Antiviral and antiproliferative activities of human leukocyte interferon potentiated by cimetidine in vitro.

The influence of cimetidine on antiviral activity of leukocyte interferon (IFN-alpha (Le] was studied in plaque-reduction assays using Utrecht (U) amnion cells challenged with vesicular stomatitis virus (VSV) and in CPE inhibition assays using A549 cells challenged with encephalomyocarditis (EMC) virus and WISH cells challenged with VSV. The IFN-alpha (Le)-induced antiviral activity was slightly enhanced in cells treated with cimetidine, whereas cimetidine treatment alone did not show any antiviral effect. The observed titer (OT) was significantly higher (p less than 0.05) in cells treated with cimetidine together with IFN-alpha (Le) compared with the control without cimetidine. The effect of cimetidine on IFN-alpha (Le)-induced cell growth inhibition was studied on Daudi (a Burkitt's lymphoma cell line) and on G361 (a melanoma cell line) cells. The growth of these cells was slightly suppressed by cimetidine alone. When cells were treated with IFN-alpha (Le)/cimetidine, the cell growth inhibition rates were significantly higher (p less than 0.02) than the rates obtained with IFN-alpha (Le) or cimetidine alone. These results indicate that cimetidine can enhance the antiviral as well as the antiproliferative activities of IFN-alpha (Le) in "in vitro" studies.