Binding of human gamma-interferon to human epidermal tumor cells with different susceptibilities

The in vitro antiproliferative effect of highly purified recombinant human gamma-interferon was studied with special reference to specific binding to tumor cells of interferon (IFN) labeled with 125I. Recombinant human gamma-interferon markedly suppressed the growth of 6 of 10 human epidermal tumor cell lines tested; the concentration required to inhibit the growth of susceptible cell lines by 50% ranged from 8 to 36 units/ml (13.6 to 61.2 pM), whereas those for the other cell lines were higher than 10,000 units/ml. These anticellular effects were compatible with the suppressive effects of IFN on cellular DNA synthesis. Labeled IFN bound specifically to the susceptible cells, which showed, from the Scatchard analysis, 870 to 7700 binding sites/cell with apparent Kd of 1.70 to 5.84 X 10(-11) M. There was little binding of the labeled IFN to the resistant cells and nonspecific binding occurring in the presence of a 1000-fold excess of unlabeled IFN accounted for 40 to 90% of the total binding. These results suggest that specific binding sites for recombinant human gamma-interferon exist on the resistant cell lines.