Improved cellular uptake of chitosan-modified PLGA nanospheres by A549 cells

Preparation and characterization of vinculin-targeted polymer-lipid nanoparticle as intracellular delivery vehicle

Intracellular delivery vehicles have been extensively investigated as these can serve as an effective tool in studying the cellular mechanism, by delivering functional protein to specific locations of the cells. In the current study, a polymer–lipid nanoparticle (PLN) system was developed as an intracellular delivery vehicle specifically targeting vinculin, a focal adhesion protein associated with cellular adhesive structures, such as focal adhesions and adherens junctions. The PLNs possessed an average size of 106 nm and had a positively charged surface. With a lower encapsulation efficiency 32% compared with poly(lactic-co-glycolic) acid (PLGA) nanoparticles (46%), the PLNs showed the sustained release profile of model drug BSA, while PLGA nanoparticles demonstrated an initial burst-release property. Cell-uptake experiments using mouse embryonic fibroblasts cultured in fibrin–fibronectin gels observed, under confocal microscope, that the anti-vinculin conjugated PLNs could successfully ship the cargo to the cytoplasm of fibroblasts, adhered to fibronectin–fibrin. With the use of cationic lipid, the unconjugated PLNs were shown to have high gene transfection efficiency. Furthermore, the unconjugated PLNs had nuclear-targeting capability in the absence of nuclear-localization signals. Therefore, the PLNs could be manipulated easily via different type of targeting ligands and could potentially be used as a powerful tool for cellular mechanism study, by delivering drugs to specific cellular organelles.

Airway delivery of peptides and proteins using nanoparticles

Delivery of peptides and proteins via the airways is one of the most exciting potential applications of nanomedicine. These macromolecules could be used for many therapeutic applications, however due to their poor stability in physiological medium and difficulties in delivering them across biological barriers, they are very difficult to use in therapy. Nanoparticulate drug delivery systems have emerged as one of the most promising technologies to overcome these limitations, owing mainly to their proven capacity to cross biological barriers and to enter cells in high yields, thus improving delivery of macromolecules. In this review, we summarize the current advances in nanoparticle designed for transmucosal delivery of peptides and proteins. Challenges that must be overcome in order to derive clinical benefits are also discussed.

Chemico-physical investigation of tenofovir loaded polymeric nanoparticles

Tenofovir (PMPA), an acyclic nucleoside phosphonate analog, is one of the most important drugs used for the HIV treatment. Unfortunately, several adverse reactions are related to its i.v. administration owing to the saturation of an anionic renal transporter. In order to improve the drug administration, the PMPA was embedded into a new type of nanocarriers based on poly-(D,L-lactide-co-glycolide) (PLGA) and/or chitosan (CH). The strategies for the preparation of nanoparticles (Nps) with a more efficient drug loading respect to the one reported in the literature for PMPA nanoencapsulation were investigated. CH was added in the first inner emulsion or in the external phase during the second emulsion of water/oil/water (W/O/W) Nps. The addition of CH in the first inner emulsion was the most promising technique. The Nps have a Z-average of 230 nm, a Z-potential of -3 mV and an EE% of 15 that was 2.5-3 times higher than that obtained with PLGA Nps or CH Nps. In vitro release studies showed a limited control on drug release in phosphate buffer (pH 7.4) while an initial burst effect followed by a slow drug release was observed in acidic receiving phase (pH 4.6). These results suggest the PLGA/CH Nps should be an effective and attractive anti-HIV drug carrier to study the cellular uptake and drug delivery on target cells such as macrophages.

