Drug Release Kinetics and Transport Mechanisms from Semi-interpenetrating Networks of Gelatin and Poly(ethylene glycol) diacrylate

Purpose  To elucidate the key parameters affecting solute transport from semi-interpenetrating networks (sIPNs) comprised of poly(ethylene glycol) diacrylate (PEGdA) and gelatin that are partially crosslinked, water-swellable and biodegradable. Effects of material compositions, solute size, solubility, and loading density have been investigated. Materials and Methods  sIPNs of following gelatin/PEGdA weight-to-weight ratios were prepared: 10:15, 10:20, 10:30, 15:15, 20:15. Five model solutes of different physicochemical properties were selected, i.e. silver sulfadiazine (AgSD), bupivacaine hydrochloride (Bup), sulfadiazine sodium (NaSD), keratinocyte growth factor (KGF), and bovine serum albumin conjugated with fluorescein isothiocyanate (BSA-FITC). Release studies were performed and the results were analyzed using three hydrogel based common theories (free volume, hydrodynamic and obstruction). Results  The release kinetics of model solutes was influenced by each factor under investigation. Specifically, the initial release rates and intra-gel diffusivity decreased with increasing PEGdA content or increasing solute molecular weight. However, the initial release rate and intra-gel diffusivity increased with increasing gelatin content or increasing solute water solubility, which contradicted with the classical hydrogel based solute transport theories, i.e. increasing polymer volume leads to decreased solute diffusivity within the gel. Conclusion  This analysis provides structure-functional information of the sIPN as a potential therapeutic delivery matrix.     

Release characteristics of a model plasmid DNA encapsulated in biodegradable poly(ethylene glycol fumarate)/acrylamide hydrogel microspheres

Biodegradable hydrogel microspheres were synthesized by free radical suspension copolymerization of poly(ethylene glycol fumarate) macromer with bisacrylamide (PEGF/PAM). The acidic initiator ammonium persulphate in combination with the basic accelerator, N,N,N′,N′-tetramethyethylenediamine, were used to form the PEGF/PAM hydrogel at a neutral pH. The equilibrium water content of the microspheres was greater than 90% w/w. A model double stranded plasmid DNA (dsDNA) coding for the enhanced green fluorescence protein (pEGFP) gene was encapsulated in the hydrogel and the effect of loading and water content before swelling on release kinetics was investigated. Fluorescent confocal microscopy demonstrated that the encapsulated dsDNA was in the biologically active double stranded configuration. The highest loading of 0.81?mg?ml^?1 resulted in the best encapsulation efficiency of 95%. For that loading, 6% of the dsDNA was released in 25 days at a rate of 16?ng?ml^?1. The highest water content of 70% resulted in the highest burst release of 27% and 14% of the dsDNA was released in 25 days at a rate of 30?ng?ml^?1. For elucidating the release mechanism, the network mesh size was compared with the radius of gyration (R_g) of the dsDNA plasmid. The mesh size was 7?nm, which was less than R_g of the dsDNA (31?nm) but greater than the chain diameter of 1.1?nm. Since the mesh size was less than R_g, the release mechanism was by reptation of the segments of dsDNA within the tube formed by the network chains between crosslinks. These results indicate that the hydrogel mesh size and the size of the plasmid control the release mechanism.     

Release characteristics of a model plasmid DNA encapsulated in biodegradable poly(ethylene glycol fumarate)/acrylamide hydrogel microspheres

Biodegradable hydrogel microspheres were synthesized by free radical suspension copolymerization of poly(ethylene glycol fumarate) macromer with bisacrylamide (PEGF/PAM). The acidic initiator ammonium persulphate in combination with the basic accelerator, N,N,N',N'-tetramethyethylenediamine, were used to form the PEGF/PAM hydrogel at a neutral pH. The equilibrium water content of the microspheres was greater than 90% w/w. A model double stranded plasmid DNA (dsDNA) coding for the enhanced green fluorescence protein (pEGFP) gene was encapsulated in the hydrogel and the effect of loading and water content before swelling on release kinetics was investigated. Fluorescent confocal microscopy demonstrated that the encapsulated dsDNA was in the biologically active double stranded configuration. The highest loading of 0.81 mg ml(-1) resulted in the best encapsulation efficiency of 95%. For that loading, 6% of the dsDNA was released in 25 days at a rate of 16 ng ml(-1). The highest water content of 70% resulted in the highest burst release of 27% and 14% of the dsDNA was released in 25 days at a rate of 30 ng ml(-1). For elucidating the release mechanism, the network mesh size was compared with the radius of gyration (Rg) of the dsDNA plasmid. The mesh size was 7 nm, which was less than Rg of the dsDNA (31 nm) but greater than the chain diameter of 1.1 nm. Since the mesh size was less than Rg, the release mechanism was by reptation of the segments of dsDNA within the tube formed by the network chains between crosslinks. These results indicate that the hydrogel mesh size and the size of the plasmid control the release mechanism.     

