|Other names||GTx-024; MK-2866; Ostarine; S-22|
|Elimination half-life||24 hours|
|CompTox Dashboard (EPA)|
|Chemical and physical data|
|Molar mass||389.33 g/mol g·mol−1|
|3D model (JSmol)|
|Melting point||132 to 136 °C (270 to 277 °F)|
Enobosarm, also known as ostarine, is an investigational selective androgen receptor modulator (SARM) developed by GTx, Inc. for the treatment of conditions such as muscle wasting and osteoporosis, formerly under development by Merck & Company.
According to a 2009 paper authored by GTx, "Readers are cautioned to note that the name ostarine is often mistakenly linked to the chemical structure of [S-4], which is also known as andarine. The chemical structure of ostarine has not been publicly disclosed." A 2009 review stated "Recently, GTx disclosed that compound 5 had advanced into clinical trials. The patent application described detailed data in an initial proof-of-concept Phase IIa clinical trial. It is not explicitly stated that compound 5 is Ostarine (MK-2866).
As of now, the mechanism of action of Enobosarm is still being debated and requires further investigation.
GTx Incorporated was founded in Memphis in 1997 and licensed rights to enobosarm from the University of Tennessee Research Foundation; the SARM compounds were invented by James T. Dalton, Duane D. Miller, Karen A. Veverka and their research teams at Ohio State University, the University of Tennessee and GTx, respectively.
In August 2011, there was a double-blind, placebo controlled phase II trial that focused on elderly men and postmenopausal women concluded that Enobosarm showed statistically significant improvements in total lean body mass and physical function without the negative side effects that are normally present with steroids.
In August 2013, GTx announced that enobosarm had failed in two Phase III clinical trials to treat wasting in people with lung cancer. The company had invested around $35 million in the development of the drug. The company said at that time that is planned to pursue approval of enobosarm in Europe; the company was also still developing GTx-758 for castration-resistant prostate cancer.
Enobosarm and other SARMs have been quoted by the FDA to have serious side effects ranging from risk of heart attack to stroke and liver damage.
Many clinical trials have shown that SARMs are well tolerated in users, however, leading to increased muscle mass, with minimal side effects.
One clinical trial conducted in 2008 also found that enobosarm actually decreased cholesterol levels in test subjects.
Society and culture
SARMs including enobosarm may be and have been used by athletes to assist in training and increase physical stamina and fitness, potentially producing effects similar to anabolic steroids. For this reason, SARMs were banned by the World Anti-Doping Agency in January 2008, despite no drugs from this class yet being in clinical use, and blood tests for all known SARMs have been developed. There are a variety of known cases of doping in sports with enobosarm by professional athletes.
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- "Enobosarm fails endpoints in Ph III study". The Pharma Letter. 20 August 2013.
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- "GTx begins Phase II trial of enobosarm to treat women with stress urinary incontinence - Drug Development Technology". Drug Development Technology. 14 January 2016.
- "GTx's Enobosarm Fails Phase II Trial in Stress Urinary Incontinence; Stock Plunges 90%+". Retrieved 1 August 2019.
- "FDA In Brief: FDA warns against using SARMs in body-building products". Retrieved 1 August 2019.
- Dalton, James T.; Barnette, Kester G.; Bohl, Casey E.; Hancock, Michael L.; Rodriguez, Domingo; Dodson, Shontelle T.; Morton, Ronald A.; Steiner, Mitchell S. (September 2011). "The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial". Journal of Cachexia, Sarcopenia and Muscle. 2 (3): 153–161. doi:10.1007/s13539-011-0034-6. ISSN 2190-5991. PMC 3177038. PMID 22031847.
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- Thevis, Mario; Kohler, Maxie; Thomas, Andreas; Maurer, Joachim; Schlörer, Nils; Kamber, Matthias; Schänzer, Wilhelm (13 February 2008). "Determination of benzimidazole- and bicyclic hydantoin-derived selective androgen receptor antagonists and agonists in human urine using LC–MS/MS". Analytical and Bioanalytical Chemistry. 391 (1): 251–261. doi:10.1007/s00216-008-1882-6. PMID 18270691.
- "Dynamic Technical Formulations, LLC. Issues a Voluntary Nationwide Recall of Tri-Ton Due to the Presence of Andarine and Ostarine". U.S. Food & Drug Administration. May 19, 2017.
- Bieler, Des (25 July 2019). "Failed PED test has a highly paid offensive lineman sharing polygraph results". Washington Post. Retrieved 25 July 2019.
One of the NFL’s highest-paid offensive linemen claimed Wednesday that he did not knowingly take a banned substance he says got him a four-game suspension — and he took a polygraph test in an attempt to prove it.