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Polyurethanes (PUs) are formed by a reaction between isocyanates and diols to yield polymers with urethane bonds (-NH-COO-) in their main chain. A great variety of building blocks is commercially available that allows the chemical and physical properties of PUs to be tailored to their target applications, particularly for the biomedical and pharmaceutical fields. This article reviews the synthesis and characterization of PUs and PU-copolymers, as well as their in vitro and in vivo biodegradability and biocompatibility. Particular emphasis is placed on the use of PUs for the controlled release of drugs and for the (targeted) delivery of biotherapeutics., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Purpose: To investigate the in vitro release of octreotide acetate, a somatostatin agonist, from microspheres based on a hydrophilic polyester, poly(D,L-lactide-co-hydroxymethyl glycolide) (PLHMGA)., Methods: Spherical and non-porous octreotide-loaded PLHMGA microspheres (12 to 16 μm) and loading efficiency of 60-70% were prepared by a solvent evaporation. Octreotide release profiles were compared with commercial PLGA formulation (Sandostatin LAR(®)); possible peptide modification with lactic, glycolic and hydroxymethyl glycolic acid units was monitored., Results: PLHMGA microspheres showed burst release (~20%) followed by sustained release for 20-60 days, depending on the hydrophilicity of the polymer. Percentage of released loaded peptide was high (70-90%); > 60% of released peptide was native octreotide. PLGA microspheres did not show peptide release for the first 10 days, after which it was released in a sustained manner over the next 90 days; > 75% of released peptides were acylated adducts., Conclusions: PLHMGA microspheres are promising controlled systems for peptides with excellent control over release kinetics. Moreover, substantially less peptide modification occurred in PLHMGA than in PLGA microspheres.

Purpose: To study the release of a model protein, bovine serum albumin (BSA), from microspheres of an hydroxylated aliphatic polyester, poly(lactic-co-hydroxymethyl glycolic acid) (PLHMGA)., Methods: BSA-loaded microspheres were prepared by a double emulsion solvent evaporation method. The effect of copolymer composition and the molecular weight of the copolymer on in vitro release and degradation were studied. The integrity of the released BSA was studied by fluorescence spectroscopy and size exclusion chromatography (SEC)., Results: Microspheres prepared from PLHMGA with 50% hydroxymethyl glycolic acid (HMG) showed a burst release followed by a sustained release in 5-10 days. PLHMGA microspheres prepared from a copolymer with 35% and 25% HMG showed a sustained release of BSA up to 80% for 30 and 60 days, respectively. The release of BSA was hardly affected by the molecular weight of the polymer. Fluorescence spectroscopy and SEC showed that the released BSA preserved its structural integrity. Microspheres were fully degradable, and the degradation time increased from approximately 20 days to 60 days when the HMG content decreased from 50% to 25%., Conclusions: Taking the degradation and release data together, it can be concluded that the release of BSA from PLHMGA microspheres is governed by degradation of the microspheres.

The purpose of this study was to investigate the suitability of a novel hydroxylated aliphatic polyester, poly(lactic-co-hydroxymethyl glycolic acid) (PLHMGA), as controlled release system for pharmaceutical proteins. Dextran Blue (as a macromolecular model compound) and lysozyme-loaded PLHMGA and PLGA (control formulation) microspheres were prepared by a solvent evaporation technique. The Dextran Blue and lysozyme loaded PLHMGA microspheres prepared with 10% polymer solution showed, because of a high porosity, a high burst release (35-75%) and the remaining content was released in a sustained manner for 15-20 days. The microspheres prepared with 15 and 20% polymer solution had a lower porosity and showed a pulsed release after day 8 and in 27 days they released more than 90% of Blue Dextran. The release of lysozyme was incomplete, likely due to aggregation of part of the encapsulated protein. Spectroscopic analysis of the released lysozyme indicated fully preserved secondary/tertiary structure and an enzyme activity assay showed that the specific activity of the released protein was maintained. An in vitro degradation study showed that the release of Blue Dextran and lysozyme is essentially controlled by the degradation of the microspheres. This study shows that microspheres made of the hydroxylated aliphatic polyester, poly(lactic-co-hydroxymethyl glycolic acid), are promising systems for the controlled release of pharmaceutical proteins.

