Mechanistic Study on the Degradation of Hydrolysable Core-Crosslinked Polymeric Micelles.

Core-crosslinked polymeric micelles (CCPMs) are an attractive class of nanocarriers for drug delivery. Two crosslinking approaches to form CCPMs exist: either via a low-molecular-weight crosslinking agent to connect homogeneous polymer chains with reactive handles or via cross-reactive handles on polymers to link them to each other (complementary polymers). Previously, CCPMs based on methoxy poly(ethylene glycol)-b-poly[N-(2-hydroxypropyl) methacrylamide-lactate] (mPEG-b-PHPMAmLacn) modified with thioesters were crosslinked via native chemical ligation (NCL, a reaction between a cysteine residue and thioester resulting in an amide bond) using a bifunctional cysteine containing crosslinker. These CCPMs are degradable under physiological conditions due to hydrolysis of the ester groups present in the crosslinks. The rapid onset of degradation observed previously, as measured by the light scattering intensity, questions the effectiveness of crosslinking via a bifunctional agent. Particularly due to the possibility of intrachain crosslinks that can occur using such a small crosslinker, we investigated the degradation mechanism of CCPMs generated via both approaches using various analytical techniques. CCPMs based on complementary polymers degraded slower at pH 7.4 and 37 °C than CCPMs with a crosslinker (the half-life of the light scattering intensity was approximately 170 h versus 80 h, respectively). Through comparative analysis of the degradation profiles of the two different CCPMs, we conclude that partially ineffective intrachain crosslinks are likely formed using the small crosslinker, which contributed to more rapid CCPM degradation. Overall, this study shows that the type of crosslinking approach can significantly affect degradation kinetics, and this should be taken into consideration when developing new degradable CCPM platforms.

Modular core-shell polymeric nanoparticles mimicking viral structures for vaccination.

Recent advances in the development of protein-based vaccines have expanded the opportunities for preventing and treating both infectious diseases as well as cancer. However, the development of readily and efficient antigen delivery systems capable of stimulating strong cytotoxic T-lymphocyte (CTL) responses remains a challenge. With the attempt to closely mimic the properties of viruses in terms of their size and molecular organization, we constructed RNA (which is a ligand for Toll-like receptor 7 (TLR7) and TLR8) and antigen-loaded nanoparticles resembling the structural organization of viruses. Cationic polymers containing either azide or bicyclo[6.1.0]nonyne (BCN) groups were synthesized as electrostatic glue that binds negatively charged single stranded RNA (PolyU) to form a self-crosslinked polyplex core. An azide-modified model antigen (ovalbumin, OVA) and a BCN-modified mannosylated or galactosylated polymer were sequentially conjugated to the RNA core via disulfide bonds using copper free click chemistry to form the shell of the polyplexes. The generated reducible virus mimicking particles (VMPs) with a diameter of 200 nm and negatively surface charge (-14 mV) were colloidally stable in physiological conditions. The immunogenicity of these VMP vaccines was evaluated both in vitro and in vivo. The surface mannosylated VMPs (VMP-Man) showed 5 times higher cellular uptake by bone marrow derived DCs (BMDCs) compared to galactosylated VMP (VMP-Gal) counterpart. Moreover, VMP-Man efficiently activated DCs and greatly facilitated MHC I Ag presentation in vitro. Vaccination of mice with VMP-Man elicited strong OVA-specific CTL responses as well as humoral immune responses. These results demonstrate that the modular core-shell polymeric nanoparticles described in this paper are superior in inducing strong and durable immune responses compared to adjuvanted protein subunit vaccines and offer therefore a flexible platform for personalized vaccines.

Preclinical evaluation of thermosensitive poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate)-grafted liposomes for cancer thermochemotherapy.

