Monoclonal antibody and liposomes

Bispecific antibody (HER2 × mPEG) enhances anti-cancer effects by precise targeting and accumulation of mPEGylated liposomes

Targeted antibodies and methoxy-PEGylated nanocarriers have gradually become a mainstream of cancer therapy. To increase the anti-cancer effects of targeted antibodies combined with mPEGylated liposomes (mPEG-liposomes), we describe a bispecific antibody in which an anti-methoxy-polyethylene glycol scFv (αmPEG scFv) was fused to the C-terminus of an anti-HER2 (αHER2) antibody to generate a HER2 × mPEG BsAb that retained the original efficacy of a targeted antibody while actively attracting mPEG-liposomes to accumulate at tumor sites. HER2 ×mPEG BsAb can simultaneously bind to HER2-high expressing MCF7/HER2 tumor cells and mPEG molecules on mPEG-liposomal doxorubicin (Lipo-Dox). Pre-incubation of HER2 × mPEG BsAb with cells increased the endocytosis of Lipo-DiD and enhanced the cytotoxicity of Lipo-Dox to MCF7/HER2 tumor cells. Furthermore, pre-treatment of HER2 × mPEG BsAb enhanced the tumor accumulation and retention of Lipo-DiR 2.2-fold in HER2-high expressing MCF7/HER2 tumors as compared to HER2-low expressing MCF7/neo1 tumors. Importantly, HER2 × mPEG BsAb plus Lipo-Dox significantly suppressed tumor growth as compared to control BsAb plus Lipo-Dox in MCF7/HER2 tumor-bearing mice. These results indicate that HER2 × mPEG BsAb can enhance tumor accumulation of mPEG-liposomes to improve the therapeutic efficacy of combination treatment. Anti-mPEG scFv can be fused to any kind of targeted antibody to generate BsAbs to actively attract mPEG-drugs and improve anti-cancer efficacy. STATEMENT OF SIGNIFICANCE: Antibody targeted therapy and PEGylated drugs have gradually become the mainstream of cancer therapy. To enhance the anti-cancer effects of targeted antibodies combined with PEGylated drugs is very important. To this aim, we fused an anti-PEG scFv to the C-terminal of HER2 targeted antibodies to generate a HER2×mPEG bispecific antibody (BsAb) to retain the original efficacy of targeted antibody whilst actively attract mPEG-liposomal drugs to accumulate at tumor sites. The present study demonstrates pre-treatment of HER2×mPEG BsAb can enhance tumor accumulation of mPEG-liposomal drugs to improve the therapeutic efficacy of combination treatment. Anti-mPEG scFv can be fused to any kind of targeted antibody to generate BsAbs to actively attract mPEG-drugs and improve anti-cancer efficacy.

Lamellar sheet exfoliation of single lipid vesicles by a membrane-active peptide

Using total internal fluorescence microscopy, highly parallel measurements of single lipid vesicles unexpectedly reveal that a small fraction of vesicles rupture in multiple discrete steps when destabilized by a membrane-active peptide which is in contrast to classical solubilization models.

Antibody-Hapten Recognition at the Surface of Functionalized Liposomes Studied by SPR: Steric Hindrance of Pegylated Phospholipids in Stealth Liposomes Prepared for Targeted Radionuclide Delivery

Targeted PEGylated liposomes could increase the amount of drugs or radionuclides delivered to tumor cells. They show favorable stability and pharmacokinetics, but steric hindrance of the PEG chains can block the binding of the targeting moiety. Here, specific interactions between an antihapten antibody (clone 734, specific for the DTPA-indium complex) and DTPA-indium-tagged liposomes were characterized by surface plasmon resonance (SPR). Non-PEGylated liposomes fused on CM5 chips whereas PEGylated liposomes did not. By contrast, both PEGylated and non-PEGylated liposomes attached to L1 chips without fusion. SPR binding kinetics showed that, in the absence of PEG, the antibody binds the hapten at the surface of lipid bilayers with the affinity of the soluble hapten. The incorporation of PEGylated lipids hinders antibody binding to extents depending on PEGylated lipid fraction and PEG molecular weight. SPR on immobilized liposomes thus appears as a useful technique to optimize formulations of liposomes for targeted therapy.

