'Stealth' corona-core nanoparticles surface modified by polyethylene glycol (PEG): influences of the corona (PEG chain length and surface density) and of the core composition on phagocytic uptake and plasma protein adsorption

Biodistribution properties of nanoparticles based on mixtures of PLGA with PLGA–PEG diblock copolymers

The basic characteristics and the biodistribution properties of nanoparticles prepared from mixtures of poly(lactide-co-glycolide) (PLGA) with poly(lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) copolymers were investigated. A PLGA(45)-PEG(5) copolymer of relatively low PEG content and a PLGA(5)-PEG(5) copolymer of relatively high PEG content were included in the study. Increasing the PLGA-PEG content of the PLGA/PLGA-PEG mixture, or when PLGA(45)-PEG(5) was replaced by PLGA(5)-PEG(5), a decrease in the size of the nanoparticles and an increase in the rate of PEG loss from the nanoparticles were observed. The blood residence of the PLGA/PLGA(45)-PEG(5) nanoparticles increased as their PLGA-PEG content was increased, reaching maximum blood longevity at 100% PLGA(45)-PEG(5). On the contrary, the blood residence of PLGA/PLGA(5)-PEG(5) nanoparticles exhibited a plateau maximum in the range of 80-100% PLGA(5)-PEG(5). At PLGA-PEG proportions lower than 80%, the PLGA/PLGA(45)-PEG(5) nanoparticles exhibited lower blood residence than the PLGA/PLGA(5)-PEG(5) nanoparticles, whereas at PLGA-PEG proportions higher than 80%, the PLGA/PLGA(45)-PEG(5) nanoparticles exhibited higher blood residence than the PLGA/PLGA(5)-PEG(5) nanoparticles. These findings indicate that apart from the surface PEG content, the biodistribution properties of the PLGA/PLGA-PEG nanoparticles are also influenced by the size of the nanoparticles and the rate of PEG loss from the nanoparticles.

Polymeric micelles based on amphiphilic scorpion-like macromolecules: novel carriers for water-insoluble drugs

PURPOSE

The objective was to evaluate amphiphilic scorpion-like macromolecules (AScMs) as drug carriers for hydrophobic drugs.

METHODS

Indomethacin (IMC) was incorporated into two AScM micelles (M12P5 and M12P2) by the O/W emulsion technique. The influences of IMC:polymer feed ratio and molecular weight of the hydrophilic block of AScMs on the micelle size, IMC entrapment efficiency and release behavior were investigated. Furthermore, cytotoxicity of the AScMs was evaluated with human umbilical vein endothelial cells (HUVEC).

RESULTS

The maximal IMC entrapment efficiency in M12P5 and M12P2 micelles (72.3 and 20.2%, respectively) was obtained at ratios of 0.1 to 1 for indomethacin:polymer. The sizes of IMC-loaded M12P5 and Mi2P2 polymeric micelles were <20 nm with a narrow size distribution. In vitro release studies revealed that IMC released from MI2P5 and M12P2 polymeric micelles showed sustained release behavior during the 24 h of experiment. Additionally, M12P5 and M12P2 polymeric micelles did not induce remarkable cytotoxicity against HUVEC cells at concentrations up to 1 and 0.5 mM, respectively.

CONCLUSION

The amphiphilic scorpion-like macromolecules may be useful as novel drug carriers because of their small size, ability to encapsulate hydrophobic drugs and release them in a sustained manner as well as low cytotoxicity.

Double-Coated Poly (Butylcynanoacrylate) Nanoparticulate Delivery Systems for Brain Targeting of Dalargin Via Oral Administration

The aim of this study is to evaluate oral administration of poly (butylcyanoacrylate) nanoparticulate delivery systems (PBCA-NDSs), double-coated with Tween 80 and poly (ethylene) glycol (PEG) 20000 for brain delivery of hexapeptide dalargin, an anti-nociceptive peptide that does not cross blood-brain barrier (BBB) by itself. Studies have proven the brain uptake of Tween 80 overcoated nanoparticles after intravenous administration, but studies for brain delivery of nanoparticles after oral administration had been limited due to reduced bioavailability of nanoparticles and extensive degradation of the peptide and/or nanoparticles by gastrointestinal enzymes. To address this problem, dalargin-loaded PBCA-NDS were successively double-coated with Tween 80 and PEG 20000 in varied concentrations of up to 2% each. Measurement of in vivo central anti-nociceptive effect of dalargin along with a dose response curve was obtained by the tail flick test following the oral administration of PBCA-NDSs to mice. Results from the tail flick test indicated that significant dalargin-induced analgesia was observed from PBCA-NDSs with double-coating of Tween and PEG in comparison with single-coating of either Tween or PEG. Hence, it could be concluded that surface coated PBCA-NDS can be used successfully for brain targeting of dalargin or other peptides administered orally. However, further studies are required to elucidate the exact transport mechanism of PBCA-NDSs from gastrointestinal tract to brain.

Nanotechnology for the biologist

Nanotechnology refers to research and technology development at the atomic, molecular, and macromolecular scale, leading to the controlled manipulation and study of structures and devices with length scales in the 1- to 100-nanometers range. Objects at this scale, such as "nanoparticles," take on novel properties and functions that differ markedly from those seen in the bulk scale. The small size, surface tailorability, improved solubility, and multifunctionality of nanoparticles open many new research avenues for biologists. The novel properties of nanomaterials offer the ability to interact with complex biological functions in new ways-operating at the very scale of biomolecules. This rapidly growing field allows cross-disciplinary researchers the opportunity to design and develop multifunctional nanoparticles that can target, diagnose, and treat diseases such as cancer. This article presents an overview of nanotechnology for the biologist and discusses "nanotech" strategies and constructs that have already demonstrated in vitro and in vivo efficacy.