Thermosensitive liposomes grafted with cholesterol-conjugated poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate) (chol-pHPMAlac) have been developed for heat-induced release of doxorubicin (DOX). These liposomes release DOX completely during mild hyperthermia, but their interaction with blood cells and cancer cells has not been studied. Following intravenous administration, liposomes may interact with plasma proteins and various types of cells (e.g., endothelial cells, platelets, and macrophages), which would reduce their disposition in the tumor stroma. Interaction between liposomes and platelets may further cause platelet activation and thrombosis, which could lead to vascular occlusion and thromboembolic complications. The aim was to investigate DOX release kinetics in the presence of serum, stability, in vitro uptake by and toxicity to cancer cells and somatic cells, and platelet activating potential of the chol-pHPMAlac liposomes. DOX release was determined spectrofluorometrically. Liposome stability was determined in buffer and serum by dynamic light scattering and nanoparticle tracking analysis. Association with/uptake by and toxicity of empty liposomes to AML-12, HepG2 (both hepatocyte-derived cancer cells), RAW 264.7 (macrophages), and HUVEC (endothelial) cells was assayed in vitro. Platelet activation was determined by analysis of P-selectin expression and fibrinogen binding. DOPE:EPC liposomes (diameter = 135 nm) grafted with 5% chol-pHPMAlac (cloud point (CP) = 16 °C; Mn = 8.5 kDa) released less than 10% DOX at 37 °C in 30 min, whereas complete release took place at 47 °C or higher within 10 min. The size of these liposomes remained stable in buffer and serum during 24 h at 37 °C. Fluorescently labeled but DOX-lacking chol-pHPMAlac-liposomes exhibited poor association with/uptake by all cells under investigation, were not cytotoxic, and did not activate platelets in both buffered solution and whole blood. In conclusion, thermosensitive chol-pHPMAlac-grafted liposomes rapidly release DOX during mild hyperthermia. The liposomes are stable in a physiological milieu, are not taken up by cells that are encountered in an in vivo setting, and are non-antagonistic towards platelets. Chol-pHPMAlac-grafted liposomes are therefore good candidates for DOX delivery to tumors and temperature-triggered release in tumor stroma.

Post-PEGylated and crosslinked polymeric ssRNA nanocomplexes as adjuvants targeting lymph nodes with increased cytolytic T cell inducing properties.

Potent adjuvants are highly demanded for most protein and peptides based vaccine candidates in clinical development. Recognition of viral single stranded (ss)RNA by innate toll-like receptors 7/8 in dendritic cells results in a cytokine environment supportive to the establishment of long lasting antibody responses and Th1 oriented T cell immunity. To fully exploit the immunestimulatory properties of ssRNA, it needs to be adequately formulated to ensure its optimal delivery to dendritic cells in the vaccine draining lymph nodes. In the present paper, we report on the design of ssRNA nanocomplexes formed by complexation of the cationic poly(carbonic acid 2-dimethylamino-ethyl ester 1-methyl-2-(2-methacryloylamino)-ethyl ester) (pHPMA-DMAE) based polymeric carrier and ssRNA. The resulting ssRNA nanocomplexes were subsequently PEGylated through copper-free click chemistry using PEG-bicyclo[6.1.0]nonyne (PEG-BCN) and cross-linked via disulfide bonds to increase their stability. The obtained near-neutral charged PEGylated ssRNA nanocomplexes (~150 nm) combined ssRNA protection with highly efficient delivery of ssRNA to DCs in the vaccine draining lymph nodes after subcutanuously administration. When co-administrated with a model antigen (soluble ovalbumin (OVA)), ssRNA nanocomplexes were far more efficient at inducing CD8 cytolytic T cells when compared to OVA co-adminstarted with naked ssRNA. Furthermore, IgG2c antibody titers, indicative of Th1 skewed T cell responses, were >10 times increased by complexing ssRNA into the PEGylated nanocomplexes. This study highlights the potential of post-functionalizing ssRNA nanocomplexes by copper-free click chemistry and these findings indcate that this potent ssRNA adjuvant may profoundly improve the efficacy of a variety of vaccines requiring Th1-type immunity.

The Use of Magnetic Resonance Imaging for Non-Invasive Assessment of Venofer® Biodistribution in Rats.

PURPOSE: The aim of this study was to determine the potential of magnetic resonance imaging to evaluate the biodistribution of exogenous iron within 24 h after one single injection of Venofer® (iron sucrose). METHODS: Venofer® was evaluated in vitro for its ability to generate contrast in MR images. Subsequently, iron disposition was assessed in rats with MRI, in vivo up to 3 h and post mortem at 24 h after injection of Venofer®, at doses of 10- and 40 mg/kg body weight (n = 2 × 4), or saline (n = 4). RESULTS: Within 10-20 min after injection of Venofer®, transverse relaxation rates (R2) clearly increased, representative of a local increase in iron concentration, in liver, spleen and kidney, including the kidney medulla and cortex. In liver and spleen R2 values remained elevated up to 3 h post injection, while the initial R2 increase in the kidney was followed by gradual decrease towards baseline levels. Bone marrow and muscle tissue did not show significant increases in R2 values. Whole-body post mortem MRI showed most prominent iron accumulation in the liver and spleen at 24 h post injection, which corroborated the in vivo results. CONCLUSIONS: MR imaging is a powerful imaging modality for non-invasive assessment of iron distribution in organs. It is recommended to use this whole-body imaging approach complementary to other techniques that allow quantification of iron disposition at a (sub)cellular level.

