Different roles of cell surface and exogenous glycosaminoglycans in controlling gene delivery by arginine-rich peptides with varied distribution of arginines

Internalization of PEI-based complexes in transient transfection of HEK293 cells is triggered by coalescence of membrane heparan sulfate proteoglycans like Glypican-4

Polymer-cationic mediated gene delivery is a well-stablished strategy of transient gene expression (TGE) in mammalian cell cultures. Nonetheless, its industrial implementation is hindered by the phenomenon known as cell density effect (CDE) that limits the cell density at which cultures can be efficiently transfected. The rise in personalized medicine and multiple cell and gene therapy approaches based on TGE, make more relevant to understand how to circumvent the CDE. A rational study upon DNA/PEI complex formation, stability and delivery during transfection of HEK293 cell cultures has been conducted, providing insights on the mechanisms for polyplexes uptake at low cell density and disruption at high cell density. DNA/PEI polyplexes were physiochemically characterized by coupling X-ray spectroscopy, confocal microscopy, cryo-transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). Our results showed that the ionic strength of polyplexes significantly increased upon their addition to exhausted media. This was reverted by depleting extracellular vesicles (EVs) from the media. The increase in ionic strength led to polyplex aggregation and prevented efficient cell transfection which could be counterbalanced by implementing a simple media replacement (MR) step before transfection. Inhibiting and labeling specific cell-surface proteoglycans (PGs) species revealed different roles of PGs in polyplexes uptake. Importantly, the polyplexes uptake process seemed to be triggered by a coalescence phenomenon of HSPG like glypican-4 around polyplex entry points. Ultimately, this study provides new insights into PEI-based cell transfection methodologies, enabling to enhance transient transfection and mitigate the cell density effect (CDE).

Cell-penetrating peptides with nanoparticles hybrid delivery vectors and their uptake pathways

Cell-penetrating peptides (CPPs) are molecules that improve the cellular uptake of various molecular payloads that do not easily traverse the cellular membrane. CPPs can be found in pharmaceutical and medical products. The vast majority of cell-penetrating chemicals that are discussed in published research are peptide based. The paper also delves into the various applications of hybrid vectors. Because CPPs are able to carry cargo across the cellular membrane, they are a viable candidate for use as a suitable carrier for a wide variety of cargoes, such as siRNA, nanoparticles, and others. In which we discuss the CPPs, their classification, uptake mechanisms, hybrid vector systems, nanoparticles and their uptake mechanisms, etc. Further in this paper, we discuss CPPs conjugated to Nanoparticles, Combining CPPs with lipids and polymeric Nanoparticles in A Conjugated System, CPPs conjugated to nanoparticles for therapeutic purposes, and potential therapeutic uses of CPPs as delivery molecules. Also discussed the preclinical and clinical use of CPPS, intracellular trafficking of nanoparticles, and activatable and bioconjugated CPPs.

Cell-Penetrating and Enzyme-Responsive Peptides for Targeted Cancer Therapy: Role of Arginine Residue Length on Cell Penetration and In Vivo Systemic Toxicity

For the improved delivery of cancer therapeutics and imaging agents, the conjugation of cell-penetrating peptides (CPPs) increases the cellular uptake and water solubility of agents. Among the various CPPs, arginine-rich peptides have been the most widely used. Combining CPPs with enzyme-responsive peptides presents an innovative strategy to target specific intracellular enzymes in cancer cells and when combined with the appropriate click chemistry can enhance theranostic drug delivery through the formation of intracellular self-assembled nanostructures. However, one drawback of CPPs is their high positive charge which can cause nonspecific binding, leading to off-target accumulation and potential toxicity. Hence, balancing cell-specific penetration, toxicity, and biocompatibility is essential for future clinical efficacy. We synthesized six cancer-specific, legumain-responsive RnAANCK peptides containing one to six arginine residues, with legumain being an asparaginyl endopeptidase that is overexpressed in aggressive prostate tumors. When conjugated to Alexa Fluor 488, R1-R6AANCK peptides exhibited a concentration- and time-dependent cell penetration in prostate cancer cells, which was higher for peptides with higher R values, reaching a plateau after approximately 120 min. Highly aggressive DU145 prostate tumor cells, but not less aggressive LNCaP cells, self-assembled nanoparticles in the cytosol after the cleavage of the legumain-specific peptide. The in vivo biocompatibility was assessed in mice after the intravenous injection of R1-R6AANCK peptides, with concentrations ranging from 0.0125 to 0.4 mmol/kg. The higher arginine content in R4-6 peptides showed blood and urine indicators for the impairment of bone marrow, liver, and kidney function in a dose-dependent manner, with instant hemolysis and morbidity in extreme cases. These findings underscore the importance of designing peptides with the optimal arginine residue length for a proper balance of cell-specific penetration, toxicity, and in vivo biocompatibility.

