crops can contribute to remarkable increase in global food supply, with improved yield and resistance to plant diseases or insect pests. The development of biotechnology introducing exogenous nucleic acids in transgenic plants is important for plant health management. Different genetic engineering methods for DNA delivery, such as biolistic methods, Agrobacterium tumefaciens-mediated transformation, and other physicochemical methods have been developed to improve translocation across the plasma membrane and cell wall in plants. Recently, the peptide-based gene delivery system, mediated by cell-penetrating peptides (CPPs), has been regarded as a promising non-viral tool for efficient and stable gene transfection into both animal and plant cells. CPPs are short peptides with diverse sequences and functionalities, capable of agitating plasma membrane and entering cells. Here, we highlight recent research and ideas on diverse types of CPPs, which have been applied in DNA delivery in plants. Various basic, amphipathic, cyclic, and branched CPPs were designed, and modifications of functional groups were performed to enhance DNA interaction and stabilization in transgenesis. CPPs were able to carry cargoes in either a covalent or noncovalent manner and to internalize CPP/cargo complexes into cells by either direct membrane translocation or endocytosis. Importantly, subcellular targets of CPP-mediated nucleic acid delivery were reviewed. CPPs offer transfection strategies and influence transgene expression at subcellular localizations, such as in plastids, mitochondria, and the nucleus. In summary, the technology of CPP-mediated gene delivery provides a potent and useful tool to genetically modified plants and crops of the future.

Novel branched amphiphilic peptides for nucleic acids delivery

Highly efficient and safe non-viral vectors for nucleic acids delivery have attracted much attention due to their potential applications in gene therapy, gene editing and vaccination against infectious diseases, and various materials have been investigated and designed as delivery vectors. Herein, we designed a series of branched amphiphilic peptides (BAPs) and tested their applications as pDNA/mRNA delivery vectors. The BAP structure was inspired by the phospholipids, in which lysine oligomers were used as the "polar head", segments containing phenylalanine, histidine and leucine were used as the "hydrophobic tails", and a lysine residue was used as the branching point. By comparing the gel retardation, particle sizes and zeta potentials of the BAP/pDNA complexes of the short-branch BAPs (BAP-V1 ∼ BAP-V4), we determined the optimal lysine oligomer was K₆. However, their cell transfection efficiencies were not satisfactory, and thus three long-branch BAPs (BAP-V5 ∼ BAP-V7) were further designed. In these long-branch BAPs, more hydrophobic residues were added and the overall amphiphilicity increased accordingly. The results showed that these three BAPs could effectively compact the nucleic acids, including both pDNA and mRNA, and all could transfect nucleic acids into HEK 293 cells, with low cytotoxicity. Among the three long-branch BAPs, BAP-V7 (bis(FFLFFHHH)-K-K₆) showed the best transfection efficiency at N/P = 10, which was better than the commercial transfection reagent PEI-25 K. These results indicate that increased amphiphilicity would also benefit for BAP mediated nucleic acid delivery. The designed BAPs provide more documents of such novel type of nucleic acids delivery vectors, which is worth of further investigation as a new gene theranostic platforms.

Spatiotemporal three-dimensional transport dynamics of endocytic cargos and their physical regulations in cells

Intracellular transport, regulated by complex cytoarchitectures and active driving forces, is crucial for biomolecule translocations and relates to many cellular functions. Despite extensive knowledge obtained from two-dimensional (2D) experiments, the real three-dimensional (3D) spatiotemporal characteristics of intracellular transport is still unclear. With 3D single-particle tracking, we comprehensively studied the transport dynamics of endocytic cargos. With varying timescale, the intracellular transport changes from thermal-dominated 3D-constrained motion to active-dominated quasi-2D motion. Spatially, the lateral motion is heterogeneous with peripheral regions being faster than perinuclear regions, while the axial motion is homogeneous across the cells. We further confirmed that such anisotropy and heterogeneity of vesicle transport result from actively directed motion on microtubules. Strikingly, inside the vesicles, we observed endocytic nanoparticles make diffusive motions on their inner membranes when microtubules are absent, suggesting endocytic cargos are normally localized at the inner vesicle membranes through a physical connection to the microtubules outside during transport.

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Endocytic transport changes from 3D-constrained to quasi-2D motions with timescales

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Lateral motion is heterogeneous while axial motion is homogeneous across the cells

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Microtubules cause the anisotropy and heterogeneity of vesicle transport

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Endocytic particles make diffusive motion on the inner membrane of vesicles

Amphiphilic Cell-Penetrating Peptides Containing Natural and Unnatural Amino Acids as Drug Delivery Agents