Effects of the presence or absence of a protein corona on silica nanoparticle uptake and impact on cells

Nanoparticles enter cells through active processes, thanks to their capability of interacting with the cellular machinery. The protein layer (corona) that forms on their surface once nanoparticles are in contact with biological fluids, such as the cell serum, mediates the interactions with cells in situ. As a consequence of this, here we show that the same nanomaterial can lead to very different biological outcomes, when exposed to cells in the presence or absence of a preformed corona. In particular, silica nanoparticles exposed to cells in the absence of serum have a stronger adhesion to the cell membrane and higher internalization efficiency, in comparison to what is observed in medium containing serum, when a preformed corona is present on their surface. The different exposure conditions not only affect the uptake levels but also result in differences in the intracellular nanoparticle location and impact on cells. Interestingly, we also show that after only one hour of exposure, a corona of very different nature forms on the nanoparticles exposed to cells in the absence of serum. Evidence suggests that these different outcomes can all be connected to the different adhesion and surface properties in the two conditions.

In vitro and in vivo characterization of temoporfin-loaded PEGylated PLGA nanoparticles for use in photodynamic therapy

Aims: In this study we evaluated temoporfin-loaded polyethylene glycol (PEG) Poly-(D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs) as a new formulation for potential use in cancer treatment. Materials & methods: NPs were characterized for their photophysical properties, temoporfin release, cellular uptake and intracellular localization, and dark and photocytotoxicities of temoporfin by using A549, MCF10A neoT and U937 cell lines. In vivo imaging was performed on athymic nude-Foxn1 mice. Results: Temoporfin was highly aggregated within the NPs and the release of temoporfin monomers was faster from PEGylated PLGA NPs than from non-PEGylated ones. PEGylation significantly reduced the cellular uptake of NPs by the differentiated promonocytic U937 cells, revealing the stealth properties of the delivery system. Dark cytotoxicity of temoporfin delivered by NPs was less than that of free temoporfin in standard solution (Foscan®, Biolitec AG [Jena, Germany]), whereas phototoxicity was not reduced. Temoporfin delivered to mice by PEGylated PLGA NPs exhibits therapeutically favorable tissue distribution. Conclusion: These encouraging results show promise in using PEGylated PLGA NPs for improving the delivery of photosensitizers for photodynamic therapy.

Original submitted 30 March 2011; Revised submitted 9 July 2011

Low molecular-weight chitosan as a pH-sensitive stealth coating for tumor-specific drug delivery

When a nanoparticle is developed for systemic application, its surface is typically protected by poly(ethylene glycol) (PEG) to help prolonged circulation and evasion of immune clearance. On the other hand, PEG can interfere with interactions between nanocarriers and target cells and negatively influence the therapeutic outcomes. To overcome this challenge, we propose low molecular-weight chitosan (LMWC) as an alternative surface coating, which can protect the nanomedicine in neutral pH but allow cellular interactions in the weakly acidic pH of tumors. LMWCs with a molecular weight of 2-4 kDa, 4-6.5 kDa, and 11-22 kDa were produced by hydrogen peroxide digestion and covalently conjugated with poly(lactic-co-glycolic acid) (PLGA). Nanoparticles created with PLGA-LMWC conjugates showed pH-sensitive cell interactions, which enabled specific drug delivery to cells in a weakly acidic environment. The hydrophilic LMWC layer reduced opsonization and phagocytic uptake. These properties qualify LMWCs as a promising biomaterial for pH-sensitive stealth coating.

Advances in microscopy and complementary imaging techniques to assess the fate of drugs ex vivo in respiratory drug delivery: an invited paper

The technical advances in microscopy imaging techniques have been applied to assess the fate of drugs for researching respiratory drug delivery in ex vivo and in vivo experiments. Recent developments in optical imaging (confocal microscopy, multi-photon microscopy, fluorescence imaging (FLI) and bioluminescence imaging (BLI)), and in non-optical imaging (magnetic resonance imaging (MRI), computing tomography (CT), positron-emission tomography (PET) and single-photon-emission computed tomography (SPECT)) are presented with their derivative medical devices. Novel microscopy have been utilized to address many biological questions in basic research and are becoming powerful clinical tools for non-invasive objective diagnosis, guided treatment, and monitoring therapies. The goal of this paper is to present recent advances in microscopy imaging techniques and to discuss their novel applications in respiratory drug delivery imaging.