Serum-Resistant Ternary DNA Polyplexes for Suicide Gene Therapy of Uterine Leiomyoma

Uterine leiomyoma (UL) is a prevalent benign tumor in women that frequently gives rise to a multitude of reproductive complications. The use of suicide gene therapy has been proposed as a highly promising method for treating UL. To achieve successful gene therapy, it is essential to develop carriers that can efficiently transport nucleic acids into targeted cells and tissues. The instability of polyplexes in blood and other biological fluids is a crucial factor to consider when using non-viral carriers. In this study, we present serum-resistant and cRGD-modified DNA complexes for targeted delivery genes to UL cells. Ternary polyplexes were formed by incorporating cystine-cross-linked polyglutamic acid modified with histidine residues. We employed two techniques in the production of cross-linked polyanionic coating: matrix polymerization and oxidative polycondensation. In this study, we investigated the physicochemical properties of ternary DNA complexes, including the size and zeta-potential of the nanoparticles. Additionally, we evaluated cellular uptake, toxicity levels, transfection efficiency and specificity in vitro. The study involved introducing the HSV-TK gene into primary UL cells as a form of suicide gene therapy modeling. We have effectively employed ternary peptide-based complexes for gene delivery into the UL organtypic model. By implementing in situ suicide gene therapy, the increase in apoptosis genes expression was detected, providing conclusive evidence of apoptosis occurring in the transfected UL tissues. The results of the study strongly suggest that the developed ternary polyplexes show potential as a valuable tool in the implementation of suicide gene therapy for UL.

Surface-Engineered Mucus Penetrating Nucleic Acid Delivery Systems with Cell Penetrating Peptides for the Lungs

Nucleic acids, both DNA and small RNAs, have emerged as potential therapeutics for the treatment of various lung disorders. However, delivery of nucleic acids to the lungs is challenging due to the barrier property imposed by mucus, which is further reinforced in disease conditions such as chronic obstructive pulmonary disease and asthma. The presence of negatively charged mucins imparts the electrostatic barrier property, and the mesh network structure of mucus provides steric hindrance to the delivery system. To overcome this, the delivery system either needs to be muco-inert with a low positive charge such that the interactions with mucus are minimized or should have the ability to transiently dismantle the mucus structure for effective penetration. We have developed a mucus penetrating system for the delivery of both small RNA and plasmid DNA independently. The nucleic acid core consists of a nucleic acid (pDNA/siRNA) and a cationic/amphipathic cell penetrating peptide. The mucus penetrating coating consists of the hydrophilic biopolymer chondroitin sulfate A (CS-A) conjugated with a mucolytic agent, mannitol. We hypothesize that the hydrophilic coating of CS-A would reduce the surface charge and decrease the interaction with negatively charged mucins, while the conjugated mannitol residues would disrupt the mucin-mucin interaction or decrease the viscosity of mucus by increasing the influx of water into the mucus. Our results indicate that CS-A-mannitol-coated nanocomplexes possess reduced surface charge, reduced viscosity of artificial mucus, and increased diffusion in mucin suspension as well as increased penetration through the artificial mucus layer as compared to the non-coated ones. Further, the coated nanocomplexes showed low cytotoxicity as well as higher transfection in A-549 and BEAS-2B cells as compared to the non-coated ones.

On the Biology of Werner's Complex

Werner's Complex, as a cationic coordination complex (CCC), has hitherto unappreciated biological properties derived from its binding affinity to highly anionic biomolecules such as glycosaminoglycans (GAGs) and nucleic acids. Competitive inhibitor and spectroscopic assays confirm the high affinity to GAGs heparin, heparan sulfate (HS), and its pentasaccharide mimetic Fondaparinux (FPX). Functional consequences of this affinity include inhibition of FPX cleavage by bacterial heparinase and mammalian heparanase enzymes with inhibition of cellular invasion and migration. Werner's Complex is a very efficient condensing agent for DNA and tRNA. In proof-of-principle for translational implications, it is demonstrated to display antiviral activity against human cytomegalovirus (HCMV) at micromolar concentrations with promising selectivity. Exploitation of non-covalent hydrogen-bonding and electrostatic interactions has motivated the unprecedented discovery of these properties, opening new avenues of research for this iconic compound.

