PLGA microspheres containing plasmid DNA: preservation of supercoiled DNA via cryopreparation and carbohydrate stabilization

Formulation and characterization of poly (β amino ester) microparticles for genetic vaccine delivery

Microparticulate delivery systems are a promising and versatile enhancement to DNA vaccines because they can target large payloads of plasmid and immunomodulating materials to antigen presenting cells (APC). A pH sensitive poly-beta amino ester (PBAE) has been recently described which substantially increases adjuvancy and delivery efficiency of such microparticle formulations. This work describes the characterization and formulation considerations specific to these PBAE containing microparticles. PBAE increases the supercoiled content and overall effective loading of plasmid DNA. This polymer also significantly buffers the pH microenvironment created by ester bond degradation, rendering encapsulated plasmid more suitable for transfection. Release of plasmid from microparticles is controllable based on the amount of PBAE in the composition. Transfection is dependant upon phagocytosis, and is optimal for 15% and 25% PBAE microparticle formulations. However, larger quantities of PBAE may be toxic to cells indicating that the 15% PBAE formulation is a suitable candidate for delivery in future studies with disease specific, DNA vaccines.

Neurotrophin releasing single and multiple lumen nerve conduits

Tissue engineering strategies for nerve repair employ polymer conduits termed guidance channels and bridges to promote regeneration for peripheral nerve injury and spinal cord injury, respectively. An approach for fabrication of nerve conduits with single and multiple lumens capable of controlled release of neurotrophic factors was developed. These conduits were fabricated from a mixture of poly(lactide-co-glycolide) (PLG) microspheres and porogen (NaCl) that was loaded into a mold and processed by gas foaming. The porosity and mechanical properties of the constructs were regulated by the ratio of porogen to polymer microsphere. The neurotrophin, nerve growth factor (NGF), was incorporated into the conduit by either mixing the protein with microspheres or encapsulating the protein within microspheres prior to gas foaming. A sustained release was observed for at least 42 days, with the release rate controlled by method of incorporation and polymer molecular weight. Released NGF retained its bioactivity, as demonstrated by its ability to stimulate neurite outgrowth from primary dorsal root ganglion (DRG). In vivo results indicate that conduits retain their original architecture, and allow for cellular infiltration into the channels. Polymer conduits with controllable lumen diameters and protein release may enhance nerve regeneration by guiding and stimulating neurite outgrowth.

Bone regeneration in a rat cranial defect with delivery of PEI-condensed plasmid DNA encoding for bone morphogenetic protein-4 (BMP-4)

Gene therapy approaches to bone tissue engineering have been widely explored. While localized delivery of plasmid DNA encoding for osteogenic factors is attractive for promoting bone regeneration, the low transfection efficiency inherent with plasmid delivery may limit this approach. We hypothesized that this limitation could be overcome by condensing plasmid DNA with nonviral vectors such as poly(ethylenimine) (PEI), and delivering the plasmid DNA in a sustained and localized manner from poly(lactic-co-glycolic acid) (PLGA) scaffolds. To address this possibility, scaffolds delivering plasmid DNA encoding for bone morphogenetic protein-4 (BMP-4) were implanted into a cranial critical-sized defect for time periods up to 15 weeks. The control conditions included no scaffold (defect left empty), blank scaffolds (no delivered DNA), and scaffolds encapsulating plasmid DNA (non-condensed). Histological and microcomputed tomography analysis of the defect sites over time demonstrated that bone regeneration was significant at the defect edges and within the defect site when scaffolds encapsulating condensed DNA were placed in the defect. In contrast, bone formation was mainly confined to the defect edges within scaffolds encapsulating plasmid DNA, and when blank scaffolds were used to fill the defect. Histomorphometric analysis revealed a significant increase in total bone formation (at least 4.5-fold) within scaffolds incorporating condensed DNA, relative to blank scaffolds and scaffolds incorporating uncondensed DNA at each time point. In addition, there was a significant increase both in osteoid and mineralized tissue density within scaffolds incorporating condensed DNA, when compared with blank scaffolds and scaffolds incorporating uncondensed DNA, suggesting that delivery of condensed DNA led to more complete mineralized tissue regeneration within the defect area. This study demonstrated that the scaffold delivery system encapsulating PEI-condensed DNA encoding for BMP-4 was capable of enhancing bone formation and may find applications in other tissue types.

Novel approaches to vaccine delivery

Although the currently available vaccines represent an outstanding success story in modern medicine and have had a dramatic effect on morbidity and mortality worldwide, it is clear that improvements are required in the current vaccine delivery technologies. Improvements are required to enable the successful development of vaccines against infectious diseases that have so far proven difficult to control with conventional approaches. Improvements may include the addition of novel injectable adjuvants or the use of novel routes of delivery, including mucosal immunization. Mucosal delivery may be required to provide protection against pathogens that infect at mucosal sites, including sexually transmitted diseases. Alternatively, novel approaches to delivery, including mucosal administration, may be used to improve compliance for existing vaccines. Of particular interest for safer mass immunization campaigns are needle-free delivery devices, which would avoid problems due to needle re-use in many parts of the world and would avoid needle-stick injuries.

Mucosal adjuvants and delivery systems for protein-, DNA- and RNA-based vaccines

Almost all vaccinations today are delivered through parenteral routes. Mucosal vaccination offers several benefits over parenteral routes of vaccination, including ease of administration, the possibility of self-administration, elimination of the chance of injection with infected needles, and induction of mucosal as well as systemic immunity. However, mucosal vaccines have to overcome several formidable barriers in the form of significant dilution and dispersion; competition with a myriad of various live replicating bacteria, viruses, inert food and dust particles; enzymatic degradation; and low pH before reaching the target immune cells. It has long been known that vaccination through mucosal membranes requires potent adjuvants to enhance immunogenicity, as well as delivery systems to decrease the rate of dilution and degradation and to target the vaccine to the site of immune function. This review is a summary of current approaches to mucosal vaccination, and it primarily focuses on adjuvants as immunopotentiators and vaccine delivery systems for mucosal vaccines based on protein, DNA or RNA. In this context, we define adjuvants as protein or oligonucleotides with immunopotentiating properties co-administered with pathogen-derived antigens, and vaccine delivery systems as chemical formulations that are more inert and have less immunomodulatory effects than adjuvants, and that protect and deliver the vaccine through the site of administration. Although vaccines can be quite diverse in their composition, including inactivated virus, virus-like particles and inactivated bacteria (which are inert), protein-like vaccines, and non-replicating viral vectors such as poxvirus and adenovirus (which can serve as DNA delivery systems), this review will focus primarily on recombinant protein antigens, plasmid DNA, and alphavirus-based replicon RNA vaccines and delivery systems. This review is not an exhaustive list of all available protein, DNA and RNA vaccines, with related adjuvants and delivery systems, but rather is an attempt to highlight many of the currently available approaches in immunopotentiation of mucosal vaccines.

