Visualizing superficial human bladder cancer cell growth in vivo by green fluorescent protein expression

There has been no reliable orthotopic model available to visualize the growth of human superficial bladder cancer over time and to evaluate the efficacy of intravesical therapies. We have developed a novel approach to accomplish this task by generating human superficial bladder tumor cells to stably express high levels of green fluorescent protein (GFP) in vivo. Superficial bladder tumors were produced in athymic mice by intravesical instillation. In our initial studies tumors were quantitated by image analysis at a single time point, and the results compared to the estimation of the percentage of GFP cells present using flow cytometry after obtaining single cell suspensions of normal and tumor cells in the same bladder. A high correlation between the two methods was seen. Therefore, in subsequent studies, approximately 1 week after the intravesical instillation of the GFP expressing cancer cells a small incision was made to expose the bladder. The anterior, posterior, and lateral images of each bladder were captured to visualize GFP-expressing tumors. The ratio of green fluorescence pixel area, which represented the tumor burden, to the total area of the bladder was then calculated. A similar procedure was performed at 2, 3, and 4 weeks after instillation of the tumor cells. Using this procedure tumor progression over time could be measured in each mouse. By using this approach, it will now be possible to monitor the initial tumor sizes in the bladder of each mouse and then to evaluate the efficacy of various intravesical therapy protocols including intravesical gene therapy alone or in combination with other treatment modalities.