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

Polymeric nanomedicines for the treatment of hepatic diseases

The liver is an important organ in the human body and performs many functions, such as digestion, detoxification, metabolism, immune responses, and vitamin and mineral storage. Therefore, disorders of liver functions triggered by various hepatic diseases, including hepatitis B virus infection, nonalcoholic steatohepatitis, hepatic fibrosis, hepatocellular carcinoma, and transplant rejection, significantly threaten human health worldwide. Polymer-based nanomedicines, which can be easily engineered with ideal physicochemical characteristics and functions, have considerable merits, including contributions to improved therapeutic outcomes and reduced adverse effects of drugs, in the treatment of hepatic diseases compared to traditional therapeutic agents. This review describes liver anatomy and function, and liver targeting strategies, hepatic disease treatment applications and intrahepatic fates of polymeric nanomedicines. The challenges and outlooks of hepatic disease treatment with polymeric nanomedicines are also discussed.

Effect of hydrophile-lipophile balance of the linker in Gal/GalNAc ligands on high-affinity binding of galactosylated liposomes by the asialoglycoprotein receptor

In this study, we explored the effect of the hydrophile-lipophile balance (HLB) in the linker unit of Galactose (Gal)/N-acetylgalactosamine (GalNAc) ligands on their affinity toward asialoglycoprotein receptors (ASGPRs). Two Gal/GalNAc ligands with lipophilic linkers-{(5-cholesten-3b-ol)[(2-acetamido-2-deoxy-d-galactopyranose-6-o)sebacate]} (CHS-6-GalNAc) and {(5-cholesten-3b-ol)[(d-galactopyranose-6-o)sebacate]} (CHS-6-Gal)-and two with hydrophilic linkers-{(5-cholesten-yl)[(4-O-b-D-galactopyranosyl)-D-glucitol-6-yl]sebacate} (CHS-1-Gal) and {(5-cholesten-3a-ol)[(2-acetamido-2-deoxy-d-galactopyranose-6-o)3,6-dioxa-octanedioate]} (CHS-PEG₂-6-GalNAc)-were synthesized by enzymatic catalysis. Compared with unmodified liposomes, all Gal/GalNAc ligand-modified liposomes showed higher efficiency toward the hepatocyte target as evaluated by weighted-average overall drug-targeting efficiency (Te*) in vivo and HepG2 cell uptake efficiency in vitro. The ligands containing linkers with high HLB values (i.e., CHS-PEG₂-6-GalNAc and CHS-1-Gal) exhibited higher ASGPR affinity than those containing linkers with low HLB values (i.e., CHS-6-GalNAc and CHS-6-Gal). We used molecular-dynamics (MD) simulations to investigate the structure-activity relationship between the HLB value of the linker in a ligand and ASGPR affinity. MD simulation results indicated that a Gal/GalNAc ligand with a more hydrophilic linker (i.e., higher HLB value) unit tended to have a higher solvent-accessible surface area (SASA), leading to lower steric hindrance for effective ASGPR recognition. The results of this study will provide an improved design for Gal/GalNAc ligand-based surface-modified liposomes with high ASGPR affinity.

Why nanoparticles prefer liver macrophage cell uptake in vivo

Effective delivery of therapeutic and diagnostic nanoparticles is dependent on their ability to accumulate in diseased tissues. However, most nanoparticles end up in liver macrophages regardless of nanoparticle design after administration. In this review, we describe the interactions of liver macrophages with nanoparticles. Liver macrophages have significant advantages in interacting with circulating nanoparticles over most target cells and tissues in the body. We describe these advantages in this article. Understanding these advantages will enable the development of strategies to overcome liver macrophages and deliver nanoparticles to targeted diseased tissues effectively. Ultimately, these approaches will increase the therapeutic efficacy and diagnostic signal of nanoparticles.

Liposomal doxorubicin as targeted delivery platform: Current trends in surface functionalization

Liposomal delivery systems have significantly enhanced the efficacy and safety of chemotherapeutic agents compared to free (non-liposomal) formulations. Liposomes are vesicles made up of lipophilic bilayer and a hydrophilic core which provides perfect opportunity for their application as transport vehicle for various therapeutic and diagnostic agents. Doxorubicin is the most exploited chemotherapeutic agent for evaluation of different liposomal applications, as its physicochemical properties permit high drug entrapment and easy remote loading in pre-formulated liposomes. Pegylated liposomal doxorubicin clinically approved and, on the market, Doxil®, exemplifies the benefits offered upon the surface modification of liposome with polyethylene glycol. This unique formulation prolonged the drug residence time in the circulation and increased accumulation of doxorubicin in tumor tissue via passive targeting (enhanced permeability and retention effect). However, there is ample scope for further improvement in the efficiency of targeting tumors by coupling biological active ligands onto the liposome surface to generate intelligent drug delivery systems. Small biomolecules such as peptides, fraction of antibodies and carbohydrates have the potential to target receptors present on the surface of the malignant cells. Hence, active targeting of malignant cells using functionalised nanocarrier (liposomes encapsulated with doxorubicin) have been attempted which is reviewed in this article.

