1. ¹Department of Neurosurgery, Saiseikai Kumamoto Hospital, 5-3-1 Chikami, Kumamoto 861-4193, Japan
2. ²Department of Neurosurgery, Kumamoto University School of Medicine, 1-1-1 Honjo, Kumamoto 860-8556, Japan
3. ³Shionogi Institute for Medical Science, 2-5-1 Mishima, Settsu, Osaka 566-0022, Japan
4. ⁴Gene Delivery and Expression Sciences, 6325 Dennison Street, San Diego, CA 92122, USA

Correspondence: Toru Nishi, Fax: +81 96 351 8795. E-mail: t-nishi@skh.saiseikai.or.jp

Received 27 May 2004; Accepted 27 July 2004.

Abstract

We report the use of plasmid DNA-mediated combination gene therapy for tumor-bearing mice using in vivo electroporation, also called electro-gene therapy (EGT), that resulted in uncomplicated and complete cures in more than 90% of the mice. Subcutaneously inoculated CT26 tumors in syngeneic BALB/c mice were subjected to repeated EGT treatments consisting of intratumoral co-injection of naked plasmids encoding the cytokine interleukin-12 (IL-12) (p35 and p40 subunits) and the suicide gene herpes simplex virus thymidine kinase (HSV-tk), followed by in vivo electroporation. The early anti-tumor effect was always stronger, and the rate of cure, as seen in the long-term follow-up, was always greater in the groups treated with combination EGT than in those treated with IL-12 or HSV-tk EGT alone. Systemic levels of IL-12 and IFN- increased in both combination and IL-12-alone EGT-treated groups. Moreover, combination EGT for established subcutaneous tumors strongly reduced hematogenous lung metastases and increased survival time when live CT26 tumor cells were injected through the tail vein. Limited experiments on C57/B16 mice with murine melanoma also showed very similar trends. These results suggest that this simple and safe method of plasmid-mediated combination EGT may provide a potentially effective gene therapy for cancer.