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.     

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.     

Vascular targeting of doxorubicin using cationic liposomes

Tumor vessel has been recognized as an important target for anticancer therapy. Cationic liposomes have been shown to selectively target tumor endothelial cells, thus can potentially be used as a carrier for chemotherapy agents. In this study, cationic liposomes containing 20 mol% cationic lipid dimethyl dioctadecyl ammonium bromide (DDAB) and loaded with doxorubicin (DOX) were prepared and characterized. The cationic liposomal DOX showed 10.8 and 9.1 times greater cytotoxicity than control PEGylated liposomal DOX in KB oral carcinoma and L1210 murine lymphocytic leukemia cells, and 7.7- and 6.8-fold greater cytotoxicity compared to control neutral non-PEGylated liposomal DOX, repectively, in these two cell lines. Although cationic liposomal DOX had higher tumor accumulation at 30 min after intravenous administration compared to control liposomes (p<0.05), DOX uptake of these liposomes at 24h post-injection was similar to that of PEGylated liposomal DOX (p>0.05) and approximately twice the levels of the free drug and non-PEGylated liposomes. In a murine tumor model generated using L1210 cells, increased survival rate was obtained with cationic liposomal DOX treatment compared to free DOX (p<0.01), neutral liposome control (p<0.01), as well as PEGylated liposomes (p<0.05). In conclusion, the cationic liposomal DOX formulation produced superior in vitro cytotoxicity and in vivo antitumor activity, and warrants further investigation.     

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.     

Folate receptor-mediated liposomal delivery of a lipophilic boron agent to tumor cells in vitro for neutron capture therapy

Purpose. This study was aimed at the in vitro evaluations of folate receptor (FR)-targeted liposomes as carriers for a lipophilic boron agent, K[nido-7-CH₃(CH₂)₁₅-7,8-C₂B₉H₁₁], in FR-overexpressing tumor cells for neutron capture therapy. Methods. Large unilamellar vesicles (200 nm in diameter) were prepared with the composition of egg PC/chol/K[nido-7-CH₃(CH₂)₁₅-7,8-C₂B₉H₁₁] (2:2:1, mol/mol), with an additional 0.5 mol % of folate-PEG-DSPE or PEG-DSPE added for the FR-targeted or nontargeted liposomal formulations, respectively. Results. Boron-containing, FR-targeted liposomes readily bound to KB cells, an FR-overexpressing cell line, and were internalized via FR-mediated endocytosis. The boron uptake in cells treated with these liposomes was approximately 10 times greater compared with those treated with control liposomes. In contrast, FR-targeted and nontargeted liposomes showed no difference in boron delivery efficiency in F98 cells, which do not express the FR. The subcellular distribution of the boron compound in KB cells treated with the FR-targeted liposomes was investigated by cellular fractionation experiments, which showed that most of the boron compound was found in either the cytosol/endosomal or cell membrane fractions, indicating efficient internalization of the liposomal boron. Conclusion. FR-targeted liposomes incorporating the lipophilic boron agent, K[nido-7-CH₃(CH₂)₁₅-7,8-C₂B₉H₁₁], into its bilayer were capable of specific receptor binding and receptor-mediated endocytosis in cultured KB cells. Such liposomes warrant further investigations for use in neutron capture therapy.     

Synthesis and evaluation of a novel ligand for folate-mediated targeting liposomes