Lipoproteins-Nanocarriers as a Promising Approach for Targeting Liver Cancer: Present Status and Application Prospects

The prevalence of liver cancer is increasing over the years and it is the fifth leading cause of mortality worldwide. The intrusive features and burden of low survival rate make it a global health issue in both developing and developed countries. The recommended chemotherapy drugs for patients in the intermediate and advanced stages of various liver cancers yield a low response rate due to the nonspecific nature of drug delivery, thus warranting the search for new therapeutic strategies and potential drug delivery carriers. There are several new drug delivery methods available to ferry the targeted molecules to the specific biological environment. In recent years, the nano assembly of lipoprotein moieties (lipidic nanoparticles) has emerged as a promising and efficiently tailored drug delivery system in liver cancer treatment. This increased precision of nano lipoproteins conjugates in chemotherapeutic targeting offers new avenues for the treatment of liver cancer with high specificity and efficiency. This present review is focused on concisely outlining the knowledge of liver cancer diagnosis, existing treatment strategies, lipoproteins, their preparation, mechanism and their potential application in the treatment of liver cancer.

A framework for designing delivery systems

The delivery of medical agents to a specific diseased tissue or cell is critical for diagnosing and treating patients. Nanomaterials are promising vehicles to transport agents that include drugs, contrast agents, immunotherapies and gene editors. They can be engineered to have different physical and chemical properties that influence their interactions with their biological environments and delivery destinations. In this Review Article, we discuss nanoparticle delivery systems and how the biology of disease should inform their design. We propose developing a framework for building optimal delivery systems that uses nanoparticle-biological interaction data and computational analyses to guide future nanomaterial designs and delivery strategies.

Lipid-based nanoparticle technologies for liver targeting

Liver diseases such as hepatitis, cirrhosis, and hepatocellular carcinoma are global health problems accounting for approximately 800 million cases and over 2 million deaths per year worldwide. Major drawbacks of standard pharmacological therapies are the inability to deliver a sufficient concentration of a therapeutic agent to the diseased liver, and nonspecific drug delivery leading to undesirable systemic side effects. Additionally, depending on the specific liver disease, drug delivery to a subset of liver cells is required. In recent years, lipid nanoparticles have been developed to passively and actively target drugs to the liver. The success of this approach has been highlighted by the FDA-approval of the first liver-targeting lipid nanoparticle, ONPATTRO, in 2018 and many other promising candidate technologies are expected to follow. This review summarizes recent developments of various lipid-based liver-targeting technologies, namely solid-lipid nanoparticles, liposomes, niosomes and micelles, and discusses the challenges and future perspectives in this field.

[Lactose-based glycoconjugates with variable spacers for design of liver-targeted liposomes]

Asialoglycoprotein receptors are highly abundant on the hepatocyte surface and have specific binding sites for blood serum glycoproteins. Such discovery resulted in development of liver-targeted drug delivery systems because modification of the liposomal surface by carbohydrate derivatives results in an increase of endocytosis, which facilitates selective uptake of such systems by hepatocytes. In this study we have synthesized novel lactose derivatives containing a palmitic hydrophobic domain. They were used for modification of the liposome surface. Transfection activity of modified liposomes was analyzed on the HepG2 cell line (hepatocytes) and showed an increase in the transfection efficiency as compared to the non-modified liposomes. At the same time transfection activities of modified and non-modified liposomes were similar in the case of a non-hepatocyte cell line (293T). The novel lactose-based glycoconjugates may be a promising tool for developing efficient vectors for delivery of nucleic acids to hepatocytes.

Dynamic formation of nanostructured particles from vesicles via invertase hydrolysis for on-demand delivery

Controlled hydrolysis via invertase action alters molecular shape and therefore lipid curvature, consequently triggering the release of encapsulated drug.

Inclusion of new 5-fluorouracil amphiphilic derivatives in liposome formulation for cancer treatment

Liposomes containing novel 5-fluorouracil derivatives differing in the length of their polyoxyethylenic spacer were shown active against colorectal tumor cells.

Recognition of concanavalin A by cationic glucosylated liposomes

The specificity of carbohydrate-lectin interaction has been reported as an attractive strategy for drug delivery in cancer therapy because of the high levels of lectins in several human malignancies. A novel cationic glucosylated amphiphile was therefore synthesized, as a model system, to attribute specificity toward d-glucose receptors to liposome formulations. Fluorescence experiments demonstrated that the monomeric glucosylated amphiphile is capable of interacting with fluorescently labeled concanavalin A, a D-glucose specific plant lectin. The interaction of concanavalin A with liposomes composed of a phospholipid and the glucosylated amphiphile was demonstrated by agglutination observed by optical density and dynamic laser light scattering measurements, thus paving the way to the preparation of other glycosilated amphiphiles differing for the length of polyoxyethylenic spacer, the sugar moieties, and/or the length of the hydrophobic chain.