Transfection of a mouse dendritic cell line by plasmid DNA-loaded PLGA microparticles in vitro

Targeting of DC for DNA vaccination may be achieved by DNA-loaded poly(lactide-co-glycolide) (PLGA) biodegradable microparticles, since DC efficiently capture these microparticles in vitro and in vivo. DNA was encapsulated in PLGA microparticles by spray-drying. Various additives were tested and process parameters adjusted in order to prevent degradation of the DNA during encapsulation. The highest degree of supercoiled DNA was maintained by adding a strong buffering agent, such as PBS or NaHCO(3), whereas the cryoprotective lactose did not show a significant protective effect. DNA-containing PLGA microparticles were administered to a mouse DC line. Transfection efficacy was compared with commonly employed cationic transfectants and was visually assessed by green fluorescent protein expression. Transfection rate was very low in DC for all microparticle formulations and was comparable with commonly used cationic transfectants. It is concluded that the transfection of DC using PLGA microparticles is feasible, but efforts need to be undertaken to improve transfection efficiency in vitro, which may in addition lead to improved immune responses in vivo.

Charged polylactide co-glycolide microparticles as antigen delivery systems

Polymeric microparticles with encapsulated antigens have become well-established in the last decade as potent antigen delivery systems and adjuvants, with experience being reported from many groups. However, the authors have recently shown that an alternative approach involving charged polylactide co-glycolide (PLG) microparticles with surface adsorbed antigen(s) can also be used to deliver antigen into antigen-presenting cell populations. The authors have described the preparation of cationic and anionic PLG microparticles that have been used to adsorb a variety of agents, to include plasmid DNA, recombinant proteins and adjuvant active oligonucleotides. These novel PLG microparticles were prepared using a w/o/w solvent evaporation process in the presence of the anionic surfactants, such as dioctyl sodium sulfosuccinate, or cationic surfactants, such as hexadecyl trimethyl ammonium bromide. Antigen binding to the charged PLG microparticles was influenced by both electrostatic interaction and other mechanisms, including hydrophobic interactions. Adsorption of antigens to microparticles resulted in the induction of significantly enhanced immune responses in comparison with alternative approaches. The surface adsorbed microparticle formulation offers an alternative way of delivering antigens as a vaccine formulation.

Microspheres for controlled release drug delivery

Controlled release drug delivery employs drug-encapsulating devices from which therapeutic agents may be released at controlled rates for long periods of time, ranging from days to months. Such systems offer numerous advantages over traditional methods of drug delivery, including tailoring of drug release rates, protection of fragile drugs and increased patient comfort and compliance. Polymeric microspheres are ideal vehicles for many controlled delivery applications due to their ability to encapsulate a variety of drugs, biocompatibility, high bioavailability and sustained drug release characteristics. Research discussed in this review is focused on improving large-scale manufacturing, maintaining drug stability and enhancing control of drug release rates. This paper describes methods of microparticle fabrication and the major factors controlling the release rates of encapsulated drugs. Furthermore, recent advances in the use of polymer microsphere-based systems for delivery of single-shot vaccines, plasmid DNA and therapeutic proteins are discussed, as well as some future directions of microsphere research.

Sustained in Vivo Gene Delivery from Agarose Hydrogel Prolongs Nonviral Gene Expression in Skin

Prolonging gene expression in skin using safe, nonviral gene delivery techniques could impact skin regeneration and wound healing, decrease infection, and potentially improve the success of tissue-engineered skin. To this end, an injectable, agarose-based delivery system was tested and shown to prolong nonviral gene expression in the skin. DNA was compacted with polylysine to improve DNA stability in the presence of nucleases. Up to 25 microg of compacted luciferase plasmid with or without agarose hydrogel was injected intradermally in rodents. Bioluminescence imaging was used for longitudinal, noninvasive monitoring of gene expression in vivo for 35 days. Injections of DNA in solution produced gene expression for only 5-7 days, whereas the sustained release of compacted DNA from the agarose system prolonged expression, with more than 500 pg (20% of day 1 levels) of luciferase per site for at least 35 days. Southern blotting confirmed that the agarose system extended DNA retention, with significant plasmid present through day 7, as compared with DNA in solution, which had detectable DNA only on day 1. Histology revealed that agarose invoked a wound-healing response through day 14. Tissue-engineering and wound-healing applications may benefit from the agarose gene delivery system.

Release characteristics of a model plasmid DNA encapsulated in biodegradable poly(ethylene glycol fumarate)/acrylamide hydrogel microspheres

Biodegradable hydrogel microspheres were synthesized by free radical suspension copolymerization of poly(ethylene glycol fumarate) macromer with bisacrylamide (PEGF/PAM). The acidic initiator ammonium persulphate in combination with the basic accelerator, N,N,N',N'-tetramethyethylenediamine, were used to form the PEGF/PAM hydrogel at a neutral pH. The equilibrium water content of the microspheres was greater than 90% w/w. A model double stranded plasmid DNA (dsDNA) coding for the enhanced green fluorescence protein (pEGFP) gene was encapsulated in the hydrogel and the effect of loading and water content before swelling on release kinetics was investigated. Fluorescent confocal microscopy demonstrated that the encapsulated dsDNA was in the biologically active double stranded configuration. The highest loading of 0.81 mg ml(-1) resulted in the best encapsulation efficiency of 95%. For that loading, 6% of the dsDNA was released in 25 days at a rate of 16 ng ml(-1). The highest water content of 70% resulted in the highest burst release of 27% and 14% of the dsDNA was released in 25 days at a rate of 30 ng ml(-1). For elucidating the release mechanism, the network mesh size was compared with the radius of gyration (Rg) of the dsDNA plasmid. The mesh size was 7 nm, which was less than Rg of the dsDNA (31 nm) but greater than the chain diameter of 1.1 nm. Since the mesh size was less than Rg, the release mechanism was by reptation of the segments of dsDNA within the tube formed by the network chains between crosslinks. These results indicate that the hydrogel mesh size and the size of the plasmid control the release mechanism.

