Targeted drug delivery via folate receptors

Targeted delivery via selective cellular markers can potentially increase the efficacy and reduce the toxicity of therapeutic agents. The folate receptor (FR) has two glycosyl phosphatidylinositol (GPI)-anchored isoforms, α and β. FR-α expression is frequently amplified in epithelial cancers, whereas FR-β expression is found in myeloid leukemia and activated macrophages associated with chronic inflammatory diseases. Conjugates of folic acid and anti-FR antibodies can be taken up by cancer cells via receptor-mediated endocytosis, thus providing a mechanism for targeted delivery to FR+ cells. The aim of this article is to provide a brief overview of applications of FR targeting in drug delivery, with an emphasis on the strategy of using folate as a targeting ligand. In order to do this, recent literature is surveyed on targeted delivery via both FR sub-types, as well as new findings on selective receptor upregulation in the targeted cells. A wide variety of molecules and drug carriers, including imaging agents, chemotherapeutic agents, oligonucleotides, proteins, haptens, liposomes, nanoparticles and gene transfer vectors have been conjugated to folate and evaluated for FR-targeted delivery. Substantial targeting efficacy has been found both in vitro and in vivo. In addition, mechanisms and methods for selective FR upregulation have been uncovered, which might enhance the effectiveness of the FR-targeted delivery strategy. FR-α serves as a useful marker for cancer, whereas FR-β serves as a marker for myeloid leukemia and chronic inflammatory diseases. FR-targeted agents have shown promising efficacy in preclinical models and significant potential for future clinical application in a wide range of diseases.     

Targeted drug delivery via folate receptors

Targeted delivery via selective cellular markers can potentially increase the efficacy and reduce the toxicity of therapeutic agents. The folate receptor (FR) has two glycosyl phosphatidylinositol (GPI)-anchored isoforms, alpha and beta. FR-alpha expression is frequently amplified in epithelial cancers, whereas FR-beta expression is found in myeloid leukemia and activated macrophages associated with chronic inflammatory diseases. Conjugates of folic acid and anti-FR antibodies can be taken up by cancer cells via receptor-mediated endocytosis, thus providing a mechanism for targeted delivery to FR+ cells. The aim of this article is to provide a brief overview of applications of FR targeting in drug delivery, with an emphasis on the strategy of using folate as a targeting ligand. In order to do this, recent literature is surveyed on targeted delivery via both FR sub-types, as well as new findings on selective receptor upregulation in the targeted cells. A wide variety of molecules and drug carriers, including imaging agents, chemotherapeutic agents, oligonucleotides, proteins, haptens, liposomes, nanoparticles and gene transfer vectors have been conjugated to folate and evaluated for FR-targeted delivery. Substantial targeting efficacy has been found both in vitro and in vivo. In addition, mechanisms and methods for selective FR upregulation have been uncovered, which might enhance the effectiveness of the FR-targeted delivery strategy. FR-alpha serves as a useful marker for cancer, whereas FR-beta serves as a marker for myeloid leukemia and chronic inflammatory diseases. FR-targeted agents have shown promising efficacy in preclinical models and significant potential for future clinical application in a wide range of diseases.     

A folate receptor-targeted liposomal formulation for paclitaxel

A novel liposomal formulation of paclitaxel targeting the folate receptor (FR) was synthesized and characterized. This formulation was designed to overcome vehicle toxicity associated with the traditional Cremophor EL-based formulation and to provide the added advantages of prolonged systemic circulation time and selective targeting of the FR, which is frequently overexpressed on epithelial cancer cells. The formulation had the composition of dipalmitoyl phosphatidylcholine/dimyristoyl phosphatidylglycerol/monomethoxy-polyethylene glycol (PEG)2000-distearoyl phosphatidylethanolamine/folate-PEG3350-distearoyl phosphatidylethanolamine (DPPC/DMPG/mPEG-DSPE/folate-PEG-DSPE) at molar ratios of (85.5:9.5:4.5:0.5) and a drug-to-lipid molar ratio of 1:33. The liposomes were prepared by polycarbonate membrane extrusion. The mean particle size of the liposomes was 97.1 nm and remained stable for at least 72 h at 4 degrees C. FR-targeted liposomes of the same lipid composition entrapping calcein were shown to be efficiently taken up by KB oral carcinoma cells, which are highly FR+. FR-targeted liposomes containing paclitaxel showed 3.8-fold greater cytotoxicity compared to non-targeted control liposomes in KB cells. Plasma clearance profiles of paclitaxel in the liposomal formulations were then compared to paclitaxel in Cremophor EL formulation. The liposomal formulations showed much longer terminal half-lives (12.33 and 14.23 h for FR-targeted and non-targeted liposomes, respectively) than paclitaxel in Cremophor EL (1.78 h). In conclusion, the paclitaxel formulation described in this study has substantial stability and favorable pharmacokinetic properties. The FR-targeted paclitaxel formulation is potentially useful for treatment of FR+ tumors and warrants further investigation.     

