Antitumoral Effect of Sunitinib-eluting Beads in the Rabbit VX2 Tumor Model.

Purpose To measure plasmatic sunitinib concentration (PSC) and intratumoral sunitinib concentration (ITSC) after transcatheter arterial chemoembolization (TACE) with two different sizes of sunitinib-eluting beads (SEBs) in rabbits with VX2 hepatic allografts and to investigate treatment effects on vascular endothelial growth factor receptor type 2 (VEGFR2) phosphorylation, tumor volume, and histopathologic changes. Materials and Methods The protocol was approved by the French Ethics Committee for Animal Experiments (Comité d'Ethique en Expérimentation Animale du Centre INRA de Jouy-en-Josas et AgroParisTech, or COMETHEA, approval no. 11/028). Two experiments were performed. In the first, seven animals received 0.05 mL of 100-300-µm SEBs (1.5 mg of sunitinib) in the hepatic artery, and six animals received saline injections. In the second, eight animals received 0.05 mL of 70-150-µm SEBs (1.5 mg of sunitinib), seven received 0.05 mL of 70-150-µm unloaded beads, and seven received oral sunitinib (6 mg every day). Tumor size was monitored with ultrasonography. PSC, ITSC, and phosphorylation of VEGFR2 were assessed on days 1 and 14. After the animals were sacrificed, histopathologic analysis was performed. The Kruskal-Wallis test, Mann-Whitney U test, and Fisher exact test were used to look for statistically significant differences between groups. Results Maximum PSC after TACE with 100-300-µm SEBs was 0.002 µg/mL on day 1. ITSC was 17.8 µg/g on day 1 and 0.16 µg/g on day 14. After TACE with 70-150-µm SEBs, ITSC was 40.4 µg/g on day 1 and 27.4 µg/g on day 14. Phosphorylation of VEGFR2 was inhibited until day 14 after TACE with both sizes of SEBs. The size of VX2 tumors treated with 70-150-µm SEB TACE increased less (-2%) than that of tumors treated with unloaded beads (+42%) and oral sunitinib (6 mg every day; +1853%; P = .044). Conclusion SEB TACE resulted in minimal PSC, high ITSC, and sustained VEGFR2 phosphorylation inhibition until day 14. (©) RSNA, 2016.

Drug-eluting beads loaded with antiangiogenic agents for chemoembolization: in vitro sunitinib loading and release and in vivo pharmacokinetics in an animal model.

PURPOSE: The combination of embolic beads with a multitargeted tyrosine kinase inhibitor that inhibits tumor vessel growth is suggested as an alternative and improvement to the current standard doxorubicin-eluting beads for use in transarterial chemoembolization. This study demonstrates the in vitro loading and release kinetics of sunitinib using commercially available embolization microspheres and evaluates the in vitro biologic efficacy on cell cultures and the resulting in vivo pharmacokinetics profiles in an animal model. MATERIALS AND METHODS: DC Bead microspheres, 70-150 µm and 100-300 µm (Biocompatibles Ltd., Farnham, United Kingdom), were loaded by immersion in sunitinib solution. Drug release was measured in saline in a USP-approved flow-through apparatus and quantified by spectrophotometry. Activity after release was confirmed in cell culture. For pharmacokinetics and in vivo toxicity evaluation, New Zealand white rabbits received sunitinib either by intraarterial injection of 100-300 µm sized beads or per os. Plasma and liver tissue drug concentrations were assessed by liquid chromatography-tandem mass spectroscopy. RESULTS: Sunitinib loading on beads was close to complete and homogeneous. A total release of 80% in saline was measured, with similar fast-release profiles for both sphere sizes. After embolization, drug plasma levels remained below the therapeutic threshold (< 50 ng/mL), but high concentrations at 6 hours (14.9 µg/g) and 24 hours (3.4 µg/g) were found in the liver tissue. CONCLUSIONS: DC Bead microspheres of two sizes were efficiently loaded with sunitinib and displayed a fast and almost complete release in saline. High liver drug concentrations and low systemic levels indicated the potential of sunitinib-eluting beads for use in embolization.

Comparative study of chemoembolization loadable beads: in vitro drug release and physical properties of DC bead and hepasphere loaded with doxorubicin and irinotecan.