Recognition of an unnatural difluorophenyl nucleotide by uracil DNA glycosylase

The DNA repair enzyme uracil DNA glycosylase (UDG) utilizes base flipping to recognize and remove unwanted uracil bases from the genome but does not react with its structural congener, thymine, which differs by a single methyl group. Two factors that determine whether an enzyme flips a base from the duplex are its shape and hydrogen bonding properties. To probe the role of these factors in uracil recognition by UDG, we have synthesized a DNA duplex that contains a single difluorophenyl (F) nucleotide analogue that is an excellent isostere of uracil but possesses no hydrogen bond donor or acceptor groups. By using binding affinity measurements, solution (19)F NMR, and solid state (31)P[(19)F] rotational-echo double-resonance (REDOR) NMR measurements, we establish that UDG partially unstacks F from the duplex. However, due to the lack of hydrogen bonding groups that are required to support an open-to-closed conformational transition in UDG, F cannot stably dock in the UDG active site. We propose that F attains a metastable unstacked state that mimics a previously detected intermediate on the uracil-flipping pathway and suggest structural models of the metastable state that are consistent with the REDOR NMR measurements.

Delivery systems for small molecule drugs, proteins, and DNA: the neuroscience/biomaterial interface

Manipulation of cellular processes in vivo by the delivery of drugs, proteins or DNA is of paramount importance to neuroscience research. Methods for the presentation of these molecules vary widely, including direct injection (either systemic or stereotactic), osmotic pump-mediated chronic delivery, or even implantation of cells engineered to indefinitely secrete a factor of interest. Biomaterial-based delivery systems represent an alternative to more traditional approaches, with the possibility of increased efficacy. Drug-releasing biomaterials, either as injectable microspheres or as three-dimensional implants, can deliver a molecule of interest (including small molecule drugs, biologically active proteins, or DNA) over a more prolonged period of time than by standard bolus injection, avoiding the need for repeated administration. Furthermore, sustained-release systems can maintain therapeutic concentrations at a target site, thus reducing the chance for toxicity. This review summarizes applications of polymer-based delivery of small molecule drugs, proteins, and DNA specifically relevant to neuroscience research. We detail the fabrication procedures for the polymeric systems and their utility in various experimental models. The biomaterial field offers unique experimental tools with downstream clinical application for the study and treatment of neurologic disease.

PELGE Nanoparticles as New Carriers for the Delivery of Plasmid DNA

Biodegradable monomethoxy(polyethyleneglycol)-poly(lactide-co-glycolide)-monomethoxy(poly-ethyleneglycol) (PELGE) copolymers were synthesized by ring-opening polymerization to formulate plasmid DNA loaded nanoparticles. A double emulsion method with polyvinyl alcohol as the emulsifier in the external aqueous phase was employed to prepare nanoparticles. The effects of monomethoxypoly(ethyleneglycol) (mPEG) segments in the polymer on particle size, zeta potential, encapsulation efficiency and in vitro release were investigated. It was found that the introduction of a certain amount of hydrophilic mPEG segments in the copolymer chains could improve the affinity of copolymer with plasmid DNA and enhance the emulsification ability of the copolymer. Thus DNA loaded nanoparticles with smaller particle sizes and higher encapsulation efficiencies were obtained by using PELGE copolymer as the matrix.

The role of branched polyesters and their modifications in the development of modern drug delivery vehicles

Branched polyesters consisting of poly (vinyl alcohol) (PVA) grafted with chains of poly (lactic-co-glycolic acid) (PLGA) represent a new class of biodegradable polymers showing significant potential for the development of a variety of drug delivery vehicles. The amphiphilic character and the resulting increase in hydrophilicity of this class of polymers provide advantages when packaging sensitive drug molecules, such as proteins, peptides or DNA. Furthermore, the PVA backbone can be modified, for example, with sulfobutyl moieties or amine structures, to create polymers with negative or positive charges. The ability to modify not only the backbone but also the length of the PLGA side chains results in an extremely flexible polymer system, which can be adapted to meet the needs of almost any drug substance. Further, the rate of biodegradation may also be manipulated through polymer modification to achieve half-lives ranging from several hours to several weeks. This review provides an overview of the three major groups of branched polyesters based upon poly (vinyl alcohol)-grafted poly (lactic-co-glycolic acid) (PVA-g-PLGA), namely, the neutrally charged PVA-g-PLGA, the negatively charged sulfobutyl-modified PVA-g-PLGA and the positively charged amine-modified PVA-g-PLGA, as well as their use in various drug delivery systems.

PLGA:Poloxamer and PLGA:Poloxamine Blend Nanoparticles: New Carriers for Gene Delivery

The main objective of the present work was the development of new nanoparticulate carrier systems for the delivery of plasmid DNA. These new carriers consist of a blend matrix formed by a poly(lactic-co-glycolic acid) (PLGA) copolymer and polyoxyethylene derivatives. More specifically, we have prepared nanostructures with different PLGA:poloxamer and PLGA:poloxamine compositions by an optimized emulsification-solvent diffusion technique and studied the potential of these carriers for the encapsulation and controlled release of plasmid DNA. Depending on the particle composition, the encapsulation efficiency of the model plasmid pEGFP-C1 varied between 30% and 45%. All formulations provided continuous and controlled release of the plasmid with minimal burst effect. In addition, the release rate and duration was dependent on the composition of the particle matrix. Moreover, gel electrophoresis and cell culture (MCF-7 cell line) assays allowed us to confirm that the biologically active form of the plasmid was preserved during the particle preparation process and also during its release. Cell culture experiments also indicated that the new nanoparticles do not exhibit toxic effects on these cells at concentrations up to 5 mg/mL. Altogether, these results indicate that these composite nanostructures present a promising approach for the delivery of plasmid DNA.

