Comparison of the effects of the antiestrogens EM-800 and tamoxifen on the growth of human breast ZR-75-1 cancer xenografts in nude mice (original) (raw)

Although estrone supplementation in ovariectomized (OVX) nude mice bearing ZR-75-1 xenografts caused a 365% increase in average tumor size during the 4-month treatment period, administration of the antiestrogen EM-800 at the daily oral doses of 50, 150, or 400 microg completely prevented estrogen-stimulated tumor growth. At the same doses of tamoxifen, tumor size was inhibited to 189, 117, and 120% above pretreatment values. However, when EM-800 (150 microg/day) was added to the daily 150- and 400-microg doses of tamoxifen, final tumor size was decreased further to 12 and 38% above pretreatment values, respectively. EM-800 (400 microg daily) administered to estrone-supplemented OVX mice caused complete, partial, and stable responses in 11, 22, and 49% of estrone-stimulated tumors, respectively, whereas 19% (7 of 37) progressed. At the same dose of tamoxifen, the corresponding responses were 3% (complete response), 3% (partial response), and 25% (no change), whereas 69% (22 of 32) of...