Gonadotropin-releasing hormone antagonists (GnRH antagonists) are a class of medications that antagonize the

gonadotropin-releasing hormone receptor The gonadotropin-releasing hormone receptor (GnRHR), also known as the luteinizing hormone releasing hormone receptor (LHRHR), is a member of the seven-transmembrane, G-protein coupled receptor (GPCR) family. It is the receptor of gonadotropin-r ...

(GnRH receptor) and thus the action of

gonadotropin-releasing hormone Gonadotropin-releasing hormone (GnRH) is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and release ...

(GnRH). They are used in the treatment of prostate cancer, endometriosis,

uterine fibroids Uterine fibroids, also known as uterine leiomyomas or fibroids, are benign smooth muscle tumors of the uterus. Most women with fibroids have no symptoms while others may have painful or heavy periods. If large enough, they may push on the bl ...

female infertility Female infertility refers to infertility in women. It affects an estimated 48 million women, with the highest prevalence of infertility affecting women in South Asia, Sub-Saharan Africa, North Africa/Middle East, and Central/Eastern Europe and Cen ...

in assisted reproduction, and for other indications. Some GnRH antagonists, such as

cetrorelix Cetrorelix (, ), or cetrorelix acetate (, ), sold under the brand name Cetrotide, is an injectable gonadotropin-releasing hormone (GnRH) antagonist. A synthetic decapeptide, it is used in assisted reproduction to inhibit premature luteinizing h ...

, are similar in structure to natural GnRH (a

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...

made by neurons in the hypothalamus) but that have an antagonistic effect, while other GnRH antagonists, such as

elagolix Elagolix, sold under the brand name Orilissa, is a gonadotropin-releasing hormone antagonist (GnRH antagonist) medication which is used in the treatment of pain associated with endometriosis in women. It is also under development for the trea ...

and

relugolix Relugolix, sold under the brand names Orgovyx and Relumina and as one component of Myfembree, is a gonadotropin-releasing hormone antagonist (GnRH receptor antagonist) medication which is used in the treatment of prostate cancer in men and ute ...

, are

non-peptide Within the fields of molecular biology and pharmacology, a small molecule or micromolecule is a low molecular weight (≤ 1000 daltons) organic compound that may regulate a biological process, with a size on the order of 1 nm. Many drugs are ...

and

small-molecule Within the fields of molecular biology and pharmacology, a small molecule or micromolecule is a low molecular weight (≤ 1000 daltons) organic compound that may regulate a biological process, with a size on the order of 1 nm. Many drugs ar ...

compounds. GnRH antagonists compete with natural GnRH for binding to GnRH receptors, thus decreasing or blocking GnRH action in the body.

Medical uses

Prostate cancer

Testosterone promotes growth of many prostate

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

s and therefore reducing circulating testosterone to very low (

castration Castration is any action, surgical, chemical, or otherwise, by which an individual loses use of the testicles: the male gonad. Surgical castration is bilateral orchiectomy (excision of both testicles), while chemical castration uses pharma ...

) levels is often the treatment goal in the management of men with advanced prostate cancer. GnRH antagonists are used to provide fast suppression of testosterone without the surge in testosterone levels that is seen when treating patients with GnRH agonists. In patients with advanced disease, this surge in testosterone can lead to a flare-up of the tumour, which can precipitate a range of clinical symptoms such as

bone pain Bone pain (also known medically by several other names) is pain coming from a bone, and is caused by damaging stimuli. It occurs as a result of a wide range of diseases or physical conditions or both, and may severely impair the quality of life. ...

urethral obstruction Urinary tract obstruction is a urologic disease consisting of a decrease in the free passage of urine through one or both ureters and/or the urethra. It is a cause of urinary retention. Complete obstruction of the urinary tract requires prompt tr ...

, and

spinal cord compression Spinal cord compression is a form of myelopathy in which the spinal cord is compressed. Causes can be bone fragments from a vertebral fracture, a tumor, abscess, ruptured intervertebral disc or other lesion. When acute it can cause a medica ...