Microparticles for the delivery of DNA vaccines

DNA vaccines have demonstrated a lack of adequate potency in humans, which has necessitated the exploration of various adjunct technologies. Inefficient delivery of DNA vaccines, particularly to antigen-presenting cells, may be contributing to this lack of potency. One effective means of facilitating delivery of DNA vaccines to APCs is through the use of microparticles. In this article, we review the background and rationale for microparticles as a vaccine delivery system, data demonstrating their utility and mode of action for DNA delivery, and the prospects for their development.

Plasmid-DNA loaded chitosan microspheres for in vitro IL-2 expression

Interleukin-2 (IL-2) expression plasmid (pCXWN-hIL-2) loaded chitosan microspheres were evaluated for using in gene-based immunotherapy. Chitosan microspheres containing pCXWN-hIL-2 were prepared by using a precipitation technique. In addition, the effects of different factors such as the concentration (0.35-0.70%) and the molecular weight of chitosan (low and medium molecular weights), the plasmid amount (5-10 microg/ml) and the presence of glutaraldehyde during the encapsulation process, on microsphere characteristics were investigated. The size of microspheres changed between 1.45 and 2.00 microm. All the formulation factors affected the size of microspheres. The structure of plasmid remained unchanged during the encapsulation process and the release studies. Plasmid encapsulation efficiency of chitosan microspheres was high (82-92%). The zeta potential values of microspheres was approximately +5.2 to +12.4 mV. In vitro release properties of microspheres changed with formulation variables. In vitro release of DNA changed with the concentration and molecular weight of chitosan and initial plasmid amount. Addition of glutaraldehyde is not necessary for a formulation. MAT-LyLu, the rat prostate adenocarcinoma cell line, was used for the determination of the in vitro transfectional activity of IL-2 encoding plasmid DNA loaded chitosan microspheres and the level of IL-2 expressed into the cells was assayed using a ELISA kit. High level of IL-2 expression was obtained with plasmid-loaded chitosan microspheres. Microspheres showed similar IL-2 production as lipofectin. The molecular weight of chitosan used and the amount of plasmid influenced the in vitro IL-2 production in the cells. Encapsulation of IL-2 encoding gene into chitosan microspheres might be a useful strategy to increase the expression and to control the delivery of cytokine gene to cells.

Enhanced protective efficacy of a tuberculosis DNA vaccine by adsorption onto cationic PLG microparticles

Immunization with plasmid DNA vectors represents a promising new approach to vaccination. It has been shown to elicit humoral and cellular immunity and protection in various infection models. Here, we assessed the immunogenicity and protective efficacy of a DNA vaccine vector encoding the antigen 85A (Ag85A) of Mycobacterium tuberculosis. Since intramuscular (i.m.) immunization with naked DNA requires considerable amounts of DNA in order to be effective, we evaluated a strategy to reduce the amount of DNA needed. To this end, we used Ag85A DNA adsorbed onto cationic poly(DL-lactide-co-glycolide) (PLG) microparticles and observed similar levels of protection against aerosol challenge in mice using doses of PLG-DNA two orders of magnitude lower than with naked DNA itself.

Degradation kinetics of high molecular weight poly(L-lactide) microspheres and release mechanism of lipid:DNA complexes

Plasmid DNA encoding the green lantern protein was ion-paired with 1,2-dioleoyl, 3-trimethylammonium propane (DOTAP) at a (+/-) charge ratio of (1:1) to form a hydrophobic ion-pair (HIP) complex using the Bligh and Dyer method, and transferred into methylene chloride. Precipitation with a compressed antisolvent (PCA) was then employed to encapsulate plasmid DNA into poly(L-lactide) (PLLA) microspheres. The hydrophobicity of DOTAP:DNA complexes allowed consistently high encapsulation efficiencies (>70%) to be achieved. Release of the DOTAP:DNA complex from PLLA microspheres exhibited minimal burst and a short (ca. 1 week) lag phase, followed by sustained release over a 20 week period. Release kinetics were consistent with a simple Fickian diffusion model. No correlation was identified between release rate of soluble poly(L-lactide) species (< or =10 lactate units) from PLLA and the DNA release kinetics. Only approximately 12% of the polymer was degraded into soluble poly(L-lactide) over the time frame where approximately 90% of the plasmid load had been released.

Multilayered thin films that sustain the release of functional DNA under physiological conditions

The development of thin films and coatings that control the release of DNA from the surfaces of materials could have a significant impact on localized approaches to gene therapy. Here, we report multilayered polyelectrolyte assemblies that sustain the release of functional plasmid DNA from the surfaces of model substrates under physiological conditions. Multilayered assemblies consisting of alternating layers of plasmid DNA encoding for enhanced green fluorescent protein (EGFP) and a synthetic degradable polyamine were deposited on planar silicon and quartz substrates using a layer-by-layer fabrication process. Film growth was monitored by ellipsometry and UV spectrophotometry and correlated linearly with the number of polymer and plasmid layers deposited. In general, the thickness of deposited layers was found to be a function of both the pH and the ionic strength of the polyelectrolyte solutions used. Films up to 100 nm thick were investigated in this study. These assemblies erode gradually upon incubation in phosphate-buffered saline at 37 degrees C, as determined by ellipsometry and UV spectrophotometry, and sustain the release of incorporated plasmid into the incubation medium for a period of up to 30 h. Characterization of the released plasmid by agarose gel electrophoresis revealed that the DNA was released in a relaxed, open circular, rather than supercoiled, topology; subsequent cell transfection experiments demonstrated that the released plasmid is transcriptionally viable and promotes the expression of EGFP in the COS-7 cell line. These layered materials could represent an approach to the controlled administration of one or more functional DNA constructs from the surfaces of biomedical materials and devices.

Controlled release systems for DNA delivery

Adapting controlled release technologies to the delivery of DNA has the potential to overcome extracellular barriers that limit gene therapy. Controlled release systems can enhance gene delivery and increase the extent and duration of transgene expression relative to more traditional delivery methods (e.g., injection). These systems typically deliver vectors locally, which can avoid distribution to distant tissues, decrease toxicity to nontarget cells, and reduce the immune response to the vector. Delivery vehicles for controlled release are fabricated from natural and synthetic polymers, which function either by releasing the vector into the local tissue environment or by maintaining the vector at the polymer surface. Vector release or binding is regulated by the effective affinity of the vector for the polymer, which depends upon the strength of molecular interactions. These interactions occur through nonspecific binding based on vector and polymer composition or through the incorporation of complementary binding sites (e.g., biotin-avidin). This review examines the delivery of nonviral and viral vectors from natural and synthetic polymers and presents opportunities for continuing developments to increase their applicability.

