Preparation of neo-galactosylated liposomes and their interaction with mouse peritoneal macrophages

Carbohydrate anchored lipid nanoparticles

Nanotechnology has been a dynamic field for formulation scientists with multidisciplinary research being conducted worldwide. Advancements in development of functional nanosystems have led to evolution of breakthrough technologies. Lipidic nanosystems, in particular, are highly preferred owing to their non-immunogenic safety profiles along with a range of versatile intrinsic properties. Surface modification of lipid nanoparticles by anchoring carbohydrates to these systems is one such attractive drug delivery technology. Carbohydrates confer interesting properties to the nanosystems such as stealth, biostability, bioavailability, reduced toxicity due to decreased immunogenic response, targeting potential as well as ease of commercial availability. The carbohydrate anchored systems can be developed using methods such as adsorption, incorporation (nanoprecipitation or solvent displacement method), crosslinking and grafting. Current review provides a detailed overview of potential lipid based nanoparticulate systems with an emphasis on liposomes, solid lipid nanoparticles, nanostructures lipid carriers and micelles. Review further explores basics of surface modification, methods applied therein, advantages of carbohydrates as surface modifiers, their versatile applications, techniques for characterization of carbohydrate anchored systems and vital regulatory aspects concerned with these specialized systems.

Liposomes for targeting hepatocellular carcinoma: use of conjugated arabinogalactan as targeting ligand

Present study investigates the potential of chemically modified (Shah et al., 2013) palmitoylated arabinogalactan (PAG) in guiding liposomal delivery system and targeting asialoglycoprotein receptors (ASGPR) which are expressed in hepatocellular carcinoma (HCC). PAG was incorporated in liposomes during preparation and doxorubicin hydrochloride was actively loaded in preformed liposomes with and without PAG. The liposomal systems with or without PAG were evaluated for in vitro release, in vitro cytotoxicity, in vitro cell uptake on ASGPR(+) cells, in vivo pharmacokinetic study, in vivo biodistribution study, and in vivo efficacy study in immunocompromised mice. The particle size for all the liposomal systems was below 200 nm with a negative zeta potential. Doxorubicin loaded PAG liposomes released significantly higher amount of doxorubicin at pH 5.5 as compared to pH 7.4, providing advantage for targeted tumor therapy. Doxorubicin in PAG liposomes showed superior cytotoxicity on ASGPR(+) HepG2 cells as compared to ASGPR(-), MCF7, A549, and HT29 cells. Superior uptake of doxorubicin loaded PAG liposomes as compared to doxorubicin loaded conventional liposomes was evident in confocal microscopy studies. Higher AUC in pharmacokinetic study and higher deposition in liver was observed for PAG liposomes compared to conventional liposomes. Significantly higher tumor suppression was noted in immunocompromised mice for mice treated with PAG liposomes as compared to the conventional liposomes. Targeting ability and superior activity of PAG liposomes is established pre-clinically suggesting potential of targeted delivery system for improved treatment of HCC.

Bone marrow-targeted liposomal carriers

INTRODUCTION

Bone marrow-targeted drug delivery systems appear to offer a promising strategy for advancing diagnostic, protective and/or therapeutic medicine for the hematopoietic system. Liposome technology can provide a drug delivery system with high bone marrow targeting that is mediated by specific phagocytosis in bone marrow.

AREA COVERED

This review focuses on a bone marrow-specific liposome formulation labeled with technetium-99 m. Interspecies differences in bone marrow distribution of the bone marrow-targeted formulation are emphasized. This review provides a liposome technology to target bone marrow. In addition, the selection of proper species for the investigation of bone marrow targeting is suggested.

EXPERT OPINION

It can be speculated that the bone marrow macrophages have a role in the delivery of lipids to the bone marrow as a source of energy and for membrane biosynthesis or in the delivery of fat-soluble vitamins for hematopoiesis. This homeostatic system offers a potent pathway to deliver drugs selectively into bone marrow tissues from blood. High selectivity of the present bone marrow-targeted liposome formulation for bone marrow suggests the presence of an active and specific mechanism, but specific factors affecting the uptake of the bone marrow mononuclear phagocyte system are still unknown. Further investigation of this mechanism will increase our understanding of factors required for effective transport of agents to the bone marrow, and may provide an efficient system for bone marrow delivery for therapeutic purposes.