PURPOSE: To characterize in vitro the loadability, physical properties, and release of irinotecan and doxorubicin from two commercially available embolization microspheres. MATERIALS AND METHODS: DC Bead (500-700 microm) and Hepasphere (400-600 microm) microspheres were loaded with either doxorubicin or irinotecan solutions. Drug amount was quantified with spectrophotometry, bead elasticity was measured under compression, and bead size and loading homogeneity were assessed with microscopy image analysis. Drug release was measured over 1-week periods in saline by using a pharmacopeia flow-through method. RESULTS: Almost complete drug loading was obtained for both microsphere types and drugs. Doxorubicin-loaded DC Beads maintained their spherical shape throughout the release. In contrast, Hepaspheres showed less homogeneous doxorubicin loading and, after release, some fractured microspheres. Incomplete doxorubicin release was observed in saline over 1 week (27% +/- 2 for DC beads and 18% +/- 7 for Hepaspheres; P = .013). About 75% of this amount was released within 2.2 hours for both beads. For irinotecan, complete release was obtained for both types of beads, in a sustained manner over 2-3 hours for DC Beads, and in a significantly faster manner as a 7-minute burst for Hepaspheres. CONCLUSIONS: The two drug-eluting microspheres could be efficiently loaded with both drugs. Incomplete doxorubicin release was attributed to strong drug-bead ionic interactions. Weaker interactions were observed with irinotecan, which led to faster drug release.

Local moderate magnetically induced hyperthermia using an implant formed in situ in a mouse tumor model.

PURPOSE: We investigate a new heat delivery technique for the local treatment of solid tumors. The technique involves injecting a formulation that solidifies to form an implant in situ. This implant entraps superparamagnetic iron oxide nanoparticles (SPIONs) embedded in silica microbeads for magnetically induced moderate hyperthermia. Particle entrapment prevents phagocytosis and distant migration of SPIONs. The implant can be repeatedly heated by magnetic induction. METHODS: We evaluated heating and treatment efficacies by means of thermometry and survival studies in nude mice carrying subcutaneous human colocarcinomas. At day 1, we injected the formulation into the tumor. At day 2, a single 20-min hyperthermia treatment was delivered by 141-kHz magnetic induction using field strengths of 9 to 12 mT under thermometry. RESULTS: SPIONs embedded in silica microbeads were effectively confined within the implant at the injection site. Heat-induced necro-apoptosis was assessed by histology on day 3. On average, 12 mT resulted in tumor temperature of 47.8 degrees C, and over 70% tumor necrosis that correlated to the heat dose (AUC = 282 degrees C.min). In contrast, a 9-mT field strength induced tumoral temperature of 40 degrees C (AUC = 131 degrees C.min) without morphologically identifiable necrosis. Survival after treatment with 10.5 or 12 mT fields was significantly improved compared to non-implanted and implanted controls. Median survival times were 27 and 37 days versus 12 and 21 days respectively. CONCLUSION: Five of eleven mice (45%) of the 12 mT group survived one year without any tumor recurrence, holding promise for tumor therapy using magnetically induced moderate hyperthermia through injectable implants.

Cardiovascular effects of selected water-miscible solvents for pharmaceutical injections and embolization materials: a comparative hemodynamic study using a sheep model.

Generally, organic water-miscible solvents are used intravascularly (both intravenously and intra-arterially) for preparing two types of formulations, namely, pharmaceutical injections of poorly soluble drugs and precipitating liquid embolic polymeric materials for the minimally invasive treatment of aneurysms, arteriovenous malformations, or tumors, by arterial route. Although several of such solvents have been used in both drug delivery and interventional radiology, their safety profile is a concern. In particular, there is a lack of comparative investigations of their cardiovascular effects when injected intra-arterially. We selected 13 non-aqueous water-miscible solvents based on their capacity to solubilize drugs or embolic polymeric materials, and on their described use, at least diluted with water, in pharmaceutical formulations. Their in vivo hemodynamic toxicity in male adult sheep after infra-renal aorta catheterization has been estimated with respect to the arterial and venous pressures, as well as the heart rate. Saline solution was used as a control. Three different volumes (0.1, 0.5, and 1.0 mL) were infused rapidly. An increase in arterial pressure and concomitant decrease in venous pressure, which we considered as signs of a cardiovascular toxicity, were observed to a differing extent for all organic solvents. Changes in heart rate were negligible. Based on the intensity of arterial pressure change after a 1-mL infusion, a classification of the toxicity of the solvents following intra-arterial infusion is proposed: Solvents devoid of significant cardiovascular toxicity: dimethyl isosorbide (DMI), Glycofurol 75, polyethylene glycol 200 (PEG 200), diglyme. Solvents with moderate cardiovascular toxicity: tetrahydrofurfuryl alcohol (THFA), ethanol, acetone, Solketal, glycerol formal, dimethyl sulfoxide (DMSO). Solvents with marked cardiovascular toxicity: propylene glycol, ethyl lactate, N-methyl-2-pyrrolidone (NMP). Emphasis is put on the relative character of the proposed ranking and on the lack for certain solvents, at least in the open literature, of data pertaining at other forms of toxic effects (e.g., undesirable pharmacological action, carcinogenicity, teratogenicity, mutagenicity, and irritating and sensitizing properties), all factors that have to be considered when selecting a proper solvent.

