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Gonadotropin-releasing hormone agonist

Gonadotropin-releasing hormone agonist
Drug class
Leuprorelin, one of the most widely used GnRH agonists.
Class identifiers
SynonymsGnRH receptor agonists; GnRH blockers; GnRH inhibitors; Antigonadotropins
UseFertility medicine; Prostate cancer; Breast cancer; Menorrhagia; Endometriosis; Uterine fibroids; Hyperandrogenism; Hirsutism; Precocious puberty; Transgender people; Chemical castration for paraphilias and sex offenders
Biological targetGnRH receptor
Chemical classPeptides
Legal status
In Wikidata

A gonadotropin-releasing hormone agonist (GnRH agonist) is a type of medication which affects gonadotropins and sex hormones.[1] They are used for a variety of indications including in fertility medicine and to lower sex hormone levels in the treatment of hormone-sensitive cancers such as prostate cancer and breast cancer, certain gynecological disorders like heavy periods and endometriosis, high testosterone levels in women, early puberty in children, as a part of transgender hormone therapy, and to delay puberty in transgender youth among other uses. It is also used in the suppression of spontaneous ovulation as part of controlled ovarian hyperstimulation, an essential component in IVF. GnRH agonists are given by injections into fat, as implants placed into fat, and as nasal sprays.

Side effects of GnRH agonists are related to sex hormone deficiency and include symptoms of low testosterone levels and low estrogen levels such as hot flashes, sexual dysfunction, vaginal atrophy, penile atrophy, osteoporosis, infertility, and diminished sex-specific physical characteristics. They are agonists of the GnRH receptor and work by increasing or decreasing the release of gonadotropins and the production of sex hormones by the gonads. When used to suppress gonadotropin release, GnRH agonists can lower sex hormone levels by 95% in both sexes.[2][3][4][5]

GnRH was discovered in 1971, and GnRH analogues were introduced for medical use in the 1980s.[6][7] Their nonproprietary names usually end in -relin. The most well-known and widely used GnRH analogues are leuprorelin (brand name Lupron) and triptorelin (brand name Decapeptyl). GnRH analogues are available as generic medications. Despite this, they continue to be very expensive.

Medical uses

GnRH agonists are useful in:

Women of reproductive age who undergo cytotoxic chemotherapy have been pretreated with GnRH agonists to reduce the risk of oocyte loss during such therapy and preserve ovarian function. Further studies are necessary to prove that this approach is useful.

Available forms

GnRH agonists marketed for clinical or veterinary use
Name Brand names Approved uses Routes Launch Hits
Azagly-nafarelin Gonazon Veterinary medicine (assisted reproduction; chemical castration) Implant; Injection 2005a 9,190
Buserelin Suprefact Breast cancer; Endometrial hyperplasia; Endometriosis; Female infertility (assisted reproduction); Prostate cancer; Uterine fibroids Nasal spray; Injection; Implant 1984 253,000
Deslorelin Ovuplant; Suprelorin Veterinary medicine (assisted reproduction; chemical castration) Implant; Injection 1994 85,100
Fertirelin Ovalyse Veterinary medicine (assisted reproduction) Injection 1981 41,000
Gonadorelin Factrel; Others Cryptorchidism; Delayed puberty; Diagnostic agent (pituitary disorders); Hypogonadotropic hypogonadism; Veterinary medicine (assisted reproduction) Injection; Infusion pump; Nasal spray 1978 259,000
Goserelin Zoladex Breast cancer; Endometriosis; Female infertility (assisted reproduction); Prostate cancer; Uterine diseases (endometrial thinning agent); Uterine fibroids; Uterine hemorrhage Implant 1989 400,000
Histrelin Vantas; Supprelin LA Precocious puberty; Prostate cancer Implant 1993 283,000
Lecirelin Dalmarelin Veterinary medicine (assisted reproduction) Injection 2000a 19,700
Leuprorelin Lupron; Eligard; Procren; Prostap; Staladex Breast cancer; Endometriosis; Menorrhagia; Precocious puberty; Prostate cancer; Uterine fibroids Injection; Implant 1985 536,000
Nafarelin Synarel Precocious puberty; Endometriosis Nasal spray 1990 117,000
Peforelin Maprelin Veterinary medicine (assisted reproduction) Injection 2001a 3,240
Triptorelin Decapeptyl Breast cancer; Endometriosis; Female infertility (assisted reproduction); Paraphilias; Precocious puberty; Prostate cancer; Uterine fibroids Injection 1986 302,000
Notes: Hits = Google Search hits (as of February 2018). Footnotes: a = Launched by this year.

GnRH agonists that have been marketed and are available for medical use include buserelin, gonadorelin, goserelin, histrelin, leuprorelin, nafarelin, and triptorelin. GnRH agonists that are used mostly or exclusively in veterinary medicine include deslorelin and fertirelin. GnRH agonists can be administered by injection, by implant, or intranasally as a nasal spray. Injectables have been formulated for daily, monthly, and quarterly use, and implants are available that can last from one month to a year. With the exception of gonadorelin, which is used as a progonadotropin, all approved GnRH agonists are used as antigonadotropins.

The clinically used desensitizing GnRH agonists are available in the following pharmaceutical formulations:[10][11][12][13]

Contraindications

GnRH agonists are pregnancy category X drugs.

