Enhanced activity of H19-DTA-P4-DTA in human bladder carcinoma cell lines: The protein synthesis inhibition activity of the H19-DTA-P4-DTA vector in T24P (A-B) and HT-1376 (C-D) cells was measured as a reduction of LucSV40 activity, and was compared to the combination activity of H19-DTA + P4-DTA. Cells were cotransfected with 2 μg of LucSV40, and with the indicated concentrations of the DTA expressing vectors or LucSV40 alone. Transfection experiments were stopped after 48 hours and luciferase activity was assessed. The decrease in LucSV40 activity was determined by comparison to the same cell type transfected with LucSV40 alone as a measure for cytotoxicity. Enhanced effect of H19-DTA-P4-DTA vector at the lowest plasmid transfected concentration (0.005 μg compared to 0.005 μg + 0.005 μg of the combination transfection of both vectors H19-DTA + P4-DTA) is indicated (B, D).