Dagmar Fischer

Poly(ethylene glycol) in Drug Delivery: Pros and Cons as Well as Potential Alternatives

Poly(ethylene glycol) (PEG) is the most used polymer and also the gold standard for stealth polymers in the emerging field of polymer-based drug delivery. The properties that account for the overwhelming use of PEG in biomedical applications are outlined in this Review. The first approved PEGylated products have already been on the market for 20 years. A vast amount of clinical experience has since been gained with this polymer--not only benefits, but possible side effects and complications have also been found. The areas that might need consideration and more intensive and careful examination can be divided into the following categories: hypersensitivity, unexpected changes in pharmacokinetic behavior, toxic side products, and an antagonism arising from the easy degradation of the polymer under mechanical stress as a result of its ether structure and its non-biodegradability, as well as the resulting possible accumulation in the body. These possible side effects will be discussed in this Review and alternative polymers will be evaluated.

Rapid formation of plasma protein corona critically affects nanoparticle pathophysiology

In biological fluids, proteins bind to the surface of nanoparticles to form a coating known as the protein corona, which can critically affect the interaction of the nanoparticles with living systems. As physiological systems are highly dynamic, it is important to obtain a time-resolved knowledge of protein-corona formation, development and biological relevancy. Here we show that label-free snapshot proteomics can be used to obtain quantitative time-resolved profiles of human plasma coronas formed on silica and polystyrene nanoparticles of various size and surface functionalization. Complex time- and nanoparticle-specific coronas, which comprise almost 300 different proteins, were found to form rapidly (<0.5 minutes) and, over time, to change significantly in terms of the amount of bound protein, but not in composition. Rapid corona formation is found to affect haemolysis, thrombocyte activation, nanoparticle uptake and endothelial cell death at an early exposure time.

Recent advances in rational gene transfer vector design based on poly(ethylene imine) and its derivatives.

The continually increasing wealth of knowledge about the role of genes involved in acquired or hereditary diseases renders the delivery of regulatory genes or nucleic acids into affected cells a potentially promising strategy. Apart from viral vectors, non‐viral gene delivery systems have recently received increasing interest, due to safety concerns associated with insertional mutagenesis of retro‐viral vectors. Especially cationic polymers may be particularly attractive for the delivery of nucleic acids, since they allow a vast synthetic modification of their structure enabling the investigation of structure‐function relationships. Successful clinical application of synthetic polycations for gene delivery will depend primarily on three factors, namely (1) an enhancement of the transfection efficiency, (2) a reduction in toxicity and (3) an ability of the vectors to overcome numerous biological barriers after systemic or local administration. Among the polycations presently used for gene delivery, poly(ethylene imine), PEI, takes a prominent position, due to its potential for endosomal escape. PEI as well as derivatives of PEI currently under investigation for DNA and RNA delivery will be discussed.

Surface-modified biodegradable albumin nano- and microspheres. II: effect of surface charges on in vitro phagocytosis and biodistribution in rats.

The surface charges on biodegradable albumin nanoparticles were introduced by covalent coupling different primary amines to examine their influence on phagocytosis by macrophages under in vitro conditions. Albumin particles with a zeta potential close to zero showed a reduced phagocytic uptake in comparison with charged particles, especially nanoparticles with a positive zeta potential. The phagocytic uptake in the present study was examined using an established cell culture model based on primary mouse peritoneal macrophages and a human hematopoietic monocytic cell line (U-937) treated with phorbol-12-myristic-13-acetate to induce cell differentiation. The influence of opsonins on in vitro phagocytosis experiments was characterized using carriers pre-treated with human serum. In the presence of human serum the phagocytic activity of U-937 cells was found to be similar to primary mouse macrophages without serum. In contrast to peritoneal macrophages, U-937 cells showed no phagocytic activity in the absence of serum. In particular, only the C3b- complement deposition on the particle surface seems to promote the phagocytic process. The in vivo distribution of albumin carriers in rats was investigated using magnetic resonance imaging (MRI). No differences in blood circulation times and organ accumulation between different nanoparticle preparations with positive, neutral and negative surface charges could be observed in rats, suggesting that the in vivo fate of albumin nanoparticles is significantly influenced by factors not reflected in the in vitro cell culture models.