Effect of space length of mannose ligand on uptake of mannosylated liposome in RAW 264.7 cells: In vitro and in vivo studies

The most widely used method for increasing uptake on macrophage is specific targeting for mannose receptor (MR) presented on macrophages. Efficiency of the uptake for MR is influenced by the space length and flexibility of mannose ligand in liposome (LP). We prepared mannosylated liposomes (M-EGn-LP-ICG) encapsulated indocyanine green (ICG) with mannose ligand of various ethylene glycol units (EG), LP-ICG, and mannosylated liposome (M-LP-ICG) incorporated with p-aminophenyl-α-d-mannopyranoside. We studied the effect of space length of the mannose ligand in vitro and in vivo with prepared liposomes. A space length of two ethylene glycol units at least was needed for uptake by macrophages and the uptake was increased as the space length increased up to EG4. We measured near-infrared (NIR) fluorescence intensity by ICG and the fluorescence value of cell-associated N-(4-nitrobenzo-2-oxa-1,3-diazole) (NBD) in liposome after cellular uptake. M-EG4-LP-ICG showed lower NIR fluorescence intensity but higher NBD fluorescence value than M-LP-ICG. The result of pre-treatment with d(+)-mannose as an inhibitor showed significant decreasing in uptake of mannosylated LP-ICG but no difference in LP-ICG. These were explained that mannosylated LP-ICG was taken up by macrophages through the MR and M-EG4-LP-ICG showed more specific uptake than M-LP-ICG. We obtained images as time passed in the NIR range after intravenous administration using a Balb/c mouse with inflammatory model. The results showed high uptake in liver at early time and rapid degradation of mannosylated LP-ICG. M-EG4-LP-ICG was more selectively taken up by macrophages than M-LP-ICG.

Targeted gene delivery to hepatocytes with galactosylated amphiphilic cyclodextrins

Objectives

Achieving targeted delivery of gene medicines is desirable to maximise activity. Here, galactosylated amphiphilic cyclodextrins (CDs) are examined in terms of their ability to transfect asialoglycoprotein receptor-bearing HepG2 cells.

Methods

Cationic amphiphilic CDs were synthesised as well as amphiphilic CDs bearing galactose-targeting ligands with different linker lengths. Binding of galactosylated CDs to a galactose-specific lectin was examined by surface plasmon resonance. CDs were formulated with and without the helper lipid DOPE and complexed with plasmid DNA. Transfection was evaluated by luciferase assay. Intracellular trafficking was assessed by confocal microscopy.

Key findings

Binding of targeted CDs to a galactose-specific lectin was achieved. Binding decreased with linker length between the galactosyl group and the CD core. Contrary to the lectin binding results, transfection levels increased with an increase in linker length from 7 atoms to 15. Compared to non-targeted formulations, a significant increase in transfection was observed only in the presence of the helper lipid DOPE. Confocal microscopy revealed that DOPE caused a pronounced effect on cellular distribution.

Conclusions

The galactose-targeting ligand induced substantial increases in transfection over non-targeted formulations when DOPE was included, indicating the potential for targeted gene delivery using CD-based delivery systems.

Investigation of glucose-modified liposomes using polyethylene glycols with different chain lengths as the linkers for brain targeting

BACKGROUND

An intimidating challenge to transporting drugs into the brain parenchyma is the presence of the blood-brain barrier (BBB). Glucose is an essential nutritional substance for brain function sustenance, which cannot be synthesized by the brain. Its transport primarily depends on the glucose transporters on the brain capillary endothelial cells. In this paper, the brain-targeted properties of glucose-modified liposomes using polyethylene glycols with different chain lengths as the linkers were compared and evaluated to establish an optimized drug-delivery system.

METHODS

Coumarin 6-loaded liposomes (GLU200-LIP, GLU400-LIP, GLU1000-LIP, and GLU2000-LIP) composed of phospholipids and glucose-derived cholesterols were prepared by thin-film dispersion-ultrasound method. The BBB model in vitro was developed to evaluate the transendothelial ability of the different liposomes crossing the BBB. The biodistribution of liposomes in the mice brains was identified by in vivo and ex vivo nearinfrared fluorescence imaging and confocal laser scanning microscopy and further analyzed quantitatively by high-performance liquid chromatography.

RESULTS

Glucose-derived cholesterols were synthesized and identified, and coumarin 6-loaded liposomes were prepared successfully. The particle sizes of the four types of glucose-modified liposomes were around or smaller than 100 nm with a polydispersity index less than 0.300. GLU400-LIP, GLU1000-LIP, and GLU2000-LIP achieved higher cumulative cleared volumes on BBB model in vitro after 6 hours compared with GLU200-LIP (P < 0.05) and were significantly higher than that of the conventional liposome (P < 0.001). The qualitative and quantitative biodistribution results in the mice showed that the accumulation of GLU1000-LIP in the brain was the highest among all the groups (P < 0.01 versus LIP).

CONCLUSION

The data indicated that GLU400-LIP, GLU1000-LIP, and GLU2000-LIP all possess the potential of brain targeting, among which GLU1000-LIP, as a promising drug-delivery system, exhibited the strongest brain delivery capacity.

