What is the mechanism of Mifepristone?

Mifepristone, also known as RU-486, is a medication primarily used for the medical termination of early pregnancy. It has also been utilized in the management of high blood sugar in patients with Cushing's syndrome and for the treatment of certain types of cancer. The mechanism of action of mifepristone is multifaceted, involving several biological processes and molecular interactions.

At the core of its mechanism is its role as a competitive inhibitor of the progesterone receptor. Progesterone is a hormone vital for maintaining pregnancy. It prepares the endometrium for implantation of the fertilized egg and helps maintain the endometrial lining. Mifepristone binds to the progesterone receptor with a greater affinity than progesterone itself, thereby blocking the hormone's action. By inhibiting the effects of progesterone, mifepristone leads to changes in the endometrium, which becomes inhospitable for the embryo. This results in the detachment of the embryo from the endometrial lining.

Additionally, mifepristone has an effect on the myometrium, the muscular layer of the uterus. By blocking progesterone receptors in the myometrium, it increases uterine contractility, facilitating the expulsion of the embryo. This is often why mifepristone is used in conjunction with another medication, misoprostol, which further stimulates uterine contractions to ensure the complete expulsion of the pregnancy tissue.

Apart from its anti-progestational activity, mifepristone also exhibits antiglucocorticoid properties. It binds to the glucocorticoid receptor, blocking the action of cortisol, a stress hormone. This property is particularly useful in the treatment of conditions like Cushing's syndrome, where there is an overproduction of cortisol.

Mifepristone's anti-proliferative effects have also been explored in the context of certain types of cancer. It has been shown to inhibit the growth of cancer cells in breast cancer and endometrial cancer by blocking progesterone receptors, which are often expressed in these tumor cells. Furthermore, by inhibiting glucocorticoid receptors, mifepristone can help reduce cortisol-induced immunosuppression, potentially aiding the body's immune response to cancer cells.

In summary, the primary mechanism of mifepristone involves its role as a competitive inhibitor of the progesterone receptor, which disrupts the maintenance of the endometrial lining and increases uterine contractility, leading to the termination of pregnancy. Its antiglucocorticoid properties also make it useful in treating conditions like Cushing's syndrome and certain cancers. Understanding these mechanisms provides valuable insight into how mifepristone functions and its potential applications in medicine.