Tumor-selective targeted delivery of genes and antisense oligodeoxyribonucleotides via the folate receptor

Gene therapy is a promising approach for the treatment of cancer. The main obstacle for the clinical application of cancer gene therapy is the lack of gene transfer vectors that are safe, efficacious, and tumor-selective. In recent years, targeted gene delivery through cellular receptors, using either viral or nonviral vectors, is emerging as a novel approach to enhance the efficacy of tumor-selective gene delivery. The folate receptor (FR), which is absent in most normal tissues and elevated in over 90% of ovarian carcinomas and at a high frequency in other human malignancies, is an attractive tumor-selective target. FR-targeted vectors include folate-derivatized adenoviruses, cationic polymers, cationic liposomes, and pH-sensitive liposomes. In addition, FR-targeted liposomes have been evaluated for the targeted delivery of antisense oligodeoxyribonucleotides (ODNs). These vectors have invariably shown impressive FR-selectivity in cell culture assays and, in addition, shown promising tumor-specific gene transfer activity in several in vivo models. There are important theoretical advantages for FR-targeted vectors over traditional non-targeted vectors in therapeutic gene and oligodeoxyribonucleotides delivery in vivo to cancer cells. Further preclinical characterization of these vectors is, therefore, warranted to determine their potential utility in cancer gene therapy.     

Cholesterol as a bilayer anchor for PEGylation and targeting ligand in folate-receptor-targeted liposomes

Phospholipids have been extensively evaluated as an anchor for both PEGylation and receptor-targeting in liposomal formulations. However, cholesterol, another important component in biomembranes, has not been fully investigated as an alternative anchor. In this study, the potential role of cholesterol for anchoring PEG and folate was investigated. Cholesterol derivatives were synthesized for PEGylation (mPEG-cholesterol) and folate receptor (FR) targeting (folate-PEG-cholesterol) and incorporated into the bilayer of FR-targeted liposomal doxorubicin. The colloidal stability of these cholesterol derivative-containing liposomes was superior to non-PEGylated liposomes, indicating that steric barrier provided by mPEG-cholesterol can efficiently inhibit aggregation of liposomes. FR-targeting activity of these liposomes was demonstrated by in vitro cell-binding studies on FR-overexpressing KB cells. In addition, in vivo circulation of cholesterol-anchored liposomes was prolonged compared to non-PEGylated liposomes. These studies suggest that cholesterol is a viable bilayer anchor for synthesis of PEGylated and FR-targeted liposomes.     

Heterogeneous liposome membranes with pH-triggered permeability enhance the in vitro antitumor activity of folate-receptor targeted liposomal doxorubicin

The killing efficacy of doxorubicin from liposome-based delivery carriers has been shown to correlate strongly with its intracellular trafficking and, in particular, its fast and extensive release from the delivery carrier. However, previously explored pH-triggered mechanisms that were designed to become activated during liposome endocytosis have also been shown to interfere with the liposome stability in vivo. We have designed pH-triggered gel-phase liposomes with heterogeneous membranes for the delivery of doxorubicin. These liposomes are triggered to form "leaky" interfacial boundaries between gel-gel phase separated domains on the membrane bilayer with lowering pH. The pH-triggered mechanism does not compromise liposome stability in vivo and results in superior in vitro killing efficacy of delivered doxorubicin when liposomes are endocytosed by a clathrin-mediated pathway. In the present work, we evaluate the general applicability of these liposomes when targeted to the folate receptor (FR) of KB cancer cells in vitro and become endocytosed by a less acidic pathway: the caveolae pathway. FR-targeting liposomes exhibit almost 50% decrease in cell association for increase in liposome size from 120 to 280 nm in diameter after relatively short incubation times (up to 4 h). The fraction of internalized vesicles, however, is approximately 60% of the cell associated vesicles independent of their size. Our findings demonstrate that, for the same doxorubicin uptake per cancer cell, the killing effect of doxorubicin delivered by pH-triggered lipid vesicles is greater (IC(50) = 0.032 mM for a 6 h incubation) than when delivered by a conventional non-pH-responsive composition (IC(50) = 0.194 mM). These findings suggest higher bioexposure of cells to the therapeutic agent possibly via faster and more extensive release from the carrier. Animal studies of FR-targeting non-pH-responsive liposomal doxorubicin report stronger therapeutic potential for the targeted approach relative to nontargeted liposomes and to free doxorubicin. The findings of the present study suggest that the targeted pH-triggered liposomes could potentially further enhance the therapeutic outcomes of doxorubicin in vivo.     