A new cationic biodegradable polyphosphazene was developed, bearing both pendant primary and tertiary amine side groups, poly(2-dimethylaminoethylamine-co-diaminobutane)phosphazene (poly(DMAEA-co-BA)phosphazene). PEG and PEG-folate were coupled to polyplexes based on this poly(DMAEA-co-BA)phosphazene, leading to small (size 100 and 120nm, respectively) and almost neutral particles. In vitro tissue culture experiments showed a low cytotoxicity of both uncoated and coated polyplexes. However, the PEG coated polyplexes showed a 2-fold lower transfection activity in OVCAR 3 cells as compared to the uncoated polyplexes. On the other hand, the PEG-folate coated polyplexes had a 3-fold higher transfection than the PEGylated polyplexes. When free folate was added to the transfection medium, only the transfection activity of the targeted polyplexes was reduced, indicating internalization of the targeted PEG polyplexes via the folate receptor. Confocal laser scanning microscopy confirmed a lower binding and uptake of the PEGylated polyplexes by OVCAR-3 cells when compared to uncoated and folate-PEGylated polyplexes. While uncoated polyplexes induced aggregation of erythrocytes at polymer concentrations of 0.09microg/mL, the PEGylated systems could be incubated at ten times higher concentration before aggregation occurred indicating excellent shielding of the surface charge of the polyplexes by grafting of PEG. In conclusion, the targeted delivery of poly(DMAEA-co-BA)phosphazene bases polyplexes and their improved compatibility with erythrocytes makes them interesting for in vivo applications.

Aims: To investigate if patients' perceptions of their diabetes status is related to blood glucose self-monitoring (SMBG) behaviour, independent of self-reported disease severity., Methods: The setting of this study was a cross-sectional study among 1561 patients, 18 years or older, who filled at least two prescriptions for any glucose lowering drug between March 2002 and 2003 in the Netherlands. Using a 30-item self-administered questionnaire, data on self-monitoring behaviour (frequency of test strip use and objective of self-monitoring), perceived diabetes status and disease severity were gathered. Type 1 diabetes mellitus patients were excluded. We used logistic regression to calculate odds ratios (OR) and their 95% confidence intervals (CI)., Results: About 54% of the patients (n=841) returned evaluable questionnaires. After exclusion of 97 type 1 diabetes mellitus patients, 744 type 2 diabetes mellitus patients were included. Practising SMBG was more common among patients who rated their diabetes status as poorly or moderately controlled compared to those who rated it (very) well-controlled (OR 1.93; 95% CI: 1.20-3.12). A better perceived diabetes status was more likely in those who performed SMBG infrequently compared to those who performed SMBG frequently (p-value for trend=0.001). Self-reported factors of disease severity and personalized objectives did not affect these associations considerably., Conclusions: Among type 2 diabetes mellitus patients, SMBG behaviour is associated with patients' perceptions of diabetes status, irrespective of the self-reported disease severity.

Objective: To determine if the association between the level of community pharmacy diabetes services and six of its reported determinants is influenced by the definition of these services., Method: Cross-sectional survey among 97% of all Dutch community pharmacies (1,642) registered in 2004. Seven definitions of self-monitoring support (support to patients performing self-monitoring of blood glucose) were constructed: one based on the Dutch pharmacy practice guideline (containing five activities related to patient counselling, calibration and dispensing), one based on patient counselling activities only and five definitions based on each separate activity. Multivariable models of self-monitoring support according to the different definitions were compared., Main Outcome Measure: Associations between determinants and the different definitions of self-monitoring support, expressed as odds ratio (OR) and 95% confidence intervals (95% CI). All definitions were compared to the practice guideline definition., Results: The ORs of 14 of the 48 possible comparisons of different definitions were significantly different from one. The standardized difference ranged from 1.42 (95% CI: 1.01-1.90) to 3.05 (95% CI: 1.51-4.61). Three out of six predictive models retained different determinants compared to the multivariable model of self-monitoring support based on the guideline., Conclusion: The association between self-monitoring support and its determinants depend on the definition of self-monitoring support. This underlines the importance for pharmacy practice research to unambiguously describe the characteristics and the setting of an intervention. Only with a complete description of the intervention, the likelihood for success of implementation in another setting can be determined.

