In order to achieve tumor-specific targeting of adeno-associated virus (AAV)-mediated gene expression, the promoter of the glucose transporter isoform 1 (GLUT1) gene was cloned upstream of the enhanced green fluorescence protein (EGFP) and the herpes simplex virus thymidine kinase (HSVtk) gene. FACS analysis performed at 48 h after transient infection with rAAV/cytomegalovirus (CMV)egfp viral particles revealed an increase of fluorescence in all the cell lines tested. However, EGFP expression under control of the GLUT1 promoter element (rAAV/GTI-1.3egfp) was limited to the tumor cells and oncogene-transformed cells. Evidence for phosphorylation of the HSVtk substrates ganciclovir (GCV) and 125I-deoxycytidine was found in all transfected tumor cell lines compared to noninfected controls (HCT116: 111%; MH3924A: 130%; HaCaT-RT3: 257% increase), but not in HaCaT and HUVEC cells. Furthermore, tumor cells and the oncogene-transformed (ras) cell line HaCaT-RT3 showed a GCV-induced reduction in cell number (HCT116: -71%; MH3924A: -43% and HaCaT-RT3: -31%). No statistically relevant cytotoxic effect was observed in HaCaT (6% decrease) and HUVEC cells (2% decrease). Furthermore, a reduction of 3H-thymidine incorporation into the DNA was seen after treatment with GCV (HCT116: 38%; MH3924A: 33% and HaCaT-RT3: 37% decrease). In a therapy study of HSVtk-expressing tumors with GCV, we achieved total tumor remission.