Folate receptor–targeted quantum dot liposomes as fluorescence probes

In this study, the preparation of the novel imaging agents, folate receptor (FR)–targeted liposomes encapsulating hydrophilic CdTe quantum dots (QDs), and their use as luminescence probes for live cell imaging are reported. Hydrophilic CdTe QDs were directly synthesized in the water phase, and FR-targeted QD liposomes were prepared by hydrating the lipid thin film with CdTe suspension. Formulations were characterized by UV-visible and fluorescent measurements, liposomal particle size, and zeta potential. The targeting and imaging ability of FR-targeted liposomes were investigated against the human uterine cervix cancer cell line (HeLa). Furthermore, the cytotoxicity of QD liposomes was evaluated by HeLa cells incubated with FR-targeted QD liposomes, nontargeted QD liposomes, and free QDs. The results showed that FR-targeted QD liposomes were spherically shaped with high fluorescence yield, excellent photochemical stability, good cancer targeting, and minimal cytotoxicity. The average size of FR-targeted fluorescence liposomes was ~105?nm, and their size distribution was rather narrow. After storage at 4°C for 11 months, QD liposomes maintained similar size and did not show any leakage of QDs. FR-targeted CdTe QD liposomes, which can target tumor cells via FR-mediated endocytosis, would become an attractive probe for tumor cell or tissue imaging for a long-time monitoring.     

Targeted thermosensitive liposomes: an attractive novel approach for increased drug delivery to solid tumors

Introduction: Currently available chemotherapy is hampered by a lack in tumor specificity and resulting toxicity. Small and long-circulating liposomes can preferentially deliver chemotherapeutic drugs to tumors upon extravasation from tumor vasculature. Although clinically used liposomal formulations demonstrated significant reduction in toxicity, enhancement of therapeutic activity has not fully met expectations.

Areas covered: Low drug bioavailability from liposomal formulations and limited tumor accumulation remain major challenges to further improve therapeutic activity of liposomal chemotherapy. The aim of this review is to highlight strategies addressing these challenges. A first strategy uses hyperthermia and thermosensitive liposomes to improve tumor accumulation and trigger liposomal drug bioavailability. Image-guidance can aid online monitoring of heat and drug delivery and further personalize the treatment. A second strategy involves tumor-specific targeting to enhance drug delivery specificity and drug internalization. In addition, we review the potential of combinations of the two in one targeted thermosensitive-triggered drug delivery system.

Expert opinion: Heat-triggered drug delivery using thermosensitive liposomes as well as the use of tumor vasculature or tumor cell-targeted liposomes are both promising strategies to improve liposomal chemotherapy. Preclinical evidence has been encouraging and both strategies are currently undergoing clinical evaluation. A combination of both strategies rendering targeted thermosensitive liposomes (TTSL) may appear as a new and attractive approach promoting tumor drug delivery.     

Recent advances in liposome technologies and their applications for systemic gene delivery

The recent clinical successes experienced by liposomal drug delivery systems stem from the ability to produce well-defined liposomes that can be composed of a wide variety of lipids, have high drug-trapping efficiencies and have a narrow size distribution, averaging less than 100 nm in diameter. Agents that prolong the circulation lifetime of liposomes, enhance the delivery of liposomal drugs to specific target cells, or enhance the ability of liposomes to deliver drugs intracellularly can be incorporated to further increase the therapeutic activity. The physical and chemical requirements for optimum liposome drug delivery systems will likely apply to lipid-based gene delivery systems. As a result, the development of liposomal delivery systems for systemic gene delivery should follow similar strategies.     