Tailoring Iron Oxide Nanoparticles for Efficient Cellular Internalization and Endosomal Escape

Iron oxide nanoparticles (IONs) have been widely explored for biomedical applications due to their high biocompatibility, surface-coating versatility, and superparamagnetic properties. Upon exposure to an external magnetic field, IONs can be precisely directed to a region of interest and serve as exceptional delivery vehicles and cellular markers. However, the design of nanocarriers that achieve an efficient endocytic uptake, escape lysosomal degradation, and perform precise intracellular functions is still a challenge for their application in translational medicine. This review highlights several aspects that mediate the activation of the endosomal pathways, as well as the different properties that govern endosomal escape and nuclear transfection of magnetic IONs. In particular, we review a variety of ION surface modification alternatives that have emerged for facilitating their endocytic uptake and their timely escape from endosomes, with special emphasis on how these can be manipulated for the rational design of cell-penetrating vehicles. Moreover, additional modifications for enhancing nuclear transfection are also included in the design of therapeutic vehicles that must overcome this barrier. Understanding these mechanisms opens new perspectives in the strategic development of vehicles for cell tracking, cell imaging and the targeted intracellular delivery of drugs and gene therapy sequences and vectors.

Polyarginine-Mediated siRNA Delivery: A Mechanistic Study of Intracellular Trafficking of PCL-R15/siRNA Nanoplexes

As a cell-penetrating peptide, polyarginine is widely used in drug delivery systems based on its membrane permeation ability. Previously, we developed the mPEG-PLA-b-polyarginine(R15) triblock copolymer, which exhibited a high siRNA delivery efficiency both in vitro and in vivo. As a continued effort, here the amphiphilic diblock polymer PCL-R15 was synthesized as a simplified model to further elucidate the structure-activity relationship of arginine-based amphiphilic polymers as siRNA delivery systems, and the cellular trafficking mechanisms of the PCL-R15/siRNA nanoplexes were investigated to understand the interaction patterns between the nanoplexes and cells. Compared to the R15/siRNA complexes, the introduction of PCL moiety was found to result in the stronger interactions with cells and the enhanced transfection efficiency after the formation of condensed nanoplexes. Caveolae-mediated endocytosis and clathrin-mediated endocytosis were major routes for the internalization of PCL-R15/siRNA nanoplexes. The intracellular release of siRNA from nanoplexes was confirmed by fluorescence resonance energy transfer assay. It was also noticed that the internalized PCL-R15/siRNA nanoplexes were transported through digestive routes and trapped in lysosomes, which may be the bottleneck for efficient siRNA delivery of PCL-R15/siRNA nanoplexes. This study investigated the relationship between the polymer structure of PCL-R15 and the cellular interaction patterns, which may render implications on the rational design of polyarginine-based siRNA delivery systems.

Cartilage penetrating cationic peptide carriers for applications in drug delivery to avascular negatively charged tissues

Drug delivery to avascular, negatively charged tissues like cartilage remains a challenge. The constant turnover of synovial fluid results in short residence time of administered drugs in the joint space and the dense negatively charged matrix of cartilage hinders their diffusive transport. Drugs are, therefore, unable to reach their cell and matrix targets in sufficient doses, and fail to elicit relevant biological response, which has led to unsuccessful clinical trials. The high negative fixed charge density (FCD) of cartilage, however, can be used to convert cartilage from a barrier to drug entry into a depot by making drugs positively charged. Here we design cartilage penetrating and binding cationic peptide carriers (CPCs) with varying net charge, spatial distribution and hydrophobicity to deliver large-sized therapeutics and investigate their electro-diffusive transport in healthy and arthritic cartilage. We showed that CPC uptake increased with increasing net charge up to +14 but dropped as charge increased further due to stronger binding interactions that hindered CPC penetrability and uptake showing that weak-reversible binding is key to enable their penetration through full tissue thickness. Even after 90% GAG depletion, while CPC +14 uptake reduced by over 50% but still had a significantly high value of 148× showing that intra-tissue long-range charge-based binding is further stabilized by short-range H-bond and hydrophobic interactions. The work presents an approach for rational design of cationic carriers based on tissue FCD and properties of macromolecules to be delivered. These design rules can be extended to drug delivery for other avascular, negatively charged tissues. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) remains an untreatable disease partly due to short joint residence time of drugs and a lack of delivery methods that can effectively target the dense, avascular, highly negatively charged cartilage tissue. In this study, we designed cartilage penetrating and binding cationic peptide carriers (CPCs) that, due to their optimal charge provide adequate electrical driving force to rapidly transport OA drugs into cartilage and reach their cell and matrix targets in therapeutic doses before drugs exit the joint space. This way cartilage is converted from being a barrier to drug entry into a drug depot that can provide sustained drug release for several weeks. This study also investigates synergistic effects of short-range H-bond and hydrophobic interactions in combination with long-range electrostatic interactions on intra-cartilage solute transport. The work provides rules for rational design of cartilage penetrating charge-based carriers depending on the net charge of tissue (normal versus arthritic), macromolecule to be delivered and whether the application is in drug delivery or tissue imaging.

