Segesterone acetate

Segesterone acetate selectively binds to the progesterone receptor (PR), a transcription factor belonging to the nuclear receptor superfamily, where it acts as an agonist and transactivator. According to the findings from docking experiments, it adopts the same docking position within the PR ligand-binding domain (LBD) as progesterone but due to additional stabilizing contacts between 17α-acetoxy and 16-methylene groups and PR LBD, segesterone acetate display higher potency than progesterone. As with other progestins, segesterone acetate prevents ovulation by blocking the midcycle surge in luteinizing hormone (LH) secretion, thereby inhibiting the development of ovarian follicles. When used in combination with segesterone acetate, ethinyl estradiol potentiates the antigonadotropic of the progestin and prevents irregular shedding of the endometrium. Segesterone acetate lacks androgenic activity, and displayed binding affinity to androgen receptors that was 500- to 600-fold less than that of testosterone. It does not display binding affinity toward estrogen receptors. When the relative binding affinities of segesterone acetate to human steroid receptors were investigated in vitro, it was demonstrated that segesterone acetate binds to the glucocorticoid receptor. However, segesterone acetate did not exert any glucocorticoid activity in the in vivo assays showing no increase in liver glycogen and tyrosine transaminase TAT.