Phthalocyanines (Pcs) are a class of photosensitizers (PSs) with a strong tendency to aggregate in aqueous environment, which has a negative influence on their photosensitizing ability in photodynamic therapy. Pcs with either peripheral or axial solketal substituents, that is, ZnPc(sol)8 and Si(sol)2Pc, respectively, were synthesized and their tendency to aggregate as well as their photodynamic properties in 14C and B16F10 cell lines were evaluated. The results were compared to more hydrophilic silicon Pcs, that is, Si(PEG750)2Pc and Pc4. The order of cellular uptake was Pc4 > ZnPc(sol)8 > Si(PEG750)2Pc > Si(sol2)Pc. In contrast, Si(sol2)Pc showed the highest photocytotoxicity, while ZnPc(sol)8 did not show any photocytotoxicity up to a concentration of 10 microM in both cell types. UV/vis spectroscopy showed that Si(sol)2Pc is less prone to aggregation than ZnPc(sol)8, which can explain the lack of photoactivity of the latter. Si(sol)2Pc was predominantly located in lipid droplets, whereas Si(PEG750)2Pc was homogeneously distributed in the cytosol, which is probably the main cause of their difference in photoactivity. The very high photodynamic efficacy of Si(sol)2Pc makes this PS an interesting candidate for future studies.

Water-soluble polymers with hydrolyzable cationic side groups (structure of the monomers are shown in Figure 1) were synthesized and evaluated as DNA delivery systems. The polymers, except for pHPMA-NHEM, were able to condense plasmid DNA into positively charged nanosized particles. The rate of hydrolysis at 37 degrees C and pH 7.4 of the side groups differed widely; the fastest rate of hydrolysis was observed for HPMA-DEAE (half-life of 2 h), while HPMA-DMAPr had the lowest rate of hydrolysis (half-life of 70 h). In line with this, pHPMA-DEAE-based polyplexes showed the fastest destabilization of the polyplexes at 37 degrees C and pH 7.4. Polyplexes based on pHPMA-DEAE, pHPMA-DMAE, and pHPMA-MPPM showed release of intact DNA within 24, 48, and 48 h, respectively, after incubation at 37 degrees C and pH 7.4. PHPMA-DEAE and pHPMA-MPPM based polyplexes showed the highest transfection activity (almost twice as active as pEI). Importantly, the pHPMA-DEAE, pHPMA-MPPM, and pHPMA-BDMPAP polyplexes preserved their transfection activity in the presence of serum proteins. All polymers investigated showed a substantial lower in vitro cytotoxicity than pEI. In conclusion, pHPMA-based polyplexes are an attractive class of biodegradable vectors for nonviral gene delivery.

Background: Pharmacy practice guidelines promote the role of community pharmacies in self-monitoring of blood glucose. However, variations between Dutch pharmacies exist in the proportion of patients to whom test strips are dispensed., Objective: To assess whether variations between community pharmacies in dispensing of blood glucose test strips can be explained by differences in patient characteristics and the region in which the pharmacy is located., Setting: PHARMO-Record Linkage System containing drug dispensing histories from 40 community pharmacies of about 450,000 patients in the Netherlands., Method: We performed a retrospective cohort study. Data on prescription of all drugs and medical aids between 1991 and 2001 were extracted for all new users of antidiabetic drugs. Patients were excluded if the dispensing history did not allow classification of the type of diabetes or if the dispensing pharmacy could not be determined. The data were analysed using a Cox proportional hazard model., Main Outcome Measure: Time to first test strips dispensed., Results: We identified 8,233 starters of antidiabetic drugs. During a median follow-up of 2.1 years, 20% of the patients were dispensed test strips at least once. Community pharmacy was significantly associated with the dispensing of test strips after adjustment for patient characteristics. This association was less apparent when stratified for the geographical location of the pharmacy., Conclusion: Community pharmacy is an independent determinant of the start of use of test strips. Differences in dispensing of test strips between pharmacies are dependent on geographical region. This suggests that implementing practice guidelines for diabetes care in community pharmacy requires different approaches in different regions.

