Regression of subcutaneous B16 melanoma tumors after intratumoral delivery of an IL-15-expressing plasmid followed by in vivo electroporation

Abstract

In vivo electroporation has been used to efficiently deliver drugs and 'therapeutic' genes to tumors, including melanoma lesions. This study reports on the effect of intratumoral delivery of an optimized DNA plasmid expressing interleukin-15 (pIL-15) on established murine melanoma tumors. IL-15 has been demonstrated to have a pivotal role in the function of memory CD8+ T cells and natural killer cells, which are critical for tumor immunosurveillance. In this study, C57BL/6 mice were injected with B16.F10 melanoma cells and randomized into different experimental groups: untreated (P-V-E-), treated with pIL-15 (P+) or backbone plasmid (V+), with or without electroporation (E+ or E-). Treatment was performed intratumorally with 50 microg of plasmid on days 0, 4 and 7 and tumor volume/size, tumor regression and long-term survival were measured. At day 100 after initiation of treatment, the percentage of mice surviving with complete tumor regression in the P-V+E+, P+V-E-, P+V-E+ and P-V-E- treatment groups were 0, 12.5, 37.5 and 0%, respectively. These results demonstrate the ability of pIL-15 to mediate B16 melanoma regression, with the effect being significantly enhanced by electroporative delivery. This is the first description of the ability of a naked DNA plasmid expressing IL-15 to alone mediate complete regression of B16 melanoma tumors and underscores the potential clinical use of these plasmids for the treatment of malignant tumors when delivered with in vivo electroporation.

Figure 1

Measurement of expression of IL-15 in B16 melanoma tumor lysates after intratumoral delivery of pIL-15 with or without electroporation. The key for the letter and +/− designations for the treatment groups are provided in the Materials and methods section. The mean concentrations of tumoral IL-15 are expressed as pg/mg tumor.

Figure 2

Kaplan–Meier survival curves for C57BL/6 mice in treatment groups injected with pIL-15 or control plasmid with or without electroporation. Groups of mice (P−V−E−, P−V+E+, P+V−E− and P+V−E+) were treated as described in the Materials and methods section and were followed for tumor regression and long-term survival (up to 100 days after initiation of the treatment regimens).