Role of formulation composition in folate receptor-targeted liposomal doxorubicin delivery to acute myelogenous leukemia cells

Targeted drug delivery has the potential to improve the efficacy of a therapeutic agent while reducing its side effects. The folate receptor type beta (FR-beta) is a cell surface marker selectively expressed in the leukemic cells of approximately 70% of acute myeloid leukemia (AML) patients. Upregulation of FR-beta may also be selectively induced in AML cells by treatment with all-trans-retinoic acid (ATRA). In this study, the role of formulation composition in FR-targeted liposomal doxorubicin (DOX) delivery to AML cells was investigated. Liposomal formulations with a variable percentage of folate-polyethylene glycol distearoyl phosphatidylethanolamine (f-PEG-DSPE) were synthesized and evaluated for FR-beta-targeted DOX delivery in MV4-11 AML cells in vitro and for their pharmacokinetic properties in vivo. The formulation containing 0.5 mol % f-PEG-DSPE exhibited the highest efficiency of cellular uptake and in vitro cytotoxicity, as well as a long systemic circulation time in mice. In MV4-11 cells, the binding and cytotoxicity of FR-targeted liposomal DOX based on this formulation was also enhanced by ATRA-induced FR-beta upregulation.     

Therapeutic efficacy of the combination of doxorubicin-loaded liposomes with inertial cavitation generated by confocal ultrasound in AT2 Dunning rat tumour model

Abstract

The combination of liposomal doxorubicin (DXR) and confocal ultrasound (US) was investigated for the enhancement of drug delivery in a rat tumour model. The liposomes, based on the unsaturated phospholipid dierucoylphosphocholine, were designed to be stable during blood circulation in order to maximize accumulation in tumour tissue and to release drug content upon US stimulation. A confocal US setup was developed for delivering inertial cavitation to tumours in a well-controlled and reproducible manner. In vitro studies confirm drug release from liposomes as a function of inertial cavitation dose, while in vivo pharmacokinetic studies show long blood circulation times and peak tumour accumulation at 24–48?h post intravenous administration. Animals injected 6?mg kg^?1 liposomal DXR exposed to US treatment 48?h after administration show significant tumour growth delay compared to control groups. A liposomal DXR dose of 3?mg kg^?1, however, did not induce any significant therapeutic response. This study demonstrates that inertial cavitation can be generated in such a fashion as to disrupt drug carrying liposomes which have accumulated in the tumour, and thereby increase therapeutic effect with a minimum direct effect on the tissue. Such an approach is an important step towards a therapeutic application of cavitation-induced drug delivery and reduced chemotherapy toxicity.     

Design and development of folate appended liposomes for enhanced delivery of 5-FU to tumor cells

Folate appended sterically-stabilized liposomes (FA-SL) were investigated for tumor targeting. Liposomes were prepared using HSPC, cholesterol and FA-polyethylene glycol (PEG)-SA. The liposomes with polyethylene glycol (PEG) without folic acid which has similar lipid composition were used for comparison. Liposomal preparations were characterized for shape, size and percent entrapment. The average size of liposomes was found to be in range 124-163 nm and maximum drug entrapment was found to be 34.2-40.3%. In vitro drug release from the formulations is obeying fickian release kinetics. Cellular uptake and IC(50) values of the FR-targeted formulation were determined in vitro in FR (+) B16F10 melanoma cells. In vitro cell binding of FA-SL exhibits 11-folds higher binding to B16F10 melanoma cells in comparison to SL. In vivo cytotoxicy assay on FR targeted liposomes gave IC(50) of 1.87 microM and non-targeted liposomes gave IC(50) of 4.02 microM. In therapeutic experiments 5-fluorouracil (5-FU), SL and FA-SL were administered at the dose of 10 mg 5-FU/kg body weight to B16F10 tumor bearing Balb/c mice. Administration of FA-SL formulation results in effective reduction in tumor growth as compared with free 5-FU and SL. Results indicate that folic acid appended SL bearing 5-FU are significantly (P < 0.01) active against primary tumor and metastasis than non-targeted sterically-SL. Thus, it could be concluded that folate coupled liposomal formulations enhanced drug uptake by tumor cells.     

