Mammalian lignans enterolactone and enterodiol, alone and in combination with the isoflavone genistein, do not promote the growth of MCF‐7 xenografts in ovariectomized athymic nude mice

This study determined the effect of the mammalian lignans enterolactone (ENL) and enterodiol (END) alone and in combination with the isoflavone genistein (GEN) on the growth of MCF‐7 tumors in ovariectomized nude mice. Ovariectomized athymic nude mice with established MCF‐7 tumors were fed a basal diet (AIN‐93G) and divided into 5 groups that received daily subcutaneous injections (10 mg/kg body weight (BW)) of ENL, END, GEN, a mixture of these compounds (MIX), or vehicle as a negative control for 22 weeks. A positive control group was implanted with an estradiol pellet in order to establish an estrogenic tumor growth response. In the ENL‐ and END‐treated mice, palpable tumors regressed significantly by 91 and 83%, respectively, resulting in final tumors that were similar to the negative control tumors. However, tumor cell apoptosis was significantly enhanced by the lignans. In the GEN‐treated mice, tumors initially regressed significantly by 64% but regression ceased following prolonged treatment, resulting in final tumors that were significantly larger compared to negative control, ENL‐, and END‐treated mice, in part by increasing tumor cell proliferation. The MIX treatment significantly regressed palpable tumors by 87% similar to negative control group, with no effects on tumor cell apoptosis or proliferation. The isoflavone GEN alone promoted the growth of established MCF‐7 human breast cancer xenografts after prolonged treatment while the mammalian lignans ENL and END did not. When these phytoestrogens were given in combination, no tumor growth‐promoting effects were observed. © 2005 Wiley‐Liss, Inc.