Pharmacological and physical vessel modulation strategies to improve EPR-mediated drug targeting to tumors.

The performance of nanomedicine formulations depends on the Enhanced Permeability and Retention (EPR) effect. Prototypic nanomedicine-based drug delivery systems, such as liposomes, polymers and micelles, aim to exploit the EPR effect to accumulate at pathological sites, to thereby improve the balance between drug efficacy and toxicity. Thus far, however, tumor-targeted nanomedicines have not yet managed to achieve convincing therapeutic results, at least not in large cohorts of patients. This is likely mostly due to high inter- and intra-patient heterogeneity in EPR. Besides developing (imaging) biomarkers to monitor and predict EPR, another strategy to address this heterogeneity is the establishment of vessel modulation strategies to homogenize and improve EPR. Over the years, several pharmacological and physical co-treatments have been evaluated to improve EPR-mediated tumor targeting. These include pharmacological strategies, such as vessel permeabilization, normalization, disruption and promotion, as well as physical EPR enhancement via hyperthermia, radiotherapy, sonoporation and phototherapy. In the present manuscript, we summarize exemplary studies showing that pharmacological and physical vessel modulation strategies can be used to improve tumor-targeted drug delivery, and we discuss how these advanced combination regimens can be optimally employed to enhance the (pre-) clinical performance of tumor-targeted nanomedicines.

A stimuli responsive liposome loaded hydrogel provides flexible on-demand release of therapeutic agents.

Lysolipid-based thermosensitive liposomes (LTSL) embedded in a chitosan-based thermoresponsive hydrogel matrix (denoted Lipogel) represents a novel approach for the spatiotemporal release of therapeutic agents. The entrapment of drug-loaded liposomes in an injectable hydrogel permits local liposome retention, thus providing a prolonged release in target tissues. Moreover, release can be controlled through the use of a minimally invasive external hyperthermic stimulus. Temporal control of release is particularly important for complex multi-step physiological processes, such as angiogenesis, in which different signals are required at different times in order to produce a robust vasculature. In the present work, we demonstrate the ability of Lipogel to provide a flexible, easily modifiable release platform. It is possible to tune the release kinetics of different drugs providing a passive release of one therapeutic agent loaded within the gel and activating the release of a second LTSL encapsulated agent via a hyperthermic stimulus. In addition, it was possible to modify the drug dosage within Lipogel by varying the duration of hyperthermia. This can allow for adaption of drug dosing in real time. As an in vitro proof of concept with this system, we investigated Lipogels ability to recruit stem cells and then elevate their production of vascular endothelial growth factor (VEGF) by controlling the release of a pro-angiogenic drug, desferroxamine (DFO) with an external hyperthermic stimulus. Initial cell recruitment was accomplished by the passive release of hepatocyte growth factor (HGF) from the hydrogel, inducing a migratory response in cells, followed by the delayed release of DFO from thermosensitive liposomes, resulting in a significant increase in VEGF expression. This delayed release could be controlled up to 14days. Moreover, by changing the duration of the hyperthermic pulse, a fine control over the amount of DFO released was achieved. The ability to trigger the release of therapeutic agents at a specific timepoint and control dosing level through changes in duration of hyperthermia enables sequential multi-dose profiles. STATEMENT OF SIGNIFICANCE: This paper details the development of a heat responsive liposome loaded hydrogel for the controlled release of pro-angiogenic therapeutics. Lysolipid-based thermosensitive liposomes (LTSLs) embedded in a chitosan-based thermoresponsive hydrogel matrix represents a novel approach for the spatiotemporal release of therapeutic agents. This hydrogel platform demonstrates remarkable flexibility in terms of drug scheduling and sequencing, enabling the release of multiple agents and the ability to control drug dosing in a minimally invasive fashion. The possibility to tune the release kinetics of different drugs independently represents an innovative platform to utilise for a variety of treatments. This approach allows a significant degree of flexibility in achieving a desired release profile via a minimally invasive stimulus, enabling treatments to be tuned in response to changing symptoms and complications.

Nanogels for intracellular delivery of biotherapeutics.

