Controlled DNA delivery systems

Delivery of plasmid DNA to articular chondrocytes via novel collagen-glycosaminoglycan matrices

Our primary objective was to fabricate a porous gene-supplemented collagen-glycosaminoglycan (GSCG) matrix for sustained delivery (over a period of several weeks) of plasmid DNA to articular chondrocytes when implanted into cartilage lesions. The specific aims of this in vitro study were to determine the release kinetics profiles of plasmid DNA from the GSCG matrices, and to determine the ability of the released plasmid DNA to transfect adult canine articular chondrocytes. In particular, we evaluated the effects of two variables, cross-linking treatment and the pH at which the DNA was incorporated into the matrices, on the amount of the plasmid DNA that remained bound to the GSCG matrices after passive (nonenzymatic) leaching and on the expression of a reporter gene in articular chondrocytes grown in the GSCG matrices. Collagen-glycosaminoglycan matrices were synthesized without cross-linking, and by three cross-linking treatments: dehydrothermal (DHT) treatment, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) treatment, and exposure to ultraviolet (UV) radiation. The plasmid DNA was incorporated into the collagen-glycosaminoglycan matrices in solutions at pH 2.5 or 7.5. Transmission electron microscopy studies revealed plasmid DNA bound to the walls of the porous GSCG matrices. In general, the GSCG matrices fabricated at pH 2.5 retained a larger fraction of the initial DNA load after 28 days of incubation in Tris-EDTA buffer. The passive, solvent-mediated release of the plasmid DNA from the GSCG matrices showed a biphasic pattern consisting of a faster, early release rate over the initial 8 hr of leaching followed by a slower, late release rate that was relatively constant over the subsequent 28 days of leaching. Electrophoretic analyses revealed that the plasmid DNA released from the GSCG matrices fabricated at pH 2.5 had been linearized and/or degraded; whereas the plasmid DNA leached from the GSCG matrices prepared with a DNA solution at pH 7.5 was primarily supercoiled and linear. Plasmid DNA released from all GSCG matrix formulations was able to generate luciferase reporter gene expression in monolayer-cultured chondrocytes transfected with the aid of a commercial lipid reagent, and in chondrocytes cultured in the GSCG matrices without the aid of a supplemental transfection reagent. Luciferase expression in chondrocyte-seeded GSCG constructs was evident throughout the culture period (28 days), with the EDC and UV cross-linked matrices prepared at pH 7.5 providing the highest transgene expression levels. We conclude that released plasmid DNA continually transfected canine articular chondrocytes seeded into GSCG matrices in vitro for a 4-week period as evidenced by luciferase reporter gene expression. Thus, GSCG matrices can be fabricated to provide sustained release of plasmid DNA carrying a potential therapeutic gene.

Controlled release of plasmid DNA from cationized gelatin hydrogels based on hydrogel degradation

This paper shows achievement of the in vivo controlled release of a plasmid DNA from a biodegradable hydrogel and the consequent regulation of gene expression period. Cationization of gelatin was preformed through introduction of ethylenediamine and the gelatin prepared was crosslinked by various concentrations of glutaraldehyde to obtain cationized gelatin (CG) hydrogels as the carrier of plasmid DNA. In vivo release of plasmid DNA from the CG hydrogels was compared with the in vivo degradation of hydrogels. When CG hydrogels incorporating 125I-labeled plasmid DNA were implanted into the femoral muscle of mice, the plasmid DNA radioactivity remaining decreased with time and the retention period prolonged with a decrease in the water content of hydrogels used. The higher the water content of 125I-labeled CG hydrogels, the faster the hydrogel radioactivity remaining decreased with time. The time profile of plasmid DNA remaining in the hydrogels was in good accordance with that of hydrogel radioactivity, irrespective of the water content. Intramuscular implantation of plasmid DNA-incorporated CG hydrogels enhanced significantly expression of the plasmid DNA around the implanted site. The retention period of gene expression became longer as the hydrogel water content decreased. Fluorescent microscopic study revealed that the plasmid DNA-CG complex was detected around the hydrogel implanted even after 7-day implantation in marked contrast to the injection of plasmid DNA solution. It was concluded that in our hydrogel system, active plasmid DNA was released accompanied with the in vivo degradation of hydrogel, resulting in extended gene expression. The time profile of plasmid DNA release and the consequent gene expression was controllable by changing the water content of hydrogels.

