Further Investigation of Lipid-Substituted Poly(l-Lysine) Polymers for Transfection of Human Skin Fibroblasts

Polylysine for skin regeneration: A review of recent advances and future perspectives

There have been several attempts to find promising biomaterials for skin regeneration, among which polylysine (a homopolypeptide) has shown benefits in the regeneration and treatment of skin disorders. This class of biomaterials has shown exceptional abilities due to their macromolecular structure. Polylysine-based biomaterials can be used as tissue engineering scaffolds for skin regeneration, and as drug carriers or even gene delivery vectors for the treatment of skin diseases. In addition, polylysine can play a preservative role in extending the lifetime of skin tissue by minimizing the appearance of photodamaged skin. Research on polylysine is growing today, opening new scenarios that expand the potential of these biomaterials from traditional treatments to a new era of tissue regeneration. This review aims to address the basic concepts, recent trends, and prospects of polylysine-based biomaterials for skin regeneration. Undoubtedly, this class of biomaterials needs further evaluations and explorations, and many critical questions have yet to be answered.

α-Amino acid N-carboxyanhydride (NCA)-derived synthetic polypeptides for nucleic acids delivery

In recent years, gene therapy has come into the spotlight for the prevention and treatment of a wide range of diseases. Polypeptides have been widely used in mediating nucleic acid delivery, due to their versatilities in chemical structures, desired biodegradability, and low cytotoxicity. Chemistry plays an essential role in the development of innovative polypeptides to address the challenges of producing efficient and safe gene vectors. In this Review, we mainly focused on the latest chemical advances in the design and preparation of polypeptide-based nucleic acid delivery vehicles. We first discussed the synthetic approach of polypeptides via ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs), and introduced the various types of polypeptide-based gene delivery systems. The extracellular and intracellular barriers against nucleic acid delivery were then outlined, followed by detailed review on the recent advances in polypeptide-based delivery systems that can overcome these barriers to enable in vitro and in vivo gene transfection. Finally, we concluded this review with perspectives in this field.

Micelle-like nanoparticles as siRNA and miRNA carriers for cancer therapy

Gene therapy has emerged as an alternative in the treatment of cancer, particularly in cases of resistance to chemo and radiotherapy. Different approaches to deliver genetic material to tumor tissues have been proposed, including the use of small non-coding RNAs due to their multiple mechanisms of action. However, such promise has shown limits in in vivo application related to RNA's biological instability and stimulation of immunity, urging the development of systems able to overcome those barriers. In this review, we discuss the use of RNA interference in cancer therapy with special attention to the role of siRNA and miRNA and to the challenges of their delivery in vivo. We introduce a promising class of drug delivery system known as micelle-like nanoparticles and explore their synthesis and advantages for gene therapy as well as the recent findings in in vitro, in vivo and clinical studies.

Transfection-capable polycationic nanovectors which include PEGylated-cyclodextrin structural units: a new synthesis pathway

Polycationic nanoentities with low variability are able to act as cooperating carriers for dsDNA complexation and transport.

Micelle-like nanoparticles as carriers for DNA and siRNA

Gene therapy represents a potential efficient approach of disease prevention and therapy. However, due to their poor in vivo stability, gene molecules need to be associated with delivery systems to overcome extracellular and intracellular barriers and allow access to the site of action. Cationic polymeric nanoparticles are popular carriers for small interfering RNA (siRNA) and DNA-based therapeutics for which efficient and safe delivery are important factors that need to be optimized. Micelle-like nanoparticles (MNP) (half micelles, half polymeric nanoparticles) can overcome some of the disadvantages of such cationic carriers by unifying in one single carrier the best of both delivery systems. In this review, we will discuss how the unique properties of MNP including self-assembly, condensation and protection of nucleic acids, improved cell association and gene transfection, and low toxicity may contribute to the successful application of siRNA- and DNA-based therapeutics into the clinic. Recent developments of MNP involving the addition of stimulus-sensitive functions to respond specifically to pathological or externally applied "triggers" (e.g., temperature, pH or enzymatic catalysis, light, or magnetic fields) will be discussed. Finally, we will overview the use of MNP as two-in-one carriers for the simultaneous delivery of different agents (small molecules, imaging agents) and nucleic acid combinations.