Folate receptors (FRs) have been identified as cellular surface markers for cancer and leukemia. Liposomes containing lipophilic derivatives of folate have been shown to effectively target FR-expressing cells. Here, we report the synthesis of a novel lipophilic folate derivative, folate-polyethylene glycol-cholesterol hemisuccinate (F-PEG-CHEMS), and its evaluation as a targeting ligand for liposomal doxorubicin (L-DOX) in FR-expressing cells. Liposomes containing F-PEG-CHEMS, with a mean diameter of 120+/-20 nm, were synthesized by polycarbonate membrane extrusion and were shown to have excellent colloidal stability. The liposomes were taken up selectively by KB cells, which overexpress FR-alpha. Compared to folate-PEG-cholesterol (F-PEG-Chol), which contains a carbamate linkage, F-PEG-CHEMS better retained its FR-targeting activity during prolonged storage. In addition, F-PEG-CHEMS containing liposomes loaded with DOX (F-L-DOX) showed greater cytotoxicity (IC(50)=10.0muM) than non-targeted control L-DOX (IC(50)=57.5 microM) in KB cells. In ICR mice, both targeted and non-targeted liposomes exhibited long circulation properties, although F-L-DOX (t(1/2)=12.34 h) showed more rapid plasma clearance than L-DOX (t(1/2)=17.10h). These results suggest that F-PEG-CHEMS is effective as a novel ligand for the synthesis of FR-targeted liposomes.     

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.     

Characterization of novel mixed polyethyleneglycol modified liposomes

In our previous paper, mixed polyetheleneglycol (PEG) modification of liposomes by a mixture of 1-monomethoxypolyethyleneglycol-2,3-distearoylglycerol (PEG-DSG) with short polyoxyethylene chain and PEG-DSG with long one was shown to increase fixed aqueous layer thickness (FALT) around the liposomal membrane, and this was useful in vivo. In this study, we investigated the characterization of mixed PEG modification of liposomes with different anchors (PEG2000-DSG and PEG2000-cholesterol (CHO)). When the liposomes was modified by a mixture of PEG2000-DSG and PEG2000-CHO, FALT was increased compared to that of each single PEG-lipids modification and the most suitable mix modification (PEG2000-DSG:PEG2000-CHO = 3:1) showed a maximum FALT. This phenomenon was speculated to be based on the difference in the insertion state of the PEG anchor unit in the liposomal membrane. PEG-CHO-modified liposomes (single or mixed PEG-modified liposomes) were easily incorporated into the liposomal membranes compared with that of single PEG-DSG-modified liposomes. Namely, it was considered that the cholesterol anchor as a single chain was able to be easily introduced, compared with the DSG anchor as two chains, and induced some interaction with both PEG modification. In conclusion, it is expected that novel PEG-modified liposomes with PEG2000-DSG and PEG2000-CHO (3:1) had superior physicochemical properties.     

Tumour-selective drug delivery via folate receptor-targeted liposomes

Tumour cell-targeted liposomal delivery has the potential to enhance the therapeutic efficacy and reduce the toxicity of anticancer agents. Folate receptor (FR) expression is frequently amplified among human malignancies. FR is, therefore, potentially useful as a tumour marker for targeted drug delivery. FR-mediated liposomal delivery has been shown to enhance the antitumour efficacy of doxorubicin both in vitro and in vivo, and to overcome P-glycoprotein-mediated multi-drug resistance. In addition, FR-targeted liposomes have shown utility as effective delivery vehicles of genes and antisense oligodeoxyribonucleotides to FR(+) tumour cells. Both solid tumours and leukaemias can potentially benefit from FR-targeted drug delivery. Multiple mechanisms might contribute to greater therapeutic efficacy for FR-targeted liposomes, such as FR-dependent cytotoxicity and antiangiogenic activity. Further investigation of this promising drug delivery strategy is clearly warranted.     

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.     

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.     

Tumor cell targeting of liposome-entrapped drugs with phospholipid-anchored folic acid-PEG conjugates

Targeting of liposomes with phospholipid-anchored folate conjugates is an attractive approach to deliver chemotherapeutic agents to folate receptor (FR) expressing tumors. The use of polyethylene glycol (PEG)-coated liposomes with folate attached to the outer end of a small fraction of phospholipid-anchored PEG molecules appears to be the most appropriate way to combine long-circulating properties critical for liposome deposition in tumors and binding of liposomes to FR on tumor cells. Although a number of important formulation parameters remain to be optimized, there are indications, at least in one ascitic tumor model, that folate targeting shifts intra-tumor distribution of liposomes to the cellular compartment. In vitro, folate targeting enhances the cytotoxicity of liposomal drugs against FR-expressing tumor cells. In vivo, the therapeutic data are still fragmentary and appear to be formulation- and tumor model-dependent. Further studies are required to determine whether folate targeting can confer a clear advantage in efficacy and/or toxicity to liposomal drugs.     