In vitro and in vivo investigation of glucose-mediated brain-targeting liposomes

New glycosyl derivative of cholesterol was synthesized as a material for preparing novel liposome to overcome the ineffective delivery of normal drug formulations to brain by targeting the (glucose transporters) GLUTs on the BBB. Coumarin-6 was used as fluorescent probe. The results have shown that the cytotoxicity for the brain capillary endothelial cells (BCECs) of the glucose-mediated brain targeting liposome containing coumarin-6 was less than that of conventional liposome. The BBB model in vitro was established by coculturing of BCECs and astrocytes (ACs) of rat to test the transendothelial ability crossing the BBB. The transendothelial ability was confirmed strengthen alone with the amount of the new glycosyl derivative of cholesterol used in liposome. After i.v. administration of LIP, control liposome (CLP), and GLP-4, the AUC(0-t) of coumarin-6 for GLP-4 was 2.85 times higher than that of LIP, and 3.33 times higher than that of CLP. The C(max) of CLP-4 was 1.43 times higher than that of LIP, and 3.10 times higher than that of CLP. Both pharmacokinetics and distribution in mice were also investigated to show that this novel brain targeting drug delivery system was promising.

Sustained liver targeting and improved antiproliferative effect of doxorubicin liposomes modified with galactosylated lipid and PEG-lipid

In this study, a cleavable PEG-lipid (methoxypolyethyleneglycol 2000-cholesteryl hemisuccinate, PEG(2000)-CHEMS) linked via ester bond and galactosylated lipid ((5-cholesten-3beta-yl) 4-oxo-4-[2-(lactobionyl amido) ethylamido] butanoate, CHS-ED-LA) were used to modify doxorubicin (DOX) liposome. DOX was encapsulated into conventional liposomes (CL), galactosylated liposomes (modified with CHS-ED-LA, GalL), pegylated liposomes (modified with PEG(2000)-CHEMS, PEG-CL), and pegylated galactosylated liposomes (modified with CHS-ED-LA and PEG(2000)-CHEMS, PEG-GalL) using an ammonium sulfate gradient loading method and then intravenously injected to normal mice. Both PEG-GalL DOX and GalL DOX gave relatively high overall drug targeting efficiencies to liver ((T(e))(liver)) and were mainly taken up by hepatocyte. However, PEG-GalL DOX showed unique "sustained targeting" characterized by slowed transfer of DOX to liver and reduced peak concentrations in the liver. The biodistribution and antitumor efficacy of various DOX preparations were studied in hepatocarcinoma 22 (H22) tumor-bearing mice. The inhibitory rate of PEG-GalL DOX to H22 tumors was up to 94%, significantly higher than that of PEG-CL DOX, GalL DOX, CL DOX, and free DOX, although the tumor distribution of DOX revealed no difference between PEG-GalL DOX and PEG-CL DOX. Meanwhile, the gradual increase in the liver DOX concentration due to the sustained uptake of PEG-GalL DOX formulations resulted in lower damage to liver. In conclusion, the present investigation indicated that double modification of liposomes with PEG(2000)-CHEMS, and CHS-ED-LA represents a potentially advantageous strategy in the therapy of liver cancers or other liver diseases.

Sustained liver targeting and improved antiproliferative effect of doxorubicin liposomes modified with galactosylated lipid and PEG-lipid

In this study, a cleavable PEG-lipid (methoxypolyethyleneglycol 2000-cholesteryl hemisuccinate, PEG(2000)-CHEMS) linked via ester bond and galactosylated lipid ((5-cholesten-3beta-yl) 4-oxo-4-[2-(lactobionyl amido) ethylamido] butanoate, CHS-ED-LA) were used to modify doxorubicin (DOX) liposome. DOX was encapsulated into conventional liposomes (CL), galactosylated liposomes (modified with CHS-ED-LA, GalL), pegylated liposomes (modified with PEG(2000)-CHEMS, PEG-CL), and pegylated galactosylated liposomes (modified with CHS-ED-LA and PEG(2000)-CHEMS, PEG-GalL) using an ammonium sulfate gradient loading method and then intravenously injected to normal mice. Both PEG-GalL DOX and GalL DOX gave relatively high overall drug targeting efficiencies to liver ((T(e))(liver)) and were mainly taken up by hepatocyte. However, PEG-GalL DOX showed unique "sustained targeting" characterized by slowed transfer of DOX to liver and reduced peak concentrations in the liver. The biodistribution and antitumor efficacy of various DOX preparations were studied in hepatocarcinoma 22 (H22) tumor-bearing mice. The inhibitory rate of PEG-GalL DOX to H22 tumors was up to 94%, significantly higher than that of PEG-CL DOX, GalL DOX, CL DOX, and free DOX, although the tumor distribution of DOX revealed no difference between PEG-GalL DOX and PEG-CL DOX. Meanwhile, the gradual increase in the liver DOX concentration due to the sustained uptake of PEG-GalL DOX formulations resulted in lower damage to liver. In conclusion, the present investigation indicated that double modification of liposomes with PEG(2000)-CHEMS, and CHS-ED-LA represents a potentially advantageous strategy in the therapy of liver cancers or other liver diseases.