Influence of ligand valency on the targeting of immature human dendritic cells by mannosylated liposomes

An important challenge for the development of new generations of vaccines is the efficient delivery of antigens to antigen presenting cells such as dendritic cells. In the present study we compare the interaction of plain and targeted liposomes, containing mono-, di-, and tetraantennary mannosyl lipid derivatives, with human monocyte-derived immature dendritic cells (iDCs). Whereas efficient mannose receptor-mediated endocytosis by iDCs was observed for the mannosylated liposomes, in contrast, only nonspecific interaction with little uptake was observed with plain liposomes. In accordance with the clustering effect, liposomes prepared with multibranched mannosylated lipids displayed higher binding affinity for the mannose receptor than vesicles containing the monomannosylated analogs. Importantly, we have found that dimannosylated ligands present at the surface of the liposomes were as efficient as tetramannosylated ones to engage in multidentate interactions with the mannose receptor of iDCs, resulting in both cases in an effective uptake/endocytosis. This result will greatly facilitate, from a practical standpoint, the design of mannose-targeted vaccination constructs. Moreover, we showed that mannose-mediated uptake of liposomes did not result in an activation of iDCs. Altogether, our results suggest that antigen-associated targeted liposomes containing diantennary mannosylated lipids could be effective vectors for vaccines when combined with additional DC activation signals.

New Synthetic Glycolipids for Targeted Gene Transfer: Synthesis, Formulation in Lipoplexes and Specific Interaction with Lectin

Nonviral gene delivery systems are a promising approach for gene therapy applications, despite their low in vivo gene transfer efficiency. One approach to enhance this efficiency is to incorporate targeting elements into cationic lipid/DNA complexes (lipoplexes). Ligand-containing lipoplexes have to retain their efficiency while exposing accessible ligand on their surface. Physicochemical properties (particle size, surface charge, and efficacy of DNA complexation) of the lipoplexes largely determine their gene transfer efficiency. We synthesized glycolipids with various galactosylated head ligand and incorporated them into lipoplexes. We showed that incorporation of up to 33% mol of glycolipid did not change the physicochemical properties of lipoplexes. Some of our glycolipids yielded lipoplexes whose galactosyl heads were well exposed on the surface as demonstrated by a strong interaction with Ricinus communis agglutinin. Glycolipid-containing lipoplexes gave an efficient gene transfer on hepatocytes, although no ligand-targeted transfection could be observed.

Formulation and optimization of piroxicam proniosomes by 3-factor, 3-level Box-Behnken design

The aim of this study was to investigate the combined influence of 3 independent variables in the preparation of piroxicam proniosomes by the slurry method. A 3-factor, 3-level Box-Behnken design was used to derive a second-order polynomial equation and construct contour plots to predict responses. The independent variables selected were molar ratio of Span 60:cholesterol (X(1)), surfactant loading (X(2)), and amount of drug (X(3)). Fifteen batches were prepared by the slurry method and evaluated for percentage drug entrapment (PDE) and vesicle size. The transformed values of the independent variables and the PDE (dependent variable) were subjected to multiple regression to establish a full-model second-order polynomial equation. F was calculated to confirm the omission of insignificant terms from the full-model equation to derive a reduced-model polynomial equation to predict the PDE of proniosome-derived niosomes. Contour plots were constructed to show the effects of X(1), X(2) and X(3) on the PDE. A model was validated for accurate prediction of the PDE by performing checkpoint analysis. The computer optimization process and contour plots predicted the levels of independent variables X(1), X(2), and X(3) (0, -0.158 and -0.158 respectively), for maximized response of PDE with constraints on vesicle size. The Box-Behnken design demonstrated the role of the derived equation and contour plots in predicting the values of dependent variables for the preparation and optimization of piroxicam proniosomes.