PLGA-based nanoparticles: an overview of biomedical applications

Poly(lactic-co-glycolic acid) (PLGA) is one of the most successfully developed biodegradable polymers. Among the different polymers developed to formulate polymeric nanoparticles, PLGA has attracted considerable attention due to its attractive properties: (i) biodegradability and biocompatibility, (ii) FDA and European Medicine Agency approval in drug delivery systems for parenteral administration, (iii) well described formulations and methods of production adapted to various types of drugs e.g. hydrophilic or hydrophobic small molecules or macromolecules, (iv) protection of drug from degradation, (v) possibility of sustained release, (vi) possibility to modify surface properties to provide stealthness and/or better interaction with biological materials and (vii) possibility to target nanoparticles to specific organs or cells. This review presents why PLGA has been chosen to design nanoparticles as drug delivery systems in various biomedical applications such as vaccination, cancer, inflammation and other diseases. This review focuses on the understanding of specific characteristics exploited by PLGA-based nanoparticles to target a specific organ or tissue or specific cells.

Delivery of proteins to the brain by bolaamphiphilic nano-sized vesicles

Bolaamphiphilic cationic vesicles with acetylcholine (ACh) surface groups were investigated for their ability to deliver a model protein-bovine serum albumin conjugated to fluorescein isothiocyanate (BSA-FITC) across biological barriers in vitro and in vivo. BSA-FITC-loaded vesicles were internalized into cells in culture, including brain endothelial b.End3 cells, at 37 °C, but not at 4 °C, indicating an active uptake process. To examine if BSA-FITC-loaded vesicles were stable enough for in vivo delivery, we tested vesicle stability in whole serum. The half-life of cationic BSA-FITC-loaded vesicles with ACh surface groups that are hydrolyzed by choline esterase (ChE) was about 2 h, whereas the half-life of vesicles with similar surface groups, but which are not hydrolyzed by choline esterase (ChE), was over 5 h. Pyridostigmine, a choline esterase inhibitor that does not penetrate the blood-brain barrier (BBB), increased the stability of the ChE-sensitive vesicles to 6 h but did not affect the stability of vesicles with ACh surface groups that are not hydrolyzed by ChE. Following intravenous administration to pyridostigmine-pretreated mice, BSA-FITC encapsulated in ChE-sensitive vesicles was distributed into various tissues with marked accumulation in the brain, whereas non-encapsulated (free) BSA-FITC was detected only in peripheral tissues, but not in the brain. These results show that cationic bolaamphiphilic vesicles with ACh head groups are capable of delivering proteins across biological barriers, such as the cell membrane and the blood-brain barrier (BBB). Brain ChE activity destabilizes the vesicles and releases the encapsulated protein, enabling its accumulation in the brain.

Quantitative assessment of the comparative nanoparticle-uptake efficiency of a range of cell lines

The mechanism(s) of nanoparticle-cell interactions are still not understood. At present there is little knowledge of the relevant length- and timescales for nanoparticle intracellular entry and localization within cells, or the cell-specificity of nanoparticle uptake and localisation. Here, the effect of particle size on the in-vitro intracellular uptake of model fluorescent carboxyl-modified polystyrene nanoparticles is investigated in various cell lines. A range of micro- and nanoparticles of defined sizes (40 nm to 2 μm) are incubated with a series of cell types, including HeLa and A549 epithelial cells, 1321N1 astrocytes, HCMEC D3 endothelial cells, and murine RAW 264.7 macrophages. Techniques such as confocal microscopy and flow cytometry are used to study particle uptake and subcellular localisation, making significant efforts to ensure reproducibility in a semiquantitative approach. The results indicate that internalization of (nano)particles is highly size-dependent for all cell lines studied, and the kinetics of uptake for the same type of nanoparticle varies in the different cell types. Interestingly, even cells not specialized for phagocytosis are able to internalize the larger nanoparticles. Intracellular uptake of all sizes of particles is observed to be highest in RAW 264.7 cells (a specialized phagocytic cell line) and the lowest in the HeLa cells. These results suggest that (nano)particle uptake might not follow commonly defined size limits for uptake processes, and highlight the variability of uptake kinetics for the same material in different cell types. These conclusions have important implications for the assessment of the safety of nanomaterials and for the potential biomedical applications of nanoparticles.

