Progesterone antagonists and progesterone receptor modulators.

Since the discovery of the antiprogestin RU 486 (mifepristone), other compounds have been synthesised that function as pure progesterone antagonists or progesterone receptor modulators. The latter are mixed agonists-antagonists. Mifepristone is usually used to terminate pregnancy but these compounds have numerous other applications in female healthcare. Mifepristone is an excellent agent for emergency contraception. Many progesterone antagonists and progesterone receptor modulators display antiproliferative effects on the endometrium and thus have application in the treatment of endometriosis and uterine myoma without being associated with hypoestrogenism and bone loss. They also have contraceptive potential by suppressing follicular development, blocking the luteinising hormone surge and retarding endometrial maturation. Finally, they have clinical application in GeneSwitch system, a plasmid-based method enabling controlled expression of specific genes (e.g., erythropoietin) using a progesterone antagonist as the inducer.