High-Activity Radio-Iodine Labeling of Conventional and Stealth Liposomes

A new method to label preformed liposomes with high activities of radiohalogenated compounds has been developed. It uses activated esters of simple synthetic molecules that may be readily halogenated, such as Bolton-Hunter reagent (BH), and arginine-containing liposomes. BH, in the form of an activated ester, crosses the liposome membrane to react with arginine inside the liposomes, as demonstrated by thin-layer chromatography and by the fact that saline-containing liposomes, or hydrolyzed BH or the water soluble sulfo-BH afforded only marginal encapsulation yields. Under optimized conditions, between 37 and 55 degrees C, 62 +/- 4% (mean +/- SD) of radiolabeled BH were consistently encapsulated in the liposomes within 30 min. In molar amounts, this corresponds to a mean of 56 nmol of BH per micromol of lipids. Based on achievable specific activity, up to 2.8 GBq of iodine-131 could be entrapped per micromol of lipids. Leakage of radioactivity was very low, with less than 5% of the encapsulated activity released within 6 days at 4 degrees C in phosphate-buffered saline and less than 50% within 24 h in human serum at 37 degrees C. The labeling stability, and the fact that both conventional and PEGylated liposomes can be readily labeled with high doses of radioactivity, will make this technique useful for in vivo targeting applications, such as tumor detection (using iodine-123 or iodine-124) or therapy (with iodine-131 or astatine-211).

Doubly radiolabeled liposomes for pretargeted radioimmunotherapy

The aim of this study was to design liposomes as radioactivity carriers for pretargeted radioimmunotherapy with favorable pharmacokinetic parameters. To monitor the liposomes integrity in vivo, their surface was radiolabeled with indium-111 bound to DTPA-derivatized phosphatidylethanolamine (DSPE-DTPA) and the aqueous phase was labeled by using an original active loading technique of radioiodinated Bolton-Hunter reagent (BH) that reacts with pre-encapsulated arginine to form a positively charged conjugate ((125)I-BH-arginine). Different formulations of doubly radiolabeled liposomes were tested in vitro and in vivo to evaluate radiolabeling stability, integrity of the vesicles and their pharmacokinetics. Radiolabeling yields were high (surface >75%, encapsulation >60%) and stable (>85% after 24 h in serum 37 degrees C). In vivo, the pharmacokinetic behavior of doubly radiolabeled liposomes was strongly dependant on the formulation. Blood clearance of PEGylated liposomes (DSPC/Chol/DSPE-DTPA/DSPE-PEG5%) was 0.15 mL/h compared to a conventional formulation (DSPC/Chol/DSPE-DTPA: clearance 1.44 mL/h). Non-encapsulated BH-arginine conjugate was quickly eliminated in urine (clearance 6.04 mL/h). Blood kinetics of the two radionuclides were similar and radiochromatographic profiles of mice serum confirmed the integrity of circulating liposomes. The significant reduction of activity uptake in organs after liposome catabolism (liver and spleen), achieved by the rapid renal elimination of (125)I-BH-arginine, should bring significant improvements for targeted radionuclide therapy with sterically-stabilized liposomes.

Liposomes and immunoassays

Various aspects of the application of liposomes as a label in immunoassays are reviewed. Methods for the preparation of liposomes, from the basic film method to the more advanced dehydration-rehydration method, are discussed. Furthermore, the markers used in liposome labels, as well as the methods to conjugate liposomes to antigens or antibodies, are summarized. Liposome immunoassays are applied as homogeneous or heterogeneous assays. Homogeneous assays often rely on the lytic activity of complement on antibody-associated liposomes. Another group of homogeneous assays utilizes the inhibitory action of antibodies on the activity of conjugates of mellitin (a bee venom protein) with a hapten. Free mellitin conjugates are able to lyse liposomes effectively. Heterogeneous liposome immunoassays, performed either competitively or non-competitively, resemble more closely standard enzyme linked immunosorbent assays, with the enzyme being replaced by a liposome label. Washing steps are used to separate antigen-specifically bound liposomes from unbound liposomes. All bound liposomes are lysed with a detergent, giving an instantaneous amplification. Flow-injection liposome immunoassays and liposome immunosensors are also described as examples of other possible immunoassay formats.