Deciphering the Role of Chondroitin Sulfate in Increasing the Transfection Efficiency of Amphipathic Peptide-Based Nanocomplexes

Glycosaminoglycans, both cell-surface and exogenous, can interfere with DNA delivery efficiency of nonviral carrier systems. In this work, we report an extensive comparative study to explore the effect of exogenously added chondroitin sulfate on biophysical characteristics, cellular uptake, transfection efficiency, and intracellular trafficking of nanocomplexes formed using primary and secondary amphipathic peptides developed in our laboratory. Our results indicate that the presence of exogenous chondroitin sulfate exhibits differential enhancement in transfection efficiency of the amphipathic peptides depending upon their chemical nature. The enhancement was more pronounced in primary amphipathic peptide-based nanocomplexes as compared to the secondary counterpart. This difference can be attributed to possible alteration of the intracellular entry pathway in addition to increased extracellular stability, less cellular toxicity, and assistance in nuclear accumulation. These results imply potential use of glycosaminoglycans such as chondroitin sulfate to improve the transfection efficiency of primary amphipathic peptides for possible in vivo applications.

Glycosaminoglycan Binding and Non-Endocytic Membrane Translocation of Cell-Permeable Octaarginine Monitored by Real-Time In-Cell NMR Spectroscopy

Glycosaminoglycans (GAGs), which are covalently-linked membrane proteins at the cell surface have recently been suggested to involve in not only endocytic cellular uptake but also non-endocytic direct cell membrane translocation of arginine-rich cell-penetrating peptides (CPPs). However, in-situ comprehensive observation and the quantitative analysis of the direct membrane translocation processes are challenging, and the mechanism therefore remains still unresolved. In this work, real-time in-cell NMR spectroscopy was applied to investigate the direct membrane translocation of octaarginine (R8) into living cells. By introducing 4-trifluoromethyl-l-phenylalanine to the N terminus of R8, the non-endocytic membrane translocation of ¹⁹F-labeled R8 (¹⁹F-R8) into a human myeloid leukemia cell line was observed at 4 °C with a time resolution in the order of minutes. ¹⁹F NMR successfully detected real-time R8 translocation: the binding to anionic GAGs at the cell surface, followed by the penetration into the cell membrane, and the entry into cytosol across the membrane. The NMR concentration analysis enabled quantification of how much of R8 was staying in the respective translocation processes with time in situ. Taken together, our in-cell NMR results provide the physicochemical rationale for spontaneous penetration of CPPs in cell membranes.

Cytotoxic helix-rich oligomer formation by melittin and pancreatic polypeptide

Conversion of amyloid fibrils by many peptides/proteins involves cytotoxic helix-rich oligomers. However, their toxicity and biophysical studies remain largely unknown due to their highly dynamic nature. To address this, we chose two helical peptides (melittin, Mel and pancreatic polypeptide, PP) and studied their aggregation and toxicity. Mel converted its random coil structure to oligomeric helical structure upon binding to heparin; however, PP remained as helix after oligomerization. Interestingly, similar to Parkinson’s associated α-synuclein (AS) oligomers, Mel and PP also showed tinctorial properties, higher hydrophobic surface exposure, cellular toxicity and membrane pore formation after oligomerization in the presence of heparin. We suggest that helix-rich oligomers with exposed hydrophobic surface are highly cytotoxic to cells irrespective of their disease association. Moreover as Mel and PP (in the presence of heparin) instantly self-assemble into stable helix-rich amyloidogenic oligomers; they could be represented as models for understanding the biophysical and cytotoxic properties of helix-rich intermediates in detail.