Engineering liposomes and nanoparticles for biological targeting

Our ability to engineer nanomaterials for biological and medical applications is continuously increasing, and nanomaterial designs are becoming more and more complex. One very good example of this is the drug delivery field where nanoparticle systems can be used to deliver drugs specifically to diseased tissue. In the early days, the design of the nanoparticles was relatively simple, but today we can surface functionalize and manipulate material properties to target diseased tissue and build highly complex drug release mechanisms into our designs. One of the most promising strategies in drug delivery is to use ligands that target overexpressed or selectively expressed receptors on the surface of diseased cells. To utilize this approach, it is necessary to control the chemistry involved in surface functionalization of nanoparticles and construct highly specific functionalities that can be used as attachment points for a diverse range of targeting ligands such as antibodies, peptides, carbohydrates and vitamins. In this review we provide an overview and a critical evaluation of the many strategies that have been developed for surface functionalization of nanoparticles and furthermore provide an overview of how these methods have been used in drug delivery systems.

Molecular recognition on the supported and on the air/water interface-spread protein monolayers

Targeting of proteins at interfaces via affinity ligands or specific antibodies is important for the understanding of protein functioning in biological membranes. This review brings together a great number of research works accomplished in this field in the past decade by a variety of analytical methods. It highlights two simple in situ techniques of monitoring molecular recognition processes at interfaces recently developed in the author's laboratory. The first of these techniques is based on the measurements of surface pressure increments of a protein monolayer spread at the air/water interface at a constant area resulting from the interaction with its specific ligands injected into the aqueous subphase beneath the preformed protein monolayer. The second technique takes advantage of the feature of [(14)C]-labeled proteins that enable in situ measurements of surface density changes of adsorbed protein molecules on a solid support resulting from the interaction with its specific antibody.

Oligomethylene spacer length dependent interaction of synthetic galactolipids incorporated in phospholipid layers with ricin

As models of naturally occurring glycolipids, structurally well-determined amphiphilic compounds were prepared. The synthetic molecules have beta-D-galactopyranosyl or alpha-D-mannopyranosyl and two dodecyl groups as terminal hydrophilic sugar and hydrophobic hydrocarbon moieties, respectively. The two long alkyl chains are connected by 3,5-dioxybenzamide through ether linkages to give a lipid analog purified easily due to its absorbance of ultraviolet light. In the synthetic glycolipids, the glycoside and lipid parts are covalently bound via an oligomethylene spacer. The glycolipids could be easily incorporated into liposomes of L-alpha-phosphatidylcholine. The monoglycosyl moiety of the synthetic glycolipids possessing a hexamethylene spacer was present on the surface of the liposomes and interacted specifically with a lectin to give liposomal assemblies. Such agglutination of these liposomes induced by lectins was determined by analyses of turbidity and particle size based on dynamic light scattering and laser diffraction methods. The other liposomes possessing a shorter ethylene or longer decamethylene linker gave few lectin-induced agglutinates, indicating that these spacers were not effective for the presentation of the galacto-terminal on the liposomal surfaces. Similar spacer-dependent recognition of ricin with a galactolipid-incorporated phospholipid monolayer was confirmed by surface plasmon resonance technique on a substrate.

Influence of a neoglycolipid and its PEO-lipid moiety on the organization of phospholipid monolayers

The surface properties of the neoglycolipid (GlcNAcE(3)G(28)) and of its PEO-lipid (E(3)G(28)) moiety mixed with phospholipids (dipalmitoylphosphatidylcholine, DPPC; distearoylphosphatidylcholine, DSPC; diarachidoylphosphatidylcholine, DAPC; and dibehenoylphosphatidylcholine, DBPC) were studied in Langmuir monolayers at various mixture compositions and surface pressures. The pi-A isotherms of the pure compounds revealed that because of the presence of the sugar group in its molecule, GlcNAcE(3)G(28) collapsed at a higher surface pressure and occupied a larger molecular area than the PEO-lipid moiety. It was also observed that the presence of the PEO-lipid (E(3)G(28)) in the mixtures triggered a strong alteration of both phospholipid pi-A isotherm profiles and surface diffraction spectra, an indication that the disordering of the initially structured phospholipid monolayers took place. Unlike E(3)G(28), GlcNAcE(3)G(28) did not disorganize phospholipid monolayers but generated a partial segregation of the film-forming components. The calculated excess free energies of mixing (DeltaG(exc)) for GlcNAcE(3)G(28)-phospholipid mixtures enabled us to predict the stability of such systems.

Targeted gene delivery to hepatoma cells using galactosylated liposome-polycation-DNA complexes (LPD)

A major goal for gene therapy is to obtain targeted vectors that transfer genes efficiently to specific cell types. The liver possesses a variety of characteristics that make this organ very attractive for gene therapy. In the present study, four cholesterylated thiogalactosides 1a approximately d with different spacer length were synthesized to formulate novel lipid-polycation-DNA (LPD) complexes, which were composed of galactosylated cationic liposomes, protamine sulfate and plasmid DNA. The galactosylated LPD1c significantly improved the levels of gene expression in cultured hepatoma cells HepG2 and SMMC-7721, while LPD1a and LPD1b did not significantly improve the levels compared with non-galactosylated LPD. Meanwhile, increased transfection activity was not observed in mouse fibroblasts L929 for galactosylated LPDs. Cytotoxicity of galactosylated LPDs assay showed they had no obvious toxicities to L929 cells and HepG2 cells. In summary, the length of the spacer between the anchor and galactose residues was important for the recognition of asialoglycoprotein receptor. The LPD1c described here, combining the condensing effect of protamine and the targeting capability of cholesterylated thiogalactosides, are potentially useful gene carriers to liver parenchymal cells.