Mediating specific cell adhesion to low-adhesive diblock copolymers by instant modification with cyclic RGD peptides

One promising strategy to control the interactions between biomaterial surfaces and attaching cells involves the covalent grafting of adhesion peptides to polymers on which protein adsorption, which mediates unspecific cell adhesion, is essentially suppressed. This study demonstrates a surface modification concept for the covalent anchoring of RGD peptides to reactive diblock copolymers based on monoamine poly(ethylene glycol)-block-poly(D,L-lactic acid) (H(2)N-PEG-PLA). Films of both the amine-reactive (ST-NH-PEG(2)PLA(20)) and the thiol-reactive derivative (MP-NH-PEG(2)PLA(40)) were modified with cyclic alphavbeta3/alphavbeta5 integrin subtype specific RGD peptides simply by incubation of the films with buffered solutions of the peptides. Human osteoblasts known to express these integrins were used to determine cell-polymer interactions. The adhesion experiments revealed significantly increased cell numbers and cell spreading on the RGD-modified surfaces mediated by RGD-integrin-interactions.

Interactions between hen egg-white lysozyme, PEG2,000, and PLA50 at the air–water interface

In this paper, we compared the efficiency of polymer films, made of a poly(ethylene glycol) (PEG2,000)/poly(d,l-lactide) (PLA50) mixture, or a PEG2,000-PLA50 copolymer, to prevent adsorption of a model protein, the hen egg-white lysozyme (HEWL), at the air-water interface. This was achieved by analyzing the surface pressure/surface area curves, and the X-ray reflectivity data of the polymer films spread on a Langmuir trough, obtained in absence or in presence of the protein. For both the mixture and the copolymer, the amount of protein adsorbed at the air-water interface decreases when the density of the polymer surface coverage increases. It was shown that even in a condensed state, the polymer film made by the mixture can not totally prevent HEWL molecules to adsorb and penetrate the polymer mixed film, but however, protein molecules would not be directly exposed to the more hydrophobic phase, i.e. the air phase. It was also shown that the configuration adopted by the copolymer at the interface in its condensed state would prevent adsorption of HEWL molecules for several hours; this would be due in particular to the presence of PEG segments in the interfacial film.

Opsonization of polyethylene wear particles regulates macrophage and osteoblast responses in vitro

The cellular reaction to wear debris may result in the failure of an artificial joint's fixation to the skeleton. The influence of debris opsinization on cell activity has received little attention. This study seeks to establish whether different proteinaceous culture environments may invoke variant cellular responses to debris challenge. Consideration of the zeta potential of a low density polyethylene particle group and an ex vitro ultrahigh molecular weight polyethylene particle group revealed that the nature of the protein adsorbants is related to the concentration of the proteins in solution. Furthermore, the composition of the adsorbed layer was shown to vary with the spectra of proteins in solution. In standard cell culture conditions zeta potential approached zero, indicating the high probability of particle agglomeration. Cell challenge studies with U937 macrophages showed that BSA and FCS protein adsorption mediated increased cell adhesion, while bovine IgG showed little change over control values. No changes in behavior of osteoblastic cells were observed in similar experiments.

Amphotericin B

Invasive fungal infections are a major cause of morbidity and mortality in immunodeficient individuals (such as AIDS patients) and in transplant recipients or tumor patients undergoing immunosuppressive chemotherapy. Amphotericin B is one of the oldest, yet most efficient antimycotic agents. However, its usefulness is limited due to dose-dependent side-effects, notably nephrotoxicity. In order to improve its safety margin, new pharmaceutical formulations of amphotericin B have been designed especially to reduce its detrimental effects on the kidneys. Since the 1980s, a wide variety of new amphotericin B formulations have been brought forward for clinical testing, many of which were approved and reached market value in the 1990s. This review describes and discusses the molecular genetics, pharmacological, toxicological, and clinical aspects of amphotericin B itself and many of its innovative formulations.

Interaction of PLGA nanoparticles with human blood constituents

When nanoparticles are injected into the blood for drug delivery or drug detoxification, detrimental interaction of these particles with blood constituents must be avoided. In previous studies, the adsorption of albumin immunoglobulin G, and fibrinogen from blood plasma to a model hydrophobic polymer like polystyrene was investigated as was decreasing surface hydrophobicity, which quantitatively leads to decreasing amounts of adsorbed proteins on latex particles. However, the uptake of other blood constituents, such as inorganic blood electrolytes, by particles and the dispersion/coagulation characteristics of these particles in the blood stream have not been fully studied. Most importantly, the effect s of these particles on blood coagulation and hemolysis are not well known. In the present study, the poly(lactide-co-glycolide) acid(PLGA) nanoparticles were synthesized by using nanoprecipitation. The uptake of blood electrolytes from simulated blood fluid (SBF) and the stability (dispersion/aggregation) of nanoparticles in SBF was examined by using different loading amounts of PLGA and different contact time between PLGA nanoparticles and SBF. The interaction of particles with the organic components of blood was also studied by using the measurement of red blood cell hemolysis and blood clotting with raw PLGA, surfactant modified PLGA, and PEGylated PLGA.

