(A) The decay characteristics following initial induction of luciferase by GS-E. After a 24 hour incubation using similar conditions to those described in figure A, the medium containing GS-E was removed and the cells washed three times with complete medium without GS-E. The cells were then re incubated for various durations as shown in the graph. At set intervals triplicate wells were removed and dual luciferase assays were performed on the cell lysates. Error bars indicate mean +/- one standard error for triplicate experiments. (B) In vivo induction of gene expression in tumor xenografts. Six-to-8 week-old C3H/He origin mice were given injections in the anterior flank (2 sites per mouse) with 106 MBT-2 tumor cells suspended in 0.1 ml of serum free medium. Mice were examined every week, and tumors were measured with calipers in the greatest 2 diameters. When tumors reached 5 mm in greatest diameter, mice were injected intraperitoneally with either 45 milligrams of GS-E dissolved in 90 μl of DMSO and 360 μl of sesame oil (GS-E Addition) or with equivalent volumes of DMSO and 360 μl of sesame oil alone (Control). Cohorts of mice were euthanized at various time points following drug administration or vehicle administration and tumors processed for luciferase activity as described in the materials and methods section. Error bars indicate mean +/- one standard error for 4–6 tumors.