Oral tongue cancer is characterized by a high degree of local invasion and a high rate of metastasis to the cervical lymph nodes. Treatment options for this cancer are limited. However, gene therapy has attracted keen interest as a new strategy for refractory cancer. The aim of this study was to examine the efficiency of transfection of the exogenous p27Kip1 gene by electroporation and the antitumor activity of p27Kip1 gene therapy in radiotherapy-resistant human oral tongue cancer xenografts using mutant type (mt) pcDNA3.1-p27Kip1, followed by in vivo electroporation. Evaluation of the in vivo gene transfer method was carried out by transfecting the enhanced green fluorescence protein (EGFP) gene into xenografts by electroporation. The efficiency of p27Kip1 gene transfection was confirmed by Western blot analysis. Estimation of the reduction in size of the B88 and B88-R-Rad tumors in mice after electroporation with the p27Kip1 mt gene was examined by tumorigenesis assay. The results revealed that the efficiency of transfection of B88-EGFP and B88-R-Rad-EGFP was 58.1 and 27.4%, respectively. The growth of tumors was markedly suppressed by p27Kip1 mt gene transfection by electroporation on B88-p27Kip1 mt and B88-R-Rad-p27Kip1 mt. Furthermore, up-regulation of p27Kip1 protein was detected in B88-p27Kip1 mt and B88-R-Rad-p27Kip1 mt, while inhibition of tumor size was highly increased in B88-p27Kip1 mt compared to B88-R-Rad-p27Kip1 mt. These results indicate that the intratumoral injection of pcDNA3.1-p27Kip1 mt with electroporation exhibited a high potential antitumor activity in human oral tongue cancer cell B88 xenografts, and a slight increase in antitumor activity in the radiotherapy-resistant human oral tongue cancer cell B88-R-Rad xenografts.

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