Increased uptake of liposomal–dna complexes by lung metastases following intravenous administration

We have investigated the effects of an improved liposomal formulation (extruded DOTAP:cholesterol (DOTAP:Chol)–DNA complex) on transgene expression in tumor cells and normal cells of murine and human origin both in vitro and in vivo. In vitro, transgene expression was significantly increased (P = 0.01) in human tumor cells compared to normal human cells. The increased transgene expression was due to increased uptake of the liposome–DNA complex by tumor cell phagocytosis. Furthermore, immunohistochemical analysis demonstrated a greater transgene expression in lung tumors than in surrounding normal tissues. Increased transgene expression due to enhanced uptake of the liposome–DNA complexes by tumor cells in vivo was also demonstrated using fluorescently labeled DOTAP:Chol liposomes. Finally, evaluation of lung tissue explants obtained from patients undergoing pulmonary resection demonstrated significantly higher (P = 0.001) transgene expression in tumor cells than in normal cells. Thus, we demonstrated that intravenous injection of DOTAP:Chol–DNA complex results in increased transgene expression in tumor and is due to increased phagocytosis of the complexes by tumor cells.