Influence of serum protein on polycarbonate-based copolymer micelles as a delivery system for a hydrophobic anti-cancer agent

A new micelle system formed from methoxy (polyethylene glycol)-b-poly (5-benzyloxy-trimethylene carbonate; MePEG-b-PBTMC 5000-b-4800) was investigated as a delivery system for the hydrophobic anti-cancer agent, ellipticine. The ellipticine was loaded into the MePEG-b-PBTMC micelles with a loading efficiency of 95% using a high-pressure extrusion technique. The ellipticine-loaded micelles have a spherical morphology and an average diameter of 96 nm. The anti-cancer activity of ellipticine was confirmed to be retained following formulation in the MePEG-b-PBTMC micelles. The extent of protein adsorption to the MePEG-b-PBTMC micelles was investigated by transmission electron microscopy, dynamic light scattering and gel filtration chromatography. Overall, the amount of protein both loosely and tightly associated with the micelles was found to be minimal and insignificant. The partitioning properties of ellipticine between an aqueous medium containing protein and the MePEG-b-PBTMC micelles were examined over a range of protein concentrations. Under physiologically relevant conditions, it was found that 61% of the drug remained within the micelle fraction while 39% was in the protein-containing aqueous phase. In addition, the in vitro drug release profile of ellipticine from the micelles was fit using a modified Higuchi model and found to be accelerated in the presence of protein. These studies demonstrate that although there are no significant interactions between micelle and protein, the properties of the micelle as a delivery vehicle may be strongly influenced by protein-drug interactions.

Encapsulation of drug nanoparticles in self-assembled macromolecular nanoshells

Layer-by-Layer (LbL) stepwise self-assembly of the polyelectrolytes poly(allylamine hydrochloride) and poly(styrenesulfonate) was used to create a macromolecular nanoshell around drug nanoparticles (approximately 150 nm in diameter). Dexamethasone, a steroid often used in conjugation with chemotherapy, was chosen as a model drug and was formulated into nanoparticles using a modified solvent-evaporation emulsification method. Measurement of the zeta potential (zeta-potential) after each polyelectrolyte layer was electrostatically added confirmed the successful addition of each layer. Additionally, data acquired from X-ray photon spectroscopy (XPS) indicated the presence of peaks representative of each physisorbed polyelectrolyte layer. Surface modification of the nanoshell was performed by covalently attaching poly(ethylene glycol) (PEG) with a molecular weight of 2000 to the outer surface of the nanoshell. Zeta potential measurements and XPS indicated the presence of PEG chains at the surface of the nanoshell. The polymeric nanoshell on the surface of the drug nanoparticle provides a template upon which surface modifications can be made to create a stealth or targeted drug delivery system.

Drug transport to brain with targeted nanoparticles

Nanoparticle drug carriers consist of solid biodegradable particles in size ranging from 10 to 1000 nm (50-300 nm generally). They cannot freely diffuse through the blood-brain barrier (BBB) and require receptor-mediated transport through brain capillary endothelium to deliver their content into the brain parenchyma. Polysorbate 80-coated polybutylcyanoacrylate nanoparticles can deliver drugs to the brain by a still debated mechanism. Despite interesting results these nanoparticles have limitations, discussed in this review, that may preclude, or at least limit, their potential clinical applications. Long-circulating nanoparticles made of methoxypoly(ethylene glycol)- polylactide or poly(lactide-co-glycolide) (mPEG-PLA/PLGA) have a good safety profiles and provide drug-sustained release. The availability of functionalized PEG-PLA permits to prepare target-specific nanoparticles by conjugation of cell surface ligand. Using peptidomimetic antibodies to BBB transcytosis receptor, brain-targeted pegylated immunonanoparticles can now be synthesized that should make possible the delivery of entrapped actives into the brain parenchyma without inducing BBB permeability alteration. This review presents their general properties (structure, loading capacity, pharmacokinetics) and currently available methods for immunonanoparticle preparation.

Camptothecin derivative-loaded poly(caprolactone-co-lactide)-b-PEG-b-poly(caprolactone-co-lactide) nanoparticles and their biodistribution in mice

Triblock copolymers of poly(caprolactone-co-lactide)-b-PEG-b-poly(caprolactone-co-lactide) (PCLLA-PEG-PCLLA) were synthesized by ring opening copolymerization of caprolactone and lactide in the presence of poly(ethylene glycol) (PEG). With such triblock copolymers, PCLLA-PEG-PCLLA nanoparticles entrapping 10-hydroxycamptothecin-10,20-diisobutyl dicarbonate (HCPT-1), a derivative of the antitumor drug 10-hydroxycamptothecin (HCPT), were prepared by nano-precipitation method and characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The investigations on drug loading, in vitro release and body distribution in mice after intravenous (i.v.) administration were also carried out. It is found that the obtained nanoparticles showed smooth surface and spherical shape with the controllable size in the range of 70-180 nm, and drug loading content varied from 3.3% to 7.0% depending on the copolymer composition and preparation conditions. The in vitro release behavior exhibited a sustaining release manner and was affected by particle size as well as copolymer composition. The results of body distribution study in mice show that the blood concentration of HCPT-1 could be maintained for a long period and the tissue distribution was influenced by the particle size to some extent. These results suggest that the PCLLA-PEG-PCLLA nanoparticles seem to be a promising delivery system for poorly soluble antitumor drugs or their derivatives.

