ENHANCED CELL KILLING BY METHOTREXATE ENCAPSULATED IN FOLATE TARGETED THERMOSENSITIVE LIPOSOMES

摘要

The exploitation of folate receptor as Trojan horse to deliver folate-targeted liposomes bearing diverse cargo represents a novel therapeutic strategy to target folate receptor-expressing cells. In this paper, thermosensitive liposomes made of synthetic lipids (distearolphosphatidylcholine, DSPC and dipalmitoylphosphatidylcholine, DPPC) showing gel to liquid phase transition at 41o C, were used for encapsulation of methotrexate. The liposomes were prepared by thin film hydration method, the liposome binding constant Kb for the drug was measured using a spectroscopic assay and was found to be 57.18 (mg/ml)–1. We have studied the liposome-mediated delivery of methotrexate to breast tumor cells in vitro, the cell sensitivity study was performed at normal physiological temperature (37o C) as well as hyperthermia increased temperature of 42o C. Moreover, a targeting moiety was used by modifying the liposome surface with folate using polyethyleneglycol (PEG) as a spacer. The ability of methotrexate to inhibit tumor cell growth is increased dramatically when encapsulated in targeted (folated) thermosensitive liposomes, but decreased when encapsulated in liposomes deficient folate. The index of cell Killing expressed as IC50 was reduced dramatically from 7 μg/ml to 0.864 μg/ml upon using folate as a targeting moiety. Hyperthermia was not effective when used with non-specific targeted liposomes. However, the cytotoxicity of the drug increased dramatically upon heating folate targeted thermosensitive liposomes (the IC50 was reduced to 0.34 μg /ml).