Ligand-specific targeting of microspheres to phagocytes by surface modification with poly(L-lysine)-grafted poly(ethylene glycol) conjugate

Recent developments in nanoparticle-based drug delivery and targeting systems with emphasis on protein-based nanoparticles

BACKGROUND

Drug delivery systems with nm dimensions (nanoparticles [NPs]) are attracting increasing attention because they can sequester drugs in systemic circulation, prevent non-specific biodistribution, and target to specific tissues.

OBJECTIVE

We reviewed the recent literature pertinent to NP-based drug delivery, primarily emphasizing NPs fabricated from proteins.

METHODS

A summary of common NP fabrication techniques is provided along with the range of sizes and functional properties obtained. The NP properties critical for injectable drug delivery are reviewed, as well as the attempts to design 'tissue-specific' NPs.

RESULTS/CONCLUSIONS

It has been possible to design > 100 nm NPs from different biomaterials, and further understanding of in vivo stability and interactions with physiologic systems will lead to improved drug delivery systems.

Design opportunities for actively targeted nanoparticle vaccines

Vaccines for many infectious diseases are poorly developed or simply unavailable. There are significant technological and practical design issues that contribute to this problem; thus, a solution to the vaccine problem will require a systematic approach to test the multiple variables that are required to address each of the design challenges. Nanoparticle technology is an attractive methodology for optimizing vaccine development because design variables can be tested individually or in combination. The biology of individual components that constitute an effective vaccine is often well understood and may be integrated into particle design, affording optimal immune responses to specific pathogens. Here, we review technological variables and design parameters associated with creating modular nanoparticle vaccine systems that can be used as vectors to protect against disease. Variables, such as the material and size of the core matrix, surface modification for attaching targeting ligands and routes of administration, are discussed. Optimization of these variables is important for the development of nanoparticle-based vaccine systems against infectious diseases and cancer.

Filamentous condensation of DNA induced by pegylated poly-L-lysine and transfection efficiency

In this paper we propose a detailed analysis of structural and morphological properties of two poly-L-lysine (PLL)-based transfection formulations, PLL/DNA and pegylated PLL (PLL-g-PEG)/DNA, by means of atomic force microscopy (AFM) and transmission electron microscopy (TEM). Comparing PLL-g-PEG/DNA with PLL/DNA polyplexes, we demonstrate that, due to the presence of PEG, the particles differ not only in size, shape, and crystalline structure, but also in transfection efficiency. While PLL condensates DNA in large agglomerates, PLL grafted with polyethylene glycol 2000 can condensate DNA in long filaments with diameters of some nanometers (6-20 nm). These structures are dependent on the grafting ratio and are more efficient than compacted ones, showing that DNA uptake and processing by cell is directly related to physicochemical properties of the polyplexes.

Identification of psoralen loaded PLGA microspheres in rat skin by light microscopy

Drug delivery systems involving the use of polymers are widely studied and discovery of biocompatible polymers has become the focus of research in this area. Psoralen loaded poly(DL-lactide-co-glycolide) (PLGA) microspheres to be used in PUVA therapy (psoralen and UVA irradiation (ultraviolet A, 320-400 nm) of psoriasis were identified in paraffin sections by histological analysis. The psoralen loaded PLGA microspheres were prepared using the solvent evaporation technique. They were spherical and possessed an external smooth surface as observed by scanning electron microscopy (SEM) analysis. This study describes a modification in the routine preparation of microsphere samples for examination by light microscopy. The changes involved fixative agents and/or stains allowing the identification of microspheres containing a non-fluorescent material. The preservation and identification of microspheres in tissues for histological processing in paraffin was greatly improved by these modifications as proven by our results.