Antitumor properties of irinotecan-containing nanoparticles prepared using poly(DL-lactic acid) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)

Irinotecan-containing nanoparticles (NP) were prepared by coprecipitation with addition of water to acetone solution of poly(DL-lactic acid), poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and irinotecan, and subsequent evaporation of organic solvent. NP were purified by gel filtration and used for experiments after condensation by evaporation. The obtained NP showed the drug content of 4.5% (w/w) and the mean particle diameter of 118 nm with the particle diameter distribution between 80-210 nm. When the antitumor effect was examined at a repeated dose of 20 mg irinotecan eq/kg for 3 d (3 x 20 mg/kg) using mice bearing Sarcoma 180 subcutaneously, only NP suppressed tumor growth significantly. After i.v. injection in rats, NP maintained irinotecan plasma concentration longer than CPT-11 aqueous solution. The present nanoparticle formation is suggested as a possibly useful dosage form of irinotecan against solid tumor.     

Study of phase behavior of poly(ethylene glycol)-polysorbate 80 and poly(ethylene glycol)-polysorbate 80-water mixtures

Mixtures of poly(ethylene glycols) (PEGs) with polysorbate 80 are often used to dissolve poorly water-soluble drugs in dosage forms, where polysorbate 80 helps either in enhancing dispersion or in inhibiting precipitation of drugs once the solution is mixed with water. Binary phase diagrams of polysorbate 80 with several low molecular weight PEGs and a ternary phase diagram of polysorbate 80 with PEG 400 and water are presented. Two phases were observed in the binary mixtures when the concentration of PEG 200, PEG 300, PEG 400, or PEG 600 was >55%(w/w). The miscibility of the binary mixtures increases with an increase in temperature; the upper consolute temperatures of PEG 200-polysorbate 80, PEG 300-polysorbate 80, PEG 400-polysorbate 80, and PEG 600-polysorbate 80 mixtures were 100, 85, 75, and 40 degrees C, respectively. The upper consolute temperature of PEG 1000-polysorbate 80 could not be determined because the melting temperature of the mixtures is approximately 40 degrees C and the consolute temperature appeared to be less than this temperature. The decrease in upper consolute temperature with an increase in PEG molecular weight indicated a greater miscibility of the two components. In the ternary system, phase separation of polysorbate 80 was observed when the concentration of PEG 400 was >50-60 % (w/w), possibly because of the high exclusion volume of PEG 400.     

Mono-N-terminal poly(ethylene glycol)-protein conjugates

A site-directed method of joining proteins to poly(ethylene glycol) is presented which allows for the preparation of essentially homogeneous PEG-protein derivatives with a single PEG chain conjugated to the amine terminus of the protein. This selectivity is achieved by conducting the reductive alkylation of proteins with PEG-aldehydes at lower pH. Working examples demonstrating the application of this method to improve the delivery characteristics and therapeutic value of several proteins are provided.     

Modeling of Caffeine Release from Crosslinked Water-Swellable Gelatin and Gelatin-Maltodextrin Hydrogels

Research from this group has recently led to the development of a genipin-crosslinked gelatin gel that may be used as a controlled release matrix for bioactive compounds. This study presents a model that simulates the release of entrapped caffeine from the hydrogel and the ingress of water into these gels. Fick's second law of diffusion is used to describe the water penetration and bioactive release in the system. To validate the model, caffeine release experiments from the gel were carried out. The predicted bioactive release profiles are in very good agreement with experimental data at different gel compositions. The model may also be used for a wide range of bioactive molecules and hydrogels with different cylindrical dimensions.     

