Design of immunoliposomes directed against human ovarian carcinoma

Factors (protein/lipid ratio, pH of incubation medium, incubation time, anchor molecule density in the bilayer) affecting the covalent binding of anti-ovarian carcinoma Fab' to liposomes containing the anchor molecule MPB-PE (N-(4-(p-maleimidophenyl)butyryl)phosphatidylethanolamine) were explored. Standard experimental conditions were chosen and information on the relevant physicochemical parameters of the liposome dispersions was collected (mean particle diameter, size distribution, charge). The reproducibility of standard immunoliposomes prepared in subsequent batches in terms of Fab' binding, particle size and charge was established. In addition, preservation of immunoreactivity, no marker loss, and no aggregation/fusion was found for the standard immunoliposomes over a period of at least 3 weeks at 4 degrees C. In vitro up to 35,000 immunoliposomes were estimated to bind per human ovarian carcinoma cell. Internalization of the immunoliposomes could not be demonstrated. Electron micrographs showed binding of specific immunoliposomes to human ovarian carcinoma cells growing intraperitoneally in athymic nude mice.