Molecular assembly of alkyl chain-grafted poly(l-lysine) tuned by backbone chain length and grafted alkyl chain

Alkyl chain-grafted poly(l-lysine) vesicles with tunable molecular assembly were prepared by varying the polypeptide chain length and grafted alkyl chains.

Uptake, transport and peroral absorption of fatty glyceride grafted chitosan copolymer-enoxaparin nanocomplexes: influence of glyceride chain length

The objective of this paper is to elucidate the influence of fatty glyceride chain length in chitosan copolymers on the peroral absorption of enoxaparin. First of all, a series of chitosan copolymers with glyceryl monocaprylate (GM8), glyceryl monolaurate (GM12) and glyceryl monostearate (GM18) as the hydrophobic part were synthesized. The structure of the copolymers was characterized using proton nuclear magnetic resonance. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay demonstrated that all the copolymers were non-toxic. Enoxaparin nanocomplexes were prepared by self-assembly. Mucoadhesion of the nanocomplexes was characterized using the mucin particle method. Nanocomplex uptake and transport were quantified in Caco-2 cells and cellular localization was visualized by confocal laser scanning microscopy. Enoxaparin uptake was enhanced by nanocomplex formation, and was dependent on incubation time, concentration, temperature and glyceride chain length. The GM8 grafted chitosan-enoxaparin nanocomplex exhibited the strongest bioadhesion and the best uptake and transport in both cell culture and in vivo absorption in rats. The uptake mechanism was assumed to be adsorptive endocytosis via clathrin- and caveolae-mediated processes. In conclusion, oral absorption of enoxaparin can be further enhanced by using GM8 grafted chitosan copolymer as the carrier to form nanocomplexes.

Lipid-modified polyethylenimine-mediated DNA attraction evaluated by molecular dynamics simulations

The effect of lipid modification on polyethylenimine (PEI)-mediated DNA attraction was studied by performing umbrella sampling molecular dynamics simulations that involved PEIs modified with three different types of lipids: oleic acid (OA), linoleic acid (LA), and caprylic acid (CA). The potential of mean force between two DNA molecules in the presence of these lipid-modified PEIs was calculated using the weighted histogram analysis method, and it predicted the stability and size of the DNA aggregate. When compared to native PEI, lipid modification was found to enhance the stability of DNA aggregation in the case of long lipids (LA and OA) but reduce the stability in the case of a short lipid (CA). In addition, LA-substituted PEI was shown to form stronger DNA aggregate than OA-substituted PEI, which correlates positively with previous experimental observations.

In vitro and in vivo evaluation of chitosan graft glyceryl monooleate as peroral delivery carrier of enoxaparin

In this paper a novel copolymer, chitosan graft glyceryl monooleate (CS-GO) was synthesized and its potential as the nanocarrier for enhancing the peroral delivery of enoxaparin was studied systemically. The successful synthesis was characterized by (1)H NMR. Enoxaparin nanocomplexes were prepared by self-assembly. Mucoadhesive properties of the nanocomplexes were evaluated using mucin particle method. Uptake and transport of the nanocomplexes were investigated in Caco-2 cells. In vivo absorption was studied in rats. The therapeutic effects of the nanocomplexes were evaluated using pulmonary thromboembolism model in mice. This study demonstrated that compared to chitosan based system, hydrophobic modification of CS with GO enhanced the oral absorption of enoxaparin significantly, which is in good agreement with the enhanced mucoadhesion, cellular internalization and transport in cell culture. Cellular uptake of CS-GO based enoxaparin nanocomplexes was incubation time, enoxaparin concentration and incubation temperature dependent. The uptake mechanism was assumed to be adsorptive endocytosis via clathrin- and caveolae-mediated process. Its therapeutic efficacy was further demonstrated by pharmacodynamic study with pulmonary thromboembolism inhibition percentage 47.1%. In conclusion, CS-GO copolymer is a promising nanocarrier for enhancing the oral absorption of enoxaparin.