Intrinsically radiopaque iodine-containing polyvinyl alcohol as a liquid embolic agent: evaluation in experimental wide-necked aneurysms.

OBJECT: To evaluate iodine-containing polyvinyl alcohol (I-PVA) as a precipitating liquid embolic agent, implant characteristics--including radiopacity, setting behavior, and biocompatibility--were studied in an aneurysm model in swine. METHODS: Twelve broad-based carotid artery (CA) sidewall aneurysms were surgically constructed in six pigs. Iodine-containing polyvinyl alcohol dissolved in dimethyl sulfoxide (DMSO) was injected during temporary balloon occlusion bridging the aneurysm neck. Control angiography as well as multidetector row computerized tomography (CT) angiography was performed after 4 weeks. Harvested aneurysms were investigated histopathologically and by 3-tesla high-field magnetic resonance (MR) imaging. The mean degree of aneurysm occlusion achieved was 96%. In two aneurysms a minimal protrusion of I-PVA into the CA lumen was observed. During one embolization, leakage of the liquid embolic agent due to DMSO-induced damage of the microcatheter resulted in CA occlusion. Aneurysms embolized with I-PVA could be discriminated clearly from the parent artery on CT angiograms because there was no beam-hardening artifact. High-field MR imaging allowed a detailed depiction of the liquid embolic distribution within the aneurysm. Histologically, a mild to moderate inflammatory response was found in successfully embolized aneurysms, and the polymer mass was frequently covered by a membrane of fibroblasts and endothelial cells. CONCLUSIONS: Iodine-containing polyvinyl alcohol is a ready-to-use liquid embolic agent clearly visible under fluoroscopy; additives are not required. The setting behavior allows for controlled delivery in aneurysm cavities. Histological studies performed 4 weeks after embolization revealed no sign of toxic tissue response to the liquid embolic agent. Overall, I-PVA exhibits interesting implant characteristics in that radiopaque admixtures are not necessary, thus allowing for artifact-free evaluation of treated aneurysms by using CT and MR angiography.

Preparation of surfactant-free nanoparticles of methacrylic acid copolymers used for film coating.

The aim of the present study was to prepare surfactant-free pseudolatexes of various methacrylic acid copolymers. These aqueous colloidal dispersions of polymeric materials for oral administration are intended for film coating of solid dosage forms or for direct manufacturing of nanoparticles. Nanoparticulate dispersions were produced by an emulsification-diffusion method involving the use of partially water-miscible solvents and the mutual saturation of the aqueous and organic phases prior to the emulsification in order to reduce the initial thermodynamic instability of the emulsion. Because of the self-emulsifying properties of the methacrylic acid copolymers, it was possible to prepare aqueous dispersions of colloidal size containing up to 30% wt/vol of Eudragit RL, RS, and E using 2-butanone or methyl acetate as partially water-miscible solvents, but without any surfactant. However, in the case of the cationic Eudragit E, protonation of the tertiary amine groups by acidification of the aqueous phase was necessary to improve the emulsion stability in the absence of surfactant and subsequently to prevent droplet coalescence during evaporation. In addition, a pseudolatex of Eudragit E was used to validate the coating properties of the formulation for solid dosage forms. Film-coated tablets of quinidine sulfate showed a transparent glossy continuous film that was firmly attached to the tablet. The dissolution profile of quinidine sulfate from the tablets coated with the Eudragit E pseudolatex was comparable to that of tablets coated with an acetonic solution of Eudragit E. Furthermore, both types of coating ensured similar taste masking. The emulsification-evaporation method used was shown to be appropriate for the preparation of surfactant-free colloidal dispersions of the 3 types of preformed methacrylic acid copolymers; the dispersions can subsequently be used for film coating of solid dosage forms.