The characterization of paclitaxel-loaded microspheres manufactured from blends of poly(lactic-co-glycolic acid) (PLGA) and low molecular weight diblock copolymers

Paclitaxel-loaded biodegradable drug delivery systems manufactured from poly(lactic-co-glycolic acid) (PLGA) are known to release the drug at extremely slow rates. The objective of this study was to characterize paclitaxel-loaded microspheres composed of blends of PLGA with low molecular weight ampipathic diblock copolymers. The encapsulation and release of a series of poly(epsilon-caprolactone) (PCL)- or poly(D,L-lactic acid) (PDLLA)-co-methoxypolyethylene glycol (MePEG) diblock copolymers was measured using quantitative gel permeation chromatography. Polymeric miscibility was determined by glass transition temperature measurements using differential scanning calorimetry and paclitaxel release was measured using HPLC methods. The PCL- and PDLLA-based diblock copolymers encapsulated at high efficiency and were miscible in PLGA microspheres (30-120m microm size range). The burst phase of paclitaxel release was increased up to 20-fold by the inclusion of diblock copolymers in PLGA microspheres. Approximately 10% of the more hydrophobic PCL-based copolymers released from the microspheres in a short burst over 3 days followed by very slow release over the following 10 weeks. Only the PDLLA-based copolymer released from the PLGA microspheres in a controlled manner over 10 weeks. All microspheres containing PEG were found to have more hydrophilic surfaces (as measured by contact angle) with improved biocompatibility (reduced neutrophil activation) compared to PLGA only microspheres. These results indicate that low molecular weight polyester-based diblock copolymers may be effectively encapsulated in PLGA microspheres to increase paclitaxel release (probably through a micellization process) and improve biocompatibility.

Multifunctional cargo systems for biotechnology

One of the challenges in the field of bio-nanotechnology is the development of nano-sized delivery systems comprising different functionalities. These systems should carry bioactive substances to predefined site and unload them in controlled manner. Capsules assembled layer-by-layer have been intensively studied in the past few years owing to their ability to be modified, their capacity to encapsulate a wide range of chemicals, their responsiveness to different factors, and the variety of functionalities with which they can be enhanced. Current research focuses on the development of carriers with remote guiding and activation (optical, magnetic or ultrasound), thereby addressing unique in vivo applications with multifunctional biomaterials. Submicron-sized capsules are good models to mimic biochemical processes in a confined geometry that imitates cell organelles. Moreover, the cellular and tissue-targeted delivery of the capsules might serve as an intracellular reporter or enzymatic reactor. However, several obstacles still have to be overcome before capsule technology can be implemented. This article discusses possible solutions as well as promising applications.

Cell responses to biomimetic protein scaffolds used in tissue repair and engineering

Basic science research in tissue engineering and regenerative medicine aims to investigate and understand the deposition, growth, and remodeling of tissues by drawing together approaches from a range of disciplines. This review discusses approaches that use biomimetic proteins and cellular therapies, both in the development of clinical products and of model platforms for scientific investigation. Current clinical approaches to repairing skin, bone, nerve, heart valves, blood vessels, ligaments, and tendons are described and their limitations identified. Opportunities and key questions for achieving clinical goals are discussed through commonly used examples of biomimetic scaffolds: collagen, fibrin, fibronectin, and silk. The key questions addressed by three-dimensional culture models, biomimetic materials, surface chemistry, topography, and their interaction with cells in terms of durotaxis, mechano-regulation, and complex spatial cueing are reviewed to give context to future strategies for biomimetic technology.

Macrophage uptake of core-shell nanoparticles surface modified with poly(ethylene glycol)

