Add time:07/25/2019         Source:sciencedirect.com

The binding of an antiestrogen with the uterine estrogen receptor (R) has been studied directly in vitro using [3H]dimethylstilbestrol (DMS). The affinity of DMS for R as determined at equilibrium was similar to that of estradiol (E2) (KD ∼- 0.3 nM) when taking into account the higher nonspecific binding of DMS. The number of DMS binding sites was constantly found to be inferior to that of E2. The fact that the DMS binding entity specifically bound estrogen and antiestrogen, was destroyed by pronase, displayed an 8S sedimentation constant and interacted in vitro with DNA, strongly suggested that DMS interacted directly with R. The association of DMS to R was a simple second-order reaction while its dissociation was a first-order reaction with two slopes. The association and dissociation rate constants of the R-DMS complex were respectively slower and higher than those of the R-E2 complex. The rapid dissociation rate of DMS could be responsible for its inability to protect the receptor binding sites against thermoinactivation. [3H]DMS was able in vivo to induce the nuclear translocation of the receptor. However, as with other short-acting antiestrogens and contrary to Nafoxidine, the time of nuclear retention of R was short. These results are in agreement with the assumption that the length of the nuclear retention of R is determinant in explaining the weak agonist activity of this compound.

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