Gestrinone (R2323) binding to steroid receptors in human uterine endometrial cytosol

To understand the mechanism of biological action of gestrinone (R2323), which has a therapeutic effect against endometriosis, the binding of gestrinone to numerous classes of intracellular steroid binding proteins was studied in the human uterine endometrium. Gestrinone bound to endometrial receptors for estrogen, progesterone and androgen, but seemed not to bind to endometrial intracellular corticosteroid-binding globulin and sex hormone-binding globulin. Gestrinone occupies all specific binding sites of steroids in the steroid target cells despite the presence of endogenous steroids. It is speculated that the binding behavior of gestrinone may be related to its therapeutic effect on endometriosis. Gestrinone's more avid affinity for estrogen receptor may be the reason for the ability to use a lower clinical dose of gestrinone.