Immunoliposomes as enzyme-carriers (immuno-enzymosomes) for antibody-directed enzyme prodrug therapy (ADEPT): optimization of prodrug activating capacity

PURPOSE

Immuno-enzymosomes are tumor-specific immunoliposomes bearing enzymes on their surface. These enzymes are capable of converting relatively nontoxic prodrugs into active cytostatic agents. The enzyme beta-glucuronidase (GUS)4 was coupled to the external surface of immunoliposomes directed against ovarian carcinoma cells. This study aimed at optimization of the prodrug-activating capacity of these immuno-enzymosomes by increasing the enzyme density on the immunoliposomal surface.

METHODS

To achieve coupling of GUS to the liposomes, introduction of extra thiol groups was required. Two thiolating agents were examined: iminothiolane and SATA.

RESULTS

When iminothiolane was used, aggregation of enzymosomes was observed above enzyme densities of 10 micrograms GUS/mumol lipid (TL). An increased electrostatic repulsion of the enzymosomes, created by inclusion of additional negatively charged lipids and by lowering the ionic strength of the external aqueous medium resulted in enzyme densities > or = 20 micrograms GUS/mumol TL without aggregation. Utilizing SATA, > or = 30 micrograms GUS/mumol TL could be coupled without aggregation, even at physiological ionic strength. It was shown that the enzyme density on immuno-enzymosomes, and thus on the tumor cell surface, strongly influences the antitumor effect of the prodrug daunorubicin-glucuronide against in vitro cultured ovarian cancer cells. The antitumor effect of immuno-enzymosomes with enzyme densities of about 20 micrograms GUS/mumol TL was similar to that of the parent drug daunorubicin.

CONCLUSIONS

SATA-mediated thiolation of GUS-molecules enabled the preparation of immuno-enzymosomes with high enzyme densities while avoiding spontaneous aggregation. In vitro antitumor activity experiments showed that the improved immuno-enzymosome system is able to completely convert the prodrug daunorubicin-glucuronide into its parent compound.

Microspheres for biomedical applications: preparation of reactive and labelled microspheres

This review describes the synthesis and physico-chemical properties of reactive and labelled microspheres useful for biomedical applications. Preparation of microspheres with specific functional groups, fluorescent species, radionuclides and magnetite particles (Fe2O3) are discussed. Physico-chemical properties of microspheres, including surface charge and hydrophilicity/hydrophobicity, are also briefly covered.

Immunogenicity of immunoliposomes

Multilamellar immunoliposomes were prepared from dipalmitoylphosphatidylcholine (DPPC), cholesterol (CH), sphingomyelin (SPH) and biotinylated dipalmitoylphosphatidylethanolamine (PEB) in the molar ratio of 1:1:1:0.1 with surface linked avidin-biotinylated sheep (anti-mouse IgG) IgG (AV-sIgGB) or GK1.5 monoclonal rat (antimouse L3T4 antigen) IgG (AV-GK1.5B). The ability of these immunoliposomes to induce antibody responses against AV, sIgG or GK1.5 was determined. GK1.5B and sIgGB elicited a low-level antibody response (5-10 microgram/ml serum) after i.v. immunization and boosting. Liposomes (1 mumol) containing GK1.5B or sIgGB were more effective than free GK1.5B or sIgGB in eliciting antibodies (20-30 and 100-120 micrograms/ml serum, respectively). Liposomal AV mixed with either sIgG or GK1.5 gave antibody levels comparable to immunization with free GK1.5B or sIgGB. Liposomes with surface AV-sIgGB or AV-GK1.5B elicited antibodies against AV and high levels against GK1.5 or sIgG. Immunoliposomes possessing surface AV-sIgGB or AV-GK1.5B were eliminated from the circulation of normal mice relatively slowly (T1/2 15.5 and 30 min): in contrast, liposomal AV-sIgGB or AV-GK1.5B was rapidly eliminated from the circulation of immunized mice (T1/2 4.5 and 4.0 min). These results demonstrate that liposomes with surface IgG (immunoliposomes) are immunogenic, and that repeated administration elicits anti-IgG antibodies that result in a significant reduction in blood circulation residence times.

Liposomes and biotherapeutics

Application of liposomes as delivery system for biotherapeutic peptides and proteins may offer important therapeutic advantages over existing delivery methods. Several approaches towards achieving improved delivery of biotherapeutics with liposomes are outlined. Although the literature on this topic is sporadic and frequently incomplete, enough of a research foundation exists to justify the conclusion that liposomes can play an important role in the formulation and delivery of biotherapeutics. However, it will be necessary to understand more fully the mechanisms of action before optimum liposomal dosage forms can be designed.