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.     

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.     

Phospholipase A(2)-susceptible liposomes of anticancer double lipid-prodrugs

A novel approach to anticancer drug delivery is presented based on lipid-like liposome-forming anticancer prodrugs that are susceptible to secretory phospholipase A(2) (sPLA(2)) that is overexpressed in several cancer types. The approach provides a selective unloading of anticancer drugs at the target tissues, as well as circumvents the necessity for "conventional" drug loading. In our attempts to improve the performance of the liposomes in vivo, several PEGylated and non-PEGylated liposomal formulations composed of a retinoid prodrug premixed with the sPLA(2)-hydrolyzable DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) were prepared. Besides favorably modifying the physicochemical properties of the liposomes, the incorporation of DPPC and PEG-lipids in the liposomes should substantially enhance the enzymatic activity, as concluded from literature. In addition, one can reap benefits from the presumed permeability enhancing effect of the liberated fatty acids and lysolipids. The size distribution of the prepared liposomes as well as their phase behavior, enzymatic hydrolysis, and cytotoxicity, in the presence and absence of sPLA(2), were determined. The liposomes were around 100nm in diameter and in the gel/fluid coexistence region at 37°C. The enzymatic hydrolysis of the prodrug was pronouncedly accelerated upon the premixing with DPPC, and the hydrolysis was further enhanced by PEGylation. Interestingly, the faster hydrolysis of the prodrug and the released fatty acids and lysolipids from DPPC did not improve the cytotoxicity of the mixture; the effect of combining the prodrug with DPPC was additive and not synergistic. The data presented here question the significance of the permeability enhancing effects claimed for fatty acids and lysolipids at the target cell membrane, and whether these effects can be achieved using physiologically achievable concentrations of fatty acids and lysolipids.     

In vitro and in vivo aspects of N-acyl-phosphatidylethanolamine-containing liposomes

Incorporation of the phospholipid, N-acyl-phosphatidylethanolamine (NAPE), has shown to increase the liposomal stability towards plasma components in vitro. Besides increasing the circulation-time, NAPE has been shown to contain fusiogenic properties. Hence, fusion between NAPE-liposomes and target cells may be expected, resulting in a favorable delivery of drug to the target cell. In this study, NAPE has been tested as a potential liposomal component of phosphatidylcholine-liposomes. The liposomes were characterized by size, long-term stability and phase transition temperature (T(m)). In vivo behavior of NAPE-liposomes was determined by the blood-circulation half-life in mice. A characterization of the liposomes revealed that high content of NAPE resulted in liposomes of increased size compared to pure phosphatidylcholine-liposomes. However, the liposomes showed only a slight increase in size during storage for 5 weeks. Determination of T(m) for NAPE-liposomes showed increasing values of T(m) by increasing percentage of NAPE in the liposomal bilayer, due to the higher T(m) of NAPE compared to phosphatidylcholine. Blood-clearance studies showed an initial increase in blood-circulation of liposomes containing high amounts of NAPE. Thus, these results suggest that liposomes containing high percentage of NAPE may be a promising candidate for long-circulating liposomes, possibly in combination with other stabilizing components, e.g. cholesterol.     