Toxicology and clinical potential of nanoparticles

In recent years, nanoparticles (NPs) have increasingly found practical applications in technology, research and medicine. The small particle size coupled to their unique chemical and physical properties is thought to underlie their exploitable biomedical activities. Here, we review current toxicity studies of NPs with clinical potential. Mechanisms of cytotoxicity are discussed and the problem of extrapolating knowledge gained from cell-based studies into a human scenario is highlighted. The so-called 'proof-of-principle' approach, whereby ultra-high NP concentrations are used to ensure cytotoxicity, is evaluated on the basis of two considerations; firstly, from a scientific perspective, the concentrations used are in no way related to the actual doses required which, in many instances, discourages further vital investigations. Secondly, these inaccurate results cast doubt on the science of nanomedicine and thus, quite dangerously, encourage unnecessary alarm in the public. In this context, the discrepancies between in vitro and in vivo results are described along with the need for a unifying protocol for reliable and realistic toxicity reports.

Nanomedical system for nucleic acid drugs created with the biodegradable nanoparticle platform

Nanomedical applications of biodegradable poly(DL-lactide-co-glycolide) (PLGA) nanoparticles (NPs) developed are discussed in this review. A surface-functionalized PLGA NP platform for drug delivery was established to encapsulate a number of macromolecular drugs such as peptides and nucleic acids as well as low-molecular-weight drugs by the emulsion solvent diffusion method. The interaction of PLGA NPs with cells and tissues could be controlled by changing the surface properties of NPs, suggesting their potential utility for the intracellular drug delivery of nucleic acid-based drugs. Furthermore, orally administered NF-κB decoy oligonucleotide-loaded CS-PLGA NPs are also useful in treating experimental colitis. These approaches using surface-modified PLGA NPs could be able to open new possibilities for nucleic acid-based drug delivery via noninvasive administration method.

Effects of transport inhibitors on the cellular uptake of carboxylated polystyrene nanoparticles in different cell lines

Nanotechnology is expected to play a vital role in the rapidly developing field of nanomedicine, creating innovative solutions and therapies for currently untreatable diseases, and providing new tools for various biomedical applications, such as drug delivery and gene therapy. In order to optimize the efficacy of nanoparticle (NP) delivery to cells, it is necessary to understand the mechanisms by which NPs are internalized by cells, as this will likely determine their ultimate sub-cellular fate and localisation. Here we have used pharmacological inhibitors of some of the major endocytic pathways to investigate nanoparticle uptake mechanisms in a range of representative human cell lines, including HeLa (cervical cancer), A549 (lung carcinoma) and 1321N1 (brain astrocytoma). Chlorpromazine and genistein were used to inhibit clathrin and caveolin mediated endocytosis, respectively. Cytochalasin A and nocodazole were used to inhibit, respectively, the polymerisation of actin and microtubule cytoskeleton. Uptake experiments were performed systematically across the different cell lines, using carboxylated polystyrene NPs of 40 nm and 200 nm diameters, as model NPs of sizes comparable to typical endocytic cargoes. The results clearly indicated that, in all cases and cell types, NPs entered cells via active energy dependent processes. NP uptake in HeLa and 1321N1 cells was strongly affected by actin depolymerisation, while A549 cells showed a stronger inhibition of NP uptake (in comparison to the other cell types) after microtubule disruption and treatment with genistein. A strong reduction of NP uptake was observed after chlorpromazine treatment only in the case of 1321N1 cells. These outcomes suggested that the same NP might exploit different uptake mechanisms to enter different cell types.