Building drug delivery into tissue engineering

The creation of efficient methods for manufacturing biotechnology drugs--many of which influence fundamental but complex cell behaviours, such as proliferation, migration and differentiation--is creating new opportunities for tissue repair. Many agents are potent and multifunctional; that is, they produce different effects within different tissues. Therefore, control of tissue concentration and spatial localization of delivery is essential for safety and effectiveness. Synthetic systems that can control agent delivery are particularly promising as materials for enhancing tissue regeneration. This review discusses the state of the art in controlled-release and microfluidic drug delivery technologies, and outlines their potential applications for tissue engineering.

Anticoagulant activity of heparin following oral administration of heparin-loaded microparticles in rabbits

Heparin-loaded microparticles, prepared according to the double emulsion method with biodegradable (PCL and PLGA) and nonbiodegradable (Eudragit RS and RL) polymers used alone or in combination, with or without gelatin, were characterized in vitro and in vivo after oral administration in rabbits. The entrapment efficiency and the release of heparin were determined by a colorimetric method with Azure II. The antifactor Xa activity of heparin released in vitro after 24 h was assessed. After oral administration of heparin-loaded microparticles in rabbits, the time course of modification of the clotting time estimated by the activated partial thromboplastin time (APTT) was followed over 24 h. Microparticles with a size ranging from 80 to 280 microm were obtained. Heparin entrapment efficiency as well as heparin release depended on both the nature of the polymers and the presence of gelatin. The Eudragit polymers increased the drug loading but slowed down the heparin release, whereas gelatin accelerated the release. No change in clotting time was observed after oral administration of gelatin microparticles. Heparin-loaded microparticles prepared with blends of PLGA and Eudragit displayed a prolonged duration of action characterized by a twofold increase in APTT and a enhancement of absorption. This study demonstrated the feasibility of encapsulating heparin within polymeric particles, and the significant increase in APTT confirmed the oral absorption of heparin released from polymeric microparticles.

Drug-releasing scaffolds fabricated from drug-loaded microspheres

Biodegradable scaffolds serve a central role in many strategies for engineering tissue replacements or in guiding tissue regeneration. Typically, these scaffolds function to create and maintain a space and to provide a support for cell adhesion. However, these scaffolds also can serve as vehicles for the delivery of bioactive factors (e.g., protein or DNA) in order to manipulate cellular processes within the scaffold microenvironment. This study presents a novel approach to fabricate tissue-engineering scaffolds capable of sustained drug delivery whereby drug-loaded microspheres are fabricated into structures with controlled porosity. A double-emulsion process was used to fabricate microspheres with encapsulated DNA that retained its integrity and was released from the microspheres within 24 h. These DNA-loaded microspheres subsequently were formed into a nonporous disk or an interconnected open-pore scaffold (>94% porosity) via a gas-foaming process. The disks and scaffolds exhibited sustained plasmid release for at least 21 days and had minimal burst during the initial phase of release. This approach of assembling drug-loaded microspheres into porous and nonporous structures may find great utility in the fabrication of synthetic matrices that direct tissue formation.

Studies on the potential of microparticles entrapping pDNA-poly(aminoacids) complexes as vaccine delivery systems

Poly(D,L-lactide-co-glycolide) (PLGA) microparticles containing plasmid DNA (pDNA) have potential uses as vaccine delivery systems. Nevertheless, the established double emulsion and solvent evaporation method used to produce them is characterised by a low encapsulation efficiency (about 20%) and nicks the supercoiled DNA. The aim of this work was to develop an encapsulation process to optimise the overall encapsulation efficiency and the supercoiled DNA content, to obtain a carrier suitable for mucosal delivery of DNA vaccines. Our strategy was to reduce the global negative charge of DNA which was unfavourable to its incorporation into the polymer by condensing it with cationic poly(aminoacids) which were previously reported to improve cell transfection. In this study, after characterisation of the compaction of DNA plasmid encoding for a Green Fluorescent Protein, we demonstrated that resulting complexes were successfully encapsulated into PLGA microparticles presenting a mean size around 4.5 microns. The preliminary step of complexation enhances the yield of the process by a factor 4.1 and protects the supercoiled form. In a bacteria transformation assay, we demonstrated that extracted pDNA (naked or complexed) remained in a transcriptionally active form after encapsulation. Bovine macrophages in culture phagocytosed microparticles loaded with uncomplexed/complexed with poly(L-lysine) pDNA. The production of the Green Fluorescent Protein demonstrated that these carriers could deliver intact and functional plasmid DNA probably by escaping from lysosomal degradation.

