Additive and synergistic antitumor effects with toremifene and interferons.

MFC-7 cells were exposed to toremifene, human alpha and gamma interferons and combinations of them in vitro. Growth of the cells was followed by ATP bioluminescence method. Rats bearing DMBA-induced tumors were treated with toremifene, rat gamma interferon and their combination daily for five weeks. The growth of the tumors was followed by palpation weekly. Toremifene and interferons inhibited the growth of MCF-7 cells. Interferons alpha and gamma were additive; toremifene and interferons were additive or at the best synergistic. Toremifene inhibited the growth of DMBA-induced tumors. Rat gamma interferon alone had no clear effect on the tumor growth. Combination of toremifene and gamma interferone was the most effective treatment and did not show any detectable toxicity. Toremifene and interferons have interesting interactions. Clinical studies using the combination might be warranted.