Poly-epsilon-caprolactone microspheres and nanospheres: an overview

Poly-epsilon-caprolactone (PCL) is a biodegradable, biocompatible and semicrystalline polymer having a very low glass transition temperature. Due to its slow degradation, PCL is ideally suitable for long-term delivery extending over a period of more than one year. This has led to its application in the preparation of different delivery systems in the form of microspheres, nanospheres and implants. Various categories of drugs have been encapsulated in PCL for targeted drug delivery and for controlled drug release. Microspheres of PCL either alone or of PCL copolymers have been prepared to obtain the drug release characteristics. This article reviews the advancements made in PCL-based microspheres and nanospheres with special reference to the method of preparation of these and their suitability in developing effective delivery systems.

Application of NMR spectroscopy to the characterization of PEG-stabilized lipid nanoparticles

The main purpose of the present work was to apply NMR techniques to characterize the nanostructural organization of a new drug nanocarrier composed of tripalmitin, lecithin, and poly(ethylene glycol) (PEG)-stearate. These nanocarriers were prepared by an emulsification-solvent evaporation technique and were characterized for their composition and nanostructural architecture. The results showed that tripalmitin, present in the core of the nanoparticles, is the main component of these systems, whereas PEG-stearate is firmly attached to the surface of the nanoparticles, forming a hydrated polymeric layer. Furthermore, the results indicate that, by selecting appropriately the composition of the lipid mixtures used for nanoparticle preparation, it was possible to modulate the PEG-coating density. This rigorous characterization by NMR provided very useful information about the architectural organization of this new colloidal drug carrier and showed the potential of modern NMR techniques for the characterization of core-coated nanostructures intended for drug delivery.

Transport of PLA-PEG particles across the nasal mucosa: effect of particle size and PEG coating density

The aim of the study was to investigate the effect of the size and PEG coating density of Poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) nano- and microparticles on their transport across the nasal mucosa. Particles were made of PLA-PEG copolymers of two different molecular weights (Mw: 37 and 28 kDa) and also PLA of Mw 28 kDa, and prepared using different techniques (simple emulsion (o/w), double emulsion (w/o/w), and nanoprecipitation techniques). The particles were characterized for their size, zeta potential, morphology [Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM)], and PEG coating efficiency. Additionally, the transport of rhodamine 6G-labelled PLA-PEG and PLA particles across the rat nasal mucosa was investigated by Confocal Laser Scanning Microscopy (CLSM). The results showed that the size of PLA-PEG nanoparticles varied between 150 and 300 nm and their zeta potential between -10 and -22 mV depending on both the polymer Mw and the preparation technique. Moreover, the PEG coating efficiency (amount of PEG on the surface with respect to the total amount of PEG in the particles) was high (between 75% and 92%) and affected by the PLA Mw and also by the particles preparation technique. The greatest PEG surface density was achieved for lowest Mw PLA-PEG, using the O/W emulsification technique. The CLSM images of nasal epithelia from rats showed the importance of the PEG coating density and the size on the transmucosal transport of the fluorescent nanoparticles. More specifically, PLA-PEG particles with a high PEG coating density and a small size were more significantly transported than noncoated PLA nanoparticles and also than PLA-PEG nanoparticles with a lower coating density. In conclusion, these results showed the important role that the PEG coating has on the efficacy of PLA-PEG nanoparticles as nasal drug carriers.

Multiphoton microscopy guides neurotrophin modification with poly(ethylene glycol) to enhance interstitial diffusion

Brain-derived neurotrophic factor (BDNF) is a promising therapeutic agent for the treatment of neurodegenerative diseases. However, the limited distribution of this molecule after administration into the brain tissue considerably hampers its efficacy. Here, we show how multiphoton microscopy of fluorescently tagged BDNF in brain-tissue slices provides a useful and rapid screening method for examining the diffusion of large molecules in tissues, and for studying the effects of chemical modifications-for example, conjugating with polyethylene glycol (PEG)-on the diffusion constant. This single variable, obtained by monitoring short-term diffusion in real time, can be effectively used for rational drug design. In this study on fluorescently tagged BDNF and BDNF-PEG, we identify slow diffusion as a major contributing factor to the limited penetration of BDNF, and demonstrate how chemical modification can be used to overcome this barrier.

Pegylated polystyrene particles as a model system for artificial cells

Pegylated polystyrene particles (PS-PEG) were prepared as a model system for artificial cells, by modification of carboxyl polystyrene particles (PS-COOH) with homo- and hetero-bifunctional polyethylene glycols (PEG, MW 1500, 3400, and 5000) containing an amino end group for immobilization and an amino, hydroxyl, or methoxy end group that is exposed at the surface after immobilization. Protein adsorption from human plasma dilutions (85 v %) onto PS-PEG with a PEG surface concentration higher than 40 pmol/cm2 was reduced up to 90-95% compared with protein adsorption onto PS-COOH with a final protein surface concentration of approximately 30 ng/cm2. Two-dimensional gel electrophoresis analyses showed that 30% of the total amount of adsorbed proteins onto PS-PEG are dysopsonins (i.e., nonadhesive proteins like albumin and apolipoproteins). For PS-COOH, <15% of the amount of adsorbed proteins are dysopsonins. In addition, the generation of terminal complement compound (TCC) by PS-PEG particles with a PEG surface concentration lower than approximately 55 pmol/cm2 is not significant. The low protein adsorption, the relatively high percentage of adsorbed dysopsonins, and the low level of complement activation may prevent the uptake of PS-PEG by the mononuclear phagocytic system (MPS) in vivo. Moreover, PS-PEG (PEG surface concentration > approximately 35 pmol/cm2) shows minimal interaction with cultured human umbilical vein endothelial cells (HUVEC), which mimics the endothelial lining of the blood vessel wall.

