Development of targeted liposome drug delivery vehicle

Abstract

Coating of liposomes with polyethylene glycol (PEG) has proven to prolong the circulation time of liposomes in the blood stream. PEG prevents the binding of opsonins and subsequent uptake of the liposomes by mononuclear phagocytic system (MPS). The reduction in clearance of PEGylated liposomes from the circulation improve the bioavailability of the liposomes in the blood and increase the chance of liposomes being accumulated in tumor tissue by the enhanced permeability and retention effect (EPR). The aim of this study was therefore to investigate the incorporation and retention ability of PEGylated liposome formulations of the anticancer agent Camptothecin (CPT), and further try to develop an immunoliposomal formulation of CPT targeting the EGFR receptors on the surface of colorectal cancer cells. The results from the incorporation and retention studies showed that the formulation consisting of 79 % egg phosphatidylcholine (EPC), 20 % 1,2-di-oleyl-3- trimethylammonium-propane (DOTAP) and 1 % PEG conjugated with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE-PEG) clearly showed the highest incorporation of CPT and the most stable retention ability in different media including medium containing erythrocytes. Formulations with dimethyldioctadecylammonium (DDAB) and 4-(Dodecyloxy)-benzoic acid (DB) demonstrated lower incorporation ability and were slightly more unstable in regard to retention of CPT compared to the formulation with DOTAP. Based on these results, the PEGylated formulation with DOTAP was chosen as the basis for the immunoliposomal formulation. Bovine serum albumin (BSA) and EGFR antibodies were conjugated to the liposome surface by the inclusion of 1 % maleimide terminated DSPE-PEG into the liposome membrane. The loss of CPT from the liposomes observed during conjugation was however significant. In conclusion the presence of PEG on the liposome surface and DOTAP in the liposome bilayer seems to give the most promising PEGylated CPT formulation, which could possibly be a candidate for further in vivo studies. For the immunoliposomes, the attachment of antibodies on the surface was successful. However, due to loss of CPT during the conjugation process the method used is not optimal for this CPT liposome formulation, and further studies are needed to find a more suitable preparation method or a more stable immunoliposome formulation.