Liposomes with antibodies

Nanotechnology has led to very efficient versions of liposomes. Tiny hollow spheres only nanometers in diameter hold even tinier capsules of medicine. The spheres are made of silica covered with gold nanoparticles and when they are coated with antibodies they attach to tumor cells. The spheres are sensitive to light of specific wavelengths and when the light is applied, either heat up and destroy the tumor, or burst, releasing the drugs within the capsules directly into the tumor. 

Attempts to achieve a tissue specific transport of liposomes have recently been described. Cohen et al. coated liposomes with aggregated immunoglobulin ( 7). The take up rate of these vesicles into phagocytes could be increased by a factor of 60 compared to uncoated liposomes. 3 to 25 times more liposomes are taken up by the corresponding cells, if they are loaded with the appropriate antibodies (58). Similar attempts to achieve a "homing" have been carried out using lipid fixed antibodies (59). 

In order to study in vitro the activation potential of the vaccine formulation, 4x10 BmDCs were incubated either with 400 pg free TRP-2 or 40 pg TRP-2 in liposomal formulations. In addition, CpG-ODNs were added in this series of experiments concomitantly either in its free form (20 nmol) or in its liposomal form (5.2 nmol). The incubation took place in 4mL RPMI (with 5% PCS) for 48 hours at 37°C. After completion of the incubation, the cells were stained with antibodies specific for CD80, CD86 and MHC II molecules, which are expressed in high amounts on the surface of DCs after activation. 

Figure 2. Immune lysis of a sensitized liposome. Immobilized antibody-sensitized liposome undergoes complement-induced lysis. Released enzyme catalyzes substrate-product reaction with concomitant reduction of immobilized cofactor. The cofactor is electrochemi-cally reoxidized and the current is related to the analyte concentration. (See text for discussion.) Symbols A, analyte (antigen) Y, antibody S, sub-...

Haga et al. developed another type of immunosensor by combining an enzyme membrane immunoassay and an enzyme sensor using oxygen electrodes (HI). In this assay antigen molecules (theophylline) are attached on the surface of the liposomes and an enzyme (horseradish peroxidase) is encapsulated in the sensitized liposome. When antibody (antitheophylline antibody) and complement are added, the enzyme is released by the liposome lysis. The enzyme activity with the NADH-NAD reaction can be determined by the oxygen electrode. When antigen is added, it competitively binds to antibodies, then liposome lysis and enzyme activity are decreased. The sensitivity of this method for theophylline determination was reported as 0.7 ng/ml. 

Moreover, Voinea et al. attached antibodies against vascular cell adhesion molecule-1 (VCAM-1) overexpressed on activated human endothelial cells on liposomes with the intention of using them as drug carriers [162], A-gluraryl-PE was used as membrane anchor for the antibody coupling via its free amino groups after its activation with carbodiimide. There is no necessity of antibody modification before the coupling reaction. 

An avidin-biotin system has been used to attach antibodies in the bilayer of DDSs. Xiao et al. developed a three-step strategy to improve the tumor-to-tissue ratio of anticancer agents [184], Two antibodies specific for the CA-125 antigen that is highly expressed on NIH OVCAR-3 cells were used. These cells were prelabeled with biotinylated anti-CA-125 antibody and fluoroscein isothiocyanate (FITC)-labeled streptavidin (SAv) prior to administration of biotinylated liposomes. Both antibodies were specifically bound to the cell surface of OVCAR-3 cells but not to SK-OV-3 cells, which do not express the specific antibody. Antibody biotinylation did not affect its immunoreactivity. 

Similar to drugs, liposomes could be conjugated with antibodies, peptides and genes, among others, to expand the existing range of analytical and non-analytical applications of US. 

Matzku, S. Krempel, H. Weckenmann, H.P. Schirrma-cher, V. Sinn, H. Strieker, H. Tumour targeting with antibody-coupled liposomes failure to achieve accumulation in xenografts and spontaneous liver metastases. Cancer Immunol. Immunother. 1990, 31, 285-291. 

An approach to enhance Pgp inhibition was applied by Matsuo et al. (90). They used liposomes with a covalently bound monoclonal antibody against an extracellular epitope of Pgp (MRK-16). The binding of these liposomes to K-562/ADM cells (adriamycin-resistant human myelogenous leukemia cell line) was higher than that of IgG2A-modified liposomes and liposomes without modification. In addition, when vincristin was encapsulated in all types of liposomes, it was demonstrated that the cytotoxicity of MRK-16-modified liposomes was higher than that of IgG2a and nonmodified liposomes. 

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