2-Phenylbenzo[b]thiophene-based antiestrogens with mammary tumor inhibiting activity

In this study we extended our studies on heterocyclic antiestrogens to 2-phenylbenzo[b]thiophenes which can be considered as isosteric to the 2-phenylindole system. We synthesized a number of 6-hydroxy-2-(4-hydroxyphenyl)benzo[b]thiophenes with carbamoyl and amino functions in the side chain at carbon-3 and analyzed their biological properties. The binding affinities for the estrogen receptor are mainly influenced by the chain length whereas the hormonal profile depends on the nature of the functional group. From this study 3-[10-(2,2,3,3,4,4,4-heptafluorobutyl-methylcarbamoyl) decyl]-6-hydroxy-2-(4-hydroxyphenyl)benzo-[b]thiophene (6e) emerged as an antiestrogen with all the characteristics of a pure antagonist. It did not stimulate gene expression in HeLa cells cotransfected with the expression vector for the human estrogen receptor HEG0 and the luciferase reporter plasmid EREwtc luc nor did it show any estrogenic activity in the mouse uterus weight test. In the latter assay, it completely abrogated the stimulatory effect of estrone. Due to its antiestrogenic potency it strongly inhibited the growth of estrogen-sensitive human MCF-7 breast cancer cells with an IC50 value of 5 nM. These data suggest that an amide function in combination with the fluorination of the terminal carbon atoms is an appropriate modification to abolish the estrogenic action of the 2-phenylbenzothiophene system.