Targetability of novel immunoliposomes modified with amphipathic poly(ethylene glycol) s conjugated at their distal terminals to monoclonal antibodies

Abstract

Distearoyl-N-(3-carboxypropionoyl poly(ethylene glycol) succinyl)phosphatidylethanolamine (DSPE-PEG-COOH) was newly synthesized and used to prepare novel immunoliposomes carrying monoclonal antibodies at the distal ends of the PEG chains (Type C). Liposomes were prepared from egg phosphatidylcholine (ePC) and cholesterol (CH) (2;1, m/m) containing 6 mol% of DSPE-PEG-COOH, and a monoclonal IgG antibody, 34A, which is highly specific to pulmonary endothelial cells, was conjugated to the carboxyl groups of DSPE-PEG-COOH to give various amounts of antibody molecules per liposome. Other immunoliposomes with PEG coating (Type B) or without PEG coating (an earlier type of immunoliposome, Type A) were prepared for comparison. The average molecular weight of PEG in Type B or C immunoliposomes was 2000. Type B and Type C liposomes without antibodies showed prolonged circulation time and reduced reticulo-endothelial system (RES) uptake owing to the presence of PEG. These three different types of 34A-immunoliposomes with 30-35 antibody molecules per vesicle were injected into mice to test the immunotargetability to the lung. The efficiency of lung binding of 34A-Type B was one-half of that of 34A-Type A, though a large amount of 34A-Type B remained in the blood circulation for a long time, suggesting that the steric hindrance of PEG chains reduced not only the immunospecific antibody-antigen binding, but also the RES uptake. The degree of lung binding of 34A-Type C was about 1.3-fold higher than that of 34A-Type A, indicating that recognition by the antibodies attached to the PEG terminal was not sterically hindered and that the free PEG (i.e., that not carrying antibody) was effective in increasing the blood concentration of immunoliposomes by enabling them to evade RES uptake. The latter phenomenon was confirmed by using nonspecific antibody-Type C immunoliposomes (14-Type C), which showed a high blood level for a long time. Our approach provides a simple means of conjugating antibodies directly to the distal end of PEG which is already bound to the liposome membrane, and should contribute to the development of superior targetable drug delivery vehicles for use in diagnostics and therapy.

Cyclic RGD peptide-modified liposomal drug delivery system: enhanced cellular uptake in vitro and improved pharmacokinetics in rats

“…The method is different from that used in most recent studies, attaching peptide ligand to the distal ends of PEG-lipids. 9,14 MCC-465, a PEGylated liposomal formulation containing doxorubicin targeted with an F(ab') 2 fragment of the human monoclonal antibody (GAH), was the first targeted nanoparticle to enter clinical trials. 15 For MCC-465, GAH was covalently coupled with the liposomal membrane surface.…”

“…[7][8][9][10][11][12] There are two main ways of modifying the liposomal membrane to display targeting ligands, ie, by direct coupling with the surface or with the distal ends of PEGlipids. 7,13,14 Liposomes modified in such ways show targeting and long circulation times in vitro. However, MCC-465, a PEGylated liposomal formulation containing doxorubicin targeted with a F(ab') 2 fragment of human monoclonal antibody known as GAH, was the first targeted nanoparticle to enter clinical trials.…”

Development of a Platform of Antibody-Presenting Liposomes

“…Antibodies, mostly IgGs or their fragments, have received special interest because they can recognize and bind virtually any molecular target with high specificity and high affinity. The association of IgGs to liposomes is usually realized by chemical conjugation via hetero-bifunctional crosslinkers on the polar head of lipid molecules modified with a PEGylated reactive group [13]. This strategy of covalent coupling presents however several drawbacks, principally the lack of control of the site of protein modification which involves commonly their most accessible and/or most reactive protein amino groups, so that their molecular recognition properties may be altered due to chemical modification and/or non-optimal orientation [14].…”

Adiponectin-coated nanoparticles for enhanced imaging of atherosclerotic plaques

“…23 Likewise, functionalized groups can be attached to the distal end of the polyethylene glycol chains for coupling of active molecules. 40 Alternatively, different labels can be linked to or incorporated into the liposomes. 41,42 Proticles are less well explored, but have already proven to be very successful in drug targeting.…”