Effect of hyperthermia on the antiproliferative activities of murine alpha-, beta-, and gamma-interferon: differential enhancement of murine gamma-interferon.

Fever is frequently an important side effect of interferon (IFN) therapy. Studies have shown that culturing interferon-treated cells at elevated temperature heightens the antiproliferative activity of IFN-alpha and IFN-beta. Since IFN-gamma has also been shown to be a potent antiproliferative agent, the effect of elevated temperature on IFN-gamma activity was compared to its effect on IFN-alpha and IFN-beta. Mouse B-16 melanoma cells were simultaneously cultured under cloning conditions at a range of temperatures (37.3, 38.1, 38.6, and 39.4 degrees C) in the presence of MuIFN-alpha, MuIFN-beta, and MuIFN-gamma. The antiproliferative activities of all three interferons were enhanced by incubation at the elevated temperatures. However, the elevated temperatures had a more dramatic enhancing effect on the antiproliferative activity of MuIFN-gamma (10-fold enhancement) than of either MuIFN-alpha or MuIFN-beta (2.9- and 3.4-fold enhancement, respectively). Next, the enhancing effect of elevated temperature (39.4 degrees C) was examined for a range of interferon concentrations. The degree of the enhancing effect increased with increasing concentrations of MuIFN-gamma but not with increasing concentrations of MuIFN-alpha or MuIFN-beta. Enhancing effects of temperature as high as 14-fold were observed for 100 units of MuIFN-gamma/ml. This dramatic enhancement was observed for both natural and recombinant MuIFN-gamma and was neither a function of greater relative perception of MuIFN-gamma titer at elevated temperature nor a function of greater relative stability of MuIFN-gamma at the elevated temperature. The differential enhancement of MuIFN-gamma activity by elevated temperature appeared to be specific for the antiproliferative activity, since the antiviral activity of MuIFN-gamma was not relatively more enhanced at 39.4 degrees C than were the antiviral activities of MuIFN-alpha and MuIFN-beta. These results suggest that fever may be an important factor in maximizing the antitumor effects of MuIFN-gamma and perhaps of human IFN-gamma. They also raise the possibility that a combination treatment regimen of hyperthermia and interferon therapy, particularly IFN-gamma therapy, may provide a significant antitumor effect.