Lipid composition is important for highly efficient target binding and retention of immunoliposomes

By taking advantage of a monoclonal IgG antibody, 34A, which is highly specific to pulmonary endothelial cells, we have prepared liposomes containing various amounts of antibody molecules (immunoliposomes). These immunoliposomes accumulate specifically in the lung when injected i.v. Two lipid compositions were used: phosphatidylcholine/cholesterol/phosphatidylserine (PS), 10:5:1 (mol/mol), a composition that allows liposomes to be readily taken up by the reticuloendothelial system (RES) (liver and spleen), and phosphatidylcholine/cholesterol/ganglioside GM1, 10:5:1 (mol/mol), a composition that allows liposomes to avoid or delay the RES uptake (the so-called stealth liposomes). Although an increase in the number of antibody molecules per liposome was accompanied by an increased level of lung binding of the immunoliposomes, differences due to the lipid composition were more profound. For example, stealth immunoliposomes containing an antibody/lipid ratio = 1:37 (wt/wt) accumulated in lung to a level of 60% of the injected dose, whereas PS-containing immunoliposomes with a higher antibody/lipid ratio (1:8) only accumulated 50% of the injected dose in the lung. Conjugation of antibody to the stealth liposome did not increase the rate of liposome uptake by liver; this rate was approximately 10-fold lower than that of the PS-containing liposomes without antibody. Stealth immunoliposomes with high antibody content also showed long retention in the lung. The t1/2 of lung residence for the stealth immunoliposomes with an antibody/lipid ratio = 1:11 (wt/wt) was approximately 24 hr. The fact that stealth immunoliposomes showed a longer retention time in the lung than the PS-containing immunoliposomes of similar antibody content suggests that macrophages may play a role in the removal of the bound immunoliposomes from the pulmonary endothelium. Alternatively, dissociated stealth immunoliposomes may reenter the circulation and rebind to the lung target, causing an apparent slow overall dissociation rate. These results can be understood on the basis of two competing kinetic processes: lung binding whose rate is directly proportional to the antibody content of the immunoliposomes and uptake by RES whose rate is significantly reduced in the case of the stealth liposomes. Even for a modest level of antibody content, the half-life for target binding of immunoliposomes was significantly shorter than the half-life of liver uptake of the liposomes, resulting in a favorable target binding. Significant immunoliposome binding to the lung is not due to the fact that tail vein-injected liposomes flow through the lung capillary bed before they encounter the liver, because portal vein-injected immunoliposomes showed the same rate and extent of target binding as the tail vein-injected ones.

Tumour targeting with antibody-coupled liposomes: failure to achieve accumulation in xenografts and spontaneous liver metastases

The potential of small unilamellar liposomes coupled to anti-tumour monoclonal antibodies (immunoliposomes) to accumulate in solid tumour tissue was tested in two systems, i.e. a human malignant melanoma xenografted into nude mice and a syngeneic murine lymphoma ESb.Mp exhibiting spontaneous metastasis to the liver. Both monoclonal antibodies tested were partly released from immunoliposomes within a few hours, thus generating a seemingly constant level of circulating antibody. Nevertheless it was possible to follow the biodistribution of intact immunoliposomes by virtue of a radioiodine label incorporated into the lipid moiety. It was found that in both tumor systems, though they differed with respect to the size of lesions and maybe also to the vascular architecture of surrounding tissue, immunoliposome uptake was virtually nil. The blockade of uptake into solid tumour tissue was caused by the limited availability of immunoliposomes due to their moderate stability, but especially by the inability of the particulate carrier to extravasate.

Phototoxic liposomes coupled to an antibody that alone cannot modulate its cell-surface antigen kill selected target cells

Molecules such as antibodies that bind to cell surfaces can be used to deliver cytotoxic drugs to selected cells. To be effective the drug must usually be taken into the cells by endocytosis. In this study a T-cell line (CCRF-CEM) was effectively killed by liposomes carrying a photosensitizer and bearing the antibody OKT4 (anti-CD4). The unconjugated antibody does not induce antigenic modulation in the target cells, an indication of the absence of endocytosis, and would therefore not normally have been selected as an agent for drug delivery. It cannot, however, be concluded with certainty that the conjugates act at the cell surface and several alternative explanations of their efficacy are offered.