Lectin-mediated drug targeting: history and applications

The purpose of this paper is to review the history of using lectins to target and deliver drugs to their site of action. The hour of birth of "lectinology" may be defined as the description of the agglutinating properties of ricin, by Herrmann Stillmark in 1888, however, the modern era of lectinology began almost 100 years later in 1972 with the purification of different plant lectins by Sharon and Lis. The idea to use lectins for drug delivery came in 1988 from Woodley and Naisbett, who proposed the use of tomato lectin (TL) to target the luminal surface of the small intestine. Besides the targeting to specific cells, the lectin-sugar interaction can also been used to trigger vesicular transport into or across epithelial cells. The concept of bioadhesion via lectins may be applied not only for the GI tract but also for other biological barriers like the nasal mucosa, the lung, the buccal cavity, the eye and the blood-brain barrier.

Influence of Spacer Length on the Agglutination of Glycolipid‐Incorporated Liposomes by ConA as Model Membrane

Through a systematic investigation of the agglutination of long chain mannolipid and glucolipid incorporated liposomes by concanavalin A (ConA) it was found that the agglutination was dependent on different factors. The studied factors reported here are (1) spacer length and (2) ground lipid matrix. The threshold and the relative saturating ConA binding concentration (saturation point to attain the binding saturation condition) of glycosides with varying spacer length for agglutination are dependent on the spacer length of the glycolipid. These concentrations decrease with the increasing number of in-built ethyleneoxy spacer length in the glycolipid and find its minimum with 6 spacer units; it increases then more and more with increasing number of spacer units (>6 units). This is supposed to be due to the requirement of a proper distance of the hydrophilic determinant from the liposome surface for the response by ConA (response invoking distance), which may be most favorable in case of 6 spacer units. Further increase in number of spacer units (>6) results to an increasing probability of the bending of the spacer chain along with the terminal polar head group more and more towards the liposome surface; this leads to a reduction of the factual distance of the terminal hydrophilic head group from the liposome surface, weakening the response for ConA binding. The threshold concentration or saturation point decreases also with the rigidity of the ground lipid matrix. Increased rigidity of the ground matrix leads to a phase separation and localized 'Domain' formation with the glycolipid inside the ground matrix layer due to their immiscibility, invoking better response resulting to a reduction of required incorporated glycolipid concentration.

Specific interaction of lectins with liposomes and monolayers bearing neoglycolipids

The interaction of three lectins (wheat germ, Ulex europaeus I, and Lotus tetragonolobus agglutinins: WGA, UEA-I and LTA) with either N-acetyl-D-glucosamine or L-fucose neoglycolipids incorporated into phospholipid monolayers and liposome bilayers was studied at the air/water interface and in bulk solution. The results show that for both systems studied, synthesized neoglycolipids were capable of binding their specific lectin and that, in general, the binding of lectins increased with the increase in the molar fraction of the saccharide derivative incorporated in either the monolayers or bilayers. However, whereas for UEA-I, molecular recognition was enhanced by a strong hydrophobic interaction, for WGA and LTA successful recognition was predominantly related to the distance between neighboring sugar groups. The observed lengthy adsorption times of these lectins onto their specific ligands were attributed to interfacial conformational changes occurring in the proteins upon their adsorption at the interfaces.

Influence of spacer length on interaction of mannosylated liposomes with human phagocytic cells

PURPOSE

To improve target specificity and uptake of liposomes by macrophages, one can improve high-affinity receptor binding to mannose determinants with their 175-kDa mannose receptor (MR), which is mainly influenced by the length and flexibility of the spacer between the carbohydrate head group and liposome surface. Liposomes containing alkylmannosides with hydrophilic spacers 0 to 8 ethyleneoxy units (EO) long (Man0...Man8) were used to investigate systematically the effects of spacer length on liposome-cell interactions.

METHODS

Concanavalin A (ConA)-induced liposome aggregation was studied by turbidity measurement and cell uptake using PMA-induced HL-60 cells or native human macrophages by determining 6-CF after cell lysis or NBD-fluorescence with flow cytometry. Detection of MR in native cell populations was carried out by an antibody assay using flow cytometry; MR-representing cells were selected analytically.

RESULTS

Liposomes containing mannosides with more than one EO spacer length were specifically aggregated by ConA, indicating accessibility of the carbohydrate ligands of these derivatives. Increase in EO spacer units of incorporated mannosides (two or more EO) led to suppression of cellular uptake of mannosylated liposomes by phagocytes lacking MR (HL60, U937). The extent of suppression increased with spacer length. Liposome uptake by native macrophages expressing MR was, on the contrary, improved, particularly by Man6 and Man8.

CONCLUSIONS

Uptake of liposomes modified with Man6 or Man8 by native cells was enhanced but did not reach an optimum. Thus, Man6, Man8, and mannosides with even longer spacer arms are of potential use in receptor-mediated targeting.

