Estrogen-stimulated prolactin synthesis in vitro. Classification of agonist, partial agonist, and antagonist actions based on structure.

An in vitro assay that depends upon the synthesis of prolactin by primary cultures of dispersed cells from immature rat pituitary cells was used to study the structural requirement for estrogen action. Two categories of estrogens were identified: full estrogens (agonists) and partial estrogens (partial agonists) with antiestrogenic actions against the effects of 0.1 nM estradiol (E2). All of the agonists [diethylstilbestrol (DES), dimethylstilbestrol (DMS), R2858, and RU16117] produced a dose-related increase in prolactin synthesis equivalent to E2, although potencies were different: E2 = DES = R2858 greater than RU16117 greater than DMS. Partial agonists [ICI 3188, tri(4-hydroxyphenyl)chloroethylene, and bisphenol] each had bis(4-hydroxyphenol) substitutions at the ethylene double bond and stimulated prolactin synthesis only to about 50% of the maximal response observed with E2. Trianisylchloroethylene was weakly active as a partial agonist, but at high concentration (10 microM) was able to decrease prolactin synthesis produced by 0.1 nM E2. Previous studies from these laboratories showed that triphenylethylene derivatives with a strategically located alkyl aminoethoxyside chain are complete E2 antagonists with no agonist activity. Two series of novel compounds were assayed to determine whether their structures would predict biological activity. LN2299, the cis geometric isomer of a triphenylbromethylene, was a full agonist with activity equivalent to zuclomiphene, the cis geometric isomer of clomiphene. Cyclofenyl was a partial agonist, but deacetylation to the diphenol increased partial agonist activity and potency. However, introduction of a single pyrrolidinoethylside chain into the deacetylated cyclofenyl increased antiestrogenic potency and completely suppressed the expression of agonist activity. Finally, LN2833, with a novel C(OH)CH3 side chain in the position normally occupied by the alkylaminoethoxyside chain of most antiestrogens, produced antiestrogen activity with no estrogen properties. Antiestrogenic potency was increased in LN2839 by a phenol in the triphenylethylene in a position equivalent to the 3-phenolic hydroxyl of E2. In general, the potency and biological properties could be predicted by reference to the structure of the molecule. Potent estrogens or antiestrogens have a phenolic hydroxyl in a position that would be equivalent to the 3-phenolic hydroxyl of E2. Partial agonist action is predicted by a 4-hydroxyphenol attached to the same carbon as the phenyl ring equivalent to the A-ring of E2.(ABSTRACT TRUNCATED AT 400 WORDS)