The in vitro uptake of core-shell nanoparticles encapsulated in a bio-macromolecular nanoshell assembled from multilayered polyelectrolytes was studied. Sulfate modified fluorescent polystyrene nanobeads (diameter 200 nm) were used as a solid core upon which charged multilayers of poly-l-lysine, chitosan, and heparin sulfate are electrostatically deposited utilizing a layer-by-layer (LbL) self-assembly process. The nanoshell composed of the multilayered polyelectrolytes was modified with poly(ethylene glycol) (PEG) of varying molecular weights (either MW 2000, 5000, or 20 000 Da) to form a hydrophilic and long-circulating nanoparticle. The assembly of the nanoshell was confirmed by zeta potential, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The reversal in charge upon the deposition of alternating polyelectrolytes was observed by zeta potential measurements. The nanometer thickness of the nanoshell was confirmed by TEM. The presence of the (C-C-O)(n)() backbone in PEG at the surface of the nanoshell was confirmed by the increase in (C-O,N) peak area concentrations compared to (C-C) peak area, and these results were gathered from XPS. In vitro studies between suspension macrophages and core-shell nanoparticles were performed to determine how the hydrophilicity and the charge on the nanoshell can promote or reduce uptake. Results showed that after 24 h uptake was decreased 3-fold when PEGs of 2000 and 20 000 Da were chemisorbed to the nanoshell, as opposed to a nanoshell with either a positive or highly negative charge. Confocal microscopy aided in verifying that core-shell nanoparticles were internalized within the cell cytoplasm and were not attached to the cell surface. Protein adhesion studies with bovine serum albumin were performed to determine the relationship between surface charge and opsonization of core-shell nanoparticles. It was found that a hydrophilic surface with a low negative charge reduced protein adsorption and uptake. The in vitro uptake of macrophages and protein adsorption onto core-shell nanoparticles formed using layer-by-layer assembly has not been previously studied.

Stable cationic microparticles for enhanced model antigen delivery to dendritic cells

The objectives of this work were (i) to prepare physically stable cationic microparticles and (ii) to study the impact of the surface properties on microparticle phagocytosis and the phenotype of dendritic cells (DC). Protein loaded biodegradable microparticles from poly(lactic-co-glycolic acid) [PLGA] were produced in a micromixer-based w/o/w solvent evaporation procedure. Anionic particles were obtained by using polyvinyl alcohol (PVA) as stabilizing agent; for cationic surfaces cetyltrimethylammonium bromide (CTAB) and chitosan/PVA or DEAE-dextran/PVA blends were evaluated. In phagocytosis studies human monocytes and monocyte-derived DC were incubated with microparticles and analysed by flow cytometry. While CTAB modified microparticles lost their positive charge and aggregated due to CTAB desorption from the particle surface, the modification with chitosan and DEAE-dextran resulted in stable microparticles without cell toxicity. Due to a very low endotoxin content, phagocytosis of anionic and cationic microparticles did not induce an upregulation of maturation-associated surface markers on DC. DEAE-dextran modified microparticles showed an enhanced model protein delivery into phagocytic cells. Overall, PLGA microparticles are suitable vehicles for protein delivery to DC, which might be used for DC-based cell therapies.

In vivo targeting of dendritic cells in lymph nodes with poly(propylene sulfide) nanoparticles

Delivery of biodegradable nanoparticles to antigen-presenting cells (APCs), specifically dendritic cells (DCs), has potential for immunotherapy. This study investigates the delivery of 20, 45, and 100nm diameter poly(ethylene glycol)-stabilized poly(propylene sulfide) (PPS) nanoparticles to DCs in the lymph nodes. These nanoparticles consist of a cross-linked rubbery core of PPS surrounded by a hydrophilic corona of poly(ethylene glycol). The PPS domain is capable of carrying hydrophobic drugs and degrades within oxidative environments. 20 nm particles were most readily taken up into lymphatics following interstitial injection, while both 20 and 45nm nanoparticles showed significant retention in lymph nodes, displaying a consistent and strong presence at 24, 72, 96 and 120h post-injection. Nanoparticles were internalized by up to 40-50% of lymph node DCs (and APCs) without the use of a targeting ligand, and the site of internalization was in the lymph nodes rather than at the injection site. Finally, an increase in nanoparticle-containing DCs (and other APCs) was seen at 96h vs. 24h, suggesting an infiltration of these cells to lymph nodes. Thus, PPS nanoparticles of 20-45nm have the potential for immunotherapeutic applications that specifically target DCs in lymph nodes.

