Synergistic Antiproliferative Activity of Leukocyte Interferon in Combination with α-Difluoromethylornithine against Human Cells in Culture

α-Difluoromethylomithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase, was administered in combination with human leukocyte interferon to human lymphoblastoid (Daudi) cells in culture. True synergistic antiproliferative activity was observed at 72 hr after continuous exposure. This effect was observed regardless of the ratio of interferon to $aL-difluoro-methylomithine concentrations. Although the mechanisms by which this effect occurs are unknown, these studies provide a rationale for combination clinical trials of $aL-difluoromethylomi-thine with leukocyte interferon.