Polymeric nanoparticles for oral delivery of drugs and vaccines: a critical evaluation of in vivo studies.

Oral drug delivery is the preferred route of administration of drugs. Because of their versatility, nanoparticles often have been investigated for the delivery of a wide number of drugs by this route. This article first examines the physicochemical, pharmaceutical and technological aspects that make nanoparticles a potential oral delivery system for drugs and active biomolecules. Next, upon consideration of in vivo studies, the pharmacokinetic, pharmacological and therapeutic aspects of orally administered nanoparticles are described. Special emphasis is placed on improvement of oral bioavailability of drugs incorporated into nanoparticles. Two main mechanisms involved in enhancing drug absorption are discussed: the protection of drug by nanoparticles against harsh conditions in the gut and the prolongation of gastrointestinal transit of nanoparticles by using bioadhesive polymers. Furthermore, nanoparticle uptake by intestinal cells and oral vaccination by these colloidal carriers are also covered. In this context, the immune responses elicited as well as the protection against pathogens induced by antigen-loaded nanoparticles administered by the oral route are presented. Finally, the main limitations and perspectives of these colloidal carriers as oral drug delivery systems are discussed.

Strategic approaches for overcoming peptide and protein instability within biodegradable nano- and microparticles.

This paper reviews the major factors that are closely involved in peptide and protein degradation during the preparation of biodegradable nano- and microparticles. The various means usually employed for overcoming these obstacles are described, in order to bring to the fore the strategies for protein stabilization. Both processing and formulation parameters can be modified and are distinctly considered from a strategic point of view. We describe how partial or full protein stability retention within the carriers and during drug release might be achieved by individual or combined optimized strategies. Additionally, problems commonly encountered during protein quantification, stability determination and release are briefly reviewed. Artefacts that might occur during sampling and analytical procedures and which might hinder critical interpretation of results are discussed.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for quantitation and molecular stability assessment of insulin entrapped within PLGA nanoparticles.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was evaluated for both qualitative and quantitative analysis of insulin entrapped within poly(D,L-lactic-co-glycolic acid) nanoparticles. Quantitation was performed by adding an internal standard (arg-insulin) to defined and unknown sample solutions, in order to reduce point-to-point and sample-to-sample variability. The ratio of the peak height of insulin to the peak height of arg-insulin was plotted against the insulin concentration. In this way, an excellent linear relationship was found (R2 > 0.99). This method of quantitation was compared with classical UV spectroscopy and reverse-phase high-performance liquid chromatography measurements. All methods provided close final drug loading values for the insulin-loaded nanoparticle batches tested. Additionally, with respect to molecular stability, covalent insulin dimers were found only at trace levels in those nanoparticles. Compared with other methods, MALDI-TOF MS is a valuable tool for the characterization of proteins from nanoparticles, because no extensive extraction and complex sampling procedures are required.

Development of a nanoprecipitation method intended for the entrapment of hydrophilic drugs into nanoparticles.

This study investigates formulation and process modifications to improve the versatility of the nanoprecipitation technique, particularly with respect to the encapsulation of hydrophilic drugs (e.g. proteins). More specifically, the principal objective was to explore the influence of such modifications on nanoparticle size. Selected parameters of the nanoprecipitation method, such as the solvent and the non-solvent nature, the solvent/non-solvent volume ratio and the polymer concentration, were varied so as to obtain polymeric nano-carriers. The feasibility of such a modified method was assessed and resulting unloaded nanoparticles were characterized with respect to their size and shape. It was shown that the mean particle size was closely dependent on the type of non-solvent selected. When alcohols were used, the final mean size increased in the sequence: methanol

Adaptation and optimization of the emulsification-diffusion technique to prepare lipidic nanospheres.

