Selective inhibition of estrogen-regulated gene expression in vivo by the pure antiestrogen ICI 182,780

Estrogen-stimulated cell proliferation is thought to be mediated by the induction of growth-regulatory factors. Abnormal regulation of such factors may be associated with tumorigenesis. Two such factors, vascular endothelial growth factor and c-fos, are rapidly induced in the uterus by estrogens. We show that the induction of these transcripts by 17β-estradiol or tamoxifen is selectively blocked by the pure antiestrogen ICI 182,780 in a dose- dependent manner. This indicates that induction of the two genes requires different levels of estrogen receptor or that their induction occurs by different mechanisms. This suggests that selective dose-dependent antagonism of estrogen-dependent transcription may be possible in target tissues and tumors.