Publications

Abstract

A series of triarylethylene compounds related to 4-hydroxyclomiphene (2) in which the vinyl Cl substituent was replaced by ethyl (5), Br (6), H (7), CN (8), or NO2 (9) substituents were synthesized to facilitate studies of the molecular actions of synthetic nonsteroidal antiestrogens. The relative binding affinities of these compounds for the estrogen receptor (ER) and the antiestrogen binding site (AEBS) in MCF 7 human mammary carcinoma cells were measured and correlated with the effects of these drugs on cell proliferation kinetics. Affinities for ER and AEBS were highly correlated, illustrating that vinyl substituents influence binding to ER and AEBS in a parallel manner. All compounds except 7 had biphasic effects on cell proliferation kinetics, indicating the presence of at least two distinct mechanisms by which hydroxytriarylethylenes inhibit breast cancer cell proliferation. In the concentration range 10(-10)-10(-8) M, cell proliferation was inhibited by 60-70%, these effects were estrogen-reversible, and the degree of growth inhibition was in the order Cl greater than Et greater than Br greater than NO2 greater than CN greater than H, which paralleled the order of affinities for ER. There was no further inhibition of cell growth between 10(-8) and 10(-6) M, but at concentrations greater than 10(-6) M there was a further dose-dependent decrease in cell growth mediated by mechanisms yet to be defined but apparently distinct from ER-mediated events. In both concentration ranges, growth inhibition was accompanied by accumulation of cells in the G1 phase of the cell cycle. These data, obtained with a novel series of hydroxytriarylethylenes, have enabled clear definition of two distinct mechanisms of growth inhibition by triarylethylene antiestrogens. They also indicate that among the vinyl substitutions examined to date the Cl substituent yields the most active molecule both in terms of affinity for ER and AEBS and potency as a growth inhibitory agent.