Augmented anti-tumor therapy through natural targetability of macrophages genetically engineered by NK4 plasmid DNA

The objective of this study is to genetically engineer macrophages (Mphi) for biological activation and evaluate their anti-tumor activity in a tumor-bearing mouse model. Mouse peritoneal Mphi were incubated on the surface of a culture dish which had been coated with the complex of a cationized dextran and luciferase plasmid DNA complex plus a cell adhesion protein, Pronectin for gene transfection (reverse transfection). When compared with the conventional transfection where Mphi were transfected in the medium containing the complex, the level of gene expression by the reverse method was significantly high and the time period of gene expression was prolonged. Confocal microscopic observation revealed that the plasmid DNA was localized in the cell nucleus to a higher extent by the reverse transfection method. Following the reverse transfection of Mphi by the plasmid DNA of a hepatocyte growth factor antagonist (NK4) complexed with the cationized dextran, the NK4 protein was secreted at a higher amount for a longer time period in contrast to the conventional transfection of free plasmid DNA. The NK4-transfected Mphi exhibited a stronger inhibition activity for in vitro growth of Meth-A fibrosarcoma cells. When injected intravenously into mice carrying a mass of Meth-A tumor cells, the Mphi engineered were accumulated in the tumor tissue and showed significant anti-tumor activity. It is concluded that the Mphi injected functioned as the natural carrier of tumor targeting for anti-tumor NK4 molecules, resulting in enhanced suppression of tumor growth at a high selectivity.