Combined atomic force microscopy and optical microscopy measurements as a method to investigate particle uptake by cells

We propose a combination of atomic force microscopy (AFM) and optical microscopy for the investigation of particle uptake by cells. Positively and negatively charged polymer microcapsules were chosen as model particles, because their interaction with cells had already been investigated in detail. AFM measurements allowed the recording of adhesion forces on a single-molecule level. Due to the micrometer size of the capsules, the number of ingested capsules could be counted by optical microscopy. The combination of both methods allowed combined measurement of the adhesion forces and the uptake rate for the same model particle. As a demonstration of this system, the correlation between the adhesion of positively or negatively charged polymer microcapsules onto cell surfaces and the uptake of these microcapsules by cells has been investigated for several cell lines. As is to be expected, we find a correlation between both processes, which is in agreement with adsorption-dependent uptake of the polymer microcapsules by cells.

One-step preparation of polyelectrolyte-coated PLGA microparticles and their functionalization with model ligands

This work aimed at the development of a novel surfactant-free, one-step process for the concomitant formation of poly(lactide-co-glycolide) (PLGA) microparticles (MP) and surface coating with the polyelectrolyte chitosan, which is suitable for subsequent covalent conjugation of bioactive ligands. The technology is based on solvent extraction from an O/W-dispersion using a static micromixer. Surface coating occurred through interaction of the negatively charged, nascent PLGA MP with the polycationic chitosan, which was dissolved in the aqueous extraction fluid. Particles of 1-10 mum in diameter were produced with excellent reproducibility. The chitosan-coated PLGA MP were spherical and showed a smooth surface without pores, as demonstrated by scanning electron microscopy (SEM). The chitosan coatings were characterized by zeta potential measurements and X-ray photoelectron spectroscopy (XPS). The functional amino groups of chitosan were used to conjugate two model ligands to the coating, i.e. fluorescamine and NHS-PEG-biotin. The presence of the conjugated ligands was revealed by confocal laser scanning microscopy (CLSM) and fluorescence activated cell sorting (FACS). Evidence for biotinylation was demonstrated through binding of fluorescently labelled streptavidin. The developed platform technology is straightforward and flexible. Future studies will focus on the design of microparticulate carriers with bioactive surfaces, e.g. as antigen delivery systems.

In vitro evaluation of biodegradable microspheres with surface-bound ligands

Protein ligands were conjugated to the surface of biodegradable microspheres. These microsphere-ligand conjugates were then used in two in vitro model systems to evaluate the effect of conjugated ligands on microsphere behavior. Microsphere retention in agarose columns was increased by ligands on the microsphere surface specific for receptors on the agarose matrix. In another experiment, conjugating the lectin Ulex europaeus agglutinin 1 to the microsphere surface increased microsphere adhesion to Caco-2 monolayers compared to control microspheres. This increase in microsphere adhesion was negated by co-administration of l-fucose, indicating that the increase in adhesion is due to specific interaction of the ligand with carbohydrate receptors on the cell surface. These results demonstrate that the ligands conjugated to the microspheres maintain their receptor binding activity and are present on the microsphere surface at a density sufficient to target the microspheres to both monolayers and three-dimensional matrices bearing complementary receptors.

Biodegradable microspheres alone do not stimulate murine macrophages in vitro, but prolong antigen presentation by macrophages in vitro and stimulate a solid immune response in mice

The purpose of this study was to analyze the potential of various types of biodegradable microspheres (MS) (i) to activate in vitro cell line-derived macrophages (RAW 264.7, Mphi), and primary peritoneal and bone marrow-derived mouse Mphi, to prolong the release and presentation of microencapsulated synthetic malaria antigens by Mphi after uptake of antigen-loaded MS, and (ii) to stimulate an immune response in mice against a microencapsulated synthetic malaria antigen. The MS were made of various types of poly(lactide-co-glycolide) (PLGA) or chitosan cross-linked with tripolyphosphate. PLGA, but not chitosan MS, were efficiently ingested by Mphi. Upon exposure to the various MS types, Mphi increased only the production of reactive oxygen intermediates (ROI), while the production of nitric oxide (NO), tumor necrosis factor alpha (TNF-alpha), and the expression of cyclooxigenase-2 (COX-2), inducible NO synthase (iNOS), the cell surface markers MHC class I and II, and CD 86 remained unaffected. In vitro release of the microencapsulated antigen from PLGA50:50 MS followed a pulsatile pattern and extended over 14 weeks. This prolonged antigen release was also mirrored in the significantly prolonged antigen presentation over more than 7 days by Mphi after uptake of antigen-loaded PLGA MS. Finally, antigen-loaded PLGA MS induced a solid immune response in mice after a single s.c.-injection, which was only slightly inferior to the antibody titers measured with the control formulation with Montanide ISA720. These results suggest that MS are well tolerated by Mphi. The prolonged antigen presentation by Mphi, as measured in vitro, along with the capacity to induce a strong immune response in animals emphasize that biodegradable MS are a very promising delivery system for both preventive and immunotherapeutic vaccines.