Stability study of stavudine-loaded O-palmitoyl-anchored carbohydrate-coated liposomes

The purpose of this study was to evaluate the physicochemical stability of carbohydrate-anchored liposomes. In the present study, carbohydrate (galactose, fucose, and mannose) was palmitoylated and anchored on the surface of positively charged liposomes (PL). The stabilities of plain neutral liposomes (NL), PL, and O-palmitoyl carbohydrate-anchored liposomes were determined. The effects of storage conditions (4 degrees C +/- 2 degrees C, 25 degrees C +/- 2 degrees C/60% +/- 5% relative humidity [RH], or 40 degrees C +/- 2 degrees C/75% +/- 5% RH for a period of 10, 20, and 30 days) were observed on the vesicle size, shape, zeta potential, drug content, and in vitro ligand agglutination assay by keeping the liposomal formulations in sealed amber-colored vials (10-mL capacity) after flushing with nitrogen. The stability of liposomal formulations was found to be temperature dependent. All the liposomal formulations were found to be stable at 4 degrees C +/- 2 degrees C up to 1 month. Storage at 25 degrees C +/- 2 degrees C/60% +/- 5% RH and 40 degrees C +/- 2 degrees C/75% +/- 5% RH adversely affected uncoated liposomal formulations. Carbohydrate coating of the liposomes could enhance the stability of liposomes at 25 degrees C +/- 2 degrees C/60% +/- 5% RH and 40 degrees C +/- 2 degrees C/75% +/- 5% RH.

Reduced hematopoietic toxicity, enhanced cellular uptake and altered pharmacokinetics of azidothymidine loaded galactosylated liposomes

In order to target liposomes to the lectin receptors present on macrophages, galactosylated liposomes were prepared and characterized in vitro. O-palmitoylgalactose (OPG) for liposomal coating was synthesized by esterification of galactose with palmitoyl chloride. The galactose binding Ricinus communis lectin was employed as a model system for the determination of in vitro ligand binding capacity. Cellular drug uptake studies were performed using alveolar macrophages. Hematological changes, bone marrow toxicity, plasma and tissue distribution study of free, uncoated plain liposomal and galactosylated liposomal encapsulated azidothymidine (AZT) were determined following a bolus intravenous injection in Sprague-Dawley rats. Lectin (R. communis) carbohydrate interaction has been utilized for the effective delivery of AZT entrapped in galactosylated vesicles. Aggregation of galactosylated liposomes increased as lectin concentration was increased from 5 to 30 microg/ml. Cellular uptake of galactosylated liposomal formulation was maximum. No hematological toxicity was observed even after 10 days in case of galactosylated vesicle entrapped AZT. This formulation maintained a significant level of AZT in tissues rich in galactose specific receptors and had a prolonged residence in the body resulting in enhanced half-life of AZT. Conclusively, galactosylated liposomes are the potential candidate for targeted drug delivery and are anticipated to be promising in the treatment of AIDS6.

Characterization, stability and in-vivo distribution of asialofetuin glycopeptide incorporating DSPC/CHOL liposomes prepared by mild cholate incubation

In this study, a small triantennary asialoglycopeptide of fetuin (A-F2) was used as a ligand to direct liposomes to hepatocytes. A-F2 was cleaved from asialofetuin, purified, conjugated with fatty acids and incorporated into pre-formed sonicated DSPC/Chol (2:1) liposomes. A mild cholate incubation method for incorporating the A-F2 ligand on pre-formed vesicles was used. In preliminary in vivo experiments 111In3+ encapsulated in A-F2/palmityl liposomes was seen to accumulate in the liver of mice significantly faster than when encapsulated in non-ligand bearing liposomes of the same lipid composition (studied before), justifying further investigation of this system. The presence of the A-F2/fatty acid conjugate in a functional form on the vesicle surface was confirmed by their reversible agglutination in the presence of Ricinus communis agglutinin (RCA120). Effects of ligand incorporation on the vesicle size distribution, z-potential, membrane integrity and stability were monitored. The results demonstrate that highest ligand incorporation was achieved when liposomes and ligand were co-incubated in the presence of 1 mM sodium cholate. Incorporation increased with the length of the fatty acid used for A-F2 conjugation. Ligand-bearing liposomes were demonstrated to be smaller in diameter (about 30%) with a more positive z-potential in comparison to control vesicles while ligand incorporation did not influence the liposome membrane integrity. The size of the ligand-incorporating vesicles was maintained after 24 hours of incubation in isotonic buffer, proving that the vesicles do not aggregate. Although the preliminary biodistribution results may suggest that ligand bearing liposomes are accumulating in the liver, further cell culture, in vivo distribution and especially liver fractionation studies are required in order to clarify the intrahepatic localization of these liposomes and the ability to target liver hepatocytes in vivo.

