The effective treatment of metastases is a challenge for any cancer treatment. For immunotherapy to be beneficial in the treatment of metastatic disease, the immune system must recognize tumor cells throughout the body, which can be achieved by inducing a systemic immune response or through the creation of memory T cells following recognition of a primary tumor.
Many cytokines have been intensively investigated as potential anticancer agents. Among the many cytokines evaluated, Interleukin-12 (IL-12) has been shown to exhibit strong antitumor activities. IL-12 can upregulate the proliferation and maturation of T cells and natural killer (NK) cells, induce production of IFN-γ, inhibit angiogenesis, and upregulate expression of accessory molecules such as HLA. Unfortunately, delivery of IL-12 in the form of recombinant protein results in severe toxicity and adverse side effects, including death. Therefore, gene therapy strategies for delivery of IL-12 have been explored such as the use of viral vectors, gene gun, microspheres, direct injection of plasmid, and electroporation.
The antitumor potential of IL-12 has been reported in numerous immunotherapy studies. The proposed antitumor mechanisms of IL-12 include effects on the immune system such as the induction of IFN-γ, upregulation of T cells, and proliferation of natural killer (NK) cells. In addition, IL-12 inhibits angiogenesis, the formation of new blood vessels. This wide range of effects on the immune system as well as antiangiogenic properties results in a potentially potent antitumor treatment. Unfortunately, preclinical and clinical trials using systemic administration of recombinant IL-12 demonstrated potential adverse side effects. Administration of recombinant IL-12 locally or systemically has been reported to induce potent antitumor activity in a variety of murine tumor models, causing regression of established tumors. However, in these studies, repeated delivery of recombinant IL-12 on a daily basis was required to achieve the maximal therapeutic activity, and was also usually associated with a dose-dependent toxicity. The use of gene therapy for the delivery of IL-12, by gene gun, resulted in fewer side effects than recombinant protein therapy. Several studies using viral and nonviral gene delivery techniques have reported success in slowing and/or preventing tumor growth. However, these studies have had limited success in demonstrating complete regression of the poorly immunogenic B16.F10 melanoma and subsequent resistance to challenge.
In vivo electroporation is a gene delivery technique that has been used successfully for efficient delivery of plasmid DNA to many different tissues. Studies have reported the administration of in vivo electroporation for delivery of plasmid DNA to B16 melanomas and other tumor tissues. Although systemic administration of recombinant IL-12 revealed its antitumor potential, expression of IFN-gamma at the tumor site has been shown to be critical for successful tumor regression. Systemic and local expression of a gene or cDNA encoded by a plasmid can be obtained with administration of in vivo electroporation. Use of in vivo electroporation enhances plasmid DNA uptake in tumor tissue, resulting in expression within the tumor, and delivers plasmids to muscle tissue, resulting in systemic cytokine expression.
It has been shown that electroporation can be used to transfect cells in vivo with plasmid DNA. Recent studies have shown that electroporation is capable of enhancing delivery of plasmid DNA as an antitumor agent. Electroporation has been administered for treatment of hepatocellular carcinomas, adenocarcinoma, breast tumors, squamous cell carcinoma and B16.F10 melanoma in rodent models. The B16.F10 murine melanoma model has been used extensively for testing potential immunotherapy protocols for the delivery of IL-12 and other cytokines either as recombinant protein or by gene therapy.
Its wide range of effects on the immune system and its antiangiogenic properties make IL-12 an excellent candidate for use an as immunotherapeutic agent. Because of its potential toxicity, it is important to give careful consideration to the delivery method of IL-12. In vivo electroporation is a safe, nontoxic delivery system and has been used for efficient delivery of chemotherapeutic agents and plasmid DNA, including plasmids encoding IL-12.
Electroporation mediated in vivo delivery of the murine interleukin-12 (IL-12) gene in an expression plasmid has been shown to provide antitumor and antimetastasis activity. Various protocols are known in the art for the delivery of plasmid encoding Il-12 utilizing in vivo electroporation for the treatment of cancer. The protocols known in the art describe in vivo electroporation mediated cytokine based gene therapy, both intratumor and intramuscular, utilizing low-voltage and long-pulse currents. Prior art methods have identified these low-voltage levels to be less than 300V and long pulses to be in the area of 50 ms. Rationalization for the use of low-voltage levels and long pulse lengths for the delivery of plasmid encoding IL-12 for the treatment of tumors is based on well-known principles of electroporation and electrochemotherapy. It is known that electric pulses with moderate electric field intensity can cause temporary cell membrane permeabilization, which may then lead to rapid genetic transformation and manipulation in a wide variety of cells types including bacteria, yeasts, animal and human cells, and so forth. Conversely, electric pulses with high electric field intensity can cause permanent cell membrane breakdown and tissue damage. All prior art methods describing the administration of an electroporation protocol for delivery of IL-12 to the target tissue are based on the application of low-voltage, long length pulses. These treatment protocols known in the art have not been effective in demonstrating acceptable cure rates for tumors, including B16.F10 melanoma tumors. Additionally, the known treatment protocols have been unable to demonstrate improved long-term subject survival rates.
Accordingly, what is needed in the art is an electroporation protocol for the delivery of a plasmid encoding a therapeutic protein that will provide substantially improved results in the regression of cancer tumors while also substantially improving the long-term survival rates.