Target-specific cellular uptake of PLGA nanoparticles coated with poly(L-lysine)-poly(ethylene glycol)-folate conjugate

Poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles with anionic surface charge were surface coated with cationic di-block copolymer, poly(L-lysine)-poly(ethylene glycol)-folate (PLL-PEG-FOL) conjugate, for enhancing their site-specific intracellular delivery against folate receptor overexpressing cancer cells. The PLGA nanoparticles coated with the conjugate were characterized in terms of size, surface charge, and change in surface composition by XPS. By employing the flow cytometry method and confocal image analysis, the extent of cellular uptake was comparatively evaluated under various conditions. PLL-PEG-FOL coated PLGA nanoparticles demonstrated far greater extent of cellular uptake to KB cells, suggesting that they were mainly taken up by folate receptor-mediated endocytosis. The enhanced cellular uptake was also observed even in the presence of serum proteins, possibly due to the densely seeded PEG chains. The PLL-PEG-FOL coated PLGA nanoparticles could be potentially applied for cancer cell targeted delivery of various therapeutic agents.

In Vitro Echogenicity Characterization of Poly[lactide-coglycolide] (PLGA) Microparticles and Preliminary In Vivo Ultrasound Enhancement Study for Ultrasound Contrast Agent Application

OBJECTIVES

This work includes (1) the characterization of a reproducible poly[lactide-coglycolide] (PLGA) microparticle preparation with an optimial mean diameter and size distribution and (2) the preliminary in vivo ultrasonographic investigation of PLGA microparticles.

METHODS

A first series of PLGA microparticle preparations (1 to 15 mum) was acoustically characterized on a hydrodynamic device to select the most appropriate for ultrasound contrast agent application. Preparations of 3-microm microparticles were selected, characterized at different doses, and then injected into 20 melanoma grafted mice for contrast-enhanced power Doppler ultrasonography evaluation.

RESULTS

The 3-microm microparticles (3.26-microm mean diameter with 0.41-microm standard deviation) led to in vitro enhancement of 18.3 dB at 0.62 mg/mL. In vivo experiments showed 47% enhancement of intratumoral vascularization detection after PLGA injection, significantly correlated (P < 0.0001) with preinjection intravascularization and tumoral volume. No toxicity was histologically observed.

CONCLUSION

The 3-microm PLGA microparticles provided significant enhancement in vitro and in vivo without any toxicity.