Delivering DNA from photocrosslinked, surface eroding polyanhydrides

Sustained delivery of DNA has the potential to enhance long-term gene therapy; however, precise control of a wide range of DNA release profiles may be needed. In this work, multifunctional anhydride monomers were photocrosslinked to produce hydrophobic, highly crosslinked polymer networks that degrade by surface erosion. Surface-eroding polymers can deliver molecules of a wide range of sizes at sustained, steady rates, which is advantageous for DNA delivery, where the high molecular weight may complicate control of the release profiles. When plasmid DNA was released from photocrosslinked polyanhydride matrices, DNA recovery was low (approximately 25%). Electrophoresis indicated that the plasmid DNA was released primarily in the relaxed and supercoiled forms, yet the relative fraction of released DNA in the supercoiled form decreased over time. To improve DNA recovery and reduce the damaging effects of polymer degradation, DNA was pre-encapsulated in alginate microparticles, which served as a temporary coating that quickly dissolved upon microparticle release from the polyanhydride matrix. As photocrosslinked polyanhydrides have highly predictable drug release profiles that depend on the polymer erosion rate and implant geometry and not on the entrapped molecule size, they can serve dual purposes in many biomaterial applications where structural support and drug release would be beneficial.

Stability and release characteristics of poly(D,L-lactide-co-glycolide) encapsulated CaPi-DNA coprecipitation

The aims of this work were to determine the stability of DNA-calcium-phosphate coprecipitation (CaPi-DNA) against various conditions during double emulsification microencapsulation and assess the release and physicochemical characteristics of poly(D,L-lactide-co-glycolide) (PLGA) microparticles loading CaPi-DNA. CaPi-DNA prepared at pH 6.5 showed a good stability with over 60% CaPi-DNA remained after emulsification, but no more than 40% at pH 8.0. Polyvinyl alcohol (PVA, 1-5%) could make over 80% CaPi-DNA (pH 7.0) preserved after homogenization. The dichloromethane (DCM), mixture of DCM and ethyl acetate, ether and n-hexane (1:1) exhibited neglectable influence on CaPi-DNA under homogenization. PLGA had influenced on CaPi-DNA without any additional stabilizer, in particular, PLGA (75:25, 4%, w/v) demonstrated a profound damage with only about 10% of the original CaPi-DNA remained. PLGA microparticles loading CaPi-DNA were spherical in shape with size range of 2.0-5.0microm, and entrapment efficiency 30-50%. CaPi-DNA was found to increase the stability of pDNA in PLGA microparticles without losing its structure integrity. The release of CaPi-DNA from microparticles showed a low burst release (<7.5%) within 24h and following sustained release process. The amount of cumulated CaPi-DNA release over 30 days was: 17.6% for PLGA (lactide:glycolide=50:50), 27.3% for PLGA (65:35) and 44.8% for PLGA (75:25) microparticles, respectively. The encapsulation of CaPi-DNA in microparticles could significantly protect CaPi-DNA from degradation of nuclease with average over 80% of total DNA recovery. These results suggested that the encapsulation of CaPi-DNA in PLGA microparticles could improve stability of pDNA.

Cross-Linked Microparticles as Carriers for the Delivery of Plasmid DNA for Vaccine Development

Plasmid DNA was directly encapsulated into biocompatible polymer microparticles via radical polymerization in an inverse emulsion system. Acrylamide-based microspheres 0.2-1 microm in diameter were prepared using an acid-cleavable difunctional monomer. Retention of the DNA payload at physiological pH with complete release under acidic conditions at lysosomal pH was demonstrated. By trapping the plasmid DNA within the cross-linked microparticle, enzymatic degradation was prevented when exposed to serum nucleases. For vaccine development, these delivery vehicles were also investigated for their ability to generate immune responses when delivered to phagocytic cells of the immune system. Encapsulated plasmid DNA demonstrated immunostimulatory activity in macrophages, leading to cytokine secretion of IL-6 with a response approximately 40-fold higher than that achieved with DNA alone.

Development of a calcium phosphate co-precipitate/poly(lactide-co-glycolide) DNA delivery system: release kinetics and cellular transfection studies

One of the most common non-viral methods for the introduction of foreign deoxyribonucleic acid (DNA) into cultured cells is calcium phosphate co-precipitate transfection. This technique involves the encapsulation of DNA within a calcium phosphate co-precipitate, particulate addition to in vitro cell culture, endocytosis of the co-precipitate, and exogenous DNA expression by the transfected cell. In this study, we fabricated a novel non-viral gene transfer system by adsorbing DNA, encapsulated in calcium phosphate (DNA/Ca-P) co-precipitates, to biodegradable two- and three-dimensional poly(lactide-co-glycolide) matrices (2D-DNA/Ca-P/PLAGA, 3D-DNA/Ca-P/PLAGA). Co-precipitate release studies demonstrated an initial burst release over the first 48 h. By day 7, approximately 96% of the initially adsorbed DNA/Ca-P co-precipitate had been released. This was followed by low levels of co-precipitate release for 42 days. Polymerase chain reaction was used to demonstrate the ability of the released DNA containing co-precipitates to transfect SaOS-2 cells cultured in vitro on the 3D-DNA/Ca-P/PLAGA matrix and maintenance of the structural integrity of the exogenous DNA. In summary, a promising system for the incorporation and controlled delivery of exogenous genes encapsulated within a calcium phosphate co-precipitate from biodegradable polymeric matrices has been developed and may have applicability to the delivery of therapeutic genes and the transfection of other cell types.