Molecular targeting of liposomal nano-particles to lymphatic system

Conventional liposomal drug delivery has been associated with obvious limitations, such as a rapid absorption by the recticulo-endothelial system in the liver and spleen, a short circulation time and a low therapeutic efficacy. Various modifications of liposomal drugs have been developed to prolong the duration of actions of the drugs at target sites, reduce its adverse effects and increase therapeutic index of drugs such as polymeric conjugation and polymeric fixation on the surface of a liposome. The lymphatic system is an important highway to spread the metastasis of most human cancers including breast, colon, and lung, ovarian and prostate. To eradicate those metastatic cancer cells from the lymphatic system, several efforts have been made to develop new and efficient lymphatic targeting drug delivery systems in order to achieve a high initial lymphatic uptake and lymph node localization. Recently, molecule targeting of liposome to lymphatic system may enhance therapeutic efficacy by improving the initial lymphatic uptake and the lymph nodal retention of liposomes such as the ligand-receptor and antibodies binding on the surface of liposome. This article aims to review the emerging liposomal drug, which is targeting the lymphatic system. The significant factors associated with targeting liposomal drugs will also be discussed in more detail in this review.     

Antitumor Activity of Folate Receptor-Targeted Liposomal Doxorubicin in a KB Oral Carcinoma Murine Xenograft Model

Purpose. The expression of folate receptor (FR) is amplified in many types of human cancers. Previously, FR-targeted liposomal doxorubicin (f-L-DOX) has been shown to exhibit superior and selective cytotoxicity against FR(+) tumor cells in vitro compared to nontargeted liposomal doxorubicin (L-DOX). This study further investigates f-L-DOX for its antitumor efficacy in vivo using a murine tumor xenograft model. Methods. F-L-DOX composed of DSPC/cholesterol/PEG-DSPE/folate-PEG-DSPE (65:31:3.5:0.5, mole/mole) was prepared by polycarbonate membrane extrusion followed by remote loading of DOX. Athymic mice on a folate-free diet were engrafted with FR(+) KB cells. Two weeks later, these mice were treated with f-L-DOX, L-DOX, or free DOX in a series of six injections (given intraperitoneally on every fourth day at 10 mg/kg DOX) and monitored for tumor growth and animal survival. The plasma clearance profiles of the DOX formulations and the effect of dietary folate on plasma folate concentration were also analyzed. Results. Plasma folate level remained in the physiologic range relative to that in humans. F-L-DOX exhibited an extended systemic circulation time similar to that of L-DOX. Mice that received f-L-DOX showed greater tumor growth inhibition and a 31% higher (p < 0.01) increase in lifespan compared to those that received L-DOX. Meanwhile, free DOX given at the same dose resulted in significant toxicity and was less effective in prolonging animal survival. Conclusions. FR-targeted liposomes are a highly efficacious vehicle for in vivo delivery of anticancer agents and have potential application in the treatment of FR(+) solid tumors.     

Targeting Anticancer Drugs to Tumor Vasculature Using Cationic Liposomes

Liposomal drug delivery systems improve the therapeutic index of chemotherapeutic agents, and the use of cationic liposomes to deliver anticancer drugs to solid tumors has recently been recognized as a promising therapeutic strategy to improve the effectiveness of conventional chemotherapeutics. This review summarizes the selective targeting of cationic liposomes to tumor vasculature, the merits of incorporating the polymer polyethylene-glycol (PEG), and the impact of the molar percent of the cationic lipid included in cationic liposomes on liposomal targeting efficacy. In addition, the discussion herein includes the therapeutic benefit of a dual targeting approach, using PEG-coated cationic liposomes in vascular targeting (of tumor endothelial cells), and tumor targeting (of tumor cells) of anticancer drugs. Cationic liposomes have shown considerable promise in preclinical xenograft models and are poised for clinical development.     

Liposome-based approaches to overcome anticancer drug resistance.

Drug resistance remains an important obstacle towards better outcomes in the treatment of cancer. One general approach to overcome this problem has been to inhibit specific resistance mechanisms, such as P-glycoprotein (PGP)-mediated drug efflux, using small molecule agents or other therapeutic strategies. Alternatively, drug delivery approaches using liposomes or other carriers can in principle target drugs to tumor tissue, tumor cells, or even compartments within tumor cells. By increasing bioavailability of drugs at sites of action, these approaches may provide therapeutic advantages, including enhanced efficacy against resistant tumors. Current liposomal anthracyclines have achieved clinical use in cancer treatment by providing efficient encapsulation of drug in stable and non-reactive carriers, and there is evidence indicating potential benefit in some clinical settings involving resistant tumors. Other liposome-based strategies include constructs designed to be taken up by tumor cells, as well as further modifications to allow triggered drug release. These approaches seek to overcome drug resistance by more efficient delivery to tumor cells, and in some cases by concomitant avoidance or inhibition of drug efflux mechanisms. Newer agents employ molecular targeting, such as immunoliposomes using antibody-directed binding and internalization. These agents selectively deliver drug to tumor cells, can efficiently internalize for intracellular drug release, and can potentially enhance both efficacy and safety.     