Exogenous chondroitin sulfate glycosaminoglycan associate with arginine-rich peptide-DNA complexes to alter their intracellular processing and gene delivery efficiency

Arginine-rich peptides have been used extensively as efficient cellular transporters. However, gene delivery with such peptides requires development of strategies to improve their efficiency. We had earlier demonstrated that addition of small amounts of exogenous glycosaminoglycans (GAGs) like heparan sulfate or chondroitin sulfate to different arginine-rich peptide-DNA complexes (polyplexes) led to an increase in their gene delivery efficiency. This was possibly due to the formation of a 'GAG coat' on the polyplex surface through electrostatic interactions which improved their extracellular stability and subsequent cellular entry. In this report, we have attempted to elucidate the differences in intracellular processing of the chondroitin sulfate (CS)-coated polyplexes in comparison to the native polyplexes by using a combination of endocytic inhibitors and co-localization with endosomal markers in various cell lines. We observed that both the native and CS-coated polyplexes are internalized by multiple endocytic pathways although in some cell lines, the coated polyplexes are taken up primarily by caveolae mediated endocytosis. In addition, the CS-coat improves the endosomal escape of the polyplexes as compared to the native polyplexes. Interestingly, during these intracellular events, exogenous CS is retained with the polyplexes until their accumulation near the nucleus. Thus we show for the first time that exogenous GAGs in small amounts improve intracellular routing and nuclear accumulation of arginine-based polyplexes. Therefore, addition of exogenous GAGs is a promising strategy to enhance the transfection efficiency of cationic arginine-rich peptides in multiple cell types.

Cell-penetrating peptides for nanomedicine – how to choose the right peptide

More than two decades ago, a group of peptides, now known as cell-penetrating peptides, sparked the hope that the ultimate carrier molecules have been found. The high expectations for these peptides, which are reflected in their bold name, led to many disappointments due to the controversial results their utilization entailed and nowadays even their effectiveness has been called into question. In this review, we discuss the uptake mechanism and application of cell penetrating peptides as mediators for organelle specific delivery of nanocarriers, pointing out the possibilities as well as strategies of their successful utilization. Additionally, we provide an overview of the conjugation techniques usually employed for the attachment of cell penetrating peptides to quantum dots, as well as silver and gold nanoparticles, and we address the various aspects that need to be considered for the successful implementation of cell penetrating peptides for organelle-specific delivery of nanoparticles into cells.

Designer peptide delivery systems for gene therapy

Gene therapy has long been hailed as a revolutionary approach for the treatment of genetic diseases. The enthusiasm that greeted the harnessing of viruses for therapeutic DNA delivery has been tempered by concerns over safety. These concerns led to the development of alternative strategies for nucleic acid delivery to cells. One such strategy is the utilization of cationic peptides for the condensation of therapeutic DNA for delivery to its target. However, success of DNA as a therapy relies on its delivery to the nucleus of target cells, a process that is complicated by the many hurdles encountered following systemic administration. Non-viral peptide gene delivery strategies have sought inspiration from viruses in order to retain DNA delivering potency, but limit virulence. This review summarizes the progression of peptide-based DNA delivery systems, from rudimentary beginnings to the recent development of sophisticated multi-functional vectors that comprise distinct motifs with dedicated barrier evasion functions. The most promising peptides that achieve cell membrane permeabilization, endosomal escape and nuclear delivery are discussed.

Cell penetrating peptides: efficient vectors for delivery of nanoparticles, nanocarriers, therapeutic and diagnostic molecules

Efficient delivery of therapeutic and diagnostic molecules to the cells and tissues is a difficult challenge. The cellular membrane is very effective in its role as a selectively permeable barrier. While it is essential for cell survival and function, also presents a major barrier for intracellular delivery of cargo such as therapeutic and diagnostic agents. In recent years, cell-penetrating peptides (CPPs), that are relatively short cationic and/or amphipathic peptides, received great attention as efficient cellular delivery vectors due to their intrinsic ability to enter cells and mediate uptake of a wide range of macromolecular cargo such as plasmid DNA (pDNA), small interfering RNA (siRNAs), drugs, and nanoparticulate pharmaceutical carriers. This review discusses the various uptake mechanisms of these peptides. Furthermore, we discuss recent advances in the use of CPP for the efficient delivery of nanoparticles, nanocarriers, DNA, siRNA, and anticancer drugs to the cells. In addition, we have been highlighting new results for improving endosomal escape of CPP-cargo molecules. Finally, pH-responsive and activable CPPs for tumor-targeting therapy have been described.