Cytostatic effect of interferon alpha on human bladder cancer cells in vitro. A flow cytometric study

The cytostatic activity of interferon a-2b on human transitional cell cancer T24 cells was examined using bioluminescence assay. Interferon a in a concentration of 1 x 10(6) IU/ml had a remarkable cytostatic effect already in two-day cultures, and this effect increased still further when the cells were incubated for three and five days. In the flow cytometric study, the percentage of cells in the S-phase fraction (SPF) remained at the same level after three days of incubation with interferon a (43.6 +/- 2.7), but decreased significantly in the control cell population (25.6 +/- 1.5). If interferon a was washed away after two hours and incubation was continued for three days, the percentage of cells in the SPF was also significantly higher (43.6 +/- 3.3) than that in the control group of cells (P < 0.01).