Engineering biodegradable and multifunctional peptide-based polymers for gene delivery

The complex nature of in vivo gene transfer establishes the need for multifunctional delivery vectors capable of meeting these challenges. An additional consideration for clinical translation of synthetic delivery formulations is reproducibility and scale-up of materials. In this review, we summarize our work over the last five years in developing a modular approach for synthesizing peptide-based polymers. In these materials, bioactive peptides that address various barriers to gene delivery are copolymerized with a hydrophilic backbone of N-(2-hydroxypropyl)methacrylamide (HPMA) using reversible-addition fragmentation chain-transfer (RAFT) polymerization. We demonstrate that this synthetic approach results in well-defined, narrowly-disperse polymers with controllable composition and molecular weight. To date, we have investigated the effectiveness of various bioactive peptides for DNA condensation, endosomal escape, cell targeting, and degradability on gene transfer, as well as the impact of multivalency and polymer architecture on peptide bioactivity.

BSA Nanoparticles for siRNA Delivery: Coating Effects on Nanoparticle Properties, Plasma Protein Adsorption, and In Vitro siRNA Delivery

Developing vehicles for the delivery of therapeutic molecules, like siRNA, is an area of active research. Nanoparticles composed of bovine serum albumin, stabilized via the adsorption of poly-L-lysine (PLL), have been shown to be potentially inert drug-delivery vehicles. With the primary goal of reducing nonspecific protein adsorption, the effect of using comb-type structures of poly(ethylene glycol) (1 kDa, PEG) units conjugated to PLL (4.2 and 24 kDa) on BSA-NP properties, apparent siRNA release rate, cell viability, and cell uptake were evaluated. PEGylated PLL coatings resulted in NPs with ζ-potentials close to neutral. Incubation with platelet-poor plasma showed the composition of the adsorbed proteome was similar for all systems. siRNA was effectively encapsulated and released in a sustained manner from all NPs. With 4.2 kDa PLL, cellular uptake was not affected by the presence of PEG, but PEG coating inhibited uptake with 24 kDa PLL NPs. Moreover, 24 kDa PLL systems were cytotoxic and this cytotoxicity was diminished upon PEG incorporation. The overall results identified a BSA-NP coating structure that provided effective siRNA encapsulation while reducing ζ-potential, protein adsorption, and cytotoxicity, necessary attributes for in vivo application of drug-delivery vehicles.

Novel biomimetic vectors with endosomal-escape agent enhancing gene transfection efficiency

Low cytotoxicity and high transfection efficiency are critical issues in designing current non-viral gene delivery vectors. In the present study, a novel biomimetic lipid-polycation copolymer, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-graft-poly(l-lysine)-block-poly(ethylene glycol) (DOPE-g-PLL-b-PEG) was first synthesized and the potential of this novel hybrid lipid-polycation as efficient gene vector was further evaluated. DOPE-g-PLL-b-PEG and DNA could self-assemble into lipid modified polyion complex micelles (LPCM) through electrostatic interactions. Compared with PEG-b-PLL/DNA polyion complex micelles (PIC), LPCM could protect DNA from plasma, nuclease degradation in vitro and showed lower cytotoxicity to HepG2 and HeLa cells (P<0.05). The results of transfection study in vitro indicated that LPCM exhibited higher gene expression than PIC. Especially, the corresponding LPCM displayed the highest transfection efficiency in HeLa cells (P<0.05) when DOPE grafting ratio reached up to 30%. These results suggested that LPCM could facilitate gene transfer in cultured cells and might alleviate the drawbacks of the conventional cationic vector/DNA complexes. As a novel hybrid lipid-polycation, DOPE-g-PLL-b-PEG was valuable to be evaluated for its further application as gene carrier in vivo.