In this study, the emulsification-diffusion method traditionally used to prepare polymeric nanoparticles was adapted to obtain lipidic nanospheres (LN) using four model lipids. The method consists of dissolving the lipid in a partially water-miscible solvent (previously saturated with water) at room temperature or at controlled temperature depending on lipid solubility. This organic phase is emulsified in an aqueous solution of a stabilizing agent (saturated with solvent) by conventional stirring at the same temperature used to dissolve the lipid. This oil-in-water emulsion is then diluted with an excess of water at controlled temperature in order to provoke the diffusion from the internal phase into the external phase thereby causing lipid aggregation in the form of LN. This new approach for the preparation of LN has clear advantages over the existing methods, namely: (i) it is efficient and versatile; (ii) easy implementation and scaling up (with no need of high energy sources); (iii) high reproducibility and narrow size distribution; (iv) less physical stress (i.e., long exposure to high temperatures and to mechanical dispersion); (v) it is not necessary to dissolve the drug in the melted lipid. The selection of the water-miscible solvent and the stabilizers are critical parameters to obtain lipidic particles in the nanometric range. In general, solvents with high water miscibility and stabilizers able to form stable emulsions are preferred. The results demonstrated that it was possible to reduce the particle size by increasing the process temperature, the stirring rate, the amount of stabilizer, and by lowering the amount of lipid. Control of the preparative variables allowed to obtain LN with diameters under 100 nm. It was found that the influence of preparative parameters was associated with a mechanism based on a physicochemical instability. In this sense, it is suggested that the rapid solvent diffusion produces regions of local supersaturation near the interface, and LN are formed due to the ensuing interfacial phase transformations and lipid aggregation that occur in these interfacial domains. In terms of stability, only poly(vinyl alcohol) (PVAL) was able to preserve the physical stability of the dispersion for long periods after preparation. This effect was attributed to the ability of PVAL chains to form a strongly attached layer on the nanoparticle surface with an excellent repulsion effect.

Comparative scale-up of three methods for producing ibuprofen-loaded nanoparticles.

The lack of information related to the scaling-up of technologies used for preparing polymeric nanoparticles (NP) might hinder the introduction of these colloidal carriers into the pharmaceutical market. In the present study, the scale-up of ibuprofen-loaded NP produced by three manufacturing processes--salting-out, emulsification-diffusion and nanoprecipitation--was assessed at pilot-scale by increasing 20-fold the laboratory-batch volume from 60 ml to 1.5l. Eudragit L100-55 and poly(vinyl alcohol) (PVAL) were used as polymer and emulsifying agent, respectively. The influence of the hydrodynamic conditions on the NP characteristics such as mean size, drug content, residual PVAL and morphology was also investigated. At pilot-scale, stirring rates of 790-2000 rpm lead to NP mean sizes ranging from 557 to 174 nm for salting-out and from 562 to 230 nm for emulsification-diffusion. An increase in the stirring rate enhances the droplet break-up phenomenon which leads to the formation of finer emulsion droplets and thus smaller NP. Moreover, the influence of the stirring rate on the mean size of NP can be predicted using a model based on a simple power law. The continuous method used for nanoprecipitation scale-up allows production of NP in a reproducible way over a relatively short time. Finally, for the three methods, NP characteristics were reproduced well at both scales. However, the scale-up process induced a slight reduction in the size and drug loading of NP.

Nanoprecipitation versus emulsion-based techniques for the encapsulation of proteins into biodegradable nanoparticles and process-related stability issues.