A series of cyclic peptides, [(DipR)(WR)₄], [(DipR)₂(WR)₃], [(DipR)₃(WR)₂], [(DipR)₄(WR)], and [DipR]₅, and their linear counterparts containing arginine (R) as positively charged residues and tryptophan (W) or diphenylalanine (Dip) as hydrophobic residues, were synthesized and evaluated for their molecular transporter efficiency. The in vitro cytotoxicity of the synthesized peptides was determined in human epithelial ovary adenocarcinoma cells (SK-OV-3), human lymphoblast peripheral blood cells (CCRF-CEM), human embryonic epithelial kidney healthy cells (HEK-293), human epithelial mammary gland adenocarcinoma cells (MDA-MB-468), pig epithelial kidney normal cells (LLC-PK1), and human epithelial fibroblast uterine sarcoma cells (MES-SA). A concentration of 5–10 µM and 3 h incubation were selected in uptake studies. The cellular uptake of a fluorescent-labeled phosphopeptide, stavudine, lamivudine, emtricitabine, and siRNA was determined in the presence of peptides via flow cytometry. Among the peptides, [DipR]₅ (10 µM) was found to be the most efficient transporter and significantly improved the uptake of F’-GpYEEI, i.e., by approximately 130-fold after 3 h incubation in CCRF-CEM cells. Confocal microscopy further confirmed the improved delivery of fluorescent-labeled [DipR]₅ (F’-[K(DipR)₅]) alone and F’-GpYEEI in the presence of [DipR]₅ in MDA-MB-231 cells. The uptake of fluorescent-labeled siRNA (F’-siRNA) in the presence of [DipR]₅ with N/P ratios of 10 and 20 was found to be 30- and 50-fold higher, respectively, compared with the cells exposed to F’-siRNA alone. The presence of endocytosis inhibitors, i.e., nystatin, chlorpromazine, chloroquine, and methyl β-cyclodextrin, did not completely inhibit the cellular uptake of F’-[K(DipR)₅] alone or F’-GpYEEI in the presence of [DipR]₅, suggesting that a combination of mechanisms contributes to uptake. Circular dichroism was utilized to determine the secondary structure, while transmission electron microscopy was used to evaluate the particle sizes and morphology of the peptides. The data suggest the remarkable membrane transporter property of [DipR]₅ for improving the delivery of various small molecules and cell-impermeable negatively charged molecules (e.g., siRNA and phosphopeptide).

Bio-Membrane Internalization Mechanisms of Arginine-Rich Cell-Penetrating Peptides in Various Species

Recently, membrane-active peptides or proteins that include antimicrobial peptides (AMPs), cytolytic proteins, and cell-penetrating peptides (CPPs) have attracted attention due to their potential applications in the biomedical field. Among them, CPPs have been regarded as a potent drug/molecules delivery system. Various cargoes, such as DNAs, RNAs, bioactive proteins/peptides, nanoparticles and drugs, can be carried by CPPs and delivered into cells in either covalent or noncovalent manners. Here, we focused on four arginine-rich CPPs and reviewed the mechanisms that these CPPs used for intracellular uptake across cellular plasma membranes. The varying transduction efficiencies of them alone or with cargoes were discussed, and the membrane permeability was also expounded for CPP/cargoes delivery in various species. Direct membrane translocation (penetration) and endocytosis are two principal mechanisms for arginine-rich CPPs mediated cargo delivery. Furthermore, the amino acid sequence is the primary key factor that determines the cellular internalization mechanism. Importantly, the non-cytotoxic nature and the wide applicability make CPPs a trending tool for cellular delivery.

Apoptin gene delivery by a PAMAM dendrimer modified with a nuclear localization signal peptide as a gene carrier for brain cancer therapy

In this study, we aimed to synthesize PAMAMG3 derivatives (PAMAMG3-KRRR and PAMAMG3-HKRRR), using KRRR peptides as a nuclear localization signal and introduced histidine residues into the KRRR-grafted PAMAMG3 for delivering a therapeutic, carcinoma cell-selective apoptosis gene, apoptin into human primary glioma (GBL-14) cells and human dermal fibroblasts. We examined their cytotoxicity and gene expression using luciferase activity and enhanced green fluorescent protein PAMAMG3 derivatives in both cell lines. We treated cells with PAMAMG3 derivative/apoptin complexes and investigated their intracellular distribution using confocal microscopy. The PAMAMG3-KRRR and PAMAMG3-HKRRR dendrimers were found to escape from endolysosomes into the cytosol. The JC-1 assay, glutathione levels, and Annexin V staining results showed that apoptin triggered cell death in GBL-14 cells. Overall, these findings indicated that the PAMAMG3-HKRRR/apoptin complex is a potential candidate for an effective nonviral gene delivery system for brain tumor therapy in vitro.

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

Despite the well-recognized clinical success of therapeutic proteins, especially antibodies, their inability to penetrate the cell membrane restricts them to secretory extracellular or membrane-associated targets. Developing a direct cytosolic protein delivery system would offer unique opportunities for intracellular target-related therapeutic proteins. Here, we generated a supercharged polypeptide (SCP) with high cellular uptake efficiency, endosomal escape ability, and good biosafety and developed an SCP with an unnatural amino acid containing the phenylboronic acid (PBA) group, called PBA-SCP. PBA-SCP is capable of potently delivering proteins with various isoelectric points and molecular sizes into the cytosol of living cells without affecting their bioactivities. Importantly, cytosolically delivered antibodies remain functional and are capable of targeting, labeling, and manipulating diverse intracellular antigens. This study demonstrates an efficient and versatile intracellular protein delivery platform, especially for antibodies, and provides new possibilities for expanding protein-based therapeutics to intracellular "undruggable" targets.

Protein Delivery: If Your GFP (or Other Small Protein) Is in the Cytosol, It Will Also Be in the Nucleus

Intracellular protein delivery is a transformative tool for biologics research and medicine. Delivery into the cytosol allows proteins to diffuse throughout the cell and access subcellular organelles. Inefficient delivery caused by endosomal entrapment is often misidentified as cytosolic delivery. This inaccuracy muddles what should be a key checkpoint in assessing delivery efficiency. Green fluorescent protein (GFP) is a robust cargo small enough to passively diffuse from the cytosol into the nucleus. Fluorescence of GFP in the nucleus is a direct readout for cytosolic access and effective delivery. Here, we highlight recent examples from the literature for the accurate assessment of cytosolic protein delivery using GFP fluorescence in the cytosol and nucleus.