Many biomolecules, such as proteins and genes, are presently used as therapeutics. However, their delivery to target sites inside cells is challenging because of their large molecular size, difficulties to pass cellular membranes and their susceptibility for enzymatic and chemical degradation. Nanogels, three-dimensional networks of hydrophilic polymers, are attractive carrier systems for these biotherapeutics because they protect the biologicals against degradation and, importantly, facilitate cell internalization. Furthermore, the development of responsive nanogel delivery systems has resulted in particles that release their payloads due to a certain physiological trigger inside cells, such as in the cytosol or endocytic compartments. This paper reviews and discusses the use of nanogels, with special emphasis on biologically responsive systems, for intracellular delivery of biotherapeutics.

Nanomedicines for advanced cancer treatments: Transitioning towards responsive systems.

The development of nanomedicines for the treatment of cancer focuses on the local targeted delivery of chemotherapeutic drugs to enhance drug efficacy and reduce adverse effects. The nanomedicines which are currently approved for clinical use are mainly successful in terms of improved bioavailability and tolerability but do not necessarily increase drug performance. Therefore, there is a need for improved drug carrier systems which are able to deliver high doses of anti-cancer drugs to the tumor. Stimuli responsive carriers are promising candidates since drug release can be triggered locally in the tumor via internal (i.e. pH, redox potential, metabolite or enzyme concentration) or external (i.e. heat, ultrasound, light, magnetic field) stimuli. This review summarizes the recent progress in the transition towards stimuli responsive nanomedicines (i.e. liposomes, polymeric micelles, nanogels and mesoporous silica nanoparticles) and other therapy modalities that are currently developed in the fight against cancer like the application of ultrasound, tumor normalization and phototherapy. Furthermore, the potential role of image guided drug delivery in the development of new nanomedicines and its clinical application is discussed.

Polymeric nanoparticles for co-delivery of synthetic long peptide antigen and poly IC as therapeutic cancer vaccine formulation.

The aim of the current study was to develop a cancer vaccine formulation for treatment of human papillomavirus (HPV)-induced malignancies. Synthetic long peptides (SLPs) derived from HPV16 E6 and E7 oncoproteins have been used for therapeutic vaccination in clinical trials with promising results. In preclinical and clinical studies adjuvants based on mineral oils (such as incomplete Freund's adjuvant (IFA) and Montanide) are used to create a sustained release depot at the injection site. While the depot effect of mineral oils is important for induction of robust immune responses, their administration is accompanied with severe adverse and long lasting side effects. In order to develop an alternative for IFA family of adjuvants, polymeric nanoparticles (NPs) based on hydrophilic polyester (poly(d,l lactic-co-hydroxymethyl glycolic acid) (pLHMGA)) were prepared. These NPs were loaded with a synthetic long peptide (SLP) derived from HPV16 E7 oncoprotein and a toll like receptor 3 (TLR3) ligand (poly IC) by double emulsion solvent evaporation technique. The therapeutic efficacy of the nanoparticulate formulations was compared to that of HPV SLP+poly IC formulated in IFA. Encapsulation of HPV SLP antigen in NPs substantially enhanced the population of HPV-specific CD8+ T cells when combined with poly IC either co-encapsulated with the antigen or in its soluble form. The therapeutic efficacy of NPs containing poly IC in tumor eradication was equivalent to that of the IFA formulation. Importantly, administration of pLHMGA nanoparticles was not associated with adverse effects and therefore these biodegradable nanoparticles are excellent substitutes for IFA in cancer vaccines.

Holmium-lipiodol-alginate microspheres for fluoroscopy-guided embolotherapy and multimodality imaging.