Liposomes in the treatment of infectious diseases

Phospholipids and other polar lipids can form liposomes and similar colloidal particles that can be used as drug carrier systems. The potential of liposomal delivery systems to increase the therapeutic index (efficacy to safety ratio) of clinically important drugs has been realised with the recent approval of liposomal oncologic and antifungal drugs. The application of liposomes to the treatment of infectious diseases initially focused on intracellular pathogens, based on the natural targeting of liposomes to phagocytic cells and on the antifungal drug amphotericin B, based on its unique affinity for lipids. Recent studies with small, low-clearance liposomes have shown that more specialised formulations may provide benefits over simpler ‘first generation’ liposomes for the treatment of infectious diseases, including prolonged residence in plasma, increased tissue exposure and targeting to sites of infection. These improved biopharmaceutical properties have been associated with both curative and prophylactic activity against a range of non-intracellular pathogens, including Staphylococcus and Klebsiella. These and other highly engineered liposome formulations may provide effective delivery systems for specific antibacterial, antifungal and antiviral indications in the future. Adequate patent protection will be crucial in fully exploiting these advanced liposome technologies and in maintaining market share for liposomal products. This review discusses some of the patent issues related to liposomes and their use in the treatment of infectious diseases.     

Translocation of liposomes into cancer cells by cell-penetrating peptides penetratin and tat: a kinetic and efficacy study

Unlike conventional liposomes, sterically stabilized liposomes, with their smaller volume of distribution and reduced clearance, preferentially convey encapsulated drugs into tumor sites. Despite these improvements, intracellular delivery is hampered by the stable drug retention of the liposomes, which diminishes the efficacy of the liposomal drug. To facilitate uptake of liposomal drugs into cells, two cell-penetrating peptides, penetratin (PEN) and TAT, derived from the HIV-1 TAT protein, were studied. In contrast to control peptides, both TAT and PEN enhanced the translocation efficiency of liposomes in proportion to the number of peptides attached to the liposomal surface. A peptide number of as few as five could enhance the intracellular delivery of liposomes. The kinetics of uptake was peptide- and cell-type dependent. Intracellular accumulation of TAT-liposomes increased with incubation time, but PEN-liposomes peaked at 1 h and then declined gradually. After treatment with 1 microg/ml doxorubicin equivalents of liposome for 2 h, TAT increased the doxorubicin uptake of A431 cells by 12-fold. However, the improvement of uptake of liposomal doxorubicin was not reflected by cytotoxicity in vitro or tumor control in vivo. Our results demonstrated that merely adding CPP to a liposome encapsulating anticancer drug was inadequate in improving its antitumor activity. An additional approach to enhance the intracellular release of the encapsulated drug is obviously necessary.     

Liposomal drug formulations in the treatment of rheumatoid arthritis

Liposomes have been extensively investigated as drug delivery systems in the treatment of rheumatoid arthritis (RA). Low bioavailability, high clearance rates and limited selectivity of several important drugs used for RA treatment require high and frequent dosing to achieve sufficient therapeutic efficacy. However, high doses also increase the risk for systemic side effects. The use of liposomes as drug carriers may increase the therapeutic index of these antirheumatic drugs. Liposomal physicochemical properties can be changed to optimize penetration through biological barriers and retention at the site of administration, and to prevent premature degradation and toxicity to nontarget tissues. Optimal liposomal properties depend on the administration route: large-sized liposomes show good retention upon local injection, small-sized liposomes are better suited to achieve passive targeting. PEGylation reduces the uptake of the liposomes by liver and spleen, and increases the circulation time, resulting in increased localization at the inflamed site due to the enhanced permeability and retention (EPR) effect. Additionally liposomal surfaces can be modified to achieve selective delivery of the encapsulated drug to specific target cells in RA. This review gives an overview of liposomal drug formulations studied in a preclinical setting as well as in clinical practice. It covers the use of liposomes for existing antirheumatic drugs as well as for new possible treatment strategies for RA. Both local administration of liposomal depot formulations and intravenous administration of passively and actively targeted liposomes are reviewed.