Highly efficient electro-gene therapy of solid tumor by using an expression plasmid for the herpes simplex virus thymidine kinase gene

We report successful electro-gene therapy (ECT) by using plasmid DNA for tu mor-bearing mice. Subcutaneously inoculated CT26 tumor was subjected to ECT , which consists of intratumoral injection of a naked plasmid encoding a ma rker gene or a therapeutic gene, followed by in vivo electroporation (EP). When this treatment modality is carried out with the plasmid DNA for the gr een fluorescent protein gene, followed by in vivo EP with the optimized pul se parameters, numerous intensely bright green fluorescent signals appeared within the tumor. ECT, by using the "A" fragment of the diphtheria toxin g ene significantly inhibited the growth of tumors, by about 30%, on the flan k of mice. With the herpes simplex virus thymidine kinase gene, followed by systemic injection of ganciclovir, EGT was far more effective in retarding tumor growth, varying between 50% and 90%, compared with the other control s. Based on these results, it appears that ECT can be used successfully for treating murine solid tumors.