Drug delivery systems. 1. site-specific drug delivery using liposomes as carriers

Drug delivery systems, offering controlled delivery of biologically active agents, are rapidly gaining importance in pharmaceutical research and development. To achieve controlled drug delivery, i.e., the administration of drugs so that optimal amount reaches the target site to cure or control the disease state, increasingly sophisticated systems containing different carriers have been developed. Macromolecules represent one of the carriers involved, and they have taken on a significantly prominent role in various modes of administration of therapeutic agents. Among macromolecules, for example, synthetic copolymers, polysaccharides, liposomes, polyanions and antibodies, as drug carriers, liposomes have proved most effective for diseases affecting the reticuloendothelial system and blood cells in particular. Liposomes, which are vesicles consisting of one or more concentrically ordered assemblies of phospholipids bilayers, range in size from a nanometer to several micrometers. Phospholipids such as egg phosphatidylcholine, phosphatidylserine, synthetic dipalmitoyl-DL-alpha-phosphatidylcholine or phosphatidylinositol, have been used in conjunction with cholesterol and positively or negatively charged amphiphiles such as stearylamine or phosphatidic acid. Alteration of surface charge has been shown to enhance drug incorporation and also influence drug release. Because of the multifold characteristics as drug carriers, liposomes have been investigated extensively as carriers of anticancer agents for the past several years. Liposomal entrapments include a variety of pharmacologically active compounds such as antimalarial, antiviral, anti-inflammatory and anti-fungal agents as well as antibiotics, prostaglandins, steroids and bronchodilators to name a few. The liposomal entrapment has been shown to have considerable effect on the pharmacokinetics and tissue distribution of administered drugs. Despite the potential value of liposomes as unique carriers, the major obstacles are the first order targeting of a systemically given liposomes, physical stability and manufacture of the liposomal products and these problems still remain to be overcome. Drug delivery systems evolving in the 1980s have become increasingly dependent on fundamental cell-biology and receptor-mediated endocytotic mechanisms. Drug delivery systems during the 1990s may take advantage of the specificity of receptor-mediated uptake mechanisms as well as polymer chemistry and cell-biology in order to introduce more precise and efficient target-specific delivery systems that are based especially on the liposome technology.

Therapeutic effect of chloroquine(CQ)-containing immunoliposomes in rats infected with Plasmodium berghei parasitized mouse red blood cells: comparison with combinations of antibodies and CQ or liposomal CQ

The potential therapeutic application of chloroquine-containing immunoliposomes (Fab'-lipCQ) in a Plasmodium berghei malaria model was studied. Extending a previously described in vivo model (Peeters et al. (1988) Biochim. Biophys. Acta 943, 137-147) it was demonstrated that injection of antimouse red blood cell (anti-mRBC) Fab'-lipCQ was significantly more effective than liposome-encapsulated chloroquine (lipCQ) or free chloroquine in delaying or preventing a patent infection after intravenous injection of parasitized mouse red blood cells (p-mRBC) in rats. The results could be improved by injecting synchronized infected cells instead of non-synchronous p-mRBC in order to minimize the presence of free parasites which could easily infect rat RBC. It was further demonstrated that sequential injection of anti-mRBC IgG and lipCQ or chloroquine resulted in complete inactivation of the injected parasitized cells while Fab'-lipCQ administration resulted in a maximum score of 50% at an equal chloroquine, protein and phospholipid dose. In this report the potential of the concept of drug targeting for the effective treatment of a disease, which manifests in blood cells, was demonstrated.

In vitro drug delivery mediated by ecto-NAD+-glycohydrolase ligand-targeted liposomes

We have studied the growth-inhibitory potency of methotrexate and methotrexate-gamma-aspartate encapsulated in liposomes conjugated to ligands of ecto-NAD+-glycohydrolase (Salord, J. et al., Biochim. Biophys. Acta 886 (1986) 64-75). The ability of targeted liposomes to enhance growth inhibition, which amounted to a 4-fold reduction of the drug concentration required to inhibit cell growth by 50% as compared to nontargeted liposomes, was observed only with cells expressing this ecto-enzyme activity, i.e., Swiss 3T3 fibroblasts and RAJI, a Burkitt-type lymphoma cell line. Delivery of the encapsulated drugs was inhibited by NH4Cl and varied with the endocytic capacity of the cells. Only small unilamellar vesicles affected the growth of the lymphoma cells, whereas the fibroblasts were more sensitive to large unilamellar vesicles. With vesicles of appropriate size, there was a good correlation between the specific binding of the targeted liposomes to cells and drug delivery. Our results suggest that ecto-NAD+-glycohydrolase can provide a recognition site on target cells and mediate the internalization of targeted liposomes by a mechanism most probably related to adsorptive endocytosis.