Exploiting the anticancer effects of a nitrogen bisphosphonate nanomedicine for glioblastoma multiforme

Glioblastoma multiforme (GBM) is an incurable aggressive brain cancer in which current treatment strategies have demonstrated limited survival benefit. In recent years, nitrogen-containing bisphosphonates (N-BPs) have demonstrated direct anticancer effects in a number of tumour types including GBM. In this study, a nano-formulation with the RALA peptide was used to complex the N-BP, alendronate (ALN) into nanoparticles (NPs) < 200 nm for optimal endocytic uptake. Fluorescently labelled AlexaFluor®647 Risedronate was used as a fluorescent analogue to visualise the intracellular delivery of N-BPs in both LN229 and T98G GBM cells. RALA NPs were effectively taken up by GBM where a dose-dependent response was evidenced with potentiation factors of 14.96 and 13.4 relative to ALN alone after 72 h in LN229 and T98G cells, respectively. Furthermore, RALA/ALN NPs at the IC_50, significantly decreased colony formation, induced apoptosis and slowed spheroid growth in vitro. In addition, H-Ras membrane localisation was significantly reduced in the RALA/ALN groups compared to ALN or controls, indicative of prenylation inhibition. The RALA/ALN NPs were lyophilised to enhance stability without compromising the physiochemical properties necessary for functionality, highlighting the suitability of the NPs for scale-up and in vivo application. Collectively, these data show the significant potential of RALA/ALN NPs as novel therapeutics in the treatment of GBM.

Cell-Penetrating Peptides as a Potential Drug Delivery System for Effective Treatment of Diabetes

BACKGROUND/PURPOSE

Type 2 diabetes (T2D) is characterized by hyperglycemia resulting from the body's inability to produce and/or use insulin. Patients with T2D often have hyperinsulinemia, dyslipidemia, inflammation, and oxidative stress, which then lead to hypertension, chronic kidney disease, cardiovascular disease, and increased risk of morbidity and mortality (9th leading cause globally). Insulin and related pharmacological therapies are widely used to manage T2D, despite their limitations. Efficient drug delivery systems (DDS) that control drug kinetics may decrease side effects, allow for efficient targeting, and increase the bioavailability of drugs to achieve maximum therapeutic benefits. Thus, the development of effective DDS is crucial to beat diabetes.

METHODS

Here, we introduced a highly bioavailable vector, cell-penetrating peptides (CPPs), as a powerful DDS to overcome limitations of free drug administration.

RESULTS

CPPs are short peptides that serve as a potent tool for delivering therapeutic agents across cell membranes. Various cargoes, including proteins, DNA, RNA, liposomes, therapeutic molecules, and nanomaterials, generally retain their bioactivity upon entering cells. The mechanisms of CPPs/cargoes intracellular entry are classified into two parts: endocytic pathways and direct membrane translocation. In this article, we focus on the applications of CPPs/therapeutic agents in the treatment of diabetes. Hypoglycemic drugs with CPPs intervention can enhance therapeutic effectiveness, and CPP-mediated drug delivery can facilitate the actions of insulin. Numerous studies indicate that CPPs can effectively deliver insulin, produce synergistic effects with immunosuppressants for successful pancreatic islet xenotransplantation, prolong pharmacokinetics, and retard diabetic nephropathy.

CONCLUSION

We suggest that CPPs can be a new generation of drug delivery systems for effective treatment and management of diabetes and diabetes-associated complications.

Predicting cell-penetrating peptides using machine learning algorithms and navigating in their chemical space

Cell-penetrating peptides (CPPs) are naturally able to cross the lipid bilayer membrane that protects cells. These peptides share common structural and physicochemical properties and show different pharmaceutical applications, among which drug delivery is the most important. Due to their ability to cross the membranes by pulling high-molecular-weight polar molecules, they are termed Trojan horses. In this study, we proposed a machine learning (ML)-based framework named BChemRF-CPPred (beyond chemical rules-based framework for CPP prediction) that uses an artificial neural network, a support vector machine, and a Gaussian process classifier to differentiate CPPs from non-CPPs, using structure- and sequence-based descriptors extracted from PDB and FASTA formats. The performance of our algorithm was evaluated by tenfold cross-validation and compared with those of previously reported prediction tools using an independent dataset. The BChemRF-CPPred satisfactorily identified CPP-like structures using natural and synthetic modified peptide libraries and also obtained better performance than those of previously reported ML-based algorithms, reaching the independent test accuracy of 90.66% (AUC = 0.9365) for PDB, and an accuracy of 86.5% (AUC = 0.9216) for FASTA input. Moreover, our analyses of the CPP chemical space demonstrated that these peptides break some molecular rules related to the prediction of permeability of therapeutic molecules in cell membranes. This is the first comprehensive analysis to predict synthetic and natural CPP structures and to evaluate their chemical space using an ML-based framework. Our algorithm is freely available for academic use at http://comptools.linc.ufpa.br/BChemRF-CPPred .

