PLASMID DNA GENE-THERAPY - STUDIES WITH THE HUMAN INTERLEUKIN-2 GENE IN TUMOR-CELLS IN-VITRO AND IN THE MURINE B16 MELANOMA MODEL IN-VIVO

The plasmid DNA vector pVCL-1102 containing the coding sequence for th e human IL-2 gene was evaluated for expression in tumor cells in vitro and in vivo. In vitro transfection of murine B16 tumor cells with pVC L-1102 resulted in the expression of 36,000 IU (5.7 mu g) of biologica lly active IL-2/10(6) cells/48 h. In vitro transfection of human tumor lines and primary cultures from human biopsies with pVCL-1102 resulte d in the expression of 1,289 to 9345 IU of IL-2/10(6) cells/48 h and 3 0 to 794 IU of IL-2/10(6) cells/48 h, respectively. In vivo, direct in tratumor injection of pVCL-1102 resulted in retention of intact plasmi d DNA in the tumor tissue and IL-2 secretion by cell cultures derived from the injected tumors. Formulation of pVCL-1102 with the cationic l ipid DMRIE/DOPE inhibited DNA degradation and enhanced in vivo transfe ction efficiency over plasmid DNA alone. Antitumor activity of the pVC L-1102/DMRIE/DOPE complex was evaluated in a B16 melanoma model in mic e. An IL-2-specific effect could not be demonstrated in a subcutaneous model because the intratumor injection of plasmid DNA lacking the IL- 2 coding sequence also resulted in a significant reduction in tumor vo lume. However, an IL-2-specific effect was observed when B16 cells wer e transfected in vitro prior to implantation into the mouse. Transient transfection of B16 cells with pVCL-1102 rendered the cells less tumo rigenic in vivo and produced a significant reduction in tumor volume. These data demonstrate that a plasmid DNA expression vector can be use d to deliver the IL-2 gene to tumor cells in vitro and in vivo, result ing in the expression of significant levels of IL-2 protein. These dat a also illustrate the need for the use of appropriate controls when ev aluating the in vivo biological activity of plasmid DNA in murine tumo r models.