Syntheses of novel galactosyl ligands for liposomes and the influence of the spacer on accumulation in the rat liver

A glycoporphyrin story: from chemistry to PDT treatment of cancer mouse models

Glycoporphyrin: from bench to preclinical studies on PDX xenografted on mice.

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.

Carbohydrate-conjugated porphyrin dimers: synthesis and photobiological evaluation for a potential application in one-photon and two-photon photodynamic therapy

We report the synthesis of bioconjugated zinc porphyrin dimers 1a-e designed as photosensitizers for one-photon and two-photon excited photodynamic therapy. These macrocycles are substituted with carbohydrate units (glucose, mannose, lactose) in order to target tumor cells over-expressing lectin membrane receptors. Polarity, singlet oxygen production and in vitro photocytotoxicity are studied to determine their photodynamic therapy potentiality.

New strategy for targeting of photosensitizers. Synthesis of glycodendrimeric phenylporphyrins, incorporation into a liposome membrane and interaction with a specific lectin

Two glycodendrimeric phenylporphyrins were synthesized and their interaction with phospholipids was studied at the air-water interface and in liposome bilayers; such liposomes bearing glycodendrimeric porphyrin could constitute an efficient carrier for drug targeting in photodynamic therapy.

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.

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.

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.

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.

Tetrapyrrolic Glycosylated Macrocycles for an Application in PDT

The synthesis and characterization of amphiphilic glycoconjugated porphyrins, benzochlorin, and azaporphyrins were reported. Among these molecules, several were found to be efficient photosensitizers in an in vitro assay using the human tumoral cell line HT29. Moreover, glycosylated benzochlorin and azaporphyrins, whose absorption bands in the red region of the visible spectrum are substantially increased as compared to porphyrins, display a good photocytotoxicity on tumor cells after irradiation with wavelength above 590 nm. © 1999 Society of Photo-Optical Instrumentation Engineers.

Asialoglycoprotein receptor-mediated gene transfer using novel galactosylated cationic liposomes

We synthesized three novel galactosylated cholesterol derivatives, cholesten-5-yloxy-N-(4-((1-imino-c-beta-D-thiogalactosyl+ ++-ethyl)amino) butyl)formamide (Gal-C4-Chol) and its ethyl formamide and hexyl formamide analogues (Gal-C2-Chol, Gal-C6-Chol), to prepare liposomal gene carriers possessing the cationic charge necessary for plasmid DNA binding and galactose residues as a targetable ligand for liver parenchymal cells. Liposome/DNA complexes prepared with these lipids showed low cytotoxicity in human hepatoma HepG2 cells. Gal-C4-Chol/DC-Chol/DOPE(3:3:4) liposomes, consisting of 3:3:4 mixtures of Gal-C4-Chol, 3beta[N',N', N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol), and dioleoylphosphatidylethanolamine (DOPE), showed higher transfection activity and [32P]DNA uptake than DC-Chol/DOPE(6:4) liposomes. The presence of 20 mM galactose significantly inhibited both transfection efficiency and uptake of DNA of Gal-C4-Chol/DC-Chol/DOPE(3:3:4) and Gal-C4-Chol/DOPE(6:4) liposomes, but not those of DC-Chol/DOPE(6:4) liposomes. These results indicate that the liposome/DNA complexes prepared using novel galactosylated cholesterol derivatives are efficiently recognized by asialoglycoprotein receptors and internalized and lead to gene expression. In addition, we found that the galactosylated cholesterol derivative with a longer spacer showed higher transfection activity.

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

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