Enhanced solubility and stability of PEGylated liposomal paclitaxel: in vitro and in vivo evaluation

An improved PEGylated liposomal formulation of paclitaxel has been developed with the purpose of improving the solubility of paclitaxel as well as the physicochemical stability of liposome in comparison to the current Taxol formulation. The use of 3% (v/v) Tween 80 in the hydration media was able to increase the solubility of drug. The addition of sucrose as a lyoprotectant in the freeze-drying process increased the stability of the liposome particles. There was no significant difference in the entrapment efficiency of paclitaxel between the conventional non-PEGylated liposomes and our PEGylated liposomes. Cytotoxicity in human breast cancer cell lines (MDA-MB-231 and SK-BR-3) of our paclitaxel formulation was less potent compared to Taxol after 24h incubation, but was equipotent after 72 h due to the slower release of drug from the liposome. Our PEGylated liposomes increased the biological half-life of paclitaxel from 5.05 (+/-1.52)h to 17.8 (+/-2.35)h compared to the conventional liposomes in rats. Biodistribution studies in breast cancer xenografted nude mouse model showed that our liposomes significantly decreased the uptake in reticuloendothelial system (RES)-containing organs (liver, spleen and lung) while increasing the uptake in tumor tissues after injection compared to Taxol or the conventional liposomal formulation. Moreover, the PEGylated liposome showed greater tumor growth inhibition effect in in vivo studies. Therefore, our PEGylated liposomal formulation of paclitaxel could serve as a better alternative for the passive targeting of human breast tumors.     

Increasing bioavailability of silymarin using a buccal liposomal delivery system: preparation and experimental design investigation

Silymarin is a natural lipotropic agent of low bioavailability from oral products. The aim of our study is to prepare buccal liposomal delivery system of silymarin with higher bioavailability. The effect of lecithin:cholesterol molar ratio on the percentage drug encapsulated was investigated. The influence of fluctuating the amount of added drug was also determined. The effect of additives such as positive charge inducer, negative charge inducer and surfactants was studied using two different 2(3) full factorial designs. Furthermore, additives used to optimize liposomal product were also investigated for their optimal concentrations, release properties and in vitro permeation and absorption through chicken cheek pouch. Optimal liposomal encapsulation efficiency was found at 7:4 lecithin to cholesterol molar ratio. A decrease in entrapment efficiency with increasing cholesterol content was observed. Tween 20 or Tween 80 beyond 0.5 molar ratio decreased the entrapment efficiency. Positively charged liposomes showed superior entrapment efficiency over neutral and negatively charged liposomes. Release studies as well as permeation and absorption studies showed that hybrid liposomes prepared according to formula 3 containing lecithin, cholesterol, stearyl amine and Tween 20 in 9:1:1:0.5 molar ratio, respectively, gave the best drug absorption and permeation. It showed steady state permeation through chicken cheek pouch for 6h. This is expected to improve the bioavailability of silymarin in the developed liposomal buccal delivery system, as the results show an increase in drug penetration compared to free drug powder.     

Lectin-functionalized liposomes for pulmonary drug delivery: effect of nebulization on stability and bioadhesion.

The generation of respirable aerosols of a functionalized colloidal carrier has been investigated in this study. Lectin-functionalized liposomes, which proved to show improved cell association (using A549 cell line and primary human alveolar cells) even in the presence of a commercial lung surfactant preparation, have been developed. The stability of non-functionalized liposomes during nebulization using a jet nebulizer (Pari II provocation nebulizer, operated using an air flow of 30 l/min) was firstly investigated, and the experimental and formulation conditions were optimized and applied for the preparation of lectin-functionalized liposomes. The incorporation of cholesterol enhanced the stability of the liposomes during nebulization (from 15-20% leakage of a hydrophilic marker to 8% upon cholesterol incorporation) and upon incubation with lung surfactant preparation. Nebulization of the functionalized liposomes did not significantly influence their physical stability. Their enhanced cell binding capability (compared to non-functionalized liposomes) was also maintained. A drop in cell association compared to fresh functionalized liposomes was detected after nebulization, nevertheless, the binding was still significantly higher than that of the non-functionalized liposomes. The deposition of the liposomal preparation in lung periphery, proved by the deposition of the liposomal preparation on the lower stages of an ASTRA type cascade impinger and a mean median aerodynamic diameter (MMAD) of 2.85 microm, makes it a potential candidate as a macromolecule-drug carrier for local and/or systemic administration.