The effect of a PEG versus a chitosan coating on the interaction of drug colloidal carriers with the ocular mucosa

The influence of the surface characteristics of colloidal drug carriers in their interaction with different biological surfaces is becoming increasingly evident. In order to investigate the importance of these characteristics in their interaction with the ocular mucosa, we developed three types of nanocapsules that differ in their surface properties: poly- epsilon -caprolactone (PECL) nanocapsules, chitosan (CS)-coated PECL nanocapsules and poly(ethylene glycol) (PEG)-coated PECL nanocapsules. Two different approaches were used to form these polymer coated nanocapsules: (i) the electrostatic anchorage of the coating onto the PECL nanocapsules-in the case of CS-and (ii) the use of the previously synthesized copolymer PECL-PEG for the formation of the nanocapsules. In both cases, the systems, prepared by the interfacial deposition technique, were loaded with a fluorescent dye (rhodamine) in order to quantify and visualize their interaction with the ocular surface ex vivo and in vivo. An important conclusion from the ex vivo studies is that the developed systems, and specially the CS-coated ones, enhanced the penetration of the encapsulated dye through the cornea. This effect was not simple due to the physical presence of the nanocapsules but to their ability to carry the encapsulated compound. The second conclusion from the confocal laser scanning microscopy (CLSM) studies is that the systems were able to enter the corneal epithelium by a transcellular pathway and that the penetration rate was dependent on the coating composition. The images suggest that the PEG coating accelerates the transport of the nanocapsules across the whole epithelium, whereas the CS coating favours the retention of the nanocapsules in the superficial layers of the epithelium. The specific behaviour of CS-coated systems was also corroborated in vivo. These results indicate that the surface composition of colloidal drug carriers affects their biodistribution in the eye. Therefore, this surface modification approach can be used as a targeting strategy in ocular drug delivery.

Stealth liposomes and long circulating nanoparticles: critical issues in pharmacokinetics, opsonization and protein-binding properties

This article critically examines and evaluates the likely mechanisms that contribute to prolonged circulation times of sterically protected nanoparticles and liposomes. It is generally assumed that the macrophage-resistant property of sterically protected particles is due to suppression in surface opsonization and protein adsorption. However, recent evidence shows that sterically stabilized particles are prone to opsonization particularly by the opsonic components of the complement system. We have evaluated these phenomena and discussed theories that reconcile complement activation and opsonization with prolonged circulation times. With respect to particle longevity, the physiological state of macrophages also plays a critical role. For example, stimulated or newly recruited macrophages can recognize and rapidly internalize sterically protected nanoparticles by opsonic-independent mechanisms. These concepts are also examined.

Noninvasive Imaging of Quantum Dots in Mice

Quantum dots having four different surface coatings were tested for use in in vivo imaging. Localization was successfully monitored by fluorescence imaging of living animals, by necropsy, by frozen tissue sections for optical microscopy, and by electron microscopy, on scales ranging from centimeters to nanometers, using only quantum dots for detection. Circulating half-lives were found to be less than 12 min for amphiphilic poly(acrylic acid), short-chain (750 Da) methoxy-PEG or long-chain (3400 Da) carboxy-PEG quantum dots, but approximately 70 min for long-chain (5000 Da) methoxy-PEG quantum dots. Surface coatings also determined the in vivo localization of the quantum dots. Long-term experiments demonstrated that these quantum dots remain fluorescent after at least four months in vivo.

Surface-engineered nanoparticles for multiple ligand coupling

The design of surface-engineered nanoparticles for targeting to specific sites is a major challenge. To our knowledge, no study in the literature deals with ligand functionalization of biodegradable nanoparticles through biotin-avidin interactions. With the aim of conceiving small-sized nanoparticles which can be easily functionalized with a variety of ligands or mixtures thereof, biotinylated and PEGylated biotin-poly(ethylene glycol)-poly(epsilon-caprolactone) (B-PEG-PCL) copolymers were synthesized and used to prepare nanoparticles of around 100 nm. Avidin, followed by biotinylated wheat germ agglutinin as a model lectin, were coupled to their surface by taking advantage of the strong biotin-avidin complex formation. The cytotoxicity of the nanospheres towards Caco-2 cells in culture was negligible (more than 82% cell survival for nanoparticle concentrations up to 300 microg/well). The amount of radiolabeled poly(lactic acid) (PLA) or PEG-PLA nanoparticles associated with Caco-2 cells was only 0.7% and 1.5% of the amount added, respectively. This value was increased to 8.5% when a sufficient amount of lectin was bound to the PEG-PLA copolymer. After further studies, the biotin-PEG-coated nanoparticles could be helpful tools for studying the interaction between cells and functionalized nanoparticles with various surface characteristics (PEG layer density and thickness, ligand type and density).

Room-temperature preparation and characterization of poly (ethylene glycol)-coated silica nanoparticles for biomedical applications

Monodisperse, spherical, polyethylene glycol (PEG)-coated silica nanoparticles have been prepared at room temperature and characterized for the purpose of biomedical applications. The particles were synthesized by the hydrolysis of tetramethyl orthosilicate (TMOS) in alcohol media under catalysis by ammonia, and their size can range from about 50-350 nm in diameter. We studied the particle size and size distribution using a scanning electron microscope (SEM) and an asymmetric field-flow fractionation (AFFF) multiangle static light-scattering instrument. The chemical and/or physical binding of PEG to the silica nanoparticles was studied by infrared spectroscopy, and the weight percentage of PEG attached to the particles was quantified. The PEG-coated silica nanoparticles showed enhanced colloidal stability when redispersed into aqueous solutions from the dried state as a result of the steric stabilization function of the PEG polymer grafted on the surface of particles. A nonspecific protein-binding test was also carried out to show that the PEG coating can help reduce the protein adsorption onto the surface of the particles, relating to the biocompatibility of these PEG-coated particles. Also, the inclusion of magnetic nanoparticles into the silica particles was shown as an example of the possible applications of PEG-coated silica particles. These silica nanoparticles, as a matrix for encapsulation of certain reagents, have potential for applications to in vivo diagnosis, analysis, and measurements inside intact biologic systems.

