There is a need to improve the treatment of superficial bladder cancer. One area which holds promise is intravesical gene therapy. Recently, studies undertaken by us have shown that marked tumor regression of bladder cancers occurred after two daily intravesical administrations of an adenovirus encoding human interferon alpha (Ad-IFNalpha) using a mouse superficial bladder cancer model in which human bladder tumors are growing. A dose of 1 x 10(11) particles/ml (P/ml) was used along with 1 mg/ml of Syn3, a gene transfer-enhancing agent. Since clinical studies are being planned using this approach, it became critical to determine if one exposure and lower particle number could be equally effective. We report that indeed a single dose of Ad-IFNalpha in Syn3 at doses of 1 x 10(10)-1 x 10(11) P/ml is highly effective in reducing the size of the tumors, whereas 1 x 10(9) P/ml was not. Efficacy was also correlated with the level of IFN produced in the urine after treatment. Based on the results of the present studies, a Phase I trial is being planned for superficial bladder cancer, which will involve a single initial treatment with Ad-IFNalpha/Syn3 and measurement of IFN in the urine over time as an indicator of adequate gene transfer and expression.