The in vitro interaction of α-difluoromethyl ornithine (DFMO) and several interferons on human cell lines

The antiproliferative effects of six different human interferons were examined on two human cell lines—HM7 (human melanoma cell line) and MDA-MB-231 (human breast carcinoma cell line). A dose-response curve was developed for each interferon in which the maximum dose applied gave at least 30% growth inhibition of control values after 96—128 h of continuous exposure. An amount of α-difluoromethyl ornithine (DFMO) which caused 25% growth inhibition (0.01 mM for HM7 and 0.1 mM for MDA) was added to the cultures with various doses of each interferon. The inhibitory effects of DFMO and each interferon were additive at low concentrations. In no case was a synergistic effect observed. Unlike in the murine B-16 melanoma model, we could not show a synergistic inhibitory effect between DFMO and any of the six different interferons on two human epithelial tumor cell lines.