Pretreatment of the primigravid uterine cervix with mifepristone 30 h prior to termination of pregnancy: a double blind study

Antifertility effects of antigestogens

Since the discovery of the structure and function of steroids over 60 years ago, it has long been recognized that synthetic antagonists of the natural hormones would have potential therapeutic uses. Antagonists of mineralocorticoids, androgens and oestrogens, for example spironolactine, cyproterone, flutamide and tamoxifen, have already found a place in the management of hormone dependent conditions. In 1982, chemists at Roussel UCLAF announced that they had synthesized mifepristone (RU486) 17β-hydroxy-11(p-(dimethylamino)phenyl)-17-(1-propynyl) estra-411, 9-dien-3-one) a derivative of norethindrone which had potent antiprogestogenic as well as antiglucocorticoid activity. Although it was immediately realised that this compound would potentially have wide clinical application, its development in the last 10 years has been dominated by its abortifacient action. In the original clinical report by Herrman and colleagues it was shown that bleeding occurred when it was given to female volunteers in the second half of the menstrual cycle. In addition, complete abortion occurred in eight of 11 women who took the drug in the early weeks of pregnancy. These findings, which demonstrated that mifepristone could be used as the basis of a medical method of inducing abortion, were immediately made the focus of groups opposed to abortion on moral grounds. Experience over the last 10 years has confirmed the promise of these early studies and mifepristone, in combination with a suitable prostaglandin, is now licensed in France, UK and Sweden for use as a medical method of inducing abortion in early pregnancy.

Pharmacological properties of mifepristone: toxicology and safety in animal and human studies

Roussel Uclaf in partnership with the INSERM unit of Prof. E.E. Baulieu first discovered mifepristone (RU486) as part of a large research program on steroidal compounds with antihormone properties. Exhibiting a strong affinity to the progesterone and the glucocorticoid receptors, mifepristone exerted competitive antagonism to these hormones both in in vitro and in animal experiments. Due to its antiprogesterone activity, it was proposed that mifepristone be used for the termination of early human pregnancy. Mifepristone, at a dose of 600 mg initially used alone, was then used with a subsequent low dose of prostaglandin that led to a success rate of 95% as a medical method for early termination of pregnancy (TOP). Its use was extended to other indications, such as cervical dilatation prior to surgical TOP in the first trimester, therapeutic TOP for medical reasons beyond the first trimester, and for labor induction in case of fetal death in utero. The efficacy and safety of this treatment has been confirmed based on its use for over a decade, with close adherence to the approved recommendations. This paper describes the safety studies conducted in animals as well as the safety follow-up and side effects reported with use of the compound in various indications either approved or unapproved. The rationale for warnings and contraindications for use of the product are also explained. At lower doses, the molecule has proven promising for contraceptive purposes with few reported side effects. However, development of the product for this indication would require long-term studies. Although political and philosophical obstacles have delayed research, the use of mifepristone for other potential indications in gynecology or oncology should be investigated.

RU486 (mifepristone): mechanisms of action and clinical uses

RU486 (mifepristone) has proved to be a remarkably active antiprogesterone and antiglucocorticosteroid agent in human beings. The mechanism of action involves the intracellular receptors of the antagonized hormones (progesterone and glucocorticosteroids). At the molecular level, the most important features are high binding affinity to the receptor, interaction of the phenylaminodimethyl group in the 11 beta-position with a specific region of the receptor binding pocket, and RU486-induced transconformation differences in the ligand-binding domain. These particularities have consequences at different steps of the receptor function as compared with agonists. However, the reasoning cannot be limited to the RU486-receptor interaction, and, for instance, there is the possibility of a switch from antagonistic property to agonist activity, depending on the intervention of other signaling pathways. It would be desirable to have derivatives with only one of the two antagonistic properties (antiprogestin, antiglucocorticosteroid) in spite of similarities between steroid structures, receptors involved, and responsive machineries in target cells. Clinically, the RU486-plus-prostaglandin method is ready to be used on a large scale and is close to being as convenient and safe as any medical method of abortion may be. The early use of RU486 as a contragestive as soon as a woman fears a pregnancy she does not want will help to defuse the abortion issue. Research should now be conducted to define an efficient and convenient contraceptive method with RU486 or other antiprogestins. The usefulness of RU486 for obstetric indications, including facilitation of difficult delivery, has to be assessed rapidly. Gynecologic trials, particularly in leiomyomata, should be systemically continued. The very preliminary results obtained with tumors, including breast cancers, indicate that further studies are necessary.

Effects of mifepristone and progesterone on collagen synthesis in the human uterine cervix

Antiprogestins are used to induce first trimester abortion and to dilate the cervix before vacuum aspiration. Cervical dilatation is associated with profound changes in the connective tissue. In what respect antiprogestins interfere with this process has hitherto been sparsely investigated. The aim of present study was to examine the influence of the antiprogestin mifepristone on cervical collagen synthesis in nonpregnant, early and late pregnant women. The effects were compared with those of progesterone. The content of collagen in cervical tissue was determined by measuring hydroxyproline. Collagen synthesis was studied in vitro either by incubation of cervical tissue specimens from women, pretreated with mifepristone in vivo, in the presence of 14C-proline or by incubation of cervical tissue of not pretreated women in the presence of the isotope and mifepristone or progesterone. Pretreatment with mifepristone, but not progesterone, induced a significant increase in cervical dilatation. The cervical concentration of collagen was not altered after mifepristone administration. Pretreatment with mifepristone did not quantitatively influence the time course of radiolabeling in vitro or the pattern of radiolabeling in different protein components as revealed by electrophoresis. In vitro mifepristone, like progesterone, reduced the incorporation of 14C-proline. From the present data we conclude that mifepristone pretreatment in connection with first trimester abortion is not associated with any major changes, qualitatively or quantitatively, of collagen synthesis. However, we cannot exclude that mifepristone still may affect the de novo formation of collagen since mifepristone, administered in vitro, did reduce collagen synthesis.