Intracellular Processing of Poly(Ethylene Imine)/Ribozyme Complexes Can Be Observed in Living Cells by Using Confocal Laser Scanning Microscopy and Inhibitor Experiments

AbstractPurpose. Critical steps in the subcellular processing of poly(ethylene imine)/nucleic acid complexes, especially endosomal/lysosomal escape, were visualized by using living cell confocal laser scanning microscopy (CSLM) to obtain an insight into their mechanism. Methods. Living cell confocal microscopy was used to examine the intracellular fate of poly(ethylene imine)/ribozyme and poly(L-lysine)/ribozyme complexes over time, in the presence of and without bafilomycin A1, a selective inhibitor of endosomal/lysosomal acidification. The compartment of complex accumulation was identified by confocal microscopy with a fluorescent acidotropic dye. To confirm microscopic data, luciferase reporter gene expression was determined under similar experimental conditions. Results. Poly(ethylene imine)/ribozyme complexes accumulate in acidic vesicles, most probably lysosomes. Release of complexes occurs in a sudden event, very likely due to bursting of these organelles. After release, poly(ethylene imine) and ribozyme spread throughout the cell, during which slight differences in distribution between cytosol and nucleus are visible. No lysosomal escape was observed with poly(L-lysine)/ribozyme complexes or when poly(ethylene imine)/ribozyme complexes were applied together with bafilomycin A1. Poly(ethylene imine)/plasmid complexes exhibited a high luciferase expression, which was reduced approximately 200-fold when lysosomal acidification was suppressed with bafilomycin A1. Conclusions. Our data provide, for the first time, direct experimental evidence for the escape of poly(ethylene imine)/nucleic acid complexes from the endosomal/lysosomal compartment. CLSM, in conjunction with living cell microscopy, is a promising tool for studying the subcellular fate of polyplexes in nucleic acid/gene delivery.

Poly(2‐ethyl‐2‐oxazoline) as Alternative for the Stealth Polymer Poly(ethylene glycol): Comparison of in vitro Cytotoxicity and Hemocompatibility

Limitations of PEG in drug delivery have been reported from clinical trials. PEtOx (0.4-40 kDa) as alternative is synthesized by a living, microwave-assisted polymerization, and is directly compared to PEG of similar molar mass regarding cytotoxicity and hemocompatibility. In short-term treatments, both types of polymers are well tolerated even at high concentrations. Moderate concentration and molar mass dependent cytotoxic effects occurred only after long-term incubation at concentrations higher than therapeutic doses. PEtOx possesses not only an easy route of synthesis and beneficial physicochemical characteristics such as low viscosity and high stability, which are advantageous over PEG, but additionally in vitro toxicology comparable to PEG.

The Biopolymer Bacterial Nanocellulose as Drug Delivery System: Investigation of Drug Loading and Release using the Model Protein Albumin

Although bacterial nanocellulose (BNC) has reached enormous interest for biomedical applications because of its outstanding material properties, investigations about its potential as drug delivery system are very rare. In the present study, for the first time, the applicability of BNC as drug delivery system for proteins using serum albumin as model drug was systematically investigated. Additionally, never-dried BNC was compared with freeze-dried BNC. For both types of BNC, a dependency of concentration, temperature, time, and preswelling for albumin loading and release could be demonstrated. These findings indicated an overlay of diffusion- and swelling-controlled processes, which could be confirmed by Ritger-Peppas equation. Freeze-dried samples showed a lower uptake capacity for albumin than native BNC, which was found to be related to changes of the fiber network during the freeze drying process as demonstrated by electron microscopy and protein staining experiments. The integrity and biological activity of proteins could be retained during the loading and release processes, which was demonstrated by gel electrophoresis and the use of luciferase as biologically active molecule. In conclusion, hydrophilicity, high biocompatibility, and controllable drug loading and release render BNC an innovative and attractive biopolymer for controlled drug delivery.

Drug delivery strategies in the therapy of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a frequently occurring disease in young people, which is characterized by a chronic inflammation of the gastrointestinal tract. The therapy of IBD is dominated by the administration of anti-inflammatory and immunosuppressive drugs, which suppress the intestinal inflammatory burden and improve the disease-related symptoms. Established treatment strategies are characterized by a limited therapeutical efficacy and the occurrence of adverse drug reactions. Thus, the development of novel disease-targeted drug delivery strategies is intended for a more effective therapy and demonstrates the potential to address unmet medical needs. This review gives an overview about the established as well as future-oriented drug targeting strategies, including intestine targeting by conventional drug delivery systems (DDS), disease targeted drug delivery by synthetic DDS and disease targeted drug delivery by biological DDS. Furthermore, this review analyses the targeting mechanisms of the respective DDS and discusses the possible field of utilization in IBD.

