Liposomal pemetrexed: formulation, characterization and in vitro cytotoxicity studies for effective management of malignant pleural mesothelioma.

Pemetrexed (PMX) is a newly developed multi-targeted anti-folate with promising clinical activity in many solid tumors including malignant pleural mesothelioma (MPM). However, PMX does not show sufficient anti-tumor activity in vivo when used alone either due to inefficient delivery of adequate concentrations to tumor tissue or dose-limiting side effects. In order to overcome these problems and to achieve potent anti-tumor activity, PMX was encapsulated into a liposomal delivery system. In the present study, various formulations of liposomal PMX were prepared. The effect of formulation parameters on the encapsulation efficiency of PMX within liposomes was evaluated. In addition, the influence of drug release rate on the in vitro cytotoxicity was investigated. Encapsulation of PMX within liposomes was remarkably increased by the incorporation of cholesterol within liposomal membranes and by increasing the total lipid concentration. Encapsulation efficiency was found to be unaffected by the type of phospholipid used or the inclusion of a cation lipid, DC-6-14. Interestingly, encapsulation of PMX within "fluid" liposomes was found to allow efficient release of PMX from liposomes resulting in a potent in vitro cytotoxicity against MPM MSTO-211H cell line. On the other hand, entrapment of PMX within "solid" liposomes substantially hindered PMX release from liposomes, and thus PMX failed to exert any in vitro cytotoxicity. These results suggest that encapsulation of PMX within "fluid" liposomes might represent a novel strategy to enhance the therapeutic efficacy of PMX while minimizing the side effect encountered by the non selective delivery of free PMX to various body tissues.