We previously reported that the peptide based on Cx43, TAT-Cx43266–283, inhibits c-Src activity and exerts important effects in different types of glioma cells in vitro, including freshly removed surgical specimens of glioblastoma.28 In this study, we explored the possibility of using this peptide for therapy against malignant gliomas by studying its effect on healthy brain cells and by evaluating its antitumor effects in vivo. This evidence concerns the gene GJA1 and glioblastoma.