Evaluation of Poly (Glycerol-Adipate) Nanoparticle Uptake in an In Vitro 3-D Brain Tumor Co-Culture Model

Despite the inherent problems associated with in vivo animal models of tumor growth and metastases, many of the current in vitro brain tumor models also do not accurately mimic tumor-host brain interactions. Therefore, there is a need to develop such co-culture models to study tumor biology and, importantly, the efficacy of drug delivery systems targeting the brain. So far, few investigations of this nature have been published. In this paper we describe the development of a new model system and its application to drug delivery assessment. For our new model, a co-culture of DAOY cell brain tumor aggregates and organo-typic brain slices was developed. Initially, the DAOY aggregates attached to cerebellum slices and invaded as a unit. Single cells in the periphery of the aggregate detached from the DAOY aggregates and gradually replaced normal brain cells. This invasive behavior of DAOY cells toward organotypic cerebellum slices shows a similar pattern to that seen in vivo. After validation of the co-culture model using transmission electron microscopy, nanoparticle (NP) uptake was then evaluated. Confocal micrographs illustrated that DAOY cells in this co-culture model took up most of the NPs, but few NPs were distributed into brain cells. This finding corresponded with results of NP uptake in DAOY and brain aggregates reported elsewhere.

Nanomedicines and nanotoxicology: some physiological principles

Nanosized materials have been investigated as potential medicines for several decades. Consequently, a great deal of work has been conducted on how to exploit constructs of this size range in a beneficial way. Similarly, a number of the consequences from the use of these materials have already been considered. Nanosized materials do behave differently to low-molecular-weight drugs, the biological properties of nanomaterials being mainly dependent on relevant physiology and anatomy, which are reviewed in this article. Biodistribution, movement of materials through tissues, phagocytosis, opsonization and endocytosis of nanosized materials are all likely to have an impact on potential toxicity. In turn these processes are most likely to depend on the nanoparticle surface. Evidence from the literature is considered which suggests that our understanding of these areas is incomplete, and that biodistribution to specific sites can occur for nanoparticles with particular characteristics. However, our current knowledge does indicate which areas are of concern and deserve further investigation to understand how individual nanoparticles behave and what toxicity may be expected from them.

Uptake and metabolism of novel biodegradable poly (glycerol-adipate) nanoparticles in DAOY monolayer

A useful route for the development of antitumour therapies is by creating improved methods for delivering therapeutic agents to tumour cells or subcellular compartments and increasing retention of drugs within target cells. In this study, we have characterized nanoparticle (NP) uptake and metabolism by DAOY cells, a human medulloblastoma cell line. NPs were formed from a novel polymer, poly (glycerol-adipate) (PGA), containing Rhodamine B Isothiocyanate (RBITC) as a fluorescent marker. It was observed that the cellular uptake of NPs depends on the incubation time and the concentration of NPs in the culture medium. The studies of retention and metabolism of NPs within cells indicated that 1) faster degradation of NPs within cells compared with that in cell culture medium in vitro; 2) a small fraction of NPs were recycled back to the outside of cell, whereas most NPs entered endosomes and lysosomes; and 3) recycled NPs were re-taken up in the following 2 h incubation time. These studies thus suggested that PGA NPs could be used for localising therapeutic agents into cells, and could provide prolonged drug effects because of their long sustained release in physiological conditions and their rapid release when taken up into cells.

Solubility of drugs in the presence of gelatin: effect of drug lipophilicity and degree of ionization