Intracellular Uptake Mechanism of Bioorthogonally Conjugated Nanoparticles on Metabolically Engineered Mesenchymal Stem Cells

Nanoparticles have been used for effectively delivering imaging agents and therapeutic drugs into stem cells. However, nanoparticles are not sufficiently internalized into stem cells; thus, new delivery method of nanoparticles into stem cells is urgently needed. Herein, we develop bicyclo[6.1.0]nonyne (BCN)-conjugated gold nanoparticles (BCN-AuNPs), which can be bioorthogonally conjugated to azide (-N₃) groups on the surface of metabolically engineered stem cells via bioorthogonal click chemistry. For incorporating azide groups on the cell surface, first, human adipose-derived mesenchymal stem cells (hMSCs) were metabolically engineered with N-azidoacetylmannosamine-tetraacylated (Ac₄ManNAz). Second, clickable BCN-AuNPs were bioorthogonally conjugated to azide groups on Ac₄ManNAz-treated hMSCs. Importantly, a large amount of BCN-AuNPs was specifically conjugated to metabolically engineered hMSCs and then internalized rapidly into stem cells through membrane turnover mechanism, compared to the conventional nanoparticle-derived endocytosis mechanism. Furthermore, BCN-AuNPs entrapped in endosomal/lysosomal compartment could escape efficiently to the cytoplasm of metabolically engineered stem cells. Finally, BCN-AuNPs in stem cells were very safe, and they did not affect stem cell functions, such as self-renewal and differentiation capacity. These bioorthogonally conjugated nanoparticles on metabolically engineered stem cells can enhance the cellular uptake of nanoparticles via bioorthogonal conjugation mechanism.

Dual-Modified Liposome for Targeted and Enhanced Gene Delivery into Mice Brain

The development of neuropharmaceutical gene delivery systems requires strategies to obtain efficient and effective brain targeting as well as blood-brain barrier (BBB) permeability. A brain-targeted gene delivery system based on a transferrin (Tf) and cell-penetrating peptide (CPP) dual-functionalized liposome, CPP-Tf-liposome, was designed and investigated for crossing BBB and permeating into the brain. We selected three sequences of CPPs [melittin, Kaposi fibroblast growth factor (kFGF), and penetration accelerating sequence-R8] and compared their ability to internalize into the cells and, subsequently, improve the transfection efficiency. Study of intracellular uptake indicated that liposomal penetration into bEnd.3 cells, primary astrocytes, and primary neurons occurred through multiple endocytosis pathways and surface modification with Tf and CPP enhanced the transfection efficiency of the nanoparticles. A coculture in vitro BBB model reproducing the in vivo anatomophysiological complexity of the biologic barrier was developed to characterize the penetrating properties of these designed liposomes. The dual-functionalized liposomes effectively crossed the in vitro barrier model followed by transfecting primary neurons. Liposome tissue distribution in vivo indicated superior ability of kFGF-Tf-liposomes to overcome BBB and reach brain of the mice after single intravenous administration. These findings demonstrate the feasibility of using strategically designed liposomes by combining Tf receptor targeting with enhanced cell penetration as a potential brain gene delivery vector. SIGNIFICANCE STATEMENT: Rational synthesis of efficient brain-targeted gene carrier included modification of liposomes with a target-specific ligand, transferrin, and with cell-penetrating peptide to enhance cellular internalization. Our study used an in vitro triple coculture blood-brain barrier (BBB) model as a tool to characterize the permeability across BBB and functionality of designed liposomes prior to in vivo biodistribution studies. Our study demonstrated that rational design and characterization of BBB permeability are efficient strategies for development of brain-targeted gene carriers.

Delivery of pDNA to lung epithelial cells using PLGA nanoparticles formulated with a cell-penetrating peptide: understanding the intracellular fate

The combination of nanoparticles (NPs) and cell-penetrating peptide (CPP) represents a new opportunity to develop plasmid DNA (pDNA) delivery systems with desirable properties for lung delivery. In this study, poly(lactide-co-glycolide) (PLGA) NPs containing pDNA were formulated with and without CPP using a double-emulsion technique. NPs were characterized in regards of size, surface charge, release profile, pDNA encapsulation efficiency and pDNA integrity. Cellular uptake, intracellular trafficking, uptake mechanism and pDNA expression were assessed in both A549 and Beas-2B cells. Manufactured PLGA-NPs efficiently encapsulated pDNA with approximately 50% released in the first 24 h of incubation. Addition of CPP was essential to promote NP internalization in both cell lines, with 83.85 ± 1.2% and 96.76 ± 1.7% of Beas-2B and A549 cells, respectively, with internalized NP-DNA-CPP after 3 h of incubation. Internalization appears to occur mainly via clathrin-mediated endocytosis, with other pathways also being used by the different cell lines. An endosomal-escape mechanism seems to happen in both cell lines, and eGFP expression was observed in Beas-2B after 96 h of incubation. In summary, the NP-DNA-CPP delivery system efficiently encapsulated and protected pDNA structure and is being investigated as a promising tool for gene delivery to the lungs.

Nanodiamond uptake in colon cancer cells: the influence of direction and trypsin-EDTA treatment

Nanoparticles are routinely used in cell biology. They deliver drugs or function as labels or sensors. For many of these applications it is essential that the nanoparticles enter the cells. While some cell types readily ingest all kinds of particles, others just don't. We report that uptake can be enhanced for some cells if the particles are administered from the basolateral side of the cells (in this case from below). Compared to apical uptake (from above), we report an 8-fold increase in the number of fluorescent nanodiamonds internalized by the colon cancer cell line HT29. Up to 96% of the cells treated by a modified protocol contain at least one nanodiamond, whereas in the control group we could observe nanodiamonds in less than half of the cells. We were also able to show that simple treatment of cell clusters with trypsin-EDTA leads to the same enhancement of the nanodiamond uptake as seeding the cells on top of the nanoparticles. Although our study is focused on nanodiamonds in HT29 cells, we believe that this method could also be applicable for other nanoparticles and cells with a specific directionality.

