Modification of the copolymers poloxamer 407 and poloxamine 908 can affect the physical and biological properties of surface modified nanospheres

Immobilization of acetylcholinesterase on Pt(II) and Pt(IV) attached nanoparticles for the determination of pesticides

Pt(ii) and Pt(iv)-tagged nanoparticles have been synthesized according to the template method for the identification of pesticides. Their morphologies have been investigated using scanning electron microscopy and characterized by means of spectral measurements. Then, acetylcholinesterase (AChE) was immobilized onto the nanoparticles. The AChE immobilized Pt(ii) and Pt(iv)-tagged nanomaterials show high reusability and storage capacity. The catalytic activity of AChE followed Michaelis-Menten kinetics. Assays for enzyme activity measurements demonstrate that the nanospheres tagged with Pt(ii) have a much better performance than those with Pt(iv). Furthermore, whether or not there was any interaction between the immobilized enzyme and 1-naphthyl-N-methylcarbamate, which is a carbamate insecticide, was examined.

Negatively charged self-assembling DNA/poloxamine nanospheres for in vivo gene transfer

Over the past decade, numerous nonviral cationic vectors have been synthesized. They share a high density of positive charges and efficiency for gene transfer in vitro. However, their positively charged surface causes instability in body fluids and cytotoxicity, thereby limiting their efficacy in vivo. Therefore, there is a need for developing alternative molecular structures. We have examined tetrabranched amphiphilic block copolymers consisting of four polyethyleneoxide/polypropyleneoxide blocks centered on an ethylenediamine moiety. Cryo-electron microscopy, ethidium bromide fluorescence and light and X-ray scattering experiments performed on vector-DNA complexes showed that the dense core of the nanosphere consisted of condensed DNA interacting with poloxamine molecules through electrostatic, hydrogen bonding and hydrophobic interactions, with DNA molecules also being exposed at the surface. The supramolecular organization of block copolymer/DNA nanospheres induced the formation of negatively charged particles. These particles were stable in a solution that had a physiological ionic composition and were resistant to decomplexation by heparin. The new nanostructured material, the structure of which clearly contrasted with that of lipoplexes and polyplexes, efficiently transferred reporter and therapeutic genes in skeletal and heart muscle in vivo. Negatively charged supramolecular assemblies hold promise as therapeutic gene carriers for skeletal and heart muscle-related diseases and expression of therapeutic proteins for local or systemic uses.

Nanosuspensions: a promising drug delivery strategy

Nanosuspensions have emerged as a promising strategy for the efficient delivery of hydrophobic drugs because of their versatile features and unique advantages. Techniques such as media milling and high-pressure homogenization have been used commercially for producing nanosuspensions. Recently, the engineering of nanosuspensions employing emulsions and microemulsions as templates has been addressed in the literature. The unique features of nanosuspensions have enabled their use in various dosage forms, including specialized delivery systems such as mucoadhesive hydrogels. Rapid strides have been made in the delivery of nanosuspensions by parenteral, peroral, ocular and pulmonary routes. Currently, efforts are being directed to extending their applications in site-specific drug delivery.

Nanosizing: a formulation approach for poorly-water-soluble compounds

Poorly-water-soluble compounds are difficult to develop as drug products using conventional formulation techniques and are frequently abandoned early in discovery. The use of media milling technology to formulate poorly-water-soluble drugs as nanocrystalline particles offers the opportunity to address many of the deficiencies associated with this class of molecules. NanoCrystal Technology is an attrition process wherein large micron size drug crystals are media milled in a water-based stabilizer solution. The process generates physically stable dispersions consisting of nanometer-sized drug crystals. Nanocrystalline particles are a suitable delivery system for all commonly used routes of administration, i.e. oral, injectable (IV, SC, and IM) and topical applications. In addition, aqueous dispersions of nanoparticles can be post-processed into tablets, capsules, fast-melts and lyophilized for sterile product applications. The technology has been successfully incorporated into all phases of the drug development cycle from identification of new chemical entities to refurbishing marketed products for improving their performance and value.

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.

Polylactide-poly(ethylene glycol) micellar-like particles as potential drug carriers: production, colloidal properties and biological performance