Embolotherapy is a minimally invasive transcatheter technique aiming at reduction or complete obstruction of the blood flow by infusion of micro-sized particles in order to induce tumor regression. A major drawback of the current commercially available and clinically used microspheres is that they cannot be detected in vivo with medical imaging techniques, impeding intra- and post-procedural feedback. It can be expected that real-time monitoring of microsphere infusion and post-procedural imaging will result in better predictability and higher efficacy of the treatment. In this study, a novel microsphere formulation has been developed that can be visualized with fluoroscopy, X-ray computed tomography (CT) and magnetic resonance imaging (MRI). The microspheres were prepared with the JetCutter technique and consist of alginate (matrix-forming polymer), holmium (cross-linking and MRI contrast agent), lipiodol (radiopaque contrast agent) and Pluronic F-68 (surfactant). The mean size (±SEM) of the hydrated holmium-lipiodol-alginate microspheres (Ho-lip-ams) was 570±12 µm with a holmium content of 0.38±0.01% (w/w). Stability studies showed that the microspheres remained intact during incubation for two weeks in fetal calf serum (FCS) at 37 °C. The inclusion of lipiodol in the microspheres rendered excellent visualization capabilities for fluoroscopy and CT, whereas the holmium ions, which keep the alginate network together, also allow MR imaging. In this study it was shown that single sphere detection was possible by fluoroscopy, CT and MRI. The Ho-lip-ams were visualized in real-time, during infusion in a porcine kidney using fluoroscopy, and post-procedural, the deposition of the microspheres was examined with fluoroscopy, (cone beam rotational) CT and MRI. The different imaging modalities showed similar deposition patterns of the microspheres within the organ. The combination of intra-procedural visualization, multimodality imaging for patient follow-up and the possibility of quantification offers a new and promising method for more safe, efficient and successful embolization treatment.

Curcumin nanoformulations: a review of pharmaceutical properties and preclinical studies and clinical data related to cancer treatment.

Curcumin, a natural yellow phenolic compound, is present in many kinds of herbs, particularly in Curcuma longa Linn. (turmeric). It is a natural antioxidant and has shown many pharmacological activities such as anti-inflammatory, anti-microbial, anti-cancer, and anti-Alzheimer in both preclinical and clinical studies. Moreover, curcumin has hepatoprotective, nephroprotective, cardioprotective, neuroprotective, hypoglycemic, antirheumatic, and antidiabetic activities and it also suppresses thrombosis and protects against myocardial infarction. Particularly, curcumin has demonstrated efficacy as an anticancer agent, but a limiting factor is its extremely low aqueous solubility which hampers its use as therapeutic agent. Therefore, many technologies have been developed and applied to overcome this limitation. In this review, we summarize the recent works on the design and development of nano-sized delivery systems for curcumin, including liposomes, polymeric nanoparticles and micelles, conjugates, peptide carriers, cyclodextrins, solid dispersions, lipid nanoparticles and emulsions. Efficacy studies of curcumin nanoformulations using cancer cell lines and in vivo models as well as up-to-date human clinical trials are also discussed.

Nanomedicines for inflammatory arthritis: head-to-head comparison of glucocorticoid-containing polymers, micelles, and liposomes.

As an emerging research direction, nanomedicine has been increasingly utilized to treat inflammatory diseases. In this head-to-head comparison study, four established nanomedicine formulations of dexamethasone, including liposomes (L-Dex), core-cross-linked micelles (M-Dex), slow releasing polymeric prodrugs (P-Dex-slow), and fast releasing polymeric prodrugs (P-Dex-fast), were evaluated in an adjuvant-induced arthritis rat model with an equivalent dose treatment design. It was found that after a single i.v. injection, the formulations with the slower drug release kinetics (i.e., M-Dex and P-Dex-slow) maintained longer duration of therapeutic activity than those with relatively faster drug release kinetics, resulting in better joint protection. This finding will be instructional in the future development and optimization of nanomedicines for the clinical management of rheumatoid arthritis. The outcome of this study also illustrates the value of such head-to-head comparison studies in translational nanomedicine research.

Drug targeting to tumors: principles, pitfalls and (pre-) clinical progress.

Many different systems and strategies have been evaluated for drug targeting to tumors over the years. Routinely used systems include liposomes, polymers, micelles, nanoparticles and antibodies, and examples of strategies are passive drug targeting, active drug targeting to cancer cells, active drug targeting to endothelial cells and triggered drug delivery. Significant progress has been made in this area of research both at the preclinical and at the clinical level, and a number of (primarily passively tumor-targeted) nanomedicine formulations have been approved for clinical use. Significant progress has also been made with regard to better understanding the (patho-) physiological principles of drug targeting to tumors. This has led to the identification of several important pitfalls in tumor-targeted drug delivery, including I) overinterpretation of the EPR effect; II) poor tumor and tissue penetration of nanomedicines; III) misunderstanding of the potential usefulness of active drug targeting; IV) irrational formulation design, based on materials which are too complex and not broadly applicable; V) insufficient incorporation of nanomedicine formulations in clinically relevant combination regimens; VI) negligence of the notion that the highest medical need relates to metastasis, and not to solid tumor treatment; VII) insufficient integration of non-invasive imaging techniques and theranostics, which could be used to personalize nanomedicine-based therapeutic interventions; and VIII) lack of (efficacy analyses in) proper animal models, which are physiologically more relevant and more predictive for the clinical situation. These insights strongly suggest that besides making ever more nanomedicine formulations, future efforts should also address some of the conceptual drawbacks of drug targeting to tumors, and that strategies should be developed to overcome these shortcomings.