Polyhistidine facilitates direct membrane translocation of cell-penetrating peptides into cells

The bovine lactoferricin L6 (RRWQWR) has been previously identified as a novel cell-penetrating peptide (CPP) that is able to efficiently internalize into human cells. L6 interacts with quantum dots (QDs) noncovalently to generate stable L6/QD complexes that enter cells by endocytosis. In this study, we demonstrate a modified L6 (HL6; CHHHHHRRWQWRHHHHHC), in which short polyhistidine peptides are introduced into both flanks of L6, has enhanced cell-penetrating ability in human bronchoalveolar carcinoma A549 cells. The mechanism of cellular uptake of HL6/QD complexes is primarily direct membrane translocation rather than endocytosis. Dimethyl sulfoxide (DMSO), but not pyrenebutyrate (PB), ethanol, oleic acid, or 1,2-benzisothiazol-3(2 H)-one (BIT), slightly enhances HL6-mediated protein transduction efficiency. Neither HL6 nor HL6/QD complexes are cytotoxic to A549 or HeLa cells. These results indicate that HL6 could be a more efficient drug carrier than L6 for biomedical as well as biotechnological applications, and that the function of polyhistidine peptides is critical to CPP-mediated protein transduction.

A Delivery System for Oral Administration of Proteins/Peptides Through Bile Acid Transport Channels

Proteins and peptides are poorly absorbed via oral administration because of the gastrointestinal tract environment and lysosomal digestion after apical endocytosis. A delivery system, consisting of a deoxycholic acid-conjugated nanometer-sized carrier, may enhance the absorption of proteins in the intestine via the bile acid pathway. Deoxycholic acid is first conjugated to chitosan. Liposomes are then prepared and loaded with the model drug insulin. Finally, the conjugates are bound to the liposome surface to form deoxycholic acid and chitosan conjugate-modified liposomes (DC-LIPs). This study demonstrates that DC-LIPs can promote the intestinal absorption of insulin via the apical sodium-dependent bile acid transporter, based on observing fluorescently stained tissue slices of the rat small intestine and a Caco-2 cell uptake experiment. Images of intestinal slices revealed that excellent absorption of DC-LIPs is achieved via apical sodium-dependent bile acid transporter, and a flow cytometry experiment proved that DC-LIPs are a highly efficient delivery carrier. Caco-2 cells were also used to study the lysosome escape ability of DC-LIPs. We learned from confocal microscopy photographs that DC-LIPs can protect their contents from being destroyed by the lysosome. Finally, according to pharmacokinetic analyses, insulin-loaded DC-LIPs show a significant hypoglycemic effect with an oral bioavailability of 16.1% in rats with type I diabetes.

Synthesis of the Anionic Hydroxypropyl-β-cyclodextrin:Poly(decamethylenephosphate) Polyrotaxane and Evaluation of its Cholesterol Efflux Potential in Niemann-Pick C1 Cells

Niemann-Pick type C disease (NPC) is a lysosomal storage disease that is characterized by a progressive accumulation of unesterified cholesterol in the lysosomes leading to organ damage from cell dysfunction. Hydroxypropyl-β-cyclodextrin (HP-β-CD) is an attractive drug candidate for treating NPC, as it diminishes cholesterol accumulation in NPC cells. Systemic HP-β-CD treatment, however, is limited by rapid renal clearance. We designed a new anionic HP-β-CD polyrotaxane to act as a slow release formulation based on a polyalkylene phosphate core to improve the pharmacokinetics. The polyalkylene phosphate comprises hydrophobic decamethylene spacers linked by biodegradable anionic phosphodiester bonds. HP-β-CD was threaded onto this polymer first and α-CD afterwards to prevent burst release of the threaded HP-β-CD. Our findings show that HP-β-CD was slowly released from the watersoluble polyrotaxane over a 30 days period. The polyrotaxane provided persistently diminished cholesterol levels in NPC1 cells by 20% relative to untreated cells. These results demonstrate the therapeutic potential of this novel HP-β-CD polyrotaxane for the mobilization of aberrantly stored cholesterol in NPC1 cells.

Enhanced Uptake of Luminescent Quantum Dots by Live Cells Mediated by a Membrane-Active Peptide

The steady progress made over the past three decades in growing a variety of inorganic nanomaterials, with discreet control over their size and photophysical properties, has been exploited to develop several imaging and sensing applications. However, full integration of these materials into biology has been hampered by the complexity of delivering them into cells. In this report, we demonstrate the effectiveness of a chemically synthesized anticancer peptide to facilitate the rapid delivery of luminescent quantum dots (QDs) into live cells. We combine fluorescence imaging microscopy, flow cytometry, and specific endocytosis inhibition experiments to probe QD-peptide conjugate uptake by different cell lines. We consistently find that a sizable fraction of the internalized conjugates does not co-localize with endosomes or the nuclei. These findings are extremely promising for the potential integration of various nanomaterials into biological systems.

Acoustically-mediated intracellular delivery

Recent breakthroughs in gene editing have necessitated practical ex vivo methods to rapidly and efficiently re-engineer patient-harvested cells. Many physical membrane-disruption or pore-forming techniques for intracellular delivery, however, result in poor cell viability, while most carrier-mediated techniques suffer from suboptimal endosomal escape and hence cytoplasmic or nuclear targeting. In this work, we show that short exposure of cells to high frequency (>10 MHz) acoustic excitation facilitates temporal reorganisation of the lipid structure in the cell membrane that enhances translocation of gold nanoparticles and therapeutic molecules into the cell within just ten minutes. Due to its transient nature, rapid cell self-healing is observed, leading to high cellular viabilities (>97%). Moreover, the internalised cargo appears to be uniformly distributed throughout the cytosol, circumventing the need for strategies to facilitate endosomal escape. In the case of siRNA delivery, the method is seen to enhance gene silencing by over twofold, demonstrating its potential for enhancing therapeutic delivery into cells.

