Effect of fibroblast, lymphoid, and myeloid interferons on human tumor colony formation in vitro.

A variety of solid and hematological human tumors and normal human bone marrow specimens were assayed for colony formation in a short-term soft-agar culture system. The effect of human fibroblast, lymphoid, and myeloid interferons on inhibition of colony formation was assessed. The effect of interferon on colony formation formed a continuum from complete inhibition to stimulation of growth. Of 40 evaluable tumor specimens, 18 showed at least a 70% inhibition of colony formation in the presence of interferon, at concentrations of 1000 units/ml or less. Four specimens (acute myelogenous leukemia, osteogenic sarcoma, neuroblastoma, ovarian carcinoma) showed at least 3-fold stimulation of colony formation with interferon. Two of 12 normal bone marrow specimens grown with colony-stimulating, factor-conditioned media showed greater than 70% colony inhibition with interferon. A dose-response relationship was seen in all tumor specimens tested. While fibroblast interferon was the most active in this system, all interferons showed the same magnitude and direction of activity. Continuous exposure and 1-hr incubation of tumor cells with interferon were identical in terms of colony inhibition. These data support the ability of this assay system to select tumors responsive in vitro to interferon, suggest the optimal species and concentration for inhibition or stimulation of growth, and support a direct role of interferon in the regulation of cell growth independent of other immunoregulatory actions of interferon. Such information may prove useful for predicting response in vivo to interferon in Phase II trials.