Synthetic glycopeptide-based delivery systems for systemic gene targeting to hepatocytes

PURPOSE

To design, synthesize, and test synthetic glycopeptide-based delivery systems for gene targeting to hepatocytes by systemic administration.

METHODS

All peptides were synthesized by the solid phase method developed using Fmoc chemistry on a peptide synthesizer. The binding of galactosylated peptides to HepG2 cells and accessibility of the galactose residues on particle surface was demonstrated by a competition assay using 125I-labeled asialoorosomucoid and RCA lectin agglutination assay, respectively. DNA plasmid encoding chloramphenicol acetyl transferase (CAT) gene was complexed with a tri-galactosylated peptide (GM245.3) or tri-galactosylated lipopeptide (GM246.3) in the presence of an endosomolytic peptide (GM225.1) or endosomolytic lipopeptide (GM227.3) to obtain DNA particles of 100-150 nm in size. The plasmid/peptide complexes were added to HepG2 cell cultures or intravenously administered by tail vein injection into normal mice or rats. Plasmid uptake and expression was quantified by qPCR and ELISA, respectively.

RESULTS

Multiple antennary glycopeptides that have the ability to condense and deliver DNA plasmid to hepatocytes were synthesized and complexed with DNA plasmid to obtain colloidally stable DNA/peptide complexes. Addition of DNA/GM245.3/GM225.1 peptide complexes (1:3:1 (-/+/-)) to HepG2 cell cultures yielded CAT expression in transfected cells. The transfection efficiency was significantly reduced in the absence of galactose ligand or removal of endosomolytic peptide. Intravenous administration of DNA/GM245.3 peptide complexes (1:0.5 (-/+)) into the tail vein of normal rats yielded DNA uptake in the liver. Substitution of GM245.3 by galactosylated lipopeptide GM246.3 resulted in more stable DNA particles, and a 10-fold enhancement in liver plasmid uptake. CAT expression was detectable in liver following intravenous administration of DNA/GM246.3 complexes. Addition of endosomolytic lipopeptide GM227.3 into the complexes (DNA/ GM246.3/GM227.3 (1:0.5:1 (-/+/-))) yielded a 5-fold increase in CAT expression. Liver expression was 8-fold and 40-fold higher than lung and spleen, respectively, and localized in the hepatocytes only. The transfection efficiency in liver was enhanced by increasing DNA dose and injection volume. The plasmid uptake and expression in liver using DNA/GM246.3/GM227.3 complexes was 100-200-fold higher than DNA formulated in glucose. Tissue examination and serum biochemistry did not show any adverse effect of the DNA/GM246.3/ GM227.3 (1:0.5:1 (-/+/-)) complexes after intravenous delivery.

CONCLUSIONS

Gene targeting to hepatocytes was achieved by systemic administration of a well-tolerated synthetic glycopeptide-based delivery system. The transfection efficiency of this glycopeptide delivery system was dependent on peptide structure, endosomolytic activity, colloidal particle stability, and injection volume.

Recognition of Amphiphiles with Many Pendent Galactose Residues by Ricinus communis Agglutinin

Amphiphiles which carry many pendent galactose residues as side chains were prepared by telomerization of 2-methacryloyloxyethyl beta-D-galactopyranoside (MEGal) or 3-(2-methacryloyl aminoethylthio)propyl D-galactopyranoside (MEPGal, alpha:beta = 3.9:1) using a lipophilic radical initiator. The galactose-carrying amphiphiles (DP (degree of polymerization) = 15) incorporated in liposomes were recognized by a lectin from Ricinus communis (RCA120), which was proven by the increase in turbidity of the liposome suspension after mixing with the lectin. The recognition was largely affected by the distance between the galactose residues and the polymer main chain, and the surface density of the amphiphile in the liposomes. The liposomes containing these galactolipids were not taken up by mouse peritoneal macrophages, probably due to a steric hindrance of polymer main chains from the uptake of D-galactose receptors on the macrophages. Copyright 1999 Academic Press.