Michael-type addition as a tool for surface functionalization

Michael-type addition (conjugate addition reaction between electron-poor olefins and nucleophiles, such as thiols) has been successfully used as a convenient tool for surface functionalization. Due to its mild character, this method is potentially useful for the introduction of sensitive groups, which can provide bioactivity and targeting possibilities to surfaces of, for example, colloidal carriers. As reaction partners, in our study we have used thiols, possibly present in peptidic structures, and acrylates, at the end of protein-repellant PEG chains. Satisfactory results were obtained with thiols in solution and acrylic groups bound to the surface. Alternatively, the use of thiols on the particles, even if generated in situ, did not provide useful results.

In vitro and in vivo biologic evaluation of long-circulating biodegradable drug carriers loaded with the pure antiestrogen RU 58668

We have developed a parenteral delivery system for the administration of the highly promising pure antiestrogen RU 58668 (RU). Two types of nanoparticles (NP) made of biodegradable copolymers and coated with polyethylene-glycol (PEG) chains were prepared: nanospheres (NS) (diameter, approximately 110 nm) and nanocapsules (NC) with an oily core (diameter, approximately 250 nm). The amount of RU incorporated into NS and NC was approximately 33 vs. approximately 5 microg RU/mg of polymer, respectively. Coating with PEG chains prolonged the antiestrogenic potency of RU, as shown by a prolonged antiuterotrophic activity of encapsulated RU into PEG-poly(D,L lactic acid) (PLA) NS, as compared to that of conventional nonpegylated NS. In mice bearing MCF-7 estrogen-dependent tumors, free RU injected at 4.3 mg/kg/week by i.v. route slightly decreased the estradiol-promoted (0.5 mg/kg/week) tumor growth while RU-loaded PEG-PLA NS injected at the same dose strongly reduced it. Analysis of cell cycle parameters in tumors treated with RU indicated that RU-loaded PEG-PLA NS injected at 4.3 mg/kg/week in MCF-7 tumors decreased cyclin D(1) and cyclin E simultaneously, and increased p27. The antitumoral activity of RU encapsulated within pegylated NC was stronger than that of RU entrapped with pegylated NS loaded at an equivalent dose. Indeed, the former decreased the tumor size in nude mice transplanted with the estrogen receptor-positive but estrogen-independent MCF-7/Ras breast cancer cells at a concentration 2.5 times lower than that of the latter (0.4 mg/kg/week compared to 1 mg/kg/week). Empty PEG-PLA NS and NC were devoid of antiuterotrophic and antitumoral activities. Altogether, these results suggest that the incorporation of the pure antiestrogen RU into long-circulating NP could represent a novel antiestrogen drug delivery system for the parenteral route.

Surface modification of PLGA microspheres

Microspheres made of poly(lactic-co-glycolic acid) (PLGA) are biocompatible and biodegradable, rendering them a promising tool in the context of drug delivery. However, nonspecific adsorption of plasma proteins on PLGA micro- and nanospheres is a main limitation of drug targeting. Poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), physisorbed on flat metal oxide surfaces, has previously been shown to suppress protein adsorption drastically. The goal of our work was to characterize the efficiency of the protein repellent character of PLL-g-PEG on PLGA microspheres and to show the feasibility of introducing functional groups on the PLGA microspheres via functionalized PLL-g-PEG. To quantify the adsorbed amount of protein, a semiquantitative method that uses confocal laser scanning microscopy (CLSM) was applied. The first part of the experiment confirms the feasibility of introducing specific functional groups on PLL-g-PEG-coated PLGA microspheres. In the second part of the experiment, PLL-g-PEG-coated PLGA microspheres show a drastic decrease of adsorbed proteins by two orders of magnitude in comparison to uncoated PLGA microspheres. Low protein-binding, functionalizable microspheres provide a fundamental basis for the design of drug delivery and biosensor systems.

Polyester-poly(ethylene glycol) nanoparticles loaded with the pure antiestrogen RU 58668: physicochemical and opsonization properties

PURPOSE

The pure antiestrogen RU58668 (RU) was encapsulated within nanospheres (NS) and nanocapsules (NC) prepared from different polyester copolymers with poly(ethylene glycol) (PEG) chains. The influence of their physicochemical properties on drug release in vitro and their susceptibility to opsonization were evaluated.

METHODS

RU-loaded PEG-bearing nanoparticles (NP) prepared by interfacial deposition of preformed polymer were characterized (size, zeta potential, percentage encapsulation and loading). In vitro release kinetics were studied in the presence of 10% fetal calf serum (FCS). Their opsonization in mouse serum was evaluated by silver staining of SDS-PAGE and Western blotting of desorbed proteins.

RESULTS

The NS were smaller than NC and had a zeta potential close to zero and a higher percentage of loading. RU release from NS in vitro was reduced as compared with the dissolution profile of free RU in a serum-containing medium. Decreased opsonin adsorption at the surface of pegylated NS was observed.