Characterization of potent anticholinesterase plant oil based microemulsion.

In the present study, essential oils of three edible Thai plants, Cymbopogon citratus (Gramineae), Citrus hystrix (Rutaceae) and Zingiber cassumunar (Zingiberaceae) were comparatively tested for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities using Ellman's colorimetric method. C. citratus oil exhibited the highest activity with IC(50) values of 0.34±0.07µl/ml and 2.14±0.18µl/ml against BChE and AChE activity, respectively. It was further investigated whether microemulsions of this oil could be obtained. The effects of type of surfactant and co-surfactant as well as pH and ionic strength on the phase behavior of the oil/water system were investigated. Brij 97, Triton X-114, Tween 20 and Tween 85 were employed as surfactant whereas ethanol and hexanol were used as cosurfactants. The size analysis, electrical conductivity measurements and cholinesterase inhibition assays were done in selected microemulsion. The results revealed that the type and concentration of surfactant and co-surfactant exhibited a distinct influence on the C. citratus oil microemulsions. Moreover, the inhibitory activities of the microemulsion formulation were remarkable.

Permeation of volatile compounds through starch films.

The aim of this study was to gain insight into the factors that affect the permeation of volatiles through starch films. These films were obtained by casting gelatinized starch/water/glycerol mixtures. The films were dried and conditioned under different conditions (temperature and relative humidity) resulting in films that vary in the degree of starch crystallinity and glycerol and water content. The permeation of two model volatiles (carvone and diacetyl) at 20 degrees C and at 30, 60, or 90% relative humidity (RH) was analyzed gravimetrically. Further, the solubility of the two model compounds (under conditions where the permeation experiments were carried out) was determined. From the obtained permeation and solubility data, the diffusion coefficients of these compounds in the different starch films were calculated. The crystallinity in the starch films increased with increasing water content of the films during preparation. The water content of the resulting films in turn increased with increasing glycerol and when the films were exposed to a higher RH during drying or conditioning. For films with the same composition, the flux for diacetyl was greater than for carvone. The solubilities of diacetyl and carvone were slightly dependent on the properties of the films. It was found that with increasing starch crystallinity the diffusion coefficient for both compounds decreases, which is probably due to the impermeability of starch crystallites. Interestingly, in films with about the same extent of crystallinity, the diffusion can be described with the free volume model, with water and glycerol determining the amount of free volume.

A novel family of L-amino acid-based biodegradable polymer-lipid conjugates for the development of long-circulating liposomes with effective drug-targeting capacity.

The objective of this study was to develop biodegradable polypeptide-lipid conjugates for the design of polymer-coated long-circulating liposomes (LCL). Lipid conjugates of poly(hydroxyalkyl L-asparagine/L-glutamine) were synthesized and incorporated into 0.15 microm dipalmitoyl phosphatidylcholine (DPPC)-cholesterol liposomes. Circulation times and biodistribution were assessed in rats using a radioactive lipid marker. Evaluation of the therapeutic activity of prednisolone phosphate loaded in 0.1 microm PHEA-DPPC-cholesterol liposomes in a rat experimental arthritis model was performed to demonstrate the drug-targeting potential of the polymer-coated liposomes. Coating of liposomes with poly(hydroxyethyl L-asparagine) (PHEA) and poly(hydroxyethyl L-glutamine) (PHEG) extended the circulation half-life to a similar extent as poly(ethylene glycol) (PEG), which is normally used for the preparation of LCL. Glutamine polymers with a hydroxypropyl or a hydroxybutyl group instead of hydroxyethyl group also yield prolonged circulation, however, not to the same extent as PHEA/G. The pharmacokinetic properties of PHEA-liposomes were independent of the lipid dose even at very low lipid doses of around 50 nmol per rat. PLP was successfully entrapped in PHEA-liposomes. These liposomes were shown to be stable in the circulation and equally effective in rat experimental arthritis as PLP encapsulated in PEG-liposomes. PHEA and PHEG are attractive alternative polymers for the design of LCL: their performance is similar to that of PEG-liposomes but they have the advantage of being biodegradable.