Biodistribution of liposomes containing synthetic galactose-terminated diacylglyceryl-poly(ethyleneglycol)s

We describe the synthesis of biodegradable poly(ethyleneglycol)-coupled galactolipids in which the galactose moiety is separated from a diacylglyceride lipid anchor by poly(ethylene glycol) chains of 10, 20 or 40 oxyethylene residues (PEG10/20/40). These Gal-PEG lipids (Gal-PEG-Lip) were incorporated in the bilayer of liposomes. The surface exposure of the galactose was investigated by aggregation experiments with ricinus communis agglutinin 120. Only the liposomes containing the PEG10 galactolipid aggregated with the lectin. Therefore liposomes were prepared containing Gal-PEG10-Lip and a trace amount of [3H]cholesteryl oleyl ether with an average diameter of approximately 100 nm and injected intravenously into rats. The Gal-PEG10-Lip liposomes were cleared from plasma with a T1/2 of 0.3 h. Identically sized and composed control liposomes without the Gal-PEG10-Lip had a T1/2 of approximately 12 h. The rapid plasma elimination of the Gal-PEG10-Lip liposomes could be attributed entirely to increased uptake by the liver amounting to more than 90% of injected dose. Uptake by the spleen was decreased to less than 1% of injected dose. A single injection of N-acetylgalactosamine 1 min prior to Gal-PEG-Lip liposome administration reduced the initial rate of plasma clearance to control levels. The increased liver uptake was almost entirely attributable to increased uptake by the Kupffer cells. Incorporation of PEG-DSPE in the Gal-PEG10-Lip liposomes only partially reversed the effect of the galactolipid with respect to liver and spleen uptake as well as intrahepatic distribution. These experiments demonstrate that liposome surface-exposed galactose residues, even if attached at the distal end of a poly(ethyleneglycol) chain anchored in the liposomal bilayer are effectively recognized by the galactose particle receptor on the Kupffer cells but fail to achieve significant targeting to the asialoglycoprotein receptor on the hepatocytes.

Synthetic lipopeptides incorporated in liposomes: in vitro stimulation of the proliferation of murine splenocytes and in vivo induction of an immune response against a peptide antigen

Amphiphilic lipopeptides, such as Pam3CysAlaGly and Pam3CysSerSer, were synthesized and incorporated into liposomes, and their ability to induce the proliferation of BALB/c mouse splenocyte was tested in vitro. When compared to monophosphoryl lipid A (MPL) the following potency order was found: liposomal lipopeptides > liposomal MPL > free (emulsified) lipopeptides. These results strongly depend on the size of the vesicles used: a mitogenic effect was observed only with lipopeptides incorporated within vesicles of diameter < or = 100 nm while lipopeptides in larger vesicles (diameter approximately 300 nm) gave no response. This may be related to the necessity for the liposome-associated lipopeptides to be endocytosed to reach putative intracellular targets. As immunoadjuvanticity seems to be linked to B-lymphocyte activation, the lipopeptides represent attractive alternatives to MPL for the realization of completely synthetic liposome-based peptide vaccine formulations. This was borne out by showing that Pam3CysAlaGly and Pam3CysSerSer, when incorporated in small unilamellar vesicles carrying a covalently conjugated synthetic peptide of sequence IRGERA, corresponding to an epitope of the C-terminal region of histone H3, were able to induce a potent and long-lasting immune response.

Engineering liposomes for drug delivery: progress and problems

Liposomes were first proposed and tested as a drug delivery system 25 years ago. Since then, advances in our understanding of the fate and behaviour of liposomes at the cellular and subcellular level in vivo have allowed the rational design of constructs for use in the treatment and prevention of disease, both in experimental animals and clinically. The involvement of several liposome-based biotechnology companies in the early 1980s, paralleled by great leaps in liposome technology, has culminated in the design and licencing of formulations for the treatment of certain microbial infections and cancers, and the first liposome-based vaccine for use in humans.