Background: Patients performing self-monitoring of blood glucose (SMBG) may benefit from community pharmacy services. However, wide-scale implementation of these services is limited. Many pharmacy characteristics (eg, physical layout of the pharmacy, knowledge and competence of the pharmacy team) are reported to be relevant when implementing these services. Still, the importance of local agreements on the division of roles with, for example, local general practitioners or diabetes nurses, is less clear., Objective: To study the association between local collaboration and the level of services provided by community pharmacies to patients performing SMBG., Methods: In 2004, we performed a cross-sectional survey among all 1692 Dutch community pharmacies. Data were gathered on provision of services for SMBG, local agreements, and pharmacy characteristics. Data were analyzed using logistic regression. Associations were adjusted for pharmacy characteristics., Results: About 44% (724) of the community pharmacies returned the questionnaire. Pharmacies that were not involved in local collaborative services on patient counseling reported to provide fewer services compared with those that were involved in such agreements (OR 0.26, 95% CI 0.13 to 0.53). Similar findings were observed for agreements on calibration of SMBG equipment (0.17, 0.04 to 0.71). The associations remained after adjusting for pharmacy characteristics., Conclusions: Local collaboration on the division of roles in diabetes care between healthcare professionals is independently associated with the number of pharmacy services provided to patients performing SMBG.

Objective: Investigation of the current application of direct-to-consumer (DTC) communication on prescription only medicines via the Intemet in the Netherlands., Method: Questionnaires were sent by e-mail to 43 Dutch innovative pharmaceutical industries and 130 Patient Association and Support Groups (PASGs)., Results: In this pilot study, the response of the pharmaceutical industry was rather low but the impression is that they were willing to invest in DTC communication. The majority of the websites of PASGs did not link to websites of pharmaceutical companies. The PASGs had no opinion whether patients can make a good distinction between DTC advertising and information on websites of the pharmaceutical industry nor about the quality. PASGs did not think unambiguously about the impact on the patient-doctor relationship., Conclusion: The impact of DTC communication on prescription only medicines via the internet is not yet clear in the Netherlands.

Objective: To assess the proportion of diabetic patients who collect self-monitoring equipment for glucose testing in Dutch community pharmacies., Methods: Data were used from the PHARMO-Record Linkage System, containing pharmacy dispensing records from 1991 to 1998. The study population consisted of patients who received at least two prescriptions of insulin and/or oral hypoglycemic agents. Information was collected on patient demographics, antidiabetic drug use and self-monitoring equipment (blood glucose meters and test strips). Type of diabetes was determined for all incident users of antidiabetic drugs., Main Outcome Measure: The proportion of patients per community pharmacy, who were dispensed self-monitoring equipment at least once., Results: The study population consisted of 11,358 diabetic patients. The number of incident patients was 5,050, of whom 91.7% had type 2 diabetes. Twenty-nine pharmacies were included. The mean proportion of patients per pharmacy who received test strips at least once was 30.1% (SD = 6.7%), range 19-46%. The proportion of patients who were dispensed test strips was almost three times higher among type 1 than among type 2 patients (54% vs. 17%)., Conclusion: In comparison to other countries' published data, Dutch community pharmacies dispense relatively few glucose test materials to diabetic patients. There are substantial differences between pharmacies in dispensing test strips. Further research is needed into the determinants governing the use of test strips at both patient and pharmacy level.

In this paper, we show that water inside mesoporous cavities in zeolites can be supercooled to ca. -40 degrees C at which point homogeneous nucleation of the water takes place. The fundamental phenomena observed here are similar to those reported earlier in for example emulsion droplets or droplets in the vapor phase. However, as these zeolite materials are widely available, they may provide an easily accessible source for studies of supercooled liquids in confinements. Next to this, it is now possible to discriminate with thermoporometry between mesoporous cavities inside the zeolite crystals, in which homogeneous nucleation takes place, and mesopores that are connected to the external surface in which heterogeneous nucleation takes place.