. Drug agencies have issued warnings regarding this phenomenon in the prescribing information for GnRH agonists. As testosterone surge does not occur with GnRH antagonists, there is no need for patients to receive an

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 the ...

as flare protection during prostate cancer treatment. GnRH agonists also induce an increase in testosterone levels after each reinjection of the drug – a phenomenon that does not occur with GnRH antagonists. The reduction in testosterone levels that occurs during GnRH antagonist therapy subsequently reduces the size of the prostate cancer. This in turn results in a reduction in

prostate-specific antigen Prostate-specific antigen (PSA), also known as gamma-seminoprotein or kallikrein-3 (KLK3), P-30 antigen, is a glycoprotein enzyme encoded in humans by the ''KLK3'' gene. PSA is a member of the kallikrein-related peptidase family and is secreted b ...

(PSA) levels in the patient’s blood and so measuring PSA levels is a way to monitor how patients with prostate cancer are responding to treatment. GnRH antagonists have an immediate onset of action leading to a fast and profound suppression of testosterone and are therefore especially valuable in the treatment of patients with prostate cancer, where fast control of disease is needed. The GnRH antagonist

abarelix Abarelix, sold under the brand name Plenaxis, is an injectable gonadotropin-releasing hormone antagonist ( GnRH antagonist) which is marketed in Germany and the Netherlands. It is primarily used in oncology to reduce the amount of testosterone ma ...

was withdrawn from the United States market in 2005 and is now only marketed in Germany for use in patients with symptomatic prostate cancer. Degarelix is a GnRH antagonist that is approved for use in patients with advanced hormone-sensitive prostate cancer throughout Europe and also in the United States.

Fertility treatment

GnRH antagonists are also used for short periods in the prevention of premature LH surge and endogenous

ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilize ...

in patients undergoing ovarian hyperstimulation with FSH in preparation for ''in-vitro'' fertilization (IVF). Typically they are administered in the mid-

follicular phase The follicular phase, also known as the preovulatory phase or proliferative phase, is the phase of the estrous cycle (or, in primates for example, the menstrual cycle) during which follicles in the ovary mature from primary follicle to a ful ...

in stimulated cycles after administration of gonadotropins and prior to the administration of hCG – which is given to stimulate ovulation. This protocol is likely beneficial in women expected to be hyper-responders, and probably also those expected to be poor responders to ovarian hyperstimulation. There is probably little or no difference between GnRH antagonist and GnRH agonist protocols in terms of live birth or risk of miscarriage but GnRH antagonists probably reduce the risk of ovarian hyperstimulation syndrome. The GnRH antagonists that are currently licensed for use in

fertility treatment Assisted reproductive technology (ART) includes medical procedures used primarily to address infertility. This subject involves procedures such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), cryopreservation of gametes ...

are cetrorelix and ganirelix.

Uterine disorders

Elagolix Elagolix, sold under the brand name Orilissa, is a gonadotropin-releasing hormone antagonist (GnRH antagonist) medication which is used in the treatment of pain associated with endometriosis in women. It is also under development for the trea ...

is indicated for the treatment of moderate to severe endometriosis pain and

is indicated for the treatment of

uterine fibroid Uterine fibroids, also known as uterine leiomyomas or fibroids, are benign smooth muscle tumors of the uterus. Most women with fibroids have no symptoms while others may have painful or heavy periods. If large enough, they may push on the bl ...

Other uses

GnRH antagonists are being investigated in the treatment of women with hormone-sensitive

breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a r ...

. In men, they are being investigated in the treatment of

benign prostatic hyperplasia Benign prostatic hyperplasia (BPH), also called prostate enlargement, is a noncancerous increase in size of the prostate gland. Symptoms may include frequent urination, trouble starting to urinate, weak stream, inability to urinate, or loss o ...

and also as potential contraceptive agents. GnRH antagonists are also used as

puberty blocker Puberty blockers, also called puberty inhibitors or hormone blockers, are medicines used to postpone puberty in children. The most commonly used puberty blockers are gonadotropin-releasing hormone (GnRH) agonists, which suppress the production ...

s in

transgender youth Transgender youth are children or adolescents who do not identify with the sex they were assigned at birth. Because transgender youth are usually dependent on their parents for care, shelter, financial support, and other needs, transgender yo ...

and to suppress

sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effect ...

levels in

transgender A transgender (often abbreviated as trans) person is someone whose gender identity or gender expression does not correspond with their sex assigned at birth. Many transgender people experience dysphoria, which they seek to alleviate through ...

adolescents and adults.