Increased receptor-mediated gene delivery to the liver by protamine-enhanced-asialofetuin-lipoplexes

A novel lipidic vector composed of DOTAP/Chol liposomes, asialofetuin (AF), protamine sulfate and DNA has been developed. The resulting protamine-AF-lipoplexes improved significantly the levels of gene expression in cultured cells and in the liver upon i.v. administration. Lipoplexes containing the optimal amount of AF (1 microg/microg DNA) showed a 16-fold higher transfection activity in HepG2 cells than non-targeted (plain) complexes. The uptake by cells having asialoglycoprotein receptors (ASGPr) on their plasma membrane was decreased by the addition of free AF, indicating that AF-lipoplexes were taken up specifically by cells via ASGPr-mediated endocytosis. Results from transfections performed in cells defective in ASGPr, ie HeLa cells, confirmed this mechanism. By addition of the condensing peptide, protamine sulfate, smaller complexes were obtained, which enhanced even more the uptake of AF-complexes in HepG2 cells and in the liver. The optimal amount of protamine was 0.4 microg/mcirog DNA, and gene expression was about 5-fold over that obtained with AF-lipoplexes in the absence of the peptide, and 75-fold higher than that with plain conventional lipoplexes. Protamine-AF-lipoplexes increased by a factor of 12 luciferase gene expression in the liver of mice administered systemically via the tail vein, compared to plain complexes. In summary, our findings extend the scope of previous studies where AF-lipoplexes were used to introduce DNA into hepatocytes. The combination of targeting and protamine condensation obviated the need for partial hepatectomy, commonly required to obtain efficient gene delivery in this organ. Since protamine sulfate has been proven to be non-toxic in humans, the novel liver-specific vector described here may be useful for the delivery of clinically important genes to this organ.

Characterization of the inhibitory effect of PEG-lipid conjugates on the intracellular delivery of plasmid and antisense DNA mediated by cationic lipid liposomes

Poly(ethylene glycol)-lipid (PEG-lipid) conjugates are widely used in the field of liposomal drug delivery to provide a polymer coat that can confer favorable pharmacokinetic characteristics on particles in the circulation. More recently these lipids have been employed as an essential component in the self-assembly of cationic and neutral lipids with polynucleic acids to form small, stable lipid/DNA complexes that exhibit long circulation times in vivo and accumulate at sites of disease. However, the presence of a steric barrier lipid might be expected to inhibit the transfection activity of lipid/DNA complexes by reducing particle-membrane contact. In this study we examine what effect varying the size of the hydrophobic anchor and hydrophilic head group of PEG-lipids has on both gene and antisense delivery into cells in culture. Lipid/DNA complexes were made using unilamellar vesicles composed of 5 mole% PEG-lipids in combination with equimolar dioleoylphosphatidylethanolamine and the cationic lipid dioleyldimethylammonium chloride. Using HeLa and HepG2 cells we show that under the conditions employed PEG-lipids had a minimal effect on the binding and subsequent endocytosis of lipid/DNA complexes but they severely inhibited active gene transfer and the endosomal release of antisense oligodeoxynucleotides into the cytoplasm. Decreasing the size of the hydrophobic anchor or the size of the grafted hydrophilic PEG moiety enhanced DNA transfer by the complexes.

Immobilisation on polystyrene of diazirine derivatives of mono- and disaccharides: biological activities of modified surfaces

The potential of surface glycoengineering for biomaterials and biosensors originates from the importance of carbohydrate-protein interactions in biological systems. The strategy employed here utilises carbene generated by illumination of diazirine to achieve covalent bonding of carbohydrates. Here, we describe the synthesis of an aryl diazirine containing a disaccharide (lactose). Surface analysis techniques [X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS)] demonstrate its successful surface immobilisation on polystyrene (PS). Results are compared to those previously obtained with an aryl diazirine containing a monosaccharide (galactose). The biological activity of galactose- or lactose-modified PS samples is studied using rat hepatocytes, Allo A lectin and solid-phase semi-synthesis with alpha-2,6-sialyltransferase. Allo A shows some binding to galactose-modified PS but none to lactose-modified surfaces. Similar results are obtained with rat hepatocytes. In contrast, sialylation of lactose-modified PS is achieved but not with galactose-modified surfaces. The different responses indicate that the biological activity depends not only on the carbohydrate per se but also on the structure and length of the spacer.

Preparation of long-circulating immunoliposomes using PEG-cholesterol conjugates: effect of the spacer arm between PEG and cholesterol on liposomal characteristics

Poly(ethylene glycol)-coated liposomes were prepared with two new synthesised pegylated cholesterol (Chol) derivatives linked via carbamate bond. Poly(ethylene glycol) (PEG) was directly linked to Chol (PEG-Chol) or through a space arm of diaminebutane (PEG-L-Chol). In buffer, the physicochemical properties of PC/Chol liposomes (2/1, molar ratio) containing up to 10 mol% of pegylated Chol derivatives did not change significantly and the PEG layer at liposome surface inhibited the agglutination of biotin-liposomes induced by streptavidin. On the other hand, in serum, PEG-L-Chol seemed to reduce the interactions of liposomes with serum proteins, much more than PEG-Chol. The low steric hindrance of PEG-Chol derivative may be due to the slow conformational transition rate of the polymer, since PEG may be deeper located in the membrane. The coupling efficiency of the ligand to the functionalised amino group at the polymer end was also affected, but, its antigen-binding activity was preserved. The basic physical-chemical characteristics studied in this work are relevant to assess the application of pegylated Chol liposomes as drug delivery systems.

