GnRH anatagonist

Gonadotropin-releasing hormone antagonist
Drug class
Cetrorelix, one of the most widely used GnRH antagonists.
Class identifiers
Synonyms	GnRH receptor antagonists; GnRH blockers; GnRH inhibitors; Antigonadotropins
Use	Infertility; Prostate cancer; Precocious puberty; Breast cancer; Endometriosis; Uterine fibroids; Transgender people
Biological target	GnRH receptor
Chemical class	Peptides; Nonpeptides

Gonadotropin-releasing hormone antagonists (GnRH antagonists) are a class of medications that antagonize the gonadotropin-releasing hormone receptor (GnRH receptor) and thus the action of gonadotropin-releasing hormone (GnRH). Some are similar in structure to natural GnRH (a hormone made by neurons in the hypothalamus) but that have an antagonistic effect. These GnRH antagonists are peptide molecules that are made up multiple, often synthetically produced amino acids. Others are small-molecule, non-peptide compounds. GnRH antagonists compete with natural GnRH for binding to GnRH receptors, thus decreasing or blocking GnRH action in the body.

Testosterone promotes growth of many prostate tumors and therefore reducing circulating testosterone to very low (castration) 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, ureteral obstruction, and spinal cord compression. 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 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 (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.