Specific binding of interferon-gamma and -alpha 2a to tumor cells and their antitumor activities.

Binding activities of a recombinant human interferon-gamma (IFN-gamma) preparation with 5 human tumor cell lines, including lung large cell carcinoma PC-13, lung small cell carcinoma QG-90, amelanotic melanoma HMV-1, renal carcinoma ACHN and Burkitt lymphoma Daudi, were compared with those of IFN-alpha 2a. Three out of five human tumor cell lines, ACHN, HMV-1, and QG-90, were highly susceptible to IFN-gamma: the concentrations required to inhibit 50% of the growth of cells (IC50) of ACHN, HMV-1, and QG-90 were 26, 11 and 7 pM, respectively. IFN-alpha 2a also markedly inhibited the growth of ACHN, HMV-1 and Daudi cells: the values of IC50 for the former and latter cells were 20, 31 and 0.8 pM, respectively. With these susceptible cells, larger amounts of IFN-gamma were bound than with resistant cells. On the other hand, IFN-alpha 2a bound all cell lines, irrespective of the susceptibilities of cells. The values of the apparent dissociation constant (Kd) of binding of both IFNs ranged from 1.3 to 7.3 x 10(-10) M. The competitive binding test revealed that the binding properties of IFN-gamma were different from those of IFN-alpha 2a. Under the present experimental condition, it could be said that, with IFN-gamma, the susceptibilities of cells were linked of the expression of the receptors, but there were some exceptions with IFN-alpha 2a.