Determination of the upper size limit for uptake and processing of ligands by the asialoglycoprotein receptor on hepatocytes in vitro and in vivo

The asialoglycoprotein receptor (ASGPr) on hepatocytes plays a role in the clearance of desialylated proteins from the serum. Although its sugar preference (N-acetylgalactosamine (GalNAc) >> galactose) and the effects of ligand valency (tetraantennary > triantennary >> diantennary >> monoantennary) and sugar spacing (20 A 10 A 4 A) are well documented, the effect of particle size on recognition and uptake of ligands by the receptor is poorly defined. In the present study, we assessed the maximum ligand size that still allows effective processing by the ASGPr of mouse hepatocytes in vivo and in vitro. Here too, we synthesized a novel glycolipid, which possesses a highly hydrophobic steroid moiety for stable incorporation into liposomes, and a triantennary GalNAc(3)-terminated cluster glycoside with a high nanomolar affinity (2 nm) for the ASGPr. Incorporation of the glycolipid into small (30 nm) [(3)H]cholesteryl oleate-labeled long circulating liposomes (1-50%, w/w) caused a concentration-dependent increase in particle clearance that was liver-specific (reaching 85 +/- 7% of the injected dose at 30 min after injection) and mediated by the ASGPr on hepatocytes, as shown by competition studies with asialoorosomucoid in vivo. By using glycolipid-laden liposomes of various sizes between 30 and 90 nm, it was demonstrated that particles with a diameter of >70 nm could no longer be recognized and processed by the ASGPr in vivo. This threshold size for effective uptake was not related to the physical barrier raised by the fenestrated sinusoidal endothelium, which shields hepatocytes from the circulation, because similar results were obtained by studying the uptake of liposomes on isolated mouse hepatocytes in vitro. From these data we conclude that in addition to the species, valency, and orientation of sugar residues, size is also an important determinant for effective recognition and processing of substrates by the ASGPr. Therefore, these data have important implications for the design of ASGPr-specific carriers that are aimed at hepatocyte-directed delivery of drugs and genes.

The role of hepatocytes in the clearance of liposomes from the blood circulation

In this chapter we summarize literature and describe in more detail our own observations over a period of nearly two decennia on the role of hepatocytes in the hepatic clearance of intravenously administered liposomes. Evidence is presented indicating that, although size is an important parameter, it is not decisive in determining access of liposomes to the hepatocytes. Also lipid composition is an important parameter, including charge, rigidity and headgroup composition. The role of the fenestrated sinusoidal endothelial cells in determining liposome accessibility of hepatocytes is discussed as well as the involvement of opsonizing plasma proteins such as apolipoprotein E. Our observations led us to postulate the existence of at least four different mechanisms of interaction of liposomes with hepatocytes, i.e. an endocytic and a non-endocytic one for both neutral and negatively charged vesicles

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.

Novel galactosylated liposomes for hepatocyte-selective targeting of lipophilic drugs

Novel galactosylated neutral liposomes containing cholesten-5-yloxy-N-(4-((1-imino-2-beta-D-thiogalactosylethyl)amino)butyl)formamide (Gal-C4-Chol) as a "homing" device were developed for hepatocyte-selective drug targeting. Distearoylphosphatidylcholine (DSPC)/cholesterol (Chol) (60:40) and DSPC/Chol/Gal-C4-Chol (60:35:5) liposomes were prepared and labeled with [3H]cholesteryl hexadecyl ether (CHE). [3H]Prostaglandin E1 (PGE1) and [14C]probucol were incorporated in liposomes as model lipophilic drugs. After intravenous injection of the liposomes, mice were sacrificed at suitable time periods, and the lung, liver, kidney, spleen, and heart were excised. DSPC/Chol/Gal-C4-Chol liposomes rapidly disappeared from the blood, and 85% of the dose had accumulated in the liver within 10 min compared with hepatic accumulation of DSPC/Chol liposomes of 12%. The liver was perfused with collagenase, and liver parenchymal cells (PC) and liver nonparenchymal cells (NPC) were separated by centrifugal differentiation to determine the cellular distribution. The PC/NPC ratios for DSPC/Chol/Gal-C4-Chol and DSPC/Chol liposomes were 15.1 and 1.1, respectively. The hepatic uptake of DSPC/Chol/Gal-C4-Chol liposomes, but not that of DSPC/Chol liposomes, was significantly inhibited by the predosing of galactosylated bovine serum albumin. [14C]Probucol and [3H]PGE1 incorporated in DSPC/Chol/Gal-C4-Chol liposomes was also efficiently delivered to the liver. In conclusion, newly developed galactosylated liposomes have been proven to be a useful carrier for hepatocyte-selective targeting that will have many practical applications.