Side effects

Common side effects of the GnRH agonists and antagonists include symptoms of hypogonadism such as hot flashes, gynecomastia, fatigue, weight gain, fluid retention, erectile dysfunction and decreased libido. Long term therapy can result in metabolic abnormalities, weight gain, worsening of diabetes and osteoporosis. Rare, but potentially serious adverse events include transient worsening of prostate cancer due to surge in testosterone with initial injection of GnRH agonists and pituitary apoplexy in patients with pituitary adenoma. Single instances of clinically apparent liver injury have been reported with some GnRH agonists (histrelin, goserelin), but the reports were not very convincing. There is no evidence to indicate that there is cross sensitivity to liver injury among the various GnRH analogues despite their similarity in structure.[14] There is also a report that GnRH agonists used in the treatment of advanced prostate cancer may increase the risk of heart problems by 30%.[15]

Pharmacology

GnRH agonists act as agonists of the GnRH receptor, the biological target of gonadotropin-releasing hormone (GnRH). These drugs can be both peptides and small-molecules. They are modeled after the hypothalamic neurohormone GnRH, which interacts with the GnRH receptor to elicit its biologic response, the release of the pituitary hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH). However, after the initial "flare" response, continued stimulation with GnRH agonists desensitizes the pituitary gland (by causing GnRH receptor downregulation) to GnRH. Pituitary desensitization reduces the secretion of LH and FSH and thus induces a state of hypogonadotropic hypogonadal anovulation, sometimes referred to as "pseudomenopause" or "medical oophorectomy".[1] GnRH agonists are able to completely shutdown gonadal testosterone production and thereby suppress circulating testosterone levels by 95% or into the castrate/female range in men.[5]

Agonists do not quickly dissociate from the GnRH receptor. As a result, initially there is an increase in FSH and LH secretion (so-called "flare effect"). Levels of LH may increase by up to 10-fold,[16][17] while levels of testosterone generally increase to 140 to 200% of baseline values.[18] However, after continuous administration, a profound hypogonadal effect (i.e. decrease in FSH and LH) is achieved through receptor downregulation by internalization of receptors.[16] Generally this induced and reversible hypogonadism is the therapeutic goal. During the flare, peak levels of testosterone occur after 2 to 4 days, baseline testosterone levels are returned to by 7 to 8 days, and castrate levels of testosterone are achieved by two to four weeks.[18][16] A 7 day study of infertile women found that restoration of normal gonadotropin secretion takes 5 to 8 days after cessation of exogenous GnRH agonists.[19]

Various medications can be used to prevent the testosterone flare and/or its effects at the initiation of GnRH agonist therapy.[17][20][21] These include antigonadotropins such as progestogens like cyproterone acetate and chlormadinone acetate and estrogens like diethylstilbestrol, fosfestrol (diethylstilbestrol diphosphate), and estramustine phosphate; antiandrogens such as nonsteroidal antiandrogens like flutamide, nilutamide, and bicalutamide; and androgen synthesis inhibitors such as ketoconazole and abiraterone acetate.[17][20][21][22][23][24][25]

Hormone levels with GnRH agonists and antagonists
  • Testosterone levels during the first month of androgen deprivation therapy in men with prostate cancer treated with subcutaneous injections of a GnRH antagonist (degarelix) or agonist (leuprorelin). Doses were 240 then 80 mg/month and 7.5 mg/month, respectively.[26]
    Testosterone levels during the first month of androgen deprivation therapy in men with prostate cancer treated with subcutaneous injections of a GnRH antagonist (degarelix) or agonist (leuprorelin). Doses were 240 then 80 mg/month and 7.5 mg/month, respectively.[26]
  • Testosterone levels in the long-term androgen deprivation therapy of men with prostate cancer by different GnRH agonists administered at 3 month intervals (goserelin, triptorelin and leuprorelin). Dotted line is the threshold for the castrate range.[27]
    Testosterone levels in the long-term androgen deprivation therapy of men with prostate cancer by different GnRH agonists administered at 3 month intervals (goserelin, triptorelin and leuprorelin). Dotted line is the threshold for the castrate range.[27]

Chemistry

See also: Gonadotropin-releasing hormone receptor § Agonists

GnRH agonists are synthetically modeled after the natural GnRH decapeptide with specific modifications, usually double and single substitutions and typically in position 6 (amino acid substitution), 9 (alkylation) and 10 (deletion). These substitutions inhibit rapid degradation. Agonists with two substitutions include: leuprorelin, buserelin, histrelin, goserelin, and deslorelin. The agents nafarelin and triptorelin are agonists with single substitutions at position 6.

Chemical structures of GnRH agonists

Veterinary uses

GnRH analogues are also used in veterinary medicine. Uses include:

  • Temporary suppression of fertility in female dogs
  • Induction of ovulation in mares

See also

References

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  22. ^ Kotake T, Usami M, Akaza H, Koiso K, Homma Y, Kawabe K, Aso Y, Orikasa S, Shimazaki J, Isaka S, Yoshida O, Hirao Y, Okajima E, Naito S, Kumazawa J, Kanetake H, Saito Y, Ohi Y, Ohashi Y (November 1999). "Goserelin acetate with or without antiandrogen or estrogen in the treatment of patients with advanced prostate cancer: a multicenter, randomized, controlled trial in Japan. Zoladex Study Group". Jpn. J. Clin. Oncol. 29 (11): 562–70. doi:10.1093/jjco/29.11.562. PMID 10678560.
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  27. ^ Shim M, Bang WJ, Oh CY, Lee YS, Cho JS (July 2019). "Effectiveness of three different luteinizing hormone-releasing hormone agonists in the chemical castration of patients with prostate cancer: Goserelin versus triptorelin versus leuprolide". Investig Clin Urol. 60 (4): 244–250. doi:10.4111/icu.2019.60.4.244. PMC 6607074. PMID 31294133.
Quelle: https://en.wikipedia.org/wiki/GnRH_agonist