The solubility of seven drugs (nitrofurantoin, chlorothiazide, phenobarbital, prednisolone, griseofulvin, diazepam and piroxicam) in the absence and presence of gelatin was measured, at three different pH values (3.7, 5.0 and 7.0) at 37 degrees C. Drugs studied had different physicochemical properties (log P, pK(a), aqueous solubility) and their solubility in presence of 0.1 and 0.5% (w/v) hydrolyzed (and in some cases common) gelatin was estimated. Results show that the solubility of all drugs is significantly enhanced, especially in the presence of 0.5% gelatin. This gelatin-induced enhancement in drug solubility is higher in the pH in which acidic drugs are less ionized, especially for the less lipophilic acidic drugs (nitrofurantoin, chlorothiazide). In all cases, drug solubility in presence of gelatin is correlated with their aqueous solubility. Therefore, the established relationships between aqueous and gelatin solubility can be employed to derive an estimate of the drug solubility in presence of gelatin once its aqueous solubility is known. With the exception of piroxicam which is highly ionized and phenobarbital which is relatively soluble, there seems to be a tendency for larger gelatin-induced increases in solubility as drug lipophilicity increases or aqueous solubility decreases.

Characterization, stability and in-vivo distribution of asialofetuin glycopeptide incorporating DSPC/CHOL liposomes prepared by mild cholate incubation

In this study, a small triantennary asialoglycopeptide of fetuin (A-F2) was used as a ligand to direct liposomes to hepatocytes. A-F2 was cleaved from asialofetuin, purified, conjugated with fatty acids and incorporated into pre-formed sonicated DSPC/Chol (2:1) liposomes. A mild cholate incubation method for incorporating the A-F2 ligand on pre-formed vesicles was used. In preliminary in vivo experiments 111In3+ encapsulated in A-F2/palmityl liposomes was seen to accumulate in the liver of mice significantly faster than when encapsulated in non-ligand bearing liposomes of the same lipid composition (studied before), justifying further investigation of this system. The presence of the A-F2/fatty acid conjugate in a functional form on the vesicle surface was confirmed by their reversible agglutination in the presence of Ricinus communis agglutinin (RCA120). Effects of ligand incorporation on the vesicle size distribution, z-potential, membrane integrity and stability were monitored. The results demonstrate that highest ligand incorporation was achieved when liposomes and ligand were co-incubated in the presence of 1 mM sodium cholate. Incorporation increased with the length of the fatty acid used for A-F2 conjugation. Ligand-bearing liposomes were demonstrated to be smaller in diameter (about 30%) with a more positive z-potential in comparison to control vesicles while ligand incorporation did not influence the liposome membrane integrity. The size of the ligand-incorporating vesicles was maintained after 24 hours of incubation in isotonic buffer, proving that the vesicles do not aggregate. Although the preliminary biodistribution results may suggest that ligand bearing liposomes are accumulating in the liver, further cell culture, in vivo distribution and especially liver fractionation studies are required in order to clarify the intrahepatic localization of these liposomes and the ability to target liver hepatocytes in vivo.

Stability of SUV liposomes in the presence of cholate salts and pancreatic lipases: effect of lipid composition

The effect of bile salts (sodium cholate and sodium taurocholate), and pancreatic lipases on the structural integrity of SUV liposomes of different lipid compositions was studied. Liposomal membrane integrity was judged by bile salt or pancreatin-induced release of vesicle encapsulated 5,6-carboxyfluorescein, and vesicle size distribution before and after incubations. Bile salt concentration was 10 mM, while a saturated solution of pancreatin (mixed with equal volume of liposomes) was utilized. Results agree with earlier studies, demonstrating the instability of liposomes composed of lipids with low transition temperatures (PC and DMPC) in presence of cholates. Addition of cholesterol (1:1 lipid:chol molar ratio) does not substantially increase the encapsulated molecule retention. Nevertheless, liposomes composed of lipids with high transition temperatures (DPPC, DSPC and SM), retain significantly higher amounts of encapsulated material, under all conditions studied. Furthermore, the vesicles formed by mixing cholesterol with these lipids will possibly be sufficiently stable in the gastrointestinal tract for long periods of time. Sizing results reveal that in most cases release of encapsulated molecules is mainly caused by their leakage through holes formed on the lipid bilayer. However, in stearylamine containing DPPC and DSPC vesicles, the cholate-induced drastic decrease in vesicle size suggests total liposome disruption as the possible mechanism of encapsulated material immediate release.