PREVENTION OF RESISTANCE TO IFN-ALPHA ANTIPROLIFERATIVE ACTIVITY - CHARACTERIZATION OF THE EFFECT OF IFN-GAMMA AND SUBSTITUTION FOR IFN-GAMMA BY TUMOR-NECROSIS-FACTOR

Non-genetic resistance to the antiproliferative effects of interferon- alpha (IFN-alpha) develops in murine and human melanoma cells within 2 -4 days of exposure of the cells to IFN-alpha. Simultaneous treatment of murine B16 melanoma cells with MuIFN-gamma and MuIFN-alpha prevents the development of resistance. In this study, the ability of MuIFN-ga mma pretreatment to prevent the development of resistance was assessed for varying concentrations of MuIFN-gamma and for varying lengths of time of pretreatment. Pretreatment of the cells for 48 h with MuIFN-ga mma using concentrations as low as 5 U/ml prevents the subsequent deve lopment of resistance when the cells are cloned in the presence of MuI FN-alpha. Higher concentrations of MuIFN-gamma are more effective in p reventing the development of resistance. In addition, short MuIFN-gamm a pretreatment times, such as 2-4 h, appeared to be most effective in preventing the development of resistance. In order to determine the me chanism for this biological effect, various second messenger perturbin g chemical agents and several other biological agents were screened fo r ability to prevent the development of resistance. Neither interleuki n-2 (IL-2), epidermal growth factor (EGF), nor any of the chemical age nts examined could prevent the development of resistance, nor did they alter the ability of MuIFN-gamma to prevent the development of resist ance. Tumor necorosis factor (TNF), however, was able to substitute fo r MuIFN-gamma in preventing the development of resistance, using conce ntrations of 125 ng/ml and higher. Both simultaneous treatment of the cells with TNF and MuIFN-alpha and pretreatment of the cells with TNF before exposure of the cells to MuIFN-alpha were effective in preventi ng the development of resistance of MuIFN-alpha. The results suggest t hat IFN-gamma and TNF may share a common signaling pathway.