Transplantation of brain cells assembled around a programmable synthetic microenvironment

Cell therapy is a promising method for treatment of hematopoietic disorders, neurodegenerative diseases, diabetes, and tissue loss due to trauma. Some of the major barriers to cell therapy have been partially addressed, including identification of cell populations, in vitro cell proliferation, and strategies for immunosuppression. An unsolved problem is recapitulation of the unique combinations of matrix, growth factor, and cell adhesion cues that distinguish each stem cell microenvironment, and that are critically important for control of progenitor cell differentiation and histogenesis. Here we describe an approach in which cells, synthetic matrix elements, and controlled-release technology are assembled and programmed, before transplantation, to mimic the chemical and physical microenvironment of developing tissue. We demonstrate this approach in animals using a transplantation system that allows control of fetal brain cell survival and differentiation by pre-assembly of neo-tissues containing cells and nerve growth factor (NGF)-releasing synthetic particles.

Poly(lactic acid)-poly(ethylene glycol) nanoparticles as new carriers for the delivery of plasmid DNA

The purpose of the present work was to produce and characterize poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) nanoparticles (size lower than 300 nm) containing a high loading of plasmid DNA in a free form or co-encapsulated with either poly(vinyl alcohol) (PVA) or poly(vinylpyrrolidone) (PVP). The plasmid alone or with PVA or PVP was encapsulated by two different techniques: an optimized w/o/w emulsion-solvent evaporation technique as well as by a new w/o emulsion-solvent diffusion technique. Particle size, zeta potential, plasmid DNA loading and in vitro release were determined for the three plasmid-loaded formulations. The influence of the initial plasmid loadings (5, 10, 20 microg plasmid DNA/mg PLA-PEG) on those parameters was also investigated. The plasmid loaded into the nanoparticles and released in vitro was quantified by fluorimetry and the different molecular forms were identified by gel electrophoresis. PLA-PEG nanoparticles containing plasmid DNA in a free form or co-encapsulated with PVA or PVP were obtained in the range size of 150-300 nm and with a negative zeta potential, both parameters being affected by the preparation technique. Encapsulation efficiencies were high irrespective of the presence of PVA or PVP (60-90%) and were slightly affected by the preparation technique and by the initial loading. The final plasmid DNA loading in the nanoparticles was up to 10-12 microg plasmid DNA/mg polymer. Plasmid DNA release kinetics varied depending on the plasmid incorporation technique: nanoparticles prepared by the w/o diffusion technique released their content rapidly whereas those obtained by the w/o/w showed an initial burst followed by a slow release for at least 28 days. No significant influence of the plasmid DNA loading and of the co-encapsulation of PVP or PVA on the in vitro release rate was observed. In all cases the conversion of the supercoiled form to the open circular and linear forms was detected. In conclusion, plasmid DNA can be very efficiently encapsulated, either in a free form or in combination with PVP and PVA, into PLA-PEG nanoparticles. Additionally, depending on the processing conditions, these nanoparticles release plasmid DNA either very rapidly or in a controlled manner.

Plasmid DNA encapsulation and release from solvent diffusion nanospheres

The first step toward hydrophobic polymer-based nanospheres for gene delivery is to encapsulate and release plasmid DNA. However, encapsulating large hydrophilic molecules in very small nanospheres has been difficult, and only a few examples exist in the literature. For example, maximizing protein and peptide as well as small molecule encapsulation requires adjustments in pH or addition of excipients to charge neutralize, and make less hydrophilic, the compound to be encapsulated. Following this model, we have used a cationic lipid to load and release plasmid DNA from nanospheres made by the phase inversion/solvent diffusion method.