Temperature-sensitive poly(N-isopropylacrylamide)/poly(ethylene glycol) diacrylate hydrogel microspheres

Objective

To develop and characterize a new class of temperature-sensitive hydrogel microspheres composed of poly(N-isopropylacrylamide)/poly(ethylene glycol) diacrylate (PNIPAAm/PEG-DA).

Methods

The PNIPAAm/PEG-DA hydrogel microspheres were fabricated in two aqueous systems as a result of polymer/polymer immiscibility. Both PNIPAAm and PEG-DA were used as the precursors; the PEG-DA was also used as a cross-linker for the formation of the hydrogel microspheres. Bovine serum albumin was used as the model protein drug to examine the effects of the thermo-responsive properties of the hydrogel microspheres on the release of a protein at two different temperatures (22°C and 37°C).

Results

The hydrated PNIPAAm/PEG-DA hydrogel microspheres exhibited a swollen diameter of 50µm, with a narrow particle-size distribution. Scanning electron microscopy and environmental scanning electron microscopy observations revealed that, upon swelling, the resulting hydrogel microspheres had a regular spherical and rough surface morphology. The lower critical solution temperature (LCST) of the PNIPAAm/PEG-DA hydrogel microspheres was around 29.1°C, based on differential scanning calorimetric data. The release of BSA from the hydrogel microspheres at 37°C was slower than that at 22°C because of the thermo-responsive nature of PNIPAAm at temperatures above its LCST.

Conclusions

We believe that these kinds of PNIPAAm/PEG-DA hydrogel microspheres may have wide applications as promising drug delivery systems, because of their intelligent nature upon external temperature change.     

Spectroscopic studies on poly(ethylene glycol)-lysozyme interactions

In the present paper, different spectroscopic methods were applied to evaluate conformational changes of hen egg-white lysozyme (HEWL) in various solvents and in the presence of poly(ethylene glycol) (PEG). In citrate (0.007 M, pH=6), or in Tris (0.1 M, pH=7.4), no conformational change of the protein was measured across the range of concentrations tested. In addition, HEWL in ultra-pure water revealed no irreversible conformational change and no activity loss, at least at low concentrations (≤0.2 mg/ml). Whereas PEG can induce a reorganization of water molecules, no change of the secondary and tertiary protein conformations was observed in the presence of PEG. In addition, in the presence of PEG of various molecular weights, no change of enzymatic activity of the HEWL was observed across the range of concentrations tested.     

Biocompatibility and paclitaxel/cisplatin dual-loading of nanotubes prepared from poly(ethylene glycol)-polylactide-poly(ethylene glycol) triblock copolymers for combination cancer therapy

Nanotubes were prepared by self-assembly of the copolymer using co-solvent evaporation method. The biocompatibility of the nanotubes was assessed in comparison with spherical micelles and filomicelles prepared from poly(ethylene glycol)-poly(L-lactide-co-glycolide) (PEG-PLGA) and poly(ethylene glycol)-poly(L-lactide) (PEG-PLA), respectively. Several aspects of biocompatibility of the aggregates were considered, including agar diffusion and MTT assay, release of cytokines, hemolysis, protein adsorption, dynamic clotting in vitro, and Zebrafish embryonic compatibility in vivo. The nanotubes present good cell compatibility and blood compatibility in vitro, and almost no toxicity towards Zebrafish embryos development in vivo. Furthermore, dual-loading of hydrophilic cisplatin and hydrophobic paclitaxel was achieved in the nanotubes with high loading content and loading efficiency. The release of both drugs was slower from dual-loaded nanotubes than from single-loaded ones, but the total amount of released drugs in higher for dual-loaded nanotubes than from single-loaded ones. Cellular uptake and inhibition tests showed that the nanotubes were successfully taken up by tumor cells and effectively inhibited cell growth. It is thus concluded that PEG-PLA-PEG nanotubes with outstanding biocompatibility could be promising for co-delivery of hydrophilic and hydrophobic agents in combination cancer therapy.     