Active wound dressings based on bacterial nanocellulose as drug delivery system for octenidine

Although bacterial nanocellulose (BNC) may serve as an ideal wound dressing, it exhibits no antibacterial properties by itself. Therefore, in the present study BNC was functionalized with the antiseptic drug octenidine. Drug loading and release, mechanical characteristics, biocompatibility, and antimicrobial efficacy were investigated. Octenidine release was based on diffusion and swelling according to the Ritger-Peppas equation and characterized by a time dependent biphasic release profile, with a rapid release in the first 8h, followed by a slower release rate up to 96 h. The comparison between lab-scale and up-scale BNC identified thickness, water content, and the surface area to volume ratio as parameters which have an impact on the control of the release characteristics. Compression and tensile strength remained unchanged upon incorporation of octenidine in BNC. In biological assays, drug-loaded BNC demonstrated high biocompatibility in human keratinocytes and antimicrobial activity against Staphylococcus aureus. In a long-term storage test, the octenidine loaded in BNC was found to be stable, releasable, and biologically active over a period of 6 months without changes. In conclusion, octenidine loaded BNC presents a ready-to-use wound dressing for the treatment of infected wounds that can be stored over 6 months without losing its antibacterial activity.

PEG-functionalized microparticles selectively target inflamed mucosa in inflammatory bowel disease

INTRODUCTION The systemic therapy of inflammatory bowel diseases (IBD) by oral administration of anti-inflammatory and immunosuppressive agents is characterized by an increased probability of adverse drug reactions. A successful treatment with a simultaneous reduction in adverse events may be achieved by the administration of micro- and nanosized targeted drug delivery systems, which accumulate selectively in inflamed mucosal areas without systemic absorption. We described in a first in vivo study in IBD patients a significantly enhanced, but minor accumulation of non-functionalized poly(lactic-co-glycolic acid) (PLGA) microparticles in ulcerous lesions very recently. AIM The aim of this study was therefore the assessment of an increased targeting potential of different non-, chitosan- and polyethylene glycol (PEG)-functionalized PLGA micro- and nanoparticles to inflamed intestinal mucosa compared to healthy mucosa. MATERIALS AND METHODS For the quantification of nano- and microparticles, fluoresceinamine-labeled-PLGA was synthesized by carbodiimide reaction. Fluorescent chitosan-, PEG-, and non-functionalized PLGA micro- and nanoparticles with mean hydrodynamic diameters of 3000 nm and 300 nm were prepared by solvent evaporation technique. The targeting efficiencies in terms of particle translocation and deposition were investigated in Ussing chamber experiments. Healthy and inflamed macrobiopsies were received from routine endoscopic examinations of patients with IBD as well as control patients. RESULTS One-hundred and one Ussing chamber experiments of patients with IBD (Crohns disease: n=7 and ulcerative colitis: n=9) as well as healthy control patients (n=5) were performed. Histomorphological and electrophysiological investigations of inflamed mucosal tissues confirmed a significant alteration of mucosal barrier integrity in IBD patients (TER: healthy: 34.1 Ω cm(2); inflamed: 21.6 Ωc m(2); p=0.034). In summary, nanoparticles showed an increased translocation and deposition compared to microparticles in healthy and in inflamed mucosa. Chitosan-functionalized particles adhered onto the tissue surface and thus showed the lowest particle translocation and deposition in healthy and inflamed tissues. PEG-functionalized nanoparticles showed the highest translocation through healthy (2.31%) and inflamed mucosa (5.27%). Moreover, PEG-functionalized microparticles showed a significantly increased translocation through inflamed mucosa (3.33%) compared to healthy mucosa (0.55%; p=0.045). Notably, the particle deposition of PEG-functionalized microparticles was significantly increased in inflamed mucosa (10.8%) compared to healthy mucosa (4.1%; p=0.041). CONCLUSIONS Based on the targeted translocation and deposition to inflamed intestinal mucosa, PEG-functionalized PLGA microparticles were qualified as an innovative drug delivery system. These particles may serve as a selective treatment strategy to inflamed mucosal areas in IBD with the potential to improve therapeutic efficacy and to reduce adverse events.