In vivo sustained release of adenoviral vectors from poly(d,l-lactic-co-glycolic) acid microparticles prepared by TROMS

We have prepared and characterised injectable adenovirus-loaded polymeric microparticles to be used for in vitro and in vivo gene transfer studies. Microparticles were prepared by the water-in-oil-in-water solvent evaporation method using a novel system where the emulsification process is carried out by the turbulent injection of the phases in the total recirculation one-machine system (TROMS) apparatus. In vitro studies were performed to assess the amount of infectious adenovirus released from the microparticles, showing that these microparticles release higher amounts of infectious adenovirus than microparticles prepared by standard emulsification techniques. We also tested whether sustained release in vivo could overcome the short-lived gene expression profile which is typical of adenovirus delivery into muscle. Intramuscular injection of adenovirus-loaded microparticles in immunocompetent mice showed transgene (beta-galactosidase) expression for at least 7 weeks in two out of four muscles injected with adenovirus-loaded microparticles prepared by TROMS, but not in control muscles injected with purified adenovirus stocks.

Formulations containing poly(lactide-co-glycolide) and plasmid DNA expression vectors

DNA expression vectors have the potential to be useful therapeutics for a wide variety of applications. However, development has been hindered by the lack of systems that provide protection from nuclease-based attack, enable cell or tissue localisation, promote adequate gene expression or provide for controlled release. At least one synthetic polymer, poly(lactide-co-glycolide) (PLG), may provide benefit in this regard. This polymer has a history of safe use in humans, has been demonstrated effective as a delivery system, its use is not hindered by composition patents, and Good Manufacturing Practices grade material is readily available from commercial sources. Safety and applicability to clinical medicine have been proven by use of the polymer as a microparticle delivery vehicle for peptides (luteinizing hormone releasing hormone agonist peptides; Lupron Depot [TAP Pharmaceuticals]; Zoladex [AstraZeneca]) and proteins (human growth hormone recombinant protein, Nutropin Depot [Genentech]). This report focuses on the expanding field of PLG-based DNA delivery and provides a review on research and clinical experience with PLG-plasmid formulations.

Biodegradable microspheres for protein delivery

In a very short time, since their emergence, the field of controlled delivery of proteins has grown immensely. Because of their relatively large size, they have low transdermal bioavailabilities. Oral bioavailability is generally poor since they are poorly absorbed and easily degraded by proteolytic enzymes in the gastrointestinal tract. Ocular and nasal delivery is also unfavorable due to degradation by enzymes present in eye tissues and nasal mucosa. Thus parenteral delivery is currently most demanding and suitable for delivery of such molecules. In systemic delivery of proteins, biodegradable microspheres as parenteral depot formulation occupy an important place because of several aspects like protection of sensitive proteins from degradation, prolonged or modified release, pulsatile release patterns. The main objective in developing controlled release protein injectables is avoidance of regular invasive doses which in turn provide patient compliance, comfort as well as control over blood levels. This review presents the outstanding contributions in field of biodegradable microspheres as protein delivery systems, their methods of preparation, drug release, stability, interaction with immune system and regulatory considerations.

Sustained release of plasmid DNA using lipid microtubules and agarose hydrogel

Non-viral gene therapy typically results in low transfection efficiencies and transient gene expression. To address these limitations, two sustained delivery systems capable of releasing functional, compacted DNA for over 50 days were designed. A luciferase plasmid was compacted with a polylysine-polyethylene glycol conjugate and released from agarose hydrogel and lipid microtubule-hydrogel delivery systems for over 50 days. The released DNA was characterized structurally using sedimentation, electron microscopy, and serum stability, and functionally using in vitro transfections. The released DNA retained its physical compaction and nuclease resistance and was converted from supercoiled to nicked and linear forms. Released compacted DNA produced significant gene expression in vitro, although at lower levels than freshly compacted DNA. Thus, hydrogels and lipid microtubules successfully provided the slow release of bioactive, compacted DNA.

The effect of CTAB concentration in cationic PLG microparticles on DNA adsorption and in vivo performance

PURPOSE

Cationic PLG microparticles with adsorbed DNA have previously been shown to efficiently target antigen presenting cells in vivo for generating higher immune responses in comparison to naked DNA. In this study we tried to establish the role of surfactant (CTAB) concentration on the physical behavior of these formulations.

METHODS

Cationic PLG microparticle formulations with adsorbed DNA were prepared using a solvent evaporation technique. Formulations with varying CTAB concentrations and a fixed DNA load were prepared. The loading efficiency and 24 h DNA release was evaluated for each formulation. Select formulations were tested in vivo.

RESULTS

Higher CTAB concentration correlated with higher DNA binding efficiency on the microparticles and lower in vitro release rates. Surprisingly though, the in vivo performance of formulations with varying CTAB concentration was comparable to one another.

CONCLUSIONS

Cationic PLG microparticles with adsorbed DNA, as described here, offer a robust way of enhancing in vivo responses to plasmid DNA.

Controllable delivery of non-viral DNA from porous scaffolds

The inductive approach to tissue engineering combines three-dimensional porous scaffolds with drug delivery to direct the action of progenitor cells into a functional tissue. We present an approach to fabricate scaffolds capable of controlled, sustained delivery by the assembly and subsequent fusion of drug-loaded microspheres using a gas foaming/particulate leaching process. DNA-loaded microspheres were fabricated from the copolymers of lactide and glycolide (PLG) using a cryogenic double emulsion process. Microspheres were fabricated in four populations with mean diameters ranging from 12.3 microm to 92.5 microm. Scaffolds fabricated by fusion of these microspheres had an interconnected open pore structure, maintained DNA integrity, and exhibited sustained release for 21 days. Control over the release was obtained through manipulating the properties of the polymer, microspheres, and the foaming process. Decreasing the microsphere diameter or the molecular weight of the polymer used for microsphere fabrication led to increased rates of release from the porous scaffold. Additionally, increasing the pressure of CO(2) increased the DNA release rate. The ability to create porous polymer scaffolds capable of controlled release rates may provide a means to enhance and regulate gene transfer within a developing tissue, which will increase their utility in tissue engineering.