Bone Regeneration with Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) Using Absorbable Collagen Sponges (ACS): Influence of Processing on ACS Characteristics and Formulation

The effects of variability in three parameters (mass, cross-linking with CH₂O, and EtO sterilization) of three surgically implantable absorbable collagen sponges (ACS) were studied. Sponges soaked with recombinant human bone morphogenetic protein-2 (rhBMP-2) solution were analyzed for pH, conductivity, and rhBMP-2 precipitation. A method using trinitrobenzenesulfonic acid was developed to quantify the free amino groups of the collagen sponge. With up to 240 min exposure to CH₂O, the amount of free amino groups was reduced to 80%. In comparison, the denaturation temperature as determined by differential scanning calorimetry (DSC) after the sponges were soaked with phosphate-buffered saline, increased from 48 to 55°C, indicating stronger interactions due to cross-linking. Subsequent sterilization with EtO caused a marked decrease in the amount of free amino groups (approximately 33% of nonsterilized controls) independent of previous CH₂O treatment. However, the denaturation temperature was on average 5°C lower in sterilized sponges than in nonsterilized material. In contrast to CH₂O, exposure, the strong reaction with EtO appeared to weaken the collagen structure. Resistance of the sponge to collagenase correlated with the degree of collagen cross-linking but was slightly reduced by sterilization. In addition, the pH of ACS soaked with water was substantially increased by sterilization. Protein precipitation was a function of pH and salt concentration but there was no effect due to collagen alone. Results indicated that ACS weight has to be limited to avoid rhBMP-2 precipitation.     

Albumin release from biodegradable hydrogels composed of dextran and poly(ethylene glycol) macromer

Biodegradable hydrogels based on glycidyl methacrylate dextran (GMD) and dimethacrylate poly(ethylene glycol) (DMP) were proposed for colon-specific drug delivery. GMD was synthesized by coupling of glycidyl methacrylate with dextran in the presence of 4-(N,N-dimethyl-amino)pyridine (DMAP) using dimethylsulfoxide as a solvent. Methacrylate-terminated poly (ethylene glycol) (PEG) macromer was prepared by the reaction of PEG with methacryloyl chloride. GMD/DMP hydrogels were prepared by radical polymerization of phosphate buffer solution (0.1M, pH 7.4) of GMD and DMP, using ammonium peroxydisulfate (APS) and UV as initiating system. The synthetic GMD, DMP, and GMD/DMP hydrogels were characterized by fourier transform infrared (FT-IR) spectroscopy. The FITC-albumin loaded hydrogels were prepared by adding FITC-albumin solution before UV irradiation. Swelling capacity of GMD/DMP hydrogels was controlled not only by molecular weight of dextran, but also by incorporation ratio of DMP Degradation of the hydrogels has been studied in vitro with dextranase. FITC-albumin release from the GMD/DMP hydrogels was affected by molecular weight of dextran and the presence of dextranase in the release medium.     

Recombinant Human Bone Morphogenetic Protein-2 Binding and Incorporation in PLGA Microsphere Delivery Systems

The objective of this research was to determine the binding capacity and kinetics, and total incorporation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in microspheres made from hydrophilic and hydrophobic poly(lactide-co-glycolide) (PLGA). Polymers were characterized by molecular weight, polydispersity, and acid number. Microspheres were produced via a water-in-oil-in-water double emulsion system and characterized for bulk density, size, specific surface area, and porosity. Protein concentrations were determined by reversed phase HPLC. Protein was loaded by soaking microspheres in a buffered solution, pH 4.5, of rhBMP-2, decanting excess liquid, and vacuum drying the wetted particles. Total loading and binding were determined by comparing protein concentration remaining to non-microsphere containing samples. Polymer acid number was the dominant polymer feature affecting the binding. Higher acid values correlated with increased rhBMP-2 binding. The amount of non-bound incorporated rhBMP-2 linearly correlated with the concentration of protein used in binding. High rhBMP-2 concentrations inhibit binding to PLGA microspheres. Binding was also inhibited by increased lactide content in the PLGA polymer. The polymer characteristics controlling rhBMP-2 binding to PLGA microspheres are acid value foremost followed by molecular weight and lactide/glycolide ratio. The total amount of rhBMP-2 incorporated depends on the bound amount and on the amount of free protein present.     