Immunospecific targeting of immunoliposomes, F(ab')2 and IgG to red blood cells in vivo

In this report a model to study the fate of target cells in the blood circulation after injection of appropriate immunoliposomes is discussed. The effect of intravenous administration of antimouse RBC immunoliposomes, F(ab')2 or IgG on the fate of intravenously injected 51Cr-labelled mouse RBC (Cr-mRBC) in the mouse and, particularly, in the rat was studied. The immunoliposome was of the Fab'-MPBPE-REV type (Fab'-fragments covalently linked to reverse phase evaporation vesicles by maleimido-4-(p-phenylbutyrate)phosphatidylethanolamine). In the rat model a high blood level (80%) of the injected dose of target cells, Cr-mRBC, was maintained for several hours. The elimination by Fab'-liposomes, F(ab')2 or IgG of Cr-mRBC, and subsequent uptake into liver and spleen was dose dependent. Administration of Fab'-liposomes or F(ab')2 resulted in a preferential uptake into the spleen (above a certain dose also, but much lower, uptake into the liver was observed), while after IgG administration 51Cr-label was mainly recovered in the liver. At equal protein doses (+/- 130 micrograms) Fab'-liposomes induced a faster elimination of the Cr-mRBC and a higher uptake into the spleen than F(ab')2. The potential advantage of the use of drug-loaded immunoliposomes to eliminate target cells from the blood stream and to induce a certain pharmacological effect in the target cells, in comparison with the free antibody administration of F(ab')2 or IgG is discussed.

Lectin-mediated targeting of liposomes to a model surface. An ELISA method

Wheat germ agglutinin has been conjugated to the surfaces of sonicated phospholipid liposomes by reacting the protein derivatised with N-succinimidyl-S-acetylthioacetate (SATA) with the m-maleimidobenzoyl-N-hydroxysuccinimide (MBS) derivative of dipalmitoylphosphatidylethanolamine (DPPE) incorporated into the liposomal bilayers. The liposomes as characterised by photon correlation spectroscopy had a weight-average radius of 44 +/- 10 nm and the number of WGA molecules per liposome was in the range up to approx. 120. An ELISA method has been developed to assess the efficiency of targeting the conjugated liposomes to the antigenic determinants on a surface coated with glycophorin A (blood group B). For liposomes in which the degree of conjugation was controlled by varying the mol% DPPE-MBS from 3 to 27% targeting efficiency as assessed from the extent of inhibition of the ELISA increased by a factor of 10.

Protein immobilization on the surface of liposomes via carbodiimide activation in the presence of N-hydroxysulfosuccinimide

A method of the covalent immobilization of proteins on the surface of liposomes, containing 10% (by mol) of N-glutaryl phosphatidylethanolamine, is described. Carboxylic groups of liposomal N-glutaryl phosphatidylethanolamine were activated in the presence of water-soluble carbodiimide and N-hydroxysulfosuccinimide and reacted subsequently with protein amino groups. The liposome-protein conjugates formed contained up to 5 x 10(-4) mol protein/mol lipid. Lectins (RCA1 and WGA) upon immobilization on liposomes retained saccharide specificity and the ability to agglutinate red blood cells. The immobilization of mouse monoclonal IgG in a ratio of 3.5 x 10(-4) mol IgG/mol lipid was achieved. The liposome activation in the absence of N-hydroxysulfosuccinimide resulted in a 2-fold decrease of protein coupling yields.

Plasmid DNA adsorbed to pH-sensitive liposomes efficiently transforms the target cells

We have previously reported that plasmid DNA entrapped in the pH-sensitive immunoliposomes effectively transforms the target cells (Proc. Natl. Acad. Sci. USA, in press). In the present study, we demonstrate that DNA adsorbed on the same liposome also transforms the target cells. The transformation activity is antibody dependent, as liposomes containing no targeting antibody had reduced activity. The activity could be significantly inhibited by excess non-specific DNA (salmon sperm). Since some DNA are likely adsorbed to the liposomes during the entrapment process, the activity of the entrapped DNA is partially accounted for by the adsorbed DNA. The possibility of developing a simple DNA-mediated transfection protocol using liposome adsorbed DNA is discussed.

