DSPE-PEG-COOH

Maruyama, Kazuo. Bioscience reports 22.2 (2002): 251-266.

Pendant-type PEG immunoliposomes carry monoclonal antibodies or fragments thereof at the distal end of the PEG chain. Two different anatomical structures were considered with respect to Type C target binding. They are the mouse lung endothelium as an easily accessible site via the intravascular route and implanted solid tumors as less accessible target sites reached via extravasation. Small unilamellar liposomes (90-130 nm in diameter) were prepared from phosphatidylcholine and cholesterol (2:1, mm) containing 6 mol.% DSPE-PEG-COOH or DPPE-PEG-Mal. To target the lung vascular endothelial surface, the 34A antibody, which is highly specific for mouse lung endothelial cells, was conjugated to the PEG liposomes (34A-Type C). 34A-Type C showed significantly higher lung binding in BALB c mice than the common type immunoliposomes (without PEG derivatives), 34A-Type A. For targeting solid tumor tissues, 21B2 antibody (anti-human CEA) and its Fab' fragment were used. The targeting ability of Fab'-Type C was tested by inoculating CEA-positive human gastric cancer line MKN45 cells into BALB c nu nu mice.
The conventional liposomes used to prepare type A or type C immunoliposomes consisted of egg PC and Chol (2:1, m m) with 6 mol.% NGPE or DSPE-PEG-COOH with an average molecular weight of 3000, respectively. Type B conventional liposomes consisted of egg PC and Chol (2:1, m m) with 6 mol.% NGPE and 6 mol.% DSPE-PEG with an average molecular weight of 3000. SUVs (90-130 nm in diameter) were prepared by the REV method and then extruded through Nucleopore filters (0.1 μm). The carboxyl residues in the conventional liposomes were activated and conjugated with 34A antibody.