Versatile synthesis of bi- and tri-antennary galactose ligands: interaction with the Gal/GalNAc receptor of human hepatoma cells

We have synthesized bi- and tri-antennary galactose ligands by coupling 1-thio-beta-D-galactose derivatives to the alpha- and epsilon-amino groups of L-lysine and L-lysyl-L-lysine via highly flexible hydrophilic spacer arms that allow variation of their intergalactose distances. The interaction of these ligands with the Gal/GalNAc receptor of HepG2 cells showed a binding affinity that was: (i) in agreement with the clustering effect known to occur with more complex oligomeric structures, i.e. tri- > bi-antennary; ii) dependent on the intergalactose distances (optimal interactions were observed for the tri-antennary structures with distances > 2 nm). These ligands, that can be easily conjugated to bioactive (macro) molecule carrier systems, could be useful for their targeting to hepatocytes.

Neoglycosylated liposomes as efficient ligands for the evaluation of specific sugar receptors on macrophages in health and in experimental leishmaniasis

Receptors interacting with terminal sugars as ligands are involved in the binding of Leishmania donovani promastigotes to the macrophage surface and their subsequent internalization. Mannose and glucose are specifically involved in the binding process. Decreased binding occurs to macrophages already infected with L. donovani either in vivo or in vitro. When mannose- or glucose-bearing liposomes are used as ligands the binding shows similar trends and the percentage inhibition of binding with mannose-bearing liposomes increases when compared to that for the glucose-bearing ones. The decreased binding of the ligand seems to be due to a decrease in the number of receptors after infection. The affinity of the ligands for the binding sites either on the normal macrophages or on the infected macrophages apparently remains the same. The results based on the incorporation of [3H]phenyl alanine and supported by the binding of glycosylated liposomes to both infected and non-infected macrophages suggest that protein synthesis, in general, is suppressed in L. donovani-infected macrophages thus affecting also mannose/glucose receptor protein synthesis, resulting in fewer receptors on the macrophage surface.

Influence of the galactosyl ligand structure on the interaction of galactosylated liposomes with mouse peritoneal macrophages

Liposomes bearing at their surface mono- and triantennary galactosyl ligands were prepared and their interaction with the galactose receptor of mouse peritoneal macrophages studied. Triantennary structures were synthesized by coupling derivatives of 1-thio-beta-D-galactose to the amino groups of lysyl-lysine dipeptide. Galactosylated liposomes were obtained either by synthesis of neo-galactolipids followed by their incorporation into the vesicles or by neo-galactosylation of performed liposomes by reaction between thiol-functionalized galactosyl ligands and vesicles bearing maleimido groups. The interaction of the galactosylated liposomes with the macrophage lectin was remarkably sensitive to the topology of the ligands, i.e., a spacer-arm length about 3 nm was necessary and, in contrast to results obtained with the galactose receptor of other cells, the triantennary structure did not provide additional binding. Related to the strategy of drug delivery with targeted liposomes, these results indicate that lectins from different cells might possibly be distinguished by using multiantennary ligands having optimal geometries.

Neo-mannosylated liposomes: synthesis and interaction with mouse Kupffer cells and resident peritoneal macrophages

In order to target liposomes to cells expressing at their surface mannose receptors, e.g. mouse Kupffer cells and peritoneal macrophages, we have developed a new synthetic strategy which allows a chemically well defined preparation of neo-mannosylated vesicles. alpha-D-Thiomannopyranoside residues, substituted with a hydrophilic spacer arm and functionalized with a sulfhydryl group, were covalently coupled to preformed large unilamellar vesicles containing 4-(p-maleimidophenyl)butyryl phosphatidylethanolamine. Liposomes, containing 15 mol% of mannosyl residues, were specifically aggregated with concanavalin A; this aggregation could be reversed by an excess of free methyl alpha-D-mannopyranoside indicating that the surface ligands were freely accessible to the lectin. The neo-mannosylated liposomes presented in vitro an increased binding to cells possessing alpha-D-mannose specific binding sites. At 37 degrees C a specific binding, up to 9-fold compared to control vesicles, was observed. These neo-mannosylated vesicles represent attractive tools for targeting bio-active molecules to macrophage-associated diseases.