Innovations in oral gene delivery: challenges and potentials

The oral delivery of peptide, protein, vaccine and nucleic acid-based biotechnology products is the greatest challenge facing the drug delivery industry. Oral delivery is attractive due to factors such as ease of administration, leading to improved patient convenience and compliance, thereby reducing overall healthcare costs. The realization that gene therapy will provide a tangible and potentially huge new therapeutic opportunity has stimulated interest in oral gene delivery. Here we summarize the oral gene delivery vehicles currently in use and highlight potential areas of application, along with the challenges that need to be overcome before this new technology enters the clinic.

Sustained delivery and expression of DNA encapsulated in polymeric nanoparticles

Sustained release polymeric gene delivery systems offer increased resistance to nuclease degradation, increased amounts of plasmid DNA (pDNA) uptake, and the possibility of control in dosing and sustained duration of pDNA administration. Furthermore, such a system lacks the inherent problems associated with viral vectors. Biodegradable and biocompatible poly(DL-lactide-co-glycolide) polymer was used to enacapsulate pDNA (alkaline phosphatase, AP, a reporter gene) in submicron size particles. Gene expression mediated by the nanoparticles (NP) was evaluated in vitro and in vivo in comparison to cationic-liposome delivery. Nano size range (600 nm) pDNA-loaded in poly(DL-lactide-co-glycolide) polymer particles with high encapsulation efficiency (70%) were formulated, exhibiting sustained release of pDNA of over a month. The entrapped plasmid maintained its structural and functional integrity. In vitro transfection by pDNA-NP resulted in significantly higher expression levels in comparison to naked pDNA. Furthermore, AP levels increased when the transfection time was extended, indicating sustained activity of pDNA. However, gene expression was significantly lower in comparison with standard liposomal transfection. Seven days after i.m. injections in rats, naked pDNA and pDNA-NP were found to be significantly more potent (1-2 orders of magnitude) than liposomal pDNA. Plasmid DNA-NP treatment exhibited increased AP expression after 7 and 28 days indicating sustained activity of the NP.

Formulation and in vitro transfection efficiency of poly (D, L-lactide-co-glycolide) microspheres containing plasmid DNA for gene delivery

The stability, in vitro release, and in vitro cell transfection efficiency of plasmid DNA (pDNA) poly (D,L-lactide-co-glycolide) (PLGA) microsphere formulations were investigated. PLGA microspheres containing free and polylysine (PLL)-complexed pDNA were prepared by a water-oil-water solvent extraction/evaporation technique. Encapsulation enhanced the retention of the supercoiled structure of pDNA as determined by gel electrophoresis. PLL complexation of pDNA prior to encapsulation increased both the stability of the supercoiled form and the encapsulation efficiency. Free pDNA was completely degraded after exposure to DNase, while encapsulation protected the pDNA from enzymatic degradation. Rapid initial in vitro release of pDNA was obtained from microspheres containing free pDNA, while the release from microspheres containing PLL-complexed pDNA was sustained for more than 42 days. Bioactivity of encapsulated pDNA determined by in vitro cell transfection using Chinese hamster ovary cells (CHO) showed that the bioactivity of encapsulated pDNA was retained in both formulations but to a greater extent with PLL-complexed pDNA microspheres. These results demonstrated that PLGA microspheres could be used to formulate a controlled-release delivery system for pDNA that can protect the pDNA from DNase degradation without loss of functional activity.

Synthetic DNA delivery systems

The ability to safely and efficiently transfer foreign DNA into cells is a fundamental goal in biotechnology. Toward this end, rapid advances have recently been made in our understanding of mechanisms for DNA stability and transport within cells. Current synthetic DNA delivery systems are versatile and safe, but substantially less efficient than viruses. Indeed, most current systems address only one of the obstacles to DNA delivery by enhancing DNA uptake. In fact, the effectiveness of gene expression is also dependent on several additional factors, including the release of intracellular DNA, stability of DNA in the cytoplasm, unpackaging of the DNA-vector complex, and the targeting of DNA to the nucleus. Delivery systems of the future must fully accommodate all these processes to effectively shepherd DNA across the plasma membrane, through the hostile intracellular environment, and into the nucleus.