AP 5280 is a novel polymer-conjugated platinum anticancer agent showing promising in vitro and in vivo activity against solid tumors. The aim of this study was to develop a parenteral pharmaceutical dosage form for phase I clinical trials. AP 5280 drug substance was characterized by using a wide range of analytical techniques and showed excellent solubility in water. However, as aqueous solutions of AP 5280 proved to be labile upon sterilization by moist heat, it was decided to develop a lyophilized dosage form. Initially, glass vials were used as primary packaging, but this led to a high breakage rate, which could be completely prevented by the use of CZ resin vials. Stability studies to date show that the lyophilized product in glass vials is stable for at least 12 months when stored at 2-8 degrees C in the dark and the lyophilized product in CZ resin vials is stable for at least 6 months under these conditions. Photostability testing revealed photolability of AP 5280 drug substance and lyophilized product in both types of primary container, necessitating storage in the dark. The first clinical experiences indicate that the proposed formulation is fully applicable for use in the clinical setting.

This paper describes the development of a stable pharmaceutical dosage form for NAMI-A, a novel antimetastatic ruthenium complex, for Phase I testing. NAMI-A drug substance was characterized using several spectrometric and chromatographic techniques. In preformulation studies, it was found that NAMI-A in aqueous solution was not stable enough to allow sterilization by moist heat. The effect of several excipients on the stability of the formulation solution was investigated. None of them provided sufficient stability to allow long-term storage of an aqueous solution of NAMI-A. Therefore, a lyophilized product was developed. Five different formulations were prepared and subjected to thermogravimetric (TG) analysis and stability studies at various conditions for 1 year. Minimal degradation during the production process is achieved with a formulation solution of pH 3-4. Of the acids tested, only hydrochloric acid (HCl 0.1 mM) both stabilized the formulation solution and was compatible with the lyophilized product. This product was stable for at least 1 year when stored at -20 degrees C, 25 degrees C/60% relative humidity (RH) and 40 degrees C/75% RH, and was also photostable.

Holmium-loaded PLLA microspheres are useful systems in radioembolization therapy of liver metastases because of their low density, biodegradability and favourable radiation characteristics. Neutron activated Ho-loaded microspheres showed a surprisingly low release of the relatively small holmium complex. In this paper factors responsible for this behaviour are investigated, in particular by the use of differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy and X-ray diffraction. The holmium complex is soluble in PLLA up to 8% in films and 17% in microspheres. Interactions between carbonyl groups of PLLA, and the Ho-ion in the HoAcAc complex, explain very satisfactorily the high stability of holmium-loaded microspheres.

In this paper, a novel method is presented for the preparation of dextran hydrogels and microspheres, based on crystallization. Although dextrans are known to be well soluble in water, precipitation was observed in concentrated aqueous solutions of low molecular weight dextran (dextran 6000), whereas for solutions of dextran with higher molecular weights (dextran 40,000 and 220,000) no precipitation was observed in the time-frame studied. The kinetics of the precipitation process were studied and showed that precipitation was faster when more concentrated dextran solutions were used. Furthermore, the precipitation process was accelerated by stirring and by the presence of salts. Depending on the precipitation time, microspheres or gels were obtained. The precipitates were insoluble in water at room temperature, but readily dissolved in boiling water or DMSO. IR spectroscopy and (modulated) differential scanning calorimetry ((M)DSC) demonstrated that the precipitates were crystalline. We hypothesize that crystallization is due to association of the chains through hydrogen bonding, induced by the large polymer/water ratio in concentrated dextran 6000 solutions.

