Liposomes loaded with lipophilic prodrugs of methotrexate and melphalan as convenient drug delivery vehicles

Liposomal formulations prepared by extrusion from natural phospholipids and 1,2-dioleoylglycerol conjugates of methotrexate and melphalan (egg phosphatidylcholine-phosphatidylinositol–prodrug, 8:1:1, by mol.) were characterized by size, composition and stability. Both prodrugs were shown to incorporate completely into unilamellar liposomes with the mean size below 100 nm and form stable dispersions containing the drug concentrations relevant for systemic injections in animals. For long-term storage, the dispersions can be subjected to deep freezing (- 196 °C) and stored at - 70 °C; before usage, they should be defrosted and treated shortly in an ultrasonic bath. According to the example of methotrexate conjugate, stability of prodrug ester bond in liposomal formulation towards hydrolysis by human plasma esterases during 24-h incubation were established. Also, liposomes bearing methotrexate conjugate were shown to overcome resistance of human leukemia cells related to impaired transport of initial drug across the membrane.