Available forms

Currently approved GnRH antagonists include the

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...

molecules

, degarelix, and ganirelix and the

compounds

and

. GnRH antagonists are administered by subcutaneous injection (cetrorelix, degarelix, ganirelix), by intramuscular injection (abarelix), or by

oral administration Oral administration is a route of administration where a substance is taken through the mouth. Per os abbreviated to P.O. is sometimes used as a direction for medication to be taken orally. Many medications are taken orally because they are ...

(elagolix, relugolix). Another non-peptide and orally-active GnRH antagonist that is in development is

linzagolix Linzagolix, sold under the brand name Yselty, is a medication used in the treatment of uterine fibroids.https://www.ema.europa.eu/en/documents/product-information/yselty-epar-product-information_en.pdf Linzagolix is a small-molecule, non-peptid ...

Side effects

As with all hormonal therapies, GnRH antagonists are commonly associated with hormonal side effects such as

hot flushes Hot flashes (also known as hot flushes) are a form of flushing, often caused by the changing hormone levels that are characteristic of menopause. They are typically experienced as a feeling of intense heat with sweating and rapid heartbeat, and ...

, headache,

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...

and

weight gain Weight gain is an increase in body weight. This can involve an increase in muscle mass, fat deposits, excess fluids such as water or other factors. Weight gain can be a symptom of a serious medical condition. Description Weight gain occurs w ...

.Serono. Cetrotide prescribing information 2009. Accessed 18-6-2009.Degarelix US prescribing information 2008. Accessed 28-4-2009.Organon. Ganirelix acetate prescribing information 2009. Accessed 18-6-2009. When used in fertility treatment they can also be associated with abdominal pain and ovarian hyperstimulation. Subcutaneously administered agents are also associated with injection-site reactions and

(neither of these being GnRH agonists, but instead being antagonists) has been linked with immediate-onset systemic allergic reactions.

Pharmacology

GnRH antagonists competitively and reversibly bind to GnRH receptors in the

pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...

, blocking the release of

luteinizing hormone Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) ...

(LH) and follicle-stimulating hormone (FSH) from the anterior pituitary.Engel JB, Schally AV (February 2007). Drug Insight: clinical use of agonists and antagonists of luteinizing-hormone-releasing hormone. Nat. Clin. Pract. Endocrinol. Metab.: 3: 157-167. In men, the reduction in LH subsequently leads to rapid suppression of

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristi ...

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 stati ...

in the

testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...

; in women it leads to suppression of

estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development o ...

and progesterone production from the

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

. GnRH antagonists are able to abolish gonadal sex hormone production and to suppress sex hormone levels into the castrate range, or by approximately 95%. Unlike the GnRH agonists, which cause an initial stimulation of the

hypothalamic–pituitary–gonadal axis The hypothalamic–pituitary–gonadal axis (HPG axis, also known as the hypothalamic–pituitary–ovarian/testicular axis) refers to the hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single en ...

(HPG axis) that leads to a surge in testosterone or estrogen levels, GnRH antagonists have an immediate onset of action and rapidly reduce

levels without an initial surge.Van Poppel H, Nilsson S (June 2008). Testosterone surge: rationale for gonadotropin-releasing hormone blockers? Urology 71: 1001-1006.Gustofson RL, Segars JH, Larsen FW (November 2006). Ganirelix acetate causes a rapid reduction in estradiol levels without adversely affecting oocyte maturation in women pretreated with leuprolide acetate who are at risk of ovarian hyperstimulation syndrome. Hum. Reprod. 21: 2830-2837.

Chemistry

GnRH antagonists include

s such as

and

compounds such as

. Peptide GnRH antagonists are

GnRH analogue A GnRH modulator, or GnRH receptor modulator, also known as an LHRH modulator or LHRH receptor modulator, is a type of medication which modulates the GnRH receptor, the biological target of the hypothalamic hormone gonadotropin-releasing hormone ...

References

External links

Degarelix Product website

Fertility Lifelines website

Fertility Treatments website

Fertility Information website
{{DEFAULTSORT:Gonadotropin-Releasing Hormone Antagonist Antiandrogens Antiestrogens Antigonadotropins Gonadotropin-releasing hormone and gonadotropins Hormonal antineoplastic drugs Human female endocrine system GnRH antagonists