Lipid substitution on low molecular weight (0.6-2.0 kDa) polyethylenimine leads to a higher zeta potential of plasmid DNA and enhances transgene expression

Cationic polymers are desirable gene carriers because of their better safety profiles than viral delivery systems. Low molecular weight (MW) polymers are particularly attractive, since they display little cytotoxicity, but they are also ineffective for gene delivery. To create effective carriers from low MW polymers palmitic acid (PA) was substituted on 0.6-2.0 kDa polyethylenimines (PEIs) and their efficiency for plasmid DNA (pDNA) delivery was evaluated. The extent of lipid substitution was dependent on the lipid/PEI feed ratio and the polymer MW. While the hydrodynamic size of the polymer/pDNA complexes (polyplexes) increased or decreased depending on the extent of lipid substitution, the ζ potential of the assembled complexes was consistently higher as a result of lipid substitution. Lipid substitution generally increased the in vitro toxicity of the PEIs, but it was significantly lower than that of the 25 kDa branched PEI. The in vitro transfection efficiency of the lipid-substituted polymers was higher than that of native PEIs, which were not at all effective. The delivery efficiency was proportional to the extent of lipid substitution as well as the polymer MW. This correlated with the increased uptake of lipid-substituted polyplexes, based on confocal microscopic investigations with FITC-labeled pDNA. The addition of chloroquine further increased the transfection efficiency of lipid-substituted PEIs, indicating that endosomal release was a limiting factor affecting the efficiency of these carriers. This study indicates that lipid substitution on low MW PEIs makes their assembly more effective, resulting in better delivery of pDNA into mammalian cells.

Nonviral delivery of basic fibroblast growth factor gene to bone marrow stromal cells

Basic fibroblast growth factor (bFGF) is capable of stimulating osteogenic differentiation of preosteoblast cells in vitro and new bone tissue deposition in vivo. Delivering the gene for the protein, rather than the protein itself, is considered advantageous for bone repair since gene delivery obviates the need to produce the protein in pharmaceutical quantities. To explore the feasibility of bFGF gene delivery by nonviral methods, we transfected primary rat bone marrow stromal cells (BMSC) using cationic polymers (polyethylenimine and poly(L-lysine)-palmitic acid) in vitro. After delivering a bFGF-expression plasmid (pFGF2-IRES-AcGFP) to BMSC, the presence of bFGF in culture supernatants was detected by a commercial ELISA. As much as 0.3 ng bFGF/10(6) cells/day was obtained from the BMSC under optimal conditions. This secretion rate was approximately 100-fold lower than the secretion obtained from immortal, and easy-to-transfect, human 293T cells. These data suggest the feasibility of modifying BMSC with nonviral delivery systems for bFGF expression, but also highlight the need for substantial improvement in transfection rate for an effective therapy.

Relationship between the extent of lipid substitution on poly(L-lysine) and the DNA delivery efficiency

Poly(L-lysine) (PLL) is a commonly used polymer for nonviral gene delivery. However, the polymer exhibits significant toxicity and is not very effective for transgene expression. To enhance the gene delivery efficiency of the polymer, we imparted an amphiphilic property to PLL by substituting approximately 10% of epsilon-NH2 with several endogenous lipids of variable chain lengths (lipid carbon chain ranging from 8 to 18). Lipid-modified PLL with high molecular weight (approximately 25 vs 4 kDa) was found to be more effective in delivering plasmid DNA intracellularly in clinically relevant bone marrow stromal cells (BMSC). For lipid-substituted 25 kDa PLL, a correlation between the extent of lipid substitution and the plasmid DNA delivery efficiency was obtained. Additionally, transgene expression by BMSC significantly increased (20-25%) when amphiphilic PLLs were used for plasmid delivery as compared to native PLL and the commercial transfection agent Lipofectamine-2000. The transfection efficiency of the polymers was positively correlated with the extent of lipid substitution. The amphiphilic polymers were able to modify the cells up to 7 days after transfection, after which the expression was decreased to background levels within 1 week. We conclude that lipid-substituted PLL can be used effectively as a nonviral carrier for DNA, and the extent of lipid substitution was an important determinant of gene delivery.