Overexpression of vascular endothelial growth factor (VEGF) and its cognate receptor KDR has been linked to a more aggressive phenotype of human prostate carcinomas. The importance of signal transduction through the VEGF receptor 2 is illustrated by use of soluble KDR, which binds to VEGF and sequesters this ligand before its binding to cellular receptor. Treatment with recombinant adenovirus AdVEGF-sKDR, encoding sKDR under control of the human VEGF promoter, significantly inhibited the proliferation of human vascular endothelial cells and prostate cancer cells. AdVEGF-sKDR infection decreased migration of endothelial 1P-1B cells (61% reduction) and DU145 prostate carcinoma cells (47%) in comparison with AdCMV-Luc-infected control cells. Ionizing radiation upregulated VEGF promoter activity in prostate carcinoma and endothelial cells. AdVEGF-sKDR infection significantly reduced human vascular endothelial and prostate cancer cell proliferation and sensitized cancer cells to ionizing radiation. In vivo tumor therapy studies demonstrated significant inhibition of DU145 tumor growth in mice that received combined AdVEGF-sKDR infection and ionizing radiation versus AdVEGF-sKDR alone or radiation therapy alone. These results suggest that selective transcriptional targeting of sKDR gene expression employing a radiation inducible promoter can effectively inhibit tumor growth and demonstrate the advantage of combination radiotherapy and gene therapy for the treatment of prostate cancer.