聚乙二醇单甲醚接枝壳聚糖自组装纳米球的制备*

目的:合成聚乙二醇单甲醚接枝壳聚糖(monomethoxy poly(ethylene glycol)-grafted-chitosan,mPEG-g- CS),并制备自组装纳米球。方法:利用甲醛连接法将聚乙二醇单甲醚(monomethoxy poly(ethylene glycol),mPEG)接枝干壳聚糖(ehitosan,CS)分子,得到聚乙二醇(poly(ethylene glycol),PEG)改性的壳聚糖衍生物,并通过傅立叶红外光谱仪(Fourier transform infrared spectroscopy,FT-IR),核磁共振仪(proton nuclear magnetic resonance,~1H-NMR)对产物进行结构表征;采用超声透析法制备自组装纳米球,并通过透射电镜(transmission electron microscopy,TEM),动态激光粒度分析仪(dynamic laser light scattering,DLLS)表征了纳米球的形态和粒径;以芘为荧光探针,通过荧光检测分析测定了mPEG-g-CS的临界胶束浓度(critical micellar concentration,CMC)。结果:通过FT-IR,~1H- NMR确证了接枝产物的存在;mPEG-g-CS在水溶液中能够自组装形成球状纳米胶束,平均粒径为250 nm。结论:通过甲醛连接法制备mPEG-g-CS,具有制备方法简捷、反应周期短、易操作的优点。利用该产物制备的纳米球有望成为长循环纳米药物载体。     

Solubility of silybin in aqueous poly(ethylene glycol) solution

Silybin is a main component in silymarin, which is an antihepatotoxic polyphenolic substance isolated from the milk thistle plant, Silybum marianum. A major problem in the development of an oral solid dosage form of this drug is the extremely poor aqueous solubility. In present work, the solubility of silybin in aqueous poly(ethylene glycol) 6,000 (PEG 6,000) solution at the temperature range from 293.15 to 313.15K was measured by a solid liquid equilibrium method. The aim of this study is to investigate the possible effect of poly(ethylene glycol) concentration and temperature on the solubility of the drug, and to reveal the solubilization capacity of the polymer for the drug. Experimental results reveal that the solubility of silybin increases with the increase both in PEG's concentration and temperature. With the increase in PEG's concentration, the transfer enthalpy and entropy for silybin from water to aqueous PEG solution increases first in a positive region, and then decreases to a negative region. The transfer enthalpy is lower than the entropy term. A modified Universal Quasi Chemical (UNIQUAC) model was used to correlate solubility data.     

Preparation and characterization of novel poly(ethylene glycol) paclitaxel derivatives

Paclitaxel has been found to be very effective against several human cancers; one of the major problems with its use is its poor solubility, which makes necessary its solubilization with excipients that can determine allergic reactions often severe. The aim of this study is to develop highly water-soluble prodrugs of paclitaxel. For this purpose we prepared a series of new paclitaxel–poly(ethylene glycol) (PEG) conjugates that were characterized and evaluated for their in vitro stability and cytotoxicity. In particular, in order to modulate the release of paclitaxel from prodrugs, we prepared different compounds introducing PEG in the drug C2′ and/or C7 positions via ester or carbamate linkage. The conjugates were obtained in high purity and good yield. The carbamate prodrugs were highly stable in different media, while the compounds obtained linking PEG at C2′ position through an ester bond showed lower stability. Finally, the cytotoxic activity of the conjugates was evaluated on two cancer cell lines and the results showed that all the derivatives had a reduced cytotoxicity compared to that of paclitaxel.     

Pharmacokinetic and biodistribution properties of poly(ethylene glycol)-protein conjugates

Peptide and protein PEGylation is usually undertaken to improve the biopharmaceutical properties of these drugs and, to date, several examples of conjugates with long permanence in the body as well as with localization ability in disease sites have been reported. Although a number of studies on the in vivo behavior and fate of conjugates have been performed, forecasting their pharmacokinetics is a difficult task since the pharmacokinetic profile is determined by a number of parameters which include physiological and anatomical aspects of the recipient and physico-chemical properties of the derivative. The most relevant perturbations of the protein molecule following PEG conjugation are: size enlargement, protein surface and glycosylation function masking, charge modification, and epitope shielding. In particular, size enlargement slows down kidney ultrafiltration and promotes the accumulation into permeable tissues by the passive enhanced permeation and retention mechanism. Charge and glycosylation function masking is revealed predominantly in reduced phagocytosis by the RES and liver cells. Protein shielding reduces proteolysis and immune system recognition, which are important routes of elimination. The specific effect of PEGylation on protein physico-chemical and biological properties is strictly determined by protein and polymer properties as well as by the adopted PEGylation strategy. Relevant parameters to be considered in protein-polymer conjugates are: protein structure, molecular weight and composition, polymer molecular weight and shape, number of linked polymer chains and conjugation chemistry. The examples reported in this review show that general considerations could be useful in developing a target product, although significant deviations from the expected results can not be excluded.     