CONCLUSION

Small nanoparticulate systems containing a high load of pure antiestrogen, showing reduced drug release, have been developed. Among the six nanosphere preparations containing RU, two show a size below 200 nm, and two others undergo reduced protein adsorption in the presence of serum, compatible with increased persistence in the blood.

Poly(D,L-lactic acid)-poly(ethylene glycol)-monomethyl ether diblock copolymers control adhesion and osteoblastic differentiation of marrow stromal cells

Biodegradable polymers, such as poly(lactic acid) (PLA) and poly(lactic-coglycolic acid) (PLGA), are attractive materials for tissue engineering because of their degradative and mechanical properties, which permit scaffolds to be tailored to the individual requirements of different tissues. Although these materials support tissue development, their chemical properties offer no control of cell adhesion or function because their surfaces become immediately masked by adsorbing serum proteins when the materials come into contact with body fluids. Furthermore, adhesion proteins undergo conformational changes and a decrease in bioactivity when adsorbed to hydrophobic materials, such as PLA. To overcome these limitations, we modified the properties of PLA by synthesizing a diblock copolymer with poly(ethylene glycol) (PEG), which is known to reduce the amount of adsorbed proteins and to modify their conformation. By altering the PEG content of these diblock copolymers we were able to control the adsorption of adhesion proteins and, because cell adhesion takes place only in the presence of serum proteins, to control cell adhesion and cell shape. Marrow stromal cell differentiation to the osteoblastic phenotype was strongly improved on PEG-PLA compared with PLA, PLGA and tissue culture polystyrene and led to a 2-fold increase in alkaline phosphatase activity and mineralization.

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

PURPOSE

The purpose of this study was to demonstrate specific receptor-mediated targeting of phagocytes by functional surface coatings of microparticles, shielding from nonspecific phagocytosis and allowing ligand-specific interactions via molecular recognition.

METHODS

Coatings of the comb polymer poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) were investigated for potential to inhibit 1) nonspecific spreading of human blood-derived macrophages (MOs) and dendritic cells (DCs) on glass and 2) nonspecific phagocytosis of PLL-g-PEG-coated, carboxylated polystyrene (PS) or biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microspheres. Coating was performed by adsorption of positively charged PLL-g-PEG on negatively charged microparticles or plasma-cleaned glass through electrostatic interaction. The feasibility of ligand-specific interactions was tested with a model ligand, RGD, conjugated to PEG chains of PLL-g-PEG to form PLL-g-PEG-RGD and compared with inactive ligand conjugate, PLL-g-PEG-RDG.

RESULTS

Coatings with PLL-g-PEG largely impaired the adherence and spreading of MOs and DCs on glass. The repellent character of PLL-g-PEG coatings drastically reduced phagocytosis of coated PS and PLGA microparticles to 10% in presence of serum. With both MOs and DCs, we observed ligand-specific interactions with PLL-g-PEG-RGD coatings on glass and PS and PLGA microspheres. Ligand specificity was abolished when using inactive ligand conjugate PLL-g-PEG-RDG, whereas repellency of coating was maintained.

CONCLUSIONS

Coatings of PLL-g-PEG-ligand conjugates provide a novel technology for ligand specific targeting of microspheres to MOs and DCs while reducing nonspecific phagocytosis.

Novel graft PLLA-based copolymers: potential of their application to particle technology

This study describes the synthesis of novel biodegradable graft copolymers based on a backbone of poly (L-lactic acid) (PLLA) on which short blocks of polyacrylamide (PAcr) were grafted. Preliminary results of their potential in the field of controlled-release technologies also have been reported. The copolymers have been synthesized through the radical polymerization of acrylamide initiated by a peroxide in the presence of PLLA. Two different methodologies of synthesis, namely, in solution and in emulsion, have been tested. The structure of the copolymers was studied by (1)H-NMR and infrared spectroscopy and by differential scanning calorimetry (DSC) and cytotoxicity tests were conducted to assess their biocompatibility. The copolymers were used to prepare particles by the emulsion-solvent evaporation technique. The shapes and dimensions of the particles were dependent on the polymer type and concentration used. The surfaces of the particles were modified by the presence of polyacrylamide residues, as demonstrated by zeta-potential measurements. The release behavior of the particles was assessed by encapsulating rhodamine B as the model compound. The release was faster for the particles prepared by the grafted polymer as a consequence of its increased hydrophilicity. Based on these novel biomaterials, preliminary results suggest a potential of the particles for peroral or parenteral drug delivery.

Galactosylated Poly(N-isopropylacrylamide) Hydrogel Submicrometer Particles for Specific Cellular Uptake within Hepatocytes

Poly(N-isopropylacrylamide-co-acrylic acid) hydrogel submicrometer particles were prepared by free radical copolymerization of N-isopropylacrylamide and acrylic acid in the presence of a crosslinker above the lower critical solution temperature (LCST). They exhibited a reversible swelling and deswelling behavior: ca. 200-nm diameter below the LCST and ca. 100-nm diameter above the LCST. The hydrogel particles were tagged with fluorescent dye (FITC) in order to monitor the extent of cellular uptake and were further modified with galactose moieties to evaluate the extent of receptor-mediated endocytosis against HepG2 cells. Flow cytometry and confocal microscopy were used to investigate cellular uptake behaviors of the submicrometer particles. It was found that the extent of cellular uptake of submicrometer particles was far greater above the LCST than below the LCST, suggesting that smaller particles were taken up more readily within cells. When the submicrometer particles were galactosylated, the extent of cellular uptake increased dramatically due to receptor-mediated endocytosis. This study proposes a new possibility of controlling intracellular events such as protein and gene expression by a thermally modulated endocytosis process using thermo-sensitive microgel beads.