Loading of plasmid DNA into PLGA microparticles using TROMS (Total Recirculation One-Machine System): evaluation of its integrity and controlled release properties

Loading plasmid DNA into poly(ester) microparticles usually involves the formation of a multiple emulsion, using homogenisation techniques such as sonication or Ultra-Turrax. These procedures may negatively affect the integrity of the macromolecule and consequently its activity. The aim of this study was to prepare and evaluate DNA-loaded microparticles by TROMS (Total Recirculation One-Machine System), a new procedure that is based on the formation of a multiple emulsion by the injection of the phases under a turbulent regime. Microparticles were prepared with either Resomer) RG 502 (MP 502) or RG 756 (MP 756) and DNA loading was quantified fluorimetrically. DNA loading in MP 756 was almost twice as high as in MP 502 (510 vs. 285 ng/mg, respectively). Under both formulations, the loaded plasmid was released while maintaining its integrity for at least 24 days (MP 502) and 40 days (MP 756). Finally, the transfection efficiency was studied after injection of the microparticles (MP 502) into rat skeletal muscle and compared with naked DNA injection. Injection of naked DNA (150 microg DNA per muscle) achieved higher but variable expression levels that decreased after 3 weeks. In contrast, the muscles injected with microparticles (6.8 microg DNA per muscle) showed lower but homogeneous expression values, which were maintained for at least 3 weeks.

Novel PDGFbetaR antisense encapsulated in polymeric nanospheres for the treatment of restenosis

Nanospheres composed of the biocompatible and biodegradable polymer, poly-DL-lactide/glycolide and containing platelet-derived growth factor beta-receptor antisense (PDGFbetaR-AS) have been formulated and examined in vitro and in vivo in balloon-injured rat restenosis model. The nanospheres (approximately 300 nm) of homogenous size distribution exhibited high encapsulation efficiency (81%), and a sustained release of PDGFbetaR-AS (phosphorothioated). Cell internalization was visualized, and the inhibitory effect on SMC was observed. Partially phosphorothioated antisense sequences were found to be more specific than the fully phosphorothioated analogs. A significant antirestenotic effect of the naked AS sequence and the AS-NP (nanoparticles) was observed in the rat carotid in vivo model. The extent of mean neointimal formation 14 days after injection of AS-NP, measured as a percentage of luminal stenosis, was 32.21 +/- 4.75% in comparison to 54.89 +/- 8.84 and 53.84 +/- 5.58% in the blank-NP and SC-NP groups, respectively. It is concluded that PLGA nanospheres containing phosphorothioated oligodeoxynucleotide antisense could serve as an effective gene delivery systems for the treatment of restenosis.

Size-dependency of nanoparticle-mediated gene transfection: studies with fractionated nanoparticles

Nanoparticles formulated from biodegradable polymers such as poly (lactic acid) and poly (D,L-lactide-co-glycolide) (PLGA) are being extensively investigated as non-viral gene delivery systems due to their sustained release characteristics and biocompatibility. PLGA nanoparticles for DNA delivery are mainly formulated using an emulsion-solvent evaporation technique. However, this formulation procedure results in the formation of particles with heterogeneous size distribution. The objective of the present study was to determine the relative transfectivity of the smaller- and the larger-sized fractions of nanoparticles in cell culture. PLGA nanoparticles containing a plasmid DNA encoding luciferase protein as a marker were formulated by a multiple emulsion-solvent evaporation method (mean particle diameter = 97 +/- 3 nm) and were fractionated using a membrane (pore size: 100 nm) filtration technique. The particles that passed through the membrane were designated as the smaller-sized nanoparticles (mean diameter = 70 +/- 2 nm) and the fraction that was retained on the membrane as the larger-sized nanoparticles (mean diameter = 202 +/- 9 nm). The smaller-sized nanoparticles showed a 27-fold higher transfection than the larger-sized nanoparticles in COS-7 cell line and a 4-fold higher transfection in HEK-293 cell line. The surface charge (zeta potential), cellular uptake, and the DNA release were almost similar for the two fractions of nanoparticles, suggesting that some other yet unknown factor(s) is responsible for the observed differences in the transfection levels. The results suggest that the particle size is an important factor, and that the smaller-sized fraction of the nanoparticle formulation predominantly contributes towards their transfection.

High efficient encapsulation of plasmid DNA in PLGA microparticles by organic phase self-emulsification

To overcome the drawbacks of encapsulating plasmid DNA (pDNA) in poly (D,L-lactic-co-glycolic acid) (PLGA) by water-in-oil-in-water double-emulsion solvent-evaporation method, we have developed a novel procedure for encapsulating pDNA in PLGA microparticles called DNA organic phase self-emulsification (DOPSM). This method was based on both the extraction plasmid DNA from aqueous phase into organic phase and the spontaneous emulsification DNA in organic phase by solvent diffusion method. The efficiency of extraction plasmid DNA into organic phase is 99% and the concentration of pDNA in organic phase is up to 2.4 mg/ml. The efficiency of microencapsulation of plasmid DNA in PLGA is up to 76% and can be enhanced by lowering the pH of aqueous solution of emulsion. The microparticles size of PLGA of pDNA is in a narrow range of 1-2 microm. This procedure does not involve the high mechanical energy to emulsify which may damage the integrity of pDNA. This method can be applied to encapsulate the pDNA into microparticles of other biocompatible polymers with high efficiency.

Shear-induced degradation of plasmid DNA

The majority of gene therapy clinical trials use plasmid DNA that is susceptible to shear-induced degradation. Many processing steps in the extraction, purification, and preparation of plasmid-based therapeutics can impart significant shear stress that can fracture the phosphodiester backbone of polynucleotides, and reduce biological activity. Much of the mechanistic work on shear degradation of DNA was conducted over 30 years ago, and we rely heavily on this early work in an attempt to explain the empirical observations of more recent investigations concerning the aerosolization of plasmids. Unfortunately, the sporadic reports of shear degradation in the literature use different experimental systems, making it difficult to quantitatively compare results and reach definitive mechanistic conclusions. In this review, we describe the forces imparted to DNA during shear stress, and use published data to quantitatively evaluate their relative effects. In addition, we discuss the effects of molecular weight, strain rate, particle size, flexibility, ionic strength, gas-liquid interfaces, and turbulence on the fluid flow degradation of supercoiled plasmid DNA. Finally, we speculate on computational methods that might allow degradation rates in different experimental systems to be predicted.

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.