Aplidine is a naturally occurring cyclic depsipeptide isolated from the Mediterranean tunicate Aplidium albicans. Aplidine displays promising in vitro and in vivo antitumor activities against various solid human tumor xenografts and is therefore developed now for clinical testing. The aim of this study was to develop a stable parenteral pharmaceutical dosage form for clinical Phase I testing. Aplidine raw material was characterized by using several chromatographic and spectrometric techniques. These experiments showed that aplidine exists as two isomers. A stability-indicating HPLC assay was developed. Solubility testing showed that aplidine exhibits very poor aqueous solubility. Because solubilized aplidine showed substantial degradation under heat and light stress testing conditions, it was decided to develop a lyophilized dosage form. Freeze-drying was carried out with a 500 micrograms/mL solution of aplidine in 40% (v/v) tert-butanol in Water for Injection (WfI) containing 25 mg/mL D-mannitol as a bulking agent. Differential scanning calorimetry was applied to determine the optimal freeze-drying cycle parameters. The prototype, containing 500 micrograms aplidine and 25 mg D-mannitol per vial, was found to be the optimal formulation in terms of solubility, length of lyophilization cycle, and dosage requirements in the forthcoming Phase I clinical studies. Quality control of the freeze-dried formulation demonstrates that the manufacturing process does not affect the integrity of aplidine. The optimal reconstitution solution was found to be 15/15/70% (v/v/v) Cremophor EL/ethanol/WfI (CEW). Both reconstituted product and dilutions of the reconstituted product with normal saline (up to 1:100 v/v) appeared to be stable for at least 24 hours after preparation. Shelf-life data, available thus far, show that the lyophilized formulation is stable for at least 1 year when stored at +2-8 degrees C in the dark.

Purpose: To study the stability of polymer-plasmid complexes (polyplexes) both as an aqueous dispersion and in their lyophilized form., Methods: The characteristics of the polyplexes (size, charge and transfection potential) were monitored at different temperatures. Moreover, we studied possible changes in the secondary and tertiary structure of the plasmid by agarose gel electrophoresis and by CD spectroscopy to gain insight into the mechanism of polyplex degradation., Results: The polyplexes preserved almost their full transfection potential after aging in an aqueous solution of 20 mM Hepes (pH 7.4) containing 10% sucrose at 4 and 20 degrees C for 10 months. On the other hand, the polyplexes aged at 40 degrees C were rather unstable and lost their transfection capability with a half-life of around 2 months. During storage, conformational changes in the secondary and tertiary structure of DNA were observed. When naked plasmid DNA was aged at 40 degrees C as an aqueous solution and complexed with polymer just before the transfection experiment, a slower drop in its transfection capability was observed. The freeze-dried polyplexes using sucrose as lyoprotectant almost fully retained their transfection efficiency, even when aged at 40 degrees C for 10 months., Conclusions: This study provides information about polyplex stability in aqueous dispersions on storage and demonstrates that freeze-drying is an excellent method to ensure long term stability.

In this paper the effect of the topology of plasmid DNA (supercoiled, open-circular and linear) on its binding characteristics with the polymeric transfectant poly((2-dimethylamino)ethyl methacrylate) was studied. The formed polyplexes were also evaluated for their transfection properties in vitro in two different cell lines. Anion-exchange chromatography was used for the separation of supercoiled and open-circular plasmid from a plasmid stock solution. Linear plasmids were prepared by endonucleases that cleaved the plasmid either in the promoter region or in a region not specific for expression (ampicillin resistance region). Plasmid DNA was also heat-denatured for 6 h at 70 degrees C, resulting in DNA mainly in the open-circular and oligomeric forms. The transfection of two different cell lines was dependent on the topology of the DNA in the order supercoiled>open-circular approximately heat-denatured>linear DNA prepared by cleaving in the nonspecific region>linear DNA prepared by cleaving in the promoter region. No differences in the size of the complexes or in the quenching of the DNA-intercalating fluorophore acridine orange were found as function of the topology. However, circular dichroism spectroscopy revealed differences between the topological plasmid species, both in the free form and in the presence of excess of cationic polymer.

To preserve the size and transfection potential of polymer-plasmid complexes. Freeze-drying and freeze-thawing were used for stabilization of these complexes. The concentration of the sugars is an important factor affecting both the size and transfection capability of the complexes after freeze-drying and freeze-thawing. However, the type of lyoprotectant (sugar) used is of minor importance. It is also shown that when damage to polymer-plasmid complexes occurs, it results from the drying process but is not due to the freezing step.