Peptide and protein nanoparticle conjugates: versatile platforms for biomedical applications

Peptide- and protein-nanoparticle conjugates have emerged as powerful tools for biomedical applications, enabling the treatment, diagnosis, and prevention of disease. In this review, we focus on the key roles played by peptides and proteins in improving, controlling, and defining the performance of nanotechnologies. Within this framework, we provide a comprehensive overview of the key sequences and structures utilised to provide biological and physical stability to nano-constructs, direct particles to their target and influence their cellular and tissue distribution, induce and control biological responses, and form polypeptide self-assembled nanoparticles. In doing so, we highlight the great advances made by the field, as well as the challenges still faced in achieving the clinical translation of peptide- and protein-functionalised nano-drug delivery vehicles, imaging species, and active therapeutics.

The biological challenges and pharmacological opportunities of orally administered nanomedicine delivery

Nano-scale formulations are being developed to improve the delivery of orally administered medicines, and the interactions between nanoformulations and the gastrointestinal luminal, mucosal and epithelial environment is currently being investigated. The mucosal surface of the gastrointestinal tract is capable of trapping and eliminating large particles and pathogens as part of the natural defences of the body, it is becoming clearer that nanoformulation properties such as particle size, charge, and shape, as well as mucous properties such as viscoelasticity, thickness, density, and turn-over time are all relevant to these interactions. However, progress has been slow to utilise this information to produce effective mucous-penetrating particles. Areas covered: This review focuses on delivery method of nanomedicines both into and across the gastrointestinal mucosal surface, and aims to summarise the biological barriers that exist to successful oral nanomedicine delivery and how these barriers may be investigated and overcome. Expert commentary: Despite successes in the laboratory, no nanotechnology-enabled products are currently in clinical use which either specifically target the intestinal mucous surface or cross the epithelial barrier intact. New nanomedicine-based treatments of local diseases (intestinal cancer, inflammation, infection) and systemic diseases are advancing towards clinical use, and offer genuine opportunities to improve therapy.

Unlocking Endosomal Entrapment with Supercharged Arginine-Rich Peptides

Endosomal entrapment is a common bottleneck in various macromolecular delivery approaches. Recently, the polycationic peptide dfTAT was identified as a reagent that induces the efficient leakage of late endosomes and, thereby, enhances the penetration of macromolecules into the cytosol of live human cells. To gain further insights into the features that lead to this activity, the role of peptide sequence was investigated. We establish that the leakage activity of dfTAT can be recapitulated by polyarginine analogs but not by polylysine counterparts. Efficiencies of peptide endocytic uptake increase linearly with the number of arginine residues present. In contrast, peptide cytosolic penetration displays a threshold behavior, indicating that a minimum number of arginines is required to induce endosomal escape. Increasing arginine content above this threshold further augments delivery efficiencies. Yet, it also leads to increasing the toxicity of the delivery agents. Together, these data reveal a relatively narrow arginine-content window for the design of optimally active endosomolytic agents.

Modulating the Cellular Immune Response of Oligonucleotides by Brush Polymer-Assisted Compaction

Unwanted stimulation of the innate immune system by foreign nucleic acids has been one of the major barriers preventing bioactive sequences from reaching market. Foreign nucleic acids can be recognized by multiple pattern recognition receptors (PRRs), which trigger a signaling cascade to activate host defense systems, leading to a range of side effects. This study demonstrates that polyethylene glycol (PEG)-modified DNA strands can greatly reduce the activation of the innate immune system, and the extent of reduction is dependent upon polymer architecture. Highly branched brushes with long PEG side chains achieve the best suppression by blocking PRR interactions via a local steric effect. Interestingly, the brush polymer creates little barrier toward DNA-DNA interaction. Quantification of inflammatory cytokines in both mRNA and protein levels as well as the extent of cellular uptake shows a direct correlation between steric congestion and reduction of cellular immune response. These results suggest that the brush architecture offers unique advantages for PEGylating oligonucleotides in the context of minimizing unwanted immune system activation.

Length effects on the dynamic process of cellular uptake and exocytosis of single-walled carbon nanotubes in murine macrophage cells

Cellular uptake and exocytosis of SWCNTs are fundamental processes determining their intracellular concentration and effects. Despite the great potential of acid-oxidized SWCNTs in biomedical field, understanding of the influencing factors on these processes needs to be deepened. Here, we quantitatively investigated uptake and exocytosis of SWCNTs in three lengths-630 (±171) nm (L-SWCNTs), 390 (±50) nm (M-SWCNTs), and 195 (±63) nm (S-MWCNTs) in macrophages. The results showed that the cellular accumulation of SWCNTs was a length-independent process and non-monotonic in time, with the most SWCNTs (3950 fg/cell) accumulated at 8 h and then intracellular SWCNTs dropped obviously with time. The uptake rate of SWCNTs decreased with increasing concentration, suggesting that intracellular SWCNTs accumulation is a saturable process. After refreshing culture medium, we found increasing SWCNTs in supernatant and decreasing intracellular SWCNTs over time, confirming the exocytosis occurred. Selective inhibition of endocytosis pathways showed that the internalization of SWCNTs involves several pathways, in the order of macropinocytosis> caveolae-mediated endocytosis> clathrin-dependent endocytosis. Intriguingly, clathrin-mediated endocytosis is relatively important for internalizing shorter SWCNTs. The dynamic processes of SWCNTs uptake and exocytosis and the mechanisms revealed by this study may render a better understanding on SWCNT toxicity and facilitate the design of CNT products with mitigated toxicity and desired functions.

