LONG-TERM INHIBITORY EFFECTS OF A NOVEL ANTIESTROGEN ON THE GROWTH OFZR-75-1 AND MCF-7 HUMAN BREAST-CANCER TUMORS IN NUDE-MICE

The effects of the novel anti-estrogen EM-343 on the growth of 2 hormo ne-responsive human breast cancer tumors have been examined in athymic nude mice. At the low daily dose of 5 mu g, EM-343 administered subcu taneously for 6 months completely blocked the stimulatory effect of en dogenous estrogens on the growth of ZR-75-I and MCF-7 tumors implanted in nude mice, In addition, uterine weight decreased by 60% while ovar ian weight increased by 37%. Estrogen receptor (ER) levels measured by [H-3]-labeled estrogen binding were markedly reduced (by 96%, 96% and 92%) in ZR-75-I and MCF-7 tumors, and in the mouse uterus, respective ly, Accompanying the decrease in ER, progesterone receptor levels were reduced by 79%, 87% and 76%, respectively, in the above-mentioned tis sues following EM-343 treatment. Our data show the pure anti-estrogeni c properties of EM-343 and its high potency as an inhibitor of growth of human ZR-75-I and MCF-7 breast tumors in nude mice. (C) 1997 Wiley- Liss, Inc.