The Effect of Polycation Complexation on Methotrexate Retention in Liposomes

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Abstract
Methotrexate [used in the treatment of acute leukemia] and a methotrexate-DEAE [diethylaminoethanol] dextran complex were encapsulated in dipalmitoylphosphatidylcholine liposomes. In all cases, the degree of encapsulation of methotrexate in the methotrexate-DEAE dextran liposomes was higher than in the plain methotrexate liposomes. The kinetic permeability of methotrexate from both methotrexate and methotrexate-DEAE dextran dipalmitoylphosphatidylcholine liposomes was studied at 37.degree. C in pH 7.4 acetate buffer. All liposome systems appeared to show a biphasic 1st order kinetic release of methotrexate. The initial rapid release probably resulted from the desorption of adsorbed methotrexate. The initial rapid release probably resulted from the desorption of adsorbed methotrexate, and the subsequent slow release was from the diffusion of the entrapped drug. The desorption kinetics were separated from the diffusion process in the 1st phase by graphing. The methotrexate-DEAE dextran liposome data showed 13% methotrexate bound to the liposome surface compared to 23% methotrexate bound on the plain methotrexate liposome surface.