Localized delivery of growth factors for bone repair

Delivery of growth factors for tissue (e.g. bone, cartilage) or cell repair (e.g. nerves) is about to gain important potential as a future therapeutic tool. Depending on the targeted cell type and its state of differentiation, growth factors can activate or regulate a variety of cellular functions. Therefore, strictly localized delivery regimens at well-defined kinetics appear to be logical prerequisites to assure safe and efficacious therapeutic use of such factors and avoid unwanted side effects and toxicity, a major hurdle in the clinical development of growth factor therapies so far. This review summarizes various approaches for localized growth factor delivery as focused on bone repair. Similar considerations may apply to other growth factors and therapeutic indications. Considering the vast number of preclinical studies reported in the area of growth factor-assisted bone repair, it surprises though that only two medical products for bone repair have so far been commercialized, both consisting of a collagen matrix impregnated with a bone morphogenetic protein. The marked diversity of the reported growth factors, delivery concepts and not yet standardized animal models adds to the complexity to learn from past preclinical studies presented in the literature. Nonetheless, it is now firmly established from the available information that the type, dose and delivery kinetics of growth factors all play a decisive role for the therapeutic success of any such approach. Very likely, all of these parameters have to be adapted and optimized for each animal model or clinical case. In the future, systems for localized growth factor delivery thus need to be designed in such a way that their modular components are readily adaptable to the individual pathology. To make such customized systems feasible, close cooperative networks of biomedical and biomaterials engineers, pharmaceutical scientists, chemists, biologists and clinicians need to be established.

Microencapsulation by solvent extraction/evaporation: reviewing the state of the art of microsphere preparation process technology

The therapeutic benefit of microencapsulated drugs and vaccines brought forth the need to prepare such particles in larger quantities and in sufficient quality suitable for clinical trials and commercialisation. Very commonly, microencapsulation processes are based on the principle of so-called "solvent extraction/evaporation". While initial lab-scale experiments are frequently performed in simple beaker/stirrer setups, clinical trials and market introduction require more sophisticated technologies, allowing for economic, robust, well-controllable and aseptic production of microspheres. To this aim, various technologies have been examined for microsphere preparation, among them are static mixing, extrusion through needles, membranes and microfabricated microchannel devices, dripping using electrostatic forces and ultrasonic jet excitation. This article reviews the current state of the art in solvent extraction/evaporation-based microencapsulation technologies. Its focus is on process-related aspects, as described in the scientific and patent literature. Our findings will be outlined according to the four major substeps of microsphere preparation by solvent extraction/evaporation, namely, (i) incorporation of the bioactive compound, (ii) formation of the microdroplets, (iii) solvent removal and (iv) harvesting and drying the particles. Both, well-established and more advanced technologies will be reviewed.

Cell targeting by a generic receptor-targeted polymer nanocontainer platform

Nanotechnology promises new avenues to medical diagnosis and treatment. Of special interest are injectable nanovehicles that are programmable towards specific targets, are able to evade the immune defense, and are versatile enough to be suited as carriers of complex functionality. Biotin-functionalized (poly(2-methyloxazoline)-b-poly(dimethylsiloxane)-b-poly(2-methyloxazoline) triblock copolymers were self-assembled to form nanocontainers, and biotinylated targeting ligands were attached by using streptavidin as a coupling agent. Specifically, fluorescence-labeled nanocontainers were targeted against the scavenger receptor A1 from macrophages, an important cell in human disease. In human and transgenic cell lines and in mixed cultures, receptor-specific binding of these generic carriers was followed by vesicular uptake. Low nonspecific binding supported the "stealth" properties of the carrier while cytotoxicity was absent. This versatile carrier appears promising for diagnostic or therapeutic medical use.

Surface modification of biodegradable polyesters with fatty acid conjugates for improved drug targeting

We describe a general method for incorporating target ligands into the surface of biocompatible polyester poly(lactic-co-glycolic acid) (PLGA) 50/50 materials using fatty acids. Avidin-fatty acid conjugates were prepared and efficiently incorporated into PLGA. Avidin was chosen as an adaptor protein to facilitate the attachment of a variety of biotinylated ligands. We show that fatty acid preferentially associates with the hydrophobic PLGA matrix, rather than the external aqueous environment, facilitating a prolonged presentation of avidin over several weeks. We successfully applied this approach in both microspheres encapsulating a model protein, bovine serum albumin, and PLGA scaffolds fabricated by a salt-leaching method. Because of its ease, generality and flexibility, this strategy promises widespread utility in modifying the surface of PLGA-based materials for applications in drug delivery and tissue engineering.