The micellar-like particle systems produced from poly-D,L-lactide-poly(ethylene glycol) (PLA-PEG) copolymers have been assessed using a range of physicochemical characterisation methods, followed by in vivo studies of their biodistribution after intravenous administration to the rat. The size of the PEG chain was kept constant at 5 or 2 kDa, while the PLA size increased within a series from 2 to 25 kDa. The results obtained reveal, that in an aqueous medium the copolymers assembled into micellar-like structures, with the PLA segments forming the core and the PEG segments the surrounding corona. The size of the PLA segments dominated the process of assembly of the molecules and the characteristics of the resultant micellar-like particles. The PLA-PEG micellar particles were found to be less dynamic than those obtained from conventional surfactants. Particles formed from the lower molecular weight PLA polymers allowed a level of chain mobility while the cores of the micellar particles formed from higher molecular weight PLA appeared to be solid-like in nature. The size of the micellar particles was dependent on the copolymer molecular weight and the z-average diameter increased from 25 to 76 nm as the molecular weight of the PLA moiety increased. This provides an ability to control the particle size by adjusting the molecular weight of the PLA moiety. Following intravenous administration to the rat model, micellar-like particles smaller than approximately 70 nm accumulated in the liver, despite the fact that the PEG corona provided an effective steric stabilization effect. Micellar-like particles with a diameter of more than approximately 70 nm exhibited prolonged systemic circulation and reduced liver uptake, although the steric stabilisation of these particles was shown to be less effective. These findings agree with recent observations from other research groups; that indicate a possibility that very small particulates can pass through the sinusoidal fenestrations in the liver and gain access to the parenchymal cells of the liver.

Effect of nanoparticles on digitoxin uptake and pharmacologic activity in rat glomerular mesangial cell cultures

Our experiments analyzed the uptake of free and nanoparticles (NP)-associated digitoxin (DGT) by rat glomerular mesangial cells. NP were prepared by the nanoprecipitation method using the biodegradable polyester, polycaprolactone (PCL). Prior to in vitro experiments, the systems were characterized by means of spectrofluorimetry, dynamic light scattering, and size exclusion chromatography (SEC). The loading efficiency was 80.30 +/- 1.03% of the initial DGT amount in the preparation, and the average particle size was 176 +/- 8 and 161 +/- 6 nm for DGT-NP and "empty" NP, respectively. SEC studies revealed noncovalent interactions among the different chemical compounds in the formulation. In vitro experiments were conducted at 37 degrees C and pH 7.5 by incubating "empty" NP, free DGT or DGT-NP (10 microg PCL/mL; 100 ng DGT/mL) with glomerular mesangial cells for 30 and 60 min. Uptake of DGT by the cells was favored by its incorporation into PCL-NP and showed time dependency. After 30 min of incubation, no significant differences of drug uptake were seen between free DGT (13.1 +/- 2.8%) or DGT-NP (17.4 +/- 4.9%); however, the uptake of DGT, when it was associated to the polymeric carrier, increased by approximately 2-fold (37.8 +/- 5.7%) at 60 min, whereas no significant changes were observed for free drug (20.0 +/- 6.8%). The pharmacologic activity of the drug was evaluated by measuring the planar cell surface area (PCSA). "Empty" NP, free drug, or DGT-NP did not produce significant variations on the PCSA as compared with control cells after a 30-min incubation. Nonetheless, DGT-NP reduced the PCSA to 82.51 +/- 8.42% of control values when the incubation lasted 60 min. The ability of cells to exclude the trypan blue dye and the leakage of lactate dehydrogenase into the medium revealed no signs of increased toxicity from incorporation of DGT into PCL-NP. Therefore, PCL-NP improved drug uptake by the cells without altering the pharmacologic activity and toxicity of the drug. Thus, they can be a useful approach to target drugs to the kidneys or the heart.

In vitro displacement by rat serum of adsorbed radiolabeled poloxamer and poloxamine copolymers from model and biodegradable nanospheres

Poloxamer 407 and poloxamine 908 have been used by many research groups to modify the surface of both model latex and biodegradable nanospheres, thereby producing nanospheres that have shown reduced protein adsorption in vitro and extended circulation times in vivo. A potential limitation of such systems is the desorption of the copolymer coating layer. We describe a two-stage process to radiolabel poloxamer 407 and poloxamine 908 that has facilitated an investigation into this potential desorption, in vitro. The first stage of the labeling procedure involved the substitution of the terminal hydroxyl groups in each poly(ethylene oxide) (PEO) chain of poloxamer 407 and poloxamine 908 with an amino group. The aminated copolymers were then radiolabeled with 125Iodine Bolton-Hunter reagent. The efficiency of labeling was calculated to be approximately 20% for the tetramine poloxamine 908 and approximately 33% for the diamine poloxamer 407. Remaining free amino groups were then either acetylated, using acetic anhydride, or left in the free amino form. Covalent linkage of the radiolabel to the copolymer was confirmed by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The stability of the link between radiolabel and copolymer to hydrolysis was also confirmed; <4% loss of radiolabel occurred from poloxamine 908 after incubation in phosphate-buffered saline (PBS) at 37 degrees C for 8 days. The radiolabeled copolymers (with the free amino groups acetylated) were then used in experiments that have given the first direct evidence that adsorbed copolymers can be displaced by serum proteins in significant amounts from the surface of model and biodegradable nanospheres. The displacement was highly dependent on copolymer-nanosphere compatibility, with up to 78% of 125I tetramine poloxamine 908 being displaced from poly(lactide-co-glycolide) (PLGA) nanospheres in 24 h, compared with 20% displacement of 125I tetramine poloxamine 908 in 24 h from polystyrene nanospheres. These results have direct implication for the future design of drug delivery systems based on coated nanospheres.