Liposome encapsulation of doxorubicin: Pharmaceutical and therapeutic aspects

Abstract The influence of lipid composition on the in vitro and in vivo behavior of doxorubicin (DXR)containing liposomes (extrusion-multilamellar vesicles) was investigated in order to assess critical parameters controlling the quality of DXR-containing liposome formulations. p]A proper choice of the liposomal lipid composition appeared to be an important factor in manufacturing stable liposome dispersions with optimum pharmaceutical and therapeutic characteristics. Negatively charged liposomes were to be preferred over neutral liposomes as the inclusion of negatively charged lipids like phosphatidylserine and dipalmitoylphosphatidylglycerol yielded a higher loading capacity for DXR and an increased stability of the dispersion against agglomeration. With respect to loading capacity, inclusion of dicetylphosphate was less favourable because of the formation of lipid-drugprecipitates. Formation of insoluble non-liposomal lipid-drug complexes prevented the production of DXR-liposomes consisting of only phosphatidylserine. Instead of having a real multilamellar nature, the DXR-liposomes appeared to be uni- or oligolamellar. In general, cholesterol was a key component for reducing the leakiness of DXR-liposomes both during storage at 4–6° C over a 4-week period and in the presence of serum. However, fulfillment of these basic requirements did not guarantee long-term stability. Extensive phospholipid-stimulated chemical decomposition and loss of encapsulated DXR were observed during long-term storage of DXR-liposomes consisting of phosphatidylcholine, phosphatidylserine and cholesterol (molar ratio 10:1:4). These phenomena were not detected in dispersions with DXRliposomes prepared from dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol and cholesterol (molar ratio 10:1:10) indicating that long-term storage was a function of liposomal lipid composition. In vivo , all liposome types tested were more effective than the free drug in increasing the life span of solid IgM immunocytoma bearing rats. The prolonged survival was most likely based on a reduction in toxicity (as indicated by a protective effect against loss of body weight and delayed occurrence of albuminuria) along with preservation of antitumor activity. The therapeutic behavior of DXR-liposomes depended on the physical and chemical properties of the liposomal membrane. DXR-liposomes composed of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol and cholesterol (molar ratio 10:1:10) were the most effective in increasing the life span of tumor-bearing animals. The variation in therapeutic effect obtained with different liposomal lipid compositions underlined the necessity of a proper physico-chemical characterization of liposme preparations in order to obtain reproducible results in vivo . Furthermore, the results suggested that optimization of liposomal chemotherapy with DXR is a realistic possibility.