Mucosal immunization with HIV-1 gag DNA on cationic microparticles prolongs gene expression and enhances local and systemic immunity

There is an urgent need to develop vaccines against transmission of HIV through the vaginal and rectal mucosa. In the present study we tested the ability of DNA encoding HIV-1 gag adsorbed onto the surface of cationic polylactide co-glycolide microparticles (PLG-DNA) to induce local and systemic gag-specific immunity following mucosal delivery. We found gag-specific cell- and antibody-mediated responses in local as well as systemic lymphoid tissues following intranasal (IN) immunizations with PLG-DNA but not with naked DNA. IN immunizations with PLG-DNA, but not naked DNA, induced prolonged expression of gag protein in local and systemic lymphoid tissues. These data have important implications for DNA vaccine development.

Recent developments in adjuvants for vaccines against infectious diseases

New generation vaccines, particularly those based on recombinant proteins and DNA, are likely to be less reactogenic than traditional vaccines, but are also less immunogenic. Therefore, there is an urgent need for the development of new and improved vaccine adjuvants. Adjuvants can be broadly separated into two classes, based on their principal mechanisms of action; vaccine delivery systems and 'immunostimulatory adjuvants'. Vaccine delivery systems are generally particulate e.g. emulsions, microparticles, iscoms and liposomes, and mainly function to target associated antigens into antigen presenting cells (APC). In contrast, immunostimulatory adjuvants are predominantly derived from pathogens and often represent pathogen associated molecular patterns (PAMP) e.g. LPS, MPL, CpG DNA, which activate cells of the innate immune system. Once activated, cells of innate immunity drive and focus the acquired immune response. In some studies, delivery systems and immunostimulatory agents have been combined to prepare adjuvant delivery systems, which are designed for more effective delivery of the immunostimulatory adjuvant into APC. Recent progress in innate immunity is beginning to yield insight into the initiation of immune responses and the ways in which immunostimulatory adjuvants may enhance this process. However, a rational approach to the development of new and more effective vaccine adjuvants will require much further work to better define the mechanisms of action of existing adjuvants. The discovery of more potent adjuvants may allow the development of vaccines against infectious agents such as HIV which do not naturally elicit protective immunity. New adjuvants may also allow vaccines to be delivered mucosally.

Induction of potent immune responses by cationic microparticles with adsorbed human immunodeficiency virus DNA vaccines

The effectiveness of cationic microparticles with adsorbed DNA at inducing immune responses was investigated in mice, guinea pigs, and rhesus macaques. Plasmid DNA vaccines encoding human immunodeficiency virus (HIV) Gag and Env adsorbed onto the surface of cationic poly(lactide-coglycolide) (PLG) microparticles were shown to be substantially more potent than corresponding naked DNA vaccines. In mice immunized with HIV gag DNA, adsorption onto PLG increased CD8(+) T-cell and antibody responses by approximately 100- and approximately 1,000-fold, respectively. In guinea pigs immunized with HIV env DNA adsorbed onto PLG, antibody responses showed a more rapid onset and achieved markedly higher enzyme-linked immunosorbent assay and neutralizing titers than in animals immunized with naked DNA. Further enhancement of antibody responses was observed in animals vaccinated with PLG/DNA microparticles formulated with aluminum phosphate. The magnitude of anti-Env antibody responses induced by PLG/DNA particles was equivalent to that induced by recombinant gp120 protein formulated with a strong adjuvant, MF-59. In guinea pigs immunized with a combination vaccine containing HIV env and HIV gag DNA plasmids on PLG microparticles, substantially superior antibody responses were induced against both components, as measured by onset, duration, and titer. Furthermore, PLG formulation overcame an apparent hyporesponsiveness of the env DNA component in the combination vaccine. Finally, preliminary data in rhesus macaques demonstrated a substantial enhancement of immune responses afforded by PLG/DNA. Therefore, formulation of DNA vaccines by adsorption onto PLG microparticles is a powerful means of increasing vaccine potency.

Microparticles for intranasal immunization

Of the several routes available for mucosal immunization, the nasal route is particularly attractive because of ease of administration and the induction of potent immune responses, particularly in the respiratory and genitourinary tracts. However, adjuvants and delivery systems are required to enhance immune responses following nasal immunization. This review focuses on the use of microparticles as adjuvants and delivery systems for protein and DNA vaccines for nasal immunization. In particular we discuss our own work on poly(lactide co-glycolide) (PLG) microparticles with entrapped protein or adsorbed DNA as a vaccine delivery system. The possible mechanisms involved in the enhancement of immune responses through the use of DNA adsorbed onto PLG microparticles are also discussed.

Fabrication of porous poly(epsilon-caprolactone) microparticles for protein release

The particle morphology and in vitro release of protein from porous and non-porous PCL-F127 blended microparticles were evaluated. The BSA loaded PCL microparticles were prepared by the w/o/o/o emulsion-solvent evaporation method. Two types of homogenizer, a Polytron homogenizer and a probe ultrasonicator, were used to prepare the emulsion systems. The effects of solvent evaporation rate on the crystallinity and the performance of the microparticles were investigated. Both microparticles showed quite different shapes as well as surface morphology and release characteristics. The microparticles prepared with a Polytron homogenizer were quite porous in structure, which created channels for protein to continuously diffuse out, and resulted in sustained- and controlled-release characteristics. In addition, the initial burst release of protein from the microparticles was also reduced. Alteration of the evaporation rate of solvent did not change the crystallinity of the final microparticles. An influence of evaporation rate on the size of resulting microparticles was observed. The porous PCL microparticles were developed by choosing a proper homogenizer and fabrication conditions. Carefully controlling these variables resulted in microparticles with desirable release performance.

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.

Porous biodegradable microparticles for delivery of pentamidine

The primary objective of this study was to develop a method for the preparation of porous biodegradable controlled release formulation of poly(lactide/glycolide) (PLGA). The model drug used for this study was pentamidine. Scanning electron microscopy pictures showed that these microparticles are highly porous and spherical in shape. A comparison of particle size reveals a similar median particle size (54-68 microm) in all six batches. The particles are all smaller than 90 microm. Differential scanning calorimetry thermograms revealed that pentamidine was mostly present in the crystalline form in the microparticles and did not dissolve in PLGA. The efficiency of encapsulation of pentamidine was higher than 58% in all six batches. The amount of drug released from these microparticles was at least 12% within the first 60 min. At least 50% of the total drug was released within the first 4 h. Drug release from these microparticles continued for up to 12 h. This faster drug dissolution was due to the highly porous surface. This highly porous surface will allow large molecules to release at a much faster rate than the regular microcapsules/microspheres.