Peptide-Coated Semiconductor Polymer Dots for Stem Cells Labeling and Tracking

Stem cell therapy is rapidly moving toward translation to clinical application. To elucidate the therapeutic effect, a robust method that allows tracking of the stem cells over an extended period of time is required. Herein, semiconducting polymer dots (Pdots) are demonstrated for their use in bright labeling and tracking of human mesenchymal stem cells (MSCs) in vitro and in vivo. The Pdots coated with a cell-penetrating peptide (R8) showed remarkable endocytic uptake efficiency that was 15 times higher than that of carboxyl Pdots and more than 200 times than that of bare Pdots. The Pdot-labeled MSCs can be traced for 15 generations in vitro and tracked over 2 weeks in vivo after subcutaneous transplantation. The labeled MSCs administered through the tail vein were preferentially accumulated in the lung; this was distinctive from the distribution of free Pdots, which were primarily distributed in the liver. Based on the properties of bright labeling, excellent tracking capability, and great biocompatibility, the Pdots will be valuable in the applications of stem cell biology and regenerative medicine.

Trileucine residues in a ligand-CPP-based siRNA delivery platform improve endosomal escape of siRNA

siRNA entrapment within endosomes is a significant problem encountered with siRNA delivery platforms that co-opt receptor-mediated entry pathways. Attachment of a cell-penetrating peptide (CPP), such as nona-arginine (9R) to a cell receptor-binding ligand like the Rabies virus glycoprotein, RVG, allows effective siRNA delivery to the cytoplasm by non-endocytic pathways, but a significant amount of siRNA complexes also enters the cell by ligand-induced receptor endocytosis and remain localized in endosomes. Here, we report that the incorporation of trileucine (3 Leu) residues as an endo-osmolytic moiety in the peptide improves endosomal escape and intracellular delivery of siRNA. The trileucine motif did not affect early non-endosomal mechanism of cytoplasmic siRNA delivery but enhanced target gene silencing by >20% only beyond 24 h of transfection when siRNA delivery is mostly through the endocytic route and siRNA trapped in the endosomes at later stages were subject to release into cytoplasm. The mechanism may involve endosomal membrane disruption as trileucine residues lysed RBCs selectively under endosomal pH conditions. Interestingly <3 Leu or >3 Leu residues were not as effective, suggesting that 3 Leu residues are useful for enhancing cytoplasmic delivery of siRNA routed through endosomes.

Effect of poly-glutamate on uptake efficiency and cytotoxicity of cell penetrating peptides

Cell penetrating peptides (CPPs) were developed as vehicles for efficient delivery of various molecules. An ideal CPP-peptide should not display any toxicity against cancer cells as well as healthy cells and efficiently enter into the cell. Because of the cationic nature and the intrinsic vector capabilities, these peptides can cause cytotoxicity. One of the possible reasons for toxicity of CPPs is direct translocation and consequently, pore formation on the plasma membrane. In this study it was demonstrated that interaction of poly-glutamate with CPP considerably reduced their cytotoxicity in A549 cell. This strategy could be useful for efficient drug delivery mediated by CPP.

The Late Endosome and Its Lipid BMP Act as Gateways for Efficient Cytosolic Access of the Delivery Agent dfTAT and Its Macromolecular Cargos

Endosomal entrapment is a severely limiting bottleneck in the delivery of biologics into cells. The compound dfTAT was recently found to circumvent this problem by mediating endosomal leakage efficiently and without toxicity. Herein, we report on the mechanism of endosomal escape of this cell-penetrating peptide. By modulating the trafficking of the peptide within the endocytic pathway, we identify late endosomes as the organelles rendered leaky by dfTAT. We establish that dfTAT binds bis(monoacylglycero)phosphate (BMP), a lipid found in late endosomes, and that the peptide causes the fusion and leakage of bilayers containing BMP. Together, these data identify late endosomes as desirable gateways for cell penetration and BMP as a cellular factor that can be exploited for the development of future delivery agents.

Identification of a Short Cell-Penetrating Peptide from Bovine Lactoferricin for Intracellular Delivery of DNA in Human A549 Cells

Cell-penetrating peptides (CPPs) have been shown to deliver cargos, including protein, DNA, RNA, and nanomaterials, in fully active forms into live cells. Most of the CPP sequences in use today are based on non-native proteins that may be immunogenic. Here we demonstrate that the L5a CPP (RRWQW) from bovine lactoferricin (LFcin), stably and noncovalently complexed with plasmid DNA and prepared at an optimal nitrogen/phosphate ratio of 12, is able to efficiently enter into human lung cancer A549 cells. The L5a CPP delivered a plasmid containing the enhanced green fluorescent protein (EGFP) coding sequence that was subsequently expressed in cells, as revealed by real-time PCR and fluorescent microscopy at the mRNA and protein levels, respectively. Treatment with calcium chloride increased the level of gene expression, without affecting CPP-mediated transfection efficiency. Zeta-potential analysis revealed that positively electrostatic interactions of CPP/DNA complexes correlated with CPP-mediated transport. The L5a and L5a/DNA complexes were not cytotoxic. This biomimetic LFcin L5a represents one of the shortest effective CPPs and could be a promising lead peptide with less immunogenic for DNA delivery in gene therapy.

Vibrational spectroscopy and imaging for concurrent cellular trafficking of co-localized doxorubicin and deuterated phospholipid vesicles

Simultaneous tracking of nanoparticles and encapsulated payload is of great importance and visualizing their activity is arduous. Here we use vibrational spectroscopy to study the in vitro tracking of co-localized lipid nanoparticles and encapsulated drug employing a model system derived from doxorubicin-encapsulated deuterated phospholipid (dodecyl phosphocholine-d38) single tailed phospholipid vesicles.