Clonazepam release from core-shell type nanoparticles of poly(epsilon-caprolactone)/poly(ethylene glycol)/poly(epsilon-caprolactone) triblock copolymers

The triblock copolymer based on poly(epsilon-caprolactone) (PCL) as hydrophobic part and poly(ethylene glycol) (PEG) as hydrophilic one was synthesized and characterized. Core-shell type nanoparticles of poly(epsilon-caprolactone)/poly(ethylene glycol)/poly(epsilon-caprolactone) (CEC) block copolymer were prepared by a dialysis technique. According to the amphiphilic characters, CEC block copolymer can self-associate at certain concentration and their critical association concentration (CAC) was determined by fluorescence probe technique. CAC value of the CEC-2 block copolymer was evaluated as 0.0030 g/l. CAC values of CEC block copolymer decreased with the increase of PCL chain length, i.e. the shorter the PCL chain length, the higher the CAC values. From the observation of transmission electron microscopy (TEM), the morphologies of CEC-2 core-shell type nanoparticles were spherical shapes. Particle size of CEC-2 nanoparticles was 32.3+/-17.3 nm as a monomodal and narrow distribution. Particle size, drug loading, and drug release rate of CEC-2 nanoparticles were changed by the initial solvents and the molecular weight of CEC. The degradation behavior of CEC-2 nanoparticles was observed by 1H NMR spectroscopy. It was suggested that clonazepam (CNZ) release kinetics were dominantly governed by diffusion mechanism.     

Clonazepam release from core-shell type nanoparticles of poly(-caprolactone)/poly(ethylene glycol)/poly(-caprolactone) triblock copolymers

The triblock copolymer based on poly(-caprolactone) (PCL) as hydrophobic part and poly(ethylene glycol) (PEG) as hydrophilic one was synthesized and characterized. Core-shell type nanoparticles of poly(-caprolactone)/poly(ethylene glycol)/poly(-caprolactone) (CEC) block copolymer were prepared by a dialysis technique. According to the amphiphilic characters, CEC block copolymer can self-associate at certain concentration and their critical association concentration (CAC) was determined by fluorescence probe technique. CAC value of the CEC-2 block copolymer was evaluated as 0.0030 g/l. CAC values of CEC block copolymer decreased with the increase of PCL chain length, i.e. the shorter the PCL chain length, the higher the CAC values. From the observation of transmission electron microscopy (TEM), the morphologies of CEC-2 core-shell type nanoparticles were spherical shapes. Particle size of CEC-2 nanoparticles was 32.3±17.3 nm as a monomodal and narrow distribution. Particle size, drug loading, and drug release rate of CEC-2 nanoparticles were changed by the initial solvents and the molecular weight of CEC. The degradation behavior of CEC-2 nanoparticles was observed by ¹H NMR spectroscopy. It was suggested that clonazepam (CNZ) release kinetics were dominantly governed by diffusion mechanism.     

All-trans-retinoic acid release from core-shell type nanoparticles of poly(epsilon-caprolactone)/poly(ethylene glycol) diblock copolymer

Poly(epsilon-caprolactone)/poly(ethylene glycol) (abbreviated as CE) diblock copolymers were synthesized to make core-shell type nanoparticles for all-trans-retinoic acid (atRA). Fluorescence spectroscopy showed that critical association concentration (CAC) value decreased at higher MW of CE diblock copolymer. Drug loading characteristics were studied under various experimental conditions. Drug contents and loading efficiency increased as the MW of poly(epsilon-caprolactone) (PCL) block of CE and initial drug feeding amount increased. Solvent used and preparation method also affected drug contents and loading efficiency. According to 1H NMR using CDCl3 and D2O, specific peaks of the PCL block and drug appearing in CDCl3, disappeared at D2O, suggesting hydrophobic core with hydrophilic shell formed in water. atRA release was faster at smaller MW of copolymer and lower drug contents. Nanoparticles prepared in DMF showed faster release rate compared with those prepared in THF or acetone. Cytotoxicity of atRA against U87MG, U251MG and U343MG cell lines were increased by nanoencapsulation while empty nanoparticles of CE diblock copolymer were not significantly affected.