In a study of a series of 26 triphenylacrylonitrile derivatives (TPEs), we investigated the influence of several possibly interrelated factors on the proliferation of human breast cancer cell lines. (1) Chemical substituents: the test compounds were for the most part para-hydroxylated with increasingly bulky hydrophobic and/or basic side chains [isopropyloxy or (diethylamino)ethoxy] or standard reference compounds. (2) Relative binding affinities (RBAs): they competed diversely for [3H]estradiol (E2) binding to calf uterus cytosol and little, if at all, for binding to the [3H]tamoxifen-labeled antiestrogen binding site (AEBS) in lower speed supernatant. A multiparametric comparison of RBAs recorded for calf, rat, and mouse uterus cytosol estrogen receptor (ER) revealed a possible influence of species-specific receptor conformation and/or environment on binding. (3) Estrogen/antiestrogen potency: their stimulation and inhibition of the proliferation of the ER-positive human breast cancer cell line (MCF7) was measured. Compounds with only hydroxy substituents stimulated proliferation more markedly than methylated derivatives and had a maximum effect at 10(-11)-10(-6) M. Stimulation was related to the RBA for ER. Compounds with isopropyloxy or (diethylamino)ethoxy side chains only weakly stimulated MCF7 cell growth and more powerfully antagonized E2-promoted growth. The extent of inhibition depended upon the bulk of the side chain and could be reversed by 10(-7) M E2. Within the same concentration ranges, the test compounds were without effect on the BT20 ER-negative cell line. (4) Cytostatic and/or cytolytic activity: most compounds could arrest the proliferation of both MCF7 and BT20 cells at concentrations above 3 x 10(-6) M. This activity was thus independent of ER. Nevertheless, those compounds with a charged hydrophobic side chain, which were the most powerful antagonists of E2-promoted cell growth, were also the most cytotoxic. The overall results for all molecules on all parameters were submitted to a multivariate analysis (correspondence analysis) which revealed the progressive influence of increasing substitution by hydroxy and more bulky groups on the generation of antagonist activity and cytotoxicity.