A new triphenylethylene compound, Fc-1157a. II. Antitumor effects.

The antitumor effects of a new antiestrogen, Fc-1157a have been studied in vitro and in vivo. In vitro the effect of Fc-1157a was comparable to that of tamoxifen. The effect was dose-dependent, and at concentrations higher than 10(-6) mol/1 Fc-1157a induced real cell death of the MCF-7 cells. In DMBA-induced mammary cancer in rats Fc-1157a decreased the number of new tumors and inhibited the growth of existing tumors, these effects being statistically highly significant. The ratio of growing tumors to stable and regressing tumors was significantly decreased. Although these effects were slightly stronger with Fc-1157a than with tamoxifen, the difference between these two compounds was not statistically significant. Murine uterine sarcoma, an estrogen receptor-negative tumor, was resistant to tamoxifen, but was statistically significantly inhibited by high doses (100 and 200 mg/kg-1 day-1 for 5 days) of Fc-1157a. The antitumor effects of Fc-1157a are due mainly to the antiestrogenic activity. At high concentrations in vitro and at high doses in vivo Fc-1157a exerts antitumor effects some of which are different from those of tamoxifen and are directed even against estrogen receptor-negative tumors. The exact mechanism of the observed cytolytic effect at high doses is unknown.