Antiprogestogens or antiprogestins, also known as progesterone antagonists or progesterone blockers, are a class of

drug A drug is any chemical substance other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect. Consumption of drugs can be via insufflation (medicine), inhalation, drug i ...

s which prevent

progestogen Progestogens, also sometimes written progestins, progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestoge ...

s like

progesterone Progesterone (; P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...

from mediating their biological effects in the body. These drugs competitively inhibit progestin at progesterone receptors, acting by blocking the

progesterone receptor The progesterone receptor (PR), also known as NR3C3 or nuclear receptor subfamily 3, group C, member 3, is a protein found inside cells. It is activated by the steroid hormone progesterone. In humans, PR is encoded by a single ''PGR'' gene resi ...

(PR) and/or inhibiting or suppressing progestogen

production Production may refer to: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in the outline of industrial organization, the act of making products (goods and services) * Production as a stat ...

. Antiprogestogens are one of three types of sex hormone antagonists, alongside

antiestrogen Antiestrogens, also known as estrogen antagonists or estrogen blockers, are a class of drugs which prevent estrogens like estradiol from mediating their biological effects in the body. They act by blocking the estrogen receptor (ER) and/or inh ...

s and

antiandrogen Antiandrogens, also known as androgen antagonists or testosterone blockers, are a class of drugs that prevent androgens like testosterone and dihydrotestosterone (DHT) from mediating their biological effects in the body. They act by blocking t ...

Clinical applications

Antiprogestogens are used as

abortifacient An abortifacient ("that which will cause a miscarriage" from Latin: '' abortus'' "miscarriage" and '' faciens'' "making") is a substance that induces abortion. This is a nonspecific term which may refer to any number of substances or medications, ...

emergency contraceptive Emergency contraception (EC) is a birth control measure, used after sexual intercourse to prevent pregnancy. There are different forms of EC. Emergency contraceptive pills (ECPs), sometimes simply referred to as emergency contraceptives (ECs), ...

s, and in the treatment of

uterine fibroid Uterine fibroids, also known as uterine leiomyomas, fibromyoma or fibroids, are benign smooth muscle tumors of the uterus, part of the female reproductive system. Most people with fibroids have no symptoms while others may have painful or h ...

s. They are also being studied in the treatment of

breast cancer Breast cancer is a cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipp ...

. Examples include the

weak

partial agonist In pharmacology, partial agonists are drugs that bind to and activate a given Receptor (biochemistry), receptor, but have only partial Intrinsic activity, efficacy at the receptor relative to a full agonist. They may also be considered Ligand (bio ...

mifepristone Mifepristone, and also known by its developmental code name RU-486, is a drug typically used in combination with misoprostol to bring about a medical abortion during pregnancy. This combination is 97% effective during the first 63 days (9 wee ...

, the

selective progesterone receptor modulator A selective progesterone receptor modulator (SPRM) is an agent that acts on the progesterone receptor (PR), the biological target of progestogens like progesterone. A characteristic that distinguishes such substances from full receptor agonists ...

(SPRM)

ulipristal acetate Ulipristal acetate, sold under the brand name Ella among others, is a medication used for emergency contraception (birth control) and uterine fibroids. As emergency contraception it should be used within 120 hours of vaginally penetrating inte ...

, and the

silent antagonist A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of recep ...

aglepristone Aglepristone () (brand name Alizin; former developmental code names RU-46534, RU-534) is a synthetic, steroidal antiprogestogen related to mifepristone which is marketed by Virbac in several European countries for use in veterinary medicine. It ...

. In

medical abortion A medical abortion, also known as medication abortion or non-surgical abortion, occurs when drugs (medication) are used to bring about an abortion. Medical abortions are an alternative to surgical (also called procedural or instrumentation) a ...

, mifepristone is combined with a

prostaglandin Prostaglandins (PG) are a group of physiology, physiologically active lipid compounds called eicosanoids that have diverse hormone-like effects in animals. Prostaglandins have been found in almost every Tissue (biology), tissue in humans and ot ...

(e.g.,

gemeprost Gemeprost (16, 16-dimethyl-trans-delta2 PGE1 methyl ester) is an analogue of prostaglandin E1. Clinical use It is used as a treatment for obstetric bleeding. It is used with mifepristone to terminate pregnancy up to 24 weeks gestation. Sid ...

), while ulipristal is used for emergency contraception.

Development and approval

Several hundred antiprogestogens have been developed, but only three—

lilopristone Lilopristone (INN; development codes ZK-98734 and ZK-734) is a synthetic, steroidal antiprogestogen with additional antiglucocorticoid activity which was developed by Schering and was patented in 1985. It is described as an abortifacient and en ...

, and

onapristone Onapristone () (developmental code names ZK-89299, ZK-299) is a synthetic and steroidal antiprogestogen with additional antiglucocorticoid activity which was developed by Schering and described in 1984 but was never marketed. It is a sile ...

—have been administered to humans. Of these, only mifepristone has been approved and introduced for clinical use.

Role and mechanism of action

Progestins, including progesterone, are vital for preparing the uterus for the implantation of a fertilized egg during the luteal phase of the menstrual cycle. If fertilization, implantation, and other events necessary for pregnancy occur, increased progestin (i.e., progesterone) levels are essential in maintaining the pregnancy. Blocking the effects of progestins like progesterone is associated with anti-gestational effects, resulting in the interruption of pregnancy maintenance.

References

External links

*
Antiprogestin
entry in the public domain NCI Dictionary of Cancer Terms {{genito-urinary-drug-stub

Clinical applications

Development and approval

Role and mechanism of action

See also

References

External links