Antiproliferative effects of bacillus Calmette-Guerin and interferon alpha 2b on human bladder cancer cells in vitro.

Direct inhibitory effects of bacillus Calmette-Guérin (BCG) and interferon alpha 2b (IFN alpha 2b) on six human bladder carcinoma cell lines, UCRU-BL-13, UCRU-BL-17, UCRU-BL-28, 5637, T24 and J82, were studied using an in vitro proliferation assay. Effects on proliferation following exposure to BCG or IFN alpha 2b were analysed by [3H]thymidine incorporation over 7 days. BCG had an antiproliferative effect on all bladder lines, while sensitivity to IFN alpha 2b varied greatly, being as remarkably low as 1 U/ml for some lines. The antiproliferative effect was greatest when cells were exposed continuously to either agent, but was still evident with a limited exposure. When clinical concentrations were simulated in vitro, BCG+IFN alpha 2b was more effective than BCG alone and as effective as a double BCG concentration. We conclude that, in addition to their immunomodulatory effects, BCG and IFN alpha 2b directly inhibit the proliferation of human bladder cancer cells, and often at extremely low concentrations.