Dual targeting folate-conjugated hyaluronic acid polymeric micelles for paclitaxel delivery

A series of novel self-assembled hyaluronic acid derivatives (HA-C(18)) grafted with hydrophobic octadecyl moiety and further dual targeting folic acid-conjugated HA-C(18) (FA-HA-C(18)) were synthesized. With the increase in the degree of substitution of octadecyl group from 12.7% to 19.3%, the critical micellar concentration of HA-C(18) copolymers decreased from 37.3 to 10.0 μg/mL. Paclitaxel (PTX) was successfully encapsulated into the hydrophobic cores of the HA-C(18) and FA-HA-C(18) micelles, with encapsulation efficiency as high as 97.3%. The physicochemical properties of the polymeric micelles were measured by DLS, TEM and DSC. Moreover, in vitro release behavior of PTX was investigated by dialysis bag method and PTX was released from micelles in a near zero-order sustained manner. In vitro antitumor activity tests suggested PTX-loaded HA-C(18) and FA-HA-C(18) micelles exhibited significantly higher cytotoxic activity against MCF-7 and A549 cells compared to Taxol at a lower PTX concentration. The cellular uptake experiments were conducted by quantitative assay of PTX cellular accumulation and confocal laser scanning microscopy imaging of coumarin-6 labeled HA-C(18) and FA-HA-C(18) micelles in folate receptor overexpressing MCF-7 cells. Folate and CD44 receptor competitive inhibition studies performed by fluorescence microscopy imaging suggested intracellular delivery of HA-C(18) and FA-HA-C(18) micelles were efficiently taken up via CD44 receptor-mediated endocytosis. The folate receptor-mediated endocytosis further enhanced internalized amounts of FA-HA-C(18) micelles in MCF-7 cells, as compared with HA-C(18) micelles. The internalization pathways of PTX-loaded HA-C(18) and FA-HA-C(18) micelles might include clathrin-mediated endocytosis, caveolae-mediated endocytosis and macropinocytosis. Therefore, the present study suggested that HA-C(18) and FA-HA-C(18) copolymers as biodegradable, biocompatible and cell-specific targetable nanostructure carriers, are promising nanosystems for cellular and intracellular targeting delivery of hydrophobic anticancer drugs.

Improvements in transfection efficiency with chitosan modified poly(DL-lactide-co-glycolide) nanospheres prepared by the emulsion solvent diffusion method, for gene delivery

This study sought to evaluate the in vitro transfection efficiency of plasmid DNA (pDNA)-loaded chitosan-modified poly(DL-lactide-co-glycolide) nanospheres (CS-PLGA NS) in a gene-delivery system. Using the emulsion solvent diffusion (ESD) method, pDNA-loaded PLGA NS was prepared and the surface of the PLGA NS was modified by binding to CS. Gene transfection ability of CS-PLGA NS was examined in A549 cells. The luciferase gene was used as a reporter gene. The pattern of luciferase activity by pDNA-loaded CS-PLGA NS was initially weak, but gradually grew stronger before decreasing activity. These phenomena should be in accordance with the sustained-release profile of pDNA from PLGA NS in the cytosol and the pDNA protection against DNase. Positively charged CS-PLGA NS was found, by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay, not to exhibit cytotoxicity on A549 cells. These results suggest that CS-PLGA NS are potential contributors to efficient pDNA delivery due to their increased interactions with cells and lack of cytotoxic effects.