An overview of current delivery systems in cancer gene therapy

The main objective in gene therapy is the development of efficient, non-toxic gene carriers that can encapsulate and deliver foreign genetic materials into specific cell types such as cancerous cells. During the past two decades, enormous research in the area of gene delivery has been conducted worldwide, in particular for cancer gene therapy application. Viral vectors are biological systems derived from naturally evolved viruses capable of transferring their genetic materials into the host cells. Many viruses including retrovirus, adenovirus, herpes simplex virus (HSV), adeno-associated virus (AAV) and pox virus have been modified to eliminate their toxicity and maintain their high gene transfer capability. The limitations associated with viral vectors, however, in terms of their safety, particularly immunogenicity, and in terms of their limited capacity of transgenic materials, have encouraged researchers to increasingly focus on non-viral vectors as an alternative to viral vectors. Non-viral vectors are generally cationic in nature. They include cationic polymers such as poly(ethylenimine) (PEI) and poly(L-lysine) (PLL), cationic peptides and cationic liposomes. The newly described liposomal preparation LPD (liposomes/protamine/DNA), for example, has shown superiority over conventional liposomes/DNA complexes (lipoplexes). Although non-viral vectors are less efficient than viral ones, they have the advantages of safety, simplicity of preparation and high gene encapsulation capability. This article reviews the most recent studies highlighting the advantages and the limitations of various types of gene delivery systems used in cancer gene therapy.

Immobilisation of GM-CSF onto particulate vaccine carrier systems

Physical connection of vaccine carriers with immunostimulating cytokines may provide an interesting possibility to enhance the immune response of protective or therapeutic vaccines. As a first evaluation, various aluminium hydroxide adjuvants and poly(D,L-lactide-co-glycolide) (PLGA) microparticulates with modified positively and negatively charged surfaces were prepared to adsorb granulocyte-macrophage colony-stimulating factor (GM-CSF) under different pH conditions. Negatively charged surfaces were chosen to resemble physiological binding of GM-CSF to extracellular glycosaminoglycans, while modified positively charged surfaces may enhance GM-CSF adsorption due to electrostatic interaction. Release of GM-CSF was checked in vitro in a simulated interstitial environment. Anionic and cationic surfaces efficiently attracted GM-CSF to the carrier surface independently of the pH, while the composition of the carrier largely influenced the release of GM-CSF over time. Thus, the adsorption of GM-CSF to aluminium hydroxide adjuvants and PLGA microparticulates provides a simple and efficient possibility to physically connect the cytokine with these commonly used and potential vaccine carriers and may enable its localised delivery to the side of action.

Rational design and engineering of delivery systems for therapeutics: biomedical exercises in colloid and surface science

Engineering delivery systems of therapeutic agents has grown into an independent field, transcending the scope of traditional disciplines and capturing the interest of both academic and industrial research. At the same time, the acceleration in the discovery of new therapeutic moieties (chemical, biological, genetic and radiological) has led to an increasing demand for delivery systems capable of protecting, transporting, and selectively depositing those therapeutic agents to desired sites. The vast majority of delivery systems physically reside in the colloidal domain, while their surface properties and interfacial interactions with the biological milieu critically determine the pharmacological profiles of the delivered therapeutic agents. Interestingly though, the colloidal and surface properties of delivery systems are commonly overlooked in view of the predominant attention placed on the therapeutic effectiveness achieved. Moreover, the development and evaluation of novel delivery systems towards clinical use is often progressed by serendipity rather than a systematic design process, often leading to failure. The present article will attempt to illustrate the colloid and interfacial perspective of a delivery event, as well as exemplify the vast opportunities offered by treating, analysing and manipulating delivery systems as colloidal systems. Exploring and defining the colloid and surface nature of the interactions taking place between the biological moieties in the body and an administered delivery vehicle will allow for the rational engineering of effective delivery systems. A design scheme is also proposed on the way in which the engineering of advanced delivery systems should be practiced towards their transformation from laboratory inventions to clinically viable therapeutics. Lastly, three case studies are presented, demonstrating how rational manipulation of the colloidal and surface properties of delivery systems can lead to newly engineered systems relevant to chemotherapy, gene therapy and radiotherapy.