Different oligoarginine modifications alter endocytic pathways and subcellular trafficking of polymeric nanoparticles

Different length of oligoarginine ligands alter both endocytic pathways and subcellular trafficking of PEG-b-PCL nanoparticles.

Peptide-mediated delivery: an overview of pathways for efficient internalization

Poor cellular delivery and low bioavailability of novel potent therapeutic molecules continue to remain the bottleneck of modern cancer and gene therapy. Cell-penetrating peptides have provided immense opportunities for the intracellular delivery of bioactive cargos and have led to the first exciting successes in experimental therapy of muscular dystrophies. This review focuses on the mechanisms by which cell-penetrating peptides gain access to the cell interior and deliver cargos. Recent advances in augmenting delivery efficacy and facilitation of endosomal escape of cargo are presented, and the cell-penetrating peptide-mediated delivery of two of the most popular classes of cargo molecules, oligonucleotides and proteins, is analyzed. The arsenal of tools for oligonucleotide delivery has dramatically expanded in the last decade enabling harnessing of cell-surface receptors for targeted delivery.

Delivery of nucleic acids and nanomaterials by cell-penetrating peptides: opportunities and challenges

Many viral and nonviral systems have been developed to aid delivery of biologically active molecules into cells. Among these, cell-penetrating peptides (CPPs) have received increasing attention in the past two decades for biomedical applications. In this review, we focus on opportunities and challenges associated with CPP delivery of nucleic acids and nanomaterials. We first describe the nature of versatile CPPs and their interactions with various types of cargoes. We then discuss in vivo and in vitro delivery of nucleic acids and nanomaterials by CPPs. Studies on the mechanisms of cellular entry and limitations in the methods used are detailed.

Preparation, in vitro and in vivo evaluation of polymeric nanoparticles based on hyaluronic acid-poly(butyl cyanoacrylate) and D-alpha-tocopheryl polyethylene glycol 1000 succinate for tumor-targeted delivery of morin hydrate

Herein, we describe the preparation of a targeted cellular delivery system for morin hydrate (MH), based on a low-molecular-weight hyaluronic acid-poly(butyl cyanoacrylate) (HA-PBCA) block copolymer. In order to enhance the therapeutic effect of MH, D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) was mixed with HA-PBCA during the preparation process. The MH-loaded HA-PBCA “plain” nanoparticle (MH-PNs) and HA-PBCA/TPGS “mixed” nanoparticles (MH-MNs) were concomitantly characterized in terms of loading efficiency, particle size, zeta potential, critical aggregation concentration, and morphology. The obtained MH-PNs and MH-MNs exhibited a spherical morphology with a negative zeta potential and a particle size less than 200 nm, favorable for drug targeting. Remarkably, the addition of TPGS resulted in about 1.6-fold increase in drug-loading. The in vitro cell viability experiment revealed that MH-MNs enhanced the cytotoxicity of MH in A549 cells compared with MH solution and MH-PNs. Furthermore, blank MNs containing TPGS exhibited selective cytotoxic effects against cancer cells without diminishing the viability of normal cells. In addition, the cellular uptake study indicated that MNs resulted in 2.28-fold higher cellular uptake than that of PNs, in A549 cells. The CD44 receptor competitive inhibition and the internalization pathway studies suggested that the internalization mechanism of the nanoparticles was mediated mainly by the CD44 receptors through a clathrin-dependent endocytic pathway. More importantly, MH-MNs exhibited a higher in vivo antitumor potency and induced more tumor cell apoptosis than did MH-PNs, following intravenous administration to S180 tumor-bearing mice. Overall, the results imply that the developed nanoparticles are promising vehicles for the targeted delivery of lipophilic anticancer drugs.

Interaction between cell-penetrating peptides and acid-sensitive anionic oligopeptides as a model for the design of targeted drug carriers

Overcoming the nonspecific cellular uptake of cell-penetrating peptides (CPPs) is a major hurdle in their clinical application. Using pH as the activation switch, histidine-glutamic acid (HE) dipeptide repeats were fused to CPPs to trigger the membrane-penetrating activity at mildly acidic pH environments (i.e., pH 6.5 or below) while masking the internalization at neutral pH (i.e., pH 7.0 or above). In this study, a series of recombinant GST-fusion proteins containing an HE oligopeptide sequence (i.e., (HE)n with n = 8, 10, or 12) and a cationic CPP (i.e., YG(RG)6, YGR6G6, or Tat) were engineered for a pH-sensitive study comparing their cellular uptake and surface binding in cultured HeLa cells. Circular dichroism (CD) spectroscopy was performed to correlate differences between CPPs in secondary structure with the pH sensitivity. YGR6G6 with clustered arginine residues exhibited greater pH sensitivity in cellular uptake than YG(RG)6 with separated arginine residues. Increasing the stretch of HE repeats decreased cellular uptake and surface binding for both YG(RG)6 and YGR6G6. The ratio of cellular internalization at pH 7.5 vs 6.0 was not changed by the presence of serum. CD spectral data revealed that both (HE)10-Tat and (HE)10-YGR6G6 exhibited an unordered secondary structure, whereas (HE)10-YG(RG)6 adopted an antiparallel β-sheet conformation. This β-sheet conformation presumably stabilized the association of (HE)10 with YG(RG)6, leading to weakened pH sensitivity of (HE)10-YG(RG)6. On the other hand, the random-coiled structures, that is, (HE)10-YGR6G6 and (HE)10-Tat, both showed higher pH sensitivity as determined in cell experiments. The data presented in this study provide a basis for the future design of pH-sensitive HE-CPP carrier for targeted drug delivery.