The goal of this study was to investigate the entrapment of 3 different model proteins (tetanus toxoid, lysozyme, and insulin) into poly(D,L-lactic acid) and poly(D,L-lactic-co-glycolic acid) nanoparticles and to address process-related stability issues. For that purpose, a modified nanoprecipitation method as well as 2 emulsion-based encapsulation techniques (ie, a solid-in oil-in water (s/o/w) and a double emulsion (w(1)/o/w(2)) method) were used. The main modification of nanoprecipitation involved the use of a wide range of miscible organic solvents such as dimethylsulfoxide and ethanol instead of the common acetone and water. The results obtained showed that tetanus toxoid and lysozyme were efficiently incorporated by the double emulsion procedure when ethyl acetate was used as solvent (>80% entrapment efficiency), whereas it was necessary to use methylene chloride to achieve high insulin entrapment efficiencies. The use of the s/o/w method or the formation of a more hydrophobic protein-surfactant ion pair did not improve protein loading. The nanoprecipitation method led to a homogenous population of small nanoparticles (with size ranging from approximately 130 to 560 nm) and in some cases also improved experimental drug loadings, especially for lysozyme (entrapment efficiency > 90%). With respect to drug content determination, a simple and quick matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method provided results very close to those obtained by reverse phase-high-performance liquid chromatography. With respect to protein stability, the duration and intensity of sonication were not a concern for tetanus toxoid, which retained more than 95% of its antigenicity after treatment for 1 minute. Only a high methylene chloride:water ratio was shown to slightly decrease toxoid antigenicity. Finally, no more than 3.3% of A21 desamido insulin and only traces of covalent insulin dimer were detected in nanoparticles. In conclusion, both the double emulsion and nanoprecipitation methods allowed efficient protein encapsulation. MALDI-TOF MS allowed accurate drug content determination. The manufacturing processes evaluated did not damage the primary structure of insulin.

Controlled drug release from melt-extrudates through processing parameters: a chemometric approach.

The objective of this study was to tailor a drug release profile through the adjustment of some key processing parameters involved in melt-extrusion: die temperature, shear rate, die length and drug particle size. Two experimental designs were selected, namely a 2-level full factorial design to examine the effects and significance of the processing factors, and a central composite design of the surface responses to find the best set of factor levels to obtain given specifications of drug release. Extrudates of poly(ethylene-co-vinyl acetate) and phenylpropanolamine hydrochloride were prepared using a ram extruder. Drug release profiles from the matrix systems were fitted using a power law, for which a new mathematical expression of a burst release was provided. The burst release and exponent were selected as the responses. The processing factors had a drastic influence on the drug release. Within the domain that was investigated, the burst release and the exponent varied from 6 to 54% and 0.1 to 0.4, respectively, resulting in a time requires for 50% drug release extending from hours to weeks. These results demonstrated the possibilities of modulating the release profile by means of the processing parameters rather than through the classical approach of altering the formulation.

Intra-articular bioactivity of a p38 MAPK inhibitor and development of an extended-release system.

In the treatment of arthritic diseases, oral or systemic administration of anti-inflammatory substances, such as p38 MAPK inhibitors, is hampered by numerous side effects. To overcome them, formulations of rapid and extended drug delivery systems were studied in intra-articular administration. For the first time, VX-745, a highly selective p38 MAPK inhibitor, demonstrated in vivo bioactivity, similar to dexamethasone activity, following intra-articular administration in an antigen-induced arthritic (AIA) mouse model. The in vitro bioactivity of VX-745 was also shown on synoviocytes, reducing the IL-6 concentration. Process and formulation parameters (i.e., polymer concentration, aqueous/organic phase ratio, emulsification speed and process, and evaporation pressure) and particle characterisation (i.e., drug loading, size of particle, and surface aspect) were extensively examined to produce optimised formulations. Indeed, a burst release provides a rapid saturation of intracellular p38 MAPK to relieve patients from pain and inflammation. Then, drug diffusion would be sufficient to maintain an effective dose over 2-3 months. This study confirms the effectiveness of encapsulated p38 MAPK inhibitors in extended drug delivery systems and seems to be a promising strategy for intra-articular treatment.

Benefits of die-wall instrumentation for research and development in tabletting.

Instrumented presses used in tabletting research and development are normally equipped to measure punch force and displacement. Die-wall monitoring is rare, probably because instrumentation and calibration are quite difficult. The authors critically examine the tenets of radial pressure measurement in compression physics. The theoretical background concerning axial to radial stress transmission during the different phases of the compression cycle is presented. The literature reporting on the use of radial stress measurement to assess the self-lubricating properties of materials or the effect of lubricants is reviewed. Examples of interpretation of radial pressure cycles to define the basic material behaviour are given. The influence of particle size and shape as well as that of process and formulation variables on die-wall response are also discussed. Substantial inconsistencies can be seen in the literature with respect to the interpretation of experimental data, often because of the poor reliability of results and mostly because powders are essentially not solid, isotropic bodies. There is also a distinct lack of complementary tabletting parameters that would help understanding their comparative benefits. For this reason, original data on 13 model compounds are presented together with a classification of the materials encountered in pharmaceutical tabletting, based on selected parameters. In conclusion, none of the determined parameters, including those derived from radial pressure measurement, is able, alone, to predict the material behaviour under compression. Although die-wall instrumentation contributes little to the development of improved tablet formulations, it is valuable for characterising the mechanical properties of the materials. This is particularly advantageous given that the mechanical properties account for variations in tabletting performance to a much greater extent than the magnitude of the interparticulate attractions. Nevertheless, because of the peculiar nature of powders compared to solid, isotropic bodies, there is a need to develop new models for analysing their behaviour and to put more emphasis on examination of time-dependent deformation in the later stage of the compression cycle.