Development of a nonviral gene delivery vehicle for systemic application

Polycation vehicles used for in vitro gene delivery require alteration for successful application in vivo. Modification of polycations by direct grafting of additional components, e.g., poly(ethylene glycol) (PEG), either before or after DNA complexation, tend to interfere with polymer/DNA binding interactions; this is a particular problem for short polycations such as linear, beta-cyclodextrin-containing polycations (betaCDPs). Here, a new method of betaCDP polyplex (polycation/DNA composite structures) modification is presented that exploits the ability to form inclusion complexes between cyclodextrins and adamantane. Surface-PEGylated betaCDP polyplexes are formed by self-assembly of the polyplexes with adamantane-PEG conjugates. While unmodified polyplexes rapidly aggregate and precipitate in salt solutions, the PEGylated betaCDP polyplexes are stable at conditions of physiological salt concentration. Addition of targeting ligands to the adamantane-PEG conjugates allows for receptor-mediated delivery; galactosylated betaCDP-based particles reveal selective targeting to hepatocytes via the asialoglycoprotein receptor. Galactosylated particles transfect hepatoma cells with 10-fold higher efficiency than glucosylated particles (control), but show no preferential transfection in a cell line lacking the asialoglycoprotein receptor. Thus, surface modification of betaCDP-based polyplexes through the use of cyclodextrin/adamantane host/guest interactions endows the particles with properties appropriate for systemic application.

Relationship between complement activation, cellular uptake and surface physicochemical aspects of novel PEG-modified nanocapsules

The aim of our work was to examine the relationship between modifications of the surface of nanocapsules (NC) by adsorption or covalent grafting of poly(ethylene oxide) (PEG), and changes in their phospholipid (PL) content on complement activation (C3 cleavage) and on uptake by macrophages. The physicochemical characterization of the NC included an investigation of their properties, such as surface charge, size, hydrophilicity, morphology and homogeneity. This is the first time that such properties have been correlated with biological interactions for NC, a novel carrier system with a structure more complex than nanospheres. C3 crossed immunoelectrophoresis revealed the reduced activation for NC with longer PEG chain and higher density, although all formulations induced C3 cleavage to a lesser or greater extent. NC bearing PEG covalently bound to the surface were weaker activators of complement than plain PLA [poly(D,L-lactide)] NC or nanospheres (NS). Furthermore, the fluorescent/confocal microscopy of J774A1 cells in contact with NC reveal a dramatically reduced interaction with PEG-bearing NC. However, the way in which PEG was attached (covalent or adsorbed) seemed to affect the mechanism of uptake. Taken together, these results suggest that the low level of protein binding to NC covered with a high density of 20kDa PEG chains is likely to be due to the steric barriers surrounding these particles, which prevents protein adsorption and reduces their interaction with macrophages.

Amoxicillin-loaded polyethylcyanoacrylate nanoparticles: influence of PEG coating on the particle size, drug release rate and phagocytic uptake

Polyethyleneglycol (PEG)-coated polyethylcyanoacrylate (PECA) nanoparticles loaded with amoxicillin were prepared and the influence of the PEG coating on the particle size, zeta potential, drug release rate and phagocytic uptake by murine macrophages was studied. Experimental results show that this colloidal drug delivery system could be useful for intravenous or oral administration. The profile of amoxicillin release from PECA nanoparticles system was studied under various conditions similar to those of some corporeal fluids. In all these experiments, amoxicillin release in the free form was studied by HPLC analysis. Experimental results showed that at pH 7.4 drug release rises when molecular weight of PEG added to polymerization medium increases; in human plasma on the contrary drug release is reduced as molecular weight of PEG rises. Phagocytosis was evaluated by incubating amoxicillin-loaded PECA nanoparticles with murine macrophages and determining the amount of phagocytized nanoparticles by dosing the amoxicillin present inside the macrophages. The results of this study showed significative differences between nanoparticles prepared in the presence or in the absence of PEG and demonstrated that the PEG coating reduces the macrophages uptake. These results suggest that nanoparticles prepared in the presence of PEG are stealth carriers, which could be an injectable colloidal system able to avoid MPS recognition after intravenous injection. Experimental data of drug release at pH 1.1 and in the presence of urease, taking into account the mucoadhesive properties of polyalkylcyanoacrylate nanoparticles and the activity of the amoxicillin versus Helicobacter pylori, suggest moreover that the colloidal drug delivery system obtained in our laboratory could be useful for the treatment of diseases caused by H. pylori by peroral administration.

Comparison of protein adsorption patterns onto differently charged hydrophilic superparamagnetic iron oxide particles obtained in vitro and ex vivo

Protein adsorption patterns of superparamagnetic iron oxides (SPIO) were evaluated by two-dimensional electrophoresis (2-DE) after in vitro incubation of the particles in plasma or serum. SPIO particles having positive (MKK 1211), negative (MKA 1211), or neutral (MKG 1411) charge were used. Protein adsorption patterns of different charged SPIO particles acquired in vitro and recollected 5 min after intravenous injection into rats (ex vivo) were compared. For the uncharged MKG 1411 particles, the differences of protein adsorption patterns were negligible and only minor differences were found for the negatively charged MKA 1211 and positively charged MKK 1211 particles. A good correlation between in vitro and ex vivo data could be shown. For the evaluation of protein adsorption patterns of SPIO particles determining organ distribution and allowing estimation of site-specific delivery (drug targeting), the currently used protocol for 2-DE analysis could be confirmed.