Interleukin-12 (IL-12) has been used in numerous immunotherapy protocols against melanoma. However, delivery of IL-12 in the form of recombinant protein can result in severe toxicity, and gene therapy has had limited success against B16.F10 murine melanoma. The purpose of this study was to examine the effectiveness of in vivo electroporation for the delivery of plasmid DNA encoding IL-12 as an antitumor agent against B16.F10 melanoma. We treated mice bearing established B16.F10 melanoma tumors with intratumoral (i.t.) or intramuscular (i.m.) injections of a plasmid encoding IL-12, followed by in vivo electroporation. For i.t. treatments, we used an applicator containing six penetrating electrodes to deliver 1500-V/cm, 100-micros pulses. We administered i.m. pulses with an applicator containing four penetrating electrodes delivering 100-V/cm, 20-ms pulses. The i.t. treatment resulted in the cure of 47% of tumor-bearing mice, and 70% of cured mice were resistant to challenge with B16.F10 cells. The i.m. treatment did not result in tumor regression. We found that i.t. treatment resulted in increased levels of IL-12 and interferon-gamma (IFN-gamma) within the tumors, the influx of lymphocytes into the tumors, and reduction in vascularity. Neither i.m. nor i.t. treatment was successful against B16.F10 tumors in a nude mouse model, supporting a role for T cells in regression of this tumor model.

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In vivo electroporation (EP) is a versatile delivery method for gene transfer which can be applied to any accessible tissue. Delivery of plasmid DNA encoding therapeutic genes or cDNAs with in vivo EP has been tested extensively in preclinical melanoma models. Direct delivery to the tumor has been shown to generate a direct antitumor effect. Delivery to alternative sites may generate additional therapeutic options, for example the production of cancer vaccines, the reduction of tumor angiogenesis, or the induction of tumor cell apoptosis. Several of the preclinical therapies tested have a demonstrated therapeutic effect against melanomas. Two immunotherapies have advanced to melanoma clinical trials. Delivery of a plasmid DNA encoding interleukin-12 (IL-12) or interleukin-2 (IL-2) using electroporation was demonstrated to be a safe with no grade 3 or 4 toxicities reported. Delivery of IL-12 with electroporation resulted in significant necrosis of melanoma cells in the majority of treated tumors and significant lymphocytic infiltrate in biopsies from patients in several cohorts. In addition, clinical evidence of responses in untreated lesions suggested the induction of a systemic response following therapy. This review discusses preclinically tested electroporation gene therapies for melanoma with clinical potential and the conversion of these therapies to clinical trials.

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