The aim of this study was to gain insight into the formulation parameters affecting the size of poly((2-dimethylamino)ethyl methacrylate)-plasmid complexes (polyplexes). Experimental designs were applied to screen and optimize several variables, which may influence the complex size. In a screening design, it was demonstrated that at a fixed concentration of plasmid (40 micrograms/ml) after incubation with polymer, the size of the resulting polyplexes was highly dependent on the polymer/plasmid ratio as well as on the pH, viscosity (i.e. sucrose concentration) and ionic strength of the aqueous solution. However, the temperature, PEG 600 (up to 5% (v/v)) and Tween 80 (up to 0.2%) had a marginal effect on the size of the polyplexes. In an optimization design, the effect of the pH, polymer/plasmid ratio and Tween on the size of the polymer/plasmid complexes prepared at relatively high concentration of plasmid (50-200 micrograms/ml) was evaluated. Based on the results of the optimization design, a mathematical model was derived, which describes the relationship between the size of the polyplexes and the different formulation parameters. This model shows that even at high plasmid concentration (200 micrograms/ml), small sized polyplexes were formed at low pH and ionic strength, especially when the solution contains 20% (w/v) sucrose. This concentrated polyplex dispersion (polymer/plasmid ratio > 3/1 (w/w), 200 micrograms plasmid/ml) can be diluted down to 5 micrograms/ml plasmid without significant changes in particle size and transfection potential. At lower ratios, a growth in particle size was observed upon dilution of the complexes, which might also explain the low transfection efficiency of these polyplexes in vitro.

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) is a water-soluble cationic polymer, which is able to bind to DNA by electrostatic interactions. At a polymer/plasmid ratio above 2 (w/w) positively charged complexes were formed with a size around 0.2 microm. The transfection efficiency of polymer/plasmid complexes was evaluated in cell culture (COS-7 and OVCAR-3 cells) using a pCMV-lacZ plasmid, encoding for beta-galactosidase, as a reporter gene. The optimal transfection efficiency was found at a PDMAEMA/plasmid ratio of 3-5 (w/w). Under these conditions 3-6% of the cells were actually transfected. Like other cationic polymers, PDMAEMA is slightly cytotoxic. This activity was partially masked by complexing the polymer with DNA. A pronounced effect of the molecular weight of the polymer on the transfection efficiency was observed. An increasing molecular weight resulted in an increasing number of transfected cells. Dynamic light scattering experiments showed that high molecular weight polymers (Mw>300 kDa) were able to condense DNA effectively (particle size 0.15-0.20 microm). In contrast, when plasmid was incubated with low molecular weight PDMAEMA, large complexes were formed (size 0.5-1.0 microm). Copolymers of DMAEMA with methyl methacrylate (MMA), ethoxytriethylene glycol methacrylate (triEGMA) or N-vinyl-pyrrolidone (NVP) also acted as transfection agents. A copolymer with 20 mol % of MMA showed a reduced transfection efficiency and a substantial increased cytotoxicity compared with a homopolymer of the same molecular weight. A copolymer with triEGMA (48 mol %) showed both a reduced transfection efficiency and a reduced cytotoxicity, whereas a copolymer with NVP (54 mol %) showed an increased transfection efficiency and a decreased cytotoxicity as compared to a DMAEMA homopolymer.

In this study we investigated the use of modulated temperature differential scanning calorimetry (MTDSC) for the detection of the glass transition temperature (Tg) in freeze-dried cakes of lyoprotected liposomes and for the analysis of frozen carbohydrate solutions. The glass transition appeared in the reversing heat flow, whereas the bilayer melting endotherm was observed in the nonreversing heat flow. This enabled the detection of Tg even in samples were the glass and bilayer transition overlapped. In addition, relaxation processes occurring in nonannealed freeze-dried carbohydrate-liposome mixtures, which hinder the determination of Tg with conventional DSC, were also separated from the heat capacity related heat flow. Analysis of frozen carbohydrate solutions with MTDSC facilitated the identification of the glass transition, devitrification peak, and "softening" transition, which could help to further optimize freeze-drying conditions by rationale. Sampling and selection of experimental parameters are discussed for the special case of porous, freeze-dried cakes.