Synthesis of a novel fluorescent poly(D,L-lactide) end-capped with 1-pyrenebutanol used for the preparation of nanoparticles.

A new fluorescent polymer based on D,L-lactic acid units end-capped with 1-pyrenebutanol (PLAP) was synthesized by ring-opening polymerization. PLAP having different molecular weight could be obtained by varying the ratio of D,L-lactide and 1-pyrenebutanol. Fluorescent nanoparticles (NP) were prepared using blends of poly(D,L-lactic acid) (PLA) and the new PLAP of 6 kDa by the salting-out process. Incubation of these nanoparticles with human blood monocytes was performed in serum and the cell-associated fluorescence was analysed by flow cytometry. Monocytes in contact with NP containing increasing amounts of PLAP showed a regular increase of the fluorescence. Cells incubated with NP containing 5% (w/w) of PLAP showed high signals of fluorescence with no possible overlap with those given by blank monocytes. This demonstrated that flow cytometry performed in the UV domain was very specific. In addition, the results of cytotoxicity tests using a MTT assay method indicated that PLAP did not increase the cytotoxicity when incorporated into PLA nanoparticles.

Cell interaction studies of PLA-MePEG nanoparticles.

Poly(D,L-lactic acid)-methoxypoly(ethylene glycol) (PLA-MePEG) copolymers were synthesized by ring-opening polymerization of D,L-lactide in the presence of MePEG of different molecular weights and stannous octoate as the catalyst. The chemical composition of the diblock-copolymer PLA-MePEG was confirmed by 1H-NMR and the molecular weight and distribution were assessed by gel permeation chromatography. Nanoparticles containing Nile red as a fluorescent dye were prepared using poly(D,L-lactic acid) (PLA), blends of PLA and PLA-MePEG or PLA-MePEG alone. Incubation of nanoparticles with human blood monocytes was performed in serum or in PBS and the cell-associated fluorescence was analyzed by flow cytometry. In serum, a protective effect was obtained and the interaction of particles with mononuclear leukocytes decreased to 40%.

Towards elucidation of the drug release mechanism from compressed hydrophilic matrices made of cellulose ethers. III. Critical use of thermodynamic parameters of activation for modeling the water penetration and drug release processes.

The two main purposes of this work were: (i) to critically consider the use of thermodynamic parameters of activation for elucidating the drug release mechanism from hydroxypropyl methylcellulose (HPMC) matrices, and (ii) to examine the effect of neutral (pH 6) and acidic (pH 2) media on the release mechanism. For this, caffeine was chosen as model drug and various processes were investigated for the effect of temperature and pH: caffeine diffusion in solution and HPMC gels, and drug release from and water penetration into the HPMC tablets. Generally, the kinetics of the processes was not significantly affected by pH. As for the temperature dependence, the activation energy (E(a)) values calculated from caffeine diffusivities were in the range of Fickian transport (20-40 kJ mol⁻¹). Regarding caffeine release from HPMC matrices, fitting the profiles using the Korsmeyer-Peppas model would indicate anomalous transport. However, the low apparent E(a) values obtained were not compatible with a swelling-controlled mechanism and can be assigned to the dimensional change of the system during drug release. Unexpectedly, negative apparent E(a) values were calculated for the water uptake process, which can be ascribed to the exothermic dissolution of water into the initially dry HPMC, the expansion of the matrix and the polymer dissolution. Taking these contributions into account, the true E(a) would fall into the range valid for Fickian diffusion. Consequently, a relaxation-controlled release mechanism can be dismissed. The apparent anomalous drug release from HPMC matrices results from a coupled Fickian diffusion-erosion mechanism, both at pH 6 and 2.