Enhanced cellular association of paclitaxel delivered in chitosan-PLGA particles

We have previously demonstrated that the cellular association, cytotoxicity, and in vivo anti-tumor efficacy of paclitaxel are significantly greater when delivered in PLGA microparticles compared to nanoparticles. The purpose of this research is to test the hypothesis that mucoadhesive chitosan promotes adhesion of PLGA particles to mucus on the tumor epithelium, resulting in enhanced cellular association and cytotoxicity of paclitaxel. PLGA particles containing paclitaxel or Bodipy(®) were prepared and chitosan was either adsorbed or chemically conjugated to the particle surface. The cellular association and cytotoxicity of paclitaxel in 4T1 cells was determined. A 4-10 fold increase in cellular association of paclitaxel was observed when chitosan was adsorbed or conjugated to the PLGA particles. Chitosan-conjugated PLGA microparticles were most cytotoxic with an IC(50) value of 0.77 μM. Confocal microscopy demonstrated that chitosan-PLGA microparticles adhered to the surface of 4T1 cells. Pretreatment of either 4T1 cells or chitosan-PLGA particles with mucin resulted in significant increase in cellular association of paclitaxel. A linear correlation was established between theoretical amount of chitosan used and experimentally determined amount of chitosan adsorbed or conjugated to PLGA nanoparticles. In conclusion, cellular association and cytotoxicity of paclitaxel was significantly enhanced when delivered in chitosan-PLGA particles.

Characterization of endocytosis and exocytosis of cationic nanoparticles in airway epithelium cells

A major challenge of drug delivery using colloids via the airway is to understand the mechanism implied in their interactions with epithelial cells. The purpose of this work was to characterize the process of endocytosis and exocytosis of cationic nanoparticles (NPs) made of maltodextrin which were developed as a delivery system for antigens in vaccine applications. Confocal microscopy demonstrated that these NP are rapidly endocytosed after as little as 3 min incubation, and that the endocytosis was also faster than NP binding since most of the NPs were found in the middle of the cells around the nuclei. A saturation limit was observed after a 40 min incubation, probably due to an equilibrium becoming established between endocytosis and exocytosis. Endocytosis was dramatically reduced at 4 degrees C compared with 37 degrees C, or by NaN(3) treatment, both results suggesting an energy dependent process. Protamine pretreatment of the cells inhibited NPs uptake and we found that clathrin pathway is implied in their endocytosis. Cholesterol depletion increased NP uptake by 300% and this phenomenon was explained by the fact that cholesterol depletion totally blocked NP exocytosis. These results suggest that these cationic NPs interact with anionic sites, are quickly endocytosed via the clathrin pathway and that their exocytosis is cholesterol dependent, and are similar to those obtained in other studies with viruses such as influenza.

Chitosan-modified poly(D,L-lactide-co-glycolide) nanospheres for improving siRNA delivery and gene-silencing effects

Chitosan (CS) surface-modified poly(d,l-lactide-co-glycolide) (PLGA) nanospheres (NS) for a siRNA delivery system were evaluated in vitro. siRNA-loaded PLGA NS were prepared by an emulsion solvent diffusion (ESD) method, and the physicochemical properties of NS were investigated. The level of targeted protein expression and siRNA uptake were examined in A549 cells. CS-modified PLGA NS exhibited much higher encapsulation efficiency than unmodified PLGA NS (plain-PLGA NS). CS-modified PLGA NS showed a positive zeta potential, while plain-PLGA NS were negatively charged. siRNA uptake studies by observation with confocal leaser scanning microscopy (CLSM) indicated that siRNA-loaded CS-modified PLGA NS were more effectively taken up by the cells than plain-PLGA NS. The efficiencies of different siRNA preparations were compared at the level of targeted protein expression. The gene-silencing efficiency of CS-modified PLGA NS was higher and more prolonged than those of plain-PLGA NS and naked siRNA. This result correlated with the CLSM studies, which may have been due to higher cellular uptake of CS-modified PLGA NS due to electrostatic interactions. It was concluded that CS-modified PLGA NS containing siRNA could provide an effective siRNA delivery system.