Liposomes are effective carriers for the ocular delivery of prophylactics

Liposomes containing acetylcholinesterase were prepared by the freeze-drying method. The multilamellar morphology of the vesicles was revealed by freeze-fracture electron microscopy and their size distribution was determined by quasi-elastic light scattering. The vesicle diameters were in the range of about 0.2-4.0 micron. The liposome preparations were tested for their ocular delivery of an entrapped cholinesterase enzyme in counteracting the miotic effect of diisopropylfluorophosphate (DFP), a prototype of a family of organophosphate poisons. The topical application of the enzyme-containing liposomes to the rabbit eye was found to confer a significant level of protection against DFP-induced miosis. In comparing the prophylactic effectiveness of different enzyme-bearing liposomes, positively charged vesicles were found to be more effective than either neutral or negatively charged vesicles. Although the precise protective mechanism is not clear, our in vitro studies indicate that DFP molecules freely associate with liposomes and tear fluid promotes the release of liposome-entrapped enzymes. Thus, it is conceivable that the enzyme-liposome complex may act somewhat like a sponge by sequestering DFP molecules which diffuse into the vesicle, and also by releasing the entrapped enzyme to combine with DFP, thereby neutralizing its in vivo toxic effect.

Monoclonal antibodies and immobilized antibodies. Patents and literature

Antibodies in both their free and immobilized state have been the object of considerable industrial and academic interest. A variety of methods are used for preparing and immobilizing antibodies. Applications for monoclonal antibodies include the preparation of therapeutics, diagnostics, and in affinity fractionation. Recent US patents on monoclonal and immobilized antibodies and scientific literature on monoclonal antibodies are surveyed. A description of these patents and a list of references are given.

Solid core liposomes with encapsulated colloidal gold particles

Solid core liposomes with encapsulated colloidal gold particles were prepared through four major steps: Preparation of prevesicles with encapsulated solid cores of agarose-gelatin by emulsification of agarose-gelatin sol in organic solvent containing emulsifiers followed by cooling. Extraction of lipophilic components from prevesicles to obtain microspherules of agarose-gelatin. Introducing colloidal gold particles into microspherules and coating with protein molecules. Encapsulation of colloidal gold-bearing microspherules with the modified organic solvent spherule evaporation method for preparation of liposomes (Kim et al. (1983) Biochim. Biophys. Acta 728, 339-348 and Kim et al. (1984) Biochim. Biophys. Acta 812, 793-801). Electron micrographs showed that if liposomes were prepared by using a lipid mixture containing dioleoylphosphatidylcholine/cholesterol/dioleoylphosphatidylglycerol/tri olein (molar ratio 4.5:4.5:1:1), there was only a single continuous bilayer membrane for each solid core liposome. However, if no triolein was added to the lipid mixture, it would cause the formation of multilamellar liposomes. In both cases, there were hundreds to thousands of colloidal gold particles within each solid core liposome.

Enhanced delivery to target cells by heat-sensitive immunoliposomes

Heat-sensitive immunoliposomes are capable of releasing the entrapped content at the target cell surface upon a brief heating to the phase transition temperature of the liposome membrane. In this study we have examined the delivery efficiency of drugs entrapped in heat-sensitive immunoliposomes. Immunoliposomes composed of dipalmitoyl phosphatidylcholine with entrapped [3H]uridine were incubated with target cells at 4 degrees C. The cell-liposome mixture was then heated to 41 degrees C and the uptake of [3H]uridine into the intracellular pool of phosphorylated uridine-containing molecules was measured. The immunoliposomes showed maximal release of the uridine at 41 degrees C, the phase transition temperature of dipalmitoyl phosphatidylcholine liposomes. The largest accumulation of [3H]uridine in the target cells also took place at 41 degrees C. The initial level of uptake of [3H]uridine released from immunoliposomes by heating was greatly enhanced over that observed for free [3H]uridine and [3H]uridine released from liposomes without attached antibody. The nucleoside uptake inhibitors nitrothiobenzylinosine, dipyridamole, and unlabeled uridine were able to inhibit uptake of [3H]uridine released from immunoliposomes. This supports the hypothesis that the enhanced uptake is due to a heat-induced release of [3H]uridine at the cell surface followed by transport and phosphorylation of [3H]uridine by the target